A Versatile Synthetic Extracellular Matrix Mimic via Thiol‐Norbornene Photopolymerization

Abstract

Synthetic hydrogels with engineered, cell-mediated degradation sites are an important category of biomimetic materials. Here, hydrogels are synthesized by a step-growth reaction mechanism via a radically mediated thiol-norbornene (thiol-ene) photopolymerization. This reaction combines the advantages of ideal, homogeneous polymer network formation, facile incorporation of peptides without post-synthetic modification, and spatial and temporal control over the network evolution into a single system to produce proteolytically degradable poly(ethylene glycol) (PEG) peptide hydrogels. Using a thiol-ene photopolymerization, rapid gelation times are achieved, while maintaining high cell viability for cell encapsulation. The enzyme- and cellresponsive characteristics are demonstrated by tailoring the rate of spreading of human mesenchymal stem cells (hMSCs) through both the selection of proteolytically degradable crosslinkers and the density of the adhesion peptide RGDS. Furthermore, cellular function is manipulated spatially within the thiol-ene hydrogels through biochemical photopatterning. The high degree of spatial and temporal control over gelation, combined with robust material properties, makes thiol-ene hydrogels an excellent tool for a variety of medical and biological applications.

Versatile click alginate hydrogels crosslinked via tetrazine–norbornene chemistry

“…This thiol-ene reaction is a powerful light-mediated click reaction that is simple, reproducible, fast, and highly efficient -achieving conversions nearing completion in aqueous media [41]. Although we did not investigate the thiol-ene reaction conversion as a function of hydrogel depth specifically, several recent papers have reported the ability to functionalize the interiors of hydrogels using this method [28,30,42,43]. When click alginate hydrogels were modified with RGD peptides using this strategy, fibroblasts seeded on the gels responded with increased attachment and spreading as RGD density was raised, over a 3 day culture period.…”

“…These copper-free chemistries include strain-promoted azide-alkyne cycloaddition (SPAAC) and the inverse electron demand Diels-Alder reaction between tetrazine and norbornene [24,25]. Previous reports have used these click reactions primarily to crosslink click endfunctionalized branched polyethylene glycol (PEG) with linear crosslinkers composed of either PEG or linear peptides terminated with the appropriate click reaction pair [26][27][28][29]. The mechanical properties and swelling behavior of these click crosslinked PEG hydrogels could be tuned by varying the linear crosslinker concentration [30,31].…”

A microfluidic-based cell encapsulation platform to achieve high long-term cell viability in photopolymerized PEGNB hydrogel microspheres

“…Synthesis of the macromer 4-arm poly(ethylene glycol) tetranorbornene (PEGNB) was conducting according to established protocols 43,50,54 . Briefly, 12 grams of 20kDa 4-arm PEG (Creative PEGworks) was added to 20 mL of methylene chloride (MeCl, Sigma Aldrich) in a 40 mL scintillation flask, stirred until complete dissolution was achieved, and set aside.…”

“…Utilizing this highly reproducible platform, we were able to exploit the benefits of microfluidics to produce uniform cell-laden hydrogel microspheres at high rates. By collecting cell-laden PEGNB droplets into a centrifuge tube and exposing it to a UV source for an extended time, we overcame the relatively slow polymerization kinetics of PEGNB 43 , and achieved high post-encapsulation cell viability over the course of 30 days. Hydrogel microsphere uniformity and post-encapsulation cell viability has been compared between this platform and vortex-based cell encapsulation.…”

B 12 -dependent photoresponsive protein hydrogels for controlled stem cell/protein release

“…Through a combination of orthogonal click reactions and photochemistry, some of these synthetic hydrogels can be mechanically and chemically patterned in situ by light while being used for 3D cell culturing (12,13). Diverse photoactive chemical moieties have also been incorporated into synthetic hydrogels to create photoresponsive devices for controlled therapeutic release (5,14,15).…”