Terrence G. Vargo

Electrically charged polymeric substrates enhance nerve fibre outgrowth In vitro

The physical, chemical and electrical properties of synthetic guidance devices are known to influence nerve regeneration in vivo. In the present study, neurons were cultured directly on electrically charged polymer growth substrates to determine if local electrical charges enhance nerve fibre outgrowth in vitro. Piezoelectric polymers such as polyvinylidene fluoride (PVDF) generate transient surface charges under minute mechanical strain. Mouse neuroblastoma (Nb2a) cells were cultured directly on electrically poled (i.e. piezoelectric) and unpoled (i.e. nonpiezoelectric) PVDF substrates in serum-free and serum-containing media. Nerve fibre outgrowth was analysed 24, 48, 72 and 96 h after plating. Piezoelectric PVDF substrates generated 2-3 mV at 1200 Hz when placed on standard incubator shelves and unpoled PVDF substrates showed no output. Nb2a cells grown on piezoelectric substrates exhibited significantly greater levels of process outgrowth and neurite lengths at all time periods for both media conditions. Detailed surface characterization of PVDF substrates using electron spectroscopy for chemical analysis (ESCA) and a comprehensive wettability profile revealed that poled and unpoled PVDF was chemically indistinguishable and showed similar surface wettabilities and adhesive properties. Therefore, we conclude that enhanced process outgrowth was induced by the films piezoelectric output, making poled PVDF a unique biomaterial for which cell/polymer interactions are mediated predominantly through bulk electrical properties rather than surface properties.

Patterned neuronal attachment and outgrowth on surface modified, electrically charged fluoropolymer substrates

Fluorinated ethylenepropylene copolymer (FEP) and polyvinylidene fluoride (PVDF) can generate static and transient electrical charges, respectively, after bulk molecular rearrangements induced by electrical charging techniques. Neurons cultured on electrically active FEP and PVDF show increased levels of nerve fiber outgrowth compared to electrically neutral material. The purpose of the present study was to determine if the addition of charged surface groups to the surfaces of FEP and PVDF would modify the influence of bulk electrical charges on cultured neurons. Mouse neuroblastoma (Nb2a) cells were cultured on electrically charged and uncharged FEP and PVDF substrates with covalently modified surfaces containing hydroxyl (OH) and amine (NH2) groups. Surface chemical modification was performed on the entire surface or in discrete striped regions. Nb2a cells cultured on electrically active FEP and PVDF showed greater levels of differentiation than cells on electrically neutral substrates. The presence of NH2 groups attenuated these responses in serum-containing media. Cells attached to NH2 rich surfaces generally displayed a flatter morphology and tended to remain attached for longer time periods. Cells cultured on stripe-modified substrates in serum-containing media showed a strong preferential attachment to modified regions, especially on NH2 stripes. In summary, bulk electrical charges are more important than surface charges in stimulating Nb2a cell differentiation. Surface groups serve to modulate neuronal morphology and confer specific attachment promoting properties in serum-containing media. The development of an optimal neuronal regeneration template may require the incorporation of specific bulk and surface properties.

Adhesive Electroless Metallization of Fluoropolymeric Substrates

A process for producing patterned metal deposits on fluoropolymeric substrates is described. A metal ion—chelating organosilane is chemisorbed by self-assembly onto a fluoropolymer surface after radio-frequency glow discharge plasma surface hydroxylation. Positional modulation of the surface hydrophobicity is illustrated by wetting. The silane covalently binds an aqueous palladium catalyst and subsequent electroless deposition yields homogeneous or patterned metal deposits that exhibit excellent adhesion to the fluoropolymer.

Development of Ti Kα x radiation for electron spectroscopy for chemical analysis of polymer surfaces

It has been shown previously that implementing x‐ray sources of different energies for electron spectroscopy for chemical analysis (ESCA) of various materials can be useful. In this study ESCA with Ti Kα x radiation as the excitation source is explored for the analysis of some common technical polymers. The investigation of these polymers is used to illustrate the usefulness of a Ti Kα x‐ray source with respect to increasing the depth of ESCA analysis as well as its use in the analysis of atoms with high‐binding‐energy core level (1s) electrons, which are normally inaccessible to ESCA experiments using Mg Kα or Al Kα x radiation. Through the use of polymer standards a list of calculated sensitivity factors for C, N, O, F, Si, P, S, and Cl is derived from ESCA experiments utilizing Mg and Ti Kα x radiation. Also presented are corrected photoelectron binding energies, x‐ray excited Auger kinetic energies, and modified Auger parameters (α’) which are accessible by Ti Kα radiation. Discussion of Ti Kα x‐ray s...

A Surface Spectroscopic and Wettability Study of a Segmented Block Copolymer Poly(etherurethane)

In this study, a multitechnique surface analytical approach is used to provide comprehensive surface molecular, structural, and thermodynamic information of a segmented Poly(etherurethane) (PEU) block copolymer (Texin-985). Through sample preparation methods described in this paper, a clean stable PEU material is provided. Subsequent analysis employing Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance Fourier Transform Infrared (ATR/FT-IR), and Comprehensive Wettability Profiling provides a comprehensive molecular structure of the topmost interfacial region, ranging through a bulk analysis probing depths in the micron range. Also featured in this paper are results obtained through the implementation of a higher-energy x-radiation source for ESCA analysis. Through the use of angle-dependent ESCA utilizing Mg Kα x-radiation, used in conjunction with a Ti Kα x-radiation source, a hard- and soft-component depth profile expanded from a conventional profile of ∼20 Å to 100 Å (using a Mg anode source) to ∼20 Å to 200 Å is obtained. Due to the greater depth of analysis, we also obtain atomic ratios (using calculated sensitivity factors) which are closer to true bulk atomic percentages of Texin-985 (PEU).