Dynamic and static strain levels differentially affect the enzymatic degradation of collagen fibres

Collagen fibres are essential for the load-bearing capacity of soft biological tissues, ensuring structural integrity and function. The repair process after injury often involves collagen remodelling, including reorganisation, synthesis, and degradation. When remodelling is unbalanced, degradation can lead to mechanical strength loss and tissue failure, as often seen after anterior cruciate ligament reconstruction. It is well established that enzymatic collagen degradation is modulated by levels of static strain, with relatively low and high strain magnitudes accelerating degradation rates compared to an intermediate minimum. However, in vivo, load-bearing tissues experience more often dynamic strain, and the impact of different magnitudes of cyclic strain on collagen enzymatic breakdown remains unclear. The present study investigated whether different levels of cyclic strain alter the susceptibility of collagen to enzymatic degradation by collagenases, and compared them to static strain. Decellularised porcine patellar tendons underwent various static and cyclic strain relaxation tests with or without bacterial collagenases. Consistent with prior findings, static strain elicited maximum protection at the heel point where stiffness increases. In contrast, dynamic strain accelerated degradation regardless of average strain, indicating a magnitude-independent mechanism under dynamic loading. Additionally, the dynamic degradation rate, unlike under static stretch, was relatively unaffected in the toe region, with a decreasing trend above the heel point. These findings suggest that optimising tissue recovery with controlled collagen degradation requires carefully selecting strain values based on the loading type. Such insights enhance our understanding of collagen remodelling and inform recovery strategies. STATEMENT OF SIGNIFICANCE: Tissue repair after injury involves collagen remodelling, where degradation plays an important role. Collagen enzymatic degradation is known to be affected by static strain. However, in vivo tissues experience dynamic strains, with unclear effects. We investigated how dynamic strain alters collagen enzymatic degradation in porcine patellar tendons. As shown previously, static strain protected collagen degradation at the heel point, whereas the present study provided new insight that dynamic strain increased the degradation rate relative to static strain at all strain values and that this effect trended to be less sensitive to strain levels. These results suggest that physiological strains influence collagen degradation differently under static and dynamic loading, offering insights that may guide targeted strain applications to improve healing.