Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters

Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters | 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 Article Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters Muhammad Dawood Husain, Shenela Naqvi, Danyal Rashid Khan, Warisha Farhat, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7363924/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Graphical Abstract Abstract Owing to the growing demand for textile-based wearable soft robots for construction of exosuits and rehabilitation gloves, a detailed investigation of different types of constructing materials and geometric properties of knitted pneumatic actuators is required to achieve desired functioning. This study did comparative analysis among different seamless pneumatic actuators which were constructed by knitting yarns of different materials. The actuators featured pleats on the top layer and were shaped like tubes. We selected Viscose Polyester Nylon (VPN), Acrylic, and Polyester-punched Lycra for the top layers and low-melt Nylon yarn for the bottom layers. To assess their performance, actuators were designed with three length sizes, two widths, and three course ratios. Bending angle and distal tip force were measured on a customized test rig developed for this study. It was observed that actuators made of acrylic yarn with a 3:1 course ratio achieved the desired bending angle of 160° at just 31 kPa internal air pressure, an improved result than those developed in previous studies. These acrylic yarn actuators were also easier to knit compared to the other materials selected. While other actuators required higher internal pressure to achieve the bending angle of 160º, only a wider width (3.2 cm) produced a desired bending angle and a higher tip force (4.3 N at 32 kPa). This study highlights that the interplay of constructing materials and the geometry of pneumatic actuators significantly alters their input and output, allowing for tailored performance across different human hand/finger sizes and specific applications. Physical sciences/Engineering Physical sciences/Materials science Soft Robotics Knitted Pneumatic Actuators Pneumatic Actuation Wearable Robotics Bending Angle and Distal tip force Seamless Weft Knitting Technology Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Textiles are no longer passive material; they are becoming active components in next-generation soft robotics. The field of soft robotics is emerging, driven by the need for robots that can safely interact with humans [ 1 ]. Unlike rigid robots, soft robots, which often utilize materials with Young’s moduli comparable to those of biological muscles/tissues, conform to irregular shapes and perform delicate tasks [ 2 ] [ 3 ] [ 4 ]. Among the various actuation mechanisms, pneumatic actuation stands out due to its simplicity, high power-to-weight ratio, and improved response time. However, there are research gaps to overcome challenges related to material design and actuation control for wearable applications and assistive devices [ 5 ] [ 6 ] [ 7 ]. Therefore, a shift from conventional rigid robots to compliant textile-based robots is essential to provide comfort and resilience to the wearer [ 8 ] [ 9 ]. Recent advancements have highlighted the potential for fabric-based pneumatic actuators, particularly seamless knitted designs, to enable soft exosuits and robotic gloves. Knitted structures, with their inherent design flexibility, endurance, and ease of manufacturing, offer significant potential for developing soft actuators, particularly knitted pneumatic actuators [ 10 ] [ 11 ] [ 12 ]. These actuators, when inflated with air, provide controlled movements and can be fabricated into complex three-dimensional shapes using textile materials, allowing for required bending and distal tip force/pressure [ 13 ] [ 14 ] [ 15 ]. Despite its potential, a comprehensive understanding of the influence of material selection and geometric properties such as length, width, and course ratio on the actuation behavior needs to be investigated [ 16 ] [ 17 ] [ 18 ]. Knitting is one of the textile manufacturing processes based on the interloping of the yarns into rows (courses) and columns (wales) constituting loops or stitches [ 19 ]. A continuous strand of yarn is used to develop knitted fabric. The flatbed knitting machine is the most suitable method for producing knitted fabric mechanically, and it is most the accessible for textile prototyping. The flat bed machine forms a knitted fabric structure through a sliding action of multiple needles arranged in parallel on flat bed. The gauge of the machine is the number of needles per inch on the needle bed; therefore, it determines the fabric thickness that can be produced. Finer fabric can be knitted on high-gauge machines (12–18 needles per inch), while coarser fabrics can be knitted on lower gauge machines. In knitting machines, the yarn carrier moves across the needles to supply the yarn to the needle hook, which grabs the yarn to form the stitch and pulls it through the previously knitted help loop as shown in Fig. 2 a. The structure of inter-looped yarn gives knitted fabrics their inherent extensibility. Modern knitting machines control the movement of the needles and the yarn carriers simultaneously. These techniques help to develop intricate patterns on the computerized flat-bed knitting machines [ 20 ] [ 21 ]. In this research, multi-gauge machine was used to develop knitted actuators. The basic actuator design consists of a knitted pouch construction having plain knitted on top and the bottom layer. To this work, bending was the desired deformation, therefore an anisotropic knitted structure for an actuator was designed. The geometric parameters and type of yarns were varied to control the extensibility of the top and bottom layers as listed in Table 2 . To create comparison length, width, course ratio & the type of textile materials was selected to analyze the bending performance and distal tip force. Researchers also worked on traditional cut-and-sew actuators, which are typically formed by joining multiple layers of fabric through different techniques such as sewing, heat sealing, ultrasonic welding and adhesive bonding [ 22 ] [ 23 ]. The primary purpose of these bonding is to create enclosed chambers for pneumatic actuation. For instance, combining fabrics with contrasting mechanical properties, such as stretchable knits and strain-limiting wovens, and joining them with seams allows for controlled bending, extension, or contraction [ 24 ] [ 25 ]. Specific stitching techniques, like zigzag or overlock stitches, can further enable or limit stretching along particular directions [ 26 ] [ 8 ]. Additionally, conductive yarns can be embedded through these seams for sensing or heating purposes. While offering benefits such as light weight construction, low-profile design, and comfortability, seam actuators face several challenges [ 27 ] [ 28 ]. Traditional cut-and-sew methods can be labor intensive, time consuming, and may introduce weak points prone to failure, such as stitch failure or fabric tearing at interfaces, air tightness issues, and manual operations [ 24 ] [ 29 ]. The significance of seamless knitted actuators overcome many of these challenges, offering a more advanced and integrated approach for textile actuators [ 30 ]. Unlike seam actuators, which depends on pre-cut fabric pieces, seamless knitting approach allows the production of actuators in a convenient manner, often in a single machine run. This advanced knitting technique significantly reduces the need for labor-intensive cutting and sewing steps, leading to rapid, automated, and customizable manufacturing [ 3 ]. Furthermore, techniques like Intarsia allow layers of the knitted fabric to join seamlessly, enable the fabrication of the actuators [ 17 ] [ 31 ]. Machine knitting also facilitates the seamless integration of functionality, directly embedding sensing and heating elements using conductive yarns into the actuator structure during fabrication [ 30 ] [ 32 ]. Seamless actuators represent a significant advancement from traditional cut-and-sew methods by addressing digital textile manufacturing to produce soft robotic component for wearable applications. In this research, a multi-gauge machine was used to develop knitted actuators. The basic design of the actuator features a knitted pouch construction with a plain knitted layer on both the top and bottom. To this work, bending was the desired deformation; therefore, an anisotropic knitted structure for an actuator was designed. The geometric parameters and type of yarns were varied to control the extensibility of the top and bottom layers. To make a comparison, four lengths (23cm, 26cm, 29cm & 32cm), two widths (3.3cm & 2.2cm), three course ratios (3:1, 2:1 & 1:1), and three constructed textile materials (Acrylic, Polyester punch lycra, and Viscose Polyester Nylon VPN blended yarn) were selected to measure and analyze the bending performance and distal tip force. 2. Experimental Section This section discusses the materials, fabrication methods, experimental setup, and characterization procedures used to evaluate the knitted pneumatic actuators. 2.1 Materials All the samples were developed in the form of tubular knitted structure with different top and bottom layers. The Table 1 showed the material used for the manufacturing of tubular knitted actuator. Figure 1 illustrates each actuator consisting of a two layered fabric. Table 1 Materials used for experimentation S.No. Material Type Supplier 1 Acrylic Ring Spun 32/2 Nm Textile Yarn (Top layer) Sourced from local market at Karachi, Pakistan. 2 Polyester punched Lycra 450 D/25 D 3 VPN (Viscose Polyester Nylon) 50% Viscose; 28% Polyester; 22% Nylon yarn 48/2 Nm 4 Nylon low melt yarn 360 D Textile Yarn (Bottom layer) Commercially sourced 5 Stretchlon 200 Bladder material Commercially sourced The three yarns, including acrylic, polyester punched lycra, and viscose polyester nylon (VPN) were used to create the top layer of the seamless actuators as the main requirement for the top layer material was to have extensible/stretchable characteristics. The bottom layer yarn: i.e., nylon low melt was used as it would provide inextensibility after heat-set. The bladder is a critical component, holding pneumatic air for bending and straightening during actuation. While commercially available elongated rubber/latex balloons could be used, this research utilized High Stretch Bagging Film (Stretchlon® 200) [ 9 ] for the development of bladder via heat sealer as shown in Fig. 1 . It is a TPU (Thermoplastic polyurethane) sheet that stretches up to 500% of its original length upon mechanical or pneumatic force and readily conforms to any fitted or inserted shape. 2.2 Actuator Design and Fabrication In this study, actuator samples were produced using a 14-gauge SHIMA SEIKI SSR 112 computerized flatbed knitting machine, employing a plain knitted tubular single jersey structure. The study systematically varied actuator length, width and course ratio as key geometric parameters, alongside different top layer yarn materials, to investigate their combined influence on actuator performance. Table 2 shows the specifications of knitted pneumatic actuator and its influence on geometric properties after heat-set. The type of yarn used to make the knitted fabric has a direct relation with its stretch properties. Since, the actuator would be in tubular shape so to create difference between the top and bottom layers course ratio was also selected as an important parameter. Figure 2 depicts the overview of process flow of pneumatic weft knitted actuator. Figure 3 shows the dimensional changes in the samples (SA1 to SA4c) to after heating at 140°C for 10 minutes, resulting from shrinkage of the low melt nylon yarn. The description of each sample is mentioned in Table 2 . Table 2 Specifications and Dimensional Changes of Knitted Pneumatic Actuators After Heat Treatment. Sample Code SA1a SA1b Top Layer Acrylic Acrylic Bottom Layer Nylon Low Melt Nylon Low Melt Course ratio 3:1 3:1 Parameter After Knitting (a) After Heating (b) % diff** After Knitting After Heating % diff** Length (cm) 23.0 13.8 -40% 26.0 16.5 -37% Width (cm) 3.2 2.5 -23% 3.2 2.3 -27% Sample Code SA1c SA1d Top Layer Acrylic Acrylic Bottom Layer Nylon Low Melt Nylon Low Melt Course ratio 3:1 3:1 Parameter After Knitting After Heating % diff** After Knitting After Heating % diff** Length (cm) 29.0 17.8 -39% 32.0 18.5 -42% Width (cm) 3.2 2.5 -23% 3.2 2.4 -26% Sample Code SA2 SA3a Top Layer Acrylic Polyester punched lycra yarn (PPL) Bottom Layer Nylon Low Melt Nylon Low Melt Course ratio 3:1 3:1 Parameter After Knitting After Heating % diff** After Knitting After Heating % diff** Length (cm) 23.0 13.3 -42% 23 13.27 -42% Width (cm) 2.2 1.8 -17% 2.2 1.80 -18% Sample Code SA3b SA4a Top Layer VPN* (Viscose Polyester Nylon) Acrylic Bottom Layer Nylon Low Melt Nylon Low Melt Course ratio 3:1 2:1 Parameter After Knitting After Heating % diff** After Knitting After Heating % diff** Length (cm) 23 13.17 -43% 23.0 12.2 -47% Width (cm) 2.2 1.80 -18% 2.2 1.8 -18% Sample Code SA4b SA4c Top Layer Polyester punched lycra yarn (PPL) Acrylic Bottom Layer Nylon Low Melt Nylon Low Melt Course ratio 2:1 1:1 Parameter After Knitting After Heating % diff** After Knitting After Heating % diff** Length (cm) 23.0 13.9 -40% 23.0 13.1 -43% Width (cm) 2.2 1.8 -18% 2.2 1.8 -20% * VPN (Viscose Polyester Nylon) = 50% Viscose; 28% Polyester; 22% Nylon ** % diff = \(\:\raisebox{1ex}{$\left(a-b\right)*100$}\!\left/\:\!\raisebox{-1ex}{$a$}\right.\) 2.3 Experimental Setup To evaluate the performance of the seamless knitted actuators, a customized test rig was developed, as illustrated in Fig. 4 . This test rig was equipped with a pressure sensor to monitor the air pressure, a camera system (e.g., webcam, DSLR) for capturing images to determine bending curvature (°) via image analysis, force sensor (e.g., Compression load Cell) to measure distal tip force (N). The bending angle (º) test analyzes the change of bending angle by varying the air pressure (kPa). The distal tip force (N) tests the force generated at the distal end of the actuator under various internal pressures. LabVIEW software was used for automated control of pressure, data acquisition from sensors, and synchronization of image capture. 2.4 Experimental Procedures 2.4.1 Bending Angle Measurement For the measurement of bending angle, the inserted bladder was inflated through an air compressor. The actuator was suspended by fixing one end while the other end is free to move, as depicted in Fig. 5 . Images were captured at discrete pressure intervals (e.g., every 5 kPa from 0 to 50 kPa) during inflation. Bending angles were then measured by post-processing these captured images using image analysis software (e.g., ImageJ, Photoshop) based on the method adapted from Rehman, et.al [ 33 ]. 2.4.2 Distal tip force Measurement For distal tip force measurement, after inflating the actuator at a pressure where the bending angle is close to 160º, the inflated actuators were inserted into a customized cup designed to establish consistent contact with a load cell shown in Fig. 6 . A LabVIEW program controlled the inflation process to a maximum pressure of 50 kPa while simultaneously recording pressure and force data from the load cell. Data points were recorded at specific intervals (e.g., every 2 seconds or 2 kPa). This method was adapted from Elmoughni et.al [ 27 ]. 3. Results and Discussion This section presents the experimental results on the bending behavior and distal tip force of the knitted pneumatic actuators, discussed in the context of their intended application in assistive and rehabilitation devices. For ideal performance in grasping motions, actuators should generate higher distal tip forces at lower internal pressures to optimize energy efficiency and safety. The bending curvature is equally crucial, as it determines whether the actuator would be able to move the human hand to perform activities of daily living (ADLs). Literature suggests that the effective human index finger flexion requires a bending angle of approximately 160° and a distal tip force around 7.3 N [ 11 ]. Seamless knitted Actuators developed by Elmoughni et al.[ 27 ] had a distal tip force of 5.3 N at 150 kPa. Consequently, for assistive glove applications, the desired range of value for distal tip force would be 7–8 N, while achieving a minimum bending angle of 160°. 3.1 Bending behavior of knitted pneumatic actuators The bending behavior of seamless knitted actuators was investigated by systematically varying the pneumatic pressure within the internal bladder. The influence of key parameters including actuator length, width, yarn composition, and course ratio on actuation performance was systematically analyzed. 3.1.1 Influence of Actuator Length To evaluate the effect of length, four samples (SA1a, SA1b, SA1c and SA1d) were developed with varying lengths while maintaining consistent materials: an acrylic on top layer and a nylon low melt on bottom layer. The samples were analyzed in two distinct ways. In the first analysis (a), the bending angle was measured as the pressure was varied. The data from this analysis aimed to establish a correlation between pressure and bending angle, a relationship that is further explored in figure b. For second analysis (b), the bladder was inflated to a constant pressure of 35kPa to observe the bending angle. This specific data point was used to establish a clear relationship between controlled pressure and the resulting bending angle for each sample, which allowed for direct comparison of the effect of length. As shown in Fig. 7 a, all samples exhibited a positive correlation between applied pressure and bending angle. SA1a (23 cm) : Bending initiated at 11 kPa, reaching 167° at 32 kPa. SA1b (26 cm) : Initiated at 13 kPa, reaching 160° at 31 kPa. SA1c (29 cm) : Similar performance as SA1a. SA1d (32 cm) : Similar performance as SA1a. A length of 23 cm was identified as optimal, offering efficient bending while approximating the dimensions of a human finger, which is advantageous for wearable and grasping applications. 3.1.2 Influence of Actuator Width To investigate the influence of width, the actuator width was reduced from 3.2 cm (SA1a) to 2.2 cm (SA2). Narrower actuators required higher inflation pressure due to increased internal resistance. Bending began at approximately 18kPa, achieving 160° at 45kPa (Fig. 8 ). Despite the higher-pressure requirement, the 2.2 cm width demonstrates anatomical suitability and the potential to generate greater force through volumetric expansion, suggesting its suitability for specific applications. 3.1.3 Influence of Top Layer Material With optimal length and width established, different yarns were tested in the actuator’s top layer: air-covered polyester punched lycra (SA3a), Viscose-Polyester-Nylon blend (SA3b), and acrylic (SA2). All configurations initiated bending at ~ 19kPa, followed by significant bending: SA2 (Acrylic): Achieved 180° at 44 kPa SA3b (VPN blend): 180° at 46 kPa SA3a (Lycra blend): 180° at 48 kPa As seen in Fig. 9 , an actuator with acrylic yarn exhibited superior bending at lower pressures, highlighting its performance advantage. 3.1.4 Influence of course ratio To explore the effect of structural configuration, samples SA4a - SA4c were produced with varied course ratios, including a reduced ratio of 2:1 (top: bottom) and a balanced 1:1 (top: bottom). SA4a (Acrylic, 2:1): Reached 160° at 57 kPa. SA4b (Polyester Lycra, 2:1): bent to 160° at 56 kPa, though pleat formation was restricted due to the yarn’s compact structure. SA4c (Acrylic, 1:1): Exhibited no bending, attributed to the absence of pleats and symmetric 1:1 course ratio. The higher-pressure requirement in 2:1 structure is attributed to limited pleat flexibility and increased stiffness, especially in compact lycra-based samples. The findings confirm that pleat formation governed by a higher top-layer course ratio is critical for effective actuation as shown in Fig. 10 . By analyzing the performance of all three SA4 samples, it is evident that despite variations in the top layer material, the bending angle is primarily determined by the course ratio between the top and bottom layers. The pleats on the top layer, which facilitate bending, are a direct consequence of a higher course ratio in the top layer compared to the bottom layer of the actuator. 5.1 Distal tip force The distal tip force of the actuators was assessed across samples varying in length (SA1 series), width (SA2), top layer fiber type (SA3 series), and course ratio (SA4 series). As observed in Fig. 11 , the maximum distal tip force achieved across tested samples is 4.3 N at the applied pressure of 35 kPa, which compares to 5.4 N at 150 kPa reported in a previous study [ 27 ]. The samples exhibited varying distal tip forces and actuation responses based on their length, material composition, and structural design. Among the SA1 series, SA1a (23 cm) demonstrated the highest distal tip force of 4.3 N at 36 kPa due to its short length. As the length increased, the force generally decreased; SA1b (26 cm) achieved 2.8 N at 36 kPa but required a higher initial pressure of approximately 16 kPa, while SA1c (29 cm) had a slightly reduced distal tip force of 2.7 N at 36 kPa. The longest sample, SA1d (32 cm), exhibited the lowest force at 2.4 N at 36 kPa, attributed to inefficiencies from its increased internal volume. In contrast, samples with different material compositions, tested at higher pressures, showed improved force generation. SA2 (Acrylic Yarn) achieved 3.34 N at 50 kPa, showcasing improved distal tip force due to the presence of pleats on its top layer. Similarly, SA3a (polyester punched lycra yarn) and SA3b (Viscose Polyester Nylon blended yarn) delivered similar maximum forces of 3.38 N and 3.4 N, respectively, at 50 kPa. The SA4 series, which involved different course ratios, also showed distinct results: SA4a (2:1, Acrylic Yarn) produced a maximum force of 2.8 N at 50 kPa. SA4b (2:1, Polyester punched lycra yarn) yielded a slightly higher force of 3.4 N at 50 kPa due to its more compact structure, whereas SA4c (1:1, Acrylic and Nylon Low Melt Yarn) showed the lowest force of 1.79 N at 55 kPa, indicating limited efficiency in force generation. The results demonstrate that actuator length, width, yarn type, and course ratio significantly influence distal tip force performance. By selecting the optimal combination of these parameters, seamless actuators can be tailored for specific applications requiring precise force and bending capabilities. The results were aligned with previous work of Elmoughni et al. [ 27 ] who also highlighted the importance of actuator dimensions on the distal tip force generation. Figure 12 presents a comparative view of the pressure required to achieve a bending angle of 160° and the corresponding distal tip force output for all sample groups: Actuator length variations (SA1) samples had a limited impact on bending angle but significantly affected distal tip force, reinforcing the importance of length optimization to achieved desired distal tip force. The variation of width variation from 3.2 cm in SA1 to 2.2 cm in SA2 samples led to increased pressure requirements without substantial distal tip force gains. The textile material variation (SA3) samples resulted in similar force outputs (both internal pressure and distal tip force), validating the use of multiple yarn types. The variation in course ratio (SA4) samples with lower course ratios require more pressure, and course ratio variations also affect distal tip force. Therefore, the study discussed that actuator width and course ratio played a vital role in influencing bending efficiency and force generation compared to actuator length. Narrower actuators, though requiring higher internal pressures, showed improved forced output, making them more suitable for the compact, wearable assistive applications. Conversely, actuator’s length exhibited a comparatively minor impact on the overall bending performance; however, distal tip force measurements showed an inverse relationship with actuators length, indicating that shorter actuators generate greater force due to reduced internal volume. Notable, the higher course ratio (3:1) significantly improved the flexibility and bending capability through enhanced pleat formation, a crucial attribute for human-centric soft robotics. Conclusions The study conducted an in-depth investigation into the impact of material selection and the knitting parameters, specifically length, width, yarn type, and course ratio, on the performance of seamless knitted pneumatic actuators. By systematically altering these variables, the optimal design considerations were identified, leading to improved bending behavior and enhanced distal tip force generation, both crucial for effective soft robotic actuation. Textile material selection, as anticipated, played a crucial role in determining material stiffness and, consequently, the efficiency of the actuator. Among the tested yarns, the acrylic offered superior bending performance due to its compatibility with pleat formation. While polyester punched lycra, and viscose polyester nylon (VPN) yarns showed comparable distal tip force outputs, their more compact structure limited bending efficiency, particularly at lower course ratios. This highlights that the interplay between the textile material selection and knitting parameters is critical for integrating design approach when developing textile-based actuators. The distal tip force analysis further validated the above findings: narrow actuators generated higher force attributed to faster inflation and reduced internal air volume, while lower course ratios limit the force output. These observations establish a clear understanding of textile engineering principles intersect with robotic designs, thereby expanding the horizons of fabric-based robots, tailored for real-world use. The applications of this work are particularly relevant for the development of human-centered soft robotic technologies such as gloves, rehabilitation devices, and wearable actuators, where adaptability and light weight designs are paramount. However, this study expands upon their findings by providing a detailed analysis of the influence of geometric parameters and material considerations. While the current study provides the foundational understanding of knitted pneumatic actuators, several areas remain open for further investigation. Future work should prioritize the long-term durability testing under cyclical loading conditions to assess the fatigue resistance. Integrating feedback and control systems, such as embedded sensors or closed-loop actuation, can offer actuator’s performance in a dynamic environment. Additionally, using simulation tools to model fabric behavior during inflation will be valuable to estimate the performance output prior to fabrication. Investigation, stress-strain relationships, internal pressure mapping, and interface forces during actuations could yield deeper understandings on actuator’s performance. In conclusion, this study not only demonstrates the feasibility of using knitted textiles in soft robotics but also serves as stepping-stone towards the development of efficient and human-compatible actuator systems. By integrating the fields of textile technology and robotic design, this research will open new dimensions in assistive technology, rehabilitation devices, and wearable exosuits, ultimately contributing to responsive and accessible soft robotic solutions. The finding emphasizes that knitted actuators are an important step towards wearable robotics that seamlessly integrate with human movement, feeling more like clothing, that rigid machines. Declarations Conflicts of interest: The authors declare no conflicts of interest. Funding: Not applicable Author Contribution M.D.H. and S.N. contributed to conceptualization, supervision, writing of the original draft, and review and editing. D.R.K. and W.F. contributed to writing the original draft and to reviewing and editing. M.U.N. contributed to writing the original draft and reviewed and edited it. S.A. contributed to supervision, and to review and editing.All authors reviewed and approved the final manuscript. Acknowledgements The authors express their earnest thanks to NED University of Engineering & Technology, Karachi, Pakistan, Pakistan Science Foundation and Mälardalen University Sweden for providing support, resources and conductive work environment in generation and documentation of data. Data Availability All data generated or analyzed during this study are included in this published article, and its supplementary information files. References Schiele, A. Ergonomics of Exoskeletons: Objective Performance Metrics, in Third Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems , Salt Lake City, UT, USA, (2009). Chen, A. et al. Soft robotics: Definition and research issues, in 24th International Conference on Mechatronics and Machine Vision in Practice (M2VIP) , Auckland, New Zealand, (2017). Sanchez, V. et al. 3D Knitting for Pneumatic Soft Robotics. Adv. Funct. Mater. 33 , 26, 6 (2023). Lee, S. M. & Park, J. 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Resistive Self-Sensing Controllable Fabric‐Based Actuator: A Novel Approach to Creating Anisotropy, 7 [Online]. (2024). Atalay, O. et al. Thermally Driven 3D Seamless Textile Actuators for Soft Robotic Applications, [Online]. (2024). J., C. W. Y. J. e. a. Zhu, Advanced Fiber Materials for Wearable Electronics. Adv. Fiber Mater. 5 , 12–35 (2023). H. L. J. L. Z. e. a. Zhai, Functional Graphene Fiber Materials for Advanced Wearable. Advanced Fiber Materials , 7 , 0, pp. 443–468, (2025). Rehman, T., Faudzi, A. A. M., Ekashanti, D., Dewi, O. & Suzumori, K. M. R. M. Razif and I. N. A. M. Nordin, DESIGN AND ANALYSIS OF BENDING MOTION IN SINGLE AND DUAL CHAMBER BELLOWS STRUCTURED SOFT ACTUATORS, vol. 78, pp. 2180–3722, (2016). Additional Declarations No competing interests reported. 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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-7363924","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":516514058,"identity":"ce5d2500-706f-4c0c-97aa-a8ca2ae0f496","order_by":0,"name":"Muhammad Dawood Husain","email":"","orcid":"","institution":"NED University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"Dawood","lastName":"Husain","suffix":""},{"id":516514061,"identity":"c3fd4784-b417-4cbb-a615-f5118d7ba123","order_by":1,"name":"Shenela Naqvi","email":"","orcid":"","institution":"NED University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Shenela","middleName":"","lastName":"Naqvi","suffix":""},{"id":516514063,"identity":"5386d5da-fa54-4357-9876-2c0645815730","order_by":2,"name":"Danyal Rashid Khan","email":"","orcid":"","institution":"NED University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Danyal","middleName":"Rashid","lastName":"Khan","suffix":""},{"id":516514064,"identity":"35c0e62e-9efe-4532-b6e6-4ec1cea31852","order_by":3,"name":"Warisha Farhat","email":"","orcid":"","institution":"NED University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Warisha","middleName":"","lastName":"Farhat","suffix":""},{"id":516514068,"identity":"2d5b4e73-7457-4d7f-b6cb-0c6d4a2c279b","order_by":4,"name":"Muhammad Usama Noorani","email":"","orcid":"","institution":"NED University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"Usama","lastName":"Noorani","suffix":""},{"id":516514071,"identity":"d870ce02-1e5c-46aa-afe4-61bc56a73c9a","order_by":5,"name":"Saad Abdullah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYJACCQaGA4wN7MwNzAwVDIwNxGthBiKGMyRrYWwjQot8++GHNxhq7shuOMzY+Llw3jbZDQfYHz7Ap8XgTJqxBcOxZ8ZALc3SM7fdNt5wgMfYAK8WhgQzCQa2w4lALQ3SvNtuJwK1sEngdVj/828SDP/AWpp/884BaWF//gOvZ27kmEkwtoG1tEnzNoC0MJjh1WFw402xRWLfM+OZQC3WPMduAxk8xgQclr7xxodvd2T7jjcfvs1TcxvIaH/4Aa81IJCAwmMmqH4UjIJRMApGASEAAMRrVcaJc/FCAAAAAElFTkSuQmCC","orcid":"","institution":"Mälardalen University","correspondingAuthor":true,"prefix":"","firstName":"Saad","middleName":"","lastName":"Abdullah","suffix":""}],"badges":[],"createdAt":"2025-08-13 10:23:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7363924/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7363924/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91656392,"identity":"1333de51-0c22-4cd4-95c5-7324c49075b2","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":407450,"visible":true,"origin":"","legend":"\u003cp\u003ea) Components of the knitted pneumatic actuator, indicating the bladder material, pleated top layer, and non-pleated bottom layer, b) Views of a knitted pneumatic actuator sample (Front and Back).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/6902e0ff8ac6e1eb756b7ab4.png"},{"id":91656391,"identity":"ccdd9569-0c84-49d1-8206-a7b2b555375d","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":243270,"visible":true,"origin":"","legend":"\u003cp\u003eOverview of the development of pneumatic knitted actuator. a) Weft Knitting Machine, b) schematic of seamless actuator development with manual bladder development, c) front \u0026amp; back side of the actuator, d) Inflated actuator.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/d58fe40daee3fc9a3731b41c.png"},{"id":91656393,"identity":"56f2cd7a-3873-4b86-bec3-2772e8a612f0","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":680517,"visible":true,"origin":"","legend":"\u003cp\u003eKnitted actuator samples with indicated lengths before and after heating. Before \u0026amp; after heat treatment a) Front \u0026amp; back side of an actuator, b) Sample SA1, c) Sample SA2, d) Sample SA3a, e) Sample SA3b, f) Sample SA4a, g) Sample SA4b, h) Sample 4c\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/d2a420ce9f56d7adcd805b6a.png"},{"id":91656396,"identity":"cbba9ee2-368a-4812-8739-bac42024d80a","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":538395,"visible":true,"origin":"","legend":"\u003cp\u003eA customized test rig, designed and developed to measure actuators attributes attached with an air compressor (Model EDON ED550-25L).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/ba82beef48188d1e2eb104bd.png"},{"id":91657242,"identity":"40616278-c633-4f11-8412-d9238271ba16","added_by":"auto","created_at":"2025-09-18 18:34:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":403878,"visible":true,"origin":"","legend":"\u003cp\u003eBending Angle Measurement \u0026amp; the dialog box shows the curvature; (a) Actuator with fixed and movable end, (b) Bending initiation stage or Actuator straightening, (c) Change of angle due to varying pressure, (d) Increase in bending angle due to increase in pressure, (e) Maximum bending achieved at a specific pressure.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/d99a5cd244b7051aa59d637f.png"},{"id":91656399,"identity":"9c69e8ce-4c67-47ac-a5ce-051cca96c118","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":431908,"visible":true,"origin":"","legend":"\u003cp\u003eDistal tip force Measurement; (a) Seamless actuator with more than half the length inside the cup and deflated, (b) Actuator is pressurized, (c) Maximum pressure is achieved, (d) The LabVIEW program for Test 01 showing graph of pressure and force.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/9ae9f5fa30125976d5d0a500.png"},{"id":91657138,"identity":"921ebe6d-c4bd-4c7a-be05-539bd185705d","added_by":"auto","created_at":"2025-09-18 18:26:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":67279,"visible":true,"origin":"","legend":"\u003cp\u003ea) Effect of actuator’s length (SA1a – SA1d) on bending angle at varying pressures; b) Minimal pressure variation observed at 160° target angle.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/855aa496a439093ce08814f0.png"},{"id":91656544,"identity":"0cb42898-2d61-4193-9119-5648b7d2ad60","added_by":"auto","created_at":"2025-09-18 18:18:50","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":75477,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of actuator’s width (SA1a and SA2) on bending angle at varying pressures; minimal variation observed at 160° target angle.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/5b92ce163872b4c91bc6d128.png"},{"id":91657239,"identity":"daa30606-fcbe-4df8-b510-18b24a545507","added_by":"auto","created_at":"2025-09-18 18:34:50","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":60351,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of actuator’s material/yarn (SA2, SA3a and SA3b) on bending angle at varying pressures; minimal variation observed at 160° target angle.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/e52421065bc2643d7a351f3c.png"},{"id":91657145,"identity":"cd5cb043-3786-4e44-b492-cd34cf0c3f0f","added_by":"auto","created_at":"2025-09-18 18:26:50","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":74838,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of course ratio on actuator on bending angle (SA4a, SA4b, and SA4c) at varying pressures.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/04ca2760ffe23f079a506eea.png"},{"id":91656407,"identity":"457b42e3-7368-4fad-b500-1cfe9db63d73","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":223516,"visible":true,"origin":"","legend":"\u003cp\u003eDistal tip force response of actuator samples across varying pressures.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/a959c5ce1f4b5d33068d4a71.png"},{"id":91817280,"identity":"57cf8ba7-f25e-4789-a0d9-2905e67fccd4","added_by":"auto","created_at":"2025-09-22 06:54:32","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":99399,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of pressure requirements to achieve 160° bending angle and corresponding distal tip force outputs for various actuator designs.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/28792166bf64b1da2ebda0f1.png"},{"id":91656428,"identity":"123a7ef4-2909-4579-a6e3-88b8dd772db9","added_by":"auto","created_at":"2025-09-18 18:10:50","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"graphical-abstract","size":42558,"visible":true,"origin":"","legend":"Owing to the growing demand for textile-based wearable soft robots for construction of exosuits and rehabilitation gloves, a detailed investigation of different types of constructing materials and geometric properties of knitted pneumatic actuators is required to achieve desired functioning. This study did comparative analysis among different seamless pneumatic actuators which were constructed by knitting yarns of different materials. The actuators featured pleats on the top layer and were shaped like tubes. We selected Viscose Polyester Nylon (VPN), Acrylic, and Polyester-punched Lycra for the top layers and low-melt Nylon yarn for the bottom layers. To assess their performance, actuators were designed with three length sizes, two widths, and three course ratios. Bending angle and distal tip force were measured on a customized test rig developed for this study. It was observed that actuators made of acrylic yarn with a 3:1 course ratio achieved the desired bending angle of 160\u0026deg; at just 31 kPa internal air pressure, an improved result than those developed in previous studies. These acrylic yarn actuators were also easier to knit compared to the other materials selected. While other actuators required higher internal pressure to achieve the bending angle of 160\u0026ordm;, only a wider width (3.2 cm) produced a desired bending angle and a higher tip force (4.3 N at 32 kPa). This study highlights that the interplay of constructing materials and the geometry of pneumatic actuators significantly alters their input and output, allowing for tailored performance across different human hand/finger sizes and specific applications.","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/9af218622a8fd540ed6d8a3c.png"},{"id":97666857,"identity":"ea8e048d-e346-45ae-b8cf-f4647c759674","added_by":"auto","created_at":"2025-12-08 09:22:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4674024,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/cbb215e5-149b-4c88-a076-75f361093f13.pdf"},{"id":91657142,"identity":"79fde0b8-2ce7-45ed-8834-8ab3bdf70dd6","added_by":"auto","created_at":"2025-09-18 18:26:50","extension":"xlsx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":74600,"visible":true,"origin":"","legend":"","description":"","filename":"DataSetSupplementaryMaterial.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7363924/v1/22c21544c0c9a843d9e7551f.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTextiles are no longer passive material; they are becoming active components in next-generation soft robotics. The field of soft robotics is emerging, driven by the need for robots that can safely interact with humans [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Unlike rigid robots, soft robots, which often utilize materials with Young\u0026rsquo;s moduli comparable to those of biological muscles/tissues, conform to irregular shapes and perform delicate tasks [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Among the various actuation mechanisms, pneumatic actuation stands out due to its simplicity, high power-to-weight ratio, and improved response time. However, there are research gaps to overcome challenges related to material design and actuation control for wearable applications and assistive devices [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, a shift from conventional rigid robots to compliant textile-based robots is essential to provide comfort and resilience to the wearer [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRecent advancements have highlighted the potential for fabric-based pneumatic actuators, particularly seamless knitted designs, to enable soft exosuits and robotic gloves. Knitted structures, with their inherent design flexibility, endurance, and ease of manufacturing, offer significant potential for developing soft actuators, particularly knitted pneumatic actuators [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. These actuators, when inflated with air, provide controlled movements and can be fabricated into complex three-dimensional shapes using textile materials, allowing for required bending and distal tip force/pressure [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Despite its potential, a comprehensive understanding of the influence of material selection and geometric properties such as length, width, and course ratio on the actuation behavior needs to be investigated [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eKnitting is one of the textile manufacturing processes based on the interloping of the yarns into rows (courses) and columns (wales) constituting loops or stitches [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. A continuous strand of yarn is used to develop knitted fabric. The flatbed knitting machine is the most suitable method for producing knitted fabric mechanically, and it is most the accessible for textile prototyping. The flat bed machine forms a knitted fabric structure through a sliding action of multiple needles arranged in parallel on flat bed. The gauge of the machine is the number of needles per inch on the needle bed; therefore, it determines the fabric thickness that can be produced. Finer fabric can be knitted on high-gauge machines (12\u0026ndash;18 needles per inch), while coarser fabrics can be knitted on lower gauge machines. In knitting machines, the yarn carrier moves across the needles to supply the yarn to the needle hook, which grabs the yarn to form the stitch and pulls it through the previously knitted help loop as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. The structure of inter-looped yarn gives knitted fabrics their inherent extensibility. Modern knitting machines control the movement of the needles and the yarn carriers simultaneously. These techniques help to develop intricate patterns on the computerized flat-bed knitting machines [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In this research, multi-gauge machine was used to develop knitted actuators. The basic actuator design consists of a knitted pouch construction having plain knitted on top and the bottom layer. To this work, bending was the desired deformation, therefore an anisotropic knitted structure for an actuator was designed. The geometric parameters and type of yarns were varied to control the extensibility of the top and bottom layers as listed in Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. To create comparison length, width, course ratio \u0026amp; the type of textile materials was selected to analyze the bending performance and distal tip force.\u003c/p\u003e\u003cp\u003eResearchers also worked on traditional cut-and-sew actuators, which are typically formed by joining multiple layers of fabric through different techniques such as sewing, heat sealing, ultrasonic welding and adhesive bonding [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The primary purpose of these bonding is to create enclosed chambers for pneumatic actuation. For instance, combining fabrics with contrasting mechanical properties, such as stretchable knits and strain-limiting wovens, and joining them with seams allows for controlled bending, extension, or contraction [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Specific stitching techniques, like zigzag or overlock stitches, can further enable or limit stretching along particular directions [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Additionally, conductive yarns can be embedded through these seams for sensing or heating purposes. While offering benefits such as light weight construction, low-profile design, and comfortability, seam actuators face several challenges [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Traditional cut-and-sew methods can be labor intensive, time consuming, and may introduce weak points prone to failure, such as stitch failure or fabric tearing at interfaces, air tightness issues, and manual operations [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe significance of seamless knitted actuators overcome many of these challenges, offering a more advanced and integrated approach for textile actuators [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Unlike seam actuators, which depends on pre-cut fabric pieces, seamless knitting approach allows the production of actuators in a convenient manner, often in a single machine run. This advanced knitting technique significantly reduces the need for labor-intensive cutting and sewing steps, leading to rapid, automated, and customizable manufacturing [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Furthermore, techniques like Intarsia allow layers of the knitted fabric to join seamlessly, enable the fabrication of the actuators [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eMachine knitting also facilitates the seamless integration of functionality, directly embedding sensing and heating elements using conductive yarns into the actuator structure during fabrication [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Seamless actuators represent a significant advancement from traditional cut-and-sew methods by addressing digital textile manufacturing to produce soft robotic component for wearable applications.\u003c/p\u003e\u003cp\u003eIn this research, a multi-gauge machine was used to develop knitted actuators. The basic design of the actuator features a knitted pouch construction with a plain knitted layer on both the top and bottom. To this work, bending was the desired deformation; therefore, an anisotropic knitted structure for an actuator was designed. The geometric parameters and type of yarns were varied to control the extensibility of the top and bottom layers. To make a comparison, four lengths (23cm, 26cm, 29cm \u0026amp; 32cm), two widths (3.3cm \u0026amp; 2.2cm), three course ratios (3:1, 2:1 \u0026amp; 1:1), and three constructed textile materials (Acrylic, Polyester punch lycra, and Viscose Polyester Nylon VPN blended yarn) were selected to measure and analyze the bending performance and distal tip force.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cp\u003eThis section discusses the materials, fabrication methods, experimental setup, and characterization procedures used to evaluate the knitted pneumatic actuators.\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Materials\u003c/h2\u003e\n \u003cp\u003eAll the samples were developed in the form of tubular knitted structure with different top and bottom layers. The Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e showed the material used for the manufacturing of tubular knitted actuator. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates each actuator consisting of a two layered fabric.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMaterials used for experimentation\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS.No.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMaterial\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSupplier\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAcrylic Ring Spun 32/2 Nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eTextile Yarn (Top layer)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eSourced from local market at Karachi, Pakistan.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePolyester punched Lycra 450 D/25 D\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVPN (Viscose Polyester Nylon) 50% Viscose; 28% Polyester; 22% Nylon yarn 48/2 Nm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNylon low melt yarn 360 D\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTextile Yarn (Bottom layer)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCommercially sourced\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStretchlon 200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBladder material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCommercially sourced\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe three yarns, including acrylic, polyester punched lycra, and viscose polyester nylon (VPN) were used to create the top layer of the seamless actuators as the main requirement for the top layer material was to have extensible/stretchable characteristics. The bottom layer yarn: i.e., nylon low melt was used as it would provide inextensibility after heat-set. The bladder is a critical component, holding pneumatic air for bending and straightening during actuation. While commercially available elongated rubber/latex balloons could be used, this research utilized High Stretch Bagging Film (Stretchlon\u0026reg; 200) [\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e] for the development of bladder via heat sealer as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. It is a TPU (Thermoplastic polyurethane) sheet that stretches up to 500% of its original length upon mechanical or pneumatic force and readily conforms to any fitted or inserted shape.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Actuator Design and Fabrication\u003c/h2\u003e\n \u003cp\u003eIn this study, actuator samples were produced using a 14-gauge SHIMA SEIKI SSR 112 computerized flatbed knitting machine, employing a plain knitted tubular single jersey structure. The study systematically varied actuator length, width and course ratio as key geometric parameters, alongside different top layer yarn materials, to investigate their combined influence on actuator performance. Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows the specifications of knitted pneumatic actuator and its influence on geometric properties after heat-set.\u003c/p\u003e\n \u003cp\u003eThe type of yarn used to make the knitted fabric has a direct relation with its stretch properties. Since, the actuator would be in tubular shape so to create difference between the top and bottom layers course ratio was also selected as an important parameter. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the overview of process flow of pneumatic weft knitted actuator. Figure 3 shows the dimensional changes in the samples (SA1 to SA4c) to after heating at 140\u0026deg;C for 10 minutes, resulting from shrinkage of the low melt nylon yarn. The description of each sample is mentioned in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\" class=\"fr-table-selection-hover\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSpecifications and Dimensional Changes of Knitted Pneumatic Actuators After Heat Treatment.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample Code\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eSA1a\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eSA1b\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eTop Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBottom Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCourse ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting (a)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating (b)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLength (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e23.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e26.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-37%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-23%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-27%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample Code\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA1c\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA1d\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eTop Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBottom Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCourse ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLength (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e29.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-39%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e32.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-42%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-23%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-26%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample Code\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA3a\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eTop Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003ePolyester punched lycra yarn (PPL)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBottom Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCourse ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLength (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-42%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-42%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-17%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-18%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample Code\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA3b\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA4a\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eTop Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eVPN* (Viscose Polyester Nylon)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBottom Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCourse ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003e2:1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLength (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-43%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e23.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-47%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-18%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-18%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSample Code\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA4b\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003eSA4c\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eTop Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003ePolyester punched lycra yarn (PPL)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eAcrylic\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBottom Layer\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNylon Low Melt\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCourse ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003e2:1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e\u003cstrong\u003e1:1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Knitting\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAfter Heating\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e% diff**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eLength (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e23.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-40%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e23.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-43%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eWidth (cm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-18%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-20%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e* VPN (Viscose Polyester Nylon)\u0026thinsp;=\u0026thinsp;50% Viscose; 28% Polyester; 22% Nylon\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e** % diff = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\raisebox{1ex}{$\\left(a-b\\right)*100$}\\!\\left/\\:\\!\\raisebox{-1ex}{$a$}\\right.\\)\u003c/span\u003e\u003c/span\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Experimental Setup\u003c/h2\u003e\n \u003cp\u003eTo evaluate the performance of the seamless knitted actuators, a customized test rig was developed, as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. This test rig was equipped with a pressure sensor to monitor the air pressure, a camera system (e.g., webcam, DSLR) for capturing images to determine bending curvature (\u0026deg;) via image analysis, force sensor (e.g., Compression load Cell) to measure distal tip force (N). The bending angle (\u0026ordm;) test analyzes the change of bending angle by varying the air pressure (kPa). The distal tip force (N) tests the force generated at the distal end of the actuator under various internal pressures. LabVIEW software was used for automated control of pressure, data acquisition from sensors, and synchronization of image capture.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Experimental Procedures\u003c/h2\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.1 Bending Angle Measurement\u003c/h2\u003e\n \u003cp\u003eFor the measurement of bending angle, the inserted bladder was inflated through an air compressor. The actuator was suspended by fixing one end while the other end is free to move, as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. Images were captured at discrete pressure intervals (e.g., every 5 kPa from 0 to 50 kPa) during inflation. Bending angles were then measured by post-processing these captured images using image analysis software (e.g., ImageJ, Photoshop) based on the method adapted from Rehman, et.al [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.2 Distal tip force Measurement\u003c/h2\u003e\n \u003cp\u003eFor distal tip force measurement, after inflating the actuator at a pressure where the bending angle is close to 160\u0026ordm;, the inflated actuators were inserted into a customized cup designed to establish consistent contact with a load cell shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. A LabVIEW program controlled the inflation process to a maximum pressure of 50 kPa while simultaneously recording pressure and force data from the load cell. Data points were recorded at specific intervals (e.g., every 2 seconds or 2 kPa). This method was adapted from Elmoughni et.al [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eThis section presents the experimental results on the bending behavior and distal tip force of the knitted pneumatic actuators, discussed in the context of their intended application in assistive and rehabilitation devices. For ideal performance in grasping motions, actuators should generate higher distal tip forces at lower internal pressures to optimize energy efficiency and safety. The bending curvature is equally crucial, as it determines whether the actuator would be able to move the human hand to perform activities of daily living (ADLs). Literature suggests that the effective human index finger flexion requires a bending angle of approximately 160\u0026deg; and a distal tip force around 7.3 N [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Seamless knitted Actuators developed by Elmoughni et al.[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] had a distal tip force of 5.3 N at 150 kPa. Consequently, for assistive glove applications, the desired range of value for distal tip force would be 7\u0026ndash;8 N, while achieving a minimum bending angle of 160\u0026deg;.\u003c/p\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Bending behavior of knitted pneumatic actuators\u003c/h2\u003e\u003cp\u003eThe bending behavior of seamless knitted actuators was investigated by systematically varying the pneumatic pressure within the internal bladder. The influence of key parameters including actuator length, width, yarn composition, and course ratio on actuation performance was systematically analyzed.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1 Influence of Actuator Length\u003c/h2\u003e\u003cp\u003eTo evaluate the effect of length, four samples (SA1a, SA1b, SA1c and SA1d) were developed with varying lengths while maintaining consistent materials: an acrylic on top layer and a nylon low melt on bottom layer.\u003c/p\u003e\u003cp\u003eThe samples were analyzed in two distinct ways. In the first analysis (a), the bending angle was measured as the pressure was varied. The data from this analysis aimed to establish a correlation between pressure and bending angle, a relationship that is further explored in figure b. For second analysis (b), the bladder was inflated to a constant pressure of 35kPa to observe the bending angle. This specific data point was used to establish a clear relationship between controlled pressure and the resulting bending angle for each sample, which allowed for direct comparison of the effect of length.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, all samples exhibited a positive correlation between applied pressure and bending angle.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cem\u003eSA1a (23 cm)\u003c/em\u003e: Bending initiated at 11 kPa, reaching 167\u0026deg; at 32 kPa.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cem\u003eSA1b (26 cm)\u003c/em\u003e: Initiated at 13 kPa, reaching 160\u0026deg; at 31 kPa.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cem\u003eSA1c (29 cm)\u003c/em\u003e: Similar performance as SA1a.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cem\u003eSA1d (32 cm)\u003c/em\u003e: Similar performance as SA1a.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eA length of 23 cm was identified as optimal, offering efficient bending while approximating the dimensions of a human finger, which is advantageous for wearable and grasping applications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2 Influence of Actuator Width\u003c/h2\u003e\u003cp\u003eTo investigate the influence of width, the actuator width was reduced from 3.2 cm (SA1a) to 2.2 cm (SA2). Narrower actuators required higher inflation pressure due to increased internal resistance. Bending began at approximately 18kPa, achieving 160\u0026deg; at 45kPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Despite the higher-pressure requirement, the 2.2 cm width demonstrates anatomical suitability and the potential to generate greater force through volumetric expansion, suggesting its suitability for specific applications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e3.1.3 Influence of Top Layer Material\u003c/h2\u003e\u003cp\u003eWith optimal length and width established, different yarns were tested in the actuator\u0026rsquo;s top layer: air-covered polyester punched lycra (SA3a), Viscose-Polyester-Nylon blend (SA3b), and acrylic (SA2). All configurations initiated bending at ~\u0026thinsp;19kPa, followed by significant bending:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eSA2 (Acrylic): Achieved 180\u0026deg; at 44 kPa\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSA3b (VPN blend): 180\u0026deg; at 46 kPa\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSA3a (Lycra blend): 180\u0026deg; at 48 kPa\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eAs seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e, an actuator with acrylic yarn exhibited superior bending at lower pressures, highlighting its performance advantage.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.1.4 Influence of course ratio\u003c/h2\u003e\u003cp\u003eTo explore the effect of structural configuration, samples SA4a - SA4c were produced with varied course ratios, including a reduced ratio of 2:1 (top: bottom) and a balanced 1:1 (top: bottom).\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eSA4a (Acrylic, 2:1): Reached 160\u0026deg; at 57 kPa.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSA4b (Polyester Lycra, 2:1): bent to 160\u0026deg; at 56 kPa, though pleat formation was restricted due to the yarn\u0026rsquo;s compact structure.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSA4c (Acrylic, 1:1): Exhibited no bending, attributed to the absence of pleats and symmetric 1:1 course ratio.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe higher-pressure requirement in 2:1 structure is attributed to limited pleat flexibility and increased stiffness, especially in compact lycra-based samples. The findings confirm that pleat formation governed by a higher top-layer course ratio is critical for effective actuation as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eBy analyzing the performance of all three SA4 samples, it is evident that despite variations in the top layer material, the bending angle is primarily determined by the course ratio between the top and bottom layers. The pleats on the top layer, which facilitate bending, are a direct consequence of a higher course ratio in the top layer compared to the bottom layer of the actuator.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e5.1 Distal tip force\u003c/h2\u003e\u003cp\u003eThe distal tip force of the actuators was assessed across samples varying in length (SA1 series), width (SA2), top layer fiber type (SA3 series), and course ratio (SA4 series). As observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e, the maximum distal tip force achieved across tested samples is 4.3 N at the applied pressure of 35 kPa, which compares to 5.4 N at 150 kPa reported in a previous study [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe samples exhibited varying distal tip forces and actuation responses based on their length, material composition, and structural design. Among the SA1 series, SA1a (23 cm) demonstrated the highest distal tip force of 4.3 N at 36 kPa due to its short length. As the length increased, the force generally decreased; SA1b (26 cm) achieved 2.8 N at 36 kPa but required a higher initial pressure of approximately 16 kPa, while SA1c (29 cm) had a slightly reduced distal tip force of 2.7 N at 36 kPa. The longest sample, SA1d (32 cm), exhibited the lowest force at 2.4 N at 36 kPa, attributed to inefficiencies from its increased internal volume.\u003c/p\u003e\u003cp\u003eIn contrast, samples with different material compositions, tested at higher pressures, showed improved force generation. SA2 (Acrylic Yarn) achieved 3.34 N at 50 kPa, showcasing improved distal tip force due to the presence of pleats on its top layer. Similarly, SA3a (polyester punched lycra yarn) and SA3b (Viscose Polyester Nylon blended yarn) delivered similar maximum forces of 3.38 N and 3.4 N, respectively, at 50 kPa. The SA4 series, which involved different course ratios, also showed distinct results: SA4a (2:1, Acrylic Yarn) produced a maximum force of 2.8 N at 50 kPa. SA4b (2:1, Polyester punched lycra yarn) yielded a slightly higher force of 3.4 N at 50 kPa due to its more compact structure, whereas SA4c (1:1, Acrylic and Nylon Low Melt Yarn) showed the lowest force of 1.79 N at 55 kPa, indicating limited efficiency in force generation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe results demonstrate that actuator length, width, yarn type, and course ratio significantly influence distal tip force performance. By selecting the optimal combination of these parameters, seamless actuators can be tailored for specific applications requiring precise force and bending capabilities. The results were aligned with previous work of Elmoughni et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] who also highlighted the importance of actuator dimensions on the distal tip force generation.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e12\u003c/span\u003e presents a comparative view of the pressure required to achieve a bending angle of 160\u0026deg; and the corresponding distal tip force output for all sample groups:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eActuator length variations (SA1) samples had a limited impact on bending angle but significantly affected distal tip force, reinforcing the importance of length optimization to achieved desired distal tip force.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe variation of width variation from 3.2 cm in SA1 to 2.2 cm in SA2 samples led to increased pressure requirements without substantial distal tip force gains.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe textile material variation (SA3) samples resulted in similar force outputs (both internal pressure and distal tip force), validating the use of multiple yarn types.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe variation in course ratio (SA4) samples with lower course ratios require more pressure, and course ratio variations also affect distal tip force.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTherefore, the study discussed that actuator width and course ratio played a vital role in influencing bending efficiency and force generation compared to actuator length. Narrower actuators, though requiring higher internal pressures, showed improved forced output, making them more suitable for the compact, wearable assistive applications. Conversely, actuator\u0026rsquo;s length exhibited a comparatively minor impact on the overall bending performance; however, distal tip force measurements showed an inverse relationship with actuators length, indicating that shorter actuators generate greater force due to reduced internal volume. Notable, the higher course ratio (3:1) significantly improved the flexibility and bending capability through enhanced pleat formation, a crucial attribute for human-centric soft robotics.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe study conducted an in-depth investigation into the impact of material selection and the knitting parameters, specifically length, width, yarn type, and course ratio, on the performance of seamless knitted pneumatic actuators. By systematically altering these variables, the optimal design considerations were identified, leading to improved bending behavior and enhanced distal tip force generation, both crucial for effective soft robotic actuation.\u003c/p\u003e\u003cp\u003eTextile material selection, as anticipated, played a crucial role in determining material stiffness and, consequently, the efficiency of the actuator. Among the tested yarns, the acrylic offered superior bending performance due to its compatibility with pleat formation. While polyester punched lycra, and viscose polyester nylon (VPN) yarns showed comparable distal tip force outputs, their more compact structure limited bending efficiency, particularly at lower course ratios. This highlights that the interplay between the textile material selection and knitting parameters is critical for integrating design approach when developing textile-based actuators.\u003c/p\u003e\u003cp\u003eThe distal tip force analysis further validated the above findings: narrow actuators generated higher force attributed to faster inflation and reduced internal air volume, while lower course ratios limit the force output. These observations establish a clear understanding of textile engineering principles intersect with robotic designs, thereby expanding the horizons of fabric-based robots, tailored for real-world use. The applications of this work are particularly relevant for the development of human-centered soft robotic technologies such as gloves, rehabilitation devices, and wearable actuators, where adaptability and light weight designs are paramount. However, this study expands upon their findings by providing a detailed analysis of the influence of geometric parameters and material considerations.\u003c/p\u003e\u003cp\u003eWhile the current study provides the foundational understanding of knitted pneumatic actuators, several areas remain open for further investigation. Future work should prioritize the long-term durability testing under cyclical loading conditions to assess the fatigue resistance. Integrating feedback and control systems, such as embedded sensors or closed-loop actuation, can offer actuator\u0026rsquo;s performance in a dynamic environment. Additionally, using simulation tools to model fabric behavior during inflation will be valuable to estimate the performance output prior to fabrication. Investigation, stress-strain relationships, internal pressure mapping, and interface forces during actuations could yield deeper understandings on actuator\u0026rsquo;s performance.\u003c/p\u003e\u003cp\u003eIn conclusion, this study not only demonstrates the feasibility of using knitted textiles in soft robotics but also serves as stepping-stone towards the development of efficient and human-compatible actuator systems. By integrating the fields of textile technology and robotic design, this research will open new dimensions in assistive technology, rehabilitation devices, and wearable exosuits, ultimately contributing to responsive and accessible soft robotic solutions. The finding emphasizes that knitted actuators are an important step towards wearable robotics that seamlessly integrate with human movement, feeling more like clothing, that rigid machines.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflicts of interest:\u003c/h2\u003e\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eNot applicable\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.D.H. and S.N. contributed to conceptualization, supervision, writing of the original draft, and review and editing. D.R.K. and W.F. contributed to writing the original draft and to reviewing and editing. M.U.N. contributed to writing the original draft and reviewed and edited it. S.A. contributed to supervision, and to review and editing.All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThe authors express their earnest thanks to NED University of Engineering \u0026amp; Technology, Karachi, Pakistan, Pakistan Science Foundation and M\u0026auml;lardalen University Sweden for providing support, resources and conductive work environment in generation and documentation of data.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data generated or analyzed during this study are included in this published article, and its supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSchiele, A. 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Zhu, Advanced Fiber Materials for Wearable Electronics. \u003cem\u003eAdv. Fiber Mater.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e, 12\u0026ndash;35 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH. L. J. L. Z. e. a. Zhai, Functional Graphene Fiber Materials for Advanced Wearable. \u003cem\u003eAdvanced Fiber Materials\u003c/em\u003e, \u003cb\u003e7\u003c/b\u003e, 0, pp. 443\u0026ndash;468, (2025).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRehman, T., Faudzi, A. A. M., Ekashanti, D., Dewi, O. \u0026amp; Suzumori, K. M. R. M. Razif and I. N. A. M. Nordin, DESIGN AND ANALYSIS OF BENDING MOTION IN SINGLE AND DUAL CHAMBER BELLOWS STRUCTURED SOFT ACTUATORS, vol. 78, pp. 2180\u0026ndash;3722, (2016).\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":"Soft Robotics, Knitted Pneumatic Actuators, Pneumatic Actuation, Wearable Robotics, Bending Angle and Distal tip force, Seamless Weft Knitting Technology","lastPublishedDoi":"10.21203/rs.3.rs-7363924/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7363924/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Owing to the growing demand for textile-based wearable soft robots for construction of exosuits and rehabilitation gloves, a detailed investigation of different types of constructing materials and geometric properties of knitted pneumatic actuators is required to achieve desired functioning. This study did comparative analysis among different seamless pneumatic actuators which were constructed by knitting yarns of different materials. The actuators featured pleats on the top layer and were shaped like tubes. We selected Viscose Polyester Nylon (VPN), Acrylic, and Polyester-punched Lycra for the top layers and low-melt Nylon yarn for the bottom layers. To assess their performance, actuators were designed with three length sizes, two widths, and three course ratios. Bending angle and distal tip force were measured on a customized test rig developed for this study. It was observed that actuators made of acrylic yarn with a 3:1 course ratio achieved the desired bending angle of 160\u0026deg; at just 31 kPa internal air pressure, an improved result than those developed in previous studies. These acrylic yarn actuators were also easier to knit compared to the other materials selected. While other actuators required higher internal pressure to achieve the bending angle of 160\u0026ordm;, only a wider width (3.2 cm) produced a desired bending angle and a higher tip force (4.3 N at 32 kPa). This study highlights that the interplay of constructing materials and the geometry of pneumatic actuators significantly alters their input and output, allowing for tailored performance across different human hand/finger sizes and specific applications.","manuscriptTitle":"Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-18 18:10:45","doi":"10.21203/rs.3.rs-7363924/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":"fe6f3b25-565e-4281-8d87-3a8b5d0da149","owner":[],"postedDate":"September 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":54879146,"name":"Physical sciences/Engineering"},{"id":54879147,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-12-04T09:38:41+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-18 18:10:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7363924","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7363924","identity":"rs-7363924","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}