Cross-linked networks of hydrophilic polymers, or hydrogels, have garnered considerable interest as tissue engineering scaffolds since their water content and softness mimics the extra-cellular matrix.1 In the clinic, hydrogels are used for the treatment of macular degeneration, back pain, cartilage defects, and myocardial infarctions. While a range of cross-linking strategies exist, techniques that allow hydrogels to be injected as low viscosity solutions and then gelled in vivo are desirable. These injectable systems allow for minimally invasive implantation, reducing procedural sophistication and improving patient comfort. Previously, researchers used radical photo-polymerization for this purpose by curing injected solutions of acrylated oligomers and photo-initiators using light transmitted through the skin.2 Unfortunately, the phenyl ketone and eosin initiators commonly used limit the curing depth to just a few millimeters, because the wavelengths required for their activation are readily absorbed by chromophores in the skin. However, light from 600-1000 nm penetrates tissue effectively making the development of a long wavelength photo-initiator essential for curing injected gels deeper and more consistently between skin types. Our lab recently reported the tuned photo-cleavage of cob(III)alamin’s Co-C bond into the near infrared through direct excitation of a covalently attached infrared fluorophore.3 Normally, green light photolysis of simple alkyl cobalamins yields an alkyl radical from homolytic bond cleavage. Due to this, we reasoned that photolysis of an alkyl cobalamin modified with a red absorbing fluorophore could be a useful radical source in photo-polymerizations utilizing tissue penetrating light. In the current study, development of a cobalamin based, red light activated photo-initiator will be discussed. We will demonstrate that successful radical production and subsequent gelation of cell carrying hydrogels proceeds at 660 nm with high monomer conversions. Photolysis and gelation will also be shown to occur when initiated “trans-dermally” through an optical model of tissue. References 1. Mawad, D.; Boughton, E.; Boughton, P.; Lauto, A. Curr. Pharm. Des. 2012, 18, 2558-2575. 2. a) Hillel, A et al. Sci. Transl. Med. 2011, 3, 1-12. b) Elisseeff, J.; Anseth, K.; Sims, D.; McIntosh, W.; Randolph, M.; Langer, R. PNAS 1999, 96, 3104-3107. 3. Shell, T.; Shell, J.; Rodgers, Z.; Lawrence, D. Angew. Chemie Int. Ed. 2014, 126, 894-897.

Cobalamin-fluorophore based photoinitiators for hydrogel curing with tissue penetrating light

249th National Meeting (2015)

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