Design and optimization of thermosensitive injectable alginate-based hydrogels: potential for loading therapeutic compounds

Injectable hydrogels with high biocompatibility and easy fabrication have numerous advantages over other drug delivery systems. These can be readily injected at the tumor site, causing high loads of drugs entrapped within their structures. The aim of the present study, therefore, was to prepare an optimal formulation of alginate-based hydrogels to be thermosensitive and injectable for loading therapeutic agents and drug delivery. Here, four constituents including hydroxypropyl methylcellulose (HPMC), sodium alginate (SA), beta-glycerol phosphate (β-GP), and calcium chloride (CaCl 2 ) were used to obtain the optimal formulations. A surface response methodology (RSM), namely Box-Behnken, in the design of experiment (DOE), was employed. DOE identified 27 hydrogels, which were synthesized accordingly. Based on the gelation temperature (as an objective function), two optimal hydrogel formulations were predicted by DOE and prepared for further analysis. Rheological tests, ART-FTIR, FE-SEM, biodegradability, swelling (at PH = 7.45 and PH = 6.5), and hydrogel biocompatibility to L929 cells (staining of Dihydroetidium (DHE), Phaloidine, and Acridine Orange (AO)) were performed. Furthermore, to demonstrate the potential of the optimum hydrogels for carrying and releasing therapeutic agents, menstrual blood-derived mesenchymal stem cells exosomes (Mens-exo) were used as a model drug, and their release rate and hydrogel degradability were evaluated. The results showed that all the constituents in the hydrogels except for HPMC had significant effects on the gelling process (temperature). The two hydrogel formulations with gelling temperatures of 35° C (H1) and 37° C (H2) were selected for relevant tests. ATR-FTIR and FE-SEM analyses indicated the suitability of chemical and morphological characteristics of both hydrogel samples. The obtained storage modulus (G ') and loss modulus (G″) for gelling temperature and time, strain and frequency tests showed that H1 hydrogel has more favorable rheological properties. Furthermore, in the evaluation of degradability at PH = 6.5, H1 hydrogel was degraded in a longer time (154 hours) and was more stable than H2 (100 hours). The cells loaded in the hydrogels also indicated the superior biocompatibility of H1 hydrogel rather than the H2. Moreover, the Mens-exo loading in H1 hydrogel exhibited a sustained release with reasonable degradability of the hydrogel. The results showed that the optimal hydrogels made up of HPMC, SA, β-GP, and CaCl 2 were thermosensitive and injectable. In particular, the H1 hydrogel (SA = 0.889, HPMC = 2, β-GP = 5 and CaCl 2 = 3.306) had high potential for loading therapeutic compounds.