Implantation ofIn VitroTissue Engineered Muscle Repair Constructs and Bladder Acellular Matrices Partially RestoreIn VivoSkeletal Muscle Function in a Rat Model of Volumetric Muscle Loss Injury

Abstract

The frank loss of a large volume of skeletal muscle (i.e., volumetric muscle loss [VML]) can lead to functional debilitation and presents a significant problem to civilian and military medicine. Current clinical treatment for VML involves the use of free muscle flaps and physical rehabilitation; however, neither are effective in promoting regeneration of skeletal muscle to replace the tissue that was lost. Toward this end, skeletal muscle tissue engineering therapies have recently shown great promise in offering an unprecedented treatment option for VML. In the current study, we further extend our recent progress (Machingal et al., 2011, Tissue Eng; Corona et al., 2012, Tissue Eng) in the development of tissue engineered muscle repair (TEMR) constructs (i.e., muscle-derived cells [MDCs] seeded on a bladder acellular matrix (BAM) preconditioned with uniaxial mechanical strain) for the treatment of VML. TEMR constructs were implanted into a VML defect in a tibialis anterior (TA) muscle of Lewis rats and observed up to 12 weeks postinjury. The salient findings of the study were (1) TEMR constructs exhibited a highly variable capacity to restore in vivo function of injured TA muscles, wherein TEMR-positive responders (n=6) promoted an ≈61% improvement, but negative responders (n=7) resulted in no improvement compared to nonrepaired controls, (2) TEMR-positive and -negative responders exhibited differential immune responses that may underlie these variant responses, (3) BAM scaffolds (n=7) without cells promoted an ≈26% functional improvement compared to uninjured muscles, (4) TEMR-positive responders promoted muscle fiber regeneration within the initial defect area, while BAM scaffolds did so only sparingly. These findings indicate that TEMR constructs can improve the in vivo functional capacity of the injured musculature at least, in part, by promoting generation of functional skeletal muscle fibers. In short, the degree of functional recovery observed following TEMR implantation (BAM+MDCs) was 2.3×-fold greater than that observed following implantation of BAM alone. As such, this finding further underscores the potential benefits of including a cellular component in the tissue engineering strategy for VML injury.

Biomimetic engineered muscle with capacity for vascular integration and functional maturation in vivo

“…The ability to create engineered muscle tissues that mimic the structural, functional, and regenerative properties of native muscle would enable design of accurate in vitro models for studies of muscle physiology and development (3,4) and promote cell-based therapies for muscle injury and disease (5,6). Pioneering studies of Vandenburgh and coworkers (7) and Dennis and Kosnik (8) were the first to demonstrate in vitro engineering of functional mammalian muscle constructs, followed by other studies reporting that differentiated engineered muscle can survive and vascularize upon implantation in vivo (9)(10)(11)(12)(13). Simultaneously, various studies have shown that, compared with differentiated or committed cells, undifferentiated SCs are a more potent myogenic cell source, with the ability to engraft and replenish the host satellite cell pool and support future rounds of muscle regeneration (14)(15)(16).…”

Applications of <em>In Vivo</em> Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

“…Moreover, in vivo testing requires little surgical skill as the muscle is not isolated from its surroundings and does not require precise knots to reduce muscle/tendon slippage (as is the case for in situ or ex vivo testing) 41 . In addition, with sufficient practice, the speed of correct electrode placement and the ability to quickly make adjustments to achieve maximal force production of the muscle will ensure that protocol completion is rapid and reproducible-both within animals and across different users of the same equipment 39 . It is beneficial to begin with an assessment of the entire anterior crural component as illustrated, prior to excision of the less accessible synergistic muscles (EDL and HL) for more direct investigation of the TA muscle.…”

“…It should be noted; the EDL and HL need to be dissected out of the anterior crural compartment in order to specifically evaluate the TA muscle (they account for approximately 15-20% of the total tibialis anterior torque measured following peroneal nerve stimulation (Corona et al, 2013)). Because this approach provides comprehensive longitudinal analysis of muscle physiology/function, it can shed important mechanistic insight on numerous other types of physiological investigations as well as a variety of disease or therapeutic areas 39 . For example, in vivo muscle function testing is applicable to studies of exercise physiology, ischemia/ reperfusion research, myopathy, nerve damage/neuropathy and vasculopathy, sarcopenia, and muscular dystrophies 40 .…”

Role of regeneration in tissue repairing and therapies

“…It is a newly emerging science whose main objective is to induce the formation of new functional tissues, rather than implanting spare parts or organ transplants for replacement of diseased organs [5]. However, for regeneration of skeletal muscle functions tissue engineering muscle repair (TEMR) constituents are implanted [81]. For the same purpose, chitin is also found suitable scaffold material and highly useful matrices for tissue engineering, stem cell propagation and differentiation [82].…”