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Skin is a thin membrane which provides many biological functions, such as thermoregulation and protection from mechanical, bacterial, and viral insults. The mechanical properties of skin tissue are extremely hard to measure and may vary according to the anatomical locations of a body. However, the mechanical properties of skin at different anatomical regions have not been satisfactorily simulated by conventional engineering models. In this study, the linear elastic and nonlinear hyperelastic mechanical properties of rat skin at different anatomical locations, including back and abdomen, are investigated using a series of tensile tests. The Young's modulus and maximum stress of skin tissue are measured before the incidence of failure. The nonlinear mechanical behavior of skin tissue is also experimentally and computationally investigated through constitutive equations. Hyperelastic strain energy density functions are adjusted using the experimental results. A hyperelastic constitutive model is selected to suitably represent the axial behavior of the skin. The results reveal that the maximum stress (20%) and Young's modulus (35%) of back skin are significantly higher than that of abdomen skin. The Ogden model is selected to closely address the nonlinear mechanical behavior of the skin which can be used in further biomechanical simulations of the skin tissue. The results might have implications not only for understanding of the mechanical behavior of skin tissue at different anatomical locations, but also to give an engineering insight for a diversity of disciplines, such as dermatology, cosmetics industry, clinical decision making, and clinical intervention.

Gelatin (Gel) and poly(acrylic acid) (PAA) have so many applications in wound dressing, drug release, and tissue engineering on the basis of their easy availability, biocompatibility, and biodegradability. A composition of Gel/PAA hydrogel is widely used as a biological glue of soft tissues. However, the influence of PAA on the mechanical properties of this composite hydrogel so far has not been determined. In this study, gel hydrogels were prepared at various PAA content, i.e., 10, 20, and 30 wt%, using a thermal-initiated redox polymerization method. Afterward, as=prepared cylindrical hydrogel samples were subjected to a series of compressive loading to measure their linear elastic (elastic modulus, maximum stress and strain) and nonlinear hyperelastic (hyperelastic coefficients) mechanical properties. The potential ability of the Yeoh material model to closely address the nonlinear mechanical behavior of the hydrogel was verified using finite element (FE) modeling of the compression test. The results showed that the addition of PAA (>10 wt%) invokes a significant decrease in the Young's modulus and maximum stress of the hydrogels whereas (1 of 7)RESEARCH ARTICLE a significant increase in the maximum strain. The highest Young's modulus (25 MPa) and maximum stress (12 MPa) were observed in the hydrogels with PAA (10 wt%), whereas the highest maximum strain (43%) was detected in the Gel/PAA (30 wt%) samples. The experimental results were well compared to those anticipated by the Yeoh and FE models. The results suggested that an optimum addition of PAA not only could enhance the mechanical strength of the hydrogels but also provide a nonlinear behavior of composite hydrogels, which is suitable for soft tissue engineering. C 2014 Wiley Periodicals, Inc. Adv Polym Technol 2015, 34, 21487; View this article online at wileyonlinelibrary.com.

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Objective Compliance and viscoelastic mismatches of small diameter vascular conduits and host arteries have been the cause of conduit’s failure. Methods To reduce these mismatches, the aim of this study was to develop and characterize a polyurethane conduit, which mimics the viscoelastic behaviors of human arteries. Electrospinning technique was used to fabricate tubular polyurethane conduits with similar properties of the human common carotid artery. This was achieved by manipulating the fiber diameter by altering the syringe flow rate of the solution. The mechanical and viscoelastic properties of the fabricated electrospun polyurethane conduits were, then, compared with commercially available vascular conduits, expanded polytetrafluoroethylene, polyethylene terephthalate (Dacron®) and the healthy human common carotid arteries. In addition, a comprehensive constitutive model was proposed to capture the visco-hyperelastic behavior of the synthetic electrospun polyurethanes, commercial conduits and human common carotid arteries. Results Results showed that increasing the fiber diameter of electrospun polyurethanes from 114 to 190 nm reduced Young’s modulus from 8 to 2 MPa. Also, thicker fiber diameter yielded in higher conduits’ viscosity. Furthermore, the results revealed that proposed visco-hyperelastic model is strongly able to fit the experimental data with great precision which proofs the reliability of the proposed model to address both nonlinear elasticity and viscoelasticity of the electrospun polyurethanes, commercial conduits and human common carotid arteries. Conclusions In conclusion, statistical analysis revealed that the elastic and viscous properties of 190 nm fiber diameter conduit are very similar to that of human common carotid artery in comparison to the commercial expanded polytetrafluoroethylene and Dacron® that are up to nine and seven times stiffer than natural vessels. Therefore, based on our findings, from the mechanical point of view, by considering the amount of Young’s modulus, compliance, distensibility and viscoelastic behavior, the fabricated electrospun polyurethane with fiber diameter of 189.6 ± 52.89 nm is an optimum conduit with promising potential for substituting natural human vessels.