Ill Yong Kim

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Bioactive Composites Consisting of PEEK and Calcium Silicate Powders

Bioactive bone-repairing materials with mechanical properties analogous to those of natural bone can be obtained through the combination of bioactive ceramic fillers with organic polymers. Previously, we developed novel bioactive microspheres in a binary CaO—SiO2 system produced through a sol—gel process as filler for the fabrication of composites. In this study, we fabricate bioactive composites in which polyetheretherketone is reinforced with 0—50 vol% 30CaO · 70SiO2 (CS) microspheres. The prepared composites reinforced with CS particles form hydroxyapatite on their surfaces in simulated body fluid. The induction periods of hydroxyapatite formation on the composites decrease with increasing amount of CS particles. The mechanical properties of the composites are evaluated by three-point bending test. The composites reinforced with 20 vol% CS particles show 123.5 MPa and 6.43 GPa in bending strength and Young’s modulus, respectively.

Formation of octacalcium phosphates with co-incorporated succinate and suberate ions

Octacalcium phosphates (OCPs) co-incorporated with various molar ratios of succinate and suberate ions were synthesized by wet processing. The interplanar spacings of the (100) planes (d(100)) of OCPs formed in the presence of succinic acid (Suc) or suberic acid (Sub) were larger than those of OCPs formed without addition of a dicarboxylic acid to the reaction solvent. The increases in the interplanar spacings of the (100) planes were caused by substitution of HPO(4)(2-) by dicarboxylate ions. The OCPs with co-incorporated succinate and suberate ions, i.e. solid solutions of OCP with incorporated Suc and Sub, were formed by reactions in the presence of Suc and Sub. When the Suc/(Suc + Sub) values in the starting compositions were in the range 0.45-1.0, Suc was preferentially incorporated into the OCP. In contrast, when the Sub/(Suc + Sub) values in the starting compositions were in the range 0.60-1.0, Sub was preferentially incorporated into the OCP crystals.

Hydroxyapatite formation on titania-based materials in a solution mimicking body fluid: Effects of manganese and iron addition in anatase.

Hydroxyapatite formation on the surfaces of implanted materials plays an important role in osteoconduction of bone substitutes in bone tissues. Titania hydrogels are known to instigate hydroxyapatite formation in a solution mimicking human blood plasma. To date, the relationship between the surface characteristics of titania and hydroxyapatite formation on its surface remains unclear. In this study, titania powders with varying surface characteristics were prepared by addition of manganese or iron to examine hydroxyapatite formation in a type of simulated body fluid (Kokubo solution). Hydroxyapatite formation was monitored by observation of deposited particles with scale-like morphology on the prepared titania powders. The effect of the titania surface characteristics, i.e., crystal structure, zeta potential, hydroxy group content, and specific surface area, on hydroxyapatite formation was examined. Hydroxyapatite formation was observed on the surface of titania powders that were primarily anatase, and featured a negative zeta potential and low specific surface areas irrespective of the hydroxy group content. High specific surface areas inhibited the formation of hydroxyapatite because calcium and phosphate ions were mostly consumed by adsorption on the titania surface. Thus, these surface characteristics of titania determine its osteoconductivity following exposure to body fluid.

Formation of Oriented Hydroxyapatite Rods by Hydrothermal Treatment of Calcite Single Crystal

Morphological control on hydroxyapatite crystals has attractive prospects in research to clarify the effects of crystal planes on biological performance. Hydrothermal processing is known as a typical type of processing for fabricating well-grown crystals with unique morphology. The purpose of the present study is to examine the feasibility of well-crystallized crystals with oriented structures through hydrothermal treatment of calcite. A single crystal of calcite was applied to hydrothermal treatment in a phosphate solution at . Rod-shaped hydroxyapatite crystals with micrometer-size were formed on the {100} face of calcite after treatment, while nanometer-sized hydroxyapatite crystals were formed on the (111). The hydroxyapatite crystals formed on each plane were not morphologically changed with increasing treatment periods. An oriented structure of rod-shaped hydroxyapatite was constructed after hydrothermal treatment of {100} planes on the calcite single, while such orientation was not observed on the (111) plane after the treatment. The layer of hydroxyapatite formed on the {100} plane was thicker than that of the (111) plane. The {100} plane of calcite shows a higher reactivity than that of the (111) plane, which results in rapid crystal growth of hydroxyapatite. The difference in the morphology of the formed hydroxyapatite was governed by the reactivity of each crystal plane exposed to the surrounding solution.

Fabrication of α-Tricalcium Phosphate Ceramics through Two-Step Sintering

α-tricalcium phosphate (α-TCP), which shows higher solubility than β-TCP, is bioabsorbable and receives special attention for its ability of turning into hydroxyapatite (HAp) in a physiological condition. Problems occasionally occur as α-TCP porous body is too brittle to be handled. Compressive strengths of β-TCP and HAp dense sintered blocks are reported to be comparable to that of human cortical bone. However, α-TCP dense body has rarely been reported. For fabrication of dense sintered body, two-step sintering (TSS) was applied in this study. The TSS generally has firing processes at the lower temperatures, following that at the higher temperatures. TSS is known as one of most effective processing to prevent grain growth comparing with conventional sintering (CS). Dense body of α-TCP was fabricated by both CS and TSS. TSS processing involves heating specimens to T1 temperature, followed by holding at a relatively lower T2 temperature for 12 h. Microstructures of the sintered bodies were characterized and mechanical properties were also evaluated. The specimen prepared by TSS processing with T1 1400 °C, T2 1300 °C showed the lowest porosity (2.7%) and highest compressive strength (714 MPa) among the prepared specimens. TSS processing might be applicable on densification of calcium phosphate powders to fabricate dense body.

Formation of serrated nanorods of hydroxyapatite through organic modification under hydrothermal processing

Hydroxyapatite (HAp) ceramics are widely used as artificial bone substitutes owing to its unique biological activity, that is, bone-bonding property. HAp nanoparticles have higher potential of biological functionality than microparticles owing to their increased specific surface area (SSA) because biological functionality of the crystals is governed by their surface characteristics. HAp particles of varied size and morphology have been prepared by employing various kinds of surfactants and capping ligands. In this research, we report the formation of HAp nanorods with serrated morphology which led to an increase in SSA. We obtained HAp nanorods with serrated morphology by adding thiosalicylic acid as a capping ligand under hydrothermal conditions. The tailoring of HAp nanorods by thiosalicylic acid under hydrothermal conditions is a useful method to prepare HAp nanorods with improved functionality.

Organic-Inorganic Hybrids for Bioinert Coating on Implantable Electronic Devices

For the purpose of bioinert coating on electronic devices, we developed the non-hydrolytic sol-gel derived organic-inorganic hybrid materials by addition of epoxy groups which can adhere strongly to the surface of electronic silicon device. The adhesion and chemical properties of hybrids were investigated as a function of epoxy group contents. The hybrids were prepared from 3-metacrloxypropyltrimethoxysilane (MPTS) and 3-glycidoxypropyltrimethoxysilane (GPTS) and diphenylsilanediol. The transparent hybrids were obtained after curing by UV irradiation. The adhesion properties of the hybrids were estimated by the maximum load to resist in a scratch test. The adhesion property of the hybrids increased with addition of GPTS and the highest adhesion was obtained from the hybrid with 5-10 mol% of GPTS. From the element analysis, Si concentrations of all the solutions were less than 2 mM after soaking for 7 d. The Si concentrations were not changed with increasing soaking period. The addition of epoxy groups is effective on improvement of adhesion property of the silica-based hybrid without loosening its chemical stability.

In Vitro Aging Test for Bioactive PMMA-Based Bone Cement Using Simulated Body Fluid

Novel PMMA-based bone cement using bioactive sol-gel derived CaO-SiO2 powder in order to induce bioactivity as well as to increase its mechanical property. The novel PMMA-based bone cements formed apatite on their surfaces in Simulated Body Fluid(SBF). In the present study, a change in mechanical property of the cement was evaluated using SBF. Before soaking in SBF, its compressive strength showed 80.6±2.1MPa. After soaking in SBF for 2 weeks, 8weeks and 9 weeks, its compressive strength were changed to 83.6±1.6MPa, 87.3±2.4MPa and 85.6±1.8MPa, respectively. It is clear that from the above result, there is no decrease in its compressive strength within 9 weeks soaking in SBF. That it hardly decreases in compressive strength of 7P3S bone cement in SBF is due to the relative small amount of gel powder or its spherical shape and monosize. Therefore, the newly developed PMMA-based cement can bond to the living bone and also be effectively used as bioactive bone cement without decrease in mechanical property.

Effects of Polyethylene Glycol and Methacryloxypropyltrimethoxysilane on Morphology and Bioactivity of CaO-SiO2 Gel Prepared by Sol-Gel Method

CaO-SiO2 gels for bioactive organic-inorganic composites were prepared from tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O) by a sol-gel method with the addition of polyethylene glycol (PEG) and methacryloxypropyltrimethoxysilane (MPS). The effects of PEG and MPS on morphology and bioactivity of the gel were investigated. The samples with the nominal compositions of Ca(NO3)2:TEOS:MPS = 30:70:0 and 30:63:7 (in molar ratio) were prepared with or without coexistence of PEG at a molar ratio of (TEOS+MPS):PEG = 70:0.16. Spherical powders were obtained regardless of the addition of MPS after removal of PEG by washing, whereas the samples prepared without PEG gave crack-free bulk bodies. Incorporation of MPS was confirmed form the results of Fourier transform infrared spectroscopy (FT-IR). All the samples, regardless of addition of PEG and MPS, formed apatite on their surfaces in simulated body fluid (SBF), when washing time was 3 h during the preparation. These results show that the bioactive spherical powder of CaO-SiO2 gel modified with MPS can be obtained by the present method. It is expected to induce the increase of the chemical bonding with surrounding organic matrix when it was used as fillers for composite materials.