Faik N. Oktar

Sintering effects on mechanical properties of biologically derived dentine hydroxyapatite

In this study, the change in the mechanical properties of hydroxyapatite (HA), which is the main mineral content of bone and teeth, commonly used as an implant material, is tested for different sintering temperatures. Although HA shows great biocompatibility with the human body, its applications are limited to non-load-bearing areas and coatings due to its low mechanical properties. These mechanical properties can be improved substantially by sintering. In this study, naturally produced HA from human teeth is sintered, and density, microhardness measurements and compression tests are performed in order to find the optimum sintering temperature. The results are compared with the synthetically derived HA properties from the literature.

Sintering behavior and properties of reinforced hydroxyapatite/TCP biphasic bioceramics with ZnO-whiskers

Composite materials of hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) biphasic bioceramics and ZnO whiskers, added in amounts up to 3 wt% to an HA/β-TCP matrix, were prepared by sintering. The sintering behavior, the mechanical reinforcement (due to ZnO), and the mineralization ability of the resulting materials in simulated body fluid (SBF) were experimentally investigated. The experimental results showed that the densification and mechanical properties were improved with increasing amounts of ZnO. The presence of ZnO appeared to affect the proportion of HA/β-TCP after sintering. Doping with a high amount of ZnO favored the dissolution of the materials in SBF.

Structural, compositional, mechanical characterization and biological assessment of bovine-derived hydroxyapatite coatings reinforced with MgF2 or MgO for implants functionalization.

Hydroxyapatite (HA) is a consecrated biomaterial for bone reconstruction. In the form of thin films deposited by pulsed laser technologies, it can be used to cover metallic implants aiming to increase biocompatibility and osseointegration rate. HA of animal origin (bovine, BHA) reinforced with MgF2 (2wt.%) or MgO (5wt.%) were used for deposition of thin coatings with improved adherence, biocompatibility and antimicrobial activity. For pulsed laser deposition experiments, a KrF* (λ=248nm, τFWHM≤25ns) excimer laser source was used. The deposited structures were characterized from a physical-chemical point of view by X-Ray Diffraction, Fourier Transform Infra-Red Spectroscopy, Scanning Electron Microscopy in top- and cross-view modes, Energy Dispersive X-Ray Spectroscopy and Pull-out adherence tests. The microbiological assay using the HEp-2 cell line revealed that all target materials and deposited thin films are non-cytotoxic. We conducted tests on three strains isolated from patients with dental implants failure, i.e. Microccocus sp., Enterobacter sp. and Candida albicans sp. The most significant anti-biofilm effect against Microcococcus sp. strain, at 72h, was obtained in the presence of BHA:MgO thin films. For Enterobacter sp. strain a superior antimicrobial activity at 72h was noticed, in respect with simple BHA or Ti control. The enhanced antimicrobial performances, correlated with good cytocompatibility and mechanical properties recommend these biomaterials as an alternative to synthetic HA for the fabrication of reliable implant coatings for dentistry and other applications.

Preparation and evaluation of cerium oxide-bovine hydroxyapatite composites for biomedical engineering applications

The fabrication and characterization of bovine hydroxyapatite (BHA) and cerium oxide (CeO2) composites are presented. CeO2 (at varying concentrations 1, 5 and 10wt%) were added to calcinated BHA powder. The resulting mixtures were shaped into green cylindrical samples by powder pressing (350MPa) followed by sintering in air (1000-1300°C for 4h). Density, Vickers microhardness (HV), compression strength, scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies were performed on the products. The sintering behavior, microstructural characteristics and mechanical properties were evaluated. Differences in the sintering temperature (for 1wt% CeO2 composites) between 1200 and 1300°C, show a 3.3% increase in the microhardness (564 and 582.75HV, respectively). Composites prepared at 1300°C demonstrate the greatest compression strength with comparable results for 5 and 10wt% CeO2 content (106 and 107MPa) which are significantly better than those for 1wt% and those that do not include any CeO2 (90 and below 60MPa, respectively). The results obtained suggest optimal parameters to be used in preparation of BHA and CeO2 composites, while also highlighting the potential of such materials in several biomedical engineering applications.

ZnO Applications and Challenges

Metal oxide nanoparticles represent a new class of important materials that are increasingly being developed for use in re- search and health-related applications. Although the in vitro antibacterial activity of zinc oxides and some other zinc compounds has been known for quite some time, only in the last few years nanoparticles of ZnO have been investigated for their antibacterial activity, the knowledge about it remaining deficient. The antimicrobial activity of ZnO nanoparticles is strongly influenced by some factors such as size and the presence of light. The potential applications include, but are not limited to, topic drugs, cosmetics or component for agents that control the spread of bacterial strains (antibacterial paint in hospitals, antibacterial coatings for fabrics, antibacterial packaging for food, etc). The current review aims to present the level of knowledge accumulated on the antibacterial and antifungal activity of ZnO.

Characterization of calcium phosphate powders originating from Phyllacanthus imperialis and Trochidae Infundibulum concavus marine shells.

The study reports the preparation and characterization of powders consisting of the different phases of calcium phosphates that were obtained from the naturally derived raw materials of sea-shell origins reacted with H3PO4. Species of sea origin, such as corals and nacres, attracted a special interest in bone tissue engineering area. Nacre shells are built up of calcium carbonate in aragonite form crystallized in an organic matrix. In this work two natural marine origin materials (shells of echinoderm Sputnik sea urchin - Phyllacanthus imperialis and Trochidae Infundibulum concavus mollusk) were involved in the developing powders of calcium phosphate based biomaterials (as raw materials for bone-scaffolds) by hotplate and ultrasound methods. Thermal analyses of the as-prepared materials were made for an assessment of the thermal behavior and heat treatment temperatures. Samples from both sea shells each of them prepared by the above mentioned methods were subjected to thermal treatments at 450 °C and 850 °C in order to evaluate the crystalline transformations of the calcium phosphate structures in the heating process. By X-ray diffraction analyses various calcium phosphate phases were identified. In Sputnik sea urchins originated samples were found predominantly brushite and calcite as a small secondary phase, while in Trochidae I. concavus samples mainly monetite and HA phases were identified. Thermal treatment at 850 °C resulted flat-plate whitlockite crystals - β-MgTCP [(Ca, Mg)3 (PO4)2] for both samples regardless the preparation method (ultrasound or hotplate) or the targeted Ca/P molar ratio according with XRD patterns. Scanning electron microscopy and Fourier transformed infrared spectroscopy were involved more in the characterization of these materials and the good correlations of the results of these methods were made.

Biocompatibility Evaluation of Three Different Titanium-Hydroxyapatite Composites

Titanium reinforced with hydroxyapatite (TiHA) prepared using 15% of titanium and 3 different sinterizing temperatures 1100, 1200 and 1300 oC showed a significant increase in cell proliferation, when compared to the control.

Sintering of Synthetic Hydroxyapatite Compacts

Hydroxyapatite (HA) is a particularly attractive material for bone and tooth implants because of its chemical and crystallographic properties, which closely resemble those of bone and tooth minerals. Moreover, sintered HA material has superior biocompatibility. In this study, the compacts made of pure HA (Merck) were sintered at 1000, 1100, 1200 and 1300°C. The density, microhardness and compression strength tests were performed, in order to find out the optimum sintering temperature. As a result, average density was 2.554± 0.37 g/cm, average compression strength value was 25.22 ± 12 MPa and average value of Vickers microhardness was found as 250 ± 120 HV (kg/mm).

The Improvement of Titanium Reinforced Hydroxyapatite for Biomedical Applications

Abstract The addition of different amounts of inclusions to brittle hydroxya patite (HA) gives the advantage of tailoring and predicting the possible mechanical proper ties of the biocomposite. Biocomposite materials have been developed in order to combine the propert ies of bioactive material with the better mechanical properties of a second phase. Titanium, having superior biocompatibility, mechanical properties and corrosion resistance, is suitable as a reinforcement phase for biomedical applications. This study focuses on the effect s of sintering temperature and the amount of reinforcement phase on the mechanical properties of HA-Ti composites. The HA material used was derived from freshly-extracted human teeth wi th calcination at 850°C. Titanium powders were mixed by 5 and 10 wt % with HA and have been subjected to sintering at 1200 and 1300C for three hours. Density, microhardness, and compressive strength m easurements have been carried out. Microstructures have been investigated by SEM and the phas an lysis has been determined by the x-ray diffraction analysis . The best mechanical properties have been obtained by sintering at 1300°C for three hours with the addition of 10 wt % Ti to HA.

A new method for fabrication of nanohydroxyapatite and TCP from the sea snail cerithium vulgatum

Biphasic bioceramic nanopowders of hydroxyapatite (HA) and β-tricalcium phosphate (TCP) were prepared from shells of the sea snail Cerithium vulgatum (Bruguiere, 1792) using a novel chemical method. Calcination of the powders produced was carried out at varying temperatures, specifically at 400°C and 800°C, in air for 4 hours. When compared to the conventional hydrothermal transformation method, this chemical method is very simple, economic, due to the fact that it needs inexpensive and safe equipment, because the transformation of the aragonite and calcite of the shells into the calcium phosphate phases takes place at 80°C under the atmospheric pressure. The powders produced were determined using infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy (SEM). The features of the powders produced along with the fact of their biological origin qualify these powders for further consideration and experimentation to fabricate nanoceramic biomaterials.