Ann Thorac Surg 2005;80:1828
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Paul Simon, MD,
Marie-Theres Kasimir, MD,
Erwin Rieder, MD,
Günter Weigel, MD
Department of Cardiothoracic Surgery, and Department of Surgery, Medical University of Vienna, Waehringer Guertel 18-20, Vienna, A-1090 Austria
(Email: paul.simon{at}univie.ac.at; marie-theres.kasimir{at}meduniwien.ac.at; erwin.rieder{at}meduniwien.ac.at; gunter.weigel{at}meduniwien.ac.at).
Tissue engineering of cardiovascular tissues promises to resolve problems seen in currently used biological and prosthetic materials. Effective tissue engineering requires the fabrication of a scaffold with adequate functional and mechanical characteristics. Xenogenic materials that are antigen reduced through decellularization and polymers have been used for heart valve and vascular constructs. To achieve the aim of a bioengineered tissue that will function within the patient like autologous tissue eventually requires the repopulation of the scaffold with autologous cells. Two basic concepts are pursued: (1) ex vivo cell seeding and (2) postimplantation repopulation. The cells are supposed to cover the surface with a monolayer of endothelial cells and migrate into the scaffold, which will eventually produce the appropriate extracellular matrix components in adequate quantity for long-term stability and performance of the construct. At the same time the scaffold is implanted, it has to be absorbed in a predictable manner to safely perform mechanically until it is replaced by the newly produced matrix.
In their experiments the authors [1] describe the implantation of a novel biodegradable vascular patch, which is a compound of collagen microsponge and a polymeric scaffold composed of a poly-glycolic acid knitted mesh that is externally reinforced with woven poly-lactic acid. The investigators chose the concept of facilitated post-implantation cellular repopulation both in pigs and dogs. They present promising data with adequate strength of the patches both in the pulmonary and systemic circulation. The patches were well incorporated with endothelial coverage and repopulation of the scaffold without the use of growth factors. The authors suggest that the addition of the collagen microsponge significantly enhances the capability for in vivo repopulation with cells. However the mechanisms behind the repopulation remain speculative. To which extent contribute circulating progenitor cells, expansion from the native tissue, angiogenesis within the vascular patch, migration of fibroblasts? Does transdifferentiation of endothelial cells occur and to what extent does this contribute to repopulation of the scaffold? Are there differences between species? Although the mechanical characteristics were satisfactory in the experimental setting up to 6 months, it remains unclear whether the process of "regeneration" of the vascular patch into autologous tissue will be well controlled in the long term. It also remains to be determined whether in vivo repopulation will occur in humans as many animal species have a much higher ability to endothelialize and incorporate graft materials than humans. It appears crucial that these questions are sufficiently clarified before clinical application.
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- Iwai S, Sawa Y, Taketani S, Torikai K, Hirakawa K, Matsuda H. Novel tissue-engineered biodegradable material for reconstruction of vascular wall Ann Thorac Surg 2005;80:1821-1828.[Abstract/Free Full Text]
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