Biomedical subjects

Robert E Cohen

Publications and source records attributed to Robert E Cohen.

At least 19 recordsLinked to original sources

PubMed2007

Heterostructured magnetic nanotubes.

Heterostructured magnetic tubes with submicrometer dimensions were assembled by the layer-by-layer deposition of polyelectrolytes and nanoparticles in the pores of track-etched polycarbonate membranes. Multilayers composed of poly(allylamine hydrochloride) and poly(styrene sulfonate) assembled at high pH (pH > 9.0) were first assembled into the pores of track-etched polycarbonate membranes, and then multilayers of magnetite (Fe3O4) nanoparticles and PAH were deposited. Transmission electron microscopy (TEM) confirmed the formation of multilayer nanotubes with an inner shell of magnetite nanoparticles. These tubes exhibited superparamagnetic characteristics at room temperature (300 K) as determined by a SQUID magnetometer. The surface of the magnetic nanotubes could be further functionalized by adsorbing poly(ethylene oxide)-b-poly(methacrylic acid) block copolymers. The separation and release behavior of low molecular weight anionic molecules (i.e., ibuprofen, rose bengal, and acid red 8) by/from the multilayer nanotubes were studied because these tubes could potentially be used as separation or targeted delivery vehicles. The magnetic tubes could be successfully used to separate (or remove) a high concentration of dye molecules (i.e., rose bengal) from solution by activating the nanotubes in acidic solution. The release of the anionic molecules in physiologically relevant buffer solution showed that whereas bulky molecules (e.g., rose bengal) release slowly, small molecules (i.e., ibuprofen) release rapidly from the multilayers. The combination of the template method and layer-by-layer deposition of polyelectrolytes and nanoparticles provides a versatile means to create functional nanotubes with heterostructures that can be used for separation as well as targeted delivery.

Journal Article↗

PubMed2006

Two-level antibacterial coating with both release-killing and contact-killing capabilities.

Using a combination of an aqueous layer-by-layer deposition technique, nanoparticle surface modification chemistry, and nanoreactor chemistry, we constructed thin film coatings with two distinct layered functional regions: a reservoir for the loading and release of bactericidal chemicals and a nanoparticle surface cap with immobilized bactericides. This results in dual-functional bactericidal coatings bearing both chemical-releasing bacteria-killing capacity and contact bacteria-killing capacity. These dual-functional coatings showed very high initial bacteria-killing efficiency due to the release of Ag ions and retained significant antibacterial activity after the depletion of embedded Ag because of the immobilized quaternary ammonium salts.

Anti-Bacterial Agents↗

PubMed2006

Creating patterned carbon nanotube catalysts through the microcontact printing of block copolymer micellar thin films.

We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al(2)O(3)) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the PDMS features. The PDMS stamp is then put in contact with a substrate, and uniaxial compressive stress is applied to transfer the micellar thin film from the PDMS stamp onto the substrate in a defined pattern. The polymer is then removed by oxygen plasma etching to leave a patterned iron oxide nanocluster array on the substrate. Using these catalysts, we achieve patterned vertical growth of multiwalled CNTs, where the CNTs maintain the fidelity of the patterned catalyst, forming high-aspect-ratio standing structures.

Acrylates↗

PubMed2006

Proteasome recruitment and activation of the Uch37 deubiquitinating enzyme by Adrm1.

Uch37 is one of the three principal deubiquitinating enzymes (DUBs), and the only ubiquitin carboxy-terminal hydrolase (UCH)-family protease, that is associated with mammalian proteasomes. We show that Uch37 is responsible for the ubiquitin isopeptidase activity in the PA700 (19S) proteasome regulatory complex. PA700 isopeptidase disassembles Lys 48-linked polyubiquitin specifically from the distal end of the chain, a property that may be used to clear poorly ubiquitinated or unproductively bound substrates from the proteasome. To better understand Uch37 function and the mechanism responsible for its specificity, we investigated how Uch37 is recruited to proteasomes. Uch37 binds through Adrm1, a previously unrecognized orthologue of Saccharomyces cerevisiae Rpn13p, which in turn is bound to the S1 (also known as Rpn2) subunit of the 19S complex. Adrm1 (human Rpn13, hRpn13) binds the carboxy-terminal tail of Uch37, a region that is distinct from the UCH catalytic domain, which we show inhibits Uch37 activity. Following binding, Adrm1 relieves Uch37 autoinhibition, accelerating the hydrolysis of ubiquitin-7-amido-4-methylcoumarin (ubiquitin-AMC). However, neither Uch37 alone nor the Uch37-Adrm1 or Uch37-Adrm1-S1 complexes can hydrolyse di-ubiquitin efficiently; rather, incorporation into the 19S complex is required to enable processing of polyubiquitin chains.

Amino Acid Sequence↗

PubMed2006

pH-induced hysteretic gating of track-etched polycarbonate membranes: swelling/deswelling behavior of polyelectrolyte multilayers in confined geometry.

pH-induced hysteretic gating of track-etched polycarbonate membranes (TEPC) has been achieved by depositing layer-by-layer assembled polyelectrolyte multilayers comprising poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) at a high pH condition (pH > 9.0). Scanning electron microscopy and transmission electron microscopy showed that the average bilayer thickness of multilayers was greater within the cylindrical pores of track-etched polycarbonate membranes compared to the multilayers on planar substrates (e.g., Si wafers and the face of TEPC membranes). Swelling/deswelling properties of multilayers and gating properties of the multilayer-modified TEPC membranes were studied by measuring the flux of pH-adjusted deionized water. Large discontinuous changes in the transmembrane flux were observed, indicating that the multilayers within the cylindrical pores of TEPC membranes exhibit the discontinuous swelling/deswelling behavior observed previously for planar systems. The degree of swelling as estimated by simple models, however, showed that (PAH/PSS) multilayers in the confined geometry swelled to smaller extents compared to the same multilayers on planar substrates under the same conditions. Multilayer-modified membranes showed reversible gating properties as the pH condition of feed solution was alternated between pH 2.5 and 10.5. In situ atomic force microscopy (AFM) was used to visualize the closing of the pores as a function of time. The hysteretic gating property of the multilayer-modified TEPC membrane was utilized to achieve either a "closed" or "open" state at one pH condition depending on the pretreatment history, thereby enabling either the retention or passage of high-molecular weight polymers by varying the membrane pretreatment condition.

Journal Article↗

PubMed2006

Nanoporosity-driven superhydrophilicity: a means to create multifunctional antifogging coatings.

Multifunctional nanoporous thin films have been fabricated from layer-by-layer assembled silica nanoparticles and a polycation. The resultant multilayer films were found to exhibit both antifogging and antireflection properties. The antifogging properties are a direct result of the development of superhydrophilic wetting characteristics (water droplet contact angle <5 degrees within 0.5 s or less). The nearly instantaneous sheetlike wetting promoted by the superhydrophilic multilayer prevents light scattering water droplets from forming on a surface. The low refractive index of the multilayer film (as low as 1.22) resulting from the presence of nanopores was found to impart excellent antireflection properties. Glass slides coated on both sides with a nanoporous multilayer film exhibited transmission levels as high as 99.8%. Stable superhydrophilic wetting characteristics were obtained only after a critical number of bilayers were deposited onto a surface. The assembly conditions (solution pH and nanoparticle concentration), as well as the choice of nanoparticle size, were found to strongly influence film properties. It is suggested that the superhydrophilic behavior is driven by the rapid infiltration of water into a 3D nanoporous network created under specific assembly conditions.

Journal Article↗

PubMed2006

Controlled drug release from porous polyelectrolyte multilayers.

Microporous and nanoporous polyelectrolyte multilayer films have been explored as ultrathin coatings for controlled drug release. Ketoprofen and cytochalasin D were successfully loaded into nanoporous films and showed zero-order release kinetics over a period of many days. In addition to homogeneous porous multilayers, heterostructures comprising porous regions stacked alternately with nonporous regions were assembled. The heterostructures behaved as dielectric mirrors, which made it possible to optically monitor the loading process. The effects of varying the number of layers in porous and nonporous regions as well as the pore size on the drug release properties were studied. Nonporous regions in the film had no effect on the release rate or duration of release. The amount of drug released could be tuned by varying the number of layers in the porous regions of films, and the release rate depended on the pore size in the films. Microporous multilayers exhibited a Fickian diffusion of drug that was approximately twice as fast as the corresponding nanoporous films. Finally, cell culture experiments with WT NR6 fibroblasts confirmed that cytochalasin D retained its ability to inhibit mitosis after release from the multilayers.

Animals↗

PubMed2006

Patterned superhydrophobic surfaces: toward a synthetic mimic of the Namib Desert beetle.

The present study demonstrates a surface structure that mimics the water harvesting wing surface of the Namib Desert beetle. Hydrophilic patterns on superhydrophobic surfaces were created with water/2-propanol solutions of a polyelectrolyte to produce surfaces with extreme hydrophobic contrast. Selective deposition of multilayer films onto the hydrophilic patterns introduces different properties to the area including superhydrophilicity. Potential applications of such surfaces include water harvesting surfaces, controlled drug release coatings, open-air microchannel devices, and lab-on-chip devices.

2-Propanol↗

PubMed2006

All-nanoparticle thin-film coatings.

All-nanoparticle thin-film coatings that exhibit antireflection, antifogging (superhydrophilicity), and self-cleaning properties have been prepared via layer-by-layer deposition of TiO(2) and SiO(2) nanoparticles. The porosity and chemical composition of the coatings were determined using a simple method that is based on ellipsometry and does not require any assumptions about the refractive indices of the constituent nanoparticles. The presence of nanopores in the TiO(2)/SiO(2) nanoparticle coatings results in superhydrophilicity as well as antireflection properties. The superhydrophilicity of contaminated coatings could also be readily recovered and retained after ultraviolet irradiation.

Adsorption↗

PubMed2006

The effect of EDTA in attachment gain and root coverage.

Root surface biomodification using low pH agents such as citric acid and tetracycline has been proposed to enhance root coverage following connective tissue grafting. The authors hypothesized that root conditioning with neutral pH edetic acid would improve vertical recession depth, root surface coverage, pocket depth, and clinical attachment levels. Twenty teeth in 10 patients with Miller class I and II recession were treated with connective tissue grafting. The experimental sites received 24% edetic acid in sterile distilled water applied to the root surface for 2 minutes before grafting. Controls were pretreated with only sterile distilled water. Measurements were evaluated before surgery and 6 months after surgery. Analysis of variance was used to determine differences between experimental and control groups. We found significant postoperative improvements in vertical recession depth, root surface coverage, and clinical attachment levels in test and control groups, compared to postoperative data. Pocket depth differences were not significant (P<.01).

Adult↗

PubMed2005

The deubiquitinating enzyme UCH37 interacts with Smads and regulates TGF-beta signalling.

Disruption of components in the transforming growth factor-beta (TGF-beta) signalling cascade is a common occurrence in human cancers. TGF-beta pathway activation is accomplished via serine/threonine kinase receptors and intracellular Smad transcription factors. A key regulatory step involves specific ubiquitination by Smurfs that mediate the proteasomal degradation of Smads and/or receptors. Here, we report a novel interaction between Smads and ubiquitin C-terminal hydrolase UCH37, a deubiquitinating enzyme that could potentially reverse Smurf-mediated ubiquitination. In GST pull down experiments, UCH37 bound weakly to Smad2 and Smad3, and bound very strongly to Smad7 in a region that is distinct from the -PY- motif in Smad7 that interacts with Smurf ubiquitin ligases. Endogenous Smad7 and UCH37 formed a stable complex in U4A/JAK1 cells, and FLAG-Smad7 co-immunoprecipitated with HA-UCH37 in transfected HEK-293 cells. In addition, we show that UCH37 can deubiquitinate and stabilize the type I TGF-beta receptor. Furthermore, overexpression of UCH37 upregulates TGF-beta-dependent transcription, and this effect is reversed in cells subject to RNAi-mediated knockdown of endogenous UCH37. These findings support a new role for deubiquitinating enzymes in the control of the TGF-beta signalling pathway, and provide a novel molecular target for the design of inhibitors with therapeutic potential in cancer.

Activin Receptors, Type I↗

PubMed2005

Antibacterial properties of Ag nanoparticle loaded multilayers and formation of magnetically directed antibacterial microparticles.

Antibacterial coatings based on hydrogen-bonded multilayers containing in situ synthesized Ag nanoparticles were created on planar surfaces and on magnetic colloidal particles. We report the antibacterial properties of these coatings, determined using a disk-diffusion (Kirby-Bauer) test, as a function of the film thickness and the concentration of Ag nanoparticles in the hydrogen-bonded multilayers. The zone of inhibition (ZoI) determined by the disk-diffusion test increases as the thickness of the multilayer film is increased. Results obtained for the values of the ZoI as a function of film thickness can be described adequately with a simple diffusion model (i.e., the square of the zone of inhibition (ZoI) depended linearly on the logarithm of the thickness of the silver-loaded films). This observation suggests that, in order to incrementally increase the ZoI, an exponentially increasing amount of Ag is required within the multilayers. In general, there was no statistically significant correlation between the zone of inhibition and the number of Ag loading and reduction cycles. The duration of sustained release of antibacterial Ag ions from these coatings, however, could be prolonged by increasing the total supply of zerovalent silver in the films via multiple loading and reduction cycles. These results indicate that the release of silver is controlled by an oxidation mechanism at the surface of the nanoparticles and that repeated loading and reduction of silver leads preferentially to growth of the existing silver nanoparticles in the film as opposed to nucleation of new Ag nanoparticles. We also show that magnetic microspheres coated with silver nanoparticle loaded hydrogen-bonded multilayer thin films can be used to deliver antibacterial agents to specific locations. The minimum inhibitory concentration (MIC) of nanocomposite coated microspheres was determined by the agar dilution technique: antibacterial magnetic microspheres with higher concentrations of Ag nanoparticles exhibited lower MIC values.

Acrylic Resins↗

PubMed2005

Structure and mechanisms of the proteasome-associated deubiquitinating enzyme USP14.

The ubiquitin-specific processing protease (UBP) family of deubiquitinating enzymes plays an essential role in numerous cellular processes. Mammalian USP14 (Ubp6 in yeast) is unique among known UBP enzymes in that it is activated catalytically upon specific association with the 26S proteasome. Here, we report the crystal structures of the 45-kDa catalytic domain of USP14 in isolation and in a complex with ubiquitin aldehyde, which reveal distinct structural features. In the absence of ubiquitin binding, the catalytic cleft leading to the active site of USP14 is blocked by two surface loops. Binding by ubiquitin induces a significant conformational change that translocates the two surface loops thereby allowing access of the ubiquitin C-terminus to the active site. These structural observations, in conjunction with biochemical characterization, identify important regulatory mechanisms for USP14.

Amino Acid Sequence↗

PubMed2005

Wear reduction of orthopaedic bearing surfaces using polyelectrolyte multilayer nanocoatings.

This work explores the use of conformal polyelectrolyte multilayer (PEM) coatings for wear reduction of orthopedic bearing surfaces. These films, with easily tunable architectures, provide excellent adhesion to a wide variety of metallic, plastic, and ceramic substrates. For this study, PEM films, only a few hundred nanometers thick, were assembled by sequential adsorption of poly(acrylic acid) and poly(allylamine hydrochloride). It was observed that the pH of the polylectrolyte solutions used for film assembly needs careful consideration to avoid any adverse effects on film structure when exposed to physiological conditions of pH and ionic strength. The wear reducing capacity of these coatings in the presence of bovine calf serum-lubricant solution was established for metal/metal systems at the meso/microscale over 30 cycles of reciprocating motion, as well as for the commonly used metal/ultra-high molecular weight polyethylene (UHMWPE) system over 500,000 cycles of bi-directional motion in a macroscale pin-on-disk test. In the latter case, the use of the films reduced UHMWPE wear by up to 33% when compared with the uncoated control. This is the first clinically relevant laboratory demonstration of the wear-reducing ability of these films. Further optimization will be needed before this novel class of materials can be used by the orthopedic community.

Acrylic Resins↗

PubMed2005

Myosin V attachment to cargo requires the tight association of two functional subdomains.

The myosin V carboxyl-terminal globular tail domain is essential for the attachment of myosin V to all known cargoes. Previously, the globular tail was viewed as a single, functional entity. Here, we show that the globular tail of the yeast myosin Va homologue, Myo2p, contains two structural subdomains that have distinct functions, namely, vacuole-specific and secretory vesicle-specific movement. Biochemical and genetic analyses demonstrate that subdomain I tightly associates with subdomain II, and that the interaction does not require additional proteins. Importantly, although neither subdomain alone is functional, simultaneous expression of the separate subdomains produces a functional complex in vivo. Our results suggest a model whereby intramolecular interactions between the globular tail subdomains help to coordinate the transport of multiple distinct cargoes by myosin V.

Amino Acid Sequence↗

PubMed2005

Ubiquitin-ovomucoid fusion proteins as model substrates for monitoring degradation and deubiquitination by proteasomes.

Protein degradation by 26S proteasomes requires the coordinated action of multiple binding and catalytic activities to process ubiquitinated protein substrates. For the purpose of studying conjugate degradation independently of substrate targeting and unfolding steps, we have developed substrates based on an N-terminal fusion of ubiquitin to an irreversibly unfolded protein, the 83 amino acid HA epitope-tagged first domain of chicken ovomucoid. Fluorescent labeling of the six cysteines in the ovomucoid moiety (OM) with Lucifer Yellow iodoacetamide yields UbOM(LY); the ubiquitin in the fusion protein can be extended by the addition of a K48-linked polyubiquitin chain to form Ub(n)OM(LY). UbOM(LY) derivatives provide versatile substrates to monitor both protein degradation and deubiquitination by 26S proteasomes in vitro. Comparisons of polyubiquitin conjugates of unfolded OM(LY) with folded dihydrofolate reductase (DHFR) in degradation assays can help resolve and identify the rate-limiting steps in proteasome degradation.

Animals↗

PubMed2005

Toothbrush abrasions and noncarious cervical lesions: evolving concepts.

Toothbrush abrasion at the cervical areas of teeth is generally thought to be a result of frequent or forceful toothbrushing, faulty or vigorous technique, filament stiffness or design, dominant hand dexterity, or abrasive dentifrices. However, a review of the evidence-based literature cannot conclusively establish any one factor as the primary etiology of cervical abrasions because of inherent methodological limitations and conflicting results. Rather, a variety of factors related to toothbrushing may act in concert with dental erosion and, possibly, occlusal loading in the creation of noncarious cervical lesions. Individual variation also may make some individuals more susceptible to development and may modify the progression of those lesions. Individual variations may involve oral and dental anatomy, periodontal status or phenotype, and periodontal disease history and treatment. Further research is needed to clearly assess the interaction of all those factors in the development of cervical lesions. Therefore, awareness of a multifactorial etiology in noncarious cervical lesions may help the clinician to formulate an appropriate treatment plan for the patient.

Acids↗

PubMed2004

Bioinert solution-cross-linked hydrogen-bonded multilayers on colloidal particles.

Bioinert polyelectrolyte multilayers comprised of poly(acrylic acid) and polyacrylamide were deposited on colloidal particles (1.7 microm in diameter) at low pH conditions by layer-by-layer assembly using hydrogen-bonding interactions. The multilayer films were coated uniformly on the colloidal particles without causing any flocculation of the colloids, and the deposited films were subsequently cross-linked by a single treatment of a carbodiimide aqueous solution. The lightly cross-linked multilayer films show excellent stability at physiological conditions (pH 7.4, phosphate-buffered saline), whereas untreated multilayer films dissolved. The multilayer-coated surfaces, both on flat substrates and on colloidal particles, exhibit excellent resistance toward mammalian cell adhesion. With this new solution-based cross-linking method, bioinert H-bonded multilayer coatings offer potential for biomedical applications.

Acrylic Resins↗