Development of self-assembled, tissue-engineered ligament from bone marrow stromal cells

The human anterior cruciate ligament is ruptured 200,000 times per year in the United States, resulting in medical costs of $1 billion. The standard treatment is patellar tendon autograft, but this treatment is suboptimal because of lengthy recovery time, arthritis, donor site morbidity, and degenerative joint disease. This study aimed to engineer scaffold-free ligament analogs from a clinically relevant cell source and to examine mechanical and histological properties of the resulting engineered tissue. Porcine bone marrow stromal cells were seeded on laminin-coated substrates with silk suture segments as anchor points. Cells developed into monolayers that subsequently delaminated and self-organized into cohesive rod-like tissues that were held in tension above the substrate. After 14 days of maturation, scanning electron microscopy revealed a well-organized extracellular matrix, aligned collagen fibers, and a collagen fibril diameter of 51.1+/-77 nm. Histological evaluation showed that constructs were composed of approximately 60% collagen. During tensile tests to failure, constructs had a stress of 2.11 +/- 0.13 MPa, a strain of 28.8 +/- 0.95%, a force of 0.26 +/- 0.02 N, and a tangent modulus of 15.4+/-1.04 MPa. Mechanically and histologically, engineered ligament resembled native embryonic connective tissue and had an ultimate stress approximately 15% of native adult mouse tissue.