Functional living trileaflet heart valves grown in vitro

Background-Previous tissue engineering approaches to create heart valves ha ve been limited by the structural immaturity and mechanical properties of t he valve constructs. This study used an in vitro pulse duplicator system to provide a biomimetic environment during tissue formation to yield more mat ure implantable heart valves derived from autologous tissue. Methods and Results-Trileaflet heart valves were fabricated from novel bioa bsorbable polymers and sequentially seeded with autologous ovine myofibrobl asts and endothelial cells. The constructs were grown for 14 days in a puls e duplicator in vitro system under gradually increasing flow and pressure c onditions. By use of cardiopulmonary bypass, the native pulmonary leaflets were resected, and the valve constructs were implanted into 6 lambs (weight 19+/-2.8 kg). All animals had uneventful postoperative courses, and the va lves were explanted at 1 day and at 4, 6, 8, 16, and 20 weeks. Echocardiogr aphy demonstrated mobile functioning leaflets without stenosis, thrombus, o r aneurysm up to 20 weeks. Histology (16 and 20 weeks) showed uniform layer ed cuspal tissue with endothelium. Environmental scanning electron microsco py revealed a confluent smooth valvular surface. Mechanical properties were comparable to those of native tissue at 20 weeks. Complete degradation of the polymers occurred by 8 weeks. Extracellular matrix content (collagen, g lycosaminoglycans, and elastin) and DNA content increased to levels of nati ve tissue and higher at 20 weeks. Conclusions-This study demonstrates in vitro generation of implantable comp lete living heart valves based on a biomimetic flow culture system. These a utologous tissue-engineered valves functioned up to 5 months and resembled normal heart valves in microstructure, mechanical properties, and extracell ular matrix formation.