Optimization of flexor tendon tissue engineering with a cyclic strain bioreactor.

Abstract

Mechanical manipulation of cultured tendon cells can enhance cell proliferation and matrix production. This study aims to determine the bioreactor strain patterns (amplitude, frequency, and on/off ratio) that favor cellular proliferation, promote collagen production, and maintain morphology in candidate cell lines cultured for flexor tendon tissue engineering, including multipotent stromal cells. We studied epitenon tenocytes (Es), sheath fibroblasts (Ss), bone marrow-derived mesenchymal stem cells (BMSCs), and adipoderived stem cells (ASCs). We examined the effects of 3 patterns of cyclic uniaxial strain on cell proliferation, collagen I production, and cell morphology. Adipoderived stem cells (33% adhesion) and Ss (29%) adhered more strongly to bioreactor membranes than did Es (15%) and BMSCs (7%), p=.04. Continuous cyclic strain (CCS, 8%, 1 Hz) inhibited cell proliferation (p=.01) and increased per-cell collagen production (p=.04) in all cell types. Intermittent cyclic strain (4%, 0.1 Hz, 1 hour on/5 hours off) increased proliferation in ASCs (p=.06) and Ss (p=.04). Intermittent cyclic strain (4%, 0.1 Hz, 1 hour on/2 hours off) increased total collagen production by 25% in ASCs (p=.004) and 20% in Ss (p=.05). Cyclic strain resulted in cell alignment perpendicular to the strain axis, cytoskeletal alignment, and nuclear elongation. These morphological characteristics are similar to those of tenocytes. These results demonstrate that intermittent cyclic strain can increase cell proliferation, promote collagen I production, and maintain tenocyte morphology in vitro. Use of a cell bioreactor might accelerate the in vitro stage of tendon tissue engineering.