Interfacial Thiol-ene Photoclick Reactions for Forming Multilayer Hydrogels

Abstract

Interfacial visible light-mediated thiol-ene photo-click reactions were developed for preparing step-growth hydrogels with multilayer structures. The effect of a non-cleavage type photoinitiator eosin-Y on visible light-mediated thiol-ene photopolymerization was first characterized using in situ photo-rheometry, gel fraction, and equilibrium swelling ratio. Next, spectrophotometric properties of eosin-Y in the presence of various relevant macromer species were evaluated using UV/Vis spectrometry. It was determined that eosin-Y was able to re-initiate thiol-ene photo-click reaction even after light exposure. Due to its small molecular weight, most eosin-Y molecules readily leached out from the hydrogels. The diffusion of residual eosin-Y from pre-formed hydrogels was exploited for fabricating multilayer step-growth hydrogels. Interfacial hydrogel coating was formed via the same visible light-mediated gelation mechanism without adding fresh initiator. The thickness of the thiol-ene gel coating could be easily controlled by adjusting visible light exposure time, eosin-Y concentration initially loaded in the core gel, or macromer concentration in the coating solution. The major benefits of this interfacial thiol-ene coating system include its simplicity and cytocompatibility. The formation of thiol-ene hydrogels and coatings neither requires nor generates any cytotoxic components. This new gelation chemistry may have great utilities in controlled release of multiple sensitive growth factors and encapsulation of multiple cell types for tissue regeneration.

Visible-Light-Initiated Thiol–Acrylate Photopolymerization of Heparin-Based Hydrogels

“…29,47,48 Indeed, the 11 motivation for using (PLL-HA) 2 -(GMA-Chi) treated substrates is to pave the way to selectively retrieve cell-12 laden microgels, which can then be used as tissue building blocks in a bottom-up approach to assemble full 13 tissue constructs. 49 14 We monitored hydrogel formation using a custom optical rheometer with the ability to perform 15 simultaneous irradiation and rheological measurements ( Figure S1). During oscillatory shear with a parallel 16 plate geometry, the hydrogel precursor solution was irradiated with green light at 5 mW/cm 2 for 2.5 minutes.…”

Improving gelation efficiency and cytocompatibility of visible light polymerized thiol-norbornene hydrogels via addition of soluble tyrosine

“…The visible light crosslinked thiol-norbornene hydrogels were normally pink to red in color due to the presence of eosin-Y [53]. However, the addition of soluble tyrosine appeared to quench the redness of hydrogels in a dose-dependent manner ( Figure 5A).…”

Thiol–norbornene photoclick hydrogels for tissue engineering applications

“…38-40 The mechanism of visible light initiated thiol-norbornene reaction is similar to that of the UV-based system, except that a type II (non-cleavage type) photoinitiator (e.g., eosin-Y, rose bengal) is used. Upon visible light (400 nm < λ < 700 nm) exposure, eosin-Y is excited, causing the abstraction of hydrogen from a co-initiator and the generation of secondary radicals.…”