Pieter Stroeve

Imaging of hard- and soft-tissue structure in the oral cavity by optical coherence tomography

We have developed a prototype optical coherence tomography (OCT) system for the imaging of hard and soft tissue in the oral cavity. High-resolution images of in vitro porcine periodontal tissues have been obtained with this system. The images clearly show the enamel-cementum and the gingiva-tooth interfaces, indicating OCT is a potentially useful technique for diagnosis of periodontal diseases. To our knowledge, this is the first application of OCT for imaging biologic hard tissue.

Cell toxicity of superparamagnetic iron oxide nanoparticles

The performance of nanoparticles for biomedical applications is often assessed by their narrow size distribution, suitable magnetic saturation and low toxicity effects. In this work, superparamagnetic iron oxide nanoparticles (SPIONs) with different size, shape and saturation magnetization levels were synthesized via a co-precipitation technique using ferrous salts with a Fe(3+)/Fe(2+) mole ratio equal to 2. A parametric study is conducted, based on a uniform design-of-experiments methodology and a critical polymer/iron mass ratio (r-ratio) for obtaining SPION with narrow size distribution, suitable magnetic saturation, and optimum biocompatibility is identified. Polyvinyl alcohol (PVA) has been used as the nanoparticle coating material, owing to its low toxicity. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay is used to investigate the cell biocompatibility/toxicity effects of the samples. From the MTT assay results, it is observed that the biocompatibility of the nanoparticles, based on cell viabilities, can be enhanced by increasing the r-ratio, regardless of the stirring rate. This effect is mainly due to the growth of the particle hydrodynamic size, causing lower cell toxicity effects.

Optimal design and characterization of superparamagnetic iron oxide nanoparticles coated with polyvinyl alcohol for targeted delivery and imaging.

Superparamagnetic iron oxide nanoparticles (SPION) with narrow size distribution and stabilized by polyvinyl alcohol (PVA) were synthesized. The particles were prepared by a coprecipitation technique using ferric and ferrous salts with a molar Fe3+/Fe2+ ratio of 2. Using a design of experiments (DOE) approach, the effect of different synthesis parameters (stirring rate and base molarity) on the structure, morphology, saturation magnetization, purity, size, and size distribution of the synthesized magnetite nanoparticles was studied by various analysis techniques including X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) measurements, vibrating-sample magnetometer (VSM), transmission electron microscopy (TEM), UV-visible, and Fourier transform infrared (FT-IR) spectrometer. PVA not only stabilized the colloid but also played a role in preventing further growth of SPION followed by the formation of large agglomerates by chemisorption on the surface of particles. A rich behavior in particle size, particle formation, and super paramagnetic properties is observed as a function of molarity and stirring conditions. The particle size and the magnetic properties as well as particle shape and aggregation (individual nanoparticles, magnetic beads, and magnetite colloidal nanocrystal clusters (CNCs) are found to be influenced by changes in the stirring rate and the base molarity. The formation of magnetic beads results in a decrease in the saturation magnetization, while CNCs lead to an increase in saturation magnetization. On the basis of the DOE methodology and the resulting 3-D response surfaces for particle size and magnetic properties, it is shown that optimum regions for stirring rate and molarity can be obtained to achieve coated SPION with desirable size, purity, magnetization, and shape.

Bioelectronic silicon nanowire devices using functional membrane proteins

Modern means of communication rely on electric fields and currents to carry the flow of information. In contrast, biological systems follow a different paradigm that uses ion gradients and currents, flows of small molecules, and membrane electric potentials. Living organisms use a sophisticated arsenal of membrane receptors, channels, and pumps to control signal transduction to a degree that is unmatched by manmade devices. Electronic circuits that use such biological components could achieve drastically increased functionality; however, this approach requires nearly seamless integration of biological and manmade structures. We present a versatile hybrid platform for such integration that uses shielded nanowires (NWs) that are coated with a continuous lipid bilayer. We show that when shielded silicon NW transistors incorporate transmembrane peptide pores gramicidin A and alamethicin in the lipid bilayer they can achieve ionic to electronic signal transduction by using voltage-gated or chemically gated ion transport through the membrane pores.

An in vitro study of bare and poly(ethylene glycol)-co-fumarate-coated superparamagnetic iron oxide nanoparticles: a new toxicity identification procedure

As the use of superparamagnetic iron oxide nanoparticles (SPION) in biomedical applications increases (e.g. for targeting drug delivery and imaging), patients are likely to be exposed to products containing SPION. Despite their high biomedical importance, toxicity data for SPION are limited to date. The aim of this study is to investigate the cytotoxicity of SPION and its ability to change cell medium components. Bare and poly(ethylene glycol)-co-fumarate (PEGF)-coated SPION with narrow size distributions were synthesized. The particles were prepared by co-precipitation using ferric and ferrous salts with a molar Fe3+/Fe2+ ratio of 2. Dulbeccos modified Eagles medium (DMEM) and primary mouse fibroblast (L929) cell lines were exposed to the SPION. Variation of cell medium components and cytotoxicity due to the interactions with nanoparticles were analyzed using ultraviolet and visible spectroscopy (UV/vis) and the 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) assay methods, respectively. The toxicity amount has been traditionally identified by changes in pH and composition in cells and DMEM due to the tendency of SPION to adsorb proteins, vitamins, amino acids and ions. For in vitro toxicity assessments, a new surface passivation procedure is proposed which can yield more reliable quantitative results. It is shown that a more reliable way of identifying cytotoxicity for in vitro assessments is to use particles with saturated surfaces via interactions with DMEM before usage.

Diffusive transport in two-phase media: spatially periodic models and maxwell's theory for isotropic and anisotropic systems

Abstract The problem of diffusion and heat conduction in two-phase systems is used to illustrate the utility of approximate solutions for the closure problem associated with the method of volume averaging. Numerical solutions for spatially periodic models are compared with experimental data and with an approximate solution of the closure problem first used by Chang. Changs unit cell replaces the spatially periodic boundary conditions in the closure problem with a Dirichlet condition that leads to analytical solutions for the closure variables. These analytical solutions are identical to the classical solutions of Maxwell and Rayleigh, and the comparison between spatially periodic models and Changs unit cell indicates only minor differences between the two approaches. In this work we extend the studies of Chang to include both interfacial resistance and anisotropic systems which are generated by means of ellipsoidal unit cells. The inclusion of interfacial resistance is important for the study of diffusion in cellular systems, while the use of ellipsoidal unit cells provides a comparison between theory and experiment for diffusion in anisotropic porous media.

Biotechnical and other applications of nanoporous membranes

Recent advances mean that arrays of nearly uniform cylindrical, conical and pyramidal shaped pores can be produced in several types of substrates. Surface modification of nanopore surfaces can give unique mass transport characteristics that have recently been explored for biomolecule separation, detection and purification. Recent interest has focused on the use of nanoporous membranes for mass transfer diodes that act analogous to solid-state devices based on electron conduction. Asymmetric pores such as conical pores can show superior performance characteristics compared to traditional cylindrical pores in ion rectification. However, many phenomena for membranes with asymmetric pores still remain to be exploited in biomolecular separation, biosensing, microfluidics, logic gates, and energy harvesting and storage.

Diffusion and reaction in cellular media

Abstract This paper presents a general theoretical analysis of the problem of diffusion and chemical reaction in heterogeneous two-phase media in which membrane or interfacial resistances can be important. Volume-averaged transport equations are derived for both phases with a first-order, irreversible reaction occurring in the dispersed phase. From these equations, a one-equation model is derived and the constraints that the one-equation model must satisfy are identified. A method of closure is developed in order to determine effective diffusivities, and the influence of the membrane permeability on the effective diffusivity is illustrated for a wide range of the parameters that describe the system. Experimental data for the effective diffusivity in a cellular system are used in conjunction with our theoretical results to determine the membrane permeability of a biological system.

Gas transfer in supported films made by molecular self-assembly of ionic polymers

Abstract Asymmetric membranes for gas separation were fabricated using the layer-by-layer adsorption process based on the spontaneous self-assembly of alternating layers of cationic and anionic polymers on porous and solid support membranes. The support membranes were first dipped in a dilute solution of poly (allylamine) (a polycation) followed by dipping in a dilute solution of poly (styrenesulfonate) (a polyanion). Repeating this process, 40 polymer layers were deposited on porous poly(propylene) membranes (Celgard 2400) and 100 layers on solid dimethyl silicone membranes. Gas-transfer experiments at several temperatures indicated reduced mass permeabilities due to the adsorbed films. Permeabilities of pure CO2 and N2 through coated Celgard samples were virtually equal at all temperatures indicating dominance of Knudsen diffusion through micropores in the film. Permeabilities in coated silicone membranes indicate higher CO2/N2 selectivity than the bare membrane at elevated temperatures. Microphotography indicated the presence of breaks in the polyion complex coating on the silicone membrane. Fabrication of gas transfer membranes via self-assembly of ionic polymers offers the possibility of designing highly selective membranes as well as the ability to control the thickness and architecture of films at the molecular level.

Bacterial effects and protein corona evaluations: crucial ignored factors in the prediction of bio-efficacy of various forms of silver nanoparticles.

Because of their unique properties which are strongly dependent on the physicochemical properties of metal nanomaterials, noble metal nanostructures, particularly silver, have attracted much attention in the fields of electronics, chemistry, physics, biology, and medicine. Regarding biology and medical applications, silver nanoparticles (NPs) are recognized as a promising candidate to fight against resistant pathogens because of their significant antimicrobial activities. However, there are two major ignored issues with these NPs. First, the effect of various types of bacteria on antibacterial efficacy of silver NPs is ignored; second, there is no information on the pattern and compositions of both soft- and hard-corona proteins at the surface of NPs, which can define cellular responses to the NPs. In this article, the bacterial effect on the antibacterial capability of silver NPs with various geometries (i.e., sphere, wire, cube, and triangle) was probed; in this case, three different types of bacteria including Escherichia coli (E. coli), Bacillus subtilis, and Staphylococcus aureus were employed. The results showed that the type of bacteria can have quite a significant role in the definition of antibacterial efficacy of NPs, which has significant implications in the high yield design of NPs for antibacterial applications and will require serious consideration in the future. In addition, both soft- and hard-corona proteins were analyzed, and the effects of protein coated NPs on normal cells were evaluated. According to the results, the composition and thickness of protein coronas were strongly dependent on the physicochemical properties of silver NPs. We have found that the composition and thickness of the protein corona can evolve quite significantly as one passes from particle concentrations and shapes appropriate to in vitro cell studies to those present in in vivo studies, which has important implications for in vitro-in vivo extrapolations and will require more consideration in the future.