[page 26↓]

4.  DISCUSSION

This study demonstrates the feasibility of using autologous chondrocytes derived from auricular elastic cartilage to line the luminal surfaces of LVAD’s. Auricular elastic cartilage is an accessible source of autologous cells. Chondrocytes can be harvested from the ear under local anesthesia, and they can be isolated more efficiently than vascular smooth muscle or endothelial cells. The isolation of chondrocytes from cartilage described here is simple, fast and easy. Moreover, chondrocytes derived from auricular cartilage can adhere strongly to artificial surfaces because of their ability to manufacture collagen II, elastin and other important constituents of the extracellular matrix. Hypothetically, cardiovascular assist devices lined with auricular chondrocytes might also allow easier recruitment of circulating endothelial cells and thus improve the process known as fallout healing (11).

Support for this idea has come from development of the HeartMate® LVAD. Even in early calf studies, the HeartMate®’s artificial surfaces encouraged the immediate deposition of a stable, uniform, antithrombogenic, nonhemolytic neointimal lining (12). Later, in human studies, endothelial cells were found on samples taken from the luminal surfaces of LVAD’s after implantation (13). Presumably, blood-borne endothelial cells or endothelial cell precursors had been deposited on the blood-contacting surfaces, which may explain in large part the low reported incidence of thrombogenicity and clinical thromboembolic problems associated with the use of LVAD’s. Another study showed endothelial cells to have [page 27↓]high affinity for heparinized surfaces in addition to cell surface receptors involved in adhesion to collagen(14); this suggested that a lining of autologous chondrocytes strongly adherent to artificial surfaces might provide an ideal attachment zone for endothelial cells. Yet another study showed that genetically engineered smooth muscle cells lining the luminal surface of the HeartMate® were nonthrombogenic (9) suggesting that the use of such cells might improve the hemocompatibility of artificial surfaces.

Beyond the immediate scope of our study, our findings also have some implications for the use of auricular cartilage in tissue engineering. Other investigators have successfully used a mixed-cell population of vascular cells from ovine carotid arteries to create a heart valve on a scaffold of biodegradable porous polyhydroxyalkanoate (15). Still, the ideal cell source for tissue-engineering a heart valve seem to remain a mystery (15).

In conclusion, auricular elastic cartilage is an accessible source of autologous tissue. Chondrocytes derived from such cartilage can be efficiently harvested, isolated, cultured and seeded and can adhere very strongly to artificial surfaces because of their ability to produce collagen II, elastin and other important constituents of extracellular matrix. Therefore, auricular chondrocytes are a potential source of autologous cells for lining large cardiovascular assist devices such as LVAD’s and improving their long-term biocompatibility. Our successful short-term feasibility study in which auricular chondrocytes were used to line the luminal surfaces of a LVAD in a calf model warrants further study in vivo.


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