Biophysical Stimulation for Engineering Functional Skeletal Muscle

Abstract

Tissue engineering is a promising therapeutic strategy to regenerate skeletal muscle. However, ex vivo cultivation methods typically result in a low differentiation efficiency of stem cells as well as grafts that resemble the native tissues morphologically, but lack contractile function. The application of biomimetic tensile strain provides a potent stimulus for enhancing myogenic differentiation and engineering functional skeletal muscle grafts. We reviewed integrin-dependent mechanisms that potentially link mechanotransduction pathways to the upregulation of myogenic genes. Yet, gaps in our understanding make it challenging to use these pathways to theoretically determine optimal ex vivo strain regimens. A multitude of strain protocols have been applied to in vitro cultures for the cultivation of myogenic progenitors (adipose- and bone marrow-derived stem cells and satellite cells) and transformed murine myoblasts, C2C12s. Strain regimens are characterized by orientation, amplitude, and time-dependent factors (effective frequency, duration, and the rest period between successive strain cycles). Analysis of published data has identified possible minimum/maximum values for these parameters and suggests that uniaxial strains may be more potent than biaxial strains, possibly because they more closely mimic physiologic strain profiles. The application of these biophysical stimuli for engineering 3D skeletal muscle grafts is nontrivial and typically requires custom-designed bioreactors used in combination with biomaterial scaffolds. Consideration of the physical properties of these scaffolds is critical for effective transmission of the applied strains to encapsulated cells. Taken together, these studies demonstrate that biomimetic tensile strain generally results in improved myogenic outcomes in myogenic progenitors and differentiated myoblasts. However, for 3D systems, the optimization of the strain regimen may require the entire system including cells, biomaterials, and bioreactor, to be considered in tandem.

Engineering Biomimetic Materials for Skeletal Muscle Repair and Regeneration

“…The effects of mechanical stimulation on the function of myoblasts in 3D biomaterials has highlighted the value of physical preconditioning in enhancing myogenic differentiation and maturation . Li et al showed that applying 40% static strain for 10 h d −1 for 10 d applied to C2C12 myoblasts embedded in gelatin methacrylate (GelMA) hydrogels, induced the expression of myogenic factors including MyoD, myogenin, and MHC, which differed from findings using 2D substrates .…”

“…For example, Akimoto et al showed that applying a 20% mechanical stretch for 24 h reduced the expression level of myogenic regulatory factors such as MyoD and myogenin in C2C12 cells by almost 40% and 70%, respectively, suggesting that mechanical stretch inhibits the differentiation of C2C12 cells from forming myotubes. In contrast, other studies have shown an induction of myogenesis in C2C12 myoblasts when stimulated by uniaxial stretching ranging from 10–17%, compared to static control samples . The difference in findings may be attributed to differences in the magnitude of strain, the confluency of the cells, and potential differences in the degree of cellular adhesion on the deformable substrates during stretch.…”

“…In contrast, other studies have shown an induction of myogenesis in C2C12 myoblasts when stimulated by uniaxial stretching ranging from 10–17%, compared to static control samples. [110, 111] The difference in findings may be attributed to differences in the magnitude of strain, the confluency of the cells, and potential differences in the degree of cellular adhesion on the deformable substrates during stretch. Beside the strain level, cells subjected to uniaxial vs biaxial stretch also manifest differential responses in cellular alignment, expression of myogenic factors and degree of differentiation.…”

“…Beside the strain level, cells subjected to uniaxial vs biaxial stretch also manifest differential responses in cellular alignment, expression of myogenic factors and degree of differentiation. [110]…”

A Poroelastic Model of a Fibrous-Porous Tissue Engineering Scaffold

“…One critical function of the scaffolds is control of stem cell differentiation. Mechanical factors play an important role in this function since they can provide both the acceleration of stem cell differentiation toward a given lineage 5 , 6 and regulation of lineage fate 7 , 8 . Mechanical stimulation can be exerted through externally applied stresses/forces and strains, innate physical properties of the extracellular matrix (scaffold), or combinations of both.…”