Optimized Biomanufacturing for Treatment of Volumetric Muscle Loss Enables Physiomimetic Recovery

Volumetric muscle loss (VML) injuries are defined by loss of sufficient skeletal muscle to produce persistent deficits in muscle form and function, with devastating lifelong consequences to both soldiers and civilians. There are currently no satisfactory treatments for VML injuries. The work described herein details the implementation of a fully enclosed bioreactor environment (FEBE) system that efficiently interfaces with our existing automated bioprinting and advanced biomanufacturing methods for cell deposition on sheet-based scaffolds for our previously described tissue-engineered muscle repair (TEMR) technology platform. Briefly, the TEMR technology consists of a porcine bladder acellular matrix seeded with skeletal muscle progenitor cells and preconditioned via 10% uniaxial cyclic stretch in a bioreactor. Overall, TEMR implantation in an established rat tibialis anterior (TA) VML injury model can result in 60 to ∼90% functional recovery. However, our original study documented >50% failure rate. That is, more than half of the implanted TEMR constructs produced no functional improvement beyond no treatment/repair. The high failure rate was attributed to the untoward mechanical disruption of TEMR during surgical implantation. In a follow-up study, adjustments were made to the geometry of both the VML injury and the TEMR construct, and the "nonresponder" group was reduced from over half the TEMR-treated animals to just 33%. Nonetheless, additional improvement is needed for clinical applicability. The main objectives of the current study were twofold: (1) explore the use of advanced biomanufacturing methods (i.e., FEBE bioreactor) to further improve TEMR reliability (i.e., increase functional response rate), (2) determine if previously established bioprinting methods, when coupled to the customized FEBE system would further improve the rate, magnitude or amplitude of functional outcomes following TEMR implantation in the same rat TA VML injury model. The current study demonstrates the unequivocal benefits of a customized bioreactor system that reduces manipulation of TEMR during cell seeding and maturation via bioprinting while simultaneously maximizing TEMR stability throughout the biofabrication process. This new biomanufacturing strategy not only accelerated the rate of functional recovery, but also eliminated all TEMR failures. In addition, implementation of bioprinting resulted in more physiomimetic skeletal muscle characteristics of repaired muscle tissue.