Fabrication of quantum dot-immobilized Y2O3 microspheres with effective photoluminescence for cancer radioembolization therapy.

Microspheres composed of Y-containing materials are effective agents for cancer radioembolization therapy using ß-rays. The distribution and dynamics of these microspheres in tissues can be easily determined by providing the microspheres with an imaging function. In addition, the use of quantum dots will enable the detection of microspheres at the individual particle level with high sensitivity. In this study, core - shell quantum dots were bound to chemically modified yttria microspheres under various conditions, and the effect of reaction conditions on the photoluminescence properties of the microspheres was investigated. The quantum dots were immobilized on the surfaces of the microspheres through dehydration - condensation reactions between the carboxy groups of quantum dots and the amino groups of silane-treated microspheres. As the reaction time increased, the photoluminescence peak blue shifted, and the photoluminescence intensity and lifetime decreased. Therefore, a moderate period of the immobilization process was optimal for imparting effective photoluminescence properties. This study is expected to facilitate particle-level tracking of microsphere dynamics in biological tissues for the development of minimally invasive cancer radiotherapy of deep-seated tumors.

We have established a method to immobilize quantum dots on yttria microspheres for cancer radiotherapy and revealed that photoluminescence intensity can be optimized by controlling the immobilization treatment time.

Evaluation of a hydroxyapatite-crosslinked fish gelatin membranes.

Background/purpose: Porcine collagen is widely used in regenerative therapies to generate membranes for bone augmentation. However, porcine or bovine gelatin or collagen is often not appropriate for patients with creed and religious beliefs or for allergic reasons. In this study, we evaluated the potential of fish gelatin to generate membranes. Materials and methods: Fish gelatin and hydroxyapatite (HAp) were used at three different ratios (2:0, 2:1, 2:1.5, and 2:2) to prepare gelatin-hydroxyapatite (G-HAp) membranes via freeze-drying and heat-crosslinking. The surface morphology and cell attachment of G-HAp membranes were observed using scanning electron microscopy and confocal laser microscopy. G-HAp membrane was placed at the bottom of a well plate, and MC3T3-E1 cells were seeded on it. Cell viability and cytotoxicity were tested after 1 and 3 days of culture. Alkaline phosphatase (ALP) and alizarin red staining was performed at 10 and 21 days, respectively. Results: Viability of cells on G-HAp membrane with the gelatin:HAp ratio of 2:1.5 was significantly higher than that on membranes with other gelatin:HAp ratios. ALP and alizarin red staining showed that ALP-positive areas and calcium deposition were the highest on G-HAp membrane with the gelatin:HAp ratio of 2:1. These membranes showed negligible cytotoxicity. Conclusion: Fish-derived G-HAp membranes have the potential to promote osteogenic differentiation of MC3T3-E1 cells with negligible cytotoxicity.

Effects of multiple firings on the translucency, crystalline phase, and mechanical strength of highly translucent zirconia.

This study aimed to clarify the effects of multiple firings on the translucency, crystal structure, and mechanical strength of highly translucent zirconia. Four types of highly translucent zirconia (LAVA Esthetic, LAVA Plus, KATANA Zirconia STML, and KATANA Zirconia HTML) were fired three times at three different temperatures, and the translucency, crystal structure, and flexural strength were evaluated before and after firing. The translucency was statistically compared using repeated-measures analysis of variance; the zirconia phase composition was assessed using X-ray diffraction followed by Rietveld analysis; and the biaxial flexural strength was assessed using Weibull analysis. The translucency of LAVA Esthetic and KATANA Zirconia HTML decreased significantly after firing, and the crystal composition of LAVA Plus and KATANA Zirconia HTML changed after multiple firings, whereas multiple firings did not affect the biaxial flexural strength of any samples. Thus, multiple firings may affect the optical properties of highly translucent zirconia.

Antibacterial and osteogenic thin films on Ti-6Al-4V surface formed by passivation process in copper hydroxide solution.

Implant-associated infections are threatening and devastating complications that lead to bone destruction and loss. As a smooth surface is suitable for inhibiting bacterial adhesion, endowing antibacterial activity to the Ti surface without any structural changes in the surface topography is an effective strategy for preventing infection. The thin film on the Ti-6Al-4 V surface was functionalized to endow antibacterial activity by immersion in a Cu(OH)2 solution. The resulting surface maintains the surface topography with a surface roughness of 0.03 µm even after the immersion in the Cu(OH)2 solution. Moreover, Cu was detected at approximately 10 atom% from the surface and was present up to a depth of 30 nm of thin film. In vitro experiments revealed that the resulting surface exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus and allowed the cellular proliferation, differentiation, and calcification of MC3T3-E1 cells. Furthermore, in vivo experiments determined that the presence of Cu in the thin film on the Ti-6Al-4 V surface led to no inflammatory reactions, including bone resorption. Thus, immersion in a Cu(OH)2 solution incorporates and immobilizes Cu into the thin film on the Ti-6Al-4 V surface without any structural alternations in the surface topography, and the resulting smooth surface exhibits antibacterial activity and osteogenic cell compatibility without cytotoxicity or inflammatory reactions. Our findings provide fundamental insights into the surface design of Ti-based medical devices, to achieve bone reconstruction and infection prevention.

Passivation of Ti-6Al-4V in Cu(OH)2 solution endowed smooth thin film with antibacterial activity and osteogenic cell compatibility for potentially achieving both bone reconstruction and infection prevention.

Electrochemical Deposition of Copper on Bioactive Porous Titanium Dioxide Layer: Antibacterial and Pro-Osteogenic Activities.

Ti surfaces must exhibit antibacterial activity without cytotoxicity to promote bone reconstruction and prevent infection simultaneously. In this study, we employed a two-step electrochemical treatment process, namely, microarc oxidation (MAO) and cathodic electrochemical deposition (CED), to modify Ti surfaces. During the MAO step, a porous TiO2 (pTiO2) layer with a surface roughness of approximately 2.0 µm was generated on the Ti surface, and in the CED step, Cu was deposited onto the pTiO2 layer on the Ti surface, forming Cu@pTiO2. Cu@pTiO2 exhibited a similar structure, adhesion strength, and crystal phase to pTiO2. Moreover, X-ray photoelectron spectroscopy (XPS) confirmed the presence of Cu in Cu@pTiO2 at an approximate concentration of 1.0 atom %. Cu@pTiO2 demonstrated a sustained release of Cu ions for a minimum of 28 days in a simulated in vivo environment. In vitro experiments revealed that Cu@pTiO2 effectively eradicated approximately 99% of Staphylococcus aureus and Escherichia coli and inhibited biofilm formation, in contrast to the Ti and pTiO2 surfaces. Moreover, Cu@pTiO2 supported the proliferation of osteoblast-like cells at a rate comparable to that observed on the Ti and pTiO2 surfaces. Similar to pTiO2, Cu@pTiO2 promoted the calcification of osteoblast-like cells compared with Ti. In summary, we successfully conferred antibacterial and pro-osteogenic activities to Ti surfaces without inducing cytotoxic effects or structural and mechanical alterations in pTiO2 through the application of MAO and CED processes. Moreover, we found that the pTiO2 layer promoted bacterial growth and biofilm formation more effectively than the Ti surface, highlighting the potential drawbacks of rough and porous surfaces. Our findings provide fundamental insights into the surface design of Ti-based medical devices for bone reconstruction and infection prevention.

Formation of octacalcium phosphate with incorporated dicarboxylate ions containing disulfide bonds.

Octacalcium phosphate (OCP) is a layered compound capable of incorporating carboxylate ions within its interlayer structure. In this study, we successfully synthesised OCP with incorporated 3,3'-dithiodipropionate ions. Our finding is beneficial for the development of novel OCP-based materials with dynamic properties derived from disulfide bonds.

Development of bioinspired damage-tolerant calcium phosphate bulk materials.

Improving the damage tolerance and reliability of ceramic artificial bone materials, such as sintered bodies of hydroxyapatite (HAp), that remain in vivo for long periods of time is of utmost importance. However, the intrinsic brittleness and low damage tolerance of ceramics make this challenging. This paper reports the synthesis of highly damage tolerant calcium phosphate-based materials with a bioinspired design for novel artificial bones. The heat treatment of isophthalate ion-containing octacalcium phosphate compacts in a nitrogen atmosphere at 1000°C for 24 h produced an HAp/ß-tricalcium phosphate/pyrolytic carbon composite with a brick-and-mortar structure (similar to that of the nacreous layer). This composite exhibited excellent damage tolerance, with no brittle fracture upon nailing, likely attributable to the specific mechanical properties derived from its unique microstructure. Its maximum bending stress, maximum bending strain, Young's modulus, and Vickers hardness were 11.7 MPa, 2.8 × 10‒2, 5.3 GPa, and 11.7 kgf/mm2, respectively. The material exhibited a lower Young's modulus and higher fracture strain than that of HAp-sintered bodies and sintered-body samples prepared from pure octacalcium phosphate compacts. Additionally, the apatite-forming ability of the obtained material was confirmed in vitro, using a simulated body fluid. The proposed bioinspired material design could enable the fabrication of highly damage tolerant artificial bones that remain in vivo for long durations of time.

Proliferation and differentiation of MC3T3-E1 cells on polymethyl methacrylate cements containing Fe3O4 and TiO2 for hyperthermic treatment of metastatic bone tumors.

Polymethyl methacrylate (PMMA) bone cement is widely used to relieve pain caused by metastatic bone tumors. We previously found that PMMA bone cement containing 15 mass% or more of TiO2 showed good apatite-forming ability, and 25 mass% or more of Fe3O4 generated sufficient heat for hyperthermia under an alternating current (AC) magnetic field. In this study, the cytocompatibility of PMMA bone cement with Fe3O4:TiO2 weight ratios of 25:15 (F25T15-3/2-42) and 30:15 (F30T15-3/2-42) was evaluated using osteoblastic cells (MC3T3-E1). The proliferation and differentiation of MC3T3-E1 cells were suppressed for F25T15-3/2-42 and F30T15-3/2-42 compared to PMMA bone cement without Fe3O4 and TiO2 (F0T0-3/2-42). The release of methyl methacrylate (MMA) monomers from F25T15-3/2-42 and F30T15-3/2-42 at 7 days was about 33 and 50 times higher than that from F0T0-3/2-42, respectively. The remarkable release of MMA monomers from F25T15-3/2-42 and F30T15-3/2-42 may be responsible for the suppressed proliferation and differentiation of MC3T3-E1 cells. The release of MMA monomers was not reduced when the MMA/PMMA weight ratio was decreased from 3/2 to 1/1, however, it was significantly reduced by increasing the content of benzoyl peroxide (BPO) and N, N-dimethyl-p-toluidine (DMPT) to 8 and 4 mass% against MMA, respectively. Proliferation and differentiation of MC3T3-E1 cells on PMMA-type cements containing Fe3O4 and TiO2 with increased BPO and DMPT contents need to be investigated in the future; however, our findings will be useful for designing PMMA cements for the hyperthermic treatment of metastatic bone tumors.

Visible-Light-Enhanced Antibacterial Activity of Silver and Copper Co-Doped Titania Formed on Titanium via Chemical and Thermal Treatments.

Dental implants made of titanium (Ti) are used in dentistry, but peri-implantitis is a serious associated problem. Antibacterial and osteoconductive Ti dental implants may decrease the risk of peri-implantitis. In this study, titania (TiO2) co-doped with silver (Ag) at 2.5 at.% and copper (Cu) at 4.9 at.% was formed on Ti substrates via chemical and thermal treatments. The Ag and Cu co-doped TiO2 formed apatite in a simulated body fluid, which suggests osteoconductivity. It also showed antibacterial activity against Escherichia coli, which was enhanced by visible-light irradiation. This enhancement might be caused by the synergistic effect of the release of Ag and Cu and the generation of •OH from the sample. Dental implants with such a Ag and Cu co-doped TiO2 formed on their surface may reduce the risk of peri-implantitis.

Octacalcium phosphate with incorporated carboxylate ions: a review.

Octacalcium phosphate (OCP) belongs to a family of calcium phosphate compounds. OCP has unique crystal-chemical properties; among calcium phosphate compounds, only OCP can incorporate carboxylate ions into its crystal lattice. An OCP with incorporated carboxylate ions is called an OCP carboxylate (OCPC). OCPCs are investigated for applications in novel adsorbents, electrochemical devices, and biomaterials. Several wet methods are available for the synthesis of OCPCs, and the characteristics and advantages of each method are explained. Representative characterization methods, i.e. X-ray diffraction and Fourier transform infrared spectroscopy, used for the detection of carboxylate ion incorporation into the OCP interlayers are explained. Various carboxylic acids can be incorporated into OCP, and these types of carboxylic acid are presented with reference to the latest research results. The incorporation of carboxylate ions into OCP represents a modification of the OCP crystal at the molecular level and can impart various functions. Challenging physicochemical and biomaterial applications of OCPCs are thus introduced, although they are still in the research phase. Finally, future perspectives and challenges for OCPC research are described.

Transformation behaviour of salts composed of calcium ions and phosphate esters with different linear alkyl chain structures in a simulated body fluid modified with alkaline phosphatase.

Ceramic biomaterials have been used for the treatment of bone defects and have stimulated intense research on such materials. We have previously reported that a salt composed of calcium ions and a phosphate ester (SCPE) transformed into hydroxyapatite (HAp) in a simulated body fluid (SBF) modified with alkaline phosphatase (ALP), and proposed SCPEs as a new category of ceramic biomaterials, namely bioresponsive ceramics. However, the factors that affect the transformation of SCPEs to HAp in the SBF remained unclear. Therefore, in this study, we investigated the behaviour of calcium salts of methyl phosphate (CaMeP), ethyl phosphate (CaEtP), butyl phosphate (CaBuP), and dodecyl phosphate (CaDoP) in SBF with and without ALP modification. For the standard SBF, an X-ray diffraction (XRD) analysis indicated that these SCPEs did not readily transform into calcium phosphate. However, CaMeP, CaEtP, and CaBuP were transformed into HAp and octacalcium phosphate in the SBF modified with ALP; therefore, these SCPEs can be categorised as bioresponsive ceramics. Although CaDoP did not exhibit a sufficient response to ALP to be detected by XRD, it is likely to be a bioresponsive ceramic based on the results of morphological observations. The transformation rate for the SCPEs decreased with increasing size of the linear alkyl group of the phosphate esters. The rate-determining steps for the transformation reaction of the SCPEs were changed from the dissolution of the SCPEs to the hydrolysis of the phosphate esters with increasing size of the phosphate ester alkyl groups. These findings contribute to designing novel bioresponsive ceramic biomaterials.

Tailoring mechanical and in vitro biological properties of calcium‒silicate based bioceramic through iron doping in developing future material.

Dense iron-doped akermanite ceramics with 0.3, 0.6 and 0.9 mol% of Fe3+ were synthesized via high-speed planetary ball milling and subsequently subjected to sintering at 1200 and 1250 °C. The aim of the current work was to investigate the effect of trivalent iron (Fe3+) in tuning the physicomechanical and in vitro biological properties of akermanite. The incorporation of Fe3+ into akermanite host and sintering at a high temperature of 1200 °C resulted in a synergistic effect in enhancing the sinterability and densification of akermanite ceramics. Although varying the Fe3+ content, it was found that similar densification and mechanical properties (i.e., diametral tensile strength, Vickers microhardness and fracture toughness) were observed for the doped ceramics at 1250 °C, indicating that this newly developed formulation is temperature-dependent. Fe3+-doped akermanite ceramics revealed greater in vitro bioactivity as compared to undoped akermanite, demonstrated by better coverage of needle-like apatite precipitates after 21 days of immersion in simulated body fluid. Additionally, Rat-1 cells cultured in direct contact with Fe3+-doped akermanite ceramics showed almost double levels of cell proliferation than their undoped counterpart on both 3 and 7 days of culture. Our finding suggests that 0.9Fe-AK ceramic is a suitable formulation to be considered for future bone substitute material as it provides sufficient mechanical strength as well as good bioactivity and the ability to encourage cell proliferation.

Indirect cytotoxicity evaluations of antibacterial raw silk fabric doped with calcium, copper and zinc on fibroblasts and osteoblasts.

Antibacterial materials are widely used to prevent hospital-acquired infections. In our previous report, metal (calcium, copper or zinc)-doped raw silk fabrics were shown to possess strong antibacterial activities against Escherichia coli. However, antibacterial materials may occasionally be harmful to the human body; thus, in this study, we investigated the cytotoxicities of extracts from metal-doped raw silk fabrics with respect to fibroblasts and osteoblasts indirectly. Calcium-doped raw silk fabric demonstrated cytocompatibility with fibroblasts. Contrarily, copper- and zinc-doped raw silk fabrics remarkably decreased the cell densities of fibroblasts, indicating their cytotoxic effects. This observation could be attributed to the high concentrations of the released copper or zinc ions. However, calcium-, copper- and zinc-doped raw silk fabrics did not demonstrate any cytotoxic effects on osteoblasts because a high concentration of the serum alleviated the effects of these metal ions released from the fabrics. Thus, calcium-doped raw silk fabric is a promising antibacterial material that does not induce strong cytotoxicity. This study will facilitate the design of materials that are both antibacterial and safe.

Synthesis of Octacalcium Phosphate Containing Glutarate Ions with a High Incorporation Fraction.

Octacalcium phosphate (OCP) has received considerable attention in the field of ceramic biomaterials as an advanced functional material. It exhibits a layered structure composed of apatitic and hydrated layers and can incorporate various dicarboxylate ions into the hydrated layer. Saturated dicarboxylic acids (HOOC(CH2)nCOOH) with an odd number of methylene groups (-CH2-) exhibit lower incorporation fractions than those with an even number of methylene groups, possibly owing to a compositional dependence on the synthetic method. In this study, calcium carbonate, phosphoric acid, and various amounts of glutaric acid were used to produce glutarate-ion-incorporated OCP by a wet chemical method, which is different from the conventional synthetic strategy. While utilising 1-20 mmol of glutaric acid during synthesis did not produce the desired product, using 25 mmol of glutaric acid resulted in the formation of single-phase glutarate-ion-incorporated OCP with a Ca/P molar ratio of 1.57 and a 90% incorporation fraction of glutarate ions. This glutarate-ion-incorporation fraction is significantly higher than that reported in the previous studies (35%). Thus, the synthetic procedure proposed herein was able to produce single-phase OCP containing glutarate ions with a high incorporation fraction. Our findings can contribute to development of novel functional ceramic biomaterials in the future.

Proteomic identification of serum proteins to induce osteoconductivity of hydroxyapatite.

We performed proteomic analysis of rat serum proteins adsorbed on hydroxyapatite (HAp) and α-alumina (α-Al2O3) in order to identify proteins that specifically adsorb onto HAp and control cellular responses. Proteins with either or both molecular weight of 22-32 kDa and computed isoelectric point of 5.0-5.5 were preferentially adsorbed on HAp. In total, 182 proteins were adsorbed on both HAp and α-Al2O3, of which 14 were highly enriched on HAp, whereas 68 were adsorbed only on HAp. Therefore, 82 (14+68) proteins were further evaluated by bioinformatics and literature-based analyses. We predicted that hepatocyte growth factor and angiopoietin-like protein 3 (ANGPTL3) are candidate proteins responsible for the osteoconductivity of HAp. Although ANGPTL3 promoted the attachment and spreading of MC3T3-E1 cells, it did not promote their proliferation and differentiation. Our results suggest that specific adsorption of ANGPTL3 on HAp induced osteoconductivity by enhancing the attachment and spreading of osteoblasts.

Understanding the Steric Structures of Dicarboxylate Ions Incorporated in Octacalcium Phosphate Crystals.

Octacalcium phosphate (OCP) can incorporate various dicarboxylate ions in the interlayer spaces of its layered structure. Although not proven, these incorporated ions are believed to have a linear structure. In this study, the steric structures of twelve different dicarboxylate ions incorporated into OCP were investigated by comparing the experimentally determined interlayer distance of the OCP with the distance estimated using the molecular sizes of dicarboxylic acids calculated by considering their steric structures. The results revealed that the incorporated succinate, glutarate, adipate, pimelate, suberate, and aspartate ions possessed linear structures, whereas the incorporated azelate, sebacate, methylsuccinate, and malate ions exhibited bent structures. Further, the incorporated mercaptosuccinate ions featured linear, bent, other types of structures. Moreover, the steric structure of the incorporated malonate ion significantly differed from those of other dicarboxylate ions. The computational approach employed in this study is expected to deepen our understanding of the steric structures of dicarboxylate ions incorporated in the OCP interlayer spaces.

Cytotoxicity evaluation of iron nitride nanoparticles for biomedical applications.

Magnetic nanoparticles are widely studied for their use in various therapeutic and diagnostic purposes. As biomaterials, their biocompatibility is as important as their magnetic properties. Iron nitride (Fex Ny ) has excellent magnetic properties, and thus Fex Ny nanoparticles could be useful as potential biomaterials. However, the biocompatibility of Fex Ny nanoparticles is yet to be investigated. In this study, we assessed the biocompatibility of Fex Ny nanoparticles by evaluating their direct-contact cytotoxicity compared with that of magnetite nanoparticles (MNPs). Rat fibroblasts were incubated with the nanoparticle samples dispersed in culture medium at concentrations of 10, 50, and 100 µg/ml. The DNA concentration measurement, MTT assay, and trypan blue exclusion test were conducted after days 1 and 3 of incubation. After day 1, the cell viability decreased, and cell death increased with increasing sample concentration when compared with the control. However, after day 3, there were no significant differences when compared with the control, irrespective of the sample concentrations. Further, there were no significant differences between the Fex Ny nanoparticles and MNPs at the same concentrations in all the cytotoxicity evaluation tests. Therefore, it is suggested that Fex Ny nanoparticles might be as cytocompatible as the conventional MNPs.

Time Transient of Calcium and Phosphate Ion Adsorption by Rutile Crystal Facets in Hanks' Solution Characterized by XPS.

For the elucidation of the mechanism of calcium phosphate formation on commercially pure titanium (CP Ti) in the human body, rutile TiO2 single crystal plates with (001), (110), and (111) facets, namely, TiO2(001), TiO2(110), and TiO2(111), and polycrystalline plates (TiO2(poly)) were immersed in a simulated body fluid, Hanks' solution (Hanks), for 100-105 s, and the adsorption of calcium and phosphate ions was precisely characterized employing X-ray photoelectron spectroscopy (XPS). Previously published CP Ti data were used for comparison. Prior to immersion in Hanks, oxygen content was more than twice as high as that of titanium due to the existence of hydroxyl groups and water on the oxides. After immersion in Hanks, the composition and chemical state of the TiO2 substrates remained unchanged. Among the electrolytes contained in Hanks, only calcium and phosphate ions were adsorbed by and incorporated onto TiO2 surfaces. Adsorption of calcium ions onto rutile did not exhibit any systematic increase of calcium with immersion time except TiO2(poly). Adsorption of phosphate ions was initially constant, followed by an increase with the logarithm of immersion time. The adsorption rate of phosphate ions decreased in the following order: TiO2(001), TiO2(poly), TiO2(111), CP Ti, and TiO2(110). The coordination number and band gap of each crystal facet of rutile is important for the adsorption and incorporation of phosphate ions. Regular calcium phosphate formation on CP Ti is possibly enabled by the surface oxide film, which consists chiefly of amorphous TiO2. However, calcium phosphate formation kinetics on CP Ti differed from those on the TiO2 crystalline phase. These findings may further the understanding of CP Ti hard tissue compatibility.

Incorporation of tetracarboxylate ions into octacalcium phosphate for the development of next-generation biofriendly materials.

Octacalcium phosphate (OCP; Ca8(HPO4)2(PO4)4 ∙ 5H2O) is a precursor of hydroxyapatite found in human bones and teeth, and is among the inorganic substances critical for hard tissue formation and regeneration in the human body. OCP has a layered structure and can incorporate carboxylate ions into its interlayers. However, studies involving the incorporation of tetracarboxylic and multivalent (pentavalent and above) carboxylic acids into OCP have not yet been reported. In this study, we investigate the incorporation of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), a type of tetracarboxylic acid, into OCP. We established that pyromellitate ions could be incorporated into OCP by a wet chemical method using an acetate buffer solution containing pyromellitic acid. The derived OCP showed a brilliant blue emission under UV light owing to the incorporated pyromellitate ions. Incorporation of a carboxylic acid into OCP imparted new functions, which could enable the development of novel functional materials for biomedical applications.

Apatite formation and bacterial growth on raw silk fabric heated in argon gas.

Raw silk has the potential to be a flexible, osteoconductive material because it forms bone-like apatite on its surface in acellular simulated body fluid with ion concentrations nearly 1.5 times greater than that of human plasma (1.5SBF). It has been reported that silk-which has many similarities to raw silk-develops antibacterial properties when heated in inert gas, which may be advantageous in preventing bacterial infection. Hence, raw silk heated in inert gas may be a flexible, osteoconductive material with antibacterial activity. Thus, we examined the effect of the heat treatment of raw silk fabric on its apatite-forming ability in 1.5SBF and on the growth of Escherichia coli. Raw silk fabric was heated in argon gas at several temperatures, to a maximum of 500 °C. The results of soaking tests in 1.5SBF indicate that the apatite-forming ability of raw silk decreases with increasing temperature. This may be because favourable structures for apatite formation, such as carboxyl groups, are thermally decomposed. The results of bacterial tests indicate that raw silk fabrics heated to 300 °C or 500 °C exhibit reduced bacterial growth compared to those that were not heated or were heated only to 100 °C. This might be because hydrophobic surfaces inhibit bacterial adhesion, or because the thermal decomposition of sericin-a component of raw silk-leads to a lack of available nutrients for the bacteria. Although this study did not demonstrate the expected material properties needed for clinical applications, this research contributes to a better understanding of silk biomaterials.