Prevention of device-related tissue damage during percutaneous deployment of tissue-engineered heart valves

BACKGROUND

Endovascular application of pulmonary heart valves has been recently introduced clinically. A tissue-engineering approach was pursued to overcome the current limitations of bovine jugular vein valves (degeneration and limited longevity). However, deployment of the delicate tissue-engineered valves resulted in severe tissue damage. Therefore the objective of this study was to prevent tissue damage during the folding and deployment maneuver.

MATERIAL AND METHODS

Porcine pulmonary heart valves, small intestinal submucosa, and ovine carotid arteries were obtained from a slaughterhouse. After dissection and antimicrobial incubation, the valves were trimmed (removal of sinus and most of the muscular ring) to fit into the deployment catheter. The inside (in-stent group, n = 6) or outside (out-stent group, n = 6) of a nitinol stent was covered by an acellular small intestinal submucosa, and the valves were sutured into the stent. The valves were folded, tested for placement in the deployment catheter, and decellularized enzymatically. Myofibroblasts were obtained from carotid artery segments and seeded onto the scaffolds. The seeded constructs were placed in a dynamic bioreactor system and cultured for 16 consecutive days. After endothelial cell seeding, the constructs were folded, deployed, and processed for histology and surface electron microscopy.

RESULTS

The valves opened and closed competently throughout the entire dynamic culture. Surface electron microscopy revealed an almost completely preserved tissue in the in-stent group. Stents covered with small intestinal submucosa on the outside, however, showed severe damage.

CONCLUSION

This study demonstrates that small intestinal submucosa covering of the inside of a pulmonary valved stent can prevent stent strut-related tissue damage.

ProteinChip system technology: a powerful tool to analyze expression differences in tissue-engineered blood vessels

At the time of implantation, tissue-engineered constructs should resemble native tissues as closely as possible. At present, histology and biochemical methods are commonly used to compare tissue-engineered constructs with native tissue. A ProteinChip system based on surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI) has been developed that allows visualization of complex protein profiles from biological samples. The aim of this study was to determine whether the ProteinChip system is a suitable tool with which to compare the protein expression profiles of tissue-engineered aortic blood vessels with native tissues. Tissue-engineered blood vessel substitutes were fabricated with poly-4-hydroxybutyrate scaffolds, ovine vascular cell seeding, and dynamic tissue culture conditions. Engineered, ovine aortic, and carotid tissues were homogenized and total protein was extracted. Samples were analyzed on ProteinChip arrays. Analysis yielded reproducible protein profiles from all samples. About 150 distinct protein peaks were detected. Comparative analysis with ProteinChip software revealed that the protein profiles from native aorta and native carotid arteries were similar whereas early tissue-engineered samples displayed more distinct deviations. In conclusion, ProteinChip system technology is rapid, reproducible, and highly sensitive in highlighting differentially expressed proteins in tissue-engineered blood vessel substitutes.

Tissue Engineering of Ovine Aortic Blood Vessel Substitutes Using Applied Shear Stress and Enzymatically Derived Vascular Smooth Muscle Cells

Compared to native blood vessels, all clinically available blood vessel substitutes perform suboptimally. Numerous approaches to tissue engineer (TE) blood vessels have been pursued using different scaffold materials, cell types, and culture conditions. Several limitations however remain to be overcome prior to the potential application in the arterial system. This study aimed at tissue engineering viable ovine blood vessels suitable for implantation into the systemic circulation of sheep. In recent studies vascular smooth muscle cells (vSMC) were derived by an explant technique. However, in this study we show that homogenous populations of differentiated vSMC were only obtained by enzymatic dispersion as characterized by immunostaining for specific vSMC marker proteins. In contrast the explant method yielded predominantly less differentiated myofibroblast-like cells. Enzymatically derived vSMC were seeded onto P-4-HB scaffolds and incubated either in a pulsatile flow bioreactor or under static conditions. Dynamically cultured TE blood vessel substitutes showed confluent layered tissue formation and were completely water resistant. They displayed significantly increased ECM synthesis, DNA, and protein content as well as vSMC marker expression. Mechanical properties of bioreactor cultured TE blood vessels approached those of native aorta. In conclusion ovine, aortic blood vessel substitutes were successfully created using enzymatically derived vSMC, bioabsorbable scaffolds, and applied shear stress.