Facile Preparation of Chitosan-Alginate Crosslinked with Calcium Chloride Hydrogel as Sustained Release Fertilizers

Facile Preparation of Chitosan-Alginate Crosslinked with Calcium Chloride Hydrogel as Sustained Release Fertilizers | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Facile Preparation of Chitosan-Alginate Crosslinked with Calcium Chloride Hydrogel as Sustained Release Fertilizers Melody Kimi, Chee Jiun Chong This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3855172/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The utilization of urea in the agricultural sector as a fertilizer is susceptible to losses through volatilization and leaching. A strategy to mitigate this environmental impact involves employing a sustained-release approach for urea, thereby diminishing both the quantity and frequency of its application. These agrochemicals utilize a physical barrier to curtail the dissolution of urea, and their efficacy in fertilizer release is dictated by their physical characteristics. In the current investigation, hydrogel beads comprising urea were developed by blending biodegradable polysaccharides, specifically chitosan and alginate, in the presence of calcium chloride as a crosslinker through ionotropic gelation. The Box-Behnken design was employed to analyze the impacts of independent variables (low, medium, and high molecular weight chitosan; 2.5 to 4.5 wt% alginate; and 0.10 M to 1.00 M calcium chloride crosslinker) on encapsulation efficiency and urea release. After model evaluation, the optimal conditions for encapsulation efficiency and urea release were determined as the use of the lowest molecular weight chitosan, a medium amount of alginate, and the maximum amount of crosslinker, resulting in a loading efficiency of up to 98.5% and a urea release of only 2.2% within 2 hours. The composition of the polymeric hydrogel was found to govern encapsulation efficiency and urea release, while the swelling behaviour in water remained unaffected. The hydrogel beads exhibited a spherical morphology, and Fourier transform-infrared spectroscopy confirmed the presence of urea within the beads. chitosan alginate urea hydrogel controlled release Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction Agrochemical fertilizers play a crucial role in supplying essential nutrients to crops on agricultural lands. Enhancing the efficiency of these agrochemicals is achievable by harnessing the sustained release property of polymers. Sustained release agrochemicals, in the form of granulated compounds, gradually release nutrients into the soil from polymer-based formulations. This controlled release, facilitated by a polymer composites network, extends the presence of nutrients in the soil, contributing to soil fertility preservation and mitigating soil pollution [ 1 ]. The direct application of chemical fertilizers to plants has shown limited utilization efficiency, with only 30–35% of the nutrients being absorbed [ 2 ]. Urea, a commonly used nitrogen fertilizer, faces losses of 2–20% through volatilization, 15–25% through reactions with organic compounds in the soil, and 2–10% through leaching into water systems, raising environmental concerns [ 3 ]. Among hydrophilic polymers, two biodegradable polysaccharides, chitosan and alginate, meet the desired criteria of cost-effectiveness, environmental friendliness, and the ability to modulate fertilizer release. Alginate, a natural anionic hydrophilic polysaccharide derived from algae, forms hydrogels in the presence of divalent cations like Ca 2+ . Alginate-based materials excel in sustaining the release of urea due to their favorable swelling properties, enhancing urea loading in the prepared hydrogel [ 6 ]. However, alginate alone has drawbacks, such as high viscosity and low solubility, which can be addressed by incorporating various biomaterials into the alginate structure. Chitosan, the second most abundant polysaccharide with positive-charge in acidic pH, is obtained through the deacetylation of chitin found in the exoskeletons of crustaceans. Its favourable physicochemical and biological properties make chitosan versatile for applications in cosmetics, drug delivery, food preservation, textiles, and agriculture [ 9 ]. Hydrogels, three-dimensional networks of crosslinked polymers, can retain a large amount of water, reducing irrigation water loss and increasing fertilizer retention in the soil [ 6 ]. The ionotropic gelation method was employed to synthesize chitosan-alginate hydrogel beads, entwining urea within the biopolymer complexes. The process of extracting chitosan often employing harsh chemicals were replaced with green solvent extraction to produce chitosan of various molecular weight depending on the solvent component ratio were used in this study. The investigation focused on the influence of chitosan molecular weight, alginate amount, and crosslinker amount on the sustained release of urea from the hydrogel beads. Computational studies, using response surface methodology (RSM) software, were conducted alongside experiments. RSM, recognized for its ability to evaluate optimum reaction conditions with minimal experimental runs, proved statistically significant for encapsulation efficiency (p < 0.005) and urea release (p < 0.05). Consequently, RSM was identified as a suitable modeling method for determining the optimal synthesis conditions of chitosan-alginate hydrogel beads for the sustained release of urea [ 12 ]. Experimental techniques Materials Prepared chitosan according to our previous study are used [ 13 ] (highest molecular weight 115 kDa, 91% DDA; medium molecular weight 74 kDa, 90% DDA; lowest molecular weight 40 kDa, 86% DDA), sodium alginate with viscosity 871–9592 mPa.s was purchased from local store. All reagents were of analytical grade and were used as received without further purification. The viscosity of 5 wt% dissolved chitosan and 2.5 to 4.5 wt% aqueous sodium alginate solution at 25°C was measured with a rotational viscometer (NDJ-5S) using Rotor 1 under 12 rpm. Preparation of chitosan-alginate hydrogel beads with urea entrapment The hydrogel beads were prepared according to the procedure used by Ablouh and his coworkers [ 14 ], with some modifications. The composition of 17 prepared formulations based on chitosan, alginate and crosslinker, was listed in Table 1 . Chitosan–alginate beads were prepared by ionotropic gelation method using calcium ions as crosslinking agent. In detail, for Run 1, a crosslinking solution composed of 0.55 M CaCl 2 , 5% (w/v) chitosan and 1% (v/v) acetic acid was prepared at room temperature. The solution was constantly stirred for 30 min to obtain a homogenous suspension. A 10 mL emulsion containing 2.5 wt% alginate and 1 wt% urea was prepared by dissolving sodium alginate and urea powder in deionized water. The alginate-urea solution was pumped through a syringe and added drop by drop through an 18 G gauge blunt ended needle syringe into 10 mL of chitosan-crosslinker solution under mechanical stirring at 500 rpm. The spherical beads obtained were kept for 2 hr under continuous stirring. The beads were filtered by centrifugation, rinsed with deionized water and ethanol then dried in air overnight. The dried beads are then used to carry out urea release experiment. Table 1 Experimental design matrix and dependent variables attributed to the factors used for BBD Run Chitosan molecular weight Alginate (wt%) Crosslinker (M) X 1 X 2 X 3 Coded Actual Coded Actual Coded Actual 1 -1 Lowest -1 2.5 0 0.55 2 1 Highest -1 2.5 0 0.55 3 -1 Lowest 1 4.5 0 0.55 4 1 Highest 1 4.5 0 0.55 5 -1 Lowest 0 3.5 -1 0.10 6 1 Highest 0 3.5 -1 0.10 7 -1 Lowest 0 3.5 1 1.00 8 1 Highest 0 3.5 1 1.00 9 0 Medium -1 2.5 -1 0.10 10 0 Medium 1 4.5 -1 0.10 11 0 Medium -1 2.5 1 1.00 12 0 Medium 1 4.5 1 1.00 13 0 Medium 0 3.5 0 0.55 14 0 Medium 0 3.5 0 0.55 15 0 Medium 0 3.5 0 0.55 16 0 Medium 0 3.5 0 0.55 17 0 Medium 0 3.5 0 0.55 Particle size analysis The particle size of the dried beads was analysed using Mitutoyo 293–821 with 0.001 mm graduation micrometer. For each formulation, the particle size was calculated as the average value of the size of 10 air dried particles. Swelling study Swelling studies were carried out at room temperature on 1.0 g of dried beads placed into 5 mL of distilled water for 2 hours. The beads were recovered, gently wiped with paper towel, and weighed again. The dynamic weight change of the beads with respect to time, defined as swelling degree (Sw), was calculated according to Eq. (1). Sw (%) = (W t −W 0 )/W 0 ×100 (1) where W t is the weight of the beads in the swollen state at time t and W 0 is the initial weight of the dried beads [ 15 ]. Encapsulation efficiency The encapsulation efficiency of urea in the chitosan–alginate hydrogel beads was calculated by the formula shown in Eq. (2). EE (%) = (W u /W t ) x100 (2) where W u is the actual loading of urea and W t is the theoretical loading of urea in the beads [ 16 ]. Urea release evaluation After 2 hours of swelling, the solution was filtered to remove polymeric particles. The clear filtrate, 0.5 mL was taken from the swelling test were analyzed by UV-visible spectrophotometer to determine urea content [ 17 ]. The urea content was measured at 416 nm using 4-dimethylaminobenzaldehyde as colouring agent from the standard calibration curve. Each experiment was done in triplicate. Response surface methodology (RSM) analysis RSM implemented through a Box-Behnken design (BBD) using R Studio software, was employed to explore interactions among variables and optimize the synthesis conditions [ 18 ] for chitosan-alginate loaded urea hydrogel. The responding variables were encapsulation efficiency and urea release, both assessed using a UV-visible spectrophotometer. Three independent variables were selected for the synthesis: (X 1 ) molecular weight of chitosan (mPa.s), (X 2 ) alginate loading (wt%), and (X 3 ) crosslinker loading (M). These independent variables were examined at three levels: −1, 0, and + 1, with the corresponding ranges determined based on cost considerations and preliminary experiments defining the minimum and maximum values of the process variables. The specific process parameters and their coded levels are summarized in Table 1 . Chitosan molecular weights of 40 kDa, 74 kDa, and 115 kDa were used, while alginate loading was set at 2.5, 3.5, and 4.5 wt%. Crosslinker loading was investigated at 0.10, 0.55, and 1.00 M. A total of 17 experiments were conducted, including three replicates at five center points in the RSM analysis. This approach ensured that the prediction of results was adequately comparable to the experiments, supporting the evaluation of the selected quadratic model. Statistical analysis using analysis of variance (ANOVA) was applied to the experimental data to estimate the interaction between process variables and responses. Characterization of chitosan-alginate hydrogel beads Fourier-transform infrared spectroscopy (FTIR) spectra of the samples were recorded on Agilent Cary 630 spectrometer to identify chemical bonding and functional groups. The FTIR sample technique used was attenuated total reflection (ATR). Scanning Electron Microscope (SEM) images were taken using JSM-6390 (JEOL, USA) to identify the morphology of the samples. Results and Discussion Particle Size The average particle size of the 17 formulations ranged from 1909 to 6121 µm. Observations indicated slight variations in the mean particle size among these formulations. Consequently, it can be inferred that the syringe size, specifically the use of an 18-gauge syringe, plays a crucial role in generating larger particle sizes. Generally, employing a syringe with a needle or a pipette can result in the production of beads exceeding 1.00 mm in diameter [ 16 ]. Fourier Transform Infrared Spectroscopy FTIR spectroscopy was performed to investigate the features of each one of the polymers applied on the hydrogel formulation, as well the possible intermolecular interaction between chitosan and alginate that would affect the physical characteristics. The FTIR spectrum of the lowest molecular weight chitosan (Fig. 1 (a)) exhibited a broad band between 3500 − 3200 cm − 1 , which is attributed to the stretching of –OH overlapping with –NH 2 groups and intermolecular and intramolecular hydrogen bonds. The characteristic peaks of chitosan were observed at 2924 cm − 1 (C-H stretching), 1646 cm − 1 (C = O stretching of amide I), 1459 cm − 1 (–OH bending), 1100 − 990 cm − 1 (C-O stretching) [ 19 ]. Figure 1 (b) shows the characteristic peaks of the sodium alginate. The –OH group on the alginate shows a widened band due to hydrogen-molecular binding at 3320 cm − 1 and 1415 cm − 1 . Meanwhile, C-H stretching alkyl vibration is shown in wavenumbers 2925 cm − 1 , 1589 cm − 1 (-COO asymmetric stretching) which shows the carbonyl groups on the alginate, 1014 cm − 1 (vibration of carboxyl and ether). These absorptions were reported in alginate-cellulose-kaolin composites [ 20 ]. All hydrogel beads formulation had similar FTIR pattern. Run 7 is taken as an example of the hydrogel beads in Fig. 1 (d) with two prominent peaks showing characteristics of alginate and urea with different transmittance intensities. The infrared spectrum shows an intense broad absorption band around 3300 cm − 1 , which is attributed to the –OH group stretching vibration similar to alginate. Additionally, it indicates the high proportion of water linked to these groups [ 21 ]. The peak at 2100 cm − 1 attributed to the characteristic absorption of urea (Fig. 1 (c)) was also observed in the hydrogel spectrum indicating that urea was incorporated inside hydrogel. The intercalation of chitosan and alginate structure occurred due to crosslinking from CaCl 2 . The asymmetric band of carboxylate anions at 1589 cm − 1 shifted to higher wavelength at 1633cm − 1 in the spectra of the alginate-chitosan hydrogels. These changes suggested the electrostatic interaction between the negatively charged carboxyl groups of alginate and the positively charged amino groups of chitosan. Swelling study Figure 2 presents digital and scanning electron microscope (SEM) images of chitosan-alginate beads. Immediately following preparation, Run 7 beads (Fig. 2 (a)) exhibit a regular shape with homogeneous dimensions. They possess transparency and a uniformly smooth surface. While the drying process does not alter the bead shape, it results in a reduction of their dimensions and introduces modifications to the surface characteristics, rendering it irregular and wrinkled, as evident in the digital image (Fig. 2 (b)) and SEM image (Fig. 2 (c)). The reduction in dimension is attributed to the loss of water, inducing a decrease in the distance between polymeric chains due to the volume previously occupied by water [ 22 ]. In this context, the drying process impacts the spherical shape of the beads, causing a decrease in their size and the development of a markedly rough surface, potentially attributable to the adhesive properties of chitosan [ 23 ]. The fully swollen beads from Run 7 exhibit a regular shape and a smooth surface, as depicted in Fig. 2 (d). The chitosan-alginate hydrogel systems, when in a dry state and exposed to water, demonstrate the ability to rehydrate and undergo a swelling process, primarily associated with the hydration of the hydrophilic groups present in the polymers. Water diffuses into the polymeric chains, causing the system to swell without disintegration of the beads [ 24 ]. The considerable degree of crosslinking provides promising resistance against the escape of urea molecules through the hydrogel membrane [ 25 ]. The swelling ability varies for each formulation, with Run 11 achieving the maximum swelling degree of 77% at 2 hours, as illustrated in Fig. 3 . Limited swelling behaviour may be attributed to the formation of hydrogen bonds, enhancing structural stability and impeding the penetration of additional fluid into the deeper layers of particles, thereby restricting their swelling. Upon the addition of water, hydrogel beads immediately swell and maintain their structure. This can be attributed to the interactions between chitosan and alginate crosslinking chains, contributing to mechanical resistance, limiting fluid uptake, and preventing structure disintegration. The beads maintain a constant weight throughout the test duration. The hydrogels exhibit substantial variation in their water absorption capacity, ranging from 11% (Run 10) to 77% (Run 11). Similar findings have been reported with varying results, possibly related to the degree of deacetylation of the chitosan used [ 26 ]. Given the variations in chitosan molecular weight, amount of alginate, and amount of crosslinker in the prepared hydrogels, it is challenging to isolate the effect of each variable on the swelling capacity. Encapsulation efficiency All the formulations contain high amount of urea as shown in Fig. 4 . Generally, the urea content is homogeneously distributed in the excipient matrix. However, two formulations (Run 3 and Run 10) exhibited low encapsulation efficiency. Table 2 lists the full matrix of Box-Behnken experimental design for the three variables tested together with the observed responses for encapsulation efficiency. To examine the interaction between the independent variables with the responses of interest, a quadratic polynomial model was utilized. Using an integration of response surface methodology with Box-Behnken design together with numerical optimization of the overall desirability function, the optimum condition for maximizing encapsulation efficiency is identified. As for encapsulation efficiency response, the equation with best fit for the response is expressed where (X 1 ) molecular weight of chitosan (mPa.s), (X 2 ) alginate loading (wt%), and (X 3 ) crosslinker loading (M). $${Y}_{EE}=94.51950-9.78213{X}_{2}+9.15446{X}_{1}{X}_{2}+9.15180{X}_{2}{X}_{3}-11.55596{{X}_{2}}^{2}$$ Table 2 Experimental design matrix with response observed (Y) and predicted values (Predicted) Run X 1 X 2 X 3 Y_EE Predicted Y_EE Y_UR Predicted Y_UR 1 -1 -1 0 97.6855 101.9001 16.8233 10.5005 2 1 -1 0 92.2966 83.5912 4.2982 13.0861 3 -1 1 0 60.8710 64.0269 53.1831 41.8317 4 1 1 0 92.0992 82.3358 11.1479 14.9073 5 -1 0 -1 96.5504 89.9781 3.0646 18.7885 6 1 0 -1 91.3589 91.9521 6.8646 6.6191 7 -1 0 1 99.9062 99.0608 2.1664 4.1168 8 1 0 1 90.7667 97.0868 4.2491 -8.0526 9 0 -1 -1 93.2342 98.3431 41.2017 33.8326 10 0 1 -1 54.3076 60.4752 53.3910 50.4088 11 0 -1 1 87.7663 87.1482 14.2568 19.1609 12 0 1 1 85.4469 85.8875 25.1628 35.7371 13 0 0 0 96.5504 94.5195 21.5113 20.0714 14 0 0 0 89.3455 94.5195 10.6544 20.0714 15 0 0 0 97.4881 94.5195 20.7215 20.0714 16 0 0 0 95.2674 94.5195 21.6592 20.0714 17 0 0 0 93.4415 94.5195 30.9371 20.0714 *EE: encapsulation efficiency; UR: urea release For the encapsulation efficiency response, the linear term of alginate (X 2 ) emerged as the most influential factor (p = 0.001264), succeeded by its quadratic term (p = 0.003417). The molecular weight of chitosan and amount of crosslinker, while not directly affecting the response, influenced how alginate responded to encapsulation efficiency as the amount of alginate increased from 2.5 wt% to 4.5 wt%, as illustrated in Fig. 5 (a) and (b). The interaction terms also had a significant effect, with the interaction between the chitosan and alginate being more pronounced (p = 0.014918), followed by the interaction between alginate and crosslinker (p = 0.014939). Interestingly, as the amount of alginate increased and the crosslinker was maintained at the highest level, a higher encapsulation efficiency was achieved. Furthermore, when the alginate amount was held constant at 3.5 wt%, an increase in chitosan molecular weight led to a more consistent encapsulation efficiency, suggesting a potential optimum point. The determination coefficients of the encapsulation efficiency model, namely the multiple R 2 and the adjusted R 2 , were slightly higher at 0.844 and 0.7505 respectively. However, the difference between these two values was less than 0.2, and the p-value of the model was 0.001468 (p < 0.01), with a high p-value for the lack of fit (p = 0.593438). These combinations of statistical values indicate that the model could adequately describe the encapsulation efficiency behaviour with high statistical significance as summarised in Table 3 . The random distribution of residuals, as shown in Fig. 6 (a)-(c) for encapsulation efficiency experimental results, supports this conclusion. The concurrent effects of chitosan and alginate on the response, while maintaining the crosslinker at its maximum level are depicted in the 3D surface plots shown in Figs. 7 (a) and (b). Table 3 ANOVA results for the quadratic model of response surface for encapsulation efficiency Source Sum of Square Degree of Freedom Mean Square F Value p-value Encapsulation efficiency model 10 0.001468 \({X}_{2},{X}_{3}\) 866.59 2 433.29 11.1331 0.002859 \({{X}_{1}X}_{2}, {{X}_{1}X}_{3}, {{X}_{2}X}_{3}\) 674.13 3 224.71 5.7737 0.014815 \({{X}_{2}}^{2}\) 565.58 1 565.58 14.5321 0.003417 Residuals 389.20 10 38.92 Lack of Fit 129.55 4 32.39 0.7484 0.593438 Pure Error 259.65 6 43.27 Urea release The urea release on the 17 different formulations were done in 2 hours to examine the ability of hydrogel acting as a barrier to sustain the immediately release of urea as shown in Fig. 8 . The equation with best fit for urea release is expressed as below: $${Y}_{UR}=20.0714+8.2881{X}_{2}-7.3359{X}_{3}-14.7034{{X}_{1}}^{2}+14.7135{{X}_{2}}^{2}$$ The results in Table 4 revealed that the quadratic term of alginate (X 2 ) had the most significant effect on urea release (p = 0.01535), followed closely by the quadratic term for the molecular weight of chitosan (X 1 ) (p = 0.01540). The linear term of alginate also demonstrated a significant effect on urea release (p = 0.04234), while the crosslinker had a lesser effect (p = 0.07306). Interestingly, the interaction between these variables was not significant (p = 0.18486). Table 4 ANOVA results for the quadratic model of response surface for urea release Source Sum of Square Degree of Freedom Mean Square F Value p-value Urea Release Model 10 5.007 0.01282 \({{X}_{1},X}_{2},{X}_{3}\) 1276.25 3 425.42 3.9631 0.04234 \({{X}_{1}X}_{2}\) 217.71 1 217.71 2.0281 0.18486 \({{X}_{1}}^{2},{{X}_{2}}^{2}\) 1730.71 2 865.36 8.0614 0.00822 Residuals 1073.45 10 107.35 Lack of Fit 866.95 6 144.49 2.7988 0.16920 Pure Error 206.50 4 51.63 Despite the determination coefficients, namely the multiple R 2 and the adjusted R 2 of the urea release model, being relatively low at 0.7503 and 0.6004 respectively, the difference between these two values is less than 0.2 [ 27 ] coupled with a p-value of 0.01282 for the model (p < 0.05) and a high p-value for the lack of fit (p = 0.16920), suggests that the model is capable of adequately describing the urea release behaviour with a high degree of statistical significance. The random distribution of residuals, as depicted in Fig. 9 (a)-(c) for urea release experimental results, further corroborates this conclusion. Conclusion The utilization of a three-factor five-level central composite design proved to be a valuable tool for both characterization and optimization of chitosan–alginate hydrogel beads. Among the studied factors, the amount of alginate emerged as a key determinant significantly affecting both encapsulation efficiency (p = 0.001264) and urea release (p = 0.04716) in the chitosan-alginate beads. Based on the investigated parameters, the optimal formulation for achieving high encapsulation efficiency and controlled urea release involved the use of the lowest molecular weight chitosan, a moderate amount of alginate, and the maximum amount of cross-linker, corresponding to (− 1, 0, 1) in the experimental design. The impact of the crosslinker on reinforcing chitosan-alginate beads for sustained urea release is found to be notably significant. Declarations Acknowledgments The authors acknowledged the financial support provided by the Ministry of Higher Education Malaysia through Fundamental Research Grant Scheme (FRGS) with grant number of FRGS/1/2020/STG04/UNIMAS/02/1 Statements and Declarations Author contributions All authors contributed to material preparation, data collection, and analysis. The manuscript was mainly based on a draft written by MK and written through contributions of all authors. All authors read and approved the final manuscript. Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contribution All authors contributed to material preparation, data collection, and analysis. The manuscript was mainly based on a draft written by MK and written through contributions of all authors. All authors read and approved the final manuscript. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3855172","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":266630412,"identity":"44c59770-acf1-40e3-8158-e5db9001e460","order_by":0,"name":"Melody Kimi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAx0lEQVRIiWNgGAWjYBACCQYGxgMMbAxyQLqBaC0MIC3GpGtJJFI9EEhOO3zgwIeyw+kbbje3bvjxhyHa4AABLdLSaQkHZ5w7nLvhzsG2m71tDLkbCGmRk84xOMzbBtRyI7HtBm8DUVryP4C0pBsAtdz884cILdLSOQwgLQkgLbd52IjQIjk7zQDol3TDmSAtsm0SuTMJaZG4nfzwwYcya3m+G+nPbr75Y5PbR0gLFDTDjWBQIFJLHYIp30CcllEwCkbBKBg5AABNBE9vOnXfSAAAAABJRU5ErkJggg==","orcid":"","institution":"Universiti Malaysia Sarawak","correspondingAuthor":true,"prefix":"","firstName":"Melody","middleName":"","lastName":"Kimi","suffix":""},{"id":266630414,"identity":"1281b8ce-149e-4455-8bd2-bcbc90001014","order_by":1,"name":"Chee Jiun Chong","email":"","orcid":"","institution":"Universiti Malaysia Sarawak","correspondingAuthor":false,"prefix":"","firstName":"Chee","middleName":"Jiun","lastName":"Chong","suffix":""}],"badges":[],"createdAt":"2024-01-12 00:59:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3855172/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3855172/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49760005,"identity":"1020ec5a-d5ce-4206-8b2e-4f1b849513ae","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":16756,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of (a) extracted chitosan (b) commercial alginate (c) urea and (d) hydrogel bead\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/71ebda2d4f2ad4994a43fafe.png"},{"id":49760526,"identity":"80ada19a-eb2c-4ef8-a97d-3b6efd440ebf","added_by":"auto","created_at":"2024-01-17 15:47:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1204160,"visible":true,"origin":"","legend":"\u003cp\u003eDigital photograph of hydrogel beads (a) air dried condition (b) oven dried condition (c) swelling condition and (d) SEM image of dry bead\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/2fe0ef4ede1486b5b555559a.png"},{"id":49760014,"identity":"05450453-b11b-41a7-ad7a-f63133619551","added_by":"auto","created_at":"2024-01-17 15:39:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":44596,"visible":true,"origin":"","legend":"\u003cp\u003eSwelling (%) of each run of the hydrogel beads\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/b0843fc2ab6f699c5203e3e3.png"},{"id":49760009,"identity":"bf01f147-1da9-4582-8f0a-6715eb9deece","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":59231,"visible":true,"origin":"","legend":"\u003cp\u003eEncapsulation efficiency (%) of each run of the hydrogel beads\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/9117dc3f398ad0898c6e7efc.png"},{"id":49760010,"identity":"a79012f6-3b5c-49ef-af54-788b8db2c739","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":78271,"visible":true,"origin":"","legend":"\u003cp\u003eInteraction plot between (a) chitosan (X\u003csub\u003e1\u003c/sub\u003e) and alginate(X\u003csub\u003e2\u003c/sub\u003e) for encapsulation efficiency response and (b) alginate(X\u003csub\u003e2\u003c/sub\u003e) and crosslinker(X\u003csub\u003e3\u003c/sub\u003e) for encapsulation efficiency response\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/2a31e5192180cf2aadb34780.png"},{"id":49760006,"identity":"b14db351-e20a-4464-99d8-429bc28e7949","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":56833,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Predicted values for encapsulation efficiency vs observed values (b) Residual plot of predicted encapsulation efficiency (c) Normality of residual for encapsulation efficiency\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/9286ca53c857794c0a351d8e.png"},{"id":49760012,"identity":"9db3fc37-036c-48ec-b652-3519fcc15e05","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":417824,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface plot of concurrent effects of chitosan(X\u003csub\u003e1\u003c/sub\u003e) and alginate(X\u003csub\u003e2\u003c/sub\u003e) on the encapsulation efficiency response (b) Contour plot concurrent effects of chitosan(X\u003csub\u003e1\u003c/sub\u003e) and alginate(X\u003csub\u003e2\u003c/sub\u003e) on the encapsulation efficiency response\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/0eff8bde4327cbc62359bae9.png"},{"id":49760011,"identity":"d26c2679-c92c-43dd-aa53-55b2df27d942","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":38157,"visible":true,"origin":"","legend":"\u003cp\u003eUrea release (%) of each run of the hydrogel beads\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/8258d4ff36adb61c338af0fd.png"},{"id":49760929,"identity":"54dada5c-94f2-4cce-a148-37a518e96792","added_by":"auto","created_at":"2024-01-17 15:55:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":58259,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Predicted values for urea release vs observed values (b) Residual plot of predicted urea release (c) Normality of residual for urea release experiments\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/7a150a3d3c25b1c4d4ec3acf.png"},{"id":49760013,"identity":"0121da86-0cba-4394-bc47-0a98e5d879c6","added_by":"auto","created_at":"2024-01-17 15:39:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":447725,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface plot of concurrent effects of chitosan(X\u003csub\u003e1\u003c/sub\u003e) and alginate(X\u003csub\u003e2\u003c/sub\u003e) on the urea release response (b) Contour plot of concurrent effects of chitosan(X\u003csub\u003e1\u003c/sub\u003e) and alginate(X\u003csub\u003e2\u003c/sub\u003e) on the urea release response\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/2ea2dbe5273f59b0b921705d.png"},{"id":49914782,"identity":"da1876be-87e2-4aab-a524-e03fcd51e6cc","added_by":"auto","created_at":"2024-01-20 15:07:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2495700,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3855172/v1/992926f7-22e6-499b-a637-f3b2937db3ff.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Facile Preparation of Chitosan-Alginate Crosslinked with Calcium Chloride Hydrogel as Sustained Release Fertilizers","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAgrochemical fertilizers play a crucial role in supplying essential nutrients to crops on agricultural lands. Enhancing the efficiency of these agrochemicals is achievable by harnessing the sustained release property of polymers. Sustained release agrochemicals, in the form of granulated compounds, gradually release nutrients into the soil from polymer-based formulations. This controlled release, facilitated by a polymer composites network, extends the presence of nutrients in the soil, contributing to soil fertility preservation and mitigating soil pollution [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe direct application of chemical fertilizers to plants has shown limited utilization efficiency, with only 30\u0026ndash;35% of the nutrients being absorbed [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Urea, a commonly used nitrogen fertilizer, faces losses of 2\u0026ndash;20% through volatilization, 15\u0026ndash;25% through reactions with organic compounds in the soil, and 2\u0026ndash;10% through leaching into water systems, raising environmental concerns [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong hydrophilic polymers, two biodegradable polysaccharides, chitosan and alginate, meet the desired criteria of cost-effectiveness, environmental friendliness, and the ability to modulate fertilizer release. Alginate, a natural anionic hydrophilic polysaccharide derived from algae, forms hydrogels in the presence of divalent cations like Ca\u003csup\u003e2+\u003c/sup\u003e. Alginate-based materials excel in sustaining the release of urea due to their favorable swelling properties, enhancing urea loading in the prepared hydrogel [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, alginate alone has drawbacks, such as high viscosity and low solubility, which can be addressed by incorporating various biomaterials into the alginate structure.\u003c/p\u003e \u003cp\u003eChitosan, the second most abundant polysaccharide with positive-charge in acidic pH, is obtained through the deacetylation of chitin found in the exoskeletons of crustaceans. Its favourable physicochemical and biological properties make chitosan versatile for applications in cosmetics, drug delivery, food preservation, textiles, and agriculture [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHydrogels, three-dimensional networks of crosslinked polymers, can retain a large amount of water, reducing irrigation water loss and increasing fertilizer retention in the soil [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The ionotropic gelation method was employed to synthesize chitosan-alginate hydrogel beads, entwining urea within the biopolymer complexes. The process of extracting chitosan often employing harsh chemicals were replaced with green solvent extraction to produce chitosan of various molecular weight depending on the solvent component ratio were used in this study. The investigation focused on the influence of chitosan molecular weight, alginate amount, and crosslinker amount on the sustained release of urea from the hydrogel beads. Computational studies, using response surface methodology (RSM) software, were conducted alongside experiments. RSM, recognized for its ability to evaluate optimum reaction conditions with minimal experimental runs, proved statistically significant for encapsulation efficiency (p\u0026thinsp;\u0026lt;\u0026thinsp;0.005) and urea release (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Consequently, RSM was identified as a suitable modeling method for determining the optimal synthesis conditions of chitosan-alginate hydrogel beads for the sustained release of urea [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e"},{"header":"Experimental techniques","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003ePrepared chitosan according to our previous study are used [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] (highest molecular weight 115 kDa, 91% DDA; medium molecular weight 74 kDa, 90% DDA; lowest molecular weight 40 kDa, 86% DDA), sodium alginate with viscosity 871\u0026ndash;9592 mPa.s was purchased from local store. All reagents were of analytical grade and were used as received without further purification. The viscosity of 5 wt% dissolved chitosan and 2.5 to 4.5 wt% aqueous sodium alginate solution at 25\u0026deg;C was measured with a rotational viscometer (NDJ-5S) using Rotor 1 under 12 rpm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of chitosan-alginate hydrogel beads with urea entrapment\u003c/h2\u003e \u003cp\u003eThe hydrogel beads were prepared according to the procedure used by Ablouh and his coworkers [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], with some modifications. The composition of 17 prepared formulations based on chitosan, alginate and crosslinker, was listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Chitosan\u0026ndash;alginate beads were prepared by ionotropic gelation method using calcium ions as crosslinking agent. In detail, for Run 1, a crosslinking solution composed of 0.55 M CaCl\u003csub\u003e2\u003c/sub\u003e, 5% (w/v) chitosan and 1% (v/v) acetic acid was prepared at room temperature. The solution was constantly stirred for 30 min to obtain a homogenous suspension. A 10 mL emulsion containing 2.5 wt% alginate and 1 wt% urea was prepared by dissolving sodium alginate and urea powder in deionized water. The alginate-urea solution was pumped through a syringe and added drop by drop through an 18 G gauge blunt ended needle syringe into 10 mL of chitosan-crosslinker solution under mechanical stirring at 500 rpm. The spherical beads obtained were kept for 2 hr under continuous stirring. The beads were filtered by centrifugation, rinsed with deionized water and ethanol then dried in air overnight. The dried beads are then used to carry out urea release experiment.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design matrix and dependent variables attributed to the factors used for BBD\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eRun\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eChitosan molecular weight\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eAlginate (wt%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eCrosslinker (M)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eX\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e 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align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLowest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLowest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLowest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLowest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eParticle size analysis\u003c/h2\u003e \u003cp\u003eThe particle size of the dried beads was analysed using Mitutoyo 293\u0026ndash;821 with 0.001 mm graduation micrometer. For each formulation, the particle size was calculated as the average value of the size of 10 air dried particles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSwelling study\u003c/h2\u003e \u003cp\u003eSwelling studies were carried out at room temperature on 1.0 g of dried beads placed into 5 mL of distilled water for 2 hours. The beads were recovered, gently wiped with paper towel, and weighed again. The dynamic weight change of the beads with respect to time, defined as swelling degree (Sw), was calculated according to Eq.\u0026nbsp;(1).\u003c/p\u003e \u003cp\u003eSw (%) = (W\u003csub\u003et\u003c/sub\u003e\u0026minus;W\u003csub\u003e0\u003c/sub\u003e)/W\u003csub\u003e0\u003c/sub\u003e\u0026times;100 (1)\u003c/p\u003e \u003cp\u003ewhere W\u003csub\u003et\u003c/sub\u003e is the weight of the beads in the swollen state at time \u003cem\u003et\u003c/em\u003e and \u003cem\u003eW\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is the initial weight of the dried beads [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eEncapsulation efficiency\u003c/h2\u003e \u003cp\u003eThe encapsulation efficiency of urea in the chitosan\u0026ndash;alginate hydrogel beads was calculated by the formula shown in Eq.\u0026nbsp;(2).\u003c/p\u003e \u003cp\u003eEE (%) = (W\u003csub\u003eu\u003c/sub\u003e/W\u003csub\u003et\u003c/sub\u003e) x100 (2)\u003c/p\u003e \u003cp\u003ewhere W\u003csub\u003eu\u003c/sub\u003e is the actual loading of urea and W\u003csub\u003et\u003c/sub\u003e is the theoretical loading of urea in the beads [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eUrea release evaluation\u003c/h2\u003e \u003cp\u003eAfter 2 hours of swelling, the solution was filtered to remove polymeric particles. The clear filtrate, 0.5 mL was taken from the swelling test were analyzed by UV-visible spectrophotometer to determine urea content [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The urea content was measured at 416 nm using 4-dimethylaminobenzaldehyde as colouring agent from the standard calibration curve. Each experiment was done in triplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eResponse surface methodology (RSM) analysis\u003c/h2\u003e \u003cp\u003eRSM implemented through a Box-Behnken design (BBD) using R Studio software, was employed to explore interactions among variables and optimize the synthesis conditions [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] for chitosan-alginate loaded urea hydrogel. The responding variables were encapsulation efficiency and urea release, both assessed using a UV-visible spectrophotometer. Three independent variables were selected for the synthesis: (X\u003csub\u003e1\u003c/sub\u003e) molecular weight of chitosan (mPa.s), (X\u003csub\u003e2\u003c/sub\u003e) alginate loading (wt%), and (X\u003csub\u003e3\u003c/sub\u003e) crosslinker loading (M).\u003c/p\u003e \u003cp\u003eThese independent variables were examined at three levels: \u0026minus;1, 0, and +\u0026thinsp;1, with the corresponding ranges determined based on cost considerations and preliminary experiments defining the minimum and maximum values of the process variables. The specific process parameters and their coded levels are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Chitosan molecular weights of 40 kDa, 74 kDa, and 115 kDa were used, while alginate loading was set at 2.5, 3.5, and 4.5 wt%. Crosslinker loading was investigated at 0.10, 0.55, and 1.00 M.\u003c/p\u003e \u003cp\u003eA total of 17 experiments were conducted, including three replicates at five center points in the RSM analysis. This approach ensured that the prediction of results was adequately comparable to the experiments, supporting the evaluation of the selected quadratic model. Statistical analysis using analysis of variance (ANOVA) was applied to the experimental data to estimate the interaction between process variables and responses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of chitosan-alginate hydrogel beads\u003c/h2\u003e \u003cp\u003eFourier-transform infrared spectroscopy (FTIR) spectra of the samples were recorded on Agilent Cary 630 spectrometer to identify chemical bonding and functional groups. The FTIR sample technique used was attenuated total reflection (ATR). Scanning Electron Microscope (SEM) images were taken using JSM-6390 (JEOL, USA) to identify the morphology of the samples.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eParticle Size\u003c/h2\u003e \u003cp\u003eThe average particle size of the 17 formulations ranged from 1909 to 6121 \u0026micro;m. Observations indicated slight variations in the mean particle size among these formulations. Consequently, it can be inferred that the syringe size, specifically the use of an 18-gauge syringe, plays a crucial role in generating larger particle sizes. Generally, employing a syringe with a needle or a pipette can result in the production of beads exceeding 1.00 mm in diameter [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eFourier Transform Infrared Spectroscopy\u003c/h2\u003e \u003cp\u003eFTIR spectroscopy was performed to investigate the features of each one of the polymers applied on the hydrogel formulation, as well the possible intermolecular interaction between chitosan and alginate that would affect the physical characteristics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe FTIR spectrum of the lowest molecular weight chitosan (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)) exhibited a broad band between 3500\u0026thinsp;\u0026minus;\u0026thinsp;3200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is attributed to the stretching of \u0026ndash;OH overlapping with \u0026ndash;NH\u003csub\u003e2\u003c/sub\u003e groups and intermolecular and intramolecular hydrogen bonds. The characteristic peaks of chitosan were observed at 2924 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-H stretching), 1646 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching of amide I), 1459 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u0026ndash;OH bending), 1100\u0026thinsp;\u0026minus;\u0026thinsp;990 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-O stretching) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) shows the characteristic peaks of the sodium alginate. The \u0026ndash;OH group on the alginate shows a widened band due to hydrogen-molecular binding at 3320 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1415 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Meanwhile, C-H stretching alkyl vibration is shown in wavenumbers 2925 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1589 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (-COO asymmetric stretching) which shows the carbonyl groups on the alginate, 1014 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (vibration of carboxyl and ether). These absorptions were reported in alginate-cellulose-kaolin composites [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAll hydrogel beads formulation had similar FTIR pattern. Run 7 is taken as an example of the hydrogel beads in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d) with two prominent peaks showing characteristics of alginate and urea with different transmittance intensities. The infrared spectrum shows an intense broad absorption band around 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is attributed to the \u0026ndash;OH group stretching vibration similar to alginate. Additionally, it indicates the high proportion of water linked to these groups [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The peak at 2100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e attributed to the characteristic absorption of urea (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c)) was also observed in the hydrogel spectrum indicating that urea was incorporated inside hydrogel. The intercalation of chitosan and alginate structure occurred due to crosslinking from CaCl\u003csub\u003e2\u003c/sub\u003e. The asymmetric band of carboxylate anions at 1589 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shifted to higher wavelength at 1633cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the spectra of the alginate-chitosan hydrogels. These changes suggested the electrostatic interaction between the negatively charged carboxyl groups of alginate and the positively charged amino groups of chitosan.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSwelling study\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents digital and scanning electron microscope (SEM) images of chitosan-alginate beads. Immediately following preparation, Run 7 beads (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a)) exhibit a regular shape with homogeneous dimensions. They possess transparency and a uniformly smooth surface. While the drying process does not alter the bead shape, it results in a reduction of their dimensions and introduces modifications to the surface characteristics, rendering it irregular and wrinkled, as evident in the digital image (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b)) and SEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c)). The reduction in dimension is attributed to the loss of water, inducing a decrease in the distance between polymeric chains due to the volume previously occupied by water [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In this context, the drying process impacts the spherical shape of the beads, causing a decrease in their size and the development of a markedly rough surface, potentially attributable to the adhesive properties of chitosan [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe fully swollen beads from Run 7 exhibit a regular shape and a smooth surface, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d). The chitosan-alginate hydrogel systems, when in a dry state and exposed to water, demonstrate the ability to rehydrate and undergo a swelling process, primarily associated with the hydration of the hydrophilic groups present in the polymers. Water diffuses into the polymeric chains, causing the system to swell without disintegration of the beads [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The considerable degree of crosslinking provides promising resistance against the escape of urea molecules through the hydrogel membrane [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe swelling ability varies for each formulation, with Run 11 achieving the maximum swelling degree of 77% at 2 hours, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Limited swelling behaviour may be attributed to the formation of hydrogen bonds, enhancing structural stability and impeding the penetration of additional fluid into the deeper layers of particles, thereby restricting their swelling. Upon the addition of water, hydrogel beads immediately swell and maintain their structure. This can be attributed to the interactions between chitosan and alginate crosslinking chains, contributing to mechanical resistance, limiting fluid uptake, and preventing structure disintegration. The beads maintain a constant weight throughout the test duration. The hydrogels exhibit substantial variation in their water absorption capacity, ranging from 11% (Run 10) to 77% (Run 11). Similar findings have been reported with varying results, possibly related to the degree of deacetylation of the chitosan used [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Given the variations in chitosan molecular weight, amount of alginate, and amount of crosslinker in the prepared hydrogels, it is challenging to isolate the effect of each variable on the swelling capacity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eEncapsulation efficiency\u003c/h2\u003e \u003cp\u003eAll the formulations contain high amount of urea as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Generally, the urea content is homogeneously distributed in the excipient matrix. However, two formulations (Run 3 and Run 10) exhibited low encapsulation efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e lists the full matrix of Box-Behnken experimental design for the three variables tested together with the observed responses for encapsulation efficiency. To examine the interaction between the independent variables with the responses of interest, a quadratic polynomial model was utilized. Using an integration of response surface methodology with Box-Behnken design together with numerical optimization of the overall desirability function, the optimum condition for maximizing encapsulation efficiency is identified.\u003c/p\u003e \u003cp\u003eAs for encapsulation efficiency response, the equation with best fit for the response is expressed where (X\u003csub\u003e1\u003c/sub\u003e) molecular weight of chitosan (mPa.s), (X\u003csub\u003e2\u003c/sub\u003e) alginate loading (wt%), and (X\u003csub\u003e3\u003c/sub\u003e) crosslinker loading (M).\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$${Y}_{EE}=94.51950-9.78213{X}_{2}+9.15446{X}_{1}{X}_{2}+9.15180{X}_{2}{X}_{3}-11.55596{{X}_{2}}^{2}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design matrix with response observed (Y) and predicted values (Predicted)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRun\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eX\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eX\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eY_EE\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePredicted Y_EE\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY_UR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003ePredicted Y_UR\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e97.6855\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e101.9001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e16.8233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e10.5005\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e92.2966\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e83.5912\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.2982\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e13.0861\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e60.8710\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e64.0269\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e53.1831\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e41.8317\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e92.0992\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e82.3358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e11.1479\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e14.9073\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e96.5504\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e89.9781\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.0646\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e18.7885\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e91.3589\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e91.9521\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.8646\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e6.6191\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.9062\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.0608\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.1664\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.1168\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e90.7667\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e97.0868\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.2491\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e-8.0526\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e93.2342\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e98.3431\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e41.2017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e33.8326\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e54.3076\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e60.4752\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e53.3910\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e50.4088\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e87.7663\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e87.1482\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.2568\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e19.1609\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e85.4469\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e85.8875\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.1628\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e35.7371\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e96.5504\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e94.5195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e21.5113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e20.0714\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e89.3455\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e94.5195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.6544\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e20.0714\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e97.4881\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e94.5195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e20.7215\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e20.0714\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e95.2674\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e94.5195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e21.6592\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e20.0714\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e93.4415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e94.5195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e30.9371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e20.0714\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e*EE: encapsulation efficiency; UR: urea release\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor the encapsulation efficiency response, the linear term of alginate (X\u003csub\u003e2\u003c/sub\u003e) emerged as the most influential factor (p\u0026thinsp;=\u0026thinsp;0.001264), succeeded by its quadratic term (p\u0026thinsp;=\u0026thinsp;0.003417). The molecular weight of chitosan and amount of crosslinker, while not directly affecting the response, influenced how alginate responded to encapsulation efficiency as the amount of alginate increased from 2.5 wt% to 4.5 wt%, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) and (b). The interaction terms also had a significant effect, with the interaction between the chitosan and alginate being more pronounced (p\u0026thinsp;=\u0026thinsp;0.014918), followed by the interaction between alginate and crosslinker (p\u0026thinsp;=\u0026thinsp;0.014939). Interestingly, as the amount of alginate increased and the crosslinker was maintained at the highest level, a higher encapsulation efficiency was achieved. Furthermore, when the alginate amount was held constant at 3.5 wt%, an increase in chitosan molecular weight led to a more consistent encapsulation efficiency, suggesting a potential optimum point.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe determination coefficients of the encapsulation efficiency model, namely the multiple R\u003csup\u003e2\u003c/sup\u003e and the adjusted R\u003csup\u003e2\u003c/sup\u003e, were slightly higher at 0.844 and 0.7505 respectively. However, the difference between these two values was less than 0.2, and the p-value of the model was 0.001468 (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with a high p-value for the lack of fit (p\u0026thinsp;=\u0026thinsp;0.593438). These combinations of statistical values indicate that the model could adequately describe the encapsulation efficiency behaviour with high statistical significance as summarised in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The random distribution of residuals, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a)-(c) for encapsulation efficiency experimental results, supports this conclusion. The concurrent effects of chitosan and alginate on the response, while maintaining the crosslinker at its maximum level are depicted in the 3D surface plots shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) and (b).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eANOVA results for the quadratic model of response surface for encapsulation efficiency\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSum of Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDegree of Freedom\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEncapsulation efficiency model\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.001468\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({X}_{2},{X}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e866.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e433.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.1331\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.002859\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{X}_{1}X}_{2}, {{X}_{1}X}_{3}, {{X}_{2}X}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e674.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e224.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.7737\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.014815\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{X}_{2}}^{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e565.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e565.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.5321\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.003417\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResiduals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e389.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e38.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLack of Fit\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e129.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e32.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7484\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.593438\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure Error\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e259.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e43.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eUrea release\u003c/h2\u003e \u003cp\u003eThe urea release on the 17 different formulations were done in 2 hours to examine the ability of hydrogel acting as a barrier to sustain the immediately release of urea as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe equation with best fit for urea release is expressed as below:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$${Y}_{UR}=20.0714+8.2881{X}_{2}-7.3359{X}_{3}-14.7034{{X}_{1}}^{2}+14.7135{{X}_{2}}^{2}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe results in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e revealed that the quadratic term of alginate (X\u003csub\u003e2\u003c/sub\u003e) had the most significant effect on urea release (p\u0026thinsp;=\u0026thinsp;0.01535), followed closely by the quadratic term for the molecular weight of chitosan (X\u003csub\u003e1\u003c/sub\u003e) (p\u0026thinsp;=\u0026thinsp;0.01540). The linear term of alginate also demonstrated a significant effect on urea release (p\u0026thinsp;=\u0026thinsp;0.04234), while the crosslinker had a lesser effect (p\u0026thinsp;=\u0026thinsp;0.07306). Interestingly, the interaction between these variables was not significant (p\u0026thinsp;=\u0026thinsp;0.18486).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eANOVA results for the quadratic model of response surface for urea release\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSum of Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDegree of Freedom\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUrea Release Model\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.01282\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{X}_{1},X}_{2},{X}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1276.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e425.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.9631\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.04234\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{X}_{1}X}_{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e217.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e217.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.0281\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.18486\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{X}_{1}}^{2},{{X}_{2}}^{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1730.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e865.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.0614\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.00822\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResiduals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1073.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e107.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLack of Fit\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e866.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e144.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.7988\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.16920\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure Error\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e206.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e51.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eDespite the determination coefficients, namely the multiple R\u003csup\u003e2\u003c/sup\u003e and the adjusted R\u003csup\u003e2\u003c/sup\u003e of the urea release model, being relatively low at 0.7503 and 0.6004 respectively, the difference between these two values is less than 0.2 [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] coupled with a p-value of 0.01282 for the model (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and a high p-value for the lack of fit (p\u0026thinsp;=\u0026thinsp;0.16920), suggests that the model is capable of adequately describing the urea release behaviour with a high degree of statistical significance. The random distribution of residuals, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a)-(c) for urea release experimental results, further corroborates this conclusion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe utilization of a three-factor five-level central composite design proved to be a valuable tool for both characterization and optimization of chitosan\u0026ndash;alginate hydrogel beads. Among the studied factors, the amount of alginate emerged as a key determinant significantly affecting both encapsulation efficiency (p\u0026thinsp;=\u0026thinsp;0.001264) and urea release (p\u0026thinsp;=\u0026thinsp;0.04716) in the chitosan-alginate beads. Based on the investigated parameters, the optimal formulation for achieving high encapsulation efficiency and controlled urea release involved the use of the lowest molecular weight chitosan, a moderate amount of alginate, and the maximum amount of cross-linker, corresponding to (\u0026minus;\u0026thinsp;1, 0, 1) in the experimental design. The impact of the crosslinker on reinforcing chitosan-alginate beads for sustained urea release is found to be notably significant.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors acknowledged the financial support provided by the Ministry of Higher Education Malaysia through Fundamental Research Grant Scheme (FRGS) with grant number of FRGS/1/2020/STG04/UNIMAS/02/1\u003cstrong\u003e \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatements and Declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to material preparation, data collection, and analysis. The manuscript was mainly based on a draft written by MK and written through contributions of all authors. All authors read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose. \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to material preparation, data collection, and analysis. The manuscript was mainly based on a draft written by MK and written through contributions of all authors. All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSathisaran I, Balasubramanian M (2020) Physical characterization of chitosan/gelatin-alginate composite beads for controlled release of urea. Heliyon 6(11):e05495. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.heliyon.2020.e05495\u003c/span\u003e\u003cspan address=\"10.1016/j.heliyon.2020.e05495\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIftime MM, Ailiesei GL, Ungureanu E, Marin L (2019) Designing chitosan based eco-friendly multifunctional soil conditioner systems with urea controlled release and water retention. Carbohydr Polym 223:115040. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.carbpol.2019.115040\u003c/span\u003e\u003cspan address=\"10.1016/j.carbpol.2019.115040\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLawrencia D, Wong SK, Low DYS, Goh BH, Goh JK, Ruktanonchai UR, Soottitantawat A, Lee LH, Tang SY (2021) Controlled Release Fertilizers: A Review on Coating Materials and Mechanism of Release. Plants 10:238. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/plants10020238\u003c/span\u003e\u003cspan address=\"10.3390/plants10020238\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSahoo DR, Biswal T (2021) Alginate and its application to tissue engineering. 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Appl Surf Sci 427:340\u0026ndash;348. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.apsusc.2017.08.241\u003c/span\u003e\u003cspan address=\"10.1016/j.apsusc.2017.08.241\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"chitosan, alginate, urea, hydrogel, controlled release","lastPublishedDoi":"10.21203/rs.3.rs-3855172/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3855172/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe utilization of urea in the agricultural sector as a fertilizer is susceptible to losses through volatilization and leaching. A strategy to mitigate this environmental impact involves employing a sustained-release approach for urea, thereby diminishing both the quantity and frequency of its application. These agrochemicals utilize a physical barrier to curtail the dissolution of urea, and their efficacy in fertilizer release is dictated by their physical characteristics. In the current investigation, hydrogel beads comprising urea were developed by blending biodegradable polysaccharides, specifically chitosan and alginate, in the presence of calcium chloride as a crosslinker through ionotropic gelation. The Box-Behnken design was employed to analyze the impacts of independent variables (low, medium, and high molecular weight chitosan; 2.5 to 4.5 wt% alginate; and 0.10 M to 1.00 M calcium chloride crosslinker) on encapsulation efficiency and urea release. After model evaluation, the optimal conditions for encapsulation efficiency and urea release were determined as the use of the lowest molecular weight chitosan, a medium amount of alginate, and the maximum amount of crosslinker, resulting in a loading efficiency of up to 98.5% and a urea release of only 2.2% within 2 hours. The composition of the polymeric hydrogel was found to govern encapsulation efficiency and urea release, while the swelling behaviour in water remained unaffected. The hydrogel beads exhibited a spherical morphology, and Fourier transform-infrared spectroscopy confirmed the presence of urea within the beads.\u003c/p\u003e","manuscriptTitle":"Facile Preparation of Chitosan-Alginate Crosslinked with Calcium Chloride Hydrogel as Sustained Release Fertilizers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-17 15:39:29","doi":"10.21203/rs.3.rs-3855172/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"46ea2f55-8052-4492-9836-4d41373fb574","owner":[],"postedDate":"January 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-01-20T14:59:20+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-17 15:39:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3855172","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3855172","identity":"rs-3855172","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}