Ihtesham Rehman

Characterization of hydroxyapatite and carbonated apatite by photo acoustic FTIR spectroscopy.

An understanding of the interfacial relationship between a bioceramic implant and the adjacent bonet issue is facilitated by precise characterization of the associated structures. The structure of different commercial synthetic hydroxyapatite powders and a novel carbonated apatite have been studied with photo-acoustic (PAS) Fourier transform infrared (FTIR) spectroscopy. The PAS technique is an ideal method for analysing biomaterials, as materials can be analysed without the need to reduce the particle size or to dilute with KBr. Spectra from carbonated apatite appear to be different from those of commercial hydroxyapatite powders, with the main difference lying in the carbonate and phosphate ratio. Commercial hydroxyapatite powders from different sources have also been analysed and compared.

Fourier Transform Infrared (FTIR) Spectroscopy of Biological Tissues

Abstract This article reviews some of the recent advances on FTIR spectroscopy in areas related to natural tissues and cell biology. It is the second review publication resulting from a detailed study on the applications of spectroscopic methods in biological studies and summarizes some of the most widely used peak frequencies and their assignments. The aim of these studies is to prepare a database of molecular fingerprints, which will help researchers in defining the chemical structure of the biological tissues introducing most of the important peaks present in the natural tissues. In spite of applying different methods, there seems to be a considerable similarity in defining the peaks of identical areas of the FTIR spectra. As a result, it is believed that preparing a unique collection of the frequencies encountered in FTIR spectroscopic studies can lead to significant improvements both in the quantity and quality of research and their outcomes. This article is the first review of its kind that provides a precise database on the most important FTIR characteristic peak frequencies for researchers aiming to analyze natural tissues by FTIR spectroscopy and will be of considerable assistance to those who are focusing on the analysis of cancerous tissues by FTIR spectroscopy.

Characterization of the transformation from calcium-deficient apatite to beta-tricalcium phosphate.

The structural changes that occur during the transformation of a Ca-deficient apatite, prepared by a wet chemical method, to β-TCp were investigated. X-ray diffraction (XRD) analysis of as-prepared samples and samples calcined at temperatures between 500 and 1100 °C showed that the transformation occurs over the temperature range 710–740 °C, under non-equilibrium conditions. The change in crystallite size with increasing calcination/sintering temperature was studied by XRD using the Scherrer formula. Fourier transform infra-red (FTIR) analysis indicated considerable structural change in samples above and below this temperature range. Changes were observed in the hydroxyl, carbonate and phosphate bands as the calcination temperature was increased from 500 to 1100 °C. Even once a single β-TCP phase is obtained at 740 °C there remains a considerable amount of structural change at temperatures between 740 and 1100 °C. This effect was illustrated by an unusual change in the lattice parameters of the β-TCP structure and significant changes in the phosphate bands of FTIR spectra as the calcination temperature was increased. The results obtained in this study show that the combined experimental techniques of XRD and FTIR are excellent complimentary methods for characterizing structural changes that occur during phase transformations.

Preparation and characterization of fluoride-substituted apatites.

Apatites were prepared with three different fluoride concentrations: 0.0 mM (pure hydroxyapatite) 2.5 mM and 5 mM. Reactions were performed in aqueous medium using a reaction between diammonium orthophosphate and calcium nitrate 4-hydrate and ammonium fluoride at temperatures of 3°, 25°, 60° and 90°C. The effects of reaction temperature and fluoride concentration on the crystal morphology, phase purity and crystallinity of the precipitates were observed, using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and ion chromatography. Transmission electron micrographs revealed that the crystallites precipitated at 3°C were spheroidal, but became increasingly acicular with increasing precipitation temperature. X-ray diffraction results indicated that all the materials produced were phase pure and that the crystallinity of apatites prepared at higher precipitation temperatures was higher than those prepared at lower precipitation temperatures. A significant difference in the a-axis dimension of fluoride-substituted apatites was observed, as compared to hydroxyapatite. FTIR spectroscopy revealed a hydroxyl band at 3568 cm-1, along with a broad peak of adsorbed water in the region of 3568 cm-1 to 2670 cm-1 in the hydroxyapatite and fluoride-substituted apatite powders. Hence by careful selection of the precipitation conditions and fluoride contents, the composition and morphology of fluoride-substituted apatite may be controlled and this has interesting implications for the development of these materials for biomedical implantation.

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties

OBJECTIVE The objective of this study was to enhance the mechanical strength of glass-ionomer cements, while preserving their unique clinical properties. METHODS Copolymers incorporating several different segments including N-vinylpyrrolidone (NVP) in different molar ratios were synthesized. The synthesized polymers were copolymers of acrylic acid and NVP with side chains containing itaconic acid. In addition, nano-hydroxyapatite and fluoroapatite were synthesized using an ethanol-based sol-gel technique. The synthesized polymers were used in glass-ionomer cement formulations (Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or fluoroapatite) were also incorporated into commercial glass-ionomer powder, respectively. The synthesized materials were characterized using FTIR and Raman spectroscopy and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. RESULTS After 24h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163-167 MPa), higher diametral tensile strength (DTS) (13-17 MPa) and much higher biaxial flexural strength (23-26 MPa) in comparison to Fuji II GIC (160 MPa in CS, 12MPa in DTS and 15 MPa in biaxial flexural strength). The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177-179 MPa), higher DTS (19-20 MPa) and much higher biaxial flexural strength (28-30 MPa) as compared to the control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184 MPa for CS, 22 MPa for DTS and 33 MPa for BFS) which were statistically higher than control group. CONCLUSION It was concluded that, both NVP modified and nano-HA/FA added glass-ionomer cements are promising restorative dental materials with improved mechanical properties.

Synthesis and characterization of nano-biomaterials with potential osteological applications

The manufacture of high-surface area, un-agglomerated nano-sized (1–100 nm) bioceramic particles are of interest for many applications including injectable/controlled setting bone cements, high strength porous/non-porous synthetic bone grafts, and the reinforcing phase in nano-composites that attempt to mimic the complex structure and superior mechanical properties of bone. In the present study, we report on the manufacture of nano-particle hydroxyapatite powders by several wet chemical methods, which incorporate a freeze-drying step. In particular, it was found that the emulsion-based syntheses yielded powders with high surface areas and small primary particle sizes. Freeze drying rather than oven drying of powders prepared by conventional wet chemical synthesis yielded a nano-sized powder with a comparatively higher surface area of 113 m2/g. All powders were calcined in air in a furnace at 900 °C to investigate the effects of synthesis method on phase purity and surface area. The materials were characterized by a range of analytical methods including Fourier-transform infrared spectroscopy employing the photo acoustic (PAS-FTIR) sampling technique, BET surface area analysis, X-ray powder diffraction (XRD), and the particles were examined using a transmission electron microscope (TEM).

Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis

Nano-particle hydroxyapatite (HA) rods, were rapidly synthesised using a three pump continuous hydrothermal process (using a water feed at up to 400 degrees C and at 24 MPa): the product was obtained as a highly crystalline and phase pure material, without the need for an ageing step or subsequent heat treatment.

Preparation and characterization of a novel bioactive restorative composite based on covalently coupled polyurethane-nanohydroxyapatite fibres

Nanohydroxyapatite (n-HAp) was prepared using a sol-gel method. n-HAp powder was obtained from the gel form by heat treatment followed by grinding using ball milling. A novel polyurethane composite material was prepared by chemically binding the hydroxyapatite to the diisocyanate component in the polyurethane backbone through solvent polymerization. The procedure involved the stepwise addition of monomeric units of the polyurethane and optimizing the reagent concentrations. The resultant composite material was electrospun to form fibre mats. The fibres were less than 1mum in thickness and contained no beads or irregularities. Chemical structural characterization of both the ceramics and the novel polymers were carried out by Fourier transform infrared and Raman spectroscopy. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy and Brunauer-Emmett-Teller surface area analysis were also employed to observe the crystal lattice and size and surface area of the n-HAp. Further characterization (by energy-dispersive X-ray analysis and SEM) of the spun fibres revealed the presence of elements associated with hydroxyapatite and polyurethane without the presence of any loose particles of hydroxyapatite, indicating the formation of the covalent bond between the ceramics and the polymer backbone.

Synthesis and characterisation of magnesium substituted calcium phosphate bioceramic nanoparticles made via continuous hydrothermal flow synthesis

Continuous hydrothermal flow synthesis (CHFS) technology has been used as an efficient and direct route to produce a range of largely crystalline magnesium substituted calcium phosphate bioceramics. Initially, magnesium substituted hydroxyapatite, Mg-HA, according to the formula [Ca10−xMgx(PO4)6(OH)2] was prepared in the CHFS system for x = 0.2 [where x:(10 − x) is the Mg:Ca ratio used in the reagents]. Biphasic mixtures of Mg-HA and Mg-whitlockite were obtained corresponding to x values in the range x = 0.4–1.6. The direct synthesis of phase pure crystalline Mg-whitlockite [based on the formula (Ca3−yMgy(HPO4)z(PO4)2−2z/3] was also achieved using the CHFS system for the range y = 0.7–1.6 (this corresponds to the range x = 1.6–5.3). With increasing substitution of magnesium for calcium, the material became ever more amorphous and the BET surface area generally increased. All the as-precipitated powders (without any additional heat treatments) were analyzed using techniques including X-ray powder diffraction, Raman spectroscopy and Fourier transform infra-red spectroscopy. Transmission electron microscopy (TEM) images revealed that in the case of y = 1.2, the Mg-whitlockite material comprised of ca. 28 nm sized spheres. The use of the CHFS system in this context facilitated rapid production of combinations of particle properties (crystallinity, size, shape) that were hitherto unobtainable in a single step process.

Recent developments in processing and surface modification of hydroxyapatite

Abstract The present paper reviews the developments in the fields of bioceramic materials and laser surface microstructuring of materials. The clinical success of a bioceramic implant depends largely on the biological response at the implant interface in addition to the sufficiency of the mechanical properties for the application. The use of lasers in the present paper is largely to tailor the topography, surface properties and composition with a view to enhancing the implant biocompatibility. Developments in production methods for hydroxyapatite [HA: Ca10(PO4)6(OH)2] are also discussed with the advantages of producing nanocrystalline material via emulsion routes. The improved mechanical stability featured by nanocrystalline HA should promote clinical success in further load bearing applications.