Micro- to Nano-scale Structure and Drug Release Behavior of Solutions and Hydrogels of Poly (lactide)-Poly (ethylene oxi
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0897-J04-03.1
Micro- to Nano-scale Structure and Drug Release Behavior of Solutions and Hydrogels of Poly (lactide)-Poly (ethylene oxide)-Poly (lactide) Triblock Copolymers Sarvesh K. Agrawal1, Naomi Sanabria-DeLong2, Pete R. Jemian3, Jeannine M. Coburn1, Gregory N. Tew2, Surita R. Bhatia1 1 Department of Chemical Engineering, University of Massachusetts, Amherst, 686 North Pleasant Street, Amherst, MA 01003, 2Department of Polymer Science and Engineering, University of Massachusetts, Amherst, 120 Governors Drive, Amherst, MA, 01003 and 3 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA ABSTRACT We have performed for the first time a complete structural characterization of PLA-PEO-PLA in the solution and hydrogel states. Previous studies on hydrogels of these polymers have shown that these gels have excellent mechanical properties suitable for possible application in tissue engineering and drug delivery. We have performed SANS, USAXS and confocal microscopy to relate the change in micro to nano scale self-assembled structure of these polymers in aqueous solution with changes in the block length and stereospecificity of the PLA block. A significant difference in structure and association behavior was seen between the polymers made from amorphous D/L-lactide as compared to those with crystalline L lactide blocks. In the former case spherical micelles were seen to form whereas the latter forms nonspherical polydisperse micellar assemblies. Both polymers form an associative network structure at higher concentrations, leading to gelation. USAXS and confocal microscopy show the presence of large-scale fractal aggregates in the hydrogels of these polymers. The fractal structure was denser for the L lactide series polymers as compared to the D/L-lactide series polymers. These results show that we can tune the microstructure and thereby the mechanical strength of these gels depending upon the specific application we need it for. We also show profiles for release of hydrophobic drug sulindac from 5 weight% solutions of these polymers in phosphate buffer saline. The profiles follows an almost zero order release behavior that continues slowly and steadily over several days and is again found to be strongly dependent on the crystallinity and molecular weight of the PLA block. INTRODUCTION Copolymers based on poly (lactide) (PLA) and poly (ethylene oxide) (PEO) have been extensively studied for various biomedical applications1-7. These materials are known to form hydrogels of varying weight %, depending on the exact architecture, with transitions near body temperature8,9. In our group, we recently showed that PLLA-PEO-PLLA triblocks form stiff hydrogels with elastic modulus comparable to several native soft tissues10. Also the elastic modulus could be easily modified by modifying the length of the PLA block. Despite the widespread interest in these polymers a detailed structural characterization of these materials in solution and gel state has not been performed. In
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