Natural Polymers in Heart Valve Tissue Engineering: Strategies, Advances and Challenges

Abstract

In the history of biomedicine and biomedical devices, heart valve manufacturing techniques have undergone a spectacular evolution. However, important limitations in the development and use of these devices are known and heart valve tissue engineering has proven to be the solution to the problems faced by mechanical and prosthetic valves. The new generation of heart valves developed by tissue engineering has the ability to repair, reshape and regenerate cardiac tissue. Achieving a sustainable and functional tissue-engineered heart valve (TEHV) requires deep understanding of the complex interactions that occur among valve cells, the extracellular matrix (ECM) and the mechanical environment. Starting from this idea, the review presents a comprehensive overview related not only to the structural components of the heart valve, such as cells sources, potential materials and scaffolds fabrication, but also to the advances in the development of heart valve replacements. The focus of the review is on the recent achievements concerning the utilization of natural polymers (polysaccharides and proteins) in TEHV; thus, their extensive presentation is provided. In addition, the technological progresses in heart valve tissue engineering (HVTE) are shown, with several inherent challenges and limitations. The available strategies to design, validate and remodel heart valves are discussed in depth by a comparative analysis of in vitro, in vivo (pre-clinical models) and in situ (clinical translation) tissue engineering studies.

Keywords: heart valve replacement; heart valve tissue engineering; polysaccharides; proteins; regenerative medicine; scaffold.

Figure 1

Graphical representation of challenges in cardiac tissue engineering. Reprinted with permission from ref. [35]. Copyright 2018, Dove Medical Press.

Figure 2

A schematic view of the heart valves. Reprinted with permission from ref. [62]. Copyright 2022, Edwards Lifesciences Corporation.

Figure 3

Evolution of mechanical valves. Reprinted with permission from ref. [68]. Copyright 2022, Smithsonian Institution.

Figure 4

Types of bioprosthetic valves: (a) stented pericardial bovine bioprosthetic valves, (b) stented porcine aortic valve bioprostheses, (c) stentless bioprosthetic valves. Reprinted with permission from ref. [92]. Copyright 2018, Springer Nature.

Figure 5

Polymeric scaffolds used in HVTE.

Figure 6

Comparative analysis of the polymeric scaffolds used in HVTE.

Figure 7

Representation of aortic and mitral valve structures. (A) Aortic valve and (B) mitral valve, with the three ECM layers: ventricularis (EL), spongiosa (PG-GAG) and fibrosa (COL); the blood flow is indicated by red arrows (ventricularis closest to blood flow); valve endothelial cells (VECs, purple) and valve interstitial cells (VICs, blue). (Right) Representation of the aortic valve indicating coordinated rearrangement of the ECM fibers, and elongation of the VICs during systole (open) and diastole (closed). Reprinted with permission from ref. [111]. Copyright 2020, MDPI. (C) Detailed heart valve structure: the three inner layers (ventricularis, spongiosa and fibrosa) with proteoglycans (PG), glycosaminoglycans (GAG), collagen type I and type III, elastin and VICs and the outer layer formed by VECs. Reprinted with permission from ref. [105]. Copyright 2015, Cambridge University Pres. (D) Tissue image of trilayered structure of an aortic leaflet in sheep. The three layers consist of fibrosa (F), spongiosa (S) and ventricularis (V). Reprinted with permission from ref. [112]. Copyright 2015, SciDoc Publishers.

Figure 8

Heart valve tissue engineering strategies: in vitro TEHV, in vivo TEHV and in situ TEHV.

Figure 9

Fluorescence micrographs of VECs seeded onto substrates (bar = 100μm). Reprinted with permission from ref. [164]. Copyright 2003, Wiley Periodicals.

Figure 10

Scheme of bovine pericardium (BP) modification in solutions of CH/H₂CO₃. Reprinted with permission from ref. [166]. Copyright 2014, Elsevier.

Figure 11

Representative images depicting the cell-scaffold interactions. DiI-DAPI stained hVICs on (a) glass coverslip, (b) DBP, (c) Bio-hybrid R and (d) Bio-hybrid A scaffolds; (Dil: 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate; DAPI: 4′,6-diamidino-2-phenylindole). Adapted with permission from ref. [169]. Copyright 2016, Elsevier.

Figure 12

Live/dead assay for encapsulated VICs within HA-based hydrogels, with and without addition of Me-Gel (after 14 days). Adapted with permission from ref. [175]. Copyright 2013, Elsevier.

Figure 13

Biocompatibility of Me-Gel and mNG hydrogels. (a) Representative images of live/dead staining of cells encapsulated within the different hydrogels (scale bar = 100 μm). (b) Percent cell spreading in hydrogels. (c) Cell metabolism over time. * p < 0.05. Reprinted with permission from ref. [178]. Copyright 2021, Wiley Periodicals.

Figure 14

Live/Dead assay for encapsulated VICs within Alg/Gel hydrogel discs, (A) after 1 day and (B) after 7 days. (C) Cell viability measured based on Live/Dead images. Adapted with permission from ref. [133]. Copyright 2012, Wiley Periodicals.

Figure 15

Live/Dead assay for encapsulated SMCs within Alg/Gel hydrogel discs, (A) after 1 day and (B) after 7 days. (C) Cell viability measured based on Live/Dead images. Adapted with permission from ref. [133]. Copyright 2012, Wiley Periodicals.

Figure 16

Proliferation of CDCs on scaffolds from day 1 to day 7 (*, ** *** and **** indicate statistically significant differences (p < 0.05) between groups of different compositions). Reprinted with permission from ref. [230]. Copyright 2012, Hilaris.

Figure 17

Fluorescent images of VICs in middle layer. Adapted with permission from ref. [231]. Copyright 2018 MDPI.

Figure 18

Fluorescent images of VECs on top layer of the VECs-VICs co-culture model β1 Integrin—green; F-actin—yellow; Nuclei—blue; Cell membrane—red (scale bar: 100 μm). Adapted with permission from ref. [231]. Copyright 2018, MDPI.

Figure 19

(A) Gross appearance of the heart valve after removal from the bioreactor. (B) The fibrin-based valves (left: outflow side of closed valve; right: opened conduit cut through conduit wall following removal of the silicone cylinder). Scale: 10 mm. (C–H) Histological micrographs of trichrome-stained samples: (C,F) native ovine aortic valve leaflet and aortic wall; (E,H) conditioned leaflet and wall; (D,G) stirred tissue samples. Scale: 250 mm. Reprinted with permission from ref. [234]. Copyright 2007, Elsevier.

Figure 20

Fabrication process of the BioTexValve. (A) Multifilament PLDL fibers fixed on the frame; (B) textile composite leaflet after electrospinning; (C) molding system; (D) leaflets placement on the mold; (E) positioning of the PLDL fibers to create continuity between leaflet and wall; (F) complete valve fabrication after fibrin gel injection and demolding. Reprinted with permission from ref. [134]. Copyright 2016, Wiley.