[The bovine cartilage punch model: a tool for the in vitro analysis of biomaterials and cartilage regeneration]

In Vitro Cartilage Regeneration with a Three-Dimensional Polyglycolic Acid (PGA) Implant in a Bovine Cartilage Punch Model

Resorbable polyglycolic acid (PGA) chondrocyte grafts are clinically established for human articular cartilage defects. Long-term implant performance was addressed in a standardized in vitro model. PGA implants (+/- bovine chondrocytes) were placed inside cartilage rings punched out of bovine femoral trochleas (outer Ø 6 mm; inner defect Ø 2 mm) and cultured for 84 days (12 weeks). Cartilage/PGA hybrids were subsequently analyzed by histology (hematoxylin/eosin; safranin O), immunohistochemistry (aggrecan, collagens 1 and 2), protein assays, quantitative real-time polymerase chain reactions, and implant push-out force measurements. Cartilage/PGA hybrids remained vital with intact matrix until 12 weeks, limited loss of proteoglycans from "host" cartilage or cartilage-PGA interface, and progressively diminishing release of proteoglycans into the supernatant. By contrast, the collagen 2 content in cartilage and cartilage-PGA interface remained approximately constant during culture (with only little collagen 1). Both implants (+/- cells) displayed implant colonization and progressively increased aggrecan and collagen 2 mRNA, but significantly decreased push-out forces over time. Cell-loaded PGA showed significantly accelerated cell colonization and significantly extended deposition of aggrecan. Augmented chondrogenic differentiation in PGA and cartilage/PGA-interface for up to 84 days suggests initial cartilage regeneration. Due to the PGA resorbability, however, the model exhibits limitations in assessing the "lateral implant bonding".

In Vitro Analysis of Cartilage Regeneration Using a Collagen Type I Hydrogel (CaReS) in the Bovine Cartilage Punch Model

OBJECTIVE

Limitations of matrix-assisted autologous chondrocyte implantation to regenerate functional hyaline cartilage demand a better understanding of the underlying cellular/molecular processes. Thus, the regenerative capacity of a clinically approved hydrogel collagen type I implant was tested in a standardized bovine cartilage punch model.

METHODS

Cartilage rings (outer diameter 6 mm; inner defect diameter 2 mm) were prepared from the bovine trochlear groove. Collagen implants (± bovine chondrocytes) were placed inside the cartilage rings and cultured up to 12 weeks. Cartilage-implant constructs were analyzed by histology (hematoxylin/eosin; safranin O), immunohistology (aggrecan, collagens 1 and 2), and for protein content, RNA expression, and implant push-out force.

RESULTS

Cartilage-implant constructs revealed vital morphology, preserved matrix integrity throughout culture, progressive, but slight proteoglycan loss from the "host" cartilage or its surface and decreasing proteoglycan release into the culture supernatant. In contrast, collagen 2 and 1 content of cartilage and cartilage-implant interface was approximately constant over time. Cell-free and cell-loaded implants showed (1) cell migration onto/into the implant, (2) progressive deposition of aggrecan and constant levels of collagens 1 and 2, (3) progressively increased mRNA levels for aggrecan and collagen 2, and (4) significantly augmented push-out forces over time. Cell-loaded implants displayed a significantly earlier and more long-lasting deposition of aggrecan, as well as tendentially higher push-out forces.

CONCLUSION

Preserved tissue integrity and progressively increasing cartilage differentiation and push-out forces for up to 12 weeks of cultivation suggest initial cartilage regeneration and lateral bonding of the implant in this in vitro model for cartilage replacement materials.