Takashi Kizuki

Bone bonding bioactivity of Ti metal and Ti–Zr–Nb–Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments

Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices.

Preparation of bioactive Ti metal surface enriched with calcium ions by chemical treatment

A calcium solution treatment was applied to a NaOH-treated titanium metal to give it bioactivity, scratch resistance and moisture resistance. The titanium metal was soaked in a 5 M NaOH solution and then a 100 mM CaCl(2) solution to incorporate Ca(2+) ions into the titanium metal surface by ion exchange. This treated titanium metal was subsequently heated at 600 degrees C and soaked in hot water at 80 degrees C. The NaOH treatment incorporated approximately 5 at.% Na(+) ions into the Ti metal surface. These Na(+) ions were completely replaced by Ca(2+) ions by the CaCl(2) treatment. The number of Ca(2+) ions remained even after subsequent heat and water treatments. Although the NaOH-CaCl(2)-treated titanium metal showed slightly higher apatite-forming ability in a simulated body fluid than the NaOH-treated titanium metal, it lost its apatite-forming ability during the heat treatment. However, subsequent water or autoclave treatment restored the apatite-forming ability of the NaOH-CaCl(2)-heat-treated titanium metal. Although the apatite-forming ability of the NaOH-heat-treated titanium metal decreased dramatically when it was kept at high humidity, that of NaOH-CaCl(2)-heat-water-treated titanium metal was maintained even in the humid environment. The heat treatment increased the critical scratch resistance of the surface layer of the NaOH-CaCl(2)-treated titanium metal remarkably, and it did not deteriorate on subsequent water treatment.

Bioactivity of sol–gel-derived TiO2 coating on polyetheretherketone: In vitro and in vivo studies

UNLABELLED A polyetheretherketone (PEEK) surface was modified using a sol-gel-derived TiO2 coating in order to confer bone-bonding ability. To enhance the bonding strength of the coating layer, pretreatment with either O2 plasma or sandblasting was performed prior to sol-gel coating. Additionally, post-treatment with acid was carried out to confer apatite (calcium phosphate)-forming ability to the surface. Biomechanical and histological analyses performed using an in vivo rabbit tibia model showed that PEEK surfaces modified with sol-gel-derived TiO2 and acid post-treatment had better bone-bonding properties than uncoated PEEK surfaces. These modified surfaces also performed well in terms of their in vitro cell responses due to their modified surface chemistries and topographies. Although O2 plasma or sandblasting treatment were, for the most part, equivocal in terms of performance, we conclude that sol-gel-derived TiO2 coating followed by acid post-treatment significantly improves the bone bonding ability of PEEK surfaces, thus rendering them optimal for their use in surgical implants. STATEMENT OF SIGNIFICANCE The role of polyetheretherketone (PEEK) as an alternative biomaterial to conventional metallic implant materials has become increasingly important. However, its low bone bonding ability is yet to be resolved. This in vivo and in vitro investigation on the functionalization of PEEK surfaces highlights the utility of this material in clinical interventions that require implants, and may extend range of applications of PEEK.

Effect of titania-based surface modification of polyethylene terephthalate on bone–implant bonding and peri-implant tissue reaction

Organic polymers can be uniformly surface-modified with bioactive TiO(2) by using a sol-gel method. Titania-based surface-modified polyethylene terephthalate (TiPET) plates and fabric have shown apatite-forming ability in simulated body fluid. Here, we first investigated the bone-bonding ability and mechanical bonding strength between the surface-modified layer and the base material (PET) of TiPET plates in vivo. For clinical applicability, we also examined the bone-bonding ability of TiPET fabric and the effect of titania-based surface modification on peri-implant tissue reactions (e.g. connective tissue capsule formation) in bone in vivo. Solid PET plates and PET fabric were prepared. Test plates and fabric were surface-modified with titania solution by using a sol-gel method. Histological examinations of the plates implanted into rabbit tibiae revealed direct contact between the TiPET plate and the bone. After the detaching test, a considerable amount of bone residue was observed on the surface of the TiPET plate. This result suggests that the mechanical bond strength between surface-modified layer and the base material is stronger than that between newly generated bone and tibia, and indirectly ensures the mechanical stability of the surface-modified layer. Pulling tests and histological examinations of the TiPET fabric revealed its excellent bone-bonding ability and micro-computed tomographic images showed excellent osteoconductive ability of TiPET fabric. The connective tissue capsule was much thinner, with less inflammatory tissue around the TiPET implants than around the control samples. These results indicate that TiPET fabric possesses a mechanically stable surface-modified layer, excellent bone-bonding ability, osteoconductive ability, and biocompatibility in bone.

Improvement of Apatite-Forming Ability of Titanium Metal Enriched with Calcium Ion on its Surface

It has been shown that titanium metal subjected to NaOH and heat treatments spontaneously forms a bonelike apatite on its surface in the living body and bonds to living bone. However, its apatite-forming ability was liable to decrease when the treated titanium metal was stored in humid environment. In the present study, the NaOH-treated titanium metal was soaked in a CaCl2 solution at 40°C for 24h, heat-treated at 600°C for 1h, and then soaked in ultrapure water at 80°C for 24h. Calcium titanate was formed on the surface of the titanium metal 1µm in thickness by these treatments. The resultant titanium metal showed high scratch resistance and high apatite-forming ability in a simulated body fluid. This high apatite-forming ability was maintained even after the titanium metal was kept in 95% relative humidity at 80°C for 1 week.

Behavior of MC3T3-E1 Osteoblast-Like Cells Cultured on a Glass Substrate with Different Surface Roughness

Our experiments of mouse osteoblast-like MC3T3-E1 cells cultured on a glass substrate showed that as surface roughness of a substrate increased, cell proliferation, cell differentiation and subsequent mineralization were reduced.

Synthesis of New Biocompatible Apatite-Type Rare-Earth Silicates

Series of apatite-type rare-earth silicates were synthesi zed by a solid state reaction at 1400 °C as a new biomaterial. The synthesized apatite-type rare-earth silicate s were analyzed by X-ray diffraction (XRD) and infrared spectroscopy (IR), and lattice parameters we e calculated. Single phase of the apatite-type rare-earth silicates was obtained, and the lattic e parameters became smaller with the increase of the rare-earth content or increasing of an atomic numbe r of the substituted ions. The ceramic apatite-type rare-earth silicates were obtained by a sintering at 1400 °C, and its biocompatibility was estimated by in vitro and in vivo tests. The ceramic apatite-type rare-earth silicates had a good cell proliferation, and no inflammation was obser ved in the vicinity of the implanted ceramic. It was suggested that the ceramic apatite -type rare-earth silicates could use as a biocompatible material.

Apatite-Forming Ability of Titanium Metal Enriched with Calcium Ion on its Surface

In order to study method for preparing bioactive titanium metal, calcium ions were attempted to be incorporated into the surface of the titanium metal by ion exchange method. Titanium metal was soaked in 5M NaOH solution and 100mMCaCl2 solution and subjected to heat treatment. About 5 atom% of Na was incorporated into the surface of the titanium metal by the NaOH treatment This Na was completely replaced with calcium ion by the CaCl2 treatment and maintained even after the heat treatment. Critical detaching strength of the surface layer to the substrate of NaOH-treated titanium metal was a little increased by the CaCl2 treatment and remarkably increased by the heat treatment. Apatite-forming ability of the NaOH-treated titanium metal in SBF was increased by the CaCl2 treatment, but decreased by the subsequent heat treatment.

Effects of Serum Proteins in Apatite Layer Formed in Culture Medium on Initial Adhesion and Cell Proliferation

In cell culture medium containing serum proteins, a layer with a great role in ostelblast-like cell’s growth formed on a HAp ceramics by a coprecipitation with a deposition of a bone-like apatite and an adsorption of serum proteins. The adsorption of proteins is influential in the apatite deposition and the cell adhesion. A component of serum albumin is forming < 80% of total serum proteins, therefore we focused on the serum albumin. The serum albumin was removed from fetal bovine serum by using an albumin removal kit, and then the albumin free cell culture medium was prepared. The bone-like apatite layer was quickly formed on the HAp ceramics in the albumin free medium, however the high cell adhesion property was not confirmed. As a result of investigation of an initial cell adhesion, the initial cell adhesion property of the bone-like apatite layer was not excellent even though the layer contained the serum proteins. Moreover, the layer without serum proteins showed a meager cell adhesion property in every time of the cultivation. Therefore, it was revealed that the adsorption of the serum proteins only on the surface was not enough to the improvement of the cell growth. And a few days cultivation was required for an appearance of the remarkable effect on the cell growth on the layer formed by a coprecipitation reaction about the bone-like deposition apatite and the serum proteins adsorption.

Apatite Layer with Serum Protein as a Suitable Scaffold for Growth of Osteoblast-Like Cell

Autograft, allograft, and biomaterials had been developed for bone regeneration. In recent year, a tissue engineering technique has been paid much attention for next generation implant. A problem of bone tissue engineering to be solved is a development of the substrate that is suitable for cell adhesion, proliferation, and differentiation. A biomimic scaffold for tissue culture was proposed, and then a cell response on the scaffold was estimated. The scaffold composed by a calcium deficient apatite with an adsorbed serum protein was formed on a ceramic hydroxyapatite (HAp) and surface-modified titanium by a soaking in cell-culture medium supplemented with fetal bovine serum. Excellent results on cell proliferation and cell adhesion were obtained only on osteoblast-like cells (MC3T3-E1). An actin filament in narrow filopodium of the spindle-shaped MC3T3-E1 cells on the ceramic HAp had a regular course. On the other hand, ends of the actin filament of the widely spread cells on the apatite layer with serum protein were scattering. It was suggested that the scattering of the actin end showed an existence of fibronectin, and then tight adhesion would be obtained by the many focal adhesion. Accordingly, the effectiveness of the biomimic scaffold containing serum protein on cell growth was confirmed.