Living Autologous Heart Valves Engineered From Human Prenatally Harvested Progenitors

Do¨rthe Schmidt, MD; Anita Mol, PhD; Christian Breymann, MD; Josef Achermann, PhD;
Bernhard Odermatt, MD; Matthias Go¨ssi, PhD; Stefan Neuenschwander, PhD; Rene´ Preˆtre, MD;
Michele Genoni, MD; Gregor Zund, MD; Simon P. Hoerstrup, MD, PhD

Congenital heart valve defects is a problem that is currently only treated with surgery such as heart valve replacements, using mainly synthetic materials. Such treatment has many adverse effects such as lack of growth over the patient's lifetime, risks of thrombosis, and lifetime anticoagulation drugs needed to cope with the transplant. The authors of this paper developed a new tissue engineered heart valve using autologous cells obtained from a typical CVS (chorionic villus sampling) during preganancy.

In this study, the authors obtained the umbilical cord blood-derived EC progenitor cells from a CVS aspiration. The cells were isolated from the sampled tissue via digestion by collagenase and centrifugation/pelleting. These isolated EC progenitors were then cultured, and a separate batch were cryopreserved for later use. The scaffold for the heart valve leaflets were made from PGA (polyglycolic acid) coated with poly-4-hydroxybutyric acid. The authors fabricated the scaffold into the proper shape of the heart valve leaflets, then seeded the cells (chorionic villi) onto the scaffolds and placed the device in a perfusion bioreactor.

Two conditions were then imposed: one with straining to provide cyclic mechanical stimulation, and one without. The device was then endothelialized (to prevent platelet adhesion) by seeding with differentiated EPCs previously obtained. Characterization of the device were assays of two main types: stainng for tissue composition and mechanical testing. H&E staining showed tissue organization of the tissue engineered device to be very similar to native neonatal valve leaflets. Other types of stains have shown the expected organization of collagen with collagen fibers on the periphery layer and GAG (glucosaminoglycans) in the center of the leaflets. The authors also took SEM images of the device before and after cell seeding to confirm the endothelialization of the leaflet and look at the surface morphology inside the engineered device.

Mechanical testing of the device on a tensile tester produced stress-strain curves that show the leaflets grown in the mechanically loaded bioreactor to be stiffer (higher Young's modulus), but not as pliable as the one's that were not strained. However, the authors only made some preliminary statements and did not offer any suggestions on how to balance strength and pliabilityas to find the most appropriate way to mechanically stimulate these leaflets to best match native tissue.

This research holds much promise it that it offers a cell source for future work on pediatric tissue engineering, especially cardiovascular tissue engineering. If developed, this methods offers a minimally invasive way to harvest progenitor cells that can be used in other applications. This paper also demonstrates many of the tissue engineering challenges discussed in lecture (staining, tissue characterization) as well as some of the techniques we've been exposed to in lab (cell culture, microscopy).