Nandadulal Dandapat

Development of New Localized Drug Delivery System Based on Ceftriaxone-Sulbactam Composite Drug Impregnated Porous Hydroxyapatite: A Systematic Approach for In Vitro and In Vivo Animal Trial

ABSTRACTPurposePresent investigation deals with an extensive approach incorporating in vitro and in vivo experimentation to treat chronic osteomyelitis, using hydroxyapatite porous scaffolds.Materials and MethodsHydroxyapatite was synthesized in the laboratory by wet chemical method, different porous scaffolds have been fabricated. In vitro studies include variation of porosity with interconnectivity, pore-drug interfacial studies by SEM-EDAX and drug elution studies (by HPLC) both in contact with PBS and SBF at ~37°C. In vivo trials were based on experimental osteomyelitis in rabbit model induced in tibia by Staphylococcus aureus. Characterizations included observation of histopathology, radiology and estimation of drug in both bone and serum for 42 days by HPLC method and subsequent bone-biomaterial interface by SEM.ResultsIt was established that lower pore percentage with a distribution of mainly micro-pores were found to be superior over the higher pore percentage both in vitro and in vivo. The criteria was matched with the 50N50H samples which had 50–55% porosity with an average pore size ~110 μm, having higher interconnectivity (10–100 μm), moderately high adsorption efficiency (~50%) when loaded with CFS (drug combinations consisting of irreversible b-lactamase inhibitor and b-lactam antibiotic). CFS release from HAp implants were faster in PBS than SBF. Further, both the results of in vitro and in vivo drug elution after 42 days showed release higher than minimum inhibitory concentration of CFS against Staphylococcus aureus. In vivo studies also proved the superiority of CFS loaded HAp implants than parenteral group based on eradication of infection and new bone formation.ConclusionsHAp based porous scaffold loaded with CFS and designed porosity (in terms of micro- and macro-porosity, interconnectivity) was found to be an ideal delivery system which could locally, sustainably release the composite antibiotic in reliable manner both in terms of in vitro drug elution behaviour in contact with SBF and in vivo animal trial.

Large area deposition of polycrystalline diamond coatings by microwave plasma CVD

Polycrystalline diamond (PCD) films have been grown over 100 mm diameter silicon (100) substrate, using microwave plasma chemical vapour deposition (MPCVD) technique. The deposition was carried out inside a 15 cm diameter quartz chamber with microwave power of 15 kW at 915 MHz frequency. Uniform substrate surface temperature of 1050°C with plasma heating was maintained with simultaneous cooling arrangement. The pressure was 110 Torr and the microwave incident power was 8.5 kW. Temperature uniformity and plasma geometry over the substrate are the key parameters for producing uniformly thick MPCVD diamond films of high quality. Thickness uniformity of as-deposited films is ±10% across 100 mm diameters with a growth rate of 1 µm.h–1. The grown PCD was characterized by X-ray diffractometry (XRD), Raman spectrometry, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and bright field imaging technique. Experimental results indicate columnar growth of a very densely crystalline PCD with (111) facets of high quality morphology.

Thermal cycling behavior of alumina-graphite brazed joints in electron tube applications

Abstract Alumina was joined with graphite by active metal brazing technique at 895, 900, 905, and 910 °C for 10 min in vacuum of 0.67 mPa using Ti-Cu-Ag (68.8Ag-26.7Cu-4.5Ti; mass fraction, %) as filler material. The brazed samples were thermal cycled between 30 and 600 °C and characterized. X-ray diffraction results show strong reaction between titanium and carbon as well as titanium and alumina. Scanning electron microscopy and helium leak tests show that the initial and thermal cycled brazed samples are devoid of cracks or any other defects and hermeticity in nature. Brazing strength of the joints is found to be satisfactory.

Microwave-assisted brazing of alumina ceramics for electron tube applications

Alumina was joined with alumina using microwave-assisted and conventional brazing methods at 960∘C for 15 min using TiCuSil (68.8Ag–26.7Cu–4.5Ti in wt.%) as the brazing alloy. The brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Vickers microhardness evaluation, brazing strength measurement and helium leak test. X-ray diffraction analysis confirmed the formation of Ti-based compounds at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. The elemental compositions at the joint cross-section were determined by energy dispersive X-ray analysis. Vickers microhardness measurement indicated reliable joint performance for the microwave-assisted brazed joints during actual application in an electron tube. Brazing strength measurement and helium leak test provided the evidence for good alumina-alumina joint formation.

Influence of growth conditions on microstructure and defects in diamond coatings grown by microwave plasma enhanced CVD

Diamond coatings were grown on SiO2/Si substrate under various process conditions by microwave plasma chemical vapour deposition (MPCVD) using CH4/H2 gas mixture. In this paper, we present a microstructural study to elucidate on the growth mechanism and evolution of defects, viz., strain, dislocations, stacking faults, twins and non-diamond impurities in diamond coatings grown under different process conditions. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the diamond coatings. It has been shown that our new approach of prolonged substrate pre-treatment under hydrogen plasma yielded a new growth sequence that the SiO2 layer on the Si substrate was first reduced to yield Si layer of ∼150 nm thickness before diamond was allowed to grow under CH4–H2 plasma, created subsequently. It has also been shown that Si and O as impurity from the substrate hinders the initial diamond growth to yield non-diamond phases. It is being suggested that the crystal defects like twins, stacking faults, dislocations in the diamond grains and dislocations in the intermediate Si layer are generated due to the development of non-uniform stresses during diamond growth at high temperature.

Severe wear behaviour of alumina balls sliding against diamond ceramic coatings

At present alumina is the most widely used bio-ceramic material for implants. However, diamond surface offers very good solid lubricant for different machinery, equipment including biomedical implants (hip implants, knee implants, etc.), since the coefficient of friction (COF) of diamond is lower than alumina. In this tribological study, alumina ball was chosen as the counter body material to show better performance of the polycrystalline diamond (PCD) coatings in biomedical load-bearing applications. Wear and friction data were recorded for microwave plasma chemical vapour deposition (MWCVD) grown PCD coatings of four different types, out of which two samples were as-deposited coatings, one was chemo-mechanically polished and the other diamond sample was made free standing by wet-chemical etching of the silicon wafer. The coefficient of friction of the MWCVD grown PCD against Al2O3 ball under dry ambient condition was found in the range of 0.29–0.7, but in the presence of simulated body fluid, the COF reduces significantly, in the range of 0.03–0.36. The samples were then characterized by Raman spectroscopy for their quality, by coherence scanning profilometer for surface roughness and by electron microscopy for their microstructural properties. Alumina balls worn out (14.2 × 10−1 mm3) very rapidly with zero wear for diamond ceramic coatings. Since the generation of wear particle is the main problem for load-bearing prosthetic joints, it was concluded that the PCD material can potentially replace existing alumina bio-ceramic for their better tribological properties.

Microscopic properties of MPCVD diamond coatings studied by micro-Raman and micro-photoluminescence spectroscopy

Diamond coatings were deposited on silicon (100) substrate using the microwave plasma chemical vapour deposition (MPCVD) technique at different process conditions. Process parameters such as CH4–H 2 gas mixture concentration, microwave power, chamber pressure and substrate temperature were varied. The diamond coatings were characterized by micro-Raman and micro-photoluminescence (PL) spectroscopy techniques. In this paper we report a comparison of the overall quality of MPCVD polycrystalline diamond coatings grown under different processing conditions in terms of stress distribution, thickness uniformity and surface roughness. Micro-Raman spectroscopy studies over various points on the deposited coating showed that the Raman line widths of diamond peak varied from 3.2 to 18.3 cm−1 with the variation of CH4 and H2 gas concentration. The micro-PL spectra suggested the presence of impurity concentration and defects within the diamond coating synthesized at different processing conditions. Transmission electron microscopy (TEM) images provide the direct evidence of the presence of crystal defects which corroborates the Raman and PL results. The coherence scanning interferometry (CSI) showed that surface roughness of diamond coating varied from 0.43 to 11 μm with thickness at different positions of the three coating samples. It has been concluded that Raman line-width broadening and Raman-shift are due to the presence of crystal defects as well as non-uniform distribution of stresses present in the diamond crystals of the coating, due to the incorporation of Si as impurity element and non-uniform temperature distribution during growth. Defect density gets reduced at higher processing temperatures. It is also being proposed that better thickness uniformity and lower surface roughness can be achieved for coatings deposited at low methane concentration under optimized process conditions.

Interfacial properties of metallized alumina ceramics

An alumina ceramic material (purity-96%) was metallized by the conventional molybdenum-manganese (Mo-Mn) process in which an alumina substrate was coated with Mo-Mn paste and subsequently heat treated at 1400 °C for 10 min. During the entire process a moist H2 and N2 gas mixture (dew point-20 °C) with 3:1 ratio was passed continuously through the furnace. X-ray diffraction analysis of the metallized alumina substrate identified only molybdenum phase at the surface of the metallizing layer. The microstructural observations of the metallized alumina substrate were made by scanning electron microscopy. Energy dispersive X-ray analysis showed the elemental compositions along the cross-sectional region of the metallized alumina substrate. The adhesion of the metallic coatings on the alumina substrates was evaluated qualitatively by a scratch testing technique and quantitatively by an adhesion tester. Nanohardness measurements showed gradual change in the nanohardness values across the metallized alumina substrate.