CREATION OF VIABLE PULMONARY-ARTERY AUTOGRAFTS THROUGH TISSUE ENGINEERING

Background: ''Repair'' of many congenital cardiac defects requires the use of conduits to establish right ventricle to pulmonary artery cont inuity, At present, available homografts or prosthetic conduits lack g rowth potential and can become obstructed by tissue ingrowth or calcif ication leading to the need for multiple conduit re:placements. Tissue engineering is an approach by which cells are grown in vitro onto bio degradable polymers to construct ''tissues'' for implantation, A, tiss ue engineering approach has recently been used to construct living car diac valve leaflets from autologous cells in our laboratory, This stud y assesses the feasibility of a tissue engineering approach to constru cting tissue-engineered ''living'' pulmonary artery conduits. Material s and methods: Ovine artery (group A, n = 4) or vein (group V, n = 3) segments were harvested, separated into individual cells, expanded in tissue culture, and seeded onto synthetic biodegradable (polyglactin/p olyglycolic acid) tubular scaffolds (20 mm long x 15 mm diameter), Aft er 7 days of in vitro culture, the autologous cell/polymer vascular co nstructs were used to replace a 2 cm segment of pulmonary artery in la mbs (age 68.4 +/- 15.5 days, weight 18.7 +/- 2.0 kg), One other contro l animal received an acellular polymer tube sealed with fibrin glue wi thout autologous cells, Animals were sacrificed at intervals of 11 to 24 weeks (mean follow-up 130.3 +/- 30.8 days, mean weight 38.9 +/- 13. 0 kg) after echocardiographic and angiographic studies, Explanted tiss ue-engineered conduits were assayed for collagen (4-hydropyproline) an d calcium content, and a tissue deoxyribonucleic acid assay (bis-benzi mide dye) was used to estimate number of cell nuclei as an index: of t issue maturity, Results: The acellular control graft developed progres sive obstruction and thrombosis, All seven tissue-engineered grafts we re patent and demonstrated a nonaneurysmal increase in diameter (group A = 18.3 +/- 1.3 mm = 95.3% of native pulmonary artery; group V -17.1 +/- 1.2 mm = 86.8% of native pulmonary artery). Histologically, none of the biodegradable polymer scaffold remained in any tissue-engineere d graft by 11 weeks, Collagen content in tissue-engineered grafts was 73.9% +/- 8.0% of adjacent native pulmonary artery, Histologically, el astic fibers were present in the media layer of tissue-engineered vess el wall and endothelial specific factor VIII was identified on the lum inal surface, Deoxyribonucleic acid assay showed a progressive decreas e in numbers of cell nuclei over 11 and 24 weeks, suggesting an ongoin g tissue remodeling, Calcium content of tissue-engineered grafts was e levated (group A = 7.95 +/- 5.09; group V = 13.2 +/- 5.48; native pulm onary artery = 1.2 +/- 0.8 mg/gm dry weight), but no macroscopic calci fication was found. Conclusions: Living vascular grafts engineered fro m autologous cells and biodegradable polymers functioned well in the p ulmonary circulation as a pulmonary artery replacement. They demonstra ted an increase in diameter suggesting growth and development of endot helial lining and extracellular matrix, including collagen and elastic fibers. This tissue-engineering approach may ultimately allow the dev elopment of viable autologous vascular grafts for clinical use.