Basic fibroblast growth factor (b-FGF) may have a role in tissue-engineered chondrogenesis. However, when applied in solution, b-FGF rapidly diffuses from the implant site. In another approach for tissue engineering, poly-lactide-based copolymers have shown promise as scaffolds for chondrocytes used to tissue engineer auricular cartilage in the shape of an ear. This study evaluated the effectiveness of b-FGF impregnated in gelatin microspheres to achieve slow growth factor release for augmenting the in vivo chondrogenic response. Whereas 125I-labeled b-FGF injected in solution showed rapid in vivo clearance from the injection site (only 3% residual after 24 h), when incorporated into gelatin microspheres, 44% and 18% of the b-FGF remained at 3 and 14 days, respectively. Canine chondrocytes were isolated and grown in vitro onto ear-shaped poly-lactide/caprolactone copolymers for 1 week, then implanted into the dorsal subcutaneous tissue of nude mice; implants contained b-FGF either in free solution or in gelatin microspheres. A third group underwent preinjection of b-FGF in gelatin microspheres 4 days before chondrocyte-copolymer implantation. The implants with b-FGF-incorporated microspheres showed the greatest chondrogenic characteristics at 5 and 10 weeks postoperatively: good shape and biomechanical trait retention, strong (histologic) metachromasia, rich vascularization of surrounding tissues, and increased gene expression for type II collagen (cartilage marker) and factor VIII-related antigen (vascular marker). In the case of implant site preadministration with b-FGF-impregnated microspheres, the implant architecture was not maintained as well, and reduced vascularization and metachromasia was also apparent. In conclusion, these findings indicate that a sustained release of b-FGF augments neovascularization and chondrogenesis in a tissue-engineered cartilage construct.

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We developed a technique to form a bioabsorbable synthetic polymer (polyglycolic acid, PGA) combined with a natural polymer (fibrin) to serve as a scaffold to help retain seeded cells and improve the seeding efficiency of chondrocytes in an implantable construct. This approach was evaluated in a canine autologous implant model of bioengineered cartilage. The implantation site (subcutaneous or intrafascial) and the use of basic fibroblast growth factor (b-FGF) were also evaluated with this system. The intrafascial implantation site yielded optimal results, especially when used in conjunction with fibrin and a b-FGF sustained-release system incorporated into the complex. A thicker, more sustained cartilagenous layer was formed, with a more vascularized outer fibrous supporting tissue layer. This combined approach of implant environment selection, natural polymer for cell retention, and growth factor supplementation offers a more optimized method for generating bioengineered auricular cartilage.

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