Advantages and challenges in processing and quality control of decellularized heart valves.

More than 1000 donated aortic and pulmonary valves from predominantly European tissue banks were centrally decellularized and delivered to hospitals in Europe and Japan. Here, we report on the processing and quality controls before, during and after the decellularization of these allografts. Our experiences show that all tissue establishments, which provide native cardiovascular allografts for decellularization, meet comparably high-quality standards, regardless of their national origin. A total of 84% of all received allografts could be released as cell-free allografts. By far the most frequent reasons for rejection were non-release of the donor by the tissue establishment or severe contaminations of the native tissue donation. Only in 2% of all cases the specification for freedom from cells was not fulfilled, indicating that decellularization of human heart valves is a safe process with a very low discard ratio. In clinical use, cell-free cardiovascular allografts have been shown to be advantageous over conventional heart valve replacements, at least in young adults. These results open the discussion on the future gold standard and funding of this innovative therapeutic option for heart valve replacement.

Interaction of cells with decellularized biological materials.

The idea to create the concept of cardiovascular "tissue engineering" is based on the recognition that until then all known allogeneic/xenogeneic biological or alloplastic implant materials were associated with shortcomings, which led to graft deterioration, degradation and finally destruction. Thus, it aims to develop viable cardiovascular structures, e.g. heart valves, myocardium or blood vessels, which ideally demonstrate mechanisms of remodeling and self-repair, a high microbiological resistance, complete immunological integrity and a functional endothelial cell layer to guarantee physiological hemostasis. In our current review we aim to identify basic limitations of previous concepts, explain why the use of decellularized matrices was a logical consequence and which limitations still exist.

Experimental generation of a tissue-engineered functional and vascularized trachea.

OBJECTIVE: We sought to grow in vitro functional smooth muscle cells, chondrocytes, and respiratory epithelium on a biologic, directly vascularized matrix as a scaffold for tracheal tissue engineering. METHODS: Ten- to 15-cm-long free jejunal segments with their own vascular pedicle were harvested and acellularized from donor pigs (n = 10) and used as a vascular matrix. Autologous costal chondrocytes, smooth muscle cells, and respiratory epithelium and endothelial progenitor cells were first cultured in vitro and then disseminated on the previously acellularized vascular matrix. Histologic, immunohistologic, molecular imaging, and Western blotting studies were then performed to assess cell viability. RESULTS: The endothelial progenitor cells re-endothelialized the matrix to such an extent that endothelial cell viability was uniformly documented through 2-(18F)-fluoro-2'-deoxyglucose positron emission tomography. This vascularized scaffold was seeded with functional (according to Western blot analysis) smooth muscle cells and successfully reseeded with viable ciliated respiratory epithelium. Chondrocyte growth and production of extracellular cartilaginous matrix was observed as soon as 2 weeks after their culture. CONCLUSIONS: The fundamental elements for a bioartificial trachea were successfully engineered in vitro in a direct vascularized 10- to 15-cm-long bioartificial matrix. Future experimental work will be directed to give them a 3-dimensional aspect and a biomechanical profile of a functioning trachea.

Expansion of chondrocytes in a three-dimensional matrix for tracheal tissue engineering.

BACKGROUND: The generation of autologous tracheal implants by tissue-engineering techniques is a promising concept for otherwise untreatable patients. A functional cartilaginous backbone represents a prerequisite for any bioartificial tracheal graft. The aim of this study was to define suitable cell types and culture conditions for the generation of tracheal cartilage. METHODS: We obtained tracheal, costal, and auricular cartilage from porcine donor animals (n = 10). The chondrocytes were cultured two-dimensionally in cell flasks or mixed with a liquid collagen solution forming a three-dimensional culture system. Labeling with carboxy fluorescein diacetate succinimidyl ester (CFDA SE) and biochemical reduction of formazan served to determine cell viability and proliferation. The extracellular matrix produced by the chondrocytes was characterized by Western blot. RESULTS: The CFDA SE labeling proved viability and the MTT assays documented a proliferation of the chondrocytes over time in vitro. While the chondrocytes in the three-dimensional cell culture system produced hyaline cartilage composed of collagen II, the two-dimensional culture conditions resulted in nonspecific collagen synthesis. CONCLUSIONS: Chondrocytes grown in a three-dimensional matrix can effectively proliferate and produce cartilage and are viable for more than 2 weeks. Costal chondrocytes are suitable for tracheal cartilage tissue engineering.