Kevin Henderson Graduate Student B. S. Chemistry, 2006, UNC- Chapel Hill Cook Hall, 2057, (847)-491-7199 kevin-henderson at northwestern dot edu

Strengthening of Hydrogels Via Triblock Copolymer Self-Assembly 

An estimated 12.1% of Americans (21 million people) age 25 and older are afflicted with osteoarthritis, a degenerative joint disease most often manifested in the wearing of cartilage1. In 2001, 165,000 hip joints and 326,0002 knee joints were replaced in America with the majority of these cases attributed to osteoarthritis. The average lifetime of these replacements is between 10 to 15 years1. The development of cheaper, longer-lasting joint replacements promises not only extended relief to osteoarthritis patients, but also millions of dollars in savings to Medicare, the Department of Veterans Affairs, and insurance companies. The long-term vision of my project is the generation of high-strength artificial cartilage for use in cartilage replacement surgery.

Recent advances in double-network hydrogels enabled researchers to synthesize materials of high mechanical strength for possible applications as artificial cartilage, tendons, or ligaments3, 4. Double-network hydrogels uniquely afford an ability to combine a densely crosslinked network having a high Young’s modulus with a second, loosely crosslinked network that enhances elastic character. Gong, et al.3 demonstrated that the optimal strengths of these materials are achieved when the second network has a crosslinking density between 0-0.1 mol%. A representation of the strength of such a gel under high compressive stress is shown in Figure 1.  

Self-assembled triblock copolymers could serve to replace the loosely crosslinked network in double-network hydrogels. Figure 2 schematically depicts the appearance of this network on a molecular level: the green grid pattern represents the tightly bound, high modulus network while the red circles represent the spherical aggregations of end blocks connected by a solvated midblock.

I am working to optimize the double network hydrogel by synthesizing different triblock copolymers and controlling network ratios, molecular weights, and water concentration of resulting the resulting hydrogels.  I am also studying the effect of electrostatic interactions on mechanical properties by comparing charged versus uncharged systems. 

References:
1. Gong, J. P., Katsuyama, Y., Kurokawa, T., Osada, Y., Double-Network Hydrogels with Extremely High Mechanical Strength. Advanced Materials 2003, 15, (14), 1155-1158.
2. Tanaka, Y., Gong, J.P., Osada, Y., Novel hydrogels with excellent mechanical performance. Progress in Polymer Science 2004, 30, 1-9.
3. Santin, M., Huang, S.J., Iannance, S., Ambrosio, L., NIcolais, L., Peluso, G., Synthesis and characterization of a new interpenetrated poly(2-hydroxyethylmethacrylate)-gelatin composite polymer. Biomaterials 1996, 17, (15), 1459-1467.
4. Guvendiren, M., Shull, K.R., Self-Assembly of Acrylic Triblock Hydrogels by Vapor Phase Solvent Exchange. Soft Materials. submitted.