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Development of the phases in calcium phosphates / titanate nanotubes composites

In this work calcium phosphates/titanate nanotubes (CaP/TiNT) composites were investigated as promising coating material for orthopaedic implants. Titanium and titanium alloys are regularly used for orthopaedic implants due to their resistance to corrosion, good mechanical properties and biocompatibility. However, they are not bioactive and cannot directly bond to the living bone tissues. Therefore the bioactivity of titanium implants is improved by surface modification. Calcium phosphates (CaPs) are frequently used as coating material for orthopaedic and dental implants since they are both bioactive and biocompatible although their mechanical properties are not adequate [1]. To improve the mechanical properties of CaP, some authors added nanotubes (mostly TiO2 and carbon), but in such procedures the additional processing of nanotubes is necessary [2, 3]. The aim of this work is to study the interaction of CaP with titanate (H2Ti3O7) nanotubes (TiNT) which could be utilized for improving CaP mechanical properties. Calcium phosphates are prepared biomimeticaly in the presence of TiNT. Two different concentration of the TiNT were chosen for investigation of the phase development ; 0, 03 mg/mL and 0, 1 mg/mL. The phase development in relation to precipitation time was studied by transmission electron microscopy (TEM) and micro- Raman spectroscopy. Raman spectroscopy is suitable to study CaP+TiNT system because the most of Raman bands of CaP are in the part of spectrum where there are no intense bands of titanate nanotubes. The kinetic of phase changes in the mixed system was compared with the behaviour of a control system in which no TiNT were present. The influence of the TiNT to structural and morphological changes in early stages of CaP precipitation was studied by TEM. The beginning of octacalcium phosphate (OCP) crystallization from amorphous calcium phosphate (ACP) was observed after 10 min of precipitation in the system with 0, 1 mg/ml TiNT (Figure 1). However, after 24 h of precipitation more developed crystals were observed in the system with smaller TiNT concentration (Figure 2). Complete phase development from ACP to OCP and finally to the thermodynamically most stabile hydroxyapatite (HAP) was monitored by Raman spectroscopy. It was observed by Raman spectroscopy that the transition from ACP to OCP star after shorter time of precipitation in the case of higher concentration of titanate Croatian Microscopy Symposium - Pula, November 16- 17, 2012 29 nanotubes then in the other systems, while the rate of phase development from OCP to HAP was faster in the case of the system with lower concentration of TiNT. The observation will be discussed considering relationship of the TEM and the Raman spectroscopy results. Figure 1. TEM images of initial stage (10 min) in calcium phosphates/titanate nanotubes (CaP/TiNT) composites formation: a) control system, b) system with 0.03 mg TiNT/ml, c) system with 0.1 mg TiNT/ml. Figure 2. TEM images of calcium phosphates/titanate nanotubes (CaP/TiNT) composites after 24 h of precipitation: a) control system, b) system with 0.03 mg TiNT/ml, c) system with 0.1 mg TiNT/ml. References: [1] Ratner BD, Hoffman AS, Schoen FJ, Lemons JE. Biomaterials science. 2nd Ed, Elsevier Academic Press, Oxford, 2004. [2] Kunze J, Mueller L, Macaka JM, Greil P, Schmuki P, Mueller FA, Electrochimica Acta 53 (2008) 6995–7003 [3] Santosh Aryal, Shanta Raj Bhattarai, Remant Bahadur K.C., Myung Seob Khil, Duck-Rae Lee, Hak Yong Kim, Materials Science and Engineering A

calcium phosphates; titanate nanotubes; TEM; Raman spectroscopy

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