Mithlesh Kumar Sinha

Fabrication and characterization of porous hydroxyapatite ocular implant followed by anin vivo study in dogs

Porous hydroxyapatite ocular implant was fabricated by a novel and simple method using hydroxyapatite powder synthesized in the laboratory. The porosity and pore size of the implant were controlled to make it light in weight as well as suitable for rapid vascularization after implantation. The implant was characterized by X-ray diffraction studies, infrared spectra and chemical analysis for phase purity and chemical composition. The pore morphology and pore size distribution of the samples were investigated by scanning electron microscope (SEM). Thereafter, efficacy of the implant was examined byin vivo study in dogs. Clinical, haematological and radiological studies indicated the suitability of the implant for replacement of the lost eye of human patients.

Development of Hydroxyapatite Coating by Microplasma Spraying

Bioactive hydroxyapatite (HAP) coating (Ca/P-1.67) was developed on surgical grade SS316 L substrate using the microplasma spraying (MIPS) process with low (1.5 kW) plasmatron power. The MIPS-HAP coating showed both crystallinity and volume percent open porosity much higher than those usually reported for HAP coating deposited by the conventional macroplasma spraying (MAPS) process with high plasmatron power. The X-ray diffraction (XRD) data identified the coating to be nearly phase pure. The Fourier transformed infrared (FTIR) data suggested that a process of dehydroxylation and rehydroxylation might have occurred in the as-sprayed and post-heat treated coatings, respectively. The coating had a highly heterogeneous microstructure comprising of splats, completely and/or partially molten and unmelted splats retaining a nonflattened core, micropres, macropres, inter-, and intrasplat cracks.

Synthetic hydroxyapatite-based integrated orbital implants: A human pilot trial

PURPOSE Orbital implants are used as fillers following enucleation or evisceration surgeries to replace the lost volume for better cosmesis and motility of the artificial eye. Over the last decade porous hydroxyapatite (HAp) implants derived from the naturally occurring corals, are increasingly used. Recently synthetic HAp-based implants have been introduced. After fibrovasculrisation they have the added advantage of being directly integrated with the artificial shell, thereby increasing the motility to a great extent. The current study, evaluated the efficacy of two different models of synthetic HAp with 75% porosity and pore sizes ranging from 100 to 300 mm. METHODS Synthetic HAp powders were prepared with a novel wet chemical route. Two models of porous orbital implants with the characteristic designs for both evisceration and enucleation surgery were developed, characterised and implanted to consecutive 25 human subjects, 17 following evisceration, and 8 following enucleation. The postoperative performances of these implants were evaluated in respect to the degree of volume replacement (implant + prosthesis), presence/absence of lagophthalmos and lower eye-lid laxity, status of socket and fornices. Magnetic resonance imaging assessed the stability of the implants within the socket and progressive fibro-vascularisation within the porous scaffold as a function of time. Finally, motility of the implants as well as the prostheses (horizontal movements by Lister Perimeter) and subjective cosmetic results (qualitative) were also evaluated. RESULTS During the 2.5 years of follow-up study, no significant postoperative complications were noticed. One case, showed an anterior implant exposure of 3-4 mm, and was managed with donor scleral patch graft and one case of conjunctival thinning was corrected by re-suturing the conjunctival dehiscence. Fourteen of the 25 patients had a very good movement of the prostheses (> 20 degrees horizontal movement) and the other 11 patients had a fair motility (10 - 20 degrees). The degree of volume replacement (with prosthesis) was found to be very good in 21 patients and fair in other 4 patients. All patients reported cosmetic satisfaction. CONCLUSION Synthetic HAp-based integrated orbital implants with this modified design were found clinically safe and cosmetically acceptable.

Self-assembled structures of hydroxyapatite in the biomimetic coating on a bioinert ceramic substrate

The tribological properties of alumina ceramic are excellent due in part to a high wettability because of the hydrophilic surface and fluid film lubrication that minimizes the adhesive wear. Such surfaces are further modified with bioactive glass/ceramic coating to promote direct bone apposition in orthopedic applications. The present communication reports the biomimetic coating of calcium hydroxyapatite (HAp) on dense (2-3% porosity) alumina (alpha-Al(2)O(3)) substrate (1cm x 1cm x 0.5 cm), at 37 degrees C. After a total period of 6 days immersion in simulated body fluid (SBF), at 37 degrees C, linear self-assembled porous (pore size: approximately 0.2 microm) structures (length: approximately 375.39 microm and width: 5-6 microm) of HAp were obtained. The phenomenon has been demonstrated by self-assembly and diffusion-limited aggregation (DLA) principles. Structural and compositional characterization of the coating was carried out using SEM with EDX facility, XRD and FT-IR data.

Comparative assessment of structural and biological properties of biomimetically coated hydroxyapatite on alumina (α-Al2O3) and titanium (Ti-6Al-4V) alloy substrates

Previous reports have shown the use of hydroxyapatite (HAp) and related calcium phosphate coatings on metal and nonmetal substrates for preparing tissue-engineering scaffolds, especially for osteogenic differentiation. These studies have revealed that the structural properties of coated substrates are dependent significantly on the method and conditions used for coating and also whether the substrates had been modified prior to the coating. In this article, we have done a comparative evaluation of the structural features of the HAp coatings, prepared by using simulated body fluid (SBF) at 25 degrees C for various time periods, on a nonporous metal substrate titanium-aluminium-vanadium (Ti-6Al-4V) alloy and a bioinert ceramic substrate alpha-alumina (alpha-Al(2)O(3)), with and without their prior treatment with the globular protein bovine serum albumin (BSA). Our analysis of these substrates by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectrometry showed significant and consistent differences in the quantitative and qualitative properties of the coatings. Interestingly, the bioactivity of these substrates in terms of supporting in vitro cell adhesion and spreading, and in vivo effects of implanted substrates, showed a predictable pattern, thus indicating that some coated substrates prepared under our conditions could be more suitable for biological/biomedical applications.

Low-temperature aging of zirconia toughened alumina under humid conditions

Abstract Changes in crystalline phases resulting from low-temperature annealing of different yttria (3 mol%) and ceria (14 mol%) doped PSZ and TTA compositions were investigated under controlled humidity conditions between 150 and 250 °C up to 24 h. It was observed that 70% of the tetragonal phase in 3Y-PSZ had transformed to monoclinic phase while this effect decreased as alumina was added to the system. However, the composition with Al 2 O 3 + 15 vol% 3Y-PSZ, which had the best mechanical properties, showed appreciable dependence on hydrothermal treatment. On the contrary, Ce-doped PSZ did not show any aging degradation.

Minerological studies on five plastic fire clays

Mineralogical studies on five plastic fire clays of India have been carried out by DTA, TG and electron microscopy. Studies were done on both ‘as received’ and ‘<1 μ fraction’ of clays. Results indicated that all the clays were predominantly kaolinite in nature and showed the main endothermic peak between 540° and 590°C and the exothermic peak between 920° and 985°C. A large exothermic peak at 810°C and a weight loss of 5.35% between 700° and 900°C in case of Barachatarma clay indicated the presence of graphitic carbon in the same. Both Neyveli and Badampahar clays contained illite and goethite. Electron micrographs of Mohuamilan and Neyveli clays showed hexagonal flakes of well-ordered kaolinite. Some tubular particles were seen in Chittorpur, Neyveli and Badampahar clays in addition to the kaolinite particles.ZusammenfassungMittels DTA, TG und Elektronenmikroskopie wurden mineralogische Untersuchungen an fünf plastischen Feuertonproben aus Indien durchgeführt. Die Untersuchungen wurden einerseits an den Tonproben durchgeführt, wie man sie erhielt, andererseits an einer ‘<1 (μ-Fraktion’. Die Ergebnisse zeigten, daß alle Proben vorwiegend aus Kaolinit bestanden und intensive endotherme Peaks zwischen 540° und 590°C sowie exotherme Peaks zwischen 920° und 985°C aufwiesen. Ein intensiver exothermer Peak bei 810°C und ein Masseverlust von 5.35 % im Bereich von 700° bis 900°C bei dem Ton aus Barachatarma weisen auf die Gegenwart von Graphit in dieser Probe hin. Sowohl Ton aus Neyveli und auch aus Badampahar enthielten Illit und Geothit. Elektronenmikrographen von Ton aus Mohuamillan und Neyveli weisen hexagonale Flocken von geordnetem Kaolinit auf. Außer den Kaolinit-Partikeln konnten in den Tonproben aus Chittorpur, Neyveli und Badampahar auch noch einige tubusartige Partikel beobachtet werden.

Effect of grinding and subsequent annealing on the properties of transformation-toughened alumina ceramics

The extent of phase transformation due to grinding as well as the recovery of transformable phase upon annealing is discussed in the light of X-ray diffraction analysis and variation in mechanical properties.

Development of alumina ceramic head for hemi-hip joint prosthesis and its short term clinical report

In recent years polycrystalline alumina ceramics have been widely used as bioceramic implants in various orthopaedic applications in western countries. Alumina ceramics have been proved to be more biocompatible, resistant to corrosion and abrasion over conventional metals and, therefore, higher durability of the implants is envisaged. The present paper deals with the development of ceramic heads for hemi-hip prosthesis implants which have been implanted to 18 different human patients. Physical and mechanical characteristics and biocompatibility of these ceramic heads have been examined in short term clinical studies. The study revealed no abnormal clinical effect on the patients after 2 years of implantation.

Preparation and Characterization of Montmorillonite—Octadecylammonium Complex by X-ray and IR

A montmorlllonite-octadecylammonium intercalation compound has been prepared by treating sodium montmorillonite with alcoholic solution of octadecylamine hydrochloride. The XRD analysis of the compound prepared showed that the basal spacing increases from 12.5 A to 16.0 A. This suggests that octadecylammonium is intercalated in the interlayer space of montmorillonite. This fact has been supplemented by the IR spectra of the complex which shows the characteristic bands corresponding to—CH3, -CH2, and—NH+3 groups of alkylammonium ion.