Click by Click Microporous Annealed Particle (MAP) Scaffolds

Abstract

Macroporous scaffolds are being increasingly used in regenerative medicine and tissue repair. While our recently developed microporous annealed particle (MAP) scaffolds have overcome issues with injectability and in situ hydrogel formation, limitations with respect to tunability to be able to manipulate hydrogel strength and rigidity for broad applications still exist. To address these key issues, here we synthesized hydrogel microparticles (HMPs) of hyaluronic acid (HA) using the thiol-norbornene click reaction and then subsequently annealed HMPs into a porous scaffold using the tetrazine-norbornene click reaction. This assembly method allowed for straightforward tuning of bulk scaffold rigidity by varying the tetrazine to norbornene ratio, with increasing tetrazine resulting in increasing scaffold storage modulus, Youngs modulus, and maximum stress. These changes were independent of void fraction. Further incorporation of human dermal fibroblasts (HDFs) throughout the porous scaffold revealed the biocompatibility of this annealing strategy as well as differences in proliferation and cell-occupied volume. Finally, injection of porous HA-Tet MAP scaffolds into an ischemic stroke model showed this chemistry is biocompatible in vivo with reduced levels of inflammation and astrogliosis as previously demonstrated for other crosslinking chemistries.