Interaction ofCartilage andCeramic Matrix - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 311

In summary, inhomogeneous and rough surfaces of hydroxyapatite support the
proliferation and adhesion of chondrocytes and cartilage tissue, but lead to inferior
quality of the engineered matrix. The negative influence of the carrier shown
above was perhaps increased by a stronger adhesive strength to the tissue, com-
pared to the modified smooth and structured surface topographies.
6 Conclusion
For the repair of cartilage defects, osteochondral implants offer the possibility of
restoring cartilage tissue and additionally also the subchondral bone, and of
anchoring the cartilage effectively in the joint. In the example presented here, a
hydroxyapatite carrier was used as bone equivalent substrate and autologous
cartilage tissue, which besides bone is the second tissue in osteochondral implants,
was cultivated without a scaffold on top.
It was shown that cultivation on top of this ceramic carrier has a significant
negative influence on the quality of the in vitro generated cartilage compared to
unsupported tissue and, surprisingly, this effect was observed not only at the
interface but also in the entire cartilage formed. Results indicated that the com-
position and surface chemistry did not negatively influence cartilage quality,
whereas already moderate modification of surface structure causes slight changes
in the biomechanical quality, distribution of glycosaminoglycans, adhesive
strength between cartilage and biomaterial, and in attachment and proliferation of
a chondrocyte monolayer. These studies produced interesting results, but the
negative effect of cultivation on top of the carrier still remains inexplicable.
For example, the nutrition supply of the cartilage tissue grown on top of a carrier
was not investigated and may be limited by the impermeable carrier and holding
device. Improvements in holding device, culture conditions, porosity and pore size
of the carrier are needed to increase mass transfer.
In conclusion, the application of bioceramics—especially hydroxyapatite—
seems to be suitable for the generation of the osteochondral implants described,
but a further adaptation of the carrier to cartilage cultivation is an essential
prerequisite for success. Modulation of physical and chemical properties
may support differentiation of chondrocytes and tissue formation. In addition,
integration in the subchondral bone has to be proven and the pore diameter for
bone ingrowth has to be increased. With regard to the progress of the culti-
vation protocol, unsupported cartilage tissue with a glycosaminoglycan content
of nearly 45% compared to native porcine cartilage could be generated in vitro,
but the desired biomechanical properties of the tissue cannot be achieved at
present.
Acknowledgments We would like to thank Kerstin Michael, Ditte Siemesgelüss, Teresa Richter,
Daniel Fritsch and Nadja Holstein for their excellent technical support. The project was kindly
supported by DFG (PO 413/7-1) and by BWF-FHH (Tissue Engineering).