A novel hydroxyapatite fiber material for the regeneration of critical-sized rabbit calvaria defects.

Hydroxyapatite (HA) [Ca10 (PO4)6 (OH)2] has a high degree of chemical similarity with the mineral composition of animal bone. Hydroxyapatite fiber scaffold (HAF) is a biological material with a highly interconnected porous structure. We aimed to study the physical and biological characteristics of HAF and compare the osteogenic effects of HAF, natural osteogenic materials (NOM), and carbonate apatite (CO3Ap-DP) in the parietal defects of a rabbit's skull. X-ray analysis and histological assessment showed that HAF followed a trend of early initial osteogenesis and bone trabecular structure formation, especially at the cortical bone portion.Compared to the other two materials, HAF was more absorptive. Results indicated that HAF had the same osteoconductive and new bone formation properties as NOM and CO3Ap-DP. These findings will provide options for future material development and novel protocols for use in surgeries, ultimately leading to better patient outcomes.

Fabrication of Gentamicin-Loaded Hydroxyapatite/Collagen Bone-Like Nanocomposite for Anti-Infection Bone Void Fillers.

A gentamicin-loaded hydroxyapatite/collagen bone-like nanocomposite (GNT-HAp/Col) was fabricated and evaluated for its absorption-desorption properties, antibacterial efficacy, and cytotoxicity. The hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) powder was mixed with gentamicin sulfate (GNT) in phosphate-buffered saline (PBS) at room temperature. After 6 h mixing, the GNT adsorption in all conditions reached plateau by Langmuir's isotherm, and maximum GNT adsorption amount was 34 ± 7 µg in 250 µg/mL GNT solution. Saturated GNT-loaded HAp/Col powder of 100 mg was soaked in 10 mL of PBS at 37 °C and released all GNT in 3 days. A shaking culture method for a GNT extraction from the GNT-HAp/Col and an inhibition zone assay for the GNT-HAp/Col compact showed antibacterial efficacy to Escherichia coli (E. coli) at least for 2 days. From the release profile of the GNT from the GNT-HAp/Col powder, antibacterial efficacy would affect E. coli at least for 3 days. Further, no cytotoxicities were observed on MG-63 cells. Thus, the GNT-HAp/Col is a good candidate of bioresorbable anti-infection bone void fillers by prevention initial infections, which is the primary cause of implant-associated infection even for rapid bioresorbable materials.

Thermal denaturation behavior of collagen fibrils in wet and dry environment.

We have developed a new minimally invasive technique--integrated low-level energy adhesion technique (ILEAT)--which uses heat, pressure, and low-frequency vibrations for binding living tissues. Because the adhesion mechanism of the living tissues is not fully understood, we investigated the effect of thermal energy on the collagen structure in living tissues using ILEAT. To study the effect of thermal energy and heating time on the structure of the collagen fibril, samples were divided in two categories-wet and dry. Further, atomic force microscopy was used to analyze the collagen fibril structure before and after heating. Results showed that collagen fibrils in water denatured after 1 minute at temperatures higher than 80 °C, while partial denaturation was observed at temperatures of 80 °C and a heating time of 1 min. Furthermore, complete denaturation was achieved after 90 min, suggesting that the denaturation rate is temperature and time dependent. Moreover, the collagen fibrils in dry condition maintained their native structure even after being heated to 120 °C for 90 min in the absence of water, which specifically suppressed denaturation. However, partial denaturation of collagen fibrils could not be prevented, because this determines the adhesion between the collagen molecules, and stabilizes tissue bonding.

Effect of metal surface characteristics on the adhesion performance of the integrated low-level energies method of adhesion.

We have previously proposed a new method of adhesion using the integrated low-level energy sources heat, vibration, and pressure. This adhesion method can be used to attach biological tissue to a metal object. Effects of surface roughness and energy of the metal subject on adhesion performance were studied by using commercially pure titanium (cpTi) and stainless steel (SUS304). Surface roughness and energy were changed by sandblast treatment and heat treatment, respectively. A porcine aorta was adhered to sandblast-treated SUS304 by use of an adhesion temperature of 80 °C, a vibration amplitude of 15 µm, a pressure of 2.5 MPa, an adhesion time of 120 s, and a surface roughness of an Ra 0.25 µm. The shear tensile strength of the adhesion was 0.45 MPa. The adhesion performance was improved by roughening the surface of the metal specimen. Surface energy has an insignificant effect on adhesive strength. The adhesion performance varied depending on metal material for the same surface roughness, Ra, and energy. Results from analysis of the surface roughness profile suggested that the size of surface asperity has an effect on adhesion performance.

Development of tissue adhesion method using integrated low-level energies.

We have developed a method that allows biological tissues to be adhered together with minimal invasion by delivering integrated low-level energies from heat, pressure, and vibration. Tensile tests on adhered slices of porcine aorta were performed to determine the relationships between adhesive strength and conditions such as adhesion temperature, time, pressure, and vibration. The maximal adhesive shear tensile strength using the proposed method was 0.2MPa, which is half the strength of the porcine aorta and stronger than surgical tissue adhesive. Adhesion strength increased in proportion to temperature, time, and pressure, and also in the presence of vibration, indicating that vibrational energy contributes to the adhesive mechanism and strength. Adhesive stability, the effect of heat on adhesive strength, and the ability of tissue to adhere to artificial materials were also clarified.

Dissolution effect and cytotoxicity of diamond-like carbon coatings on orthodontic archwires.

Nickel-titanium (NiTi) has been used for implants in orthodontics due to the unique properties such as shape memory effect and superelasticity. However, NiTi alloys are eroded in the oral cavity because they are immersed by saliva with enzymolysis. Their reactions lead corrosion and nickel release into the body. The higher concentrations of Ni release may generate harmful reactions. Ni release causes allergenic, toxic and carcinogenic reactions. It is well known that diamond-like carbon (DLC) films have excellent properties, such as extreme hardness, low friction coefficients, high wear resistance. In addition, DLC film has many other superior properties as a protective coating for biomedical applications such as biocompatibility and chemical inertness. Therefore, DLC film has received enormous attention as a biocompatible coating. In this study, DLC film coated NiTi orthodontic archwires to protect Ni release into the oral cavity. Each wire was immersed in physiological saline at the temperature 37 degrees C for 6 months. The release concentration of Ni ions was detected using microwave induced plasma mass spectrometry (MIP-MS) with the resolution of ppb level. The toxic effect of Ni release was studied the cell growth using squamous carcinoma cells. These cells were seeded in 24 well culture plates and materials were immersed in each well directly. The concentration of Ni ions in the solutions had been reduced one-sixth by DLC films when compared with non-coated wire. This study indicated that DLC films have the protective effect of the diffusion and the non-cytotoxicity in corrosive environment.

Preparation of a hydroxyapatite and hydrogen peroxide composite for tooth whitening.

Hydroxyapatite (HA)/Hydrogen Peroxide (H(2)O(2)) solutions was prepared for a tooth whitening application. HA powder was immersed in the 100, 1000 and 10,000 ppm of the H(2)O(2) solutions. The HA/H(2)O(2), HA and H(2)O(2) solutions were applied to HA discs and extracted teeth for weight and whiteness change evaluation. After 24 hours, each HA disc was measured for the weight changes and each tooth was measured for the whitening changes (L(*)) using a Spectro Color Meter. The topology of the teeth surfaces were also observed using Scanning Electron Microscope (SEM). The weight of the HA disc applied with H(2)O(2) at all concentrations was lower than that applied with HA and HA/H(2)O(2) solutions. The whiteness of the teeth treated with HA/H(2)O(2) were higher than that treated with HA and H(2)O(2) only solutions. The whiteness change of the teeth treated with the HA/H(2)O(2) (10,000 ppm) showed the highest value in all solutions at L(*)=4.98+/-0.90 (p<0.05). In the SEM observation, the teeth surface treated with the H(2)O(2) showed rough and destructive holes on the enamel surface. However, the teeth surface treated with the HA/H(2)O(2) show smooth enamel surface due to covering of the destructive holes with HA powder.

A functionally graded titanium/hydroxyapatite film obtained by sputtering.

A functionally graded film of titanium/hydroxyapatite (HA) was prepared on a titanium substrate using a radio frequency magnetron sputtering. The ratio of titanium to HA was controlled by moving the target shutter. The film was composed of five layers, with overall film thickness of 1 microm. The HA was concentrated close to the surface, while the titanium concentration increased with proximity to the substrate. The bonding strength between the film and the substrate was 15.2 MPa in a pull-out test and the critical load from a scratch test was 58.85 mN. The corresponding values of a pure HA sputtered film were 8.0 MPa and 38.47 mN, respectively. The bonding strength of a pure HA plasma spray coating was 10.4 MPa in the pull-out test. The graded film and the pure HA film were sputter-coated to a thickness of 1 microm on titanium columns (10 mm in length and 4 mm in diameter). These columns were implanted in diaphyses of the femora of six adult dogs and a push-out test was carried out after 2, 4, and 12 weeks. After 12 weeks, the push-out strengths of the graded film, the pure HA film and the non-coated columns were 3.7, 3.5, and 1.0 MPa.