Showing papers by "Adam M. Rawlett published in 2010"

Surface-modified nanofibrous biomaterial bridge for the enhancement and control of neurite outgrowth

Abstract: Biomaterial bridges constructed from electrospun fibers offer a promising alternative to traditional nerve tissue regeneration substrates. Aligned and unaligned polycaprolactone (PCL) electrospun fibers were prepared and functionalized with the extracellular matrix proteins collagen and laminin using covalent and physical adsorption attachment chemistries. The effect of the protein modified and native PCL nanofiber scaffolds on cell proliferation, neurite outgrowth rate, and orientation was examined with neuronlike PC12 cells. All protein modified scaffolds showed enhanced cellular adhesion and neurite outgrowth compared to unmodified PCL scaffolds. Neurite orientation was found to be in near perfect alignment with the fiber axis for cells grown on aligned fibers, with difference angles of less than 7o from the fiber axis, regardless of the surface chemistry. The bioavailability of PCL fibers with covalently attached laminin was found to be identical to that of PCL fibers with physically adsorbed laminin, indicating that the covalent chemistry did not change the protein conformation into a less active form and the covalent attachment of protein is a suitable method for enhancing the biocompatibility of tissue engineering scaffolds. a) Electronic mail: nicole.zander@arl.army.mil

Methods for removal of residual catalyst from polymers prepared by ring opening metathesis polymerization

Abstract: Methods for removing the residual Grubbs' third generation catalyst from polymers prepared by ring opening metathesis polymerization are reported. Two strategies were investigated for reduction of the residual catalyst in the final polymer product. The first strategy involved the use of heterogeneous functionalized particles to scavenge the catalyst from the solution. Filtration of the particles followed by precipitation produced polymers with 10–60 ppm residual catalyst, depending on the type of particle used, surface functional groups, and number of equivalents. The second strategy used small organic molecules that could coordinate to the metal species and modify the solubility of the catalyst, facilitating partitioning of the catalyst into the precipitation solvent. Several types of molecules with varied functionality reduced the residual catalyst level to 30–120 ppm, depending on the loading. Hydrogenation of the polymer backbone followed by precipitation lowered the residual Ru content from 195 ppm to 10 ppm, suggesting that the difficulty of completely removing the catalyst could be a result of coordination of the metal species to the double bonds in the polymer backbone. Reducing the amount of trace catalyst significantly improved the oxidative stability of the polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Thermal and FTIR Characterization of Poly (4-vinylpyridine) Crosslinked with Metal Salts

Abstract: : We investigated the physical properties and degree of crosslinking of poly (4-vinylpyridine) (P4VP) blended with transition metal salts using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) The glass transition temperature (Tg) of the blends increased significantly upon addition of zinc (Zn) and copper (II) (Cu) salts Tg enhancement was found to be highly dependent upon the type and loading of the metal salt A maximum increase of 70 degrees C was observed at 025 molar equivalents of Zn cation Ash content from TGA was highest for the 025 zinc salt loading, indicating that the maximum amount of metal ion was incorporated into the polymer at this concentration Fourier transform infrared spectroscopy (FTIR) provided confirmation that transition metal coordination between the Zn cation and the pyridine nitrogens occured, and allowed for the quantification of pyridine binding

High-Voltage Poling of Bulk Guest-Host Polymers

Abstract: We describe for the first time the fabrication and poling of a 700 μm thick bulk piece ofpolymethylmethacrylate (PMMA) doped with various concentrations of Disperse Red 1 (DR1). Maker fringe analysis demonstrates that poling fields of 57 V/μm to 71 V/μm induce substantial ordering of the DR1 chromophores, resulting in birefringence and significant d 33 and r 33 values. The poling of thick sections of guest-host polymers will have applications for a range of electro-optic applications, including modulators and terahertz generation and detection.