Tissue engineering of heart valves: In vitro experiences

Background. Tissue engineering is a new approach, whereby techniques are be ing developed to transplant autologous cells onto biodegradable scaffolds t o ultimately form new functional tissue in vitro and in vivo. Our laborator y has focused on the tissue engineering of heart valves, and we have fabric ated a trileaflet heart valve scaffold from a biodegradable polymer, a poly hydroxyalkanoate. In this experiment we evaluated the suitability of this s caffold material as well as in vitro conditioning to create viable tissue f or tissue engineering of a trileaflet heart valve. Methods. We constructed a biodegradable and biocompatible trileaflet heart valve scaffold from a porous polyhydroxyalkanoate (Meatabolix Inc, Cambridg e, MA). The scaffold consisted of a cylindrical stent (1 x 15 x 20 mm inner diameter) and leaflets (0.3 mm thick), which were attached to the stent by thermal processing techniques. The porous heart valve scaffold (pore size 100 to 240 mu m) was seeded with vascular cells grown and expanded from an ovine carotid artery and placed into a pulsatile flow bioreactor for 1, 4, and 8 days. Analysis of the engineered tissue included biochemical examinat ion, environmental scanning electron microscopy, and histology. Results. It was possible to create a trileaflet heart valve scaffold from p olyhydroxyalkanoate, which opened and closed synchronously in a pulsatile f low bioreactor. The cells grew into the pores and formed a confluent layer after incubation and pulsatile flow exposure. The cells were mostly viable and formed connective tissue between the inside and the outside of the poro us heart valve scaffold. Additionally, we demonstrated cell proliferation ( DNA assay) and the capacity to generate collagen as measured by hydroxyprol ine assay and movat-stained glycosaminoglycans under in vitro pulsatile now conditions. Conclusions. Polyhydroxyalkanoates can be used to fabricate a porous, biode gradable heart valve scaffold. The cells appear to be viable and extracellu lar matrix formation was induced after pulsatile now exposure. (Ann Thorac Surg 2000;70:140-4) (C) 2000 by The Society of Thoracic Surgeons.