Engineering muscle constructs for the creation of functional engineered musculoskeletal tissue

Abstract

Volumetric muscle loss (VML) is a disabling condition in which current clinical procedures are suboptimal. The field of tissue engineering has many promising strategies for the creation of functional skeletal muscle in vitro. However, there are still two key limitations that prevent it from becoming a solution for treating VML. First, engineered muscle tissue must be biocompatible to facilitate muscle tissue regrowth without generating an immune response. Second, engineered muscle constructs must be scaled up to facilitate replacement of clinically relevant volumes of tissue (centimeters in diameter). There are currently no tissue engineering strategies to produce tissue constructs that are both biocompatible and large enough to facilitate clinical repair. However, recent advances in tissue engineering using synthetic scaffolds, native scaffolds, or scaffold-free approaches may lead to a solution for repair of VML injuries.

Figure 1. Reconstructive algorithm for clinical volumetric muscle loss defects

If local uninjured muscle is available, it can be used to reconstruct the VML defect. The distal tendon is cut, allowing the muscle to be rotated into the defect based on its blood supply (the artery, vein and nerve are not severed). If local muscle is unavailable, the VML defect can be reconstructed using muscle from another part of the body within the same individual (FFMT) or from another individual (CTA). The muscle to be transferred is harvested along with its artery, vein and nerve, and these are reconnected at the recipient site to re-establish an immediate blood supply. If none of these options are possible, then alternative reconstructive approaches should be considered. CTA: Composite tissue allotransplantation; FFMT: Free functional muscle transfer; VML: Volumetric muscle loss.

Figure 2. Model for parallel fusion of constructs to fabricate large-diameter muscle tissue

Small in vitro constructs (0.5–0.8 mm in diameter) are lined up in parallel and allowed to fuse to form a muscle construct width of 2.5 mm and a thickness of 1.5 mm.

Figure 3. Utilization of large tissue culture plates to increase construct size

Construct length is determined by the size of the tissue culture plate the monolayer is fabricated in. Use of larger culture plates will allow for fabrication of muscle constructs up to 18 cm in length. The construct shown was cultured in a square culture plate, allowing the construct to form along the diagonal to form constructs in excess of 15 cm.