Matthew Libera

Anti-SSA/Ro and anti-SSB/La autoantibodies bind the surface of apoptotic fetal cardiocytes and promote secretion of TNF-alpha by macrophages.

Despite the near universal association of congenital heart block and maternal Abs to SSA/Ro and SSB/La, the intracellular location of these Ags has made it difficult to substantiate their involvement in pathogenicity. To define whether components of the SSA/Ro-SSB/La complex, which translocate during apoptosis, are indeed accessible to extracellular Abs, two approaches were taken: immunoprecipitation of surface biotinylated proteins and scanning electron microscopy. Human fetal cardiocytes from 16–24-wk abortuses were cultured and incubated with staurosporine to induce apoptosis. Surface biotinylated 48-kDa SSB/La was reproducibly immunoprecipitated from apoptotic, but not nonapoptotic cardiocytes. Surface expression of SSA/Ro and SSB/La was further substantiated by scanning electron microscopy. Gold particles (following incubation with gold-labeled sera containing various specificities of anti-SSA/Ro-SSB/La Abs and murine mAb to SSB/La and 60-kDa SSA/Ro) were consistently observed on early and late apoptotic cardiocytes. No particles were seen after incubation with control antisera. To evaluate whether opsonized apoptotic cardiocytes promote inflammation, cells were cocultured with macrophages. Compared with nonapoptotic cardiocytes or apoptotic cardiocytes incubated with normal sera, apoptotic cardiocytes preincubated with affinity-purified Abs to SSB/La, 52-kDa SSA/Ro, or 60-kDa SSA/Ro increased the secretion of TNF-α from cocultured macrophages. In summary, apoptosis results in surface accessibility of all SSA/Ro-SSB/La Ags for recognition by circulating maternal Abs. It is speculated that in vivo such opsonized apoptotic cardiocytes promote an inflammatory response by resident macrophages with damage to surrounding conducting tissue.

Size dependent efficiency in Tb doped Y2O3 nanocrystalline phosphor

Abstract The luminescent efficiency in doped nanocrystalline Y 2 O 3 :Tb phosphors was found to increase with the decrease in the particle size from 100 to 40 A. This correlation was obtained from microstructural studies performed using transmission electron microscopy and luminescent measurements. The light output per Tb 3+ ion in DNC Y 2 O 3 :Tb 3+ phosphors exceeded that in the standard LaOBr:Tb 3+ phosphor.

Differential response of Staphylococci and osteoblasts to varying titanium surface roughness.

The surface roughness of metallic orthopaedic implants has typically been used to influence osseointegration and spatially control load transfer to the surrounding bone. Because of the increasing recognition of biomaterials-associated infection as a leading implant failure mode, we are interested to know the relative importance of roughness not only on surface-osteoblast interactions but also on surface-bacteria interactions. This in vitro study thus compares the effects of surface topography on Staphylococcus epidermidis and human osteoblast behavior using four clinically relevant titanium surface finishes: polished, satin, grit-blasted and plasma-sprayed. Important differences between these surfaces are manifested not only by their vertical roughness parameters but also by the lateral length scales over which topographic fluctuations occur. We find that S. epidermidis adhesion and growth is substantially higher on the satin and grit-blasted surfaces than on the polished or plasma-sprayed surfaces. The former are both substantially rougher at length scales comparable to that of bacteria. In contrast, based on imaging and biochemical assays of proliferation, differentiation and matrix formation, we find that desirable osteoblast-surface interactions are maximized on plasma-sprayed surfaces and minimized on satin-finished surfaces. We attribute these differences to the fact that the plasma-sprayed surface is relatively smooth compared to the size of an individual osteoblast, while the satin surface is rough at this length scale. These findings indicate that both the vertical and lateral character of surface roughness can be modified to not only optimize implant-bone interactions but to simultaneously minimize implant-bacteria interactions.

Polymer Multilayers with pH-Triggered Release of Antibacterial Agents

We report on the layer-by-layer design principles of poly(methacrylic acid) (PMAA) ultrathin hydrogel coatings that release antimicrobial agents (AmAs) in response to pH variations. The studied AmAs include gentamicin and an antibacterial cationic peptide L5. Adipic acid dihydrazide (AADH) is a cross-linker which, relative to ethylenediamine (EDA), increases the hydrogel hydrophobicity and introduces centers for hydrogen bonding to AmAs. AmA retention in AADH-cross-linked hydrogels in high-salt solutions was enhanced while AmA release at low pH was suppressed. L5 retains its antibacterial activity toward planktonic Staphylococcus epidermidis after release from PMAA hydrogels in response to pH decreases in the surrounding medium due to bacterial growth. Staphylococcus epidermidis adhesion and colonization was almost completely inhibited by L5 loading of hydrogels. The AmA-releasing and AmA-retaining properties of these hydrogel coatings provide new opportunities to study the fundamental mechanisms of AmA-coating-bacteria interactions and develop a new class of clinically relevant antibacterial coatings for medical devices.

Predation of human pathogens by the predatory bacteria Micavibrio aeruginosavorus and Bdellovibrio bacteriovorus

Aims:  The focus of this study was to evaluate the potential use of the predatory bacteria Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus to control the pathogens associated with human infection.

Viscoelasticity of biofilms and their recalcitrance to mechanical and chemical challenges

We summarize different studies describing mechanisms through which bacteria in a biofilm mode of growth resist mechanical and chemical challenges. Acknowledging previous microscopic work describing voids and channels in biofilms that govern a biofilms response to such challenges, we advocate a more quantitative approach that builds on the relation between structure and composition of materials with their viscoelastic properties. Biofilms possess features of both viscoelastic solids and liquids, like skin or blood, and stress relaxation of biofilms has been found to be a corollary of their structure and composition, including the EPS matrix and bacterial interactions. Review of the literature on viscoelastic properties of biofilms in ancient and modern environments as well as of infectious biofilms reveals that the viscoelastic properties of a biofilm relate with antimicrobial penetration in a biofilm. In addition, also the removal of biofilm from surfaces appears governed by the viscoelasticity of a biofilm. Herewith, it is established that the viscoelasticity of biofilms, as a corollary of structure and composition, performs a role in their protection against mechanical and chemical challenges. Pathways are discussed to make biofilms more susceptible to antimicrobials by intervening with their viscoelasticity, as a quantifiable expression of their structure and composition.

Length-Scale Mediated Adhesion and Directed Growth of Neural Cells by Surface-Patterned Poly(ethylene glycol) Hydrogels

We engineered surfaces that permit the adhesion and directed growth of neuronal cell processes but that prevent the adhesion of astrocytes. This effect was achieved based on the spatial distribution of sub-micron-sized cell-repulsive poly(ethylene glycol) [PEG] hydrogels patterned on an otherwise cell-adhesive substrate. Patterns were identified that promoted cellular responses ranging from complete non-attachment, selective attachment, and directed growth at both cellular and subcellular length scales. At the highest patterning density where the individual hydrogels almost overlapped, there was no cellular adhesion. As the spacing between individual hydrogels was increased, patterns were identified where neurites could grow on the adhesive surface between hydrogels while astrocytes were unable to adhere. Patterns such as lines or arrays were identified that could direct the growth of these subcellular neuronal processes. At higher hydrogel spacings, both neurons and astrocytes adhered and grew in a manner approaching that of unpatterned control surfaces. Patterned lines could once again direct growth at cellular length scales. Significantly, we have demonstrated that the patterning of sub-micron/nano scale cell-repulsive features at microscale lengths on an otherwise cell-adhesive surface can differently control the adhesion and growth of cells and cell processes based on the difference in their characteristic sizes. This concept could potentially be applied to an implantable nerve-guidance device that would selectively enable regrowing axons to bridge a spinal-cord injury without interference from the glial scar.

Time‐resolved reflection and transmission studies of amorphous Ge‐Te thin‐film crystallization

Measurements of the temperature and time dependence of visible diode laser transmission and reflection are combined with transmission electron microscopy (TEM) to study the crystallization of two 75 nm Ge‐Te thin films. Near‐stoichiometric Ge48Te52 transforms by the rapid growth of crystals through the film thickness followed by 2D growth in the film plane. Changes in film reflection and transmission are directly related to the volume fraction transformed. The optical measurements are interpreted in terms of classical Johnson–Mehl–Avrami kinetics. A Kissinger analysis gives an activation energy for crystallization of 1.7 eV. Isothermal measurements lead to an Avrami exponent of 4.5. The data are modeled using a numerical temperature‐dependent expression developed by Greer [Acta Metall. 30, 171 (1982)]. Off‐stoichiometric Ge54Te46 films show markedly different crystallization behavior. Transmission and reflection measurements indicate that the transformation proceeds by rapid growth of a crystalline layer ...

Self-defensive antibacterial layer-by-layer hydrogel coatings with pH-triggered hydrophobicity.

We report on negatively charged layer-by-layer (LbL) hydrogel films, which turn hydrophobic and bactericidal in response to bacteria-induced acidification of the medium. Single-component hydrogel thin films, abbreviated as PaAALbLs, consisting of chemically crosslinked poly(2-alkylacrylic acids) (PaAAs) with varying hydrophobicity [polymethacrylic acid (PMAA), poly(2-ethylacrylic acid) (PEAA), poly(2-n-propylacrylic acid) (PPAA) or poly(2-n-butylacrylic acid) (PBAA)]. With increasing polyacid hydrophobicity, the hydrogel films showed a decrease in water uptake and an increase in elastic modulus. Both parameters were strongly dependent on pH. At pH 7.4, hydrogels of higher hydrophobicity were more resistant to colonization by Staphylococcus epidermidis, with the PBAA coating showing almost negligible colonization. As the medium became more acidic due to bacterial proliferation, the more hydrophobic PEAALbL, PPAALbL and PBAALbL hydrogels became dehydrated and killed bacteria upon contact with the surface. The killing efficiency was strongly enhanced by the polymer hydrophobicity. The films remained cytocompatible with human osteoblasts, as indicated by the MTS assay and live/dead staining. Our approach exploits bacteria-responsive properties of the coating itself without the involvement of potentially toxic cationic polymers or the release of antimicrobial agents. These coatings thus demonstrate a novel approach to the antibacterial protection of tissue-contacting biomedical-device surfaces.

Oxygen-Generating Nanofiber Cell Scaffolds with Antimicrobial Properties

Many next-generation biomaterials will need the ability to not only promote healthy tissue integration but to simultaneously resist bacterial colonization and resulting biomaterials-associated infection. For this purpose, antimicrobial nanofibers of polycaprolactone (PCL) were fabricated by incorporating calcium peroxide. PCL nanofibers containing different ratios of calcium peroxide (1%, 5% and 10% (w/w)) with or without ascorbic acid were fabricated using an electrospinning technique. Antimicrobial evaluations confirmed the inhibitory properties of the nanofibers on the growth of E. coli and S. epidemidis because of a significant burst release of calcium peroxide from the nanofibers. Analysis of tissue cell response showed that despite an initial toxic effect over the first 24 h, after 4 days of culture, osteoblast viability and morphology were both healthy. These results demonstrate that oxygen-generating nanofibers can be designed and developed to provide a short-term peroxide-based antimicrobial response while still maintaining attractive tissue-integration properties.