Objectives: Current therapies for cartilage repair either do not result in regeneration of articular cartilage, or there is inadequate integration with the host tissue leading to failure of the repair. Thus, there is an interest in developing alternative approaches. The mechanisms of cartilage integration remain relatively unknown, however it is believed that chondrocyte migration is crucial to this process. Previously, we showed that platelet rich plasma (PRP) enhances in vitro cartilage tissue formation. We hypothesized that PRP will enhance the integration of bioengineered cartilage with native cartilage due to increased matrix accumulation at the interface and that PRP could promote chondrocyte migration.
Methods: Isolated bovine chondrocytes were seeded on a porous bone substitute and grown in vitro to form osteochondral-like tissue. After 7 days the biphasic constructs were soaked in PRP for 30 minutes prior to implantation into the core of a ring-shaped osteochondral explant. Controls were not soaked in PRP. The resulting implant-explant construct was cultured in a stirring bioreactor for 2 weeks (contact model). Alternatively, the PRP soaked biphasic construct was placed 2mm away from a native cartilage/bone plug of equal dimensions to assess chondrocyte migration between the two tissues (non-contact model). The integration zone was visualized histologically. A push-out test was performed to assess the strength of integration. Matrix accumulation at the zone of integration was assessed biochemically and the gene expression of the cells in this region was assessed by RT-PCR. Cell migration was evaluated by video microscopy over 8 days. Significance (p<0.05) was determined by a χ2 test, a student\'s t-test or one-way ANOVA with tukey\'s post hoc.
Conclusion: PRP soaked bioengineered cartilage implants showed improved integration with native cartilage compared to non-soaked implants perhaps due to increased matrix accumulation. Chondrocytes grew out from the in vitro formed tissue and migrated along fibers after PRP soaking. The contribution of these cells to integration requires further study.