Supercapacitors based on electrochemically deposited polypyrrole nanobricks

Simple and inexpensive electrodeposition method for the synthesis of polypyrrole (PPy) nanobricks has been reported. These PPy nanobricks are characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polypyrrole nanobricks exhibit amorphous nature as confirmed from XRD study. Based on SEM and TEM analysis, the formation of the spherical bunches of PPy nanobricks with average size of about 20–30 nm are inferred. The electrochemical performance of PPy electrode was evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge techniques. A high specific capacitance of 476 F·g^?1 was obtained within the potential range of ? 0.4 to 0.6 V in 0.5 M H₂SO₄ solution. Moreover, PPy electrode exhibited high discharge/charge efficiency of 89%.     

Cytotoxicity investigations of plasma sprayed calcium phosphate coatings

One potential alternative material to replace hydroxyapatite (HAp) as a coating material for plasma-sprayed coatings on implants for hip replacement is fluorapatite (FAp). FAp has advantages over HAp regarding the capability of being chemically stable during the coating process. This leads to surface coatings containing high apatite rates with a mechanical stability (bond strength, microhardness) comparable to HAp. From the technical point of view the production of FAp coatings is well investigated, although studies on biocompatibility of FAp coatings are fewer. This paper reports the production of HAp and FAp coatings with varying solubilities by plasma spraying and their in vitro cytotoxicity. Varying solubilities were realized by using modified plasma-spray parameters in common with suitable apatite powders with different crystallinities. Coating solubilities were evaluated by immersing the plasma-sprayed coatings in deionized water and electrolyte solution. Afterwards, cytotoxicity tests were performed using a modified half-slide technique. Cell attachment and cell morphology were evaluated. Neither HAp nor FAp coatings exhibited cytoxic influence on cells in culture. Results suggest that HAp coatings stimulate cell growth and FAp coatings do not. This could be explained by a negative effect on cell growth of the dissolved fluoride ions.     

Analysis of electrochemically deposited chromium films

Chromium films are deposited on mild steel substrates using chromic acid bath with formic acid as an additive. The effect of air annealing on the films has been investigated using hardness tests, grazing angle X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. It is observed that hardness of the chromium films goes on increasing from 1100 to 1500 VHN with annealing temperature till 500 C, which can be explained by formation of chromium carbide on the surface. The hardness of the films decreases with further annealing due to strong oxide formation as well as films cracking.     

Properties of calcium phosphate coatings deposited and modified with lasers

Physical, chemical and biological properties of calcium phosphate coatings fabricated by a pulse laser deposition method at room temperature (RT PLD) have been studied. In vitro evaluation of RT PLD coatings on bioresorbable polymers (Poly--caprolactone and Poly-L-lactide) have been carried out. It was shown that both polymers support osteoblast growth, with increased cell activity, alkaline phosphatase activity and total protein content on those surfaces that have been coated. The advantages of RT PLD coatings in biomaterials surface optimization are discussed.     

AES investigation of electrochemically deposited Co--W layers on copper

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of pH on electrochemically deposited CdSe thin films

Polycrystalline CdSe thin films have been electrodeposited at room temperature on stainless steel (ss) and fluorine doped tin oxide (FTO) coated glass substrate from aqueous electrolytes containing salts of cadmium acetate and selenium dioxide. The pH of the bath is varied from 1.75, at the interval of 0.25, to 3. The effect of pH on the photoelectrochemical (PEC), structural and optical properties of the deposited film is studied. The pH of the bath is optimized by the PEC technique and is observed to be 2.75. The analysis of the XRD patterns show that the deposited CdSe material is polycrystalline with a hexagonal crystal structure. SEM study shows that the total substrate surface is well covered by uniformly distributed spherical shaped grains. The optical absorption studies reveal that the pH of the electrolytic solution has a significant effect on the band gap of the CdSe thin film. The transition involved is direct with band gap energy E_g of 1.72 eV.     

Cytocompatibility of calcium phosphate coatings deposited by an ArF pulsed laser

In the current studies, we deposited ultra-thin hydroxyapatite films on a pure titanium substrate by pulsed laser deposition, and we examined the effects of these surfaces on rat bone marrow (RBM) cells. This method allowed deposition of 500-, 2,000-, and 5,000-A-thick hydroxyapatite films. X-ray diffraction showed that the amorphous films recrystallized to a hydroxyapatite crystal structure after annealing. The proliferation of RBM cells was unaffected by the hydroxyapatite films, but osteocalsin and alkaline phosphatase mRNA and protein levels were elevated in cells grown on 2,000- and 5,000-A-thick films. These results indicate that ultra-thin hydroxyapatite films generated by pulsed laser deposition are better at promoting osteogenesis than pure titanium surfaces.     

Dissolution behavior of simultaneous vapor deposited calcium phosphate coatings in vitro

Solubility is one of the most important properties in the field of biomaterial. The present paper evaluated the dissolution behavior of simultaneous vapor deposited calcium phosphate coatings in vitro. The coatings were immersed in calcium-free Hank's solution at different periods of time. Characterization of the coatings was performed using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Rutherford backscattering spectroscopy, prior to and after immersion. Amorphous coatings showed complete dissolution. Crystalline coatings showed that alpha tricalcium phosphate (α-TCP) phase dissolved steadily throughout the testing time leaving the stable hydroxyapatite phase undegraded. The increased in calcium and phosphate ions due to dissolution of α-TCP provided the means for reprecipitation of apatite on the coating, which became apparent after 7 days of immersion.     

Cytocompatibility of calcium phosphate coatings deposited by an ArF pulsed laser

In the current studies, we deposited ultra-thin hydroxyapatite films on a pure titanium substrate by pulsed laser deposition, and we examined the effects of these surfaces on rat bone marrow (RBM) cells. This method allowed deposition of 500-, 2000-, and 5000-Angstrom-thick hydroxyapatite films. X-ray diffraction showed that the amorphous films recrystallized to a hydroxyapatite crystal structure after annealing. The proliferation of RBM cells was unaffected by the hydroxyapatite films, but osteocalsin and alkaline phosphatase mRNA and protein levels were elevated in cells grown on 2000- and 5000-Angstrom-thick films. These results indicate that ultra-thin hydroxyapatite films generated by pulsed laser deposition are better at promoting osteogenesis than pure titanium surfaces.     

Characterization of electrochemically deposited Cu-Ni black coatings

Electrochemically deposited Cu-Ni black coatings on molybdenum substrate from ethylenediaminetetraacetic acid (EDTA) bath solution are shown to exhibit good optical properties (α=0.94, ε = 0.09). The deposit is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cu is present in metallic and +2 oxidation states in the as-prepared Cu-Ni black coating, whereas Ni²⁺ as well as Ni³⁺ species are observed in the same coating. Cu and Ni are observed in their metallic state after 10 and 20 min sputtering. X-ray initiated Auger electron spectroscopy (XAES) of Cu and Ni also agrees well with XPS investigations.     

Cellular response to calcium phosphate ceramics implanted in rabbit bone

Two hydroxyapatite ceramics, synthesized by sintering from bovine bone and from a mixture of phosphate tricalcium and natural hydroxyapatite, were implanted in bone sites in rabbits. From day 7 after implantation, osteoblast-like cells were visible with thin layers of new bone on both biomaterials. Histomorphometry showed progressive increase in volume and surface of newly formed bone. Signs of cell-dependent resorption were visible at the surface of biomaterials and newly formed bone. There was a progressive decrease in relative volume and trabecular thickness of the biomaterials. Resorption of biomaterials appears to involve two cell types: multinucleated giant cells and osteoclast-like cells. The multinucleated giant cells observed had neither tartrate resistant acid phosphatase activity (TRAP) nor a ruffled border. Vesicles and vacuoles containing crystals observed in these cells suggest phagocytosis of biomaterials. The number of these cells decreased after day 14 following implantation. The osteoclast-like cells were TRAP positive. The structured modification and the TRAP activity demonstrated in the subjacent biomaterial suggest that the dissolution of the implant may be associated to an extracellular enzymatic activity of these cells. Electron microscopy revealed a clear zone and cytoplasmic membrane infolding in these cells, suggesting a ruffled border differentiation. The number of these cells increased with delay after implantation. It was concluded that the implantation of calcium phosphate ceramics in bone leads to new bone formation as well as to resorption of the biomaterials. The mechanism of resorption appears to associate crystal endocytosis by multinucleated giant cells and more classical resorption by osteoclast-like cells.     

Effects of MgO addition on sintering of calcium phosphate ceramics and composites

Bioactive ceramics attracts much attention as materials for bone implants, because of their high biocompatibility. For example, hydroxyapatite (HA) has bone-bonding ability through a bone-like apatite layer in body environment and β-tricalcium phosphate (β-TCP) has a high bioresorbability in body environment. In addition, HA/β-TCP composites has the characteristics of both HA and TCP. However, it is difficult to sinter the composite, so that MgO has been used as a sintering agent. In the present study, effects of MgO addition on sintering calcium phosphate ceramics and composites were investigated. In order to evaluate the effect of MgO on the composites, HA, HA/β-TCP(30wt%), and HA/β-TCP(50wt%) with 1wt% MgO were prepared and characterized. To clarify the role of MgO on sintering of calcium phosphate ceramics, HA, β-TCP, and α-TCP with different TCP content (0, 1, 2, 3, 4, and 5 wt%) were also prepared. The results suggest that MgO addition densified HA/β-TCP composites and gave higher strength composites. The results of monolithic calcium phosphate ceramics indicated MgO addition was effective on β-TCP and α-TCP, not on HA. The maximum content of Ca atom in β-TCP displaced with Mg atoms in MgO might be 24 atm%.     

Adjusting the chlorhexidine content of calcium phosphate coatings by electrochemically assisted co-deposition from aqueous solutions

Currently, a number of strategies to create either biologically active or antimicrobial surfaces of biomaterials are being developed and commercially applied. However, for metallic implants in contact with bone, both osteomyelitis and a fast and stable long-term fixation of implants are challenges to be overcome, especially in the case of bad bone quality. Therefore, the present work aims to develop compound coatings of calcium phosphate phases (CPP) and chlorhexidine (CHD) that combine bioactive properties with a strategy to prevent initial bacterial adhesion and thus offer a possible solution to the two major problems of implant surgery mentioned above. Using electrochemically assisted deposition of CPP on samples of Ti6Al4V together with the pH-dependent solubility of CHD, the preparation of coatings with a wide range of CHD concentrations (150 ng/cm² to 65 μ g/cm²) from electrolytes with CHD concentrations between 50 and 200 μ M was possible, thus allowing the adaptation of implant surface properties to different surgical and patient situations. Detailed SEM and FTIR analysis showed that coatings are formed by a co-deposition process of both phases and that CHD interacts with the deposition and transformation of CPP in the coating. For high CHD contents, coatings consist of CHD crystals coated by nano-crystalline hydroxyapatite.     

Effect of hot-press treatment on electrochemically deposited antimony telluride film

Antimony telluride thin film electrochemically deposited in a triethanol based alkaline electrolyte features amorphous structure, high electrical resistance, as well as fine morphology, minor impurity incorporation and anti-corrosivity. To further improve film thermoelectric performance, this film was subjected to hot-uniaxial-press (HUP) treatment at 170-250 °C. HUP treated films revealed crystallized structures, and exhibited 2-3 orders of magnitude improvement of electrical conductance. The [TeO₃²⁻]/[SbO₂⁻] of the deposition electrolyte was utilized to fine tune film composition and thermal electrical performance. Ni diffusion from the substrate into the film was also studied, and it can be reduced by using lower temperature and shorter time of HUP treatment. Film Seebeck coefficient and power factor reached 138 μV/K and 337 μW/K²?m, respectively, at elaborated deposition and HUP conditions.     

Preparation and mechanical properties of calcium phosphate/copoly-L-lactide composites

New artificial bone materials were prepared using calcium phosphates, hydroxyapatite and -tricalicum phosphate, and copoly-L-lactide, CPLA. Calcium phosphate powder and CPLA were mixed at 453 K for 10 min with various mixing ratios. Scanning electron microscope observations indicated that the composites of -tricalicum phosphate and CPLA were homogeneously dispersed and highly adhesive. Youngs modulus of the composites was the same as bone, and bending strength was over half that of bone. The improvement of Youngs modulus compared to the original two materials was due to a composite effect. The composites are expected to be usable as artificial bone materials.     

The nanostructure of an electrochemically deposited hydroxyapatite coating

The structure of an implant's coating can significantly affect its physical and chemical properties, and eventually – its clinical performance. In this paper, the nanostructure of an electrochemically deposited hydroxyapatite (EDHA) coating was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The X-ray analysis showed that the coating consisted predominantly of the stoichiometric HA phase. However, SEM and HRTEM revealed that EDHA coating is composed of two distinct regions: the upper layer consisted of platelet crystallites preferentially grown perpendicular to the substrate surface, while the lower layer was dense and uniform and consisted of nano-sized crystallites of HA. The possible effects of these different microstructures on the implant's after-implantation behavior are discussed.     

Microstructure formation in electrochemically deposited Copper thin films

The influence of the electrochemical potential and deposition mode on the preferred orientation, morphology and microstructure of crystallites in electrochemically deposited (ECD) copper thin films was investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM) and the diffraction of back‐scattered electrons (EBSD). As a working electrode for the ECD process, thin gold layers were employed that were deposited on floating‐glass substrates in a vacuum evaporation process. With increasing negative electrochemical potential in the ECD process, the deposition mode changed from the charge transfer controlled one to the diffusion controlled one. At the highest electrochemical potentials, the copper deposition and the hydrogen release were running concurrently. The change of the deposition mode was accompanied by a change of the surface roughness of the thin films and by a change of the direction and degree of the preferred orientation of crystallites. The surface roughness of the deposited copper thin films increased with increasing electrochemical potential. Compact plate‐like crystallites with the preferred orientation {111} grew in the transport controlled deposition mode. Development of the {111} texture was supported by the {111} preferred orientation of the gold layers and by surface energy of copper, which is the lowest in the (111) plane. The diffusion controlled deposition mode was characterized by the growth of globular {110}‐oriented crystallites. The {110} texture resulted from the minimization of the anisotropic strain energy of copper via reduction of the structure defects in this deposition modus. For highest electrochemical potentials, the copper deposition run simultaneously with the development of hydrogen that resulted in growth of needle‐like crystallites with the {100} texture.     

Growth,characterization and biocompatibility of bone-like calcium phosphate layers biomimetically deposited on metallic substrata

Much research has been devoted to the coating of orthopedic and dental implants with porous ceramics, such as hydroxyapatite to increase hard tissue integration in vivo. Chemical immersion in simulated body fluids and supersaturated calcium-phosphate solutions (SCPS) have been shown to elicit apatite coatings on the order of 10–100 μm of thickness, which are very homogenous and would be more favorable to biological interaction than plasma-sprayed coatings.This study focuses on the growth, characterization and biocompatibility of bone-like apatite layers on metallic biomaterials produced through diminished time duration chemical immersion. The method presented here includes a pre-calcification step, in which samples were immersed in a boiling Ca(OH)₂ solution to initiate and increase favorable ion exchange prior to immersion. Subsequent immersion in SCPS produced homogenous coatings of calcium phosphate with a thickness of 20–30 μm, 100% coverage and crystal sizes of 1–2 μm in 3 days. Coated samples were favored biologically over non-coated samples by osteoblast cells as indicated by alkaline phosphatase activity. This study suggests that an industrially viable method of chemical immersion in a SCPS, coupled with simple pre-treatments can produce calcium phosphate coatings that favor positive biological interactions, conducive to osseointegration.