Photoclick Phase-separating Hydrogels for 3D Cell Culture and Volumetric Bioprinting

Abstract

Macroporous hydrogels facilitate solute transport and cell-cell communication in 3D, but materials allowing for in situ pore formation and 3D-printing in aqueous solutions are scarce. Here, a phase-separating thiol-ene photoresin is developed for light-assisted 3D-printing of hierarchical macroporous hydrogels that support 3D cell growth. The resin consists of norbornene-functionalized polyvinyl alcohol, di-thiol crosslinker and dextran sulfate, which can rapidly form a hydrogel with interconnected pores by photopolymerization-induced phase separation (PIPS). The pore size is tunable in the range of 2-40 μm as quantified by fast Fourier transformation of confocal imaging data and depends on light intensity, polymer composition and molecular charge. After 3D photoencapsulation, high cell viability (>90%) is achieved and cell spreading in the macroporous hydrogels is significantly higher than in conventional nanoporous hydrogels. The incorporation of a thermo-reversible gelatin network enables its printability for tomographic volumetric bioprinting in the presence of human mesenchymal stem cells. A cm-scale cell-laden hydrogel construct with vasculature-like channels and interconnected pores can be 3D-printed in 12 seconds. The materials are cell-compatible, low-cost, easy-to-make and highly efficient for PIPS and light-based 3D-printing, which is unachievable with conventional 3D-printable hydrogels. Such materials are promising for future photofabrication of complex tissues with a hierarchical porosity within seconds.

Light-based vat-polymerization bioprinting

“…DLP and other vat-polymerization techniques have been utilized to generate degradable hydrogel and elastomer scaffolds to template contractile soft tissue constructs, perfusable vasculature and topographically defined intestinal stem cell monolayers [107][108][109][110] . Although photocleavable units have yet to be widely incorporated into bioresins for vat polymerization, other sacrificial (for example, hydrolytically degradable, enzyme-cleavable, thermo-reversible) or phase-separating components can be introduced for the production of high fidelity and intrinsically porous or vascularized 3D biomaterials 63,64,[111][112][113] . Ultimately, light-based crosslinking of bioresins makes the fabrication of microscopically complex synthetic 3D tissues possible, with various possible formulations to optimize print fidelity and enable versatile post-printing modifications.…”

Tunable bicontinuous macroporous cell culture scaffolds via kinetically controlled phase separation

“…Here, we exploited polymerization-induced phase separation in a PEG-dextran solution to fabricate PEG-based hydrogels with engineered porosity for cell culture, building on recent advances in the literature. 28,36,37,55 We advanced the methods of fabrication of macroporous hydrogels by including kinetic control of the phase separation process using photopolymerization, which provided fine control over the pore size between 1 and 300 μm. Further, we established a model for porosity evolution in thiol-ene PEG-dextran systems, which can be extended to other phase separating systems under kinetic control.…”

“…36 More recently, spinodal decomposition of cross-linking poly(vinyl alcohol) and dextran formed interconnected microporous biomaterials, suggesting an inverse correlation between the photopolymerization intensity and the final pore size. 37 In non-biomedical applications, the kinetics of photopolymerization reactions were exploited to structure phaseseparating polymer systems, providing control over the size and interconnectivity of the pores. 38,39 Irradiation of the photopolymerizable monomer mixture with a UV light intensity gradient resulted in a polymer network with a porosity gradient along the propagation direction of light.…”

Aqueous Two‐Phase Emulsion Bioresin for Facile One‐Step 3D Microgel‐Based Bioprinting

“…Photopolymerization-induced phase separation has been earlier reported in a PVA/Dex system. [40] It is speculated that during the photo-crosslinking, GelMA in the continuous phase might get separated and crosslinked with the large GelMA droplets, which were likely to coalesce into a continuous and irregularly shaped hydrogel. Attributed to the displacement of the microgels when a force was applied, the Emul hydrogels showed better flexibility than the Non-Emul hydrogels, as shown in Figure 4e.…”