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ABSTRACT To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly- N, N-dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1017-1027 [ABSTRACT FROM AUTHOR]

Novel biodegradable β-tricalcium phosphate (β-TCP) cements with anti-washout properties were created on the basis of chelate-setting mechanism of inositol phosphate (IP6) using β-TCP powders. The β-TCP powders were ball-milled using ZrO beads for 0-6 h in the IP6 solutions with concentrations from 0 to 10,000 ppm. The chelate-setting β-TCP cement with anti-washout property was successfully fabricated by mixing the β-TCP powder ball-milled in 3,000 ppm IP6 solution for 3 h and 2.5 mass% NaHPO solution, and compressive strength of the cement was 13.4 ± 0.8 MPa. An in vivo study revealed that the above cement was directly in contact with host and newly formed bones without fibrous tissue layers, and was resorbed by osteoclast-like cells on the surface of the cement. The chelate-setting β-TCP cement with anti-washout property is promising for application as a novel injectable artificial bone with both biodegradability and osteoconductivity. [ABSTRACT FROM AUTHOR]

Abstract: In vertebrate bones and tooth enamel surfaces, the respective a,b-planes and c-planes of hydroxyapatite (HAp) crystals are preferentially exposed. However, the reason why the HAp crystals show different orientations depending on the type of hard tissues is not yet understood. To clarify this question, appropriate ceramic models with highly preferred orientation are necessary. In the present study, dense HAp ceramic models which have the same orientation as living bones were fabricated using composite powders of c-axis-oriented single-crystal apatite fibers (AF) and wet-synthesized apatite gels (AG). The results of crystalline identification and ultrastructural observation showed that the resulting HAp ceramics maintained the c-axis orientation of the AF particles, and their high a,b-plane orientation degrees could be maintained with small additive amounts of AG; however, when the AG content was over 30 mass%, this value decreased. The influence of orientation degree on the surface characteristics was investigated by evaluating the surface zeta-potential and wettability. These results show that increasing the a,b-plane orientation degree shifted the surface charge from negative to positive, and decreased the surface wettability. Initial cell-attachment assays were performed on these resulting ceramics using MC3T3-E1 cells as models of osteoblasts. The results show that the cell-attachment efficiency decreased with increasing a,b-plane orientation degree. [Copyright &y& Elsevier]

Adsorption of bovine serum albumin (BSA) and lysozyme (LSZ) proteins with preferred orientation to a( b)- and c-axes of single-crystal hydroxyapatite (HAp) particles, was investigated. Fiber-like HAp single crystal particles ( aHAp) and plate-like HAp single crystal particles ( cHAp) were used as models for a( b)-plane and c-plane oriented HAps, respectively, together with randomly shaped HAp particles (iHAp) as a control. The selective adsorption behaviors of negatively charged BSA and positively charged LSZ on these HAp particles were examined in a phosphate buffered saline at pH 7.3 and 25 °C for 48 h. The amount of BSA adsorption, normalized for specific surface area, was in the order of aHAp > iHAp > cHAp; however, the order for LSZ was reversed as cHAp > iHAp ≒ aHAp. These results indicate that the a( b)- and c-planes of HAp crystal have high specificity for the adsorption of acidic or basic proteins. [ABSTRACT FROM AUTHOR]

The hydroxyapatite (HAp) powder preparation process was optimized to fabricate inositol phosphate-HAp (IP6-HAp) cement with enhanced mechanical properties. Starting HAp powders were synthesized via a wet chemical process. The effect of the powder preparation process on the morphology, crystallinity, median particle size, and specific surface area (SSA) of the cement powders was examined, together with the mechanical properties of the resulting cement specimens. The smallest crystallite and median particle sizes, and the highest SSA were obtained from ball-milling of as-synthesized HAp powder under wet conditions and then freeze-drying. IP6-HAp cement fabricated with this powder had a maximum compressive strength of 23.1 ± 2.1 MPa. In vivo histological studies using rabbit models revealed that the IP6-HAp cements were directly in contact with newly formed and host bones. Thus, the present chelate-setting HAp cement is promising for application as a novel paste-like artificial bone. [ABSTRACT FROM AUTHOR]

The influence of silicon-substituted hydroxyapatite (Si-HAp) on osteogenic differentiation was assessed by biological analysis. Si-HAp was prepared by ultrasonic spray pyrolysis (USSP) technique using various amounts of Si (0, 0.8, and 1.6 mass%). Chemical analysis revealed that Si was incorporated into the hydroxyapatite (HAp) lattice with no other crystalline phase and which caused the change of crystal structure. Biological analyses showed that the Si contents affected the cell proliferation and morphology, suggesting that there is an optimal Si content for cell culture. As for differentiation, alkaline phosphatase activity and osteocalcin production of Si-HAp were higher than those of HAp. Gene expression profiles also revealed that substitution of Si (0.8 mass%) up-regulated the expression levels of osteocalcin and especially Runx2, a master gene for osteoblast development. These results suggest that incorporating Si into the HAp lattice may enhance the bioactivity, particularly during early osteoblast development. [ABSTRACT FROM AUTHOR]

Abstract: The effect of concentration of sodium inositol hexaphosphate (IP6-Na) on material properties of calcium-phosphate cement (CPC) was investigated. The starting cement powder (IP6-HAp) was prepared by grinding and surface modifying hydroxyapatite (HAp) powder in various concentrations of IP6-Na solution. To prepare the IP6-HAp cement paste, the IP6-HAp powder was mixed with water under various powder/liquid ratios (P/L= [g/mL]). Amount of IP6 adsorbed on the surface of HAp powders increased with an increment of IP6-Na concentration, leading to negative surface charge. Dispersion of IP6-HAp powders was improved with an increase of IP6-Na concentration. As for cement fabrication, the IP6-HAp powder with negative charge enabled putty-like cement paste to be prepared at the higher P/L ratio. The compressive strength fabricated from IP6-HAp powders with negative surface charge at -20mV or lower was higher than that fabricated from IP6-HAp powders with negative surface charge at -10mV or higher. This improvement of the CS may be due to the increase of packing density. [Copyright &y& Elsevier]