Preparation of chitosan-siloxane porous hybrids with hydroxyapatite for repair of skull defect

A craniotomy is performed for various neurological diseases, injuries, or conditions such as brain tumors, hematomas, aneurysms, and skull fractures. First, the small-sized holes, called “burr holes” were made to insert some surgical tools such as a shunt, a drain, an intracranial pressure monitor, and endoscope, etc. or be the starting point of removing large skull fracture. After surgery, the holes should be closed by the calcium phosphate cements or the titanium plates, because the skull defects are not spontaneously regenerated. Calcium phosphate cements (CPCs) have attracted great interest as bone substitute material. However, the cements easily flow into the brain when they are contacted and mixed with cerebrospinal fluid or blood. On the other hand, the titanium plates cause the thinning of the scalp and sometimes come out on the surface. Moreover, they interrupt the observation of affected part by MRI. Therefore, new bone substitute materials for the burr hole were required. Porous scaffold materials are necessary for the regeneration of new tissues in the tissue engineering field. High porosity is required for the tissue engineering scaffold in order to provide sufficient space for cell adhesion / proliferation, and to supply oxygen and nourishment. Chitosan-siloxane hybrids incorporated with calcium ions showed good osteocompatibility and formed apatite into alkaline phosphate solution. In this study, the porous hybrids with hydroxyapatite were implanted into the beagle skull bone defect and examined the bone regeneration. Chitosan was dissolved in 0.25 M acetic acid to obtain 2 (w/v)% chitosan solution. GPTMS and CaCl2 of predetermined quantity were added into the chitosan solution and stirred at room temperature for 1 hour. The obtained solutions were poured into a plastic container, and stood overnight. It was then frozen at -20°C, and lyophilized with the freeze-dryer. The obtained samples were soaked in 0.01 M Na2HPO4 at 80°C for 3 days. The hybrids were washed with distilled water and then freeze-dried again. The surface analysis of the samples was examined by thin film X-ray diffraction (TF-XRD) and scanning electron microscopy (SEM). The samples for in vivo animal test were sterilized by γ-ray irradiation. The samples were implanted into the skull bone defect of adult female beagles. After several periods, the bone tissue surrounding the implanted site was examined histologically. The chitosan-siloxane porous hybrids with hydroxyapatite by soaking in phosphate solution maintained their high porosity and water uptake property. The hybrids were degraded completely after 1 year implantation. The hybrids with hydroxyapatite accelerated the calcification compare with the only hybrids

Improvement of Biocompatibility of Silicone Elastomer by Surface Modification

γ-Methacryloxypropyltrimethoxysilane (γ-MPS) was grafted to silicone due to emulsion polymerization to induce Si-OH groups, in order to provide silicone with bioactivity spontaneous deposition of apatite in body fluid and to improve cytocompatibility. Apatite deposited on the grafted silicone within 7 days of soaking in 1.5 times as concentrated as the Kokubo solution. Osteoblastic cells (MC3T3-E1) were cultured on the specimens up to 7 days. After 5 days of culture, the number of MC3T3-E1 cells on the grafted specimen was much greater than that on the original specimen. These results indicated that the biocompatibility of silicone elastomer was improved by the grafting γ-MPS

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

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

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

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

Novel anti-decay self-setting paste of hydroxyapatite/collagen nanocomposite utilizing GPTMS

Bone is a typical inorganic/ortganic nanocomposite mainly composed of hydroxyapatite (HAp) nanocrystals and collagen molecules. The composition and nanostructure is closely related to bone’s biomechanical and biochemical properties. One of the most important things for bone is a bone remodeling process that maintains mechanical strength of bone to allow walking and running as well as homeostasis of calcium in our body. In fact, sintered HAp composed of HAp crystals approximately 1 µm in particle size is considered as non-bioresorbable; however HAp nanocrystals easily resorbed by osteoclasts. A hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) was successfully synthesized by the authors via self-organizing process. [1] The HAp/Col is incorporated into bone remodeling process completely as the same as the autologous bone transplanted and substituted with new bone in 3 months. Porous type HAp/Col was also developed by the authors and shows spoge-like viscoelastity in wet condition. [2] The porous HAp/Col had been tested clinically and has been being sold in Japan from April, 2013 as ReFit®. According to the clinical test [3], the HAp/Col shows higher rate of remarkable efficiency in comparison to Osferion®, porous β-tricalcium phosphate, for substitution with newly formed bone. In addition, sponge-like deformability allows to fit irregular shape of bone defects as well as to press to pack the porous HAp/Col in cavity created by removal of benign bone tumor. On the other hand, recent need from surgeon for bone filler is a self-setting bone paste with bioresorbability. Previously, the HAp/Col anti-decay self-setting paste was prepared successfully with the use of sodium alginate and calcium compounds. It showed tolerant paste properties; however, the paste contained 30 % in mass of calcium compounds that could interfered excellent biological activity of the HAp/Col. In this study, the HAp/Col paste with injectability, self-setting and anti-decay abilities was prepared using the HAp/Col powder and 1 % in volume of 3-glycidoxypropyl)methyldiethoxysilane (GPTMS) aqueous solution. The paste obtained was evaluated by viscosity, hardening behavior and anti-decay property tests. The HAp/Col was synthesized according to ref 1. The HAp/Col was compacted with specially designed mold by uniaxially press squeezing of water from the HAp/Col. The HAp/Col compact was then crushed and ball-milled to obtain the HAp/Col particles of 100 µm or less in size. The GPTMS was dissolved in pure water at 1 % in volume and steadily placed in 25 °C for 1 h to allow hydrolysis of the GPTMS to form silanol groups. The HAp/Col powder (powder phase, P) and the GPTMS aqueous solution (liquid phase, L) were mixed at 0.20-2.00 of P/L ratio in g/cm3 to obtain a HAp/Col paste. A viscosity of the HAp/Col paste obtained was measured according to ref 1. Briefly, the paste obtained was shaped to cylinder at 5 mm in diameter and 5.1 mm in hight and start pressing at 10 min after mixing by 2 kg weight for 10 min. A spread area of the paste was measured from digital photo with Image-J. Hardening behavior was measured using the viscosity test as a function of time, because softness of the paste did not allow to apply conventional the needle method. Anti-decay property was tested according to JIS T 0330-4:2012 [5]; briefly, the paste shaped in cylinder 4.8 mm in diameter and 16.5 mm in height was placed on wire mesh and, at 5 min after mixing, soaked in phosphate buffered saline for 72 h. Debris were then collected and measured their mass, and decay ratio was calculated as debris/original masses. The paste with P/L ratio of 0.2 could not shaped by its high fluidity and that of 2.0 could not shaped because of its aggregation. The paste with P/L ratio of 0.33 could injected through 18G needle and others could injected through syringe with 1.8 mm in inner diameter. The viscosity of the paste increased with increasing in P/L ratio and did not depend on the amounts of GPTMS. The initial hardening was observed first 30-40 min from mixing and gradually hardened. The paste with P/L ratio of 1.5 showed mechanical strength more than 1 MPa with viscoelastic property. No significant decay was observed for all pastes. The HAp/Col-GPTMS paste can be good candidate for high performance injectable bone filler as well as a raw material for 3D printing