Quantification of Collagen Organization Using Fractal Dimensions and Fourier Transforms

Collagen fibers and fibrils that comprise tendons and ligaments are disrupted or damaged during injury. Fibrillogenesis during healing produces a matrix that is initially quite disorganized, but remodels over time to resemble, but not replicate, the original roughly parallel microstructure. Quantification of these changes is traditionally a laborious and subjective task. In this work we applied two automated techniques, fast Fourier transformation (FFT) and fractal dimension analysis (FA) to quantify the organization of collagen fibers or fibrils. Using multi-photon images of collagen fibers obtained from rat ligament we showed that for healing ligaments, FA differentiates more clearly between the different time-points during healing. Using scanning electron microscopy images of overstretched porcine flexor tendon, we showed that combining FFT and FA measures distinguishes the damaged and undamaged groups more clearly than either method separately

Interleukin-1 Receptor Antagonist Modulates Inflammation and Scarring After Ligament Injury

Ligaments have limited regenerative potential and as a consequence, repair is protracted and results in a mechanically inferior tissue more scar-like than native ligament. We previously reported that a single injection of interleukin-1 receptor antagonist (IL-1Ra) delivered at the time of injury, decreased the number of M2 macrophage-associated inflammatory cytokines. Based on these results, we hypothesized that IL-1Ra administered after injury and closer to peak inflammation (as would occur clinically), would more effectively decrease inflammation and thereby improve healing. Since IL-1Ra has a short half-life, we also investigated the effect of multiple injections. The objective of this study was to elucidate healing of a medial collateral ligament (MCL) with either a single IL-1Ra injection delivered one day after injury or with multiple injections of IL-1Ra on days 1, 2, 3, and 4. One day after MCL injury, rats received either single or multiple injections of IL-1Ra or PBS. Tissue was then collected at days 5 and 11. Both single and multiple IL-1Ra injections reduced inflammatory cytokines, but did not change mechanical behavior. A single injection of IL-1Ra also reduced the number of myofibroblasts and increased type I procollagen. Multiple IL-1Ra doses provided no additive response and, in fact, reduced the M2 macrophages. Based on these results, a single dose of IL-1Ra was better at reducing the MCL-derived inflammatory cytokines compared to multiple injections. The changes in type I procollagen and myofibroblasts further suggest a single injection of IL-1Ra enhanced repair of the ligament but not sufficiently to improve functional behavior