Tissue engineering of semilunar heart valves : current status and future developments

Heart valve replacement represents the most common surgical therapy for end-stage valvular heart diseases. One major drawback that all heart valve replacements have in common is the lack of growth, repair, and remodeling capability once implanted into the body. The emerging field of tissue engineering is focusing on the in-vitro generation of functional, living semilunar heart valve replacements. This review presents a state-of-the-art overview of the physiological and biomechanical requirements of semilunar heart valves, focusing on the aortic valve. Moreover, recent heart valve tissue engineering is summarized and future options and improvements on the way towards clinical applications are discussed

Autologous human tissue-engineered heart valves : prospects for systemic applications

Background— Tissue engineering represents a promising approach for the development of living heart valve replacements. In vivo animal studies of tissue-engineered autologous heart valves have focused on pulmonary valve replacements, leaving the challenge to tissue engineer heart valves suitable for systemic application using human cells. Methods and Results— Tissue-engineered human heart valves were analyzed up to 4 weeks and conditioning using bioreactors was compared with static culturing. Tissue formation and mechanical properties increased with time and when using conditioning. Organization of the tissue, in terms of anisotropic properties, increased when conditioning was dynamic in nature. Exposure of the valves to physiological aortic valve flow demonstrated proper opening motion. Closure dynamics were suboptimal, most likely caused by the lower degree of anisotropy when compared with native aortic valve leaflets. Conclusions— This study presents autologous tissue-engineered heart valves based on human saphenous vein cells and a rapid degrading synthetic scaffold. Tissue properties and mechanical behavior might allow for use as living aortic valve replacement

Living patches engineered from human umbilical cord derived fibroblasts and endothelial progenitor cells

Objective: A major shortcoming in contemporary congenital heart surgery is the lack of viable replacement materials with the capacity of growth and regeneration. Here we focused on living autologous patches engineered from human umbilical cord derived fibroblasts and endothelial progenitor cells (EPCs) as a ready-to-use cell source for paediatric cardiovascular tissue engineering. Methods: EPCs were isolated from 20 ml fresh umbilical cord blood by density gradient centrifugation and myofibroblasts were harvested from umbilical cord tissue. Cells were differentiated and expanded in vitro using nutrient media containing growth factors. Before seeding, cell-phenotypes were assessed by immuno-histochemistry. Biodegradable patches fabricated from synthetic polymers (PGA/P4HB) were seeded with myofibroblasts followed by endothelialization with EPCs. All patches were cultured in a perfusion bioreactor. A subgroup of patches was additionally stimulated by cyclic strain. Analysis of the neo-tissues comprised histology, immuno-histochemistry, extracellular matrix (ECM) analysis and biomechanical testing. Results: Endothelial phenotypes of EPCs before seeding were confirmed by Ac-Dil-LDL, CD 31, von-Willebrand-Factor and eNOS staining. Histology of the seeded patches demonstrated layered viable tissue formation in all samples. The cells in the newly formed tissues expressed myofibroblast markers, such as desmin and alpha-SMA. The EPCs derived neo-endothelia showed constant endothelial phenotypes (CD 31, vWF). major constituents of ECM such as collagen and proteoglycans were biochemically detected. Stress–strain properties of the patches showed features of native-analogous tissues. Conclusions: Living tissue engineered patches can be successfully generated from human umbilical cord derived myofibroblasts and EPCs. This new cell source may enable the tissue engineering of versatile, living, autologous replacement materials for congenital cardiac interventions

The relevance of large strains in functional tissue engineering of heart valves

Background: Exposing the developing tissue to flow and pressure in a bioreactor has been shown to enhance tissue formation in tissue engineered heart valves. Animal studies showed excellent functionality of these valves in the pulmonary position. However, they lack mechanical strength for implantation in the high-pressure aortic position. Improving the in-vitro conditioning protocol is an important step towards the use of these valves as aortic heart valve replacements. In this study, the relevance of large strains to improve the mechanical conditioning protocol was investigated. Methods: Utilizing a newly developed device, engineered heart valve tissue was exposed to increasing cyclic strain in-vitro. Tissue formation and mechanical properties were analyzed and compared to unstrained controls. Results: Straining resulted in more pronounced and organized tissue formation with superior mechanical properties over unstrained controls. Overall tissue properties improved with increasing strain levels. Conclusions: The results demonstrate the significance of large strains in promoting tissue formation. This study may provide a methodological basis for tissue engineering of heart valves appropriate for systemic pressure applications