Characterizing the mechanical properties of tropoelastin protein scaffolds
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Characterizing the mechanical properties of tropoelastin protein scaffolds Audrey C. Ford1,2, Hans Machula2, Robert S. Kellar1,2, Brent A. Nelson1 Department of Mechanical Engineering and 2Department of Biology, Northern Arizona University, Flagstaff, AZ, 86011
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ABSTRACT This paper reports on mechanical characterization of electrospun tissue scaffolds formed from varying blends of collagen and human tropoelastin. The electrospun tropoelastin-based scaffolds have an open, porous structure conducive to cell attachment and have been shown to exhibit strong biocompatibility, but the mechanical character is not well known. Mechanical properties were tested for scaffolds consisting of 100% tropoelastin and 1:1 tropoelastin-collagen blends. The results showed that the materials exhibited a three order of magnitude change in the initial elastic modulus when tested dry vs. hydrated, with moduli of 21 MPa and 0.011 MPa respectively. Noncrosslinked and crosslinked tropoelastin scaffolds exhibited the same initial stiffness from 0 to 50% strain, and the noncrosslinked scaffolds exhibited no stiffness at strains >~50%. The elastic modulus of a 1:1 tropoelastin-collagen blend was 50% higher than that of a pure tropoelastin scaffold. Finally, the 1:1 tropoelastin-collagen blend was five times stiffer from 0 to 50% strain when strained at five times the ASTM standard rate. By systematically varying protein composition and crosslinking, the results demonstrate how protein scaffolds might be manipulated as customized biomaterials, ensuring mechanical robustness and potentially improving biocompatibility through minimization of compliance mismatch with the surrounding tissue environment. Moreover, the demonstration of strain-rate dependent mechanical behavior has implications for mechanical design of tropoelastin-based tissue scaffolds. INTRODUCTION Biomaterials are materials that interface with living tissues, applications of which range from contact lenses to vascular grafts and hernia patches [1]. Because biomaterials are surrounded by living tissues, the interface between foreign material and the living tissue is an essential consideration for evaluating the utility of a biomaterial [2]. The biocompatibility of a material is measured by a range of techniques, including changes in mechanical properties or surface conditions and chemical or histological identification of inflammatory indicators [3]. A candidate biomaterial must also have the required strength or elasticity for its given application [4], but mechanical characterization can be more complex than just evaluating load and extension behavior. There is evidence that the mechanical behavior of a material can play a role in its biocompatibility, with materials that better match the compliance and mechanical properties of the surrounding tissue eliciting a more favorable response [5]. Electrospinning is a method that has been applied to biomaterial production to produce micro- and nano-architectures more similar to the open micro-architecture of native extracellular matrix
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