Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Abstract

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Keywords: biochemical cues; cell behaviors; macroporous hydrogels; matrix mechanics; tissue engineering.

Figure 2

New progress in the preparation of macroporous hydrogels. (A) Porogen templating. Reprinted with permission from [171], Copyright 2022, American Chemical Society. (B) Cryogel. Reprinted with permission from [172], Copyright 2021, Elsevier. (C) Pickering emulsion. Reprinted with permission from [173], Copyright 2020, Elsevier. (D) Gas foaming. Reprinted with permission from [68], Copyright 2020, Elsevier. (E) 3D printing. Reprinted with permission from [174], Copyright 2021, Elsevier. (F) Electrospinning. Reprinted with permission from [94], Copyright Elsevier. (G) Granular hydrogel. Reprinted with permission from [100], Copyright 2021, Wiley. (H) Microribbon. Reprinted with permission from [166], Copyright 2012, Wiley.

Figure 1

Designing macroporous hydrogels to modulate major factors in cell behavior. The Figure is made with biorender (https://biorender.com/, accessed on 31 July 2022).

Figure 3

The schematic depiction and corresponding morphological evaluation of MSCs cultured in different substrate microenvironments: (A) TCP well plate, (B) encapsulated in an alginate hydrogel, and (C) seeded on a macroporous alginate scaffold. MSCs were stained with DAPI (nuclei = blue) and Phalloidin (F-Actin = green). Scales (A) and (B) = 100 μm, and (C) = 50 μm. (D) MSCs maintained long-term viability on the three substrates after 1, 3, and 7 days. (E) Alginate hydrogels and scaffolds showed similar mechanical properties. Reprinted with permission from [179], Copyright 2017, Elsevier.

Figure 4

Size affects single hMSC fate. (A) Alkaline phosphatase (ALP) staining for cells with different V1 and V3 volumes (V1 > V3). The ALP-positive cells were determined by applying an optimal threshold to the image; ALP intensity above the threshold was determined as ALP positive. (B) Quantification of differentiation after 7 days (ALP) and 10 days (Oil Red O) for cells with different volumes. Mean ± s.d., ANOVA one-way analysis followed by Tukey post-hoc test shows significance levels of * p < 0.05, ** p < 0.01. N.S. no significant difference. Reprinted with permission from [175], Copyright 2017, Springer nature.

Figure 5

Cell behavior of vascular endothelial cells in hydrogels with different pore sizes. SEM images of cross-section (A) and surface (B) of HAMA350, HAMA250, HAMA100, and HAMA hydrogels. Scales = 200 μm. (C) Representative confocal images of HUVECs on hydrogels after 7 d. The cytoskeleton was stained with iFluorTM 488 Phalloidin (green) and the nucleus was stained with DAPI (blue). Scales = 20 μm. (D) Cell 3D migration distances into HAMA350, HAMA250, HAMA100, and HAMA hydrogels after 7 d culture in vitro (* p < 0.05). (E) Cell proliferation of HUVECs seeded on HAMA350, HAMA250, HAMA100, and HAMA hydrogels after 1, 4, and 7 d by CCK-8 assay (* p < 0.05). Reprinted with permission from [194], Copyright 2022, IOP Publishing.

Figure 6

Pathways are involved in the regulation of cellular behavior by hydrogel stiffness. Reprinted with permission from [200], Copyright 2021, Springer nature.

Figure 7

(A) The relationship between cell adhesion and ECM matrix surface charge. Reprinted with permission from [226]. Copyright 2017, American Chemical Society. (B) Role of the ninth type-III domain of fibronectin in the mediation of cell-binding domain adsorption on surfaces with different chemistries. Reprinted with permission from [227], Copyright 2018, American Chemical Society.

Figure 8

Schematic illustrations of vertical 3D cryo(bio)printing and its application in muscular tissue engineering. (A) The GelMA-based hydrogel, when subjected to directional freezing, forms interconnected gradient of anisotropic microchannels along the vertical axis. (B) Vertical 3D cryo(bio)printing of hydrogel filament arrays. (C) Vertical 3D cryo(bio)printing of hydrogel filaments of different angles. (D) Multimaterial vertical 3D cryo(bio)printing of a single hydrogel filament. (E) Multimaterial vertical 3D cryo(bio)printing of hydrogel filament array. (F) Vertical 3D cryo-bioprinting for fabricating the muscle-tendon unit. Reprinted with permission from [123], Copyright 2021, Wiley.