Fracture behavior and biocompatibility evaluation of nylon-infiltrated porous hydroxyapatite

Hybrid hydroxyapatite/polymer composites were prepared by the infiltration of nylon into porous hydroxyapatite. Porous hydroxyapatite (HAp) bodies were prepared from a whisker-like powder with high aspect ratio by pressureless-sintering at various temperatures. Pore characteristics, such as the fraction of open porosity and the pore size distribution, were designed and evaluated by mercury porosimeter. Through the in situ polymerization of -caprolactam, infiltrated into the porous HAp body, a polymeric secondary phase network interpenetrated with the HAp phase was obtained. The obtained hybrid HAp/nylon composites were evaluated with respect to their fracture behavior, i.e., fracture energy, and in vitro bioactivity in simulated body fluid (SBF) in the present paper. These HAp/nylon hybrid composite have a K _IC of 1.65 MPam^1/2 and also a good bioactivity according to the results of SBF immersion tests.     

Development of carbon nanofiber reinforced hydroxyapatite with enhanced mechanical properties

In order to improve fracture toughness, carbon nanofibers (CNF) were used as reinforcement for hydroxyapatite (HA) composites. The powder mixture of CNF/HA were obtained with ball-milling technique. CNF/HA composites were sintered by hot-pressing with 7.81 and 15.6 MPa sintering pressure. Maximum sintering pressure was 1200 °C. Mechanical and physiological bio-compatibility were evaluated by four-point bending tests, indentation tests and immersion tests in simulated body fluid (SBF). The strength values of 10 vol.% CNF/HA composites sintered at 15.6 MPa is 90 MPa, which is within those of cortical bone. The fracture toughness values for CNF/HA composites are around 1.6 times higher than those obtained for HA. Equal bioactivity are obtained for CNF/HA composites.     

Solid state reaction, sintering and Pb removal activity of hydroxyapatite/zirconia layered composite

In order to form a layered hydroxyapatite/zirconia ceramic, the solid state reaction and sintering were examined by the three processes of powder mixture, dry-pressing compaction and tape cast. The solid state reaction between hydroxyapatite and zirconia occurred in the thin width of 10–50 m at interface in a layered composite body. In both sintered layer composites from dry compaction and tape cast, the significant deformation of composite bodies was observed, depending on sintering temperatures. By selecting a sintering temperature of 1200°C, we fabricated a layer ceramic composite of hydroxyapatite/zirconia exhibiting the flat film shape. The tape cast process was useful to form a porous sintered composite of hydroxyapatite and zirconia. The porous composite showed the removal performance of aqueous lead from wastewater.     

Effect of the content of hydroxyapatite nanoparticles on the properties and bioactivity of poly(l-lactide) – Hybrid membranes

Poly(l-lactide)/hydroxyapatite, PLLA/HA, composite membranes for bone regeneration with different concentrations of nanoparticles have been prepared and their physicochemical properties and bioactivity have been determined. Hydroxyapatite nanoparticles act as nucleating agent of the poly(l-lactide) crystals, as detected by DSC, and as reinforcing filler, as proven by the monotonous increase of the elastic modulus of the microporous membranes with increasing nano-filler content. The bioactivity, which regards to the use of these materials in bone regeneration, was tested by immersing the samples in a simulated body fluid, SBF. A faster deposition of a biomimetic apatite layer was observed as increases the content of hydroxyapatite nanoparticles, thus membranes with a 15% (w/w) of hydroxyapatite particles (relative to PLLA weight) present a homogeneous layer of hydroxyapatite on the surface of their pores after 7 days of immersion in SBF. An especial emphasis has been made on the influence of a plasma treatment on the bioactivity of the membranes. With this aim, the membranes were submitted to a plasma treatment previously to their immersion in a simulated body fluid. It has been observed that the surface of a PLLA membrane after 21 days of immersion in SBF is still not completely covered by hydroxyapatite whereas the same sample treated with plasma show a smooth layer of biomimetic hydroxyapatite. The increase of bioactivity achieved with this treatment was less important in high hydroxyapatite content composites.     

Apatite-forming ability of glass-ceramic apatite–wollastonite – polyethylene composites: effect of filler content

The bioactivity of a range of glass-ceramic apatite–wollastonite (A–W) – polyethylene composites (AWPEXs) with glass-ceramic A–W volume percentages ranging from 10 to 50, has been investigated in an acellular simulated body fluid (SBF) with ion concentrations similar to those of human blood plasma. The formation of a biologically active apatite layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction (TF-XRD) and field-emission scanning electron microscopy (FE-SEM). An apatite layer was formed on all the composites, with the rate of formation increasing with an increase in glass-ceramic A–W percentage. For composites with glass-ceramic A–W filler contents 30 vol %, the apatite layer was formed within 12 h of immersion, which is a comparable time for apatite formation on monolithic glass-ceramic A–W. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) demonstrated that the apatite formation on AWPEX samples with 50 vol % filler content occurred in a manner similar to that seen on pure glass-ceramic A–W, in that the calcium, silicon, and magnesium ion concentrations increased and, conversely, a decrease was observed in the phosphate ion concentration. These results indicate that a suitable in vitro response was achieved on a composite incorporating particulate glass-ceramic A–W with a particularly favorable response being observed on the AWPEX sample with 50 vol % filler content.     

Immersion behavior of hydroxyapatite (HA) powders before and after sintering

The immersion behavior of two different hydroxyapatite (HA) powders before and after sintering was investigated by soaking them in simulated body fluid (SBF) for various periods. The results showed that the mechanism of formation of bone-like apatite on the two HA powders was different due to their different phase composition. Moreover, after being sintered at a proper elevated temperature, the bioactivity of HA powders was increased.     

Structure and properties of hydroxyapatite-bioactive glass composites plasma sprayed on Ti6Al4V

Hydroxyapatite (HA)-coated Ti6Al4V has recently been used as a bone substitute in orthopaedic and dental applications because of its favourable bioactivity and mechanical properties. Studies in the literature have shown that the bioactivity of calcium phosphate bioactive glass (BG) is higher than that of HA. In an attempt to increase the bioactivity of Ha-coated Ti6Al4V and enhance the bonding strength between coating and substrate, in the present study, HA/BG composites are applied onto Ti6Al4V using a plasma spraying technique. Microstructure and phase changes of the composite coating after plasma spraying are studied. The coating-substrate bonding strength is evaluated using an Instron, following the ASTM C633 method. Results indicate that the average bonding strengths of BG, HA/BG and HA coatings are 33.0±4.3, 39.1±5.0, and 52.0±11.7 MPa, respectively. Open pores with sizes up to 50 m are found in both BG and HA/BG coatings, which are probably advantageous in including mechanical interlocking with the surrounding bone structure, once implanted. These HA/BG composites could provide a coating system with sufficient bonding strength, higher bioactivity, and a significant reduction in cost in raw materials. The future of this HA/BG composite coating system seems pretty bright.     

Effects of added c-BN seed crystals on the reaction sintering of c-BN accompanied by a conversion from h-BN to c-BN

Reaction sintering behaviour of c-BN which is accompanied by a conversion from h-BN to c-BN was investigated under high pressure (7 GPa) and temperature (1700°C) conditions for 30 to 60min. A high conversion yield of c-BN in the sintered compact was attained by adding fine-grained c-BN seed crystals (particle size 0.5 to 8m) to h-BN powder in the presence of 1 wt% NH₄NO₃ as a catalyst. An induced transformation from h-BN to c-BN occurs over a large surface area of c-BN seed crystals, which results in the formation of direct interparticle bonding between c-BN grains in the sintered compact. A fully dense sintered compact of c-BN (bulk density 98% theoretical) was obtained from the specimen of 70wt% h-BN with 30wt% added c-BN crystals having a particle size of 0.5m. This c-BN compact had an average microhardness of 5100 kg mm^–2 and a specific dielectric constant of 10.0 at a frequency of 1 MHz.     

Bone-like apatite coating on Mg-PSZ/Al2O3 composites using bioactive systems

A biomimetic method was used to promote bioactivity on zirconia/alumina composites. The composites were composed of 80 vol% Mg-PSZ and 20 vol% Al₂O₃. Samples of these bioinert materials were immersed in simulated body fluid (SBF) for 7 days on either a bed of wollastonite ceramics or bioactive glass. After those 7 days, the samples were immersed in a more concentrated solution (1.4 SBF) for 14 days. Experiments were also performed without using a bioactive system during the first stage of immersion. A bone-like apatite layer was formed on the surface of all the materials tested, using wollastonite the bioactive layer was thicker and its morphology was close to that observed on the existing bioactive systems. A thinner apatite layer consisting of small agglomerates was obtained using bioactive glass. The thickness of the ceramic layers was within the range of 15 to 30 μm.     

Effect of silane coupling agent treated bovine bone based carbonated hydroxyapatite on in vitro degradation behavior and bioactivity of PLA composites

In this study, effect of treating bovine bone based carbonated hydroxyapatite (CHA) with silane coupling agent on in vitro degradation and bioactivity of PLA composites were investigated. PLA composite specimens containing CHA and silane-treated CHA were immersed in phosphate-buffered solution at 37 °C for the periods of time up to 8 weeks. The changes in specimen weights and morphologies, pH of PBS solution and PLA molecular weight were examined. The results showed that the strong interfacial bonding between silane-treated CHA and PLA matrix significantly delayed in vitro degradation of the PLA composites. However, the bioactivity of the PLA/silane treated CHA composites, determined by the formation of poorly crystalline calcium phosphate compounds on the specimen surface after immersion in simulated body fluid (SBF), seemed to be lower than that of the PLA/CHA composite.     

Preparation and in vitro bioactivity of poly(d,l-lactide) composite containing hydroxyapatite nanocrystals

The nano-sized hydroxyapatite (n-HA) was incorporated into poly(d,l-Lactide) (PDLLA) to form a bioactive and biodegradable composite for application in hard tissue replacement and regeneration. Thin film of PDLLA composite containing 20 mass% of n-HA fillers was successfully developed through integration of solvent co-blending and hot pressing techniques. firstly, n-HA and PDLLA were chemically synthesized, respectively, then mixed together and homogeneously dispersed in N,N-dimethyl formamide(DMF) solvent, finally, the dried blended hybrid containing PDLLA matrix and n-HA fillers was put into the mould and compacted by hot-pressing machine under 8 MPa pressure at 110 °C for 15 min. In vitro studies were conducted using the simulated body fluid(SBF). Composite specimens were soaked in SBF from 1 day to 21 days prior to surface analysis. Results obtained from scanning electron microscopy(SEM) examination, Energy dispersive X-ray detector(EDX) analysis and X-ray diffraction (XRD) analysis showed that a layer of non-stoichiometric apatite formed within 7 days on HA/PDLLA composite surface after its immersion in SBF, demonstrating moderate in vitro bioactivity of n-HA/PDLLA composite, though a moderate rate of apatite formation in SBF was found on initial stage of immersion periods for n-HA/PDLLA composite, compared to the other biomaterial composite. This type of composite film exhibited certain desirable bioactive characteristics, and they are promising bone candidates to develop novel bioactive composites for biomedical application.     

Effect of powder characteristics on the sinterability of hydroxyapatite powders

The effect of different sintering conditions on the sintered density and microstructure of two different hydroxyapatite (HA) powders was examined. The powder characteristics of a laboratory synthesized HA powder (Lab HA) were low crystallinity, a bimodal particle size distribution, a median particle size of 22 m and a high specific surface area (SSA) of 63 m²/g. By contrast, a commercial calcined HA (commercial HA) was crystalline and had a median particle size of 5 m and a low SSA of 16 m²/g. The different powder characteristics affected the compactability and the sinterability of the two HA powders. Lab HA did not compact as efficiently as commercial HA, resulting in a lower green density, but the onset of sintering of powder compacts of the former was approximately 150 °C lower than the later. The effect of compaction pressure, sintering temperature, time and heating rate on the sintered densities of the two materials was studied. Varying all these sintering conditions significantly affected the sintered density of commercial HA, whereas the sintered density of Lab HA was only affected significantly by increasing the sintering temperature. The Vickers hardness, H_v, of Lab HA was greater than commercial HA for low sintering temperatures, below 1200 °C, whereas for higher sintering temperatures the commercial HA produced ceramics with greater values of hardness. These trends can be related to the sinterability of the two materials.     

Surface reaction of stoichiometric and calcium-deficient hydroxyapatite in simulated body fluid

In the present study, the immersion behavior of two kinds of sintered HA with different Ca/P ratios in two different extracellular simulated solutions (Tris buffer and Hank's solutions) was investigated and compared. Results indicated that an as-received Ca-deficient HA (FHA) had a lower Ca/P ratio, larger linear shrinkage and higher density than a stoichiometric HA (MHA). When FHA powder was calcined at 900 °C, its Ca-deficient apatite structure was unstable and a significant amount of -TCP phase was formed. When heated to 1250 °C in air, the highly crystalline apatite structure of MHA was still stable without any noticeable decomposition. The FTIR spectra indicated that both immersed MHA and FHA in Hank's solution were gradually covered with a layer of precipitated apatite during immersion. When immersed in Tris buffer solution, neither HA showed significant changes in their FTIR spectra. SEM observation indicated that the precipitation rate on immersed FHA surface was much higher than that on MHA surface when immersed in Hank's solution. The weight loss and pH data confirmed the higher dissolution rate of FHA than MHA in Hank's solution. © 2001 Kluwer Academic Publishers     

Near net-shape fabrication of hydroxyapatite glass composites

Near net-shape fabrication of hydroxyapatite (HA) glass composites has been attempted by infiltrating a glass into porous HA performs. Main efforts were put to develop glasses that are chemically compatible with HA at elevated temperatures. After extensive investigations in the phosphate and borosilicate systems, glasses of (50-55)SiO₂-(20-25)B₂O₃-(10-20)Li₂O-(0-6)CaO (wt%) composition were successfully developed. The glass shows good chemical compatibility with HA at elevated temperatures. Dense HA/glass composites can be fabricated at 850–950 C by the melt infiltration process. Investigations demonstrated a good near net-shape capability of the process, where the linear shrinkage induced by the infiltration process is less than 0.1%. Preliminary mechanical tests showed that the fracture strength and toughness of the infiltrated HA/glass composite are comparable with dense HA.     

Electrophoretic deposition of silicon-substituted hydroxyapatite/poly(ε-caprolactone) composite coatings

Silicon-substituted hydroxyapatite/poly(ε-caprolactone) composite coatings were prepared on titanium substrate by electrophoretic deposition in n-butanol and chloroform mixture. The effect of the concentration of poly(ε-caprolactone) in suspension on the morphology and the microstructure of coatings were investigated, furthermore, the thermal behavior and in vitro bioactivity were also investigated. The results show that the coarse and accidented silicon-substituted hydroxyapatite/poly(ε-caprolactone) composite coatings were obtained by electrophoretic deposition when the concentration of poly(ε-caprolactone) in suspension was 6–16 g/l. The adsorption of poly(ε-caprolactone) on the surface of Si–HA particles hinders the electrophoretic deposition of Si–HA. The shear-testing experiments indicated that the addition of poly(ε-caprolactone) in suspension is in favor of improving the bonding strength of the coatings. After immersion in simulated body fluid for 8 days, silicon-substituted hydroxyapatite/poly(ε-caprolactone) composite coatings have the ability to induce the bone-like apatite formation.     

Reinforcement of hydroxyapatite by adding P2O5-CaO glasses with Na2O, K2O and MgO

Commercial hydroxyapatite was reinforced by adding small amounts (2 and 4 wt%) of P₂O₅-based glasses during its sintering process. The composites prepared had a chemical composition closely related to the mineral part of bone tissues in terms of trace elements usually detected, such as Na, K and Mg. X-ray diffraction analysis (XRD) showed that the glass reinforced-HA composites were composed of a HA matrix and variable amounts of tricalcium phosphate phase, depending on sintering temperature and glass composition. These composites were shown to have much higher biaxial bending strength than sintered HA, 107 MPa for Ha/2% of 35P₂O₅-35CaO-10Na₂O-10K₂O-10MgO glass composite and 28 MPa for sintered HA. The presence of -tricalcium phosphate in the microstructure of the composites is an important factor in the reinforcement process.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto. Portugal, 10–13 September.     

Improved thermal shock resistant refractories from plasma-dissociated zircon

Dissociated zircon (DZ), produced in a plasma furnace recombined and sintered to about 92% of the theoretical density in the range 1300 to 1500° C The work-of-fracture of DZ increased from 20J m^–2 to 73 J m^–2 with additions of 10 wt% monoclinic zirconia particles which had a mean diameter of about 13m. Thermal shock data showed that crack propagation in DZ/ZrO₂ composites was stable.     

Dislocations in plastically deformed apatite

Dislocations were introduced at room temperature by a Vickers indentation into a biological ceramic, apatite. Two types of apatite, a single crystal of fluorapatite and a sintered polycrystal of hydroxyapatite, were studied. Specimens prepared using a focused-ion-beam technique were examined by transmission electron microscopy. Natures of dislocations were determined by the conventional g · b criterion, where the weak-beam method was also applied. The slip system in fluorapatite apatite was determined to be      

The influence of mechanochemical treatment of sintered submicrocrystalline corundum substrates on the structure of bioglass composites

The influence of mechanochemical treatment of submicrocrystalline sintered corundum on the structure of bioglass composites containing α-Al₂O₃ and CaO-SiO₂-P₂O₅ glasses was examined in the context of the possibility to form hydroxyapatite after being immersed in the simulated body fluid solution. Measurements of specific surface area and size and X-ray analysis of submicrocrystalline sintered corundum were conducted. Bioglass composites were obtained by placing submicrocrystalline sintered corundum grains in the CaO-SiO₂-P₂O₅ sol system, gelling and sintering at 800°C. The specimens were examined under a scanning electron microscope before and after immersion in the simulated body fluid solution for 24 and 120 h. Using the VCS algorithm, calculations of thermodynamic stability of compounds occurring in these bioglass composites were carried out, verifying the X-ray analysis. Original Russian Text ? B. Staniewicz-Brudnik, S. Szarska, K. Gamrat, 2008, published in Sverkhtverdye Materialy, 2008, Vol. 30, No. 6, pp. 40–48.     

Hydroxyapatite-316L fibre composites prepared by vibration assisted slip casting

To prepare hydroxyapatite (HA, or HAp)-stainless steel 316L fibre composites with up to 30 vol% 316L fibres (1 mm long and 50 m in diameter), slip casting assisted by vibration (frequency: 55 Hz; amplitude: 5 mm) was carried out, followed by both cold isostatic pressing (CIPing) and hot isostatic pressing (HIPing). With the addition of around 0.5 wt% sodium carboxymethylcellulose (Na-cmc), solids loadings up to 44 vol% were obtained in calcined HA powder-derived slips, which were castable only under the vibration. The slips were concentrated and viscous so that the preferential sedimentation of the dense and large 316L fibres could be avoided. Subsequent CIPing was able to increase the relative density of the cast and dried green compacts from 46% after casting to 60% after CIPing. With the dense and uniform green compacts of the HA-316L mixtures, final HIPing at 950 °C resulted in HA-316L fibre composites of 99% relative density. The HA-316L fibre composites had improved fracture toughness of 3.6 ± 0.3 MPa.m^0.5, due to the bridging effect of the ductile 316L fibres. However, the mechanical strength of the composites was limited by the presence of residual thermal stresses and circumferential microcracks. The HA-316L fibre composites were biocompatible and exhibited favourable bone-bonding characteristics.