Fabrication of a trileaflet heart valve scaffold from a polyhydroxyalkanoate biopolyester for use in tissue engineering

Previously, we reported the implantation of a single tissue engineered leaf let in the posterior position of the pulmonary valve in a lamb model. The m ajor problems with this leaflet replacement were the scaffold's inherent st iffness, thickness, and nonpliability. We have now created a scaffold for a trileaflet heart valve using a thermoplastic polyester. In this experiment , we show the suitability of this material in the production of a biodegrad able, biocompatible scaffold for tissue engineered heart valves. A heart va lve scaffold was constructed from a thermoplastic elastomer. The elastomer belongs to a class of biodegradable, biocompatible polyesters known as poly hydroxyalkanoates (PHAs) and is produced by fermentation (Metabolix Inc., C ambridge, MA). It was modified by a salt leaching technique to create a por ous, three-dimensional structure, suitable for tissue engineering. The tril eaflet heart valve scaffold consisted of a cylindrical stent (1 mm x 15 mm x 20 mm I.D.) containing three valve leaflets. The leaflets were formed fro m a single piece of PHA (0.3 mm thick), and were attached to the outside of the stent by thermal processing techniques, which required no suturing. Af ter fabrication, the heart valve construct was allowed to crystallize (4 de grees C for 24 h), and salt particles mere leached into doubly distilled wa ter over a period of 5 days to yield pore sizes ranging from 80 to 200 micr ons. Ten heart valve scaffolds were fabricated and seeded with vascular cel ls from an ovine carotid artery. After 4 days of incubation, the constructs were examined by scanning electron microscopy. The heart valve scaffold wa s tested in a pulsatile flow bioreactor and it was noted that the leaflets opened and closed. Cells attached to the polymer and formed a confluent lay er after incubation. One advantage of this material is the ability to mold a complete trileaflet heart valve scaffold without the need for suturing le aflets to the conduit. Second advantage is the use of only one polymer mate rial (PHA) as opposed to hybridized polymer scaffolds. Furthermore, the mec hanical properties of PHA, such as elasticity and mechanical strength, exce ed those of the previously utilized material. This experiment shows that PH As can be used to fabricate a three-dimensional, biodegradable heart valve scaffold.