Surface Modification of Carbon Fiber-Polyetheretherketone Composite to Impart Bioactivity by Using Apatite Nuclei

The authors aimed to impart the apatite-forming ability to 50 wt% carbon fiber-polyetheretherketone composite (50C-PEEK), which has more suitable mechanical properties as artificial bone materials than pure PEEK. First, the 50C-PEEK was treated with sulfuric acid in a short time to form pores on the surface. Second, the surface of the 50C-PEEK was treated with oxygen plasma to improve the hydrophilicity. Finally, fine particles of calcium phosphate, which the authors refer to as “apatite nuclei”, were precipitated on the surface of the 50C-PEEK by soaking in an aqueous solution containing multiple inorganic ions such as phosphate and calcium (modified-SBF) at pH 8.20, 25 °C. The 50C-PEEK without the modified-SBF treatment did not show the formation of apatitic phase even after immersion in simulated body fluid (SBF) for 7 days. The 50C-PEEK treated with the modified-SBF showed the formation of apatitic phase on the entire surface within 1 day in the SBF. The apatite nuclei-precipitated 50C-PEEK will be expected as a new artificial bone material with high bioactivity that is obtained without complicated fabrication processes.

Sintering of Potassium Doped Hydroxy-Fluorapatite Bioceramics

The present study describes the influence of potassium and hydroxyl substitutions on the structural, thermal and mechanical properties of fluorapatite bioceramics. A set of non-stoichiometric ion-substituted compounds, with a chemical formula of Ca10−xKx(PO4)6F(2−2x)(OH)x with 0 ≤ x ≤ 1 synthesized by the wet precipitation method, were found to be single-phase apatites crystallizing in the hexagonal P63/m space group. The structural parameters, as well as the crystallite sizes, increased accordingly to the amount of added dopant-ions. The thermal behavior of these compounds, studied within the temperature range 500–1200 °C, indicated a partial decomposition of the apatitic phase and its transformation to tricalcium phosphate β-Ca3(PO4)2 at temperatures exceeding 750 °C. A relative density of the sintered samples achieved the highest value with x = 0.25 and reached about 95% after sintering at 1050 °C for 1 h. The microstructures of the sintered samples were of a trans-granular aspect and experienced an increase in the radius of their pores as x increased. The prepared bioceramic materials were mechanically characterized by means of Young’s modulus, flexural strength and fracture toughness measurements. The overall trend of these parameters evolved comparably to the relative density, and the maximum values obtained for x = 0.25 were measured to be 96 MPa, 47 MPa and 1.14 MPa·m1/2, respectively.

Retarding Bioactivity Effect of Ciprofloxacin Incorporated in Polyvinyl Alcohol/Bioglass Scaffold as Bone Graft

The biomaterials are used for many biomedical applications. The main objective of the present work was to investigate the potential role of Bioglass (Melting)- Polyvinyl alcohol (BG (M)-PVA) and Bioglass (Melting)-Polyvinyl alcohol-20%Ciprofloxacin (BG (M)-PVA-20Cip) in regenerative bone capacity. These composites were implanted in the femoral condyles of Wistar rats and compared to that of ovariectomised groups. Our results noted, after the different period of implantation (15, 30, 60 and 90 days), that the Alkaline phosphatase (ALP) and Acid phosphatase (ACP) activities showed an excellent osteoinductive property of BG (M)-PVA, that this phenomena decreased with the presence of ciprofloxacin. Physico-chemical techniques (ICP-OES and SEM) were engaged to highlight the influence of antibiotic on the structure, porosity and bioactivity of a porous Glass-PVA before and after implantation. The results obtained by ICP-OES showed a rapid reduction in silicon (Si) and sodium (Na), and noted an accelerator increase in calcium (Ca) and phosphorus (P) ion concentrations in BG (M)-PVA that the BG (M)-PVA-20Cip. This result is confirmed by SEM. We can conclude that the loading of ciprofloxacin in BG (M)-PVA is characterized by a retard effect of formation of apatitic phase.

Observation of Transformation Behavior of Octacalcium Phosphate to Hydroxyapatite

Octacalcium phosphate (OCP) is regarded as a precursor of hydroxyapatite (HA) which is a main inorganic comstituent of human bones and teeth. OCP is becoming regarded as an important biomaterial. Recently, implanted OCP was found to be converted to apatitic phase in the body and support bone regeneration. Therefore, it is important to reveal the transformation mechanism of OCP to HA for revealing the mechanism of bone formation and for the development of biomedical materials for bone. In this study, we focused on the dissolution of OCP and precipitation of HA. OCP particles were immersed in distilled water at 60 °C. The temporal change of the immersed powders and immersing solution were examined, and the transformation mechanism of OCP to HA was discussed. As there was an unreactive period in the first stage of the transformation, HA crystals seemed to grow easily once HA nuclei were formed. It is speculated that HA nuclei formed on OCP crystals by heterogeneous nucleation, and then HA crystals grow using calcium and phosphoric ions supplied from dissolved OCP.

Phosphate Precipitation in Biofilms and Flocs

The experiments have confirmed that denitrification in biofilms may lead to calcium phosphate precipitation inside the biofilms due to the increased pH created by the denitrification reaction. This has been shown in a laboratory fixed film reactor with well defined geometry and feed with well defined substrates. The phosphate precipitate was in one case found similar to a carbonate containing apatitic phase. It accumulated in the bio-film to 9.3% P based on dry solids. A mathematical model has been developed relating the phosphate to nitrate molar removal rates to the concentration of phosphate, calcium, bicarbonate, the solubility of the solid phosphate phase and the type of carbon source used for denitrification. The model was supported by the experiments. The experiments show that the biofilm precipitation may be of significant practical interest, but factors as filamentous growth on the biofilm surface or precipitation of an easy soluble amorphous calcium phosphate can also make the biofilm precipitation insignificant. The precipitation effect is expected to be feasible in floes, if a homogeneous biomatrix with a thickness of more than approx. 100 µm exist in the floc substructure.

Formation of CaHPO4 · 2H2O from Enamel Mineral and Its Relationship to Caries Mechanism

Tooth enamel, when treated with dilute H3PO4 solutions, dissolved incongruently with formation of large CaHPO4 · 2HO2O crystals. Equilibrated solutions were saturated with respect to CaHPO4 · 2H2O, and a mineral more soluble than well-crystallized, synthetic Ca5(PO 4)3OH, probably an impure, defective apatite. The CaHPO 4·2H2O crystals formed at considerably higher pH values than expected because of enhanced solubility of the apatitic phase in enamel. Pyrolysis of carious enamel revealed the presence of acidic calcium phosphate presumed to be CaHPO4·2H2O.