Russell J. Composto

The inhibition of Staphylococcus epidermidis biofilm formation by vancomycin-modified titanium alloy and implications for the treatment of periprosthetic infection.

Peri-prosthetic infections are notoriously difficult to treat as the biomaterial implant is ideal for bacterial adhesion and biofilm formation, resulting in decreased antibiotic sensitivity. Previously, we reported that vancomycin covalently attached to a Ti alloy surface (Vanc-Ti) could prevent bacterial colonization. Herein we examine the effect of this Vanc-Ti surface on Staphylococci epidermidis, a Gram-positive organism prevalent in orthopaedic infections. By direct colony counting and fluorescent visualization of live bacteria, S. epidermidis colonization was significantly inhibited on Vanc-Ti implants. In contrast, the gram-negative organism Escherichia coli readily colonized the Vanc-Ti rod, suggesting retention of antibiotic specificity. By histochemical and SEM analysis, Vanc-Ti prevented S. epidermidis biofilm formation, even in the presence of serum. Furthermore, when challenged multiple times with S. epidermidis, Vanc-Ti rods resisted bacterial colonization. Finally, when S. epidermidis was continuously cultured in the presence of Vanc-Ti, the bacteria maintained a Vanc sensitivity equivalent to the parent strain. These findings indicate that antibiotic derivatization of implants can result in a surface that can resist bacterial colonization. This technology holds great promise for the prevention and treatment of periprosthetic infections.

Patchy and Multiregion Janus Particles with Tunable Optical Properties

Multiregion and patchy optically active Janus particles were synthesized via a hierarchical self-assembly process. Gold nanoparticles were assembled on the top surfaces of nano- and submicrometer silica particles, which were selectively protected on their bottom surfaces by covalent attachment to a copolymer film. The morphologies of the gold particle layer, and the resulting optical properties of the Janus particles, were tuned by changing the surface energy between the silica and gold particles, followed by annealing.

Nanorod Self-Assembly for Tuning Optical Absorption

Metallic nanoparticles that absorb and concentrate light are leading to greater efficiencies in nanophotonic devices. By confining gold nanorods (Au NRs) in a polymer film, we can control their spacing and orientation and, in turn, the absorption and polarization characteristics of the nanocomposite. In this study, we systematically increase the volume fraction of Au NRs (φrod) (aspect ratio v=3.3) while maintaining a uniform dispersion. As φrod increases from 1 to 16 vol %, the spacing between rods decreases from 120 to 20 nm and scales as φrod φ0.4. Simultaneously, the local 2D orientational order parameter increases linearly with φrod, although the rods are globally isotropic. The Au NR dispersion is found to depend on the enthalpic interactions between poly(ethylene glycol) brush grafted to the Au NRs and the poly(methyl methacrylate) matrix chains. Furthermore, the plasmon resonance exhibits a red shift with increasing φrod, and coupling is observed for separations up to 70 nm. Because NR spacing and orientation can be finely controlled using polymer matrix, these films are ideally suited for understanding fundamental behavior (e.g., plasmon coupling) as well as practical devices (e.g., solar cells).

MUTUAL DIFFUSION IN THE MISCIBLE POLYMER BLEND: POLYSTYRENE:POLY (XYLENYL ETHER)

We have used forward recoil spectrometry to measure the mutual diffusion and tracer diffusion coefficients, D and D*, in the miscible polymer blend of deuterated polystyrene (d-PS):poly(xylenyl ether) (PXE). Using the “fast theory” of mutual diffusion, D is related to the D*, degree of polymerization N, and volume fraction φ of the individual blend components by, D = 2 φ (1-φ) [D* PS N PS + φD* PXE N PXE ](χ S -χ), where χ and χs are tne Flory interaction parameter of the blend and its value at the spinodal. From the measured values of the D*’s and D at a volume fraction φ=0.55 of d-PS, the interaction parameter χ=0.112-62/T was estimated as a function of temperature T(K). At low T, D was much larger than D*’s due to the large negative value of χ whereas at high T, D becomes less than the D*’s as χ becomes positive (thermodynamic slowing down). Similar measurements show that χ is not markedly composition-dependent in the d-PS:PXE blends.

Micropatterning of three-dimensional electrospun polyurethane vascular grafts.

The uniform alignment of endothelial cells inside small-diameter synthetic grafts can be directed by surface topographies such as microgrooves and microfibers to recapitulate the flow-induced elongation and alignment of natural endothelium. These surface micropatterns may also promote directional migration and potentially improve anastomotic ingrowth of endothelial cells inside the synthetic grafts. In this paper, we developed electrospinning and spin casting techniques to pattern the luminal surface of small-diameter polyurethane (PU) grafts with microfibers and microgrooves, respectively, and evaluated endothelial cell orientation on these surface micropatterns. Tracks of circumferentially oriented microfibers were generated by electrospinning PU onto a mandrel rotated at high velocity, whereas longitudinal tracks of microgrooves were generated by spin casting PU over a rotating poly(dimethylsiloxane) mold. We found that both PU grafts possessed longitudinal Youngs moduli in the range of 0.43 ± 0.04 to 2.00 ± 0.40 MPa, comparable with values obtained from native artery. Endothelial cells seeded onto the grafts formed confluent monolayers with individual cells exhibiting elongated morphology parallel to the micropatterns. The cells were phenotypically similar to natural endothelium as assessed by the expression of the endothelial cell-specific marker, vascular endothelial cell cadherin. In addition, the cells were also responsive to stimulation with the pro-inflammatory cytokine tumor necrosis factor-α as assessed by the inducible expression of intercellular adhesion molecule-1. These results demonstrate that our micropatterned PU grafts possessed longitudinal Youngs moduli in the same range as native vascular tissue and were capable of promoting the formation of aligned and cytokine-responsive endothelial monolayers.

The Form of the Enriched Surface Layer in Polymer Blends

The concentration profile at the surface in blends of deuterated and protonated polystyrene (d-PS and PS) is inferred from measurements of neutron reflectivity and secondary-ion mass spectrometry, using constraints provided by forward recoil spectrometry and X-ray reflectometry results on the same samples. The surface is enriched in d-PS, the volume fraction and the decay length of which are in good agreement with the predictions of mean-field theory but the form of the profile shows small, but statistically significant, deviations from that predicted by the theory.

Thin film polymer blends undergoing phase separation and wetting: Identification of early, intermediate, and late stages

Using forward recoil spectrometry and atomic force microscopy, the phase evolution of a critical blend thin film of deuterated poly(methyl methacrylate) (dPMMA) and poly(styrene-ran-acrylonitrile) (SAN) is found to develop by three distinct stages. During the early stage, dPMMA-rich wetting layers rapidly grow at the air/polymer and polymer/substrate interfaces. A hydrodynamic flow mechanism is proposed based on the scaling of the layer thickness with time, t−1, and the direct observation of an interconnected, bicontinuous morphology across the depletion zone. The lateral wave number of this morphology grows rapidly as t−1 but slows down to t−1/3 when the phase size approaches the film thickness. During the intermediate stage, the wetting layer thins and, concurrently, dPMMA-rich domains spanning the SAN-rich middle grow as t−0.41 in good agreement with an interfacially driven growth model. During the late stage, these capillary fluctuations eventually cause spontaneous rupturing of the middle layer resul...

Application of ion scattering techniques to characterize polymer surfaces and interfaces

Ion beam analysis techniques, particularly elastic recoil detection (ERD) also known as forward recoil spectrometry (Frcs) has proven to be a value tool to investigate polymer surfaces and interfaces. A review of ERD, related techniques and their impact on the field of polymer science is presented. The physics of the technique is described as well as the underlying principles of the interaction of ions with matter. Methods for optimization of ERD for polymer systems are also introduced, specifically techniques to improve the depth resolution and sensitivity. Details of the experimental setup and requirements are also laid out. After a discussion of ERD, strategies for the subsequent data analysis are described. The review ends with the breakthroughs in polymer science that ERD enabled in polymer diffusion, surfaces, interfaces, critical phenomena, and polymer modification.

Nanogel Carrier Design for Targeted Drug Delivery.

Polymer-based nanogel formulations offer features attractive for drug delivery, including ease of synthesis, controllable swelling and viscoelasticity as well as drug loading and release characteristics, passive and active targeting, and the ability to formulate nanogel carriers that can respond to biological stimuli. These unique features and low toxicity make the nanogels a favorable option for vascular drug targeting. In this review, we address key chemical and biological aspects of nanogel drug carrier design. In particular, we highlight published studies of nanogel design, descriptions of nanogel functional characteristics and their behavior in biological models. These studies form a compendium of information that supports the scientific and clinical rationale for development of this carrier for targeted therapeutic interventions.

Tuning optical properties of gold nanorods in polymer films through thermal reshaping

The thermal reshaping of gold nanorods (NRs) in a poly(methyl methacrylate) (PMMA) nanocomposite film is investigated by UV-vis and TEM. To ensure dispersion, the NRs are modified with PEG brushes, and then dispersed in PMMA. Thermal annealing of the PMMA–NR film results in a blue shift of the longitudinal plasmon resonance, caused by a decrease in the length of the NR. The rate of the blue shift increases as temperature increases from 100 °C to 200 °C, and the longitudinal absorption peak approaches a constant value that scales linearly with temperature. We demonstrate a potential application by fabricating a device with a gradient in optical properties.