Au nanoparticle-decorated aragonite microdumbbells for enhanced antibacterial and anticancer activities.

The present work reports the very first hydrothermal synthesis of 100% triclinic phase pure aragonite (A1) with microdumbbell microstructural architecture and Au Nanoparticle-decorated (AuNP-decorated) aragonites (A2, A3 and A4) with spherical, pentagonal/hexagonal and agglomerated AuNP-decorated microdumbbells having triclinic aragonite phase as the major and cubic AuNPs as the minor phase. Even in dark the AuNP-decorated aragonites (especially A2) show efficacies as high 90% against gram-negative e.g., Pseudomonas putida (P. putida) bacteria. Further the AuNP-decorated aragonites (A3) show anti-biofilm capability of as high as about 20% against P. putida. Most importantly the AuNP-decorated aragonites (A3) offer anti-cancer efficacy of as high as 53% while those of A1, A2, and A4 are e.g., 26%, 46% and 37%, respectively. For the very first time, based on detailed investigations, the mechanisms behind such advance antibiofilm and anticancer activities are linked to the generation of excess labile toxic reactive oxygen species (ROS). Thus, these materials show enormous potential as futuristic, multi-functional biomaterials for anti-bacterial, anti-biofilm and anti-cancer applications.

Effect of fluorine substitution on sintering behaviour, mechanical and bioactivity of hydroxyapatite.

Fluorine substituted hydroxyapatite (FAp) with different degree of fluorine (F) substitution, has been synthesized using hydrothermal synthesis method. In the present work, as synthesized powders were consolidated by sintering at 1200 °C in air for 1 h. The sintered specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) for phase analysis. Further, fluorine intake in the sintered specimens was evaluated using ion chromatography (IC). XRD peaks clearly showed biphasic nature of the sintered specimen. However, the sintered samples containing more than ∼60% fluorine substitution showed no ß-tricalcium phosphate (ß-TCP) phase formation. The IC results revealed that the degree of fluoridation decreased significantly in the sintered specimen compare to the respective as synthesized powders. The effect of actual fluorine content in the sintered specimens was further evaluated in terms of sinterability, surface energy, mechanical properties and in vitro cytocompatibility study. The surface energy of the sintered specimen decreased from 51.8 mN/m to 42.5 mN/m, in which degree of fluoridation varies from 0% to 110%. The in vitro cytocompatibility of the sintered specimen were carried out against mouse osteoblast cell line (MC3T3-E1). In vitro study showed that all the samples were nontoxic but cell proliferation for the samples containing more than 40% fluorine substitution became significantly low.

Phase pure, high hardness, biocompatible calcium silicates with excellent anti-bacterial and biofilm inhibition efficacies for endodontic and orthopaedic applications.

Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanoparticles (CSNPs) of the α-wollastonite phase without using any surfactant or peptizer at the lowest ever reported calcination temperature of 850 °C. Further, the phase purity is confirmed by quantitative phase analysis. The nano-network like microstructure of the CSNPs is characterized by FTIR, Raman, XRD, FESEM, TEM, TGA, DSC etc. techniques to derive the structure property correlations. The performance efficacies of the CSNPs against gram-positive e.g., S. pyogenes and S. aureus (NCIM2127) and gram-negative e.g., E. coli (NCIM2065) bacterial strains are studied. The biocompatibility of the CSNPs is established by using the conventional mouse embryonic osteoblast cell line (MC3T3). In addition, the biofilm inhibition efficacies of two varieties of CSNPs e.g., CSNPs(W) and CSNPs(WC) are investigated. Further, the interconnection between ROS e.g., superoxide (O2.-) and hydroxyl radical (.OH) generation capabilities of CSNPs and their biofilm inhibition efficacies is clearly established for the very first time. Finally, the mechanical responses of the CSNPs at the microstructural length scale are investigated by nanoindentation. The results confirm that the α-wollastonite phases present in CSNPs(W) and CSNPs(WC) possess extraordinarily high nanohardness and Young's moduli values. Therefore, these materials are well suited for orthopaedic and endodontic applications.

Nano- and micro-tribological behaviours of plasma nitrided Ti6Al4V alloys.

Plasma nitriding of the Ti-6Al-4V alloy (TA) sample was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as TAPN. The TA and TAPN samples were characterized by XRD, Optical microscopy, FESEM, TEM, EDX, AFM, nanoindentation, micro scratch, nanotribology, sliding wear resistance evaluation and in vitro cytotoxicity evaluation techniques. The experimental results confirmed that the nanohardness, Young's modulus, micro scratch wear resistance, nanowear resistance, sliding wear resistance of the TAPN samples were much better than those of the TA samples. Further, when the data are normalized with respect to those of the TA alloy, the TAPN sample showed cell viability about 11% higher than that of the TA alloy used in the present work. This happened due to the formation of a surface hardened embedded nitrided metallic alloy layer zone (ENMALZ) having a finer microstructure characterized by presence of hard ceramic Ti2N, TiN etc. phases in the TAPN samples, which could find enhanced application as a bioimplant material.

ROS mediated high anti-bacterial efficacy of strain tolerant layered phase pure nano-calcium hydroxide.

The present work provides the first ever report on extraordinarily high antibacterial efficacy of phase pure micro-layered calcium hydroxide nanoparticles (LCHNPs) even under dark condition. The LCHNPs synthesized especially in aqueous medium by a simple, inexpensive method show adequate mechanical properties along with the presence of a unique strain tolerant behaviour. The LCHNPs are characterized by FTIR, Raman spectroscopy, XRD, Rietveld analysis, FE-SEM, TEM, TG-DTA, surface area, particle size distribution, zeta potential analysis and nanoindentation techniques. The LCHNPs have 98.1% phase pure hexagonal Ca(OH)2 as the major phase having micro-layered architecture made up of about ~100-200nm thick individual nano-layers. The nanomechanical properties e.g., nanohardness (H) and Young's modulus (E) of the LCHNPs are found to have a unique load independent behavior. The dielectric responses (e.g., dielectric constant and dielectric loss) and antibacterial properties are evaluated for such LCHNPs. Further, the LCHNPs show much better antibacterial potency against both gram-positive e.g., Staphylococcus aureus (S. aureus) and gram-negative e.g., Pseudomonas putida (P. putida) bacteria even in dark especially, with the lowest ever reported MIC value (e.g., 1 µg ml-1) against the P. putida bacterial strain and exhibit ROS mediated antibacterial proficiency. Finally, such LCHNPs has almost ~8-16% inhibition efficacy towards the development of biofilm of these microorganisms quantified by colorimetric detection process. So, such LCHNPs may find potential applications in the areas of healthcare industry and environmental engineering.

Nanotribological response of a plasma nitrided bio-steel.

AISI 316L is a well known biocompatible, austenitic stainless steel (SS). It is thus a bio-steel. Considering its importance as a bio-prosthesis material here we report the plasma nitriding of AISI 316L (SS) followed by its microstructural and nanotribological characterization. Plasma nitriding of the SS samples was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as SSPN. The experimental results confirmed the formations of an embedded nitrided metal layer zone (ENMLZ) and an interface zone (IZ) between the ENMLZ and the unnitrided bulk metallic layer zone (BMLZ) in the SSPN sample. These ENMLZ and IZ in the SSPN sample were richer in iron nitride (FeN) chromium nitride (CrN) along with the austenite phase. The results from nanoindentation, microscratch, nanoscratch and sliding wear studies confirmed that the static contact deformation resistance, the microwear, nanowear and sliding wear resistance of the SSPN samples were much better than those of the SS samples. These results were explained in terms of structure-property correlations.

Nanomechanical responses of human hair.

Here we report the first ever studies on nanomechanical properties e.g., nanohardness and Young׳s modulus for human hair of Indian origin. Three types of hair samples e.g., virgin hair samples (VH), bleached hair samples (BH) and Fe-tannin complex colour treated hair samples (FT) with the treatment by a proprietary hair care product are used in the present work. The proprietary hair care product involves a Fe-salt based formulation. The hair samples are characterized by optical microscopy, atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDAX) genesis line map, EDAX spot mapping, nanoindentation, tensile fracture, and X-ray diffraction techniques. The nanoindentation studies are conducted on the cross-sections of the VH, BH and FT hair samples. The results prove that the nanomechanical properties e.g., nanohardness and Young׳s modulus are sensitive to measurement location e.g., cortex or medulla and presence or absence of the chemical treatment. Additional results obtained from the tensile fracture experiments establish that the trends reflected from the evaluations of the nanomechanical properties are general enough to hold good. Based on these observations a schematic model is developed. The model explains the present results in a qualitative yet satisfactory manner.