O.P. Pandey

A review of bioactive glasses: Their structure, properties, fabrication and apatite formation

Bioactive glass and glass-ceramics are used in bone repair applications and are being developed for tissue engineering applications. Bioactive glasses/Bioglass are very attractive materials for producing scaffolds devoted to bone regeneration due to their versatile properties, which can be properly designed depending on their composition. An important feature of bioactive glasses, which enables them to work for applications in bone tissue engineering, is their ability to enhance revascularization, osteoblast adhesion, enzyme activity and differentiation of mesenchymal stem cells as well as osteoprogenitor cells. An extensive amount of research work has been carried out to develop silicate, borate/borosilicate bioactive glasses and phosphate glasses. Along with this, some metallic glasses have also been investigated for biomedical and technological applications in tissue engineering. Many trace elements have also been incorporated in the glass network to obtain the desired properties, which have beneficial effects on bone remodeling and/or associated angiogenesis. The motivation of this review is to provide an overview of the general requirements, composition, structure-property relationship with hydroxyapatite formation and future perspectives of bioglasses.Attention has also been given to developments of metallic glasses and doped bioglasses along with the techniques used for their fabrication.

Excitation induced tunable emission in biocompatible chitosan capped ZnS nanophosphors

Colloidal semiconductor nanomaterials exhibit color modulation which can be useful for various optoelectronic and biolabelling applications. Previous studies on CdSe and CdTe have shown tunable color modulation by varying the size of nanomaterials but toxicity of cadmium has created doubt for its end applications as biosensor. The recent work on ZnS:Mn2+ doped semiconductor has shown some viability for biolabelling but for tunable behavior particles of different doping concentration needs to be synthesized. In the present work all the above problems were considered and viable solution has been given to use ZnS:Mn2+ doped semiconductor using chitosan as capping agent. Here we report deliberate color modulation for chitosan capped ZnS:Mn2+ nanoparticles (NPs) synthesized in single step instead of many samples of different size. The tunable behavior is achieved by varying the excitation wavelength in same sample. Shifting of emission peak from dopant related emission at 590 nm (d states of Mn2+) to 481 nm de...

Gamma ray induced modifications of quaternary silicate glasses

This paper reports the effects of gamma ray irradiation and glass composition on the optical and infrared spectra of quaternary silicate glasses. Experimental results reveal the formation of radiation-induced absorption bands in the visible region attributed to nonbridging oxygen hole centres. The band gap energy and the width of the energy tail above the mobility gap have been measured before and after irradiation. The decrease in the energy gap values has been discussed in terms of radiation-induced structural modifications and the glass composition. Changes in the infrared spectra with progressive gamma irradiation have been observed and explained with reference to the radiolysis of Si–O–Si bonds.

Antibacterial activity of silver: the role of hydrodynamic particle size at nanoscale.

Silver shows the highest antimicrobial activities amongst all metals. It is better than many first line antibiotics. The antimicrobial properties of silver can be tuned by altering its physical and surface properties. Researchers have demonstrated enhancement in the antibacterial properties of silver with decreasing particle size from bulk to nano. In the present article, we study the effect of particle size of silver at nanoscale on their antimicrobial properties. Two samples of silver nanoparticles (SNPs) of same physical size (≈8 nm) but different hydrodynamic size (59 and 83 nm) are prepared by chemical reduction of AgNO3 with oleylamine followed by phase transfer with triblock copolymer Pluronic F-127. Their antimicrobial properties are investigated by microdilution method against clinically important strains of gram positive (S. aureus and B. megaterium) and gram negative (P. vulgaris and S. sonnei) bacteria. Nearly 38-50% enhancement in the antibacterial action of SNPs was observed when their hydrodynamic size was reduced to 59 nm from 83 nm. It has been observed that the antibacterial action of SNPs was governed by their hydrodynamic size and not by their crystallite and physical size. The phenomenological model was also proposed which makes an attempt to explain the microscopic mechanism responsible for the size dependent antibacterial activities of silver.

Role of Different Range of Particle Size on Wear Characteristics of Al–Rutile Composites

The present article describes in detail the wear behavior of rutile-reinforced LM13 alloy composite at elevated temperatures. Rutile particles in different amounts were reinforced into LM13 alloy by the stir casting route. The microhardness measured at different areas indicates good interfacial bonding. Wear tests were conducted for composites containing rutile particles in 10 wt.% and 15 wt.% with variation in particle size (50–75 µm and 106–125 µm). The presence of ceramic particle in the matrix improves the hardness, wear resistance, thermal stability, and durability of the materials. The wear of composite at 200°C presented entirely different wear behavior mode than that at 250°C. The wear rate of fine size reinforced composite was substantially lower than that of coarse size reinforced composite with higher load at 200°C. A transition from mild-to-severe wear in composite was observed with higher load above 150°C. The morphology of wear track and debris indicates that nucleation of cracks around the void on the interface of the particles is the main cause of surface damage.

Effect of Particle Size on Wear Behavior of Al–Garnet Composites

Metal matrix composites are the potential candidate for the variety of structural applications such as those in aerospace, transportation, and defense because of the wide range of mechanical properties they possess. The present study aims to analyze the effect of particle size on the microstructural features, microhardness and wear behavior of composites. Composites reinforced with garnet particles of different size range (fine 50–75 µm) and (coarse 106–125 µm) in Al–Si alloy (LM13) were prepared by stir casting route. The microstructure obtained reveals nearly uniform distribution of ceramic particles inside the LM13 alloy matrix. Reinforcement of fine size particles has led to the increase in hardness of fine size reinforced composite to nearly 9% over coarse size reinforced composites, whereas wear resistance improved by 7% and 5% for 10 and 15 wt% reinforcement, respectively. However, the wear resistance increased considerably up to 13% for fine size reinforced composite when the reinforcement content was increased from 10 to 15 wt%.

Tunable emission in surface passivated Mn-ZnS nanophosphors and its application for Glucose sensing

The present work describes the tunable emission in inorganic-organic hybrid NPs which can be useful for optoelectronic and biosensing applications. In this work, Mn- ZnS nanoparticles emitting various colors, including blue and orange, were synthesized by simple chemical precipitation method using chitosan as a capping agent. Earlier reports describe that emission color characteristics in nanoparticles are tuned by varying particle size and with doping concentration. Here in this article tunable emission has been achieved by varying excitation wavelength in a single sample. This tunable emission property with high emission intensity was further achieved by changing capping concentration keeping host Mn-ZnS concentration same. Tunable emission is explained by FRET mechanism. Commission Internationale de l’Eclairage (CIE) chromaticity coordinates shifts from (0.273, 0.20) and (0.344, 0.275) for same naocrystals by suitably tuning excitation energy from higher and lower ultra-violet (UV) range. Synthesized n...

A growth kinetic study of ultrafine monodispersed silver nanoparticles

In this article we report the growth kinetics of ultrafine monodispersed silver nanoparticles prepared via thermal reduction of silver nitrate with oleylamine. Effect of nucleation and growth temperature and time on the quality and quantity of silver nanoparticles was monitored in terms of product yield, crystal phase, morphology, aggregation, particle size and size distribution. To understand the effect of kinetic parameters, purified silver nanoparticles were characterized by UV-visible, FTIR and photon correlation spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetry (TG). Irrespective of the kinetic conditions, oleylamine always reduces AgNO3 into spherical Ag nanoparticles with simple cubic structure. The nanoparticle yield is highest for 21 mM oleylamine. Its size decreases with increasing oleylamine concentration and levels off at 3.5 nm with a polydispersity of 0.12. When concentration of oleylamine is <15 mM, agglomerated silver nanoparticles resulted while they self-assembled into hexagonal close pack structure when oleylamine is ≥15 mM. Nucleation at 200 °C for 30 min and growth at 150 °C for 4 h are the optimum processing parameters for highest nanoparticle yield (60%), lowest particle size (3.5 nm) and polydispersity index (0.12) with no or very little agglomeration.

Evolution of structural and thermal properties of carbon-coated TaC nanopowder synthesized by single step reduction of Ta-ethoxide

Carbon-coated nano tantalum carbide (TaC) has been synthesized at 800 °C using tantalum-ethoxide precursor by the single step chemical reaction route without using any external carbon source. The XRD results of the synthesized samples indicate that formation of TaC starts immediately upon heating but the complete transformation is observed only after 10 h of holding at 800 °C. The 10h sample shows distinct decarburization and oxidation peaks in DSC/DTG. The surface weighted sizes obtained from double-Voigt method were confirmed by BET. The BET analysis shows that synthesized powders have large surface area and contain a mixture of micropores and mesopores. The morphology and particle size distribution analysis shows that the powders are of faceted to spherical shape with thin carbon coating having size variation primarily between 20–40 nm. DSC/TG, XRD and microstructure analysis results have been used to predict the mechanism for the formation of the carbon coated nano-TaC particles.

Combined and individual doxorubicin/vancomycin drug loading, release kinetics and apatite formation for the CaO–CuO–P2O5–SiO2–B2O3 mesoporous glasses

The novel mesoporous glass series based on (25 − x)CaO–xCuO–10P2O5–5B2O3–60SiO2 (x = 2.5, 5, 7.5, 10) has been prepared using the sol–gel technique. The pore size of the prepared mesoporous bioactive glasses (MBG) lies between 6.1 and 9.1 nm, whereas the surface area varies from 281 to 418 m2 g−1. The pH variation, zeta potential, Fourier transform infra-red (FTIR) spectroscopy and simulated body fluid (SBF) studies indicated the in vitro bioactivity of all the MBGs. The MBGs were loaded with the anticancerous and antibacterial drugs, doxorubicin and vancomycin, respectively. The increasing copper content predominantly influenced the bioactive properties as well as the drug loading and release kinetics of the doxorubicin and vancomycin drugs. In addition to the individual loading of drugs in the MBG, both the drugs were also loaded together in the MBG to investigate the effect of combined loading on the release capability of the MBGs.