Mechanical regulation of matrix reorganization and phenotype of smooth muscle cells and mesenchymal stem cells in 3D matrix

In an effort to develop small-diameter tissue-engineered vascular grafts (< 6 mm), collagen and fibrin gels seeded with human aortic smooth muscle cells (HASMCs) were constructed in a three-dimensional tubular environment and subjected to mechanical stimulation to investigate changes in cellular response and matrix remodeling. After testing various collagen and fibrin concentrations, experiments indicated 2:1 mg/mL of collagen:fibrin constructs with embedded HASMCs contracted as well as the pure fibrin, at 54% their original length after 3 days, indicating enhanced cellular activity and matrix remodeling . Vascular constructs were cultured for three days before undergoing pulsatile 10% cyclic strain at 1 Hz for three days. RT-PCR showed that cyclic strain increased the gene expression of SMC markers α-actin and SM22, indicating that mechanical stimulation induces SMCs to a more contractile phenotype. Histology showed a more compacted collagen fiber structure for mechanically stimulated constructs compared to the looser collagen network in static constructs. The effects of 3D mechanical strain were also tested on mesenchymal stem cells (MSCs), which can be a possible source for SMCs. Cyclic strain increased α-actin and SM22 gene expression in MSCs, suggesting the differentiation of MSCs into a SMC phenotype.