Strategy for improving cell-mediated vascularized soft tissue formation in a hydrogen peroxide-triggered chemically-crosslinked hydrogel

Abstract

The physically-crosslinked collagen hydrogels can provide suitable microenvironments for cell-based functional vascular network formation due to their biodegradability, biocompatibility, and good diffusion properties. However, encapsulation of cells into collagen hydrogels results in extensive contraction and rapid degradation of hydrogels, an effect known from their utilization as a pre-vascularized graft in vivo. Various types of chemically-crosslinked collagen-based hydrogels have been successfully synthesized to decrease volume contraction, retard the degradation rate, and increase mechanical tunability. However, these hydrogels failed to form vascularized tissues with uniformly distributed microvessels in vivo. Here, the enzymatically chemically-crosslinked collagen-Phenolic hydrogel was used as a model to determine and overcome the difficulties in engineering vascular networks. Results showed that a longer duration of inflammation and excessive levels of hydrogen peroxide limited the capability for blood vessel forming cells-mediated vasculature formation in vivo. Lowering the unreacted amount of crosslinkers reduced the densities of infiltrating host myeloid cells by half on days 2–4 after implantation, but blood vessels remained at low density and were mainly located on the edge of the implanted constructs. Co-implantation of a designed spacer with cell-laden hydrogel maintained the structural integrity of the hydrogel and increased the degree of hypoxia in embedded cells. These effects resulted in a two-fold increase in the density of perfused blood vessels in the hydrogel. Results agreed with computer-based simulations. Collectively, our findings suggest that simultaneous reduction of the crosslinker-induced host immune response and increase in hypoxia in hydrogen peroxide-triggered chemically-crosslinked hydrogels can effectively improve the formation of cell-mediated functional vascular networks.

The Rheology and Printability of Cartilage Matrix-Only Biomaterials

“…Depending on the polymer, some hydrogels can swell out or contract after fabrication, which may lead to dislodgment or poor integration with the existing tissue after in situ gelation. Collagen hydrogels are known for contracting [ 52 , 53 ] and given the high collagen content of cartilage matrix, the swelling and absorption of water of cartilage matrix-based hydrogels is a vitally important parameter. All the MeSDVC hydrogels (10 wt%) in the current study had similar swelling ratios to the 10 wt% MeSDVC hydrogels (~10) we previously characterized [ 25 ].…”

Vascularization in Bioartificial Parenchymal Tissue: Bioink and Bioprinting Strategies

“…ECM composition and structural binding motifs in bioinks can also affect vascularization within bioartificial tissue [ 40 , 46 , 47 , 57 ]. Bioinks, therefore, often contain biomaterials such as collagen and fibrin, which have been reported to support angiogenic growth due to their binding motifs [ 39 , 58 , 59 , 60 ] ( Table 1 ). In addition, naturally derived materials such as hyaluronic acid, dextran, agarose, and gelatin, but also synthetic materials such as PEG, can be adapted to enable vascularization [ 47 , 57 ] ( Table 1 ).…”

“…Study evidence suggests enhanced integrin-mediated adherence of endothelial cells (ECs) by integration of arginine–glycine–aspartic acid sequencing (RGD) motifs [ 42 , 47 ] ( Table 1 ). Such motifs are present in natural hydrogel materials such as collagen, gelatin, gelatin methacrylol, fibrin, and hyaluronic acid [ 55 , 58 , 61 ]. In alginate, agarose, and PEG hydrogels, such motifs are missing but can be added to the bioink formulation [ 42 , 62 , 63 ].…”

“…Thus, there is study evidence that coculture with endothelial-stabilizing cells enhances vessel network formation, e.g., by growth factor secretion and direct cell–cell interactions [ 33 , 42 , 60 , 63 , 89 , 99 ]. Mesenchymal stem cells, sometimes also referred to as medicinal signaling cells [ 100 ], have been widely used in tissue-engineering strategies with the intention of promoting functional vascularization by VEGF secretion [ 17 , 39 , 42 , 58 , 59 , 101 ]. Additionally, mesenchymal stem cells have the potential to differentiate to smooth muscle cells, thereby further resembling the natural vascular cellular composition [ 42 , 84 , 100 ] ( Table 1 ).…”

“…After sufficient crosslinking, the sacrificial materials are removed [ 110 ]. Removal can be accomplished by dissolution with a solvent [ 14 , 47 , 85 , 86 , 103 , 106 , 110 , 111 ], temperature regulation [ 14 , 27 , 46 , 83 , 104 , 105 , 106 , 110 ], or pH regulation [ 58 , 85 ], leaving a microfluidic network of patterned microchannels or even vascular tree-like channels in the construct [ 22 , 47 , 83 , 87 , 110 ]. Perfusion of such a network with ECs and their subsequent partial adherence has the potential to result in coating of the inner wall [ 27 , 47 , 63 , 83 , 87 , 105 , 111 ] ( Figure 3 a).…”