Injectable Microporous Annealed Particle Hydrogel Based on Guest–Host‐Interlinked Polyethylene Glycol Maleimide Microgels

Abstract

Microporous annealed particle (MAP) hydrogels have emerged as a versatile biomaterial platform for regenerative medicine. MAP hydrogels have been used for the delivery of cells and organoids but often require annealing post‐injection by an external source. An injectable, self‐annealing MAP hydrogel with reversible interparticle linkages based on guest–host functionalized polyethylene glycol‐maleimide (PEG‐MAL) microgels is engineered. The effect of guest–host linkages is evaluated on different types of microgels fabricated by either batch emulsion or mechanical fragmentation methods. Batch emulsion generates small spherical microgels with controllable (10–100 μm) diameters and mechanical fragmentation generates irregular microgels with larger diameters (100–200 μm). Spherical microgels (15 μm) show self‐healing behavior and have completely recovered from high strain while fragmented microgels (133 μm) do not recover. Guest–host interactions significantly contribute to the mechanical properties of spherical microgels but have no effect on fragmented microgels. Spherical microgels are superior to the fragmented microgels for co‐injection of immune cells and pancreatic islets due to their lower force of injection, demonstrating more homogeneously distributed cells and greater cell viability after injection. Based on these studies, the spherical guest–host MAP hydrogels provide a controllable, injectable scaffold for engineered microenvironments and cell delivery applications.

Single versus dual microgel species for forming guest‐host microporous annealed particlePEG‐MALhydrogel

“…We generated two different types of MAP‐PEG hydrogel with secondary crosslinking: (1) one with inter‐particle only interactions between two microgel species each functionalized with either a guest or host molecule (Inter‐MAP‐PEG) and (2) one with both intra‐ and inter‐particle guest‐host interactions where all microgels are homogeneously functionalized with both guest and host molecules (Intra‐MAP‐PEG) (Figure 1B,C). Synthesis of guest‐host precursor molecules was performed by conjugating Ada‐thiol (Ada‐SH) and mono‐thiol‐β‐CD (β‐CD‐SH) to the PEG‐4MAL before crosslinking per our previously published methods 7,10 . For Inter‐MAP‐PEG, Ada‐SH and β‐CD‐SH were added to separate batches of the PEG‐4MAL and allowed to react for 30 min before crosslinking with PEG‐4SH in a water‐in‐oil emulsion.…”

“…Guest‐host interactions are noncovalent, shear‐reversible interactions that are composed of a guest and host molecule. One of the most well‐characterized guest‐host interactions is the β‐cyclodextrin (β‐CD)/adamantane (Ada) interaction 7,10,18–24 . β‐CD is a cyclic oligosaccharide of repeating D‐glucose units that form a cup‐like morphology with a hydrophobic core.…”

“…We and others have demonstrated that microgel particles can be interlinked using secondary crosslinking mechanisms, stabilizing the overall MAP hydrogel structure 2,7,8,10,11 . Examples of secondary crosslinking mechanisms include covalent interparticle annealing by methods such as photo‐crosslinking, enzymatic crosslinking, and click chemistry 6,11–13 .…”

“…Ada is a small hydrophobic hydrocarbon that acts as the guest molecule and can couple with the hydrophobic core of the β‐CD 24 . Previously, we designed polyethylene glycol maleimide (PEG‐MAL) MAP hydrogel interlinked with guest‐host interactions 7,10 . The MAP hydrogel was formed by mixing two different populations of microgels, one conjugated with Ada and the other with β‐CD.…”

“…One of the most well-characterized guest-host interactions is the β-cyclodextrin (β-CD)/adamantane (Ada) interaction. 7,10,[18][19][20][21][22][23][24] β-CD is a cyclic oligosaccharide of repeating D-glucose units that form a cup-like morphology with a hydrophobic core. Ada is a small hydrophobic hydrocarbon that acts as the guest molecule and can couple with the hydrophobic core of the β-CD.…”