PEG-POSS Hybrid Polyurethanes: Mechanically Robust Nanostructured Hydrogels
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1060-LL03-10
PEG-POSS Hybrid Polyurethanes: Mechanically Robust Nanostructured Hydrogels Jian Wu1, Qing Ge1, and Patrick T Mather1,2 1 Chemical Engineering Department,and Polymer Program,Institute of Materials Sciece, University of Connecticut, Storrs, CT, 06269 2 Syracuse Biomaterials Institute and Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, NY, 13244 ABSTRACT A series of unique hybrid thermoplastic polyurethanes (TPUs) was synthesized using PEG as soft segment and incorporating an isobutyl-functionalized POSS diol (TMP POSS diol) in the hard segment. The molecular weight of PEG was systematically varied to include 10, 20, and 35 kDa, while the mole ratio of POSS diol (as chain extender) to PEG was in range from 3:1 to 8:1 with samples featuring a PEG molecular weight of 10 kDa. The diisocyanate employed for TPU polymerization was 4,4’-methylenebis(phenyl-isocyanate) (MDI). We found that the hydrophobic hard segments (POSS) can form crystalline structures driven by micro-phase separation, this being due to significant thermodynamic incompatibility between POSS and ethylene oxide units. The POSS nano-crystals thus formed serve as physical crosslinking sites within an inorganic-organic hybrid network. This affords a new hybrid organic-inorganic hydrogel in the water-swollen state. The equilibrium swelling ratio increased monotonically with PEG loading and ranged from ~70% to ~600%. The shear modulus, G, of the hybrid hydrogels was observed to span 0.3 < G < 4.0 MPa – values commonly found for elastomers, not hydrogels. Indeed, the hydrogel stiffness can be finely tuned through the POSS:PEG molar ratio, as this predictably controls swelling in water. INTRODUCTION Hydrogels are well-known and important in biomedical applications due to their natural hydrophilicity and biocompatibility nature.1 However, hydrogels are usually mechanically weak.2,3 So, a prominent challenge to biomaterials scientists exists to precisely, easily and costeffectively increase and control the mechanical properties of hydrogels. Being biocompatible, nontoxic, non-immunogenicity and non-antigenic, poly(ethylene glycol) (PEG) is one of the most widely investigated synthetic polymers used for designing hydrogels with desired properties in the biotechnology and biomedical applications.4,5 PEG-based hydrogels can be obtained either by covalent crosslinking4,6 or by physical crosslinking through the entanglement of PEG chains, or intermolecular complexation by hydrogen bonds between PEG and other polymers.7 In contrast to covalent hydrogel networks, physical networks feature advantages of being reversible, injectable, and processible. Polyhedral oligosilsesquioxane (POSSTM) is a class of hybrid molecule with an inorganic (silicon-oxygen) core and eight variable organic vertex groups. When covalently incorporated with hydrophilic PEG, hydrophobic POSS macromers can be expected to aggregate and crystallize to form nanoscale crystals induced by micro-phase separation due to thermodynamic incompatibility between hy
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