IN VITRO PREPARATIONS AND STUDIES ON THE SUBSTITUTION OF CADMIUM AND LEAD IONS ON BIOMIMETIC HYDROXYAPATITE NANOCRYSTALS
IN VITRO PREPARATIONS AND STUDIES ON THE SUBSTITUTION OF CADMIUM AND LEAD IONS ON BIOMIMETIC HYDROXYAPATITE NANOCRYSTALS
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Date
2016-12
Authors
OCHIGBO, Victor
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Abstract
The hydrothermal and wet precipitation methods are successful routes to synthesize high purity hydroxyapatite (HA) as well as Cadmium and Lead doped hydroxyapatites at physiological conditions. In this research, Ca(NO3)2.4H2O and NH4H2PO4 were chosen as the precursor materials used to synthesize HA. HA was first synthesized via optimization of the wet precipitation method under vigorous stirring using various precursor concentrations of 0.5, 1.0, 1.5 and 2.0M. The prepared HA powders were calcined at different temperatures of 300, 500, 800 and 1100oC for 3 hours and were characterized using XRF/EDX, FTIR and XRD. The FTIR bands were distinct, narrower with increased intensities when the precursor concentration and calcination temperature increases. XRF/EDX indicates an increase in Ca/P ratio as calcination temperature increased from 300°C to 500°C and at a particular calcination temperature, an increase in precursor concentration showed an irregular increase in the Ca/P ratio, an indication of a weak effect of precursor concentration on Ca/P ratio. XRD showed that as the precursor concentration is increased, with respect to the calcination temperature, peak intensities increased. These observations of peak intensities and degree of crystallinity are reflected with a corresponding increase in crystallite size (D) with increase in both the precursor concentration and calcination temperature. The result showed that the HA particles were all in nano regime for all the precursor concentrations, although, the 0.5M precursor concentration and calcination temperature of 300oC gave the HA with greater similarity to the natural bone apatite as regards the Ca/P ratio. Based on the optimum conditions (0.5M and 300 oC) investigated at the first stage of the synthesis, further synthesis was carried out using the wet precipitation and hydrothermal methods at physiological conditions of pH and temperature (7.4 and 37 oC). The as-prepared powders were characterized via XRF/EDX, FTIR, XRD, SEM, PSA, BET, TEM and TG/DTA. The result obtained indicated particle nano-size particle with sizes of 26 nm ± 5% and 29 nm ± 5% respectively for the wet
precipitation and hydrothermal methods and these were found to be thermally stable up to 1200oC. SEM images showed a non-uniform particle with various degrees of agglomeration that were observed to be highest for the hydrothermally prepared HA compared to the wet precipitated HA. The synthesized HA samples by both methods were then tested for their bioactivity via in-vitro analysis by immersion of the HA in a simulated body fluid (SBF) solution for 21 days. The pH of the SBF was constantly monitored for ion exchange and the percentage weight loss of the HA were estimated suggesting the biodegradation of HA in SBF. After the incubation period, the HA powder were then characterized via XRF/EDX, FTIR, XRD and SEM and the result indicated high bioactivity of the HA powders. Based on the good response of bioactivity for these HA’s, they were subsequently doped with cadmium (Ca2+) and lead (Pb2+) ions from chloride and nitrate sources respectively and further characterized using XRF/EDX, FTIR, XRD and SEM. The result particularly the XRD studies indicated that while (Ca2+) ion was adsorption onto the hydroxyapatite (HA), (Pb2+) ion was incorporated into the hydroxyapatite (HA), to different degrees depending on the HA synthetic route. The effect of lead (Pb2+) on the HA produced a slight increase in the lattice parameters of the apatite structure resulting in a slight shift of the XRD patterns for Pb-HA samples when compared to the Cadmium (Cd2+) ions’ effect. This change on lattice parameters is due the larger ionic radius of Pb2+ (1.30Ao) than Cd2+ (0.97Ao) with respect to Ca2+ (0.99Ao). Toxicologically, HA prepared via hydrothermal method is preferred to those prepared from the wet precipitation because the HA from the hydrothermal method adsorbs less of the metal dopant from solution suggesting that it will adsorb less amount of such metal from the total burden of it present in the bone when it is used as artificial bone or bone filler/implants. However, when quantity of HA is the research problem, the wet precipitation (WT) method is recommended as it produced a larger quantity of the powder than the hydrothermal method. This quantity increased as precursor concentration is increased. The
wet precipitation method is also recommended for use because it is less complicated and less expensive than the hydrothermal method.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
IN PARTIAL FULFILLMENT OF THE REQUIREMNENTS FOR THE AWARD
OF THE
DEGREE OF DOCTOR OF PHILOSOPHY IN ANALYTICAL CHEMISTRY
DEPARTMENT OF CHEMISTRY
FACULTY OF PHYSICAL SCIENCES
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
VITRO PREPARATIONS,, STUDIES,, SUBSTITUTION,, CADMIUM,, LEAD IONS,, BIOMIMETIC HYDROXYAPATITE NANOCRYSTALS