Preparation of a Near-Infrared Ray Absorption Film from N-Phenylthiocarbamoyl Chitosan Derivative

We recently observed that the decanoylation of N-phenylthiocarbamoyl chitosan (2) with a mixture of decanoic anhydride and pyridine at 60 °C for 24 h afforded N,N-(decanoyl)phenythiocarbamoyl-/2-isothiocynato chitosan decanoate (3b) rather than the expected product N,N-(decanoyl)phenylthiocarbamoyl chitosan decanoate (3a). This result suggested that some of the N,N-(decanoyl)phenylthiocarmbamoyl groups had been converted to isothiocyanate groups during the decanoylation process. The subsequent reaction of compound 3b with aniline gave N,N-(decanoyl)phenylthiocarbamoyl/N-phenylthiocarbamoyl chitosan decanoate (4) in high yield. A solution of compound 4 in CHCl₃ was then added to a solution of copper decanoate (5) in the same solvent, and the resulting mixture was cast onto a glass plate to give a cast film. The film was annealed at 200 °C in an oven to give a greenish film, which showed good near-infrared absorption characteristic in the range of 800–2200 nm.     

In vitro apatite formation on organic–inorganic hybrids in the CaO–SiO<Subscript>2</Subscript>–PO<Subscript>5/2</Subscript>–poly(tetramethylene oxide) system

The osteoconduction potential of artificial materials is usually evaluated in vitro by apatite formation in a simulated body fluid (SBF) proposed by Kokubo and his colleagues. This paper reports the compositional dependence of apatite formation on organic–inorganic hybrids in the CaO–SiO₂–PO_5/2–poly(tetramethylene oxide) system, initiated from tetraethoxysilane (TEOS), triethyl phosphate (OP(OEt)₃), calcium chloride (CaCl₂) and poly(tetramethylene oxide)(PTMO) modified with alkoxysilane. Formation of an apatite layer was observed on the surface of the organic–inorganic hybrids with molar ratios of TEOS/OP(OEt)₃ ranging from 100/0 to 20/80. The rate of apatite formation remarkably decreased when the hybrids were synthesized with TEOS/OP(OEt)₃ ratios of 40/60 or less. Hybrids without TEOS showed no apatite formation in SBF for up to 14 days. Addition of small amounts of OP(OEt)₃ to TEOS in the hybrids led to the high dissolution of calcium and silicate, while addition of large amounts of OP(OEt)₃ decreased the dissolution of calcium and silicate ions and resulted in reduced apatite formation regardless of the dissolution of phosphate ions from the hybrids.     

Effect of silicate incorporation on in vivo responses of α-tricalcium phosphate ceramics

In addition to calcium phosphate-based ceramics, glass-based materials have been utilized as bone substitutes, and silicate in these materials has been suggested to contribute to their ability to stimulate bone repair. In this study, a silicate-containing α-tricalcium phosphate (α-TCP) ceramic was prepared using a wet chemical process. Porous granules composed of silicate-containing α-TCP, for which the starting composition had a molar ratio of 0.05 for Si/(P + Si), and silicate-free α-TCP were prepared and evaluated in vivo. When implanted into bone defects that were created in rat femurs, α-TCP ceramics either with or without silicate were biodegraded, generating a hybrid tissue composed of residual ceramic granules and newly formed bone, which had a tissue architecture similar to physiological trabecular structures, and aided regeneration of the bone defects. Supplementation with silicate significantly promoted osteogenesis and delayed biodegradation of α-TCP. These results suggest that silicate-containing α-TCP is advantageous for initial skeletal fixation and wound regeneration in bone repair.     

Hydroxyapatite formation on porous ceramics of alpha-tricalcium phosphate in a simulated body fluid

Alpha-tricalcium phosphate (α-TCP) ceramic is a bioresorbable material that degrades in bone tissue after implantation, since it exhibits higher solubility than beta-tricalcium phosphate (β-TCP) ceramics. The high solubility of α-TCP in an aqueous solution causes its transformation into hydroxyapatite (HAp) through hydrolysis. While one expects the formation of hydroxyapatite after exposure to an aqueous solution mimicking a body environment, we occasionally find variation in HAp formation in the simulated body fluid (SBF). In the present study, HAp formation resulting from exposure to SBF was investigated for some types of α-TCP ceramics with different porosities and specific surface area. Reduced porosity and large surface area of porous specimens may increase the local density of Ca²⁺ in the surrounding SBF to increase the degree of supersaturation with respect to HAp. Thus, the porosity and specific surface area are significant parameters for determining not only bioabsorbability but also the ability to form HAp.     

Tubular hydroxyapatite formation through a hydrothermal process from α-tricalcium phosphate with anatase

Hydroxyapatite (HA) is a useful substance because of its biocompatibility and adsorption capability. Tubular HA particles are highly attractive as novel tissue scaffolds and as drug carriers because of their hollow structures. We previously found that tubular HA particles were formed when a mixture of α-tricalcium phosphate (α-TCP) and anatase was hydrothermally treated. However, the formation mechanism is still unclear. In this study, we investigated the effect of anatase on the formation of tubular HA particles. The formation of tubular HA particles was enhanced when a pellet of a mixture of α-TCP and anatase was UV-irradiated before hydrothermal treatment. The tubular HA formation was observed only when anatase particles with adequate size were added in adequate quantities. We found that the surface properties, size, and quantity of the anatase particles were important for the formation of tubular HA particles. The tubular HA particles were not formed in the early stages of the reaction, they were formed only after some crystal growth had occurred. The anatase particles controlled the nucleation and crystal growth of HA.     

A composite of hydroxyapatite with electrospun biodegradable nanofibers as a tissue engineering material

Biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as a nanofibrous film by electrospinning and composited with hydroxyapatite (HAp) by soaking in simulated body fluid. Compared with a PHBV cast (flat) film, the electrospun PHBV nanofibrous film was hydrophobic. However, after HAp deposition, both of the surfaces were extremely hydrophilic. The degradation rate of HAp/PHBV nanofibrous films in the presence of polyhydroxybutyrate depolymerase was very fast. Nanofiber formation increased the specific surface area and HAp enhanced the invasion of enzyme into the film by increasing surface hydrophilicity. The surface of the nanofibrous film showed enhanced cell adhesion over that of the flat film, although cell adhesion was not significantly affected by the combination with HAp.     

Behavior of osteoblast-like cells on calcium-deficient hydroxyapatite ceramics composed of particles with different shapes and sizes

In designing the biomaterials, it is important to control their surface morphologies, because they affect the interactions between the materials and cells. We previously reported that porous calcium-deficient hydroxyapatite (HA) ceramics composed of rod-like particles had advantages over sintered porous HA ceramics; however, the effects of the surface morphology of calcium-deficient HA ceramics on cell behavior have remained unclear. Using a hydrothermal process, we successfully prepared porous calcium-deficient HA ceramics with different surface morphologies, composed of plate-like particles of 200–300, 500–800 nm, or 2–3 μm in width and rod-like particles of 1 or 3–5 μm in width, respectively. The effects of these surface morphologies on the behavior of osteoblast-like cells were examined. Although the numbers of cells adhered to the ceramic specimens did not differ significantly among the specimens, the proliferation rates of cells on the ceramics decreased with decreasing particle size. Our results reveal that controlling the surface morphology that is governed by particle shape and size is important for designing porous calcium-deficient HA ceramics.