Design and evaluation of an auxetic biaxial substrate straining device for tissue engineering applications

Abstract

Mechanical forces play a critical role in cellular behaviour, yet devising systems capable of applying multiaxial strain to three-dimensional (3D) tissue engineering substrates remains challenging. This study introduces an innovative approach using 3D-printed auxetic re-entrant honeycomb meshes to convert uniaxial tension into biaxial straining of cell-laden collagen hydrogel substrates by utilising the unconventional negative Poisson's ratio. Key findings demonstrate that polypropylene (PP) meshes exhibited enhanced compliance and ductility compared to conventional poly-l-lactide (PLA) alternatives, making them particularly suitable for this application. Across all auxetic designs, the tensile moduli of the PP meshes were approximately 6 times lower, and their ultimate tensile strains remained at 0.66—approximately 17 times higher than that of PLA meshes. Critically, when human dermal fibroblasts were cultured on the strained collagen gels, their aspect ratio increased by 59 % while maintaining random alignment, providing proof of concept for true biaxial mechanical stimulation. This approach offers a versatile and accessible tool for advancing research in mechanobiology and tissue engineering by enabling the exploration of cellular responses to physiologically relevant mechanical environments.