Synthesis and characterization of strontium-lanthanum apatites

Two series of strontium-lanthanum apatites, Sr_10−xLa_x(PO₄)_6−x(SiO₄)_xF₂ and Sr_10−xLa_x(PO₄)_6−x(SiO₄)_xO with 0 ≤ x ≤ 6, were synthesized by solid state reaction in the temperature range of 1200-1400 °C. The obtained materials were characterized by powder X-ray diffraction, infrared absorption spectroscopy and solid ³¹P Nuclear Magnetic Resonance. Pure solid solutions were obtained within a limited range of unsubstituted phosphate and silicate apatites. A variation of the lattice parameters was observed, with an increase of a and a decrease of c parameters, related to the radius of the corresponding substituted ions.     

Synthesis and thermal expansion of some lanthanide-containing apatites

Compounds with the general formula CaLn₄(SiO₄)₃O (Ln = Pr, Sm, Eu), belonging to the apatite class, have been prepared by solid-state reactions and have been studied at high temperatures by high-temperature X-ray diffraction and differential scanning calorimetry. The results demonstrate that the volume expansivity of these apatites and its temperature coefficient are determined by the ionic radius of the lanthanides.     

Synthesis and characterizations of a fluoride-releasing dental restorative material

The aim was to develop an obturating material which has the tendency to release fluoride and minimize interfaces with tooth. Nano-fluorapatite (nFA) powder was synthesized by sol–gel. The composite based on polyurethane (PU) was obtained by chemically binding the nFA (10, 15, 20% wt/wt) to the diisocyanate component by utilizing in-situ polymerization. The procedure involved stepwise addition of monomeric units of PU, and optimizing the reagent concentrations to synthesize composite. The structural, phase and morphological analysis of nFA was evaluated. The structural, fluoride release and in-vitro adhesion analysis with tooth structure of PU/nFA was conducted. For fluoride release analysis the samples were stored in artificial saliva and deionized water for periodical time intervals. Bond strength of composites was analyzed by push-out test. Chemical linkage was achieved between PU and nFA without intermediate coupling agent. The insignificant difference of fluoride release pattern was observed in artificial saliva and (p ≥ 0.05) deionized water. The PU/nFA composite provided sustained release of fluoride over a long period of time. The composite showed more adhesion toward tooth structure with the increase in concentration of nFA. Bond strength of composite was in accordance with root canal filling material, hence, the material with anti-cariogenic properties can be used as an obturating material.     

Effect of electron-beam irradiation on water wettability of hydroxy apatites for artificial bone

The influence of electron-beam irradiation on the wettability of hydroxy apatites (HAP) has been investigated. The wettability was evaluated from the interfacial energy between HAP and water. It was measured by the contact angle of distilled water on HAP. Electron-beam irradiation increases the wettability. Based on the rate process, the influence of electron-beam irradiation on wettability is discussed. Using electron-beam irradiation, we can precisely control the surface condition of HAP. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microporosity enhances bioactivity of synthetic bone graft substitutes

This paper describes an investigation into the influence of microporosity on early osseointegration and final bone volume within porous hydroxyapatite (HA) bone graft substitutes (BGS). Four paired grades of BGS were studied, two (HA70-1 and HA70-2) with a nominal total porosity of 70% and two (HA80-1 and HA80-2) with a total-porosity of 80%. Within each of the total-porosity paired grades the nominal volume fraction of microporosity within the HA struts was varied such that the strut porosity of HA70-1 and HA80-1 was 10% while the strut-porosity of HA70-2 and HA80-2 was 20%. Cylindrical specimens, 4.5 mm diameter × 6.5 mm length, were implanted in the femoral condyle of 6 month New Zealand White rabbits and retrieved for histological, histomorphometric, and mechanical analysis at 1, 3, 12 and 24 weeks. Histological observations demonstrated variation in the degree of capillary penetration at 1 week and bone morphology within scaffolds 3–24 weeks. Moreover, histomorphometry demonstrated a significant increase in bone volume within 20% strut-porosity scaffolds at 3 weeks and that the mineral apposition rate within these scaffolds over the 1–2 week period was significantly higher. However, an elevated level of bone volume was only maintained at 24 weeks in HA80-2 and there was no significant difference in bone volume at either 12 or 24 weeks for 70% total-porosity scaffolds. The results of mechanical testing suggested that this disparity in behaviour between 70 and 80% total-porosity scaffolds may have reflected variations in scaffold mechanics and the degree of reinforcement conferred to the bone-BGS composite once fully integrated. Together these results indicate that manipulation of the levels of microporosity within a BGS can be used to accelerate osseointegration and elevate the equilibrium volume of bone.     

PET fiber fabrics modified with bioactive titanium oxide for bone substitutes

A rectangular specimen of polyethylene terephthalate (PET) was soaked in a titania solution composed of titanium isopropoxide, water, ethanol and nitric acid at 25 °C for 1 h. An amorphous titanium oxide was formed uniformly on the surface of PET specimen, but did not form an apatite on its surface in a simulated body fluid (SBF) within 3 d. The PET plate formed with the amorphous titanium oxide was subsequently soaked in water or HCl solutions with different concentrations at 80 °C for different periods of time. The titanium oxide on PET was transformed into nano-sized anatase by the water treatment and into nano-sized brookite by 0.10 M HCl treatment at 80 °C for 8 d. The former did not form the apatite on its surface in SBF within 3 d, whereas the latter formed the apatite uniformly on its surface. Adhesive strength of the titanium oxide and apatite layers to PET plate was increased by pre-treatment of PET with 2 wt% NaOH solution at 40 °C for 2 h. A two-dimensional fabric of PET fibers 24 μm in diameter was subjected to the NaOH pre-treatment at 40 °C, titania solution treatment at 25 °C and subsequent 0.10 M HCl treatment at 80 °C. Thus treated PET fabric formed the apatite uniformly on surfaces of individual fibers constituting the fabric in SBF within 3 d. Two or three dimensional PET fabrics modified with the nano-sized brookite on surfaces of the individual fibers constituting the fabric by the present method are believed to be useful as flexible bone substitutes, since they could be integrated with living bone through the apatite formed on their constituent fibers.     

Synthesis and distribution of cations in substituted lead phosphate lacunar apatites

Synthesis of apatites, Pb_7.4Bi_0.3Na_2.3(PO₄)₆ (I), Pb_7.36Bi_0.32Na_2.08Li_0.24(PO₄)₆ (II) and Pb_5.78Bi_0.81Ca_0.60Na_2.81(PO₄)₆ (III), with anion vacancy were carried out during solid state reactions. The three compounds of apatite-type structure crystallize in the hexagonal system, space group P6₃/m. In every compound, a preferential occupation of the (6h) site by Pb and Bi cations is shown revealing the influence of their lone electronic pair. The introduction of calcium increases the quantity of bismuth in these apatites. Alkaline metals occupy mainly the (4f) site. Infrared spectroscopy is correlated to the bonding scheme. A connection between the cations occupying (4f) sites and the c cell parameters is presented.     

Design of bioactive bone substitutes based on biomineralization process

A material able to form bone-like apatite on its surface in the living body bonds to living bone through the apatite layer. Functional groups such as Si-OH, Ti-OH, Zr-OH, Nb-OH and Ta-OH induce apatite formation in the living body. On the basis of these findings, various kinds of bioactive materials with different mechanical properties can be designed. For example, bioactive titanium metal, its alloys and tantalum metal can be obtained by forming a thin sodium titanate or tantalate layer on their surfaces by NaOH solution and heat treatments.Bioactive organic polymers can be obtained by forming a thin CaO–SiO₂ or TiO₂ layer on their surfaces by a sol–gel method. These bioactive materials are believed to be useful as unique bone substitutes.     

Elastic properties of apatites

One of the prime motives for studying the elastic properties of the apatites stems from the occurrence of hydroxyapatite, OHAp, in calcified tissue. In this paper the isotropic elastic contents of crystalline apatite solids are determined from measurements of elastic wave velocities through powders under pressure. Once obtained, these elastic constants are used to model the elastic behaviour of a two-phase composite material having one phase more rigid than the other by a factor of 2.4. The results are then used in a general discussion of the probable order of magnitude of the elastic constants of the organic non-crystalline phase in bones and teeth, under the assumption of a two-phase system.     

Hydroxyapatite bone substitutes developed via replication of natural marine sponges

The application of synthetic cancellous bone has been shown to be highly successful when its architecture mimics that of the naturally interconnected trabeculae bone it aims to replace. The following investigation demonstrates the potential use of marine sponges as precursors in the production of ceramic based tissue engineered bone scaffolds. Three species of natural sponge, Dalmata Fina (Spongia officinalis Linnaeus, Adriatic Sea), Fina Silk (Spongia zimocca, Mediterranean) and Elephant Ear (Spongia agaricina, Caribbean) were selected for replication. A high solid content (80 %wt), low viscosity (126 mPas) hydroxyapatite slurry was developed, infiltrated into each sponge species and subsequently sintered, producing a scaffold structure that replicated pore architecture and interconnectivity of the precursor sponge. The most promising of the ceramic tissue engineered bone scaffolds developed, Spongia agaricina replicas, demonstrated an overall porosity of 56–61% with 83% of the pores ranging between 100 and 500 μm (average pore size 349 μm) and an interconnectivity of 99.92%.     

Synthesis of hexagonal lanthanum germanate apatites through site selective isovalent doping with yttrium

Apatite-type lanthanum silicates/germanates have been attracting considerable interest as a new class of oxide ion conductors, whose conductivity is mediated by oxide ion interstitials. For the germanates, it has been shown that, depending on composition, the cell can be either hexagonal or triclinic, with evidence for reduced low-temperature conductivities for the latter, attributed to increased defect trapping in this lower symmetry cell. In this paper we show that site selective doping of Y into the triclinic apatite-type oxide ion conductors, La_9.33+z(GeO₄)₆O_2+3z/2 (0.33 ≤ z ≤ 0.67) results in a hexagonal lattice for the complete series with correspondingly enhanced low-temperature conductivity.     

Synthesis and characterization of carbonate hydroxyapatite

Substituted apatite ceramics are of clinical interest as they offer the potential to improve the bioactive properties of implants. Carbonate hydroxyapatite (CHA) has been synthesized by an aqueous precipitation method and precipitates with two different levels of carbonate, processed as powders. Sintering experiments were performed to establish the influence of carbonate in significantly reducing the temperature required to prepare high-density ceramics when compared with stoichiometric hydroxyapatite (HA). High-temperature X-ray diffraction was used to characterize the phase stability of the apatites on sintering. Increasing carbonate content was shown to reduce the temperature at which decomposition occurred, to phases of CaO and -TCP. Mechanical testing, performed using biaxial flexure, showed that the CHA specimens had strengths similar to stoichiometric HA. © 1998 Kluwer Academic Publishers     

超细碳酸钡粒子的合成

采用共沉淀法合成了碳酸钡粒子。通过添加合适的晶形控制剂,合成了球状和哑铃状的碳酸钡粉体,利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)进行了表征,并对不同晶形碳酸钡的形成机理进行了初步的探讨。     

Ion exchanges in apatites for biomedical application

The modification of the composition of apatite materials can be made by several processes corresponding to ion exchange reactions which can conveniently be adapted to current coatings and ceramics and are an alternative to setting up of new synthesis methods. In addition to high temperature thermal treatments, which can partly or almost totally replace the monovalent OH^– anion of stoichiometric hydroxyapatite by any halogen ion or carbonate, aqueous processes corresponding to dissolution-reprecipitation reactions have also been proposed and used. However, the most interesting possibilities are provided by aqueous ion exchange reactions involving nanocrystalline apatites. These apatites are characterised by the existence on the crystal surface of a hydrated layer of loosely bound mineral ions which can be easily exchanged in solution. This layer offers a possibility to trap mineral ions and possibly active molecules which can modify the apatite properties. Such processes are involved in mineralised tissues and could be used in biomaterials for the release of active mineral species.     

Application of K/Sr co-doped calcium polyphosphate bioceramic as scaffolds for bone substitutes

Ion doping is one of the most important methods to modify the properties of bioceramics for better biodegrade abilities, biomechanical properties, and biocompatibilities. This paper presents a novel ion doping method applied in calcium polyphosphate (CPP)-based bioceramic scaffolds substituted by potassium and strontium ions (K/Sr) to form (K/Sr–CPP) scaffolds for bone tissue regeneration. The microstructure and crystallization of the scaffolds were detected by scanning electron microscopy and X-ray diffraction. Compressive strength and degradation tests were assessed to evaluate the mechanical and chemical stabilities of K/Sr–CPP in vitro. The cell biocompatibility was measured with respect to the cytotoxicity of the extractions of scaffolds. Muscle pouches and bone implantation were performed to evaluate the biodegradability and osteoconductivity of the scaffolds. The results indicated that the obtained K/Sr–CPP scaffolds had a single beta-CPP phase. The unit cell volume and average grain size increased but the crystallization decreased after the ions were doped into the CPP structure. The K/Sr–CPP scaffolds yielded a higher compressive strength and a better degradation property than the pure CPP scaffold. The MTT assay and in vivo results reveal that the K/Sr–CPP scaffolds exhibited a better cell biocompatibility and a tissue biocompatibility than CPP and hydroxyapatite scaffolds. This study proves the potential applications of K/Sr–CPP scaffolds in bone repair.     

Hybrid bilayered chitosan-xanthan/PCL scaffolds as artificial periosteum substitutes for bone tissue regeneration

Journal of Materials Science - The periosteum, a bilayered membrane that covers bone surfaces, acts as a source of bone-forming cells and plays a pivotal role in bone homeostasis and defect...