Rehabilitative exercise and spatially patterned nanofibrillar scaffolds enhance vascularization and innervation following volumetric muscle loss

Abstract

Muscle regeneration can be permanently impaired by traumatic injuries, despite the high regenerative capacity of skeletal muscle. Implantation of engineered biomimetic scaffolds to the site of muscle ablation may serve as an attractive off-the-shelf therapeutic approach. The objective of the study was to histologically assess the therapeutic benefit of a three-dimensional spatially patterned collagen scaffold, in conjunction with rehabilitative exercise, for treatment of volumetric muscle loss. To mimic the physiologic organization of skeletal muscle, which is generally composed of myofibers aligned in parallel, three-dimensional parallel-aligned nanofibrillar collagen scaffolds were fabricated. When implanted into the ablated murine tibialis anterior muscle, the aligned nanofibrillar scaffolds, in conjunction with voluntary caged wheel exercise, significantly improved the density of perfused microvessels, in comparison to treatments of the randomly oriented nanofibrillar scaffold, decellularized scaffold, or in the untreated control group. The abundance of neuromuscular junctions was 19-fold higher when treated with aligned nanofibrillar scaffolds in conjunction with exercise, in comparison to treatment of aligned scaffold without exercise. Although, the density of de novo myofibers was not significantly improved by aligned scaffolds, regardless of exercise activity, the cross-sectional area of regenerating myofibers was increased by > 60% when treated with either aligned and randomly oriented scaffolds, in comparison to treatment of decellularized scaffold or untreated controls. These findings demonstrate that voluntary exercise improved the regenerative effect of aligned scaffolds by augmenting neurovascularization, and have important implications in the design of engineered biomimetic scaffolds for treatment of traumatic muscle injury.

Pre-Innervated Tissue Engineered Muscle Promotes a Pro-Regenerative Microenvironment Following Volumetric Muscle Loss

“…Aligned nanofiber scaffolds are the preferred biomaterial for muscle reconstruction since they not only promote myofibers alignment but can also be stacked to provide bulk to the engineered tissue. Aligned nanofiber scaffolds have been shown to facilitate NMJ formation in vitro as well as promote alignment of regenerating myofibers in vivo as compared to randomly oriented nanofibers 19,27,37 .…”

“…Most tissue engineering strategies towards VML repair are evaluated in small animal models 44 . Cell based approaches generally comprise of cell lines (mouse/human) or primary cells and hence are carried out in athymic animals to allow in vivo survival and maturation of the constructs 19,27,44,45 .…”

“…The ECM secreted by skeletal myofibers is arranged in a network of micronano fibrils which are aligned along the myofibers. Aligned nanofiber-based scaffolds accurately replicate the topographical cues of native ECM architecture and has been reported to promote aligned myogenesis, cell migration, survival and angiogenesis 19 .…”

Musculoskeletal Regeneration, Rehabilitation, and Plasticity Following Traumatic Injury

“…Alarmingly, a recent systematic review, meta-analysis, and network meta-analysis of VML injury studies that included quantitative functional analyses [98] determined that in animal models, rehabilitation approaches for VML injury resulted in worse functional outcomes than if the injury was left to its natural sequela. This work specifically focused on studies testing rehabilitation in animal models in the form of voluntary wheel running, chronic-intermittent electrical nerve stimulation and/or passive range of motion exercises resulting in only modest functional improvements [84,[99][100][101][102][103]. Collectively, these limited clinical and pre-clinical studies indicate that the remaining muscle does not fully recover strength, may be resistant to rehabilitation, and results in long-term disability.…”

The regenerative rehabilitation collection: a forum for an emerging field

“…Nakayama et al demonstrate the ability of a three-dimensional nanofibrillar scaffold in combination with an exercise protocol to restore tissue structure and composition in a murine model of volumetric muscle loss (VML). 2 In designing the construct, careful attention was taken to design the scaffold in a way that both is biocompatible and closely mimics the architecture and mechanical properties of native skeletal muscle. Despite the biomimetic nature of the construct, the investigators found that implantation of the scaffold alone yielded no benefit in vascularity or muscle regeneration.…”