Brian P. Grady

Recent Developments Concerning the Dispersion of Carbon Nanotubes in Polymers

The ability to control the dispersion of carbon nanotubes in polymers is key to most applications of nanotube-polymer composites. This feature article describes recent advances in methods used to disperse carbon nanotubes and considers how these methods affect dispersion on different length scales. It is becoming increasing clear that perfect dispersion is not desired for many applications, in particular for electrical conductivity, and controlling the dispersion is key for proper function of the composite in its intended application.

Carbon nanotube-polymer composites: Manufacture, Properties, and Applications

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Magnetic nanoparticles: inner ear targeted molecule delivery and middle ear implant.

Superparamagnetic iron oxide nanoparticles (SNP) composed of magnetite (Fe3O4) were studied preliminarily as vehicles for therapeutic molecule delivery to the inner ear and as a middle ear implant capable of producing biomechanically relevant forces for auditory function. Magnetite SNP were synthesized, then encapsulated in either silica or poly (D,L,-Lactide-co-glycolide) or obtained commercially with coatings of oleic acid or dextran. Permanent magnetic fields generated forces sufficient to pull them across tissue in several round window membrane models (in vitrocell culture, in vivo rat and guinea pig, and human temporal bone) or to embed them in middle ear epithelia. Biocompatibility was investigated by light and electron microscopy, cell culture kinetics, and hair cell survival in organotypic cell culture and no measurable toxicity was found. A sinusoidal magnetic field applied to guinea pigs with SNP implanted in the middle ear resulted in displacements of the middle ear comparable to 90 dB SPL.

Fabrication of protein dot arrays via particle lithography.

The ability to pattern a surface with proteins on both the nanometer and the micrometer scale has attracted considerable interest due to its applications in the fields of biomaterials, biosensors, and cell adhesion. Here, we describe a simple particle lithography technique to fabricate substrates with hexagonally patterned dots of protein surrounded by a protein-repellent layer of poly(ethylene glycol). Using this bottom-up approach, dot arrays of three different proteins (fibrinogen, P-selectin, and human serum albumin) were fabricated. The size of the protein dots (450 nm to 1.1 microm) was independent of the protein immobilized but could be varied by changing the size of the latex spheres (diameter=2-10 microm) utilized in assembling the lithographic bead monolayer. These results suggest that this technique can be extended to other biomolecules and will be useful in applications where arrays of protein dots are desired.

Correlating viscoelastic measurements of fracturing fluid to particles suspension and solids transport

An experimental study was performed to understand the relationship between fluid characteristics and its solids transport and sand suspension capabilities. In this study, borate crosslinked guar gels were prepared at three different pHs. The linear guar was crosslinked with borate crosslinker at concentrations from zero to the values where the gel exhibited phase separation at each pH. These gels were then characterized for viscoelastic properties and suspension settling velocities. At each pH, a crosslinker concentration was selected to evaluate the gels for their solids transport behavior in two large size slot models. The gels that satisfactorily transported solids through the slots had similar elastic moduli. The results show that the fluid elasticity, not viscosity, correlates with the solids transport capability of the crosslinked guar gels. Furthermore, the drag coefficients for the suspensions settling in the crosslinked gels prepared at three pHs were dissimilar, even at similar Weissenberg numbers. The drag on the suspensions settling in the viscoelastic guar gels was observed to be both more and less than the drag on the suspensions settling in the Newtonian fluids. Further work is needed to better understand these drag behaviors on the suspensions settling in viscoelastic guar gels.

Lateral confinement effects on the structural properties of surfactant aggregates: SDS on graphene

The structure of aqueous sodium dodecyl sulfate (SDS) surfactant aggregates formed on small graphene sheets and graphene nanoribbons has been studied using all-atom molecular dynamics simulations. Because the edges of the carbonaceous supports confine laterally the surfactant aggregates, by changing the size of the support (diameter of graphene sheets and width of graphene nanoribbons) it is possible to investigate lateral confinement effects on the aggregate morphology. The results are compared to those available on graphite, with no lateral confinement. Aqueous SDS aggregates were studied on 2.0 nm, 5.0 nm, and 10.0 nm circular graphene sheets and on 2.0 and 5.0 nm wide graphene nanoribbons. For the first time our results show that, because of lateral confinement provided by the graphene edges, SDS yields multiple layers, hemispheres, hemicylinders or multiple hemispheres depending on the graphene size and shape. Results are quantified in terms of morphology of the surfactant aggregates, order parameter of the adsorbed surfactant aggregates, and number of water molecules at contact with the carbonaceous support.

Experimental Studies on the Adsorption of Two Surfactants on Solid−Aqueous Interfaces: Adsorption Isotherms and Kinetics

A quartz crystal microbalance with dissipation (QCM-D) was used to measure the adsorption from aqueous solutions of CTAB (cationic) and C(12)E(6) (nonionic) surfactants on gold and silica surfaces. QCM-D allows for the determination of adsorption isotherms and also the monitoring of the dynamics of adsorption in real time. By considering the atomic-scale roughness of the solid surfaces and the surface area per head group at the air/water interface, our experiments indicate that at bulk concentrations above the critical micelle concentration adsorbed C(12)E(6) forms a monolayer-like structure on both surfaces and CTAB yields a bilayer-like structure. Although our measurements do not allow us to discriminate between the morphology of the aggregates (i.e., between flat monolayers, hemicylinders, or hemispheres in the case of C(12)E(6) and between flat bilayers, cylinders, or spheres in the case of CTAB), these results are particularly significant when compared to recent QCM-D data reported by Macakova et al. (Macakova, L.; Blomberg, E.; Claesson, P. M. Langmuir 2007, 23, 12436). These authors reported that QCM-D overestimates the amount of CTAB adsorbed on silica by as much as 30-40% as a result of entrapped water. Our analysis suggests that the effect of entrapped solvent is not as important as previously assumed and, in fact, QCM-D may not overestimate the amount of CTAB adsorbed when roughness is considered. Results for the kinetics of adsorption suggest that the aggregate structure as well as whether micelles are present may influence the adsorption mechanism. We discuss our results in the perspective of molecular theories for both the equilibrium and kinetics of surfactant adsorption.

Enhanced angiogenesis of modified porcine small intestinal submucosa with hyaluronic acid-poly(lactide-co-glycolide) nanoparticles: from fabrication to preclinical validation.

Hyaluronic acid-poly(de-co-glycolide) nanoparticles (HA-PLGA NPs) were synthesized to stabilize the porous structure of porcine small intestinal submucosa (SIS), to improve surface biocompatibility and to enhance performance in tissue regeneration. HA-PLGA NPs were characterized for size, zeta potential, surface morphology, and HA loading. Human microvascular endothelial cells responded to HA-PLGA NPs and HA-PLGA modified SIS (HA-PLGA-SIS) with elevated cell proliferation. HA-PLGA-SIS significantly enhanced neo-vascularization in an in ovo chorioallantoic membrane angiogenesis model. The angiogenic capability of the newly fabricated HA-PLGA-SIS was tested in a canine bladder augmentation model. Urinary bladder augmentation was performed in beagle dogs following hemi-cystectomy using HA-PLGA-SIS. The regenerated bladder was harvested at 10 weeks post augmentation and vascularization was evaluated using CD31 immunohistochemical staining. Bladder regenerated with HA-PLGA-SIS had significantly higher vascular ingrowth compared to unmodified SIS. This study shows that HA-PLGA NPs may represent a new approach for modifying naturally derived SIS biomaterials in regenerative medicine.

Use of surfactants to remove water based inks from plastic films

Abstract Direct reuse of plastic film with printing results in a colored polymer, which is less stiff and weaker than the original plastic upon re-extrusion. There is substantial economical and environmental incentive to remove the ink (deink) from heavily printed plastic film so that it can be reused to produce clear films. In this study, a commercial polyethylene film with water-based ink printing was deinked using different surfactants under a variety of conditions. At a pH of 12, water (containing no surfactant) can achieve about 90% deinking, but less basic solutions are less effective; at a pH 10 and below, insignificant-deinking occurs. Solutions of cationic surfactant are the most effective at deinking, showing high efficiency at surfactant concentrations both above and below the critical micelle concentration (CMC) over a pH range of 5–12. Amphoteric surfactant is effective above the CMC over a wide pH range. Both anionic and nonionic surfactants are only effective at deinking above the CMC at very basic conditions, with anionic surfactant being only slightly better than just water even at these high pH levels. The cationic surfactant is most effective and the anionic surfactant is least effective, possibly because the binder is an acidic acrylate with a negative charge.

Magnetic targeted delivery of dexamethasone acetate across the round window membrane in guinea pigs.

Hypothesis Magnetically susceptible PLGA nanoparticles will effectively target the round window membrane (RWM) for delivery of dexamethasone-acetate (Dex-Ac) to the scala tympani. Background Targeted delivery of therapeutics to specific tissues can be accomplished using different targeting mechanisms. One technology includes iron oxide nanoparticles, susceptible to external magnetic fields. If a nanocomposite composed of biocompatible polymer (PLGA), magnetite, and Dex-Ac can be pulled into and across the mammalian RWM, drug delivery can be enhanced. Method In vitro targeting and release kinetics of PLGA-magnetite-Dex-Ac nanoparticles first were measured using a RWM model. Next, these optimized nanocomposites were targeted to the RWM by filling the niche in anesthetized guinea pigs. A permanent magnet was placed opposite the RWM for 1 hour. Cochlear soft tissues, perilymph, and RWM were harvested after euthanasia and steroid levels were measured using HPLC. Results Membrane transport, in vitro, proved optimal targeting using a lower particle magnetite concentration (1 versus 5 or 10 mg/ml). In vivo targeted PLGA-magnetite-Dex-Ac particles had an average size of 482.8 ± 158 nm (DLS) and an average zeta potential −19.9 ± 3.3 mV. In 1 hour, there was significantly increased cochlear targeted delivery of Dex or Dex-Ac, compared with diffusion alone. Conclusion Superparamagnetic PLGA-magnetite-Dex-Ac nanoparticles under an external magnetic field (0.26 mT) for 1 hour significantly increased Dex-Ac delivery to the inner ear. The RWM was not completely permeated and also became loaded with nanocomposites, indicating that delivery to the cochlea would continue for weeks by PLGA degradation and passive diffusion.