(268b) Mechanically Stimulated Mesenchymal Stem Cells Form Tendon-like Tissue

Authors: 
Abousleiman, R., University of Oklahoma
McFetridge, P. S., University of Oklahoma
Sikavitsas, V. I., University of Oklahoma


Tendons are inelastic collagenous anatomical tissues that connect muscles to bone. They possess high tensile strength but have poor intrinsic healing capabilities. Tendon injuries affect several individuals yearly and in many cases prevent participation in daily activities and work capabilities. According to the Bureau of Labor Statistics 57,420 total workers in the United States were affected from repetitive motion disorders in 2003. Those who experienced tendonitis lost, on an average, 11 days of work. More than 232,000 Achilles tendon sports injuries were documented in the year 2002. One quarter of Achilles tendon overuse injuries reported by athletes require surgery. Almost one quarter of the athletes who undergo surgery require further future operations. Most tendon injuries are a result of overuse rather than trauma, which results in the degeneration and morphological alteration of collagen fibers. The exact causes of collagen degeneration are still not very well understood. Overuse of tendons causes continuous damage to the tissue that eventually escalates into a pathology when the repetitive strain overcomes the ability of the tendon to repair itself. Tendon healing, when possible, requires prolonged durations of rest and immobility. Currently autografts and allografts are being used in tendon replacement surgeries. Donor site morbidity and inflicted pain are the major two problems in autografts. On the other hand, most individuals using allografts develop an immune response. Lacking a satisfactory clinical treatment for tendon pathologies research has been directed toward exploring alternative approaches. Since immobilization lowers the ultimate strength of tendons eminently, several researches have been conducted on the effect of stretching on tissue engineered tendons. It has been shown that dynamic mechanical loading rearranges collagen fibers parallel to the direction of the applied force giving the constructs a tendon-like appearance. Bone marrow mesenchymal stem cells (MSC's) are undifferentiated pluripotent cells that have the potential to differentiate into a number of lineages including tendons. Due to their availability and ability to proliferate and differentiate, MSC's have been widely employed to treat several pathologies. Given the suitable biomechanical and biophysical environment cells would start secreting matrix that would eventually form neotissue. The type and properties of secreted matrix depends on the different stimuli that cells are subjected to. In our study, we are developing a tissue engineered tendon model using decellularized veins as scaffolds. We hypothesize that culturing MSC seeded constructs under cyclic mechanical loading conditions would enhance tendogenesis in-vitro. Veins extracted from umbilical cords were used as scaffolds for seeding MSC's. The veins were initially decellularized in 1% sodium dodecyl sulfate (SDS) and then dehydrated in 75% ethanol. Thus, the scaffold used was primarily composed of type I collagen, the most abundant protein in tendons; and was rich in growth factors that are abundantly present in the extracellular matrix of the Wharton's jelly surrounding the wall of the vein. Scaffolds were then seeded with type I collagen and MSC's (600,000 cells per cord) under sterile conditions and cultured for periods of one and two weeks. A bioreactor was designed to apply cyclic loading on seeded scaffolds under sterile conditions. Statically cultured samples were used as controls. Samples from two time frames, 1 week and 2 weeks, were tested for tensile strength, cellularity, and morphology. After one week only, mechanicallly stimulated samples had almost 90% higher tensile strength than the static controls. Moreover, samples cultured in the bioreactor were 60% more cellular than those cultured under static condition. Microscopically, mechanically stimulated samples showed tendon-like parallel orientation of collagen fibers as opposed to a random orientation for static constructs