Near-instantaneous volumetric printing of complex scaffolds comprised of tough PEG-based hydrogels

Abstract

Poly(ethylene glycol) (PEG) multi-functional building blocks are employed to construct robust hydrogel scaffolds by means of the photo-induced thiol-norbornene (NB) reaction. By systematically exploring various parameters, including polymer concentration, molar mass, PEG-NB molecular architecture, and thiol crosslinker topology, the mechanical properties of PEG-based hydrogels are finely tailored. Compressive moduli range from similar to 0.006-2.0 MPa, and maximum stresses range from similar to 0.38 MPa to 23 MPa, effectively matching diverse tissue engineering application requirements. Notably, all hydrogel formulations demonstrated rapid gelation kinetics, crosslinking in less than 5 seconds under illumination with visible light (i.e., 405 nm), with low photoinitiator concentrations (i.e., 0.05-0.3 wt%). Furthermore, the PEG-based hydrogels are shown to be compatible with volumetric additive manufacturing (VAM), leading to intricate 3-dimensional structures with robust mechanical integrity. Utilizing thiol-NB chemistry enables fast fabrication of complex and mechanically robust geometries without tedious post-curing/post-processing. Compression testing confirms the robustness of these printed objects after fabrication (modulus 375 +/- 16 kPa and maximum stress of 7.0 +/- 0.3 MPa). This combination of speed, ability to form complex geometries without supporting elements, and robust mechanics opens new horizons for tissue engineering applications for hydrogels, paving the way for novel surgical techniques and regenerative therapies.