R. Roop Kumar

Functionally graded bioactive coatings of hydroxyapatite/titanium oxide composite system

Abstract Hydroxyapatite powder (P81B, HA, Plasma Biotal, UK) was mixed with titanium oxide (TiO 2 ) in different weight percentages for producing functionally graded bioactive coatings. Composite coatings were made on Ti6Al4V metal substrate. A functionally graded coating was obtained by coating titanium oxide (TiO 2 ) powders of known particle size as the first layer, which was sintered at 900 °C for a few minutes. Coating of subsequent layers of HA–TiO 2 composites of different weight ratios (75% TiO 2 and 25% HA, 50% TiO 2 and 50% HA, 25% TiO 2 and 75% HA, and 100% HA) were performed in sequence and these layers were sintered again at 900 °C for a few minutes so as to ensure a good adhesion between layers. The coatings were subsequently subjected to various characterization such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier infra-red spectroscopy (FTIR) and hardness studies. The XRD results confirmed the presence of the corresponding components in HA composites. SEM micrographs showed the surface morphology of the functionally graded layers, and the presence of elements was also identified by EDX analysis which confirms the versatility of the coating technique performed at low temperature. Nano-indentation studies revealed that HA–TiO 2 –Ti functionally graded coating yielded 15.1 and 0.405 GPa as the hardness and modulus values, respectively.

Modulus and hardness evaluations of sintered bioceramic powders and functionally graded bioactive composites by nano-indentation technique

Abstract Nano-indentation experiments on various sintered bioceramic powders and bioceramic functionally graded coatings, were performed with a berkovich indenter to establish an improved method for determining hardness and elastic modulus from load and displacement data. The materials included, spherical hydroxyapatite, SHA (Taihei chemicals, Japan), hydroxyapatite powders of different batches namely, P81B, P88 and P120 (Plasma Biotal, UK), in-house hydroxyapatite, HA and alpha tri-calcium phosphate, αTCP (Merck, Germany), functionally graded coatings (FGCs) of HA–G–Ti and HA–αTCP–Ti. The elastic modulus and hardness values of all the materials were obtained by nano-indentation with the corresponding load–displacement curves confirming the characteristic properties of the sintered materials and functionally graded coatings. The results showed that the SHA powder yielded the highest modulus and hardness value and P88 (HA) showed the least value confirming that its relatively softer than other bioactive powders. Furthermore, the continuous stiffness measurement also showed that SHA yielded the best mechanical property. In case of the FGCs, HA–G–Ti yielded higher values of modulus and hardness in comparison with HA–αTCP–Ti.

Chitosan-mediated crystallization and assembly of hydroxyapatite nanoparticles into hybrid nanostructured films

The synthesis and subsequent assembly of nearly spherical nano-hydroxyapatite (nHA) particles in the presence of trace amounts of the polysaccharide chitosan was carried out employing a wet chemical approach. Chitosan addition during synthesis not only modulated HA crystallization but also aided in the assembly of nHA particles onto itself. Solvent extraction from these suspensions formed iridescent films, of which the bottom few layers were rich in self-assembled nHA particle arrays. The cross-section of these hybrid films revealed compositional and hence structural grading of the two phases and exhibited a unique morphology in which assembled nHA particles gradually gave way to chitosan-rich top layers. Transmission electron microscope and selected area electron diffraction studies suggested that the basal plane of HA had interacted with chitosan, and scanning electron microscope studies of the hybrid films revealed multi-length scale hierarchical architecture composed of HA and chitosan. Phase identification was carried out by X-ray diffraction (XRD) and Rietveld analysis of digitized XRD data showed that the basic apatite structure was preserved, but chitosan inclusion induced subtle changes to the HA unit cell. The refinement of crystallite shape using the Popa method clearly indicated a distinct change in the growth direction of HA crystallites from [001] to [100] with increasing chitosan concentration. The paper also discusses the likelihood of chitosan phosphorylation during synthesis, which we believe to be a pathway, by which chitosan molecules chemically interact with calcium phosphate precursor compounds and orchestrate the crystallization of nHA particles. Additionally, the paper suggests several interesting biomedical applications for graded nHA–chitosan nanostructured films.

Functionally graded coatings of HA–G–Ti composites and their in vivo studies

Abstract Hydroxyapatite (HA) was synthesized by the wet chemical method using phosphoric acid (H 3 PO 4 ) and calcium hydroxide Ca(OH) 2 aqueous solutions. The prepared HA powders were fired at various temperatures ranging from 200 to 1200 °C for 2 h to obtain different degrees of crystallinity. The HA powders having different crystallinities were mixed with glass (G) in different weight percentages to form HA–G ceramics. The properties of the HA–G ceramics and the reaction of glass with HA were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infra-red spectrometry (FTIR). HA fired at higher temperature showed higher crystallinity and lower solubility. HA slightly reacted with glass and formed a small amount boron containing apatite. HA–G ceramic powders were coated on pure titanium substrate to obtain functionally graded layers of HA–G ceramics. The hydroxyapatite–glass–titanium (HA–G–Ti) composites consisting of HA fired at 400, 800 and 1200 °C were implanted in the femur bone of dog to examine the in vivo behavior of the implant. The pull-out strength between the HA–G–Ti composite and the bone demonstrated that the composite using HA fired at 1200 °C showed the highest pull-out test value of 20.6 MPa and good biocompatibility.

Biomimetic deposition of hydroxyapatite on brushite single crystals grown by the gel technique

Abstract Recently, attention has been paid to the production of hydroxyapatite (HA) single crystals or whiskers for making a variety of bioactive composites as new implant materials. Brushite single crystals were grown by gel technique at room temperature by chemical reaction method using Ca(NO 3 ) 2 ·4H 2 O and (NH 4 ) 2 HPO 4 as the reactants. Sodium silicate solution was used as the gel medium. The growth parameters, such as the gel density, concentration of the two reactants and pH of the medium, were varied to optimize the suitable growth conditions of brushite crystals. Single crystals of brushite of size nearly 10 mm in length were obtained when 1 M of (NH 4 ) 2 HPO 4 and 2 M of Ca(NO 3 ) 2 ·4H 2 O were used as the inner and outer reactants, respectively. The grown crystals were used as the seed crystals for HA deposition under electrochemical hydrothermal treatment in SBF solution. Experiments were performed by varying the temperature from 80°C to 200°C, current from 25 to 150 mA, and time from 10 to 60 min. A thick layer deposition of HA was obtained at 140°C for a time interval of 30 min by passing 100-mA current. Brushite single crystals and HA-coated brushite crystals were subjected to various characterizations, such as XRD, FTIR and SEM, to confirm the HA deposition on brushite.

Synthesis and Characterisation of Hydroxyapatite Nano-Rods/Whiskers

The use of precipitation chemistry to synthesize hydroxyapatite (HA) normally yields nano-crystals with various morphology and sizes depending on the synthesis conditions (e.g., temperature, concentration, level of agitation, pH, etc.). This study involved the synthesis of HA nano-rods/whiskers by modifying an existing chemical route for HA synthesis. The nano-rods were characterised for their structure and morphology and subsequently sintered. The mechanical properties of the sintered compacts were also assessed.

Growth of single crystals of bismuth sulpho iodide in gel

Single crystals of bismuth sulpho iodide have been grown in sodium silicate gel at room temperature by diffusing suitable reactants. In the first batch of experiments 3 to 7 g solution of BiCl3 was diffused into the gel containing 10 to 15% KI. Platelets of dimensions upto 5 mm were obtained in a period of 30 days. When thiourea of concentration 5 to 10% was used as the inner reactant and 2 to 4g of BiI3 dissolved in 50% HI was used as the outer reactant, thin needles of BiSI were obtained. Larger thick needles of BiSI were also obtained when thiourea was used as the inner reactant and solutions of Bi2O3 and BiI3 were used as the outer reactants. Similarly in the next batch of experiments H2S was used as the inner reactant instead of thiourea and the same outer reactants were diffused. Platelets of dimensions 5 to 8 mm in size were obtained. The effects due to gel density, concentration of the reactants and the neutral gel on nucleation are also discussed.

Hydroxyapatite-Chitosan Hybrid Nano-Materials

Self-assembled nano-materials are currently an area of research with high throughput due to the opportunities it provides to fields ranging from semiconductor engineering to gene delivery. There is also considerable interest in nano-particulate systems that attain a lower energy state by self-assembly through favorable and repeated surface interactions as they mimic those commonly found in natural biological systems. This work presents a simple route to first synthesise a highly stable suspension of nano-hydroxyapatite (~40nm) with chitosan and subsequently self-assemble the suspended nano-hydroxyapatite particulates onto a substrate.

Synthesis, Structural, Optical, Morphological and Elemental Characterization of CTAB Capped CdS Quantum Dots by Facile Chemical Precipitation Technique

In the present work, we report synthesis of CTAB capped cadmium sulphide quantum dots (CdS QDs) employing facile chemical precipitation technique in non aqueous medium at room temperature. Cadmium nitrate tetra hydrate and sodium sulphide flakes and cetyltrimethyl ammonium bromide (CTAB) was used as a precursors and capping agent respectively. The Powder X-Ray Diffraction (PXRD) confirms the hexagonal wurtzite structure and Field Emission Scanning Electron Microscopy (FESEM) shows the nanocrystalline nature. FESEM images showed a distribution of spherical particles with the diameter of 5.6–7.8 nm with the mean diameter of 7.1 nm. The change in band gap with size-quantization was investigated by reflectance UV spectroscopy. The functional groups were analyzed by the Fourier Transform Infrared Spectroscopy (FTIR) and elemental composition of the synthesized sample was determined by the EDX analysis.

Nanobioceramics: synthesis, characterization, and applications

Nanobioceramics based on Hydroxyapatite (HA) and its composites were synthesized using radio frequency (RF) induction suspension plasma spraying with a wet suspension as feedstock. The liquid suspension precursors were axially injected into the RF plasma at various plate powers (plasma energies), chamber pressures, probe distances and plasma gas flow rates. The processed powders varied in size according to the cyclones designed to collect the powders from medium to ultra-fine. The chamber collecting ultra-fine powder contained particles ranging from 10nm to 4μm. This study suggests that the processing parameters associated with the production of the ultra-fine powders interact in a complex manner but can be rationalised by considering the overall thermal treatment experienced by the particulates during plasma treatment.