(393f) Effect of Uniaxial Cyclic Stretch Duration On ECM Protein Expression by Ligament Progenitor Cells On Electrospun Fibrous Meshes

A tissue-engineered ligament is a promising alternative to hamstring and patellar tendon grafts for anterior cruciate ligament (ACL) reconstruction, but strategies must be developed to form oriented neo-tissues with high tensile strength. Our hypothesis is that this may be accomplished by conditioning ligament progenitor cells, seeded on oriented fiber scaffolds, with uniaxial cyclic mechanical stretch. Here, the cyclic stretch is intended to induce the ligament progenitor cells to express extracellular matrix (ECM) proteins, while the oriented fibers provide contact guidance cues to maintain cell alignment and promote collagen fibril organization parallel to the axis of stretch. For this project we have developed a biodegradable, biocompatible poly (ester-urethane urea) (PEUUR) elastomer from 2000 Da polycaprolactone, 1,6-diisocyanatohexane, and 1,3-propanediol bis(4-aminobenzoate) with a bulk modulus 18 MPa and a strain to failure of more than 400%. When electrospun from a 10% solution in 1,1,1,3,3,3-hexafluoro-2-propanol onto a collecting drum rotating at 7.9 m/s, this PEUUR forms a fused fiber mesh consisting of partially aligned 890 nm diameter fibers. In our preliminary studies, we have found that this mesh supports adhesion, alignment, and proliferation of bone marrow-derived ligament progenitor cells. In addition, when these meshes are cyclically loaded in a stretch bioreactor (Figure 1) to 8% strain at 0.5 Hz for 1 hr, once daily for two days, the cell remain adherent and aligned (Figure 2), and express ligament ECM proteins type I collagen and decorin and ligament selective proteins scleraxis and tenomodulin comparable to unload controls. In our current work we are extending this cyclic stretch duration with the goal of enhancing expression and deposition of ligament ECM proteins. The results of these ongoing studies will be presented. In addition, our strategy for processing these thin (200 μm thick) meshes into cords suitable for ACL replacement will be described.