Tenocytic extract and mechanical stimulation in a tissue-engineered tendon construct increases cellular proliferation and ECM deposition

Chemical and mechanical stimulation, when properly utilized, positively influence both the differentiation of in vitro cultured stem cells and the quality of the deposited extracellular matrix (ECM). This study aimed to find if cell-free extract from primary tenocytes can positively affect the development of a tissue-engineered tendon construct, consisting of a human umbilical vein (HUV) seeded with mesenchymal stem cells (MSCs) subjected to cyclical mechanical stimulation. The tenocytic cell-free extract possesses biological material from tendon cells that could potentially influence MSC tenocytic differentiation and construct development. We demonstrate that the addition of tenocytic extract in statically cultured tendon constructs increases ECM deposition and tendon-related gene expression of MSCs. The incorporation of mechanical stimulation (2% strain for 30 min/day at 0.5 cycles/min) with tenocytic extract further improved the MSC seeded HUV constructs by increasing cellularity of the construct by 37% and the ultimate tensile strength by 33% compared to the constructs with only mechanical stimulation after 14 days. Furthermore, the addition of mechanical stimulation to the extract supplementation produced longitudinal ECM fibril alignment along with dense connective tissue, reminiscent of natural tendon.