Current Strategies for the Regeneration of Skeletal Muscle Tissue

Abstract

Traumatic injuries, tumor resections, and degenerative diseases can damage skeletal muscle and lead to functional impairment and severe disability. Skeletal muscle regeneration is a complex process that depends on various cell types, signaling molecules, architectural cues, and physicochemical properties to be successful. To promote muscle repair and regeneration, various strategies for skeletal muscle tissue engineering have been developed in the last decades. However, there is still a high demand for the development of new methods and materials that promote skeletal muscle repair and functional regeneration to bring approaches closer to therapies in the clinic that structurally and functionally repair muscle. The combination of stem cells, biomaterials, and biomolecules is used to induce skeletal muscle regeneration. In this review, we provide an overview of different cell types used to treat skeletal muscle injury, highlight current strategies in biomaterial-based approaches, the importance of topography for the successful creation of functional striated muscle fibers, and discuss novel methods for muscle regeneration and challenges for their future clinical implementation.

Keywords: hydrogels; scaffold topographies; skeletal muscle cells; tissue engineering.

Figure 1

Demonstration of scaffold-based tissue engineering strategies for regeneration of skeletal muscle. (A) In vitro engineering uses cell-loaded preconditioned constructs to improve cell viability/survival, integration of the graft, and reinnervation. (B) In vivo engineering employs cell-laden biomaterials without extensive preconditioning. The differentiation should occur at the injury site after the transplantation. (C) In situ engineering uses acellular structures as its operating principle. The structure and biochemical properties of biomaterials enhance the infiltration of cells and regeneration of the tissue. Reprinted from [8] with permission from Elsevier.

Figure 2

(A) Schematic of candidate cells of myogenic or non-myogenic origin, including satellite cells (SCs), myoblasts, muscle-derived stem cells, pericytes, mesoangioblasts, and mesenchymal stromal cells (MSCs) from bone marrow or adipose tissue, and induced pluripotent stem cells (iPSCs). Reproduced from [15] Copyright 2019 open access by Creative Commons Attribution 4.0 International License. (B) Schematic of SC isolation and in vitro expansion on artificial niches. (C) Differentiation steps of adult myogenesis showing the myotube formation from SCs. After muscle injury or within normal muscle turnover, quiescent SCs are activated. (D) Schematic of somatic cell reprogramming to obtain iPSCs and subsequent formation of skeletal myogenic progenitors. (B–D) reproduced from [17] Copyright 2015 with permission from Elsevier.

Figure 3

(A) Hand-held printed gelatine-methacryloyl (GelMA) hydrogels. (i) In vivo application of GelMA hydrogel scaffolds, (ii) before VML surgery, post-VML surgery, post in situ printing of GelMA hydrogel, (iii) F-actin/DAPI staining of encapsulated cells in GelMA construct. Reproduced with permission from [14] Copyright (2020) American Chemical Society. (B) Preparation of composite hydrogel scaffolds by incorporating the aligned nanofibers yarns and formation of aligned myotubes. Reproduced with permission from [145]. Copyright (2015) American Chemical Society.

Figure 4

(A) Schematic image of fibrinogen substrate electrospun fibers with different topographies, which direct the cell morphology and phenotype. Reprinted from [202]. Copyright 2019, with permission from Elsevier. (B) Tubular scaffold structure; (i) surface and (ii) cross-section images with (iii) SEM images of outer and inner layers. Reproduced from [203]. Copyright 2019 with permission from Elsevier. (C) Scheme of the nanofiber yarns (NFYs)-network (NET) scaffolds fabricated by a weaving technique and GelMA hydrogel shell layer prepared by UV irradiation. Reproduced with permission from [204]. Copyright 2017 American Chemical Society.

Figure 5

(A) SEM images of different microgrooved collagen scaffolds. Top-view and vertical cross-sectional view are shown. Flat collagen scaffold (control), collagen scaffolds with mean microgroove widths of 120 µm (G120), 200 µm (G200), and 380 µm (G380). Scale bar = 100 µm. (B) Myotube formation after cultivation of L6 myoblasts for 14 days. F-actin and myosin heavy chain (MHC) staining were performed to visualize myoblasts and myotube formation. Scale bar = 200 µm. Reproduced from [210]. Copyright (2015) with permission from Elsevier.

Figure 6

(A) Detection of hypoxia in the dECM sponge, dECM hydrogel, and 3D printed muscle constructs with pimonidazole staining and (B) immunofluorescence images of human skeletal muscle cells in constructs. Reproduced from [213]. Copyright (2019) with permission Elsevier. (C) Fluorescence microscopy images of F-Actin (red)/DAPI (blue) stained C2C12 cells and (D) Corresponding frequency of F-Actin filament orientations, O30 (d = 330 µm, p = 30 kPa), O40 (d = 330 µm, p = 40 kPa) and R60 (d = 250 µm, p = 60 kPa), d: nozzle diameter, p: extrusion pressure. Scale bars: 200 µm. Reproduced from [214]. Copyright 2020 open access by Creative Commons Attribution 4.0 International License.