Consequences of decellularisation on the biomechanical and biological properties of a porcine tendon at a whole-tendon and sub-tendon scale

Anterior cruciate ligament (ACL) ruptures occur in 1 – 10 in 1000 people annually, increasingly affecting younger populations. Around 400 thousand ACL reconstructions (ACLR) are performed annually, relying on autografts and allografts, both with disadvantages including donor site morbidity, limited availability and structural degradation causing a reduction in the graft’s mechanical properties. An alternative solution could be to use decellularised porcine superflexor tendon (pSFT) as a biocompatible graft. Decellularisation removes the cellular components from the tissue, providing a non-immunogenic, highly conserved extracellular matrix scaffold. However, the effect of the decellularisation process on the structure and biomechanics of pSFT have not been fully elucidated. The aim of this study was to investigate the biological and biomechanical consequences of the decellularisation process on pSFT using a hierarchical approach, analysing at different levels of scale to prove its suitability to act as a graft for ACLR. It was found that alternative solutions to phosphate buffered saline used during end-stage washes of the decellularisation process reduced pSFT swelling while effectively removing cellular components. It was apparent that the decellularisation process affected the interfascicular matrix of pSFT, contributing to the changes seen in collagen crimp and mechanical properties of whole tendon, while also observed in the topography at the sub-tendon scale. The complete mechanical profile of decellularised pSFT was obtained for the first time, showing the tensile and compressive properties were mostly comparable to native pSFT, with no significant loss of collagenous or non-collagenous components. Fascicle structures showed a mostly unaltered arrangement of fibre and fibril structures, with an apparent loss of endotendineum post-decellularisation. Although there is a need for further studies to investigate the biocompatibility, nanomechanics, proteomics and recellularisation of pSFT, particularly at the sub-tendon scale, this study demonstrated decellularised superflexor tendon is a viable biological graft for ACLR.