38 research outputs found
Mechanisms for covalent immobilization of horseradish peroxi-dase on ion beam treated polyethylene
The mechanism that provides the observed strong binding of biomolecules to
polymer sur-faces modified by ion beams is investigated. The surface of
polyethylene (PE) was modified by plasma immersion ion implantation with
nitrogen ions. Structure changes including car-bonization and oxidation were
observed in the modified surface layer of PE by Raman spec-troscopy, FTIR ATR
spectroscopy, atomic force microscopy, surface energy measurement and XPS
spectroscopy. An observed high surface energy of the modified polyethylene was
attributed to the presence of free radicals on the surface. The surface energy
decay with stor-age time after PIII treatment was explained by a decay of the
free radical concentration while the concentration of oxygen-containing groups
increased with storage time. Horseradish per-oxidase was covalently attached
onto the modified PE surface. The enzymatic activity of co-valently attached
protein remained high. A mechanism based on the covalent attachment by the
reaction of protein with free radicals in the modified surface is proposed.
Appropriate blocking agents can block this reaction. All aminoacid residues can
take part in the covalent attachment process, providing a universal mechanism
of attachment for all proteins. The long-term activity of the modified layer to
attach protein (at least 2 years) is explained by stabilisa-tion of unpaired
electrons in sp2 carbon structures. The native conformation of attached
pro-tein is retained due to hydrophilic interactions in the interface region. A
high concentration of free radicals on the surface can give multiple covalent
bonds to the protein molecule and de-stroy the native conformation and with it
the catalytic activity. The universal mechanism of protein attachment to free
radicals could be extended to various methods of radiation damage of polymers
Tomographic interferometry of a filtered high-current vacuum arc plasma
Tomography of a plasma enables the distribution of electron density to be visualized. We report on the design of two tomographic interferometer systems used to measureplasma electron density distributions in a high-current pulsed cathodic vacuum arc. The method is shown to be capable of microsecond time resolution. The spatial resolution of the quasioptical interferometer operating at 2 mm wavelength is 20 mm and the spatial resolution of the waveguide-based interferometer operating at 8 mm wavelength is 50 mm. In both cases the resolution achieved depends on the launching and receiving geometries. We developed criteria for assessing the tomogram for artifacts arising from limited sampling. First results of the spatial and temporal history of plasma in a high-current vacuum arc guided by a curved magnetic filter are presented and indicate poloidal field fluctuations reminiscent of magnetohydrodynamic instabilities in pinches. The applicability of the tomographic interferometry method to optimize plasma transport through the filter is also demonstrated.This work was in
part supported by the Australian Research Council
Substrate-Regulated Growth of Plasma-Polymerized Films on Carbide-Forming Metals
Although plasma polymerization is
traditionally considered as a
substrate-independent process, we present evidence that the propensity
of a substrate to form carbide bonds regulates the growth mechanisms
of plasma polymer (PP) films. The manner by which the first layers
of PP films grow determines the adhesion and robustness of the film.
Zirconium, titanium, and silicon substrates were used to study the
early stages of PP film formation from a mixture of acetylene, nitrogen,
and argon precursor gases. The correlation of initial growth mechanisms
with the robustness of the films was evaluated through incubation
of coated substrates in simulated body fluid (SBF) at 37Ā° for
2 months. It was demonstrated that the excellent zirconium/titanium-PP
film adhesion is linked to the formation of metallic carbide and oxycarbide
bonds during the initial stages of film formation, where a 2D-like,
layer-by-layer (Frankāvan der Merwe) manner of growth was observed.
On the contrary, the lower propensity of the silicon surface to form
carbides leads to a 3D, island-like (VolmerāWeber) growth mode
that creates a sponge-like interphase near the substrate, resulting
in inferior adhesion and poor film stability in SBF. Our findings
shed light on the growth mechanisms of the first layers of PP films
and challenge the property of substrate independence typically attributed
to plasma polymerized coatings
Plasma ion implantation enabled bio-functionalization of PEEK improves osteoblastic activity
Slow appositional growth of bone in vivo is a major problem associated with polyether ether ketone (PEEK) based orthopaedic implants. Early stage promotion of osteoblast activity, particularly bone nodule formation, would help to improve contact between PEEK implantable materials and the surrounding bone tissue. To improve interactions with bone cells, we explored here the use of plasma immersion ion implantation (PIII) treatment of PEEK to covalently immobilize biomolecules to the surface. In this study, a single step process was used to covalently immobilize tropoelastin on the surface of PIII modified PEEK through reactions with radicals generated by the treatment. Improved bioactivity was observed using the human osteoblast-like cell line, SAOS-2. Cells on surfaces that were PIII-treated or tropoelastin-coated exhibited improved attachment, spreading, proliferation, and bone nodule formation compared to cells on untreated samples. Surfaces that were both PIII-treated and tropoelastin-coated triggered the most favorable osteoblast-like responses. Surface treatment or tropoelastin coating did not alter alkaline phosphatase gene expression and activity of bound cells but did influence the expression of other bone markers including osteocalcin, osteonectin, and collagen I. We conclude that the surface modification of PEEK improves osteoblast interactions, particularly with respect to bone apposition, and enhances the orthopedic utility of PEEK
The effect of phase difference between powered electrodes on RF plasmas
This paper presents the results of measurements carried out on plasmas created in five different RF discharge systems. These systems all have two separately powered RF (13.56 MHz) electrodes, but differ in overall size and in the geometry of both vacuum chambers and RF electrodes or antennae. The two power supplies were synchronized with a phase-shift controller. We investigated the influence of the phase difference between the two RF electrodes on plasma parameters and compared the different system geometries. Single Langmuir probes were used to measure the plasma parameters in a region between the electrodes. Floating potential and ion density were affected by the phase difference and we found a strong influence of the system geometry on the observed phase difference dependence. Both ion density and floating potential curves show asymmetries around maxima and minima. These asymmetries can be explained by a phase dependence of the time evolution of the electrode-wall coupling within an RF-cycle resulting from the asymmetric system geometry
High entropy alloy thin films on SS304 substrates: Evolution of microstructure and interface modulated by energetic condensation in nanoscale
High entropy alloys (HEAs), as a novel material in the 21st century, possess several advantages, such as excellent corrosion & oxidation resistance and high mechanical properties. HEA thin films show these favourable properties with lower material costs than their bulk counterparts. Studying the HEA film-substrate interface represents challenges but is of extreme importance for the understanding of growth mechanisms with important implications for film adhesion. However, most HEA films were deposited on monocrystalline silicon substrates with limited practical applicability. Further, where commercial stainless steel, aluminium or titanium alloy substrates were used, the microstructure and chemistry at the interface were neglected. Here, we deposited AlCrFeCoNiCu0.5 HEA thin films on stainless steel 304 (SS304) substrates using cathodic arc deposition with different substrate biases. The crystallography and microstructure were investigated using an X-ray and electron-microscopy based chatacterization. A transition of an incoherent to semi-coherent interface was observed from 0Ā V to -50Ā V of the substrate bias. Energy dispersive spectroscopy demonstrated a transition of Cr2O3 to aluminum oxide across the interface. The nanoindentation tests revealed the significant improvement of mechanical properties of SS304 with HEA coatings. High-strength HEA (8.0Ā Ā±Ā 0.2Ā GPa) thin films with semi-coherent interfaces were manufactured on SS304
Nanosecond Responses of Proteins to Ultra-High Temperature Pulses
Observations of fast unfolding events in proteins are typically restricted to <100Ā°C. We use a novel apparatus to heat and cool enzymes within tens of nanoseconds to temperatures well in excess of the boiling point. The nanosecond temperature spikes are too fast to allow water to boil but can affect protein function. Spikes of 174Ā°C for catalase and ā¼290Ā°C for horseradish peroxidase are required to produce irreversible loss of enzyme activity. Similar temperature spikes have no effect when restricted to 100Ā°C or below. These results indicate that the āspeed limitā for the thermal unfolding of large proteins is shorter than 10(ā8) s. The unfolding rate at high temperature is consistent with extrapolation of low temperature rates over 12 orders of magnitude using the Arrhenius relation
Temperature Activated Diffusion of Radicals through Ion Implanted Polymers
Plasma immersion ion implantation
(PIII) is a promising technique for immobilizing biomolecules on the
surface of polymers. Radicals generated in a subsurface layer by PIII
treatment diffuse throughout the substrate, forming covalent bonds
to molecules when they reach the surface. Understanding and controlling
the diffusion of radicals through this layer will enable efficient
optimization of this technique. We develop a model based on site to
site diffusion according to Fickās second law with temperature
activation according to the Arrhenius relation. Using our model, the
Arrhenius exponential prefactor (for barrierless diffusion), <i>D</i><sub>0</sub>, and activation energy, <i>E</i><sub>A</sub>, for a radical to diffuse from one position to another
are found to be 3.11 Ć 10<sup>ā17</sup> m<sup>2</sup> s<sup>ā1</sup> and 0.31 eV, respectively. The model fits experimental
data with a high degree of accuracy and allows for accurate prediction
of radical diffusion to the surface. The model makes useful predictions
for the lifetime over which the surface is sufficiently active to
covalently immobilize biomolecules and it can be used to determine
radical fluence during biomolecule incubation for a range of storage
and incubation temperatures so facilitating selection of the most
appropriate parameters
Correlation between film structures and potential limits for hydrogen and oxygen evolutions at a-C:N film electrochemical electrodes
A correlation between film structures and the width of the potential windows defined by the dihydrogen and dioxygen evolutions in aqueous media at nitrogen-doped amorphous carbon thin film electrodes prepared using a filtered cathodic vacuum arc system is reported. A range of film structures were obtained by changing the nitrogen mass flow rate during deposition, and the film structures were determined using electron energy-loss spectroscopy. For the film electrodes, the width of the potential windows in 0.1 M NaOH and in 0.1 M HāSOā at a current density of 100 Ī¼A/cmĀ² exceed those for glassy carbon electrodes, and increase with an increase in the spĀ³C fraction in the a-C:N materials. A film electrode with a rich spĀ²C content, has a lower electrical resistance, but still possesses a relatively large potential window. These features combined allow the materials to be tailored for particular electroanalysis