Stephen H. Foulger

Host-derived loss of dentin matrix stiffness associated with solubilization of collagen.

Matrix metalloproteinases (MMPs) bound to dentin matrices are activated during adhesive bonding procedures and are thought to contribute to the progressive degradation of resin-dentin bonds over time. The purpose of this study was to evaluate the changes in mechanical, biochemical, and structural properties of demineralized dentin treated with or without chlorhexidine (CHX), a known MMP-inhibitor. After demineralizing dentin beams in EDTA or phosphoric acid (PA), the baseline modulus of elasticity (E) of each beam was measured by three-point flexure. Specimens were pretreated with water (control) or with 2% CHX (experimental) and then incubated in artificial saliva (AS) at 37 degrees C for 4 weeks. The E of each specimen was remeasured weekly and, the media was analyzed for solubilized dentin collagen at first and fourth week of incubation. Some specimens were processed for electron microscopy (TEM) immediately after demineralization and after 4 weeks of incubation. In EDTA and PA-demineralized specimens, the E of the control specimens fell (p < 0.05) after incubation in AS, whereas there were no changes in E of the CHX-pretreated specimens over time. More collagen was solubilized from PA-demineralized controls (p < 0.05) than from EDTA-demineralized matrices after 1 or 4 weeks. Less collagen (p < 0.05) was solubilized from CHX-pretreated specimens demineralized in EDTA compared with PA. TEM examination of control beams revealed that prolonged demineralization of dentin in 10% PA (12 h) did not denature the collagen fibrils.

Perfluorocyclobutyl Copolymers for Microphotonics

The copolymerization of aryl bis- and tris-trifluorovinyl other monomers aromatic perfluorocyclobutyl (PFCB) polymers, via thermally initiated stepgrowth cycloaddition chemistry. PFCB polymers and their copolymers enjoya unique combination of attributes well suited for applications in photonic technologies, such as broad tailorability of refractive indices and thermo-optic coefficients, low transmission losses as 1300 and 1550 nm, high thermal, mechanical, and optical stability, and excellent melt and solution processability. Planar PFCB structures lif can be processed by direct micro-transfer molding, which is a first step towards rapid soft-lithographic fabrication of polymer planar lightwave circuits. Copolymerization chemistry and processing parameters and characterization, including thermal (T g ≃120-350°C) and optical properties trefractive indices from 1.443 to 1.308 at 1550 nm, thermooptic coefficients dn/dT-7×10 - 5 K - 1 to -1.5×10 - 6 K - 1 ), birefringence (< 0.003), and temporal stability of refractive index, are described.

Effects of ethanol addition on the water sorption/solubility and percent conversion of comonomers in model dental adhesives

OBJECTIVES This study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents. METHODS Five methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm x 0.8 mm). Photo-activation was performed for 80s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy. RESULTS Water sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p<0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption (p>0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 (p<0.05). Despite the increased DC of ethanol-solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values. SIGNIFICANCE Negative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.

Multimodal multiplex spectroscopy using photonic crystals

Spatio-spectral transmission patterns induced on low coherence fields by disordered photonic crystals can be used to construct optical spectrometers. Experimental results suggest that 1-10 nm resolution multimodal spectrometers for diffuse source analysis may be constructed using a photonic crystal mounted on a focal plane array. The relative independence of spatial and spectral modal response in photonic crystals enables high efficiency spectral analysis of diffuse sources..

Preparation of poly(3,4-ethylenedioxythiophene)(PEDOT) coated silica core–shell particles and PEDOT hollow particles

Nanometre-sized PEDOT-silica core-shell particles were synthesized and self-assembled into crystalline colloidal arrays with a reflection peak in the visible region; these particles were also etched with hydrofluoric acid to produce hollow PEDOT particles.

Optical properties of perfluorocyclobutyl polymers

As the interest in utilizing fluoropolymers in a greater number of value-added photonic applications continues to grow, so does the necessity for accurate and broadband characterization of their optical properties. This paper provides the canonical optical properties of the refractive index and the extinction coefficient for two perfluorocyclobutyl-based polymers over the spectral range from approximately 0.13 μm to 33 μm, including their respective Sellmeier coefficients. In addition, the data are used to compare Sellmeier versus Cauchy fits to dispersion data in order to elucidate the potential pitfalls in computing system-level design criterion, such as bandwidth.

Inkjet-printed electrochromic devices utilizing polyaniline–silica and poly(3,4-ethylenedioxythiophene)–silica colloidal composite particles

Polyanline (PANI)–silica and poly(3,4-ethylenedioxythiophene) (PEDOT)–silica colloidal composite particles having a diameter of 200–300 nm were synthesized, then converted to intrinsically conducting polymer (ICP)-inks viasolvent exchange. These inks could be inkjet-printed on indium tin oxide-coated poly(ethylene terephthalate) films (ITO-PET film) using a commercial desktop inkjet printer. These PANI–silica or PEDOT–silica/ITO-PET assemblies were utilized as the active layer in electrochromic devices (ECDs). A number of devices were fabricated that exhibited 500 µm size patterning and utilized spatially controlled printing of the particles to allow for a dual image display. In addition, the PANI and PEDOT-based particles were blended into a single ICP ink that allowed for a wider absorption tuning range of the final ECD.

Electroluminescent colloidal inks for flexographic roll-to-roll printing

The academic and commercial interest in organic light-emitting devices is motivated in part by the potential of building devices utilizing simple and inexpensive fabrication routes, for example, commercial printing techniques. The focus on synthetically challenging small molecules and π-conjugated polymers for these devices is countered by the alternative of developing emissive materials that utilize an electroluminescent dye embedded in a hole and electron transporting host. In this effort, we exploit readily obtainable materials and simple fabrication routes to produce light-emitting colloidal particles, which in turn allows us to invoke the concept of a “particle device”. Specifically, we present colloidally based organic light emitting devices that can be designed to produce a range of colors by mixing together various ratios of red-, green-, and blue-emitting particles. These aqueous-based colloids are adaptable to form printing inks and may be utilized in fabricating devices through high-throughput commercial printing technologies.

Selective Imaging and Killing of Cancer Cells with Protein-Activated Near-Infrared Fluorescing Nanoparticles

We present a general approach for the selective imaging and killing of cancer cells using protein-activated near-infrared emitting and cytotoxic oxygen generating nanoparticles. Poly(propargyl acrylate) (PA) particles were surface modified through the copper-catalyzed azide/alkyne cycloaddition of azide-terminated indocyanine green (azICG), a near-infrared emitter, and poly(ethylene glycol) (azPEG) chains of various molecular weights. The placement of azICG onto the surface of the particles allowed for the chromophores to complex with bovine serum albumin when dispersed in PBS that resulted in an enhancement of the dye emission. In addition, the inclusion of azPEG with the chromophores onto the particle surface resulted in a synergistic ninefold enhancement of the fluorescence intensity, with azPEGs of increasing molecular weight amplifying the response. Human liver carcinoma cells (HepG2) overexpress albumin proteins and could be employed to activate the fluorescence of the nanoparticles. Preliminary PDT studies with HepG2 cells combined with the modified particles indicated that a minor exposure of 780 nm radiation resulted in a statistically significant reduction in cell growth.

Polymer microstructured fibers by one-step extrusion

For the first time to our knowledge, polymer-based microstructured fibers with complex cross-sections are directly produced via melt extrusion. Two principal types of fibers were fabricated: a microstructured fiber of a single polymer with a hexagonal array of air holes and a bicomponent fiber consisting of approximately 60 coaxial rings. From the latter, strong visible iridescence was observed and is shown to exhibit a mechanochromic response. This approach, the mainstay of the textile trade for decades, offers a means of continuous high-volume low-cost manufacturing of polymer (and conceivably soft-glass) fibers. For example, in the present effort, 128 coaxially microstructured fibers were fabricated simultaneously at rates exceeding 1200 m/min from industrially mainstream polymers. This approach offers an important step forward towards commoditizing microstructured fibers and open new doors for optical engineering in fashion, marking/identification, and numerous military applications.