Condensed-Matter Physics & Materials Science Seminar

"Using Stereochemistry to Control Structure and Rheology: Teaching Old Biomaterials New Tricks"

Presented by Surita Bhatia, University of Massachusetts Amherst

Monday, May 7, 2007, 10:00 am — Small Seminar Room, Bldg. 510

Soft biomaterials derived from amphiphilic polymers have received considerable attention in the last decade. The ability to tune the modulus of implantable materials to match that of native tissue is crucial for scaffolding applications; unfortunately, a significant limitation of current polymeric biomaterials is a lack of mechanical robustness and a low elastic modulus. I will discuss a collaborative effort to address these issues using hydrogels of poly(lactic acid)-poly(ethylene oxide)-poly(lactic acid) (PLA-PEO-PLA) triblock copolymers. These materials form associative network gels with the PLA domains serving as network junctions. Our work distinguishes itself from previous studies through controlled stereochemistry of the PLA blocks and crystallinity of the junction points. We can create nanoscale crystalline junctions through use of copolymers in which the PLA block is poly(L-lactic acid) (PLLA), or amorphous junctions through copolymers in which the PLA blocks contain a racemic mixture of D-lactic acid and L-lactic acid (PRLA). The crystalline junctions in the PLLA-based gels cause a significant increase in the elastic modulus over the PRLA gels, allowing us to create gels with elastic moduli that are an order of magnitude higher than previously reported with PLA-based associative gels. The modulus is also very sensitive to PLA block length and can be easily tuned to match the moduli of native tissue such as cartilage. We have also shown that crystalline PLA domains lead to a microporous gel structure, which is useful for tissue engineering applications, and that PLA block length and stereochemistry can be used to control the drug release characteristics of our systems. Finally, we have incorporated inorganic nanoparticles into these gels and have demonstrated that this enhances the elastic modulus and improves viability of encapsulated chondrocytes.


Biosketch:

Surita Bhatia’s research interests lie in the area of complex fluids, polymeric

Hosted by: James Misewich

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