Structural biomimetics in soft synthetic composite materials: A proof-of-concept alginate-polyamide soft hierarchical composite

Natural materials often consist of hierarchical architectures, which are extremely efficient in mechanical terms. Whereas the structure-function relationship is well-studied in natural hard materials, soft materials are not getting equal at-tention, despite their high prevalence in nature. These soft materials are usually constructed as fiber-reinforced composites consisting of diverse structural motifs that result in an overall unique mechanical behavior. In this study, as a proof-of-concept, a soft biomimetic composite was fabricated from a hierarchical electrospun polyamide fiber, reinforcing a hydrogel matrix and creating a simple synthetic analog for natural soft composites. This material system investigates the structure-function relationship between the structure and mechanical function by mimicking different structural motifs. The polyamide-hydrogel composite exhibited large deformations and nonlinear material behavior. Varying degrees of crimping enabled a controlled strain stiffening behavior and engineered transition from matrix-dominated to fiber-dominated behavior. We also observed that the individual nanofibers in our bundles created cross-bridges with the matrix and within the bundle, making the material system more resistant to failure. Our bio-inspired composite demonstrated mechanical behaviors similar to natural soft com-posites, which can aid in the future design and development of the next generation of soft architectural composites.