Search

The electrochemical behaviour of CP-Ti (commercially pure-Ti) and Ti–6Al–4V, commonly used implant materials, particularly for orthopedic and osteosynthesis applications, were investigated together with that of other Ti based alloys viz. Ti–13Nb–13Zr, Ti–15V–3Cr–3Al–3Sn, Ti–13Nb–20Zr, Ti–20Nb–20Zr and gum metal. The corrosion properties were evaluated through the analysis of the corrosion potential variation with time, potentiodynamic polarisation curves, and electrochemical impedance spectroscopy (EIS) test results. Very low current densities were obtained (order of nA cm−2) from the polarisation curves, indicating a typical passive behaviour for all investigated alloys in artificial physiological solution. The corrosion rates obtained were in the order CP-Ti>Ti–6Al–4V>Ti–15V–3Cr–3Al–3Sn>Ti–20Nb–20Zr>Gum metal>Ti–13Nb–13Zr. The EIS results clearly revealed the capacitive behaviour (high corrosion resistance) with phase angles close to −60° and high impedance values (order of 104 Ω cm2) at low and medium ...

Hydroxyapatite Ca10(PO4)6(OH)2 has attracted widespread interest from both orthopedic and dental fields due to its excellent biocompatibility and tissue bioactivity properties. Since nanophase materials can mimic the dimensions of constituent components of natural tissues, the implants developed from nanophase material could serve as a successful alternative. However, the defects of hydroxyapatite ceramics, mainly brittleness and low fracture toughness, have been overcome by the use of nanophase hydroxyapatite coatings on the implant surfaces that integrate the good mechanical properties of metals and the bioactivity of hydroxyapatite. In the present investigation, Sol–gel hydroxyapatite was prepared from two different phosphorus precursors such as triethyl phosphate and phosphorus pentoxide respectively with calcium nitrate tetrahydrate as a calcium precursor. The effects of pH and liquid P31 Nuclear Magnetic Resonance spectroscopy for the solution aged at different periods were investigated and the synthesized hydroxyapatite powder was characterized by Transmission electron microscopy, X-ray Powder Diffraction, Fourier transform infrared spectroscopy and thermal analysis respectively. In order to fully understand the bioactivity of the synthesized materials, they were coated on 316L Stainless Steel implant surface by spin coating method at the spin speed of 2,000 Revolutions per minute. The effect of nanoparticles on the surface of 316L Stainless Steel implant was studied by adhesive strength measurements. The corrosion resistance property of the hydroxyapatite coatings was evaluated by electrochemical impedance analysis. From the results, it was observed that the hydroxyapatite coatings obtained from different precursors have very high resistance to corrosion with higher adhesive strength.

Glass-ceramic was prepared by sol–gel method using Ca(NO3)2·4H2O and P2O5 as Ca and P precursors, respectively. In order to improve the bioactivity of the implant material, glass-ceramic (β-Ca2P2O7) coating was developed on 316L SS substrate by spin coating method. Coating was annealed at different temperatures and its corrosion resistance was evaluated by electrochemical polarization and impedance analysis using Ringer’s solution as electrolyte. The results from the present study, show excellent corrosion resistance for coated 316L SS, corroborated by the high values of charge transfer resistance from impedance analysis and higher breakdown and repassivation potential with the corresponding lower current density from polarization measurements. Based on the results, the glass-ceramic coating on 316L SS can be considered as a corrosion resistant material.

Hydroxyapatite (HAP) was synthesised by a precipitation method, using naturally available chicken eggshell (Ca source) and phosphoric acid (P source). The synthesised powder was electrophoretically deposited on 316L stainless steel (316L SS). The chemical composition of the synthesised powder was analysed. Ca was estimated by conventional EDTA titration and P by a gravimetric method. The Ca/P ratio was found to be 1·67, which resembles the stoichiometric HAP ratio. Fourier transform infrared (FT-IR) and powder X-ray diffraction (XRD) techniques were employed to confirm HAP formation. FT-IR spectra showed the characteristic peaks for phosphate and hydroxyl groups. The XRD results revealed that the major characteristic peaks of HAP appear in the regions of approximately 26°, 28°, 29°, 30–35°, 39°, 46°, 49° and 50° (2θ) and also indicated that no impurities are formed during HAP formation. The in vitro evaluation of HAP coated 316L SS was performed in simulated body fluid (Ringer’s solution) of pH 7·...

Sodium polyacrylate (SPA) is a popular super absorbent commonly used in children diapers, sanitary pads, adult diapers etc. The use of SPA is in force from past 30 years and the newer applications like as food preservant are evolving. SPA is recently discovered by our group for improvement of sensitivity of colorimetric agents. Though the discovery of improvement in sensitivity is phenomenal, the mechanism still remains a puzzle. A typical assay reagent contains colorimetric/fluorescent reagents, buffers, salts, stabilizers etc. These chemicals are known to influence the water absorptivity of SPA. If we were to perform chemical/biochemical assays on SPA absorbed reagents effect of salts and other excipients on colorimetric/fluorescence compounds absorbed on SPA is very important. The hofmeister series are standard for studying effect of salts on permeability, stability, aggregation, fluorescence quenching etc. We recently studied affect of urea, sodium chloride, ammonium sulfate, guanidine thiocayanate on fluorescence characteristics of fluorescence compounds and noted that except urea all other reagents have resulted in fluorescence quenching and urea had an opposite effect and increased the fluorescence intensity. This result was attributed to the different water structure around fluorescent in urea solution versus other chaotropic agents.

Donor –linker –acceptor (DSSA) is a concept in fluorescence chemistry with acceptor being a fluorescent compound (FRET) or quencher. The DSSA probes used to measure thiol levels in vitro and in vivo. The reduction potential of these dyes are in the range of −0.60 V, much lower than the best thiol reductant reported in literature, the DTT (−0.33 V). DSSA disulphide having an unusually low reduction potential compared to the typical thiol reductants is a puzzle. Secondly, DSSA probes have a cyclized rhodamine ring as acceptor which does not have any spectral overlap with fluorescein, but quenches its absorbance and fluorescence. To understand the structural features of DSSA probes, we have synthesized DSSANa and DSSAOr. The calculated reduction potential of these dyes suggest that DSSA probes have an alternate mechanism from the FRET based quenching, namely hydrophobic interaction or dye to dye quenching. The standard reduction potential change with increasing complexity and steric hindrance of the molecule is small, suggesting that ultra- low Eo’ has no contribution from the disulphide linker and is based on structural interactions between fluorescein and cyclized rhodamine. Our results help to understand the DSSA probe quenching mechanism and provide ways to design fluorescent probes.

Glycyrrhiza glabra is an ancient herbal medicine rich in large number of secondary metabolites which attribute to its therapeutic properties. These metabolites are usually obtained from field grown plants and their yields vary greatly on the basis of environmental conditions. Plant tissue culture can thus be a preferred method for consistent production of such metabolites. This study dealt with the enhancement of flavonoids through precursor feeding in callus cultures of G. glabra and investigated the influence of cinnamic acid on phenylalanine ammonia lyase (PAL) activity and production of licochalcone A, liquirtigenin and licoisoflavone B. Unorganized callus cultures were established from young leaf explants on Murashige and Skoog’s (MS) medium supplemented with NAA (1mg/l), BAP (0.5 mg/l) and various concentrations of cinnamic acid. Flavonoids were obtained from calli through solvent extraction and were identified and quantified through Gas-Chromatography Mass spectrometry. Cinnamic acid supplementation at appropriate concentrations (50mg/100ml for licochalcone A and liquirtigenin, and 125mg/100ml for licoisoflavone B) significantly increased their production to 1.28, 1.2 and 9.76 folds respectively. However, prolonged treatment of cinnamic acid at concentration beyond 50mg/100ml led to decrease in the production of liquirtigenin and licochalcone A , but caused fair increase in licoisoflavone B. Also cinnamic acid concentrations higher than 50mg/100ml reduced the activity of PAL enzyme due to its feedback inhibition, but at the same time might have modulated other intermediate enzymes of the pathway like chalcone isomerase favoring the formation of licoisoflavone B. Therefore, this study provides clear evidences of enzymatic regulation of phenylpropanoid pathway by cinnamic acid in G. glabra callus cultures.

Metallic materials having good mechanical properties, high corrosion resistance, and good compatibility with biological materials are used as orthopedic devices. Type 316L stainless steel is the most widely used material for implant fabrication in India for orthopedic applications owing to their good corrosion resistance, hot and cold workability, excellent mechanical properties, and availability at low cost. However, it faces corrosion-related problems in physiological environment and thus releases toxic metal ions into the tissues surrounding the implants. Hence, hydroxyapatite (HAP) coatings over the metal implant have been developed as an alternative method to improve the surface conditions of the base metal. In the present investigation, the development of a sol-gel-derived hydroxyapatite coating on 316L SS is being explored. The corrosion resistance behavior of the coating was assessed through electrochemical studies involving cyclic polarization experiments and impedance analysis in Ringer's solution. The results have indicated that the sol-gel-derived HAP coatings exhibited excellent resistance to localized attack on pristine 316L SS.