Recellularization of decellularized heart valves: Progress toward the tissue-engineered heart valve

Abstract

The tissue-engineered heart valve portends a new era in the field of valve replacement. Decellularized heart valves are of great interest as a scaffold for the tissue-engineered heart valve due to their naturally bioactive composition, clinical relevance as a stand-alone implant, and partial recellularization in vivo. However, a significant challenge remains in realizing the tissue-engineered heart valve: assuring consistent recellularization of the entire valve leaflets by phenotypically appropriate cells. Many creative strategies have pursued complete biological valve recellularization; however, identifying the optimal recellularization method, including in situ or in vitro recellularization and chemical and/or mechanical conditioning, has proven difficult. Furthermore, while many studies have focused on individual parameters for increasing valve interstitial recellularization, a general understanding of the interacting dynamics is likely necessary to achieve success. Therefore, the purpose of this review is to explore and compare the various processing strategies used for the decellularization and subsequent recellularization of tissue-engineered heart valves.

Keywords: Tissue-engineered heart valve; decellularization; recellularization.

Figure 1.

(a–d) H&E and (e–h) Movat’s pentachrome staining highlighting the effects of decellularization by SDS (b, f), trypsin (c, g), and Triton X-100 (d, h) compared to native tissue (a, e). All three methods show effective removal of cellular and nuclear material. SDS slides show preservation of leaflet structure and ECM components. Trypsin slides show a “loosening” of the ECM network and loss of structural proteins. Triton X-100 slides show good preservation of leaflet structure but loss of GAGs from the ECM. Source: Figure reprinted from Liao et al. with permission. Copyright 2008 Elsevier: Biomaterials.

Figure 2.

H&E-stained sections highlighting the autologous recellularization of decellularized (dAV) and cryopreserved (cAV) aortic valves after implantation in sheep. Histology of aortic wall: cAV after 3 months (a) and after 9 months (c) with signs of rejection and leukocyte infiltration; dAV after 3 months (b) and after 9 months (d) without any signs of rejection and with partial re-endothelialization and ingrowth of interstitial cells. The same findings are shown in the aortic sinus: cAV degeneration after 3 months (e) and after 9 months (g); dAV sinus without signs of rejection and with partial re-endothelialization and recellularization of leaflet base after 3 months (f) and even more recellularization after 9 months (h). Leaflets from the cAV show massive degeneration and destruction after 3 months (i) and after 9 months (k); dAV distal leaflets show partial re-endothelialization after 3 months (j) and after 9 months (l). (S) shows sinus side of the leaflet. Source: Figure reprinted from Baraki et al. with permission. Copyright 2009 Elsevier: Biomaterials.

Figure 3.

Immunological staining demonstrating successful recellularization of leaflets from pulmonary valves conjugated with CD133 and implanted in the pulmonary position in sheep. Texas Red–labeled secondary antibodies show αSMA (top row) and vimentin (bottom row), and the nuclei are DAPI counterstained. Percentage values are the percent of cells with positive expression compared to the total number of cells which represent the mean calculated from all three leaflets. Note the high αSMA expression in the tissue-engineered leaflets compared to native leaflets. L denotes lumen. * indicates p < 0.05. Scale bars are 100 µm. Source: Figure reprinted from Williams et al. with permission. Copyright 2015 Springer Science: Journal of Cardiovascular Translational Research.