Click by Click Microporous Annealed Particle (MAP) Scaffolds

Abstract

density of 0.58 and jamming can occur. In our laboratory, we crosslink HMPs to each other to generate a stable scaffold, rather than rely on jamming such that the void spaces surrounding the beads are sufficiently large for cellular growth and the scaffold is structurally stable. We termed these bulk hydrogels microporous annealed particle (MAP) scaffolds due to the micron sized voids (pores) formed in between packed beads. MAP scaffolds support modifications with bioactive ligands to modulate cell behavior, can be used for cell culture in vitro, [1][2][3][4][5][6][7][8] and support tissue ingrowth in vivo. [2][3][4][5] Of particular interest is that injection of MAP scaffolds into wound sites results in reduced inflammation and improved tissue regeneration. [3,4,9,10] We have shown that the innate microporosity of MAP scaffolds enables a greater prorepair response in the wound site after stroke compared to a nonporous gel of the same composition. [5] The "plug and play" modularity of MAP building blocks enables the incorporation of different materials, signals, and crosslinking schemes to tune the scaffolds for unique tissue engineering applications. Herein, we demonstrate the generation of hyaluronic acid HMPs, the modification of HMPs with ligands, and the crosslinking of HMPs to form MAP scaffolds using thiol-norbornene and tetrazine-norbornene click reactions and their use in vitro and in vivo.HMP interlinking to form MAP scaffolds can be achieved upon injection due to the shear thinning properties of these granular materials and the use of biocompatible mechanisms for annealing. Our current method to fabricate MAP scaffolds for use in vivo utilizes the coagulation enzyme FXIIIa, which is a transglutaminase. [2,5,11] The HMPs are packed and linked between K and Q peptides, recognized by FXIIIa, on their surface. For applications in wound healing, polyethylene glycol (PEG) HMPs annealed with FXIIIa in situ have been shown to promote cutaneous tissue regeneration by supporting cell migration and support tissue structure formation. In vivo responses to these injectable PEG MAP scaffolds include re-epithelialization, vascular development, and growth of hair follicles. [2] Utilizing the native extracellular matrix component hyaluronic acid (HA) with FXIIIa for scaffold fabrication accelerates brain repair processes after stroke. [5] Compared to both sham injections and nonporous gels, HA MAP reduces Macroporous scaffolds are being increasingly used in regenerative medicine and tissue repair. While the 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 hydrogel microparticles (HMPs) of hyaluronic acid (HA) are synthesized using the thiol-norbornene click reaction and then HMPs are subsequently annealed into a porous scaffold using the tetrazine-norbornene click reacti...

Biomaterials-Mediated Regulation of Macrophage Cell Fate

“…MAP scaffolds can also be designed with spatial heterogeneity, where physical or chemical gradients can be maintained during injection due to the jamming properties of granular materials (Darling et al, 2018;Riley et al, 2019). Remarkably, MAP gels have already demonstrated great promises in promoting functional tissue repair in wound healing and stroke with a reduced inflammatory response (e.g., reduced CD11b+ immune cell infiltration) (Griffin et al, 2015(Griffin et al, , 2020Sideris et al, 2016;Nih et al, 2017;Darling et al, 2020). Specifically, in stroke infarct areas filled with MAP gels, there is a much higher ratio of infiltrating pro-reparative arginase 1+ (Arg-1+) macrophage comparing to no treatment control (Sideris et al, 2019).…”

3D Printing of Microgel Scaffolds with Tunable Void Fraction to Promote Cell Infiltration

“…Microgel size is another factor that can be used to control void fraction. [16,22,23] In one example, controlling the particle size from 10 to 100 μm resulted in void fractions ranging from 0.12 to 0.29. [22] This closely matches the predicted theoretical limit of void fraction for deformable microgels of uniform size (≈0.26).…”

Recent Advances in Injectable Hydrogels for Controlled and Local Drug Delivery

“…The injection of Tetra-PEG-Tet and HA-Norb into an ischemic stroke model reduced levels of inflammation and astrogliosis, indicating the good biocompatibility of this type of crosslinking in vivo. [81] Another thiol-Michael addition click reaction-based injectable hydrogel was described by Pupkaite et al They chemically crosslinked thiol group-modified collagen with 8-arm polyethylene glycol-maleimide through a thiol-Michael addition click reaction. That allowed for the formation of injectable hydrogels with shear-thinning and self-healing properties because of the low degree of thiol modification on collagen and the formation of an interhelical assembly.…”