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Enzymatically crosslinked microporous hydrogel scaffolds that form in situ promote dermal healing Evaluation of: Griffin DR, Weaver WM, Scumpia PO, DiCarlo D, Segura T. Accelerated wound healing by injectable microporous gel scaffolds assembled from annealed building blocks. Nat. Mater. 14, 737–744 (2015). Tunable scaffolds that respond to environmental factors could enable enhanced tissue integration and wound healing. To achieve this goal, scaffold designs have incorporated biomimetic functionality, including thrombin-activated factor XIII (FXIIIa) crosslinking [1], matrix metalloproteinase responsiveness [2] and mechanical matching [3]. Scaffolds that can alter their properties in situ in response to environmental stimuli are desired to achieve changes in stiffness, shape, release and degradation that can lead to improved tissue regeneration. In this study, Griffin et al. describe a bottom-up strategy to fabricating scaffolds that accelerate wound healing [4]. They use a microfluidic approach to form hydrogel microparticle (microgel) building blocks that can establish interconnected network structures upon FXIIIa-mediated crosslinking. These microporous annealed particles (MAPs) incorporate reactive multiarmed poly(ethylene)glycol-vinyl sulfone, the commonly used RGD cell adhesion peptide and the K and Q noncanonical transglutaminase peptide substrates with cysteine-terminated matrix metalloproteinase-sensitive peptides that allow for cell-controlled material degradation. Scaffolds are annealed by FXIIIa addition and can be injected into wound sites for in situ solidification and shape-conformation. These MAPs are mechanically robust and can be tuned to achieve storage moduli from 10 to 1000 Pa, which fall within the stiffness range of soft tissues. In vitro studies demonstrate that MAP scaffolds enable 3D cellular network formation and cell proliferation and survival after 6 days. In vivo studies in SKH1-HR and Balb/c epidermal wound healing models demonstrate integration of MAP scaffolds after 24 h, significant wound closure as compared with nonporous chemically matched controls after 5 days or physically matched control scaffolds up to 7 days. 5 days following injection of MAP scaffolds, keratin-5, keratin-14 and CD49f staining revealed re-epithelialization, and PECAM-1, NG2 and PDGFR-β staining indicated that the scaffolds promoted complex vascular development. MAP scaffolds were also able to sustain normal hair follicle formation when compared with normal tissue. The scaffolds promoted less CD11b cell infiltration as compared with nonporous controls after 5 days, which suggests that MAP scaffolds cause a lower immune response. Taken together, MAP scaffolds promote accelerated wound healing by utilizing natural enzymatic mechanisms and mimicking favorable mechanical and degradation properties to facilitate cell infiltration and proliferation. The study may have benefited from evaluating wound closure, dermal regeneration and Our panel of experts highlight the most important research articles across the spectrum of topics relevant to the field of regenerative medicine