John A. Nychka

Bioactive Glass 45S5 Powders: Effect of Synthesis Route and Resultant Surface Chemistry and Crystallinity on Protein Adsorption from Human Plasma

Despite its medical applications, the mechanisms responsible for the osseointegration of bioactive glass (45S5) have yet to be fully understood. Evidence suggests that the strongest predictor for osseointegration of bioactive glasses, and ceramics, with bone tissue as the formation of an apatitic calcium phosphate layer atop the implanted material, with osteoblasts being the main mediator for new bone formation. Most have tried to understand the formation of this apatitic calcium phosphate layer, and other bioresponses between the host and bioactive glass 45S5 using Simulated Body Fluid; a solution containing ion concentrations similar to that found in human plasma without the presence of proteins. However, it is likely that cell attachment is probably largely mediated via the adsorbed protein layer. Plasma protein adsorption at the tissue bioactive glass interface has been largely overlooked. Herein, we compare crystalline and amorphous bioactive glass 45S5, in both melt-derived as well as sol–gel forms. Thus, allowing for a detailed understanding of both the role of crystallinity and powder morphology on surface ions, and plasma protein adsorption. It was found that sol–gel 45S5 powders, regardless of crystallinity, adsorbed 3–5 times as much protein as the crystalline melt-derived counterpart, as well as a greater variety of plasma proteins. The devitrification of melt-cast 45S5 resulted in only small differences in the amount and variety of the adsorbed proteome. Surface properties, and not material crystallinity, play a role in directing protein adsorption phenomena for bioactive glasses given the differences found between crystalline melt-cast 45S5 and sol–gel derived 45S5.

Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator.

We report a simple approach to fabricate zinc oxide (ZnO) nanowire based electricity generators on three-dimensional (3D) graphene networks by utilizing a commercial polyurethane (PU) sponge as a structural template. Here, a 3D network of graphene oxide is deposited from solution on the template and then is chemically reduced. Following steps of ZnO nanowire growth, polydimethylsiloxane (PDMS) backfilling and electrode lamination completes the fabrication processes. When compared to conventional generators with 2D planar geometry, the sponge template provides a 3D structure that has a potential to increase power density per unit area. The modified one-pot ZnO synthesis method allows the whole process to be inexpensive and environmentally benign. The nanogenerator yields an open circuit voltage of ∼0.5 V and short circuit current density of ∼2 μA/cm(2), while the output was found to be consistent after ∼3000 cycles. Finite element analysis of stress distribution showed that external stress is concentrated to deform ZnO nanowires by orders of magnitude compared to surrounding PU and PDMS, in agreement with our experiment. It is shown that the backfilled PDMS plays a crucial role for the stress concentration, which leads to an efficient electricity generation.

The effect of air-abrasion and heat treatment on the fracture behavior of Y-TZP.

OBJECTIVES This study evaluated how the flexural strength and fracture behavior of a zirconia-based ceramic (Y-TZP) were affected by pre- and post-sintering mechanical and thermal treatments. METHODS Treatments included sandblasting with different particle size and type (30μm SiO2; 50 and 110μm Al2O3) and thermal conditioning. Two hundred bar-shaped specimens of pre-sintered Y-TZP ceramic (Lava Frame, 3M) were prepared (specimen dimensions: 25mm length×4mm width×0.7mm thickness) and divided into three groups (before sintering, after sintering and after sintering with heating treatment). The before sintering group specimens were airborne-particle abraded prior to dense sintering. Specimens from the after sintering group were airborne-particle abraded after sintering. The after sintering with heating treatment group specimens were submitted to a heating procedure after airborne-particle abrasion. The controls were the specimens that were sintered and not treated with any conditioning procedures. The specimens from all experimental conditions were analyzed by SEM, CLSM and XRD. All specimens were tested in four-point bending. Data were statistically analyzed using one-way ANOVA and Post Hoc tests (α=0.05). A Weibull analysis was used to analyze the strength reliability. RESULTS Sandblasting pre-sintered zirconia before sintering significantly decreased the flexural strength, except when the smallest blasting particles were used (30μm SiO2). Phase transformation (t-m) was observed after sandblasting and reverse transformation (m-t) was observed after heating. SIGNIFICANCE Sandblasting with 30μm SiO2 and 50μm Al2O3 allowed lower phase transformation. However, 30mm SiO2 presented better reliability.

In vitro bioactivity of 45S5 bioactive glass as a function of indentation load.

Many fabrication routes used to process biomaterials result in residual stresses. The presence of residual stress can cause failure or even change the dissolution rates of many materials, in particular biomaterials that are designed to be resorbed. Stored strain energy can add extra thermodynamic driving force for dissolution and result in varied dissolution rates depending on the sign of the stress. This work describes in vitro testing in phosphate buffer solution after micro-indenting the surface of bioactive glass 45S5 discs with varying loads. Indentation and fracture characteristics of the bioactive glass are discussed. Local dissolution and morphology of mineral deposits at the surface were analyzed by scanning electron microscopy to determine the effects of local residual stresses on bioactivity. It was found that the compressive stress field surrounding indents (above a threshold indentation load) slowed the dissolution of the bioactive glass significantly.

Structure, phases, and mechanical response of Ti-alloy bioactive glass composite coatings.

Porous titanium alloy-bioactive glass composite coatings were manufactured via the flame spray deposition process. The porous coatings, targeted for orthodontic and bone-fixation applications, were made from bioactive glass (45S5) powder blended with either commercially pure titanium (Cp-Ti) or Ti-6Al-4V alloy powder. Two sets of spray conditions, two metallic particle size distributions, and two glass particle size distributions were used for this study. Negative control coatings consisting of pure Ti-6Al-4V alloy or Cp-Ti were sprayed under both conditions. The as-sprayed coatings were characterized through quantitative optical cross-sectional metallography, X-ray diffraction (XRD), and ASTM Standard C633 tensile adhesion testing. Determination of the porosity and glassy phase distribution was achieved by using image analysis in accordance with ASTM Standard E2109. Theoretical thermodynamic and heat transfer modeling was conducted to explain experimental observations. Thermodynamic modeling was performed to estimate the flame temperature and chemical environment for each spray condition and a lumped capacitance heat transfer model was developed to estimate the temperatures attained by each particle. These models were used to establish trends among the choice of alloy, spray condition, and particle size distribution. The deposition parameters, alloy composition, and alteration of the feedstock powder size distribution had a significant effect on the coating microstructure, porosity, phases present, mechanical response, and theoretical particle temperatures that were attained. The most promising coatings were the Ti-6Al-4V-based composite coatings, which had bond strength of 20±2MPa (n=5) and received reinforcement and strengthening from the inclusion of a glassy phase. It was shown that the use of the Ti-6Al-4V-bioactive glass composite coatings may be a superior choice due to the possible osteoproductivity from the bioactive glass, the potential ability to support tissue ingrowth and vascular tissue, and the comparable strength to similar coatings.

Comparison of non-ideal solution theories for multi-solute solutions in cryobiology and tabulation of required coefficients.

Thermodynamic solution theories allow the prediction of chemical potentials in solutions of known composition. In cryobiology, such models are a critical component of many mathematical models that are used to simulate the biophysical processes occurring in cells and tissues during cryopreservation. A number of solution theories, both thermodynamically ideal and non-ideal, have been proposed for use with cryobiological solutions. In this work, we have evaluated two non-ideal solution theories for predicting water chemical potential (i.e. osmolality) in multi-solute solutions relevant to cryobiology: the Elliott et al. form of the multi-solute osmotic virial equation, and the Kleinhans and Mazur freezing point summation model. These two solution theories require fitting to only single-solute data, although they can make predictions in multi-solute solutions. The predictions of these non-ideal solution theories were compared to predictions made using ideal dilute assumptions and to available literature multi-solute experimental osmometric data. A single, consistent set of literature single-solute solution data was used to fit for the required solute-specific coefficients for each of the non-ideal models. Our results indicate that the two non-ideal solution theories have similar overall performance, and both give more accurate predictions than ideal models. These results can be used to select between the non-ideal models for a specific multi-solute solution, and the updated coefficients provided in this work can be used to make the desired predictions.

A regenerable copper mesh based oil/water separator with switchable underwater oleophobicity

A Cu2O coated Cu mesh with micro-scale surface structure was produced by a controlled UV-ozone treatment. The modified Cu mesh exhibited superhydrophilicity and underwater superoleophobicity. To achieve switchable wettability, the meshs superhydrophilicity was converted to superhydrophobicity by application of a self-assembled monolayer (SAM) with stearic acid (SA), which can be repeatedly reversed to its original state (superhydrophilicity and underwater superoleophobicity) by UV treatment that causes SA decomposition. Gravity-driven kerosene/water separation was demonstrated with the separation efficiency remaining over 95% after 20 cycles for both “water-removal” and “oil-removal” separation modes.

Wettability of biomimetic thermally grown aluminum oxide coatings

In this paper, wettability behavior of a rough but intrinsically hydrophilic oxide ceramic, formed via simple thermal oxidation of a commercial metallic alloy in laboratory air, has been analyzed. Drop shape analysis (DSA) revealed static water contact angles for the rough ceramic surfaces up to 128° (greater than for Teflon™). We propose the high apparent contact angles to be a result of surface roughening via the morphological changes of the oxide scale with oxidation conditions. The surface morphological changes occurring during the growth of the oxide film resulted in the formation of vertical platelets that ably shifted the wetting behavior from a Wenzel to an unstable Cassie-Baxter state. The platelet morphology of the ceramic resembles the structure of epicuticular waxes on certain species of superhydrophobic leaves. Moreover, surface textures for very short oxidation times were also found to increase hydrophilicity in the scale and reduce the contact angle by imparting a Wenzel state. Various characterization techniques (XRD, XPS, and SEM) were performed in order to detect the crystallographic phases in the scales, analyze carbon content and determine the morphology of the oxide layer. Morphological features of the oxide platelets were quantified and platelet width, spacing and height were found to correlate well with the apparent contact angle trend as a function of oxidation time.

Preparation of fabric strain sensor based on graphene for human motion monitoring

To date, wearable sensors are increasingly finding their way into application of healthcare monitoring, body motion detection and so forth. A stretchable and wearable strain senor was fabricated on the basis of commercially available spandex/nylon fabric by the integration of conductive graphene network. Specifically, a simple graphene oxide dip-reduce method that enabled scalable fabrication pathway was employed. The good recovery of the graphene-coated fabric led to consistent resistance values despite the strain applied on the fabric and exhibited high gauge factor around 18.5 at 40.6% strain. Moreover, the graphene-coated fabric sensor could detect human motions such as finger bending with acceptable mechanical properties against un-coated fabrics, indicating that it has huge potential in wearable sensors applications.

Improving the compatibility of an Y-TZP/porcelain system using a new composite interlayer composition.

The aim of this study was to evaluate the effects of different cooling procedures and a new composite interlayer composition on the flexural strength, and veneer delamination resistance, of an all-ceramic veneered translucent Y-TZP core. One hundred twenty bar-shaped specimens of a translucent Y-TZP ceramic were prepared and divided into three groups: (1) no composite interlayer; (2) a glass interlayer (silica-based glass); (3) a mixed composite interlayer of glass and porcelain veneer material. A veneering porcelain (with and without a composite interlayer) was applied on the specimen surface and sintered. Each core-veneer group was cooled using a rapid or a slow cooling rate. All specimens were tested in four-point bending. Data were statistically analyzed using two-way ANOVA, followed by Post-Hoc tests with Bonferroni correction (α=0.05) and Weibull analysis. The group with no interlayer using the rapid cooling technique exhibited the highest flexural strength. However, with low reliability and the greatest delaminated area of porcelain under tension. A glass interlayer between porcelain veneer and zirconia core presents as a good alternative for maintaining flexural strength and porcelain veneer delamination resistance in zirconia based restorations.