Increasing Cross-Linking Efficiency of Methacrylated Chondroitin Sulfate Hydrogels by Copolymerization with Oligo(Ethylene Glycol) Diacrylates
2013
Khanlari, Anahita | Detamore, Michael S. | Gehrke, Stevin H.
A simple method was developed for increasing the modulus of methacrylated chondroitin sulfate (MCS) hydrogels. Photopolymerized MCS gels are relatively soft with low cross-link density, but copolymerization of MCS with 0.5 to 2.0 wt % oligo(ethylene glycol) diacrylates (OEGDA) increased the moduli over an order of magnitude. The shear modulus of gels was amplified 2–25 times by increasing the methacrylation extent and copolymerizing with higher molar mass OEGDAs (up to 700 Da). In contrast, copolymerizing MCS with oligomers of ethylene glycol dimethacrylate (OEGDMA) reduced the moduli from that of MCS alone. The cross-linking appears to occur primarily by incorporation of methacrylate groups of different MCS molecules into common kinetic chains rather than by linking different kinetic chains together by EG linking chains since monoacrylate monomers enhanced cross-linking nearly as much as the diacrylates. The difference between the copolymerization behaviors of OEGDAs vs analogous OEGDMAs was hypothesized to be the result of differences in their reactivity ratios, as the latter suppressed copolymerization. The fracture strains of gels were ∼20% regardless of the extent of cross-linking, likely the consequence of the limited chain extensibility of chondroitin sulfate in water. The addition of modest amounts of low molecular weight monomers of appropriate reactivity is hypothesized to be a generally useful method to adjust the modulus of methacrylated polysaccharide gels to desired levels over a broad range.
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