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

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.