Evaluation of the matrix-synthesis potential of crosslinked hyaluronan gels for tissue engineering of aortic heart valves.

Our goal is to fabricate continuous sheets of elastin atop non-biodegradable hydrogels (hylans) containing crosslinked hyaluronan, a glycosaminoglycan. Such elastin-hyaluronan composites may be useful to tissue engineer replacements for the glycosaminoglycan- and elastin-rich layers of the native aortic valve cusp. Neonatal rat aortic smooth muscle cells were cultured atop hylan gels with micro-textured surfaces, and on plastic, and the components of the extracellular matrix (collagen, elastin) were periodically analyzed. The hylan substrates induced the cells to proliferate more rapidly and over longer time periods (approximately 4 weeks) relative to those cultured on plastic (2-3 weeks). Consequently, at all assay times, the amounts of elastin was derived from the hylan-based cell cultures was 25% or more than that derived from cells cultured on plastic. However, when elastin content was normalized to the cell DNA content, no significant differences were found in the two substrates beyond the first two weeks of culture. Conversely, at culture times greater than 2 weeks, cells cultured atop hylan gels produced amounts of collagen/nanogram of DNA that were approximately 56% less than that synthesized by cells cultured on plastic. Cells grown on hylan deposited an unusual matrix layer, rich in elastin, at the hylan-cell interface. This elastin was found to be organized into fenestrated sheets and loose elastin fibers, structures that were also isolated from the elastin matrix of the ventricularis layer of porcine aortic valve cusps. We have thus demonstrated that hylan gels are useful as substrates to induce elastin synthesis in culture to obtain structures that resemble the elastin matrix of the native aortic valve.