Shoji Takeda

Mold fabrication and biological assessment of porous DNA–chitosan complexes

A previous study revealed that DNA-chitosan complex prepared from the reaction between native DNA and chitosan in aqueous solution has suitable porosity for cell seeding, is nontoxic, and causes only a mild soft-tissue response. This simple and easy fabrication method for porous DNA-chitosan complex provides for a wide variety of applications as a scaffold material. The present study evaluated whether rinsing with PBS solution can fabricate DNA-chitosan complex in a mold and the histopathological responses of rat soft tissues to fabricated DNA-chitosan complexes. DNA-chitosan complex paste was prepared by mixing distilled water and freeze-dried water-rinsed DNA-chitosan complex powder. A DNA-chitosan complex disk could be fabricated by rinsing with PBS buffer and subsequently freeze-drying the DNA-chitosan complex paste in the mold. Thus, a wide range of applications of DNA-chitosan complex for tissue engineering can be anticipated using the present easy fabrication method. The porosity of the disk was 85%, and many pores were visible in the DNA-chitosan complex (before fabrication) and in the fabricated DNA-chitosan disk. The values of the complex disks gradually reduced in the tissues although 60% of disks remained in the tissues. In conclusion, an easy fabrication method for making porous DNA-chitosan complex disks was developed. It was found that the fabrication method can delay the biodegradation of the DNA-chitosan complex disk without serious tissue responses in vivo. DNA-chitosan complex is promising as a scaffold material, and a wide range of applications of DNA-chitosan complex for tissue engineering are anticipated.

A novel strategy for preparing nanoporous biphasic calcium phosphate of controlled composition via a modified nanoparticle-assembly method.

Biphasic calcium phosphate (BCP) consisting of hydroxyapatite (HAp) and β-tricalcium phosphate is usually prepared by thermal decomposition of calcium-deficient HAp (CDHAp). However, the calcium deficiency and morphology of CDHAp are difficult to manipulate in parallel. In this study, we report a novel strategy for controlling the composition of nanoporous BCP by using only CDHAp nanoparticles with specific properties (Ca/P molar ratio, 1.61; particle size, 50 nm) as a building block and by adjusting the calcium deficiency of the nanoparticle-assembled CDHAp (Ca/P molar ratio, 1.50-1.67; pore size, 8 nm) with the addition of water-soluble Ca(NO3)2 or (NH4)2HPO4. After thermal treatment at 1000 °C, the composition of BCP could be predictably controlled by adjusting the Ca/P ratio of the nanoparticle-assembled CDHAp. Changes in the Ca/P ratio did not significantly affect the surface morphology of BCP, but the grain size (210-300 nm) and pore size (140-170 nm) tended to increase slightly as the Ca/P ratio decreased. The porosity significantly decreased upon the addition of Ca salts (porosity, 20%) or PO4 salts (porosity, 14%) compared with that of the sample without additives (porosity, 53%). In vitro tests demonstrated enhanced cell adhesion on nanoporous BCP compared with densely sintered pure HAp, and cell differentiation was promoted on the nanoporous pure HAp.

Fabrication of dispersible calcium phosphate nanocrystals via a modified Pechini method under non-stoichiometric conditions

Various techniques for preparing ceramic nanoparticles have been developed; however, most of them start from a preparation of precursor nanoparticles that are generally amorphous or in poorly crystallized phases. Thermal treatments used to obtain crystalline phases typically result in the sintering of the products into large polycrystals. In this study, we developed a process to fabricate dispersible hydroxyapatite (HAp; Ca10(PO4)6(OH)2) nanocrystals via a modified Pechini method, which is a sol-gel like solid-state synthesis method for the preparation of multicomponent oxides. We demonstrated that the HAp nanocrystals sintered into large polycrystals ranging in size from several tens to several hundreds of microns via a conventional Pechini method using the stoichiometric Ca/P molar ratio of 1.67. When the Ca/P molar ratio in the precursor was >1.67, a mixture of HAp nanocrystals and removable CaO matrix was obtained. The HAp nanocrystals were dispersed in aqueous media mostly in the form of nanoparticles when the amount of CaO matrix was sufficiently greater than the amount of HAp.

Expansion of nanosized pores in low-crystallinity nanoparticle-assembled plates via a thermally induced increase in solid-state density

We investigated thermally induced changes in a low-crystallinity hydroxyapatite (HAp)-nanoparticle-assembled plate containing nanosized pores. We first prepared an aqueous dispersion of low-crystallinity HAp nanoparticles (particle size, 48 nm) via a wet chemical process and then prepared the nanoparticle-assembled plate by drying the dispersion on an oil substrate to prevent crack formation. Before the plates were subjected to heat treatments, they contained 7.9-nm-sized pores because of the gap between the nanoparticles, and their porosity was 60%. After the heat treatments (600-1100 °C) were performed for 1 h, the solid-state density determined using helium pycnometry increased from 2.85 to 3.21 g/cm(3), and the pore size increased from 7.9 to 250 nm. These results indicate that the pore size expanded because of increases in crystallinity and density, despite the large decrease in the total volume because of thermally induced sintering of the nanoparticles.

A Novel Approach to Prepare Hydroxyapatite-Coated Biodegradable Polymer Microspheres Loaded with Magnetic Fe3O4 via Nanoparticle-Stabilized Emulsions

HAp-nanoparticle-coated biodegradable polymer microspheres loaded with magnetic Fe3O4 particles can be successfully prepared by evaporating volatile oil (dichloromethane) from HAp-nanoparticle-stabilized oil droplets containing biodegradable polymer and Fe3O4 particles without any molecular surfactants or polymeric stabilizers. In this study it was found that the hydrophobic surface modification for the Fe3O4 particles was a key factor to prepare stable HAp-nanoparticle-stabilized oil droplets (and HAp-nanoparticle-coated polymer microspheres) loaded with magnetic Fe3O4 particles.

Ambiguous Transition from Fretting to Sliding of Biomedical Alloys

An intensive amplitude arrangement for reciprocal tribocontact of biomedical alloys, Ag-20.0Pd-14.5Cu-12.0Au, Au-5.0Pt-2.0Pd-9.2Ag-15.0Cu and Ti-29Nb-13Ta-4.6Zr was conducted in order to check the details of friction and wear alterations around the transition from fretting to sliding. It is shown that the friction force exhibits stagnation for the Ag alloy and decrease for the Au alloy and the Ti alloy in certain domain of oscillating amplitude. Beyond the domain the friction force increases with the amplitude, and below the lower threshold and above the upper threshold triboevent is complete fretting and sliding respectively. Observation of friction-force waveform and SEM topography found, a hybrid mechanism of fretting and sliding is dominant in the amplitude domain, and the strong adhesion between the self-mated alloys is responsible to this exhibition.