The influence of scaffold fibre architecture on tenocyte tissue production under intermittent dynamic culture

Surgical intervention involving grafts is often required to treat ruptured Achilles tendons. Synthetic grafts for this purpose have a number of advantages but have yet to be translated to clinic, due to an inability to reproduce the complex architecture and thus biomechanics of the native collagen fibre structure. This study examined the influence of scaffold fibre architecture in combination with intermittent dynamic culture on the composition of extracellular matrix (ECM) deposited by isolated rabbit tenocytes. Scaffolds were prepared using melt electrowriting having fibre patterns similar to those reported for tendon tissue, with either bi-directionally crimped fibres or unidirectionally crimped with orthogonal linear fibres. The bi-directionally crimped scaffolds were designed such that they had a negative Poisson's ratio (auxetic nature) similar to that reported for the human Achilles tendon (AT). The scaffolds were seeded with rabbit tenocytes, precultured under static conditions for one week, then either dynamically stimulated in intermittent uniaxial tension (4 % strain, 1 Hz, 1 h/day) or maintained in static culture for 2 weeks. Dynamic intermittent stimulation promoted increased cell proliferation and ECM synthesis on both scaffold architectures in comparison to static controls. However, the tenocytes cultured on the bi-directional, auxetic scaffolds produced more total collagen and less sulfated glycosaminoglycans (sGAG) per cell with an overall collagen:sGAG ratio within the range reported for healthy human tissue at 10:1 in contrast to the 4:1 ratio of the ECM deposited on the scaffolds with the unidirectional crimped, non-auxetic fibre pattern. The increase in collagen content on the auxetic scaffolds was also reflected in a higher tensile modulus. These findings demonstrate the impact of fibre crimp unfolding on tenocyte response to mechanical loading and highlight the benefits of replicating the complexity of the AT fibre architecture in developing grafts for surgical repair of ruptured ATs. STATEMENT OF SIGNIFICANCE: Synthetic grafts for Achilles tendon (AT) repair have predominantly used a uniaxial crimped fibre architecture. However, the collagen fibre architecture of the AT is more complex, having multidimensional fibre crimping. This crimp pattern is considered responsible for the auxetic nature of the human AT, and tenocyte response to scaffolds with multidimensional fibre architectures has not been explored to date. Our findings demonstrate the importance of replicating the multidimensional nature of fibre architecture and suggest the benefits of incorporating an auxetic response in graft designs.