Light-mediated chemistries serve as invaluable tools for the formation and modulation of material properties when and where desired. Providing exquisite control of reaction rate often under mild conditions, such approaches are particularly powerful for probing and directing biological systems. Here, we highlight two biologically-relevant applications of photochemistry: 1) imparting three-dimensional structure to peptides via cyclization followed by orthogonal conjugation for cell targeting and 2) controlling the crosslink density and modulus of materials initially and temporally with the rate of photopolymerization and a dual cure approach (Figure 1). In the first application, we established the use of sequential orthogonal click reactions, specifically a photoinitiated thiol-ene and strain promoted azide-alkyne cycloaddition (SPAAC), for the facile synthesis of a functionalized cyclic peptide (i.e., azido cyclic RGD) and subsequent conjugation to hydrogels and small molecules with application in 3D cell culture and in cell targeting, respectively. In the second application, we established a rate-based, dual cure approach for controlling the crosslink density and elasticity of materials. Specifically, hydrogels first were formed using visible light (455 nm LED) with the photoinitiator lithium acylphosphinate to initiate the polymerization of bioinert multi-arm poly(ethylene glycol) norbornene with linear dithiol. This photopolymerization using thiol-ene click chemistry with was less efficient with 455 nm light than with typical long wavelength UV (365 nm); yet, the slower rate of polymerization allowed facile manipulation of the mechanical properties of the resulting matrix (E ~ 1 – 20+ kPa), relevant for mimicking a variety of soft tissues. Further, dangling end group present as defects within these networks were exploited in a second cure to increase crosslink density temporally, ‘stiffening’ these synthetic matrices. Broadly, these approaches highlight the utility of using light for controlling conjugation reactions and related material properties of relevance for the design of biomaterial-based tools to probe and direct the function and fate of cells in culture and in the body.

Deploying light-mediated chemistries for the formation and modulation of biomaterial properties

2019 Spring National Meeting

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