Bioactive PMMA bone cement modified with combinations of phosphate group-containing monomers and calcium acetate

Bone cement from polymethylmethacrylate powder and methylmethacrylate liquid has been successfully demonstrated as artificial material to anchor joint replacements in bone. However, it lacks the capability to bond directly to bone, so long-term implantation leads to an increased risk of loosening. Bioactive materials show better performance in fixation to bone, and the chemical bonding depends on bone-like apatite formation. This is triggered by surface reactions with body fluid. For these reactions, superficial functional groups like silanol (Si–OH) are ideal sites to induce apatite nucleation and the release of Ca2+ ions accelerates the apatite growth. Therefore, incorporation of materials containing these key components may provide the cement with apatite-forming ability. In this study, phosphoric acid 2-hydroxyethyl methacrylate ester or bis[2-(methacryloyloxy)ethyl] phosphate supplying a phosphate group (PO4H2) was added into methylmethacrylate liquid, while calcium acetate as a source of Ca2+ ions was mixed into polymethylmethacrylate powder. The influences of the combinations on the setting time and compressive strength were also investigated. Apatite was formed on the cements modified with 30 mass% of phosphoric acid 2-hydroxyethyl methacrylate ester or bis[2-(methacryloyloxy)ethyl] phosphate. The induction period was shortened with increased amounts of Ca(CH3COO)2. The setting time could be controlled by the Ca(CH3COO)2/monomer mass ratio. Faster setting was achieved at a ratio close to the mixing ratio of the powder/liquid (2:1), and both increases and decreases in the amount of Ca(CH3COO)2 prolonged the setting time based on this ratio. The highest compressive strength was 88.8 ± 2.6 MPa, higher than the lowest limit of ISO 5833 but was lower than that of the simulated body fluid-soaked reference. The increase of additives caused the decline in compressive strength. In view of balancing apatite formation and clinical standard, bis[2-(methacryloyloxy)ethyl] phosphate is more suitable as an additive, and the optimal modification is a combination of 30 mass% of bis[2-(methacryloyloxy)ethyl] phosphate and 20 mass% of Ca(CH3COO)2

Apatite-forming ability of vinylphosphonic acid-based copolymer in simulated body fluid: effects of phosphate group content

Phosphate groups on materials surfaces are known to contribute to apatite formation upon exposure of the materials in simulated body fluid and improved affinity of the materials for osteoblast-like cells. Typically, polymers containing phosphate groups are organic matrices consisting of apatite–polymer composites prepared by biomimetic process using simulated body fluid. Ca2+ incorporation into the polymer accelerates apatite formation in simulated body fluid owing because of increase in the supersaturation degree, with respect to apatite in simulated body fluid, owing to Ca2+ release from the polymer. However, the effects of phosphate content on the Ca2+ release and apatite-forming abilities of copolymers in simulated body fluid are rather elusive. In this study, a phosphate-containing copolymer prepared from vinylphosphonic acid, 2-hydroxyethyl methacrylate, and triethylene glycol dimethacrylate was examined. The release of Ca2+ in Tris-NaCl buffer and simulated body fluid increased as the additive amount of vinylphosphonic acid increased. However, apatite formation was suppressed as the phosphate groups content increased despite the enhanced release of Ca2+ from the polymer. This phenomenon was reflected by changes in the surface zeta potential. Thus, it was concluded that the apatite-forming ability of vinylphosphonic acid-2-hydroxyethyl methacrylate-triethylene glycol dimethacrylate copolymer treated with CaCl2 solution was governed by surface state rather than Ca2+ release in simulated body fluid

Apatite formation on a hydrogel containing sulfinic acid group under physiological conditions

Natural bone consists of apatite and collagen fiber. Bioactive materials capable to bonding to bone tissue are clinically used as bone-repairing materials. Apatite-organic polymer composites exhibit bone-bonding abilities and mechanical properties similar to those of natural bone, and these materials can be prepared using biomimetic processes in simulated body fluid (SBF). Specific functional groups such as sulfonic and carboxylic acid groups are known to induce the heterogeneous nucleation of apatite in SBF. However, it remains unclear whether structurally related sulfinic acid groups can contribute to apatite formation in the same way, despite sodium sulfonate being used in biomedical applications as a radical polymerization promoter in adhesive dental resin. Herein, we report the preparation of a new hydrogel containing sulfinic acid groups from sodium 4-vinylbenzenesulfinate and 2-hydroxyethyl methacrylate using a radical polymerization reaction and the subsequent incorporation of Ca2+ ions into this material. We also investigated the apatite-forming behavior of these hydrogels in SBF. Hydrogels containing sulfinic acid groups showed higher apatite-forming ability than those without sulfinic acid groups. In addition, the apatite layer formed on the former showed tight adhesion to the hydrogel. This phenomenon was attributed to the heterogeneous nucleation of apatite, induced by the sulfinic acid groups

Biomineralization behavior of a vinylphosphonic acid-based copolymer added with polymerization accelerator in simulated body fluid

AbstractApatite-polymer composites have been evaluated in terms of its potential application as bone substitutes. Biomimetic processes using simulated body fluid (SBF) are well-known methods for preparation of such composites. They are reliant on specific functional groups to induce the heterogeneous apatite nucleation and phosphate groups possess good apatite-forming ability in SBF. Improving the degree of polymerization is important for obtaining phosphate-containing polymers, because the release of significant quantities of monomer or low molecular weight polymers can lead to suppression of the apatite formation. To date, there have been very few studies pertaining to the effect of adding a polymerization accelerator to the polymerization reaction involved in the formation of these composite materials under physiological conditions. In this study, we have prepared a copolymer from triethylene glycol dimethacrylate and vinylphosphonic acid (VPA) in the presence of different amounts of sodium p-toluenesulfinate (p-TSS) as a polymerization accelerator. The effects of p-TSS on the chemical durability and apatite formation of the copolymers were investigated in SBF. The addition of 0.1–1.0wt% of p-TSS was effective for suppressing the dissolution of the copolymers in SBF, whereas larger amount had a detrimental effect. A calcium polyvinylphosphate instead of the apatite was precipitated in SBF

Bioactive Carbon-PEEK Composites Prepared by Chemical Surface Treatment

Polyetheretherketone (PEEK) has attracted much attention as an artificial intervertebral spacer for spinal reconstruction. Furthermore, PEEK plastic reinforced with carbon fiber has twice the bending strength of pure PEEK. However, the PEEK-based materials do not show ability for direct bone bonding, i.e., bioactivity. Although several trials have been conducted for enabling PEEK with bioactivity, few studies have reported on bioactive surface modification of carbon–PEEK composites. In the present study, we attempted the preparation of bioactive carbon-PEEK composites by chemical treatments with H2SO4 and CaCl2. Bioactivity was evaluated by in vitro apatite formation in simulated body fluid (SBF). The apatite formation on the carbon–PEEK composite was compared with that of pure PEEK. Both pure PEEK and carbon-PEEK composite formed the apatite in SBF when they were treated with H2SO4 and CaCl2; the latter showed higher apatite-forming ability than the former. It is conjectured that many functional groups able to induce the apatite nucleation, such as sulfo and carboxyl groups, are incorporated into the dispersed carbon phase in the carbon–PEEK composites

Structure of Yttrium and Phosphorus-Containing Microspheres Prepared by Spray Dry Method

Microspheres containing yttrium (Y) and/or phosphorus (P) around 25 µm are useful for radioembolization therapy because they are activated to β-emitter by neutron bombardment and infused in blood vessels in the neighborhood of tumors to irradiateβ-rays to the tumors. In this study, we attempt to prepare Y and P-containing microspheres by spray drying method. Starting solution containing yttrium nitrate and phosphoric acid in equimolar ratio was spray dried under various conditions. Microspheres 5-30 µm in size are obtained when the starting solution with polyvinyl alcohol (PVA) binder was spray-dried at the atomizing pressure of 0.05 MPa. When the microspheres were heated at 1100ºC for 1 h, they precipitated Y-containing crystals such as yttrium phosphate (YPO4), yttrium oxide (Y2O3), yttrium polyphosphate (Y(PO3)3) and yttrium tetraphosphate (Y2P4O13) but most of them were ruptured. Without the PVA binder, small microspheres around 5 µm in size were formed but their shape remained even after the heat treatment. We found that the atomizing pressure of spray dryer remarkably affects the size of microspheres and PVA binder is essential to obtain microspheres around 25 µm, but addition of pH adjuster to starting solution is not essential. This study proposed the criterion of conditions to prepare Y and P-containing microspheres by spray drying method

The investigation of bioactivity and mechanical properties of glass ionomer cements prepared from Al2O3-SiO2 glass and poly(γ-glutamic acid)

The glass ionomer cement as one of the dental cements has been subjected to be widespread application in restoring tooth structure. Most of glass ionomer cements employ the poly(acrylic acid) (PAA) as the liquid phase, but the presence of PAA inhibits the apatite formation on the surface in the body environment, which is an essential requirement for exhibiting bone-bonding ability (bioactivity). In this study, poly(γ-glutamic acid) (γ-PGA), a kind of biopolymer, was utilized for cement preparation. The effort of preparation parameters including the glass powders/liquid ratio (P/L) and the concentration of γ-PGA on diametral tensile strength were investigated. A maximum diametral tensile strength value of MPa was obtained when the cement sample was prepared by P/L ratio of 1 : 1 and the γ-PGA concentration of 30% after aging for 3 days. The TF-XRD patterns, SEM images, and EDX spectra suggested that the cement induced a precipitation of calcite on the surface after 7 days of immersion in stimulated body fluid (SBF), although the apatite formation was not observed. The present results suggest that the cement has potential to show bioactivity in vivo, because calcite is also reported to be bioactive

Design of novel bioactive materials through organic modification of calcium silicate

Bioactive ceramics have attractive feature for bone repair such as direct bone-bonding in the body. However their clinical application is limited to low loaded portions due to their inappropriate mechanical performances such as higher brittleness and lower flexibility than natural bone. The essential condition for artificial materials to show bioactivity is formation of bone-like apatite on their surfaces in body environment. This apatite formation is triggered by silanol (Si–OH) group on the material surfaces and release of Ca2+. These findings bring us an idea that novel bioactive materials with high flexibility can be designed by organic modification of calcium silicate. We synthesized organic–inorganic hybrids from organic polymers including 2-hydroxyethylmethacrylate (HEMA), starch and alginate by modification with alkoxysilane and calcium chloride. The hybrids formed apatite on their surfaces in simulated body fluid (SBF, Kokubo solution). Such a modification was also effective for providing conventional polymethylmethacrylate (PMMA)-based bone cement with bioactivity.IX Conference and Exhibition of the European Ceramic Society: June 19-23, 2005, Portorož, Sloveni

Yttrium phosphate microspheres with enriched phosphorus content prepared for radiotherapy of deep-seated cancer

Ceramic microspheres composed of β-emitters are useful for in situ radiotherapy of deep-seated cancer by implantation around the tumor. In addition, microspheres 20–30 µm in diameter can combine β-emission with the embolization effect. Yttrium phosphate is an attractive candidate material for such microspheres, because both Y and P play roles as β-emitters. The half-life of 31P is known to be much larger than that of 90Y. Therefore, it is expected that yttrium phosphate microspheres with high P content can maintain a longer radiotherapy effect. In the present study, preparation of microspheres with enriched P content has been attempted by water-in-oil emulsions using polyphosphate as a starting material. Yttrium phosphate microspheres with a higher P/Y molar ratio (2.5) than in previously reported YPO4 microspheres were obtained. It was found that emulsification for sufficient time (more than 10 min) is necessary to obtain microspheres that are 20–30 µm in size. Although the microspheres released Y sparingly, they released larger amounts of P than previously reported YPO4 microspheres in a simulated body environment. Heat treatment at moderate temperature can suppress P release to some extent. Further improvement in chemical durability through surface modification is essential for long-term clinical use

Deposition of hydroxyapatite on SiC nanotubes in simulated body fluid

SiC nanotubes can become candidate reinforcement materials for dental and orthopedic implants due to their light weight and excellent mechanical properties. However, the development of bioactive SiC materials has not been reported. In this study, hydroxyapatites were found on SiC nanotubes treated with NaOH and subsequently HCl solution after soaking in simulated body fluid. On the other hand, hydroxyapatites did not deposit on as-received SiC nanotubes, the SiC nanotubes with NH4OH solution treatment and SiC bulk materials with NaOH and subsequently HCl solution treatment. Therefore, we succeeded in the development of bioactive SiC nanotubes by downsizing SiC materials to nanometer size and treating with NaOH and subsequently HCl solutions for the first time