Venkatesan Nandakumar

Friction stir processing of magnesium-nanohydroxyapatite composites with controlled in vitro degradation behavior.

Nano-hydroxyapatite (nHA) reinforced magnesium composite (Mg-nHA) was fabricated by friction stir processing (FSP). The effect of smaller grain size and the presence of nHA particles on controlling the degradation of magnesium were investigated. Grain refinement from 1500μm to ≈3.5μm was observed after FSP. In vitro bioactivity studies by immersing the samples in supersaturated simulated body fluid (SBF 5×) indicate that the increased hydrophilicity and pronounced biomineralization are due to grain refinement and the presence of nHA in the composite respectively. Electrochemical test to assess the corrosion behavior also clearly showed the improved corrosion resistance due to grain refinement and enhanced biomineralization. Using MTT colorimetric assay, cytotoxicity study of the samples with rat skeletal muscle (L6) cells indicate marginal increase in cell viability of the FSP-Mg-nHA sample. The composite also showed good cell adhesion.

In vitro and in vivo studies of biodegradable fine grained AZ31 magnesium alloy produced by equal channel angular pressing.

The objective of the present work is to investigate the role of different grain sizes produced by equal channel angular pressing (ECAP) on the degradation behavior of magnesium alloy using in vitro and in vivo studies. Commercially available AZ31 magnesium alloy was selected and processed by ECAP at 300°C for up to four passes using route Bc. Grain refinement from a starting size of 46μm to a grain size distribution of 1-5μm was successfully achieved after the 4th pass. Wettability of ECAPed samples assessed by contact angle measurements was found to increase due to the fine grain structure. In vitro degradation and bioactivity of the samples studied by immersing in super saturated simulated body fluid (SBF 5×) showed rapid mineralization within 24h due to the increased wettability in fine grained AZ31 Mg alloy. Corrosion behavior of the samples assessed by weight loss and electrochemical tests conducted in SBF 5× clearly showed the prominent role of enhanced mineral deposition on ECAPed AZ31 Mg in controlling the abnormal degradation. Cytotoxicity studies by MTT colorimetric assay showed that all the samples are viable. Additionally, cell adhesion was excellent for ECAPed samples particularly for the 3rd and 4th pass samples. In vivo experiments conducted using New Zealand White rabbits clearly showed lower degradation rate for ECAPed sample compared with annealed AZ31 Mg alloy and all the samples showed biocompatibility and no health abnormalities were noticed in the animals after 60days of in vivo studies. These results suggest that the grain size plays an important role in degradation management of magnesium alloys and ECAP technique can be adopted to achieve fine grain structures for developing degradable magnesium alloys for biomedical applications.

High glycolic poly (DL lactic co glycolic acid) nanoparticles for controlled release of meropenem

Nanospheres of low molecular weight poly lactic co glycolic acid (PLGA) with high glycolic acid content (10:90) and polylactic acid (PLA) are synthesized and loaded with meropenem, a broad spectrum antibiotic. The loading efficiency of the drug is 82 and 70% in PLGA 10:90 and PLA respectively. The rate of drug release is higher with PLGA 10:90 (3.2 μg/s) than with PLA (2.4 μg/s). Eighty and 60% of the encapsulated drug is released from the two polymers in 30 days respectively. Initial burst followed by sustained drug release is observed which is mathematically explained using a biphasic model. The drug release from the former polymer leads to two times lower E. coli growth than the release from the latter. The nanoparticles are biocompatible with no significant effect on the viability of 3T3 cells. This study indicates that PLGA 10:90 can be used for the delivery of antibiotics for interim period, especially for post orthopaedic surgeries.

Characterization and applications of cyclic β-(1,2)-glucan produced from R. meliloti

Cyclic β-(1,2)-glucan, with a degree of polymerization ranging from 17–28, without any substitution and a molar mass of 3101.5 Da, was produced from Rhizobium Meliloti MTCC-3402 in glutamic acid and a mannitol medium. The size of this glucan was less than those reported from oats and yeast. The main fraction was with 19 glucose residues (cavity size of 0.92 nm) and a melting temperature of 134.1 °C. Glucan encapsulates drugs (85–99%) such as curcumin, dexamethasone, reserpine, 6-methylcoumarin, 4-hydroxycoumarin and 4 methyl umbelliferone very efficiently. The encapsulation efficiency was better for hydrophobic than hydrophilic drugs (correlation coefficient of 0.92). Glucan was not cytotoxic towards L6 myoblast and 3T3 fibroblast cells and could be produced on the nanometer scale (average particle size 50–200 nm). Glucan exhibited dose dependent radical scavenging antioxidant activity. It was able to bind to dyes including methyl violet, trypan blue and bromocresol green indicating that the latter could be used in vivo at very low concentrations. Glucan decolorized coomassie brilliant blue R, bromophenol blue and bromocresol purple opening up applications in effluent treatment industries.

Toxicity of high glycolic poly(DL-lactic-co-glycolic acid) stabilized ruthenium nanoparticles against human promyelocytic leukemia cells

High glycolic poly-(lactic-co-glycolic acid) stabilized ruthenium nanoparticles were toxic towards human promyelocytic leukemia cells (HL60) and the mode of cell death was by apoptosis and in contrast it was not toxic towards blood lymphocytes. There was a significant increase in the oxidative stress within these cells and the toxicity of nanoparticles towards HL 60 cells could be attributed to the TGF β mediated signal transduction. This study indicated that such polymer stabilized ruthenium nanoparticles could be used as a selective anticancer agent.

A novel microwave recipe for an antibiofilm titanium surface

A microwave based method for the surface modification of titanium was demonstrated for biomedical applications. The surfaces were characterized using XRD, HR-SEM and Goniometer. The absence of rutile, anatase and brookite phases and the presence of an amorphous near-native oxide film were confirmed. The microwave oxidized (MWO) surfaces exhibited a significant antibiofilm activity against Escherichia coli and Staphylococcus aureus. In the presence and absence of the water pot, the oxidation times of 60 and 20min demonstrated a high antibiofilm property respectively. The surfaces turned more hydrophobic with increasing oxidation time. The viability of L6 cells remained unaffected on the MWO oxidized surfaces, signifying no loss in biocompatibility. This systematic study presents MWO as a promising technique for solving the biofilm problem faced by the otherwise robust titanium.