Multiphasic collagen fibre-PLA composites seeded with human mesenchymal stem cells for osteochondral defect repair: an in vitro study.

A promising approach for the repair of osteochondral defects is the use of a scaffold with a well-defined cartilage-bone interface. In this study, we used a multiphasic composite scaffold with an upper collagen I fibre layer for articular cartilage repair, separated by a hydrophobic interface from a lower polylactic acid (PLA) part for bone repair. Focusing initially on the engineering of cartilage, the upper layer was seeded with human mesenchymal stem cells (hMSCs) suspended in a collagen I hydrogel for homogeneous cell distribution. The constructs were cultured in a defined chondrogenic differentiation medium supplemented with 10 ng/ml transforming growth factor-beta1 (TGFbeta1) or in DMEM with 10% fetal bovine serum as a control. After 3 weeks a slight contraction of the collagen I fibre layer was seen in the TGFbeta1-treated group. Furthermore, a homogeneous cell distribution and chondrogenic differentiation was achieved in the upper third of the collagen I fibre layer. In the TGFbeta1-treated group cells showed a chondrocyte-like appearance and were surrounded by a proteoglycan and collagen type II-rich extracellular matrix. Also, a high deposition of glycosaminoglycans could be measured in this group and RT-PCR analyses confirmed the induction of chondrogenesis, with the expression of cartilage-specific marker genes, such as aggrecan and collagen types II and X. This multiphasic composite scaffold with the cartilage layer on top might be a promising construct for the repair of osteochondral defects.

Regeneration of articular cartilage--evaluation of osteochondral defect repair in the rabbit using multiphasic implants.

OBJECTIVE: To investigate whether two different multiphasic implants could initiate and sustain repair of osteochondral defects in rabbits. The implants address the malleable properties of cartilage while also addressing the rigid characteristics of subchondral bone. DESIGN: The bone region of both devices consisted of D, D-L, L-polylactic acid invested with hyaluronan (HY). The cartilage region of the first device was a polyelectrolytic complex (PEC) hydrogel of HY and chitosan. In the second device the cartilage region consisted of type I collagen scaffold. Eighteen rabbits were implanted bilaterally with a device, or underwent defect creation with no implant. At 24 weeks, regenerated tissues were evaluated grossly, histologically and via immunostaining for type II collagen. RESULTS: PEC devices induced a significantly better repair than untreated shams. Collagen devices resulted in a quality of repair close to that of the PEC group, although its mean repair score (19.0+/-4.2) did not differ significantly from that of the PEC group (20.4+/-3.7) or the shams (16.5+/-6.3). The percentage of hyaline-appearing cartilage in the repair was highest with collagen implants, while the degree of bonding of repair to the host, structural integrity of the neocartilage, and reconstitution of the subchondral bone was greatest with PEC devices. Cartilage in both device-treated sites stained positive for type II collagen and GAG. CONCLUSIONS: Both implants are capable of maintaining hyaline-appearing tissue at 24 weeks. The physicochemical region between the cartilage and bone compartments makes these devices well suited for delivery of different growth factors or drugs in each compartment, or different doses of the same factor. It also renders these devices excellent vehicles for chondrocyte or stem cell transplantation.

Viscoelastic behavior of osteoarthritic cartilage.

We have studied the incremental stress-strain behavior of human articular cartilage in tension in an attempt to understand the molecular basis for fibrillation and fissure formation in osteoarthritis. Our results indicate that the elastic spring constant for collagen in the direction per pendicular to the cleavage line pattern is about 1.6 GPa (2.3 GPa after correction for the collagen content) and the collagen fibril length is between 0.558 pm at low strains and 1.24 pm at high strains for normal cartilage. Values for the elastic spring constant and collagen fibril length were both found to decrease in OA. The value of the elastic spring constant for collagen perpendicular to the cleavage line pattern is similar to that calculated based on stress-strain curves reported by Kempson. Our results indicate that the elastic spring constant for collagen and the collagen fibril length decrease as the extent of fibrillation and fissure formation increase. Decreases in the elastic spring constant of collagen are consistent with loss of the superficial layer, degradation of proteoglycans and collagen, and subsequent mechanical fatigue. However, changes in the polymer volume fraction are consistent with enzymatic degradation preceding mechanical disruption. It is concluded that osteoarthritic changes to cartilage involve enzymatic degradation of matrix components and fibril fragmentation that is promoted by subsequent mechanical loading.

Relationship among biomechanical, biochemical, and cellular changes associated with osteoarthritis.

Articular cartilage that lines the surface of long bones is a multilayered material. The superficial layer consists of collagen fibrils and chondrocytes that run parallel to the joint surface. In the deeper layers, the collagen fibrils are more randomly arranged and support vertical units termed chondrons containing rows of chondrocytes. In the deepest layers, the collagen fibrils run almost vertically and ultimately insert into the underlying subchondral bone. Osteoarthritis (OA) is a disease that affects articular cartilage and is characterized by enzymatic and mechanical breakdown of the extracellular matrix, leading to cartilage degeneration, exposure of subchondral bone, pain, and limited joint motion. Changes in mechanical properties of articular cartilage associated with OA include decreases in modulus and ultimate tensile strength. These changes parallel the changes observed after enzymatic degradation of either collagen or proteoglycans in cartilage. Results of recent viscoelastic studies on articular cartilage suggest that the elastic modulus of collagen and fibril lengths decrease in OA and are associated with a loss of the superficial zone and a decreased ability of articular cartilage to store elastic energy during locomotion. It is suggested that osteoarthritic changes to cartilage involve enzymatic degradation of matrix components and fibril fragmentation that is promoted by subsequent mechanical loading.