Comparison of 2 Different Formulations of Artificial Bone for a Hybrid Implant With a Tissue-Engineered Construct Derived From Synovial Mesenchymal Stem Cells: A Study Using a Rabbit Osteochondral Defect Model.

BACKGROUND: Previously, we developed a hybrid implant composed of hydroxyapatite (HA)-based artificial bone coupled with a mesenchymal stem cell (MSC)-based scaffold-free tissue-engineered construct (TEC) and demonstrated its feasibility for osteochondral repair. Beta-tricalcium phosphate (ßTCP) may be a promising alternative to HA, as it is a highly biocompatible material and is resorbed more rapidly than HA in vivo. HYPOTHESIS: A ßTCP-based hybrid TEC implant will exhibit superior osteochondral repair when directly compared with an HA-based hybrid implant, as tested using a rabbit osteochondral defect model. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral defects were created in the femoral groove of skeletally mature rabbits. The TEC and artificial bone, using either HA or ßTCP with the same porosities and similar mechanical properties, were hybridized and then implanted in the defects. A histological evaluation and microindentation testing were performed for the assessment of repair tissue. RESULTS: Osteochondral defects treated with the TEC/ßTCP implants showed more rapid subchondral bone repair at 1 month, but the cartilaginous tissue deteriorated over time out to 6 months after implantation. Osteochondral defects treated with the TEC/HA implants maintained good histological quality out to 6 months after implantation and also exhibited better biomechanical properties at 6 months as compared with the TEC/ßTCP implants. CONCLUSION: Contrary to our hypothesis, the TEC/HA hybrid implant facilitated better osteochondral repair than did the TEC/ßTCP implant. The results of the present study suggest the importance of a stable restoration of subchondral bone for long-term effective osteochondral repair rather than rapid remodeling of subchondral bone. CLINICAL RELEVANCE: This study contributes to the future selection of suitable materials for patients with osteochondral lesions.

Zone-specific integrated cartilage repair using a scaffold-free tissue engineered construct derived from allogenic synovial mesenchymal stem cells: Biomechanical and histological assessments.

The purpose of the present study was to investigate the zone-specific integration properties of articular cartilage defects treated in vivo with scaffold-free three-dimensional tissue-engineered constructs (TECs) derived from allogenic synovial mesenchymal stem cells (MSCs) in a porcine model. The TEC derived from the synovial MSCs was implanted into chondral defects in the medial femoral condyle of the knee. The integration boundary of repair tissue with the adjacent host cartilage was morphologically and biomechanically evaluated at 6 months post-implantation. Histological assessments showed that the repair tissue in each zone was well integrated with the adjacent host cartilage, with an apparent secure continuity of the extracellular matrix. There were no significant differences in histological scores between the integration boundary and the center of the repair tissue at every zone. Nonetheless, in all the specimens subjected to mechanical testing, failure occurred at the integration boundary. The average tensile strength of the integration boundary vs normal cartilage was 0.6 vs 4.9, 3.0 vs 12.6, and 5.5 vs 12.8MPa at the superficial, middle, and deep layers, respectively. Thus, these results indicate the most fragile point in the repair tissue remained at the integration boundary in spite of the apparent secure tissue continuity and equivalent histological quality with the center of the repair tissue. Such tissue vulnerability at the surface integration boundary could affect the long-term durability of the tissue repair, and thus, special consideration will be needed in the post-operative rehabilitation programming to enhance the longevity of such repair tissues in response to normal knee loading.

Osteochondral repair using a scaffold-free tissue-engineered construct derived from synovial mesenchymal stem cells and a hydroxyapatite-based artificial bone.

For an ideal osteochondral repair, it is important to facilitate zonal restoration of the subchondral bone and the cartilage, layer by layer. Specifically, restoration of the osteochondral junction and secure integration with adjacent cartilage could be considered key factors. The purpose of the present study was to investigate the feasibility of a combined material comprising a scaffold-free tissue-engineered construct (TEC) derived from synovial mesenchymal stem cells (MSCs) and a hydroxyapatite (HA) artificial bone using a rabbit osteochondral defect model. Osteochondral defects were created on the femoral groove of skeletally mature rabbits. The TEC and HA artificial bone were hybridized to develop a combined implant just before use, which was then implanted into defects (N=23). In the control group, HA alone was implanted (N=18). Histological evaluation and micro-indentation testing was performed for the evaluation of repair tissue. Normal knees were used as an additional control group for biomechanical testing (N=5). At hybridization, the TEC rapidly attached onto the surface of HA artificial bone block, which was implantable to osteochondral defects. Osteochondral defects treated with the combined implants exhibited more rapid subchondral bone repair coupled with the development of cartilaginous tissue with good tissue integration to the adjacent host cartilage when assessed at 6 months post implantation. Conversely, the control group exhibited delayed subchondral bone repair. In addition, the repair cartilaginous tissue in this group had poor integration to adjacent cartilage and contained clustered chondrocytes, suggesting an early osteoarthritis (OA)-like degenerative change at 6 months post implantation. Biomechanically, the osteochondral repair tissue treated with the combined implants at 6 months restored tissue stiffness, similar to normal osteochondral tissue. The combined implants significantly accelerated and improved osteochondral repair. Specifically, earlier restoration of subchondral bone, as well as good tissue integration of repair cartilage to adjacent host tissue could be clinically relevant in terms of the acceleration of postoperative rehabilitation and longer-term durability of repaired articular surface in patients with osteochondral lesions, including those with OA. In addition, the combined implant could be considered a promising MSC-based bio-implant with regard to safety and cost-effectiveness, considering that the TEC is a scaffold-free implant and HA artificial bone has been widely used in clinical practice.

Detection of abnormalities in the superficial zone of cartilage repaired using a tissue engineered construct derived from synovial stem cells.

The present study investigated the surface structure and mechanical properties of repair cartilage generated from a tissue engineered construct (TEC) derived from synovial mesenchymal stem cells at six months post-implantation compared to those of uninjured cartilage. TEC-mediated repair tissue was cartilaginous with Safranin O staining, and had comparable macro-scale compressive properties with uninjured cartilage. However, morphological assessments revealed that the superficial zone of TEC-mediated tissue was more fibrocartilage-like, in contrast to the middle or deep zones that were more hyaline cartilage-like with Safranin O staining. Histological scoring of the TEC-mediated tissue was significantly lower in the superficial zone than in the middle and deep zones. Scanning electron microscopy showed a thick tangential bundle of collagen fibres at the most superficial layer of uninjured cartilage, while no corresponding structure was detected at the surface of TEC-mediated tissue. Immunohistochemical analysis revealed that PRG4 was localised in the superficial area of uninjured cartilage, as well as the TEC-mediated tissue. Friction testing showed that the lubrication properties of the two tissues was similar, however, micro-indentation analysis revealed that the surface stiffness of the TEC-repair tissue was significantly lower than that of uninjured cartilage. Permeability testing indicated that the TEC-mediated tissue exhibited lower water retaining capacity than did uninjured cartilage, specifically at the superficial zone. Thus, TEC-mediated tissue exhibited compromised mechanical properties at the superficial zone, properties which need improvement in the future for maintenance of long term repair cartilage integrity.

The influence of skeletal maturity on allogenic synovial mesenchymal stem cell-based repair of cartilage in a large animal model.

One of the potential factors that may affect the results of mesenchymal stem cell (MSC)-based therapy is the age of donors and recipients. However, there have been no controlled studies to investigate the influence of skeletal maturity on the MSC-based repair of cartilage. The purpose of this study was to compare the repair quality of damaged articular cartilage treated by a scaffold-free three-dimensional tissue-engineered construct (TEC) derived from synovial MSCs between immature and mature pigs. Synovial MSCs were isolated from immature and mature pigs and the proliferation and chondrogenic differentiation capacities were compared. The TEC derived from the synovial MSCs were then implanted into equivalent chondral defects in the medial femoral condyle of both immature and mature pigs, respectively. The implanted defects were morphologically and biomechanically evaluated at 6 months postoperatively. There was no skeletal maturity-dependent difference in proliferation or chondrogenic differentiation capacity of the porcine synovial MSCs. The TEC derived from synovial MSCs promoted the repair of chondral lesion in both immature and mature pigs without the evidence of immune reaction. The repaired tissue by the TEC also exhibited similar viscoelastic properties to normal cartilage regardless of the skeletal maturity. The results of the present study not only suggest the feasibility of allogenic MSC-based cartilage repair over generations but also may validate the use of immature porcine model as clinically relevant to test the feasibility of synovial MSC-based therapies in chondral lesions.