Synthesis and Characterization of Highly

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SYNTHESIS AND CHARACTERIZATION OF HIGHLY CROSSLINKED HYALURONAN HYDROGELS Newell R. Washburn1, Sidi A. Bencherif1, Abiraman Srinivasan2, Jeffrey O. Hollinger2, Ferenc Horkay3, Krzysztof Matyjaszewski1 Departments of 1Chemistry and 2Biomedical Engineering Carnegie Mellon University, Pittsburgh, PA 15213 3 Laboratory of Integrative and Medical Biophysics National Institutes of Health, NICHD 13 South Drive, Bethesda, MD 20892 Introduction Methacrylation of hyaluronic acid (HA) with glycidyl methacrylate (GM) is a strategy for producing photocross-linkable macromers to generate biodegradable hydrogels by in-situ injection and light-induced polymerization. Facile synthesis and characterization by 1H NMR spectroscopy of a series of photopolymerizable macromers based on HA-glycidyl methacrylate (HAGM) conjugates with various degrees of methacrylation (DM) ranging from 14% to 90% are described. Aqueous solutions of HAGM were photopolymerized to yield hydrogels with high vinyl group conversions up to 99% after 10 min exposure under ultraviolet light (UV). Uniaxial compression and volumetric swelling measurements showed that HAGM hydrogels were mechanically robust with shear moduli ranging from 17 kPa to 95 kPa, with a broad range of swelling ratios. Preliminary in-vitro cell culture studies showed that these HA-based hydrogels were cytocompatible, and the introduction of the GRGDS peptide promoted adhesion and proliferation of cells to confluence after 5 d of incubation. Densely cross-linked hydrogels with a DM of 60% have been shown to be stable in culture while maintaining cytocompability and bioactivity. These highly cross-linked HAGM hydrogel systems with improved mechanical properties appear to be very attractive for biomedical applications such as drug delivery systems and tissue engineering and could expand the range of properties of crosslinked hyaluronan [1]. Experimental Materials. Hyaluronic acid (~ 1.6x106 g/mol), glycidyl methacrylate (GM), and triethylamine (TEA) were purchased from Sigma-Aldrich and used as received. Acryloyl-PEG-N-hydroxysuccinimide (ACRL-PEG-NHS, 3400 g/mol) was purchased from Nektar Therapeutics. GRGDS peptide was purchased from Bachem Bioscience Inc. Photoinitiator Irgacure 2959 (I2959) was obtained from Ciba Specialty Chemicals and used as received. All other chemicals were of reagent grade and were used without further purification. C2C12 mouse myoblast cells were obtained from American Type Culture Collection (Manassas, VA) and cultured in DMEM supplemented with fetal bovine serum and penicillin/streptomycin, all obtained from Invitrogen (Carlsbad, CA). Live/Dead® Viability/Cytotoxicity Kit were purchased from Invitrogen – Molecular Probes, Inc. (Eugene, OR). Instrumentation. High-resolution, 300 MHz proton NMR spectra were taken on a Bruker Avance 300 spectrometer. Deuterium oxide was used as solvent, and the polymer concentrations were varied between 0.5 % and 3 % by mass fraction. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was performed on a PerSeptive Biosystems Voyager STR in reflectron mode. The MALDI matrix, dihydrobenzoic acid (DHB), and the macromer were dissolved in 1 mL of mix solvent methanol/water (50:50). All MALDI samples were hand spotted on the target. Uniaxial compression measurements were used on hydrogels to assess the mechanical strength. The shear modulus was determined using uniaxial compression measurements performed by a TA.XT21 HR texture analyzer (Stable Micro Systems, UK). This apparatus measures the deformation ( 0.001 mm) as a function of an applied force ( 0.01 N). Cylindrical hydrogels (height = diameter = 5 mm) were deformed (at constant volume) between two parallel glass plates. Synthesis of Methacrylated Hyaluronic Acid. Photopolymerizable methacrylate groups were added to HA to yield HA-glycidyl methacrylate (HAGM) conjugates. Briefly, we prepared a series of HAGM polymers by treating a 0.5% w/v solution of...
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