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Biomedical subjects

Thomas P Russell

Publications and source records attributed to Thomas P Russell.

At least 19 recordsLinked to original sources
PubMed2007

Novel transparent nano- to micro-heterogeneous substrates for in-situ cell migration study.

Transparent substrates having heterogeneities ranging from nanometer to micrometer lateral length scale were fabricated to study cell migration. The surfaces were generated using thin films of block copolymers and homopolymer blends on ultra smooth transparent polyethylene terephthalate films. Results show that the lateral size scale of the surface heterogeneities affects fibroblast (NIH-3T3) adhesion, spreading and motility. More specifically, fibroblasts migrate faster on micron-sized than on nanometer-sized heterogeneities. Cell movements and morphology on the micron patterned surfaces resemble cells cultured in a 3D environment. These surfaces, therefore, can potentially be utilized as models to study cell behavior in physiologically relevant conditions which can add to our fundamental understanding of cell-substrate interactions and facilitate development of surfaces for medical devices.

3T3 Cells↗
PubMed2007

Instabilities in nanoporous media.

Rayleigh instabilities in thin polymer films confined within nanoporous alumina membranes were studied. Thin films of poly(methyl methacrylate) (PMMA) were prepared by filling cylindrical nanopores in an anodic aluminum oxide (AAO) membrane with a PMMA solution in chloroform followed by solvent evaporation. When the PMMA nanotubes were annealed above the glass transition temperature (Tg), undulations in the film thickness were observed that were induced by a Rayleigh instability. The amplitude of the undulations increased with time and eventually bridged across the cylindrical nanopore in the AAO membrane, resulting in the formation of polymer nanorods with periodic encapsulated holes. A similar behavior was observed when PMMA films were confined within carbon nanotubes (CNTs). The Rayleigh instabilities in these confined geometries offer a novel means of controlling and fabricating the polymer nanostructures. These compartmentalized nanorods may have potential applications as delivery devices.

Microscopy, Electron, Scanning↗
PubMed2006

Nanoparticle polymer composites: where two small worlds meet.

The mixing of polymers and nanoparticles is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. Recent advances reveal routes to exploit both enthalpic and entropic interactions so as to direct the spatial distribution of nanoparticles and thereby control the macroscopic performance of the material. For example, by tailoring the particle coating and size, researchers have created self-healing materials for improved sustainability and self-corralling rods for photovoltaic applications. A challenge for future studies is to create hierarchically structured composites in which each sublayer contributes a distinct function to yield a mechanically integrated, multifunctional material.

Journal Article↗
PubMed2006

Capillary filling of anodized alumina nanopore arrays.

The filling behavior of a room temperature solvent, perfluoromethylcyclohexane, in approximately 20 nm nanoporous alumina membranes was investigated in situ with small angle x-ray scattering. Adsorption in the pores was controlled reversibly by varying the chemical potential between the sample and a liquid reservoir via a thermal offset, DeltaT. The system exhibited a pronounced hysteretic capillary filling transition as liquid was condensed into the nanopores. These results are compared with Kelvin-Cohan theory, with a modified Derjaguin approximation, as well as with predictions by Cole and Saam.

Aluminum Oxide↗
PubMed2006

An optical waveguide study on the nanopore formation in block copolymer/homopolymer thin films by selective solvent swelling.

Thin films of mixtures of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) diblock copolymers and PMMA homopolymers with cylindrical PMMA microdomains oriented normal to the substrate surface were used to couple optical modes in the Kretschmann configuration, and their optical properties were investigated by optical waveguide spectroscopy (OWS). The nanopore formation in the block copolymer (BCP) waveguide layer via selective solvent swelling and subsequent reannealing was monitored in terms of shifts in the coupling mode angles. The sequential swelling/reannealing of the initial mixture film resulted in a number of discrete or partially interconnected pores instead of cylindrical pores with a high aspect ratio. The simultaneous processes occurring inside and on top of the BCP waveguide layer were discerned independently with high selectivity for p- and s-polarization.

Membranes, Artificial↗
PubMed2006

Defect-free nanoporous thin films from ABC triblock copolymers.

The self-assembly of triblock copolymers of poly(ethylene oxide-b-methyl methacrylate-b-styrene) (PEO-b-PMMA-b-PS), where PS is the major component and PMMA and PEO are minor components, provides a robust route to highly ordered, nanoporous arrays with cylindrical pores of 10-15 nm that show promise in block copolymer lithography. These ABC triblock copolymers were synthesized by controlled living radical polymerization, and after solvent annealing, thin films showing defect-free cylindrical microdomains were obtained. The key to the successful generation of highly regular, porous thin films is the use of PMMA as a photodegradable mid-block which leads to nanoporous structures with an unprecedented degree of lateral order. The power of using a triblock copolymer when compared to a traditional diblock copolymer is evidenced by the ability to exploit and combine the advantages of two separate diblock copolymer systems, the high degree of lateral ordering inherent in PS-b-PEO diblocks plus the facile degradability of PS-b-PMMA diblock copolymer systems, while negating the corresponding disadvantages, poor degradability in PS-b-PEO systems and no long-range order for PS-b-PMMA diblocks.

Biocompatible Materials↗
PubMed2006

Novel 3-D structures in polymer films by coupling external and internal fields.

A route to produce novel three-dimensional structures in thin films is demonstrated. Such structures are most difficult to produce in a simple manner without the use of multiple fabrication steps. Here, we show the generation of 3-D cage-type structures using a combination of electrohydrodynamic instabilities and dewetting in a polymer/polymer/air trilayer. Removal of one of the components by use of a selective solvent or by degradation of one of the components reveals the formation of a three-dimensional structure, where one polymer is encased in the other. Thus, by coupling an external field with a surface field inherent to the polymers, a novel fabrication strategy is shown that has clear applications in microfluidics and microelectromechanical systems with extensions to patterned surfaces and structured fluids, like block copolymers.

Journal Article↗
PubMed2006

Surface-functionalized CdSe nanorods for assembly in diblock copolymer templates.

Poly(ethylene oxide)-covered CdSe nanorods were prepared and assembled in diblock copolymer templates by floating the block copolymer templates onto aqueous nanorod solutions. The assembly was enabled by consideration of the surface ligand coverage of the nanorods. Alkane-covered CdSe nanorods prepared by state-of-the-art techniques are not compatible with this assembly process. However, poly(ethylene oxide) (PEO)-functionalized CdSe nanorods were successfully used to assemble the nanorods into the channels and pores of diblock copolymer templates. Other water-dispersible CdSe nanorods, such as those covered with 11-mercaptoundecanoic acid (MUA), did not give the desired assemblies. These results are understood by considering the surface energies of the PEO-covered CdSe nanorods in this interfacial assembly process.

Journal Article↗
PubMed2006

Ion complexation: a route to enhanced block copolymer alignment with electric fields.

We investigate the enhanced alignment of lamellar microdomains under an electric field by addition of lithium chloride (LiCl) into polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers. A significant increase of dielectric contrast resulting from the formation of lithium-PMMA complexes markedly reduces the critical electric field strength required to overcome the preferential interactions of one block with the substrate, providing a route to achieve the complete alignment of microdomains in block copolymer thin films.

Journal Article↗
PubMed2006

Cellular responses to substrate topography: role of myosin II and focal adhesion kinase.

Although two-dimensional cultures have been used extensively in cell biological research, most cells in vivo exist in a three-dimensional environment with complex topographical features, which may account for at least part of the striking differences between cells grown in vivo and in vitro. To investigate how substrate topography affects cell shape and movement, we plated fibroblasts on chemically identical polystyrene substrates with either flat surfaces or micron-sized pillars. Compared to cells on flat surfaces, 3T3 cells on pillar substrates showed a more branched shape, an increased linear speed, and a decreased directional stability. These responses may be attributed to stabilization of cell adhesion on pillars coupled to myosin II-dependent contractions toward pillars. Moreover, using FAK-/- fibroblasts we showed that focal adhesion kinase, or FAK, is essential for the responses to substrate topography. We propose that increased surface contact provided by topographic features guides cell migration by regulating the strength of local adhesions and contractions, through a FAK- and myosin II-dependent mechanism.

3T3 Cells↗
PubMed2006

"Self-corralling" nanorods under an applied electric field.

Producing densely packed arrays of nanoscopic anisotropic objects, while necessary for applications in photovoltaic and field emission devices, presents considerable challenges. Here, we present findings on the phase separation of ligand-functionalized nanorods in a polymer matrix under an applied electric field. Densely packed hexagonal arrays of nanorods are produced by this method, where the rods are oriented in the direction of the applied field. Minimization of interfacial energy between the array of nanorods and the surrounding polymer serves to corral the nanorods into the densely packed arrays observed. These findings carry implications toward advancing organic-inorganic heterojunction photovoltaic devices that are expected to benefit from the oriented, densely packed ordered arrays of nanorods produced here.

Cadmium Compounds↗
PubMed2005

Orthogonal approaches to the simultaneous and cascade functionalization of macromolecules using click chemistry.

The development of selective chemistries that are orthogonal to the diverse array of functional groups present in many polymeric systems is becoming an important tool for the synthesis and use of macromolecules in fields ranging from biomedical devices to nanotechnology. By combining copper-catalyzed cycloaddition chemistry with other synthetic transformations such as esterification, amidation, etc., highly efficient and modular simultaneous and cascade functionalization strategies have been developed. These single-step strategies for preparing multifunctional macromolecules represent a significant advance as compared to traditional multistep approaches, and the utility of these concepts is demonstrated by selective preparation of a diverse range of orthogonally functionalized vinyl polymers.

Catalysis↗
PubMed2005

A generalized approach to the modification of solid surfaces.

Interfacial interactions underpin phenomena ranging from adhesion to surface wetting. Here, we describe a simple, rapid, and robust approach to modifying solid surfaces, based on an ultrathin cross-linkable film of a random copolymer, which does not rely on specific surface chemistries. Specifically, thin films of benzocyclobutene-functionalized random copolymers of styrene and methyl methacrylate were spin coated or transferred, then thermally cross-linked on a wide variety of metal, metal oxide, semiconductor, and polymeric surfaces, producing a coating with a controlled thickness and well-defined surface energy. The process described can be easily implemented and adapted to other systems.

Journal Article↗
PubMed2005

Self-directed self-assembly of nanoparticle/copolymer mixtures.

The organization of inorganic nanostructures within self-assembled organic or biological templates is receiving the attention of scientists interested in developing functional hybrid materials. Previous efforts have concentrated on using such scaffolds to spatially arrange nanoscopic elements as a strategy for tailoring the electrical, magnetic or photonic properties of the material. Recent theoretical arguments have suggested that synergistic interactions between self-organizing particles and a self-assembling matrix material can lead to hierarchically ordered structures. Here we show that mixtures of diblock copolymers and either cadmium selenide- or ferritin-based nanoparticles exhibit cooperative, coupled self-assembly on the nanoscale. In thin films, the copolymers assemble into cylindrical domains, which dictate the spatial distribution of the nanoparticles; segregation of the particles to the interfaces mediates interfacial interactions and orients the copolymer domains normal to the surface, even when one of the blocks is strongly attracted to the substrate. Organization of both the polymeric and particulate entities is thus achieved without the use of external fields, opening a simple and general route for fabrication of nanostructured materials with hierarchical order.

Journal Article↗
PubMed2005

Nanoparticle assembly at fluid interfaces: structure and dynamics.

The self-assembly of nanoparticles at fluid interfaces, driven by the reduction in interfacial energy, was investigated. With spherical, tri-n-octyl-phosphine-oxide covered cadmium selenide (CdSe) nanoparticles (1-8 nm), thermal fluctuations compete with the interfacial segregation giving rise to a size-dependent self-assembly of the particles. The structure of the nanoparticle assembly was studied using electron microscopy, atomic force microscopy, and X-ray scattering in situ, which indicate that the particles form a densely packed monolayer. The energetics of the adsorption of nanoparticles onto the interface was revealed by time-dependent fluorescence studies on a mixture of two different sized nanoparticles at the interface. The dynamics of the nanoparticles at the fluid interface, probed using fluorescence photobleaching methods, suggests a liquid-like behavior. The results have implications in the design of hierarchical self-assemblies of nanoparticles for the one-step fabrication of devices on multiple length scales.

Journal Article↗