Key Engineering Materials Vols. 336-338

Abstract: The metabolism of biocomponents and microorganisms is widely used for the production of medical products as well as for biotechnological processes. The productivity of the related reactions can be improved by the immobilization of the living species in granules or in a gel matrix. Since these structures can suffer during operation due to their weakness a new type of porous ceramic composites was developed where the biological phase is immobilized in a rigid inorganic matrix of high permeability for fluids. During the so-called freeze gelation process (FGP) both, a highly efficient immobilization of the biocomponents and an ideal permeability is achieved. A high versatility is then offered due to the particular advantages of the freezing step necessary for the sol-gel transition and the preservation of embedded microorganisms. While the freezing conditions are decisive for the resulting porosity of the biocer, they are also crucial for the survival rate of the embedded biocomponents. The porosity can be adjusted over a wide range by controlling the composition and the freezing conditions. By the directional ice crystal growth large pore channels can be achieved inside the biocers. Thus, the embedded biocomponents are easily accessible by external reagents and biochemical reactions can proceed with a high rate. Furthermore, cell division is conceivable inside the biocers by safe immobilization at the same time. These biocers allow a wide field of applications depending on the class of immobilized biospecies. Biocatalysis with enzymes can also be applied as bioaccumulation and absorption/desorption of metal ions for separation processes of contaminated water or highly selective filters for metallic complexes in solution.

Abstract: Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and betatricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios was prepared. One kinds of HAp and one kind of β-TCP powders were used to produce porous BCP bioceramics with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20. A slip was obtained by adding a mixed powders of HAp and β-TCP to a solution 1.5% of deflocculant and 0.5 wt% of foaming agent. The optimum value for the minimum viscosity in these present slips with respect to its solid loading and the optimum amount of the deflocculant were investigated. The specimen obtained by casting a polyurethane foam with 1.5 wt% of deflocculant into a slip, and drying it under vacuum, was heated at 1150°C for 3 hours. The resultant porous BCP sintered body had large spherical pores of 300 /m with interconnecting rectangular voids. Many small pores in the size range of 2-3 /m or below were observed in the specimen obtained by heating at 1150°C for 3 hours. The dissolution test was done as follows. The obtained porous ceramics samples about 0.5g individually soaked into 30 mL of simulated body fluid (SBF) solution at 36.5°C. The calcium and phosphorous content of the SBF solution was analyzed by ICP. The porous body was dried, and characterized using SEM, XRD, and FT-IR.

Abstract: Bioactive composite of apatite-wollastonite(AW)/β-tricalcium phosphate (β-TCP) was prepared. The nucleation and growth of bio-apatite on the surface of AW/β-TCP ceramic in simulated body fluid (SBF) were investigated. The surface morphological structure, phase compositions and microstructure of the materials were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD) and infrared spectroscopy (IR); Results show that the surfaces of the AW/β-TCP composite ceramic are covered with a layer of carbonate hydroxyapatite (HCA) when soaked in SBF, which indicates their bioactivity; Such HCA layer is composed of fine ball-like HA granules. With excellent bioactivity and bio-absorption, AW/β-TCP bioactive composite ceramic is expected to be a good candidate for bone substitutes and bone tissue engineering scaffolds.

Abstract: 20wt% bioactive glass was added to the pure titanium power by means of subsonic flame spraying. Soak test in vitro was performed with the sprayed samples after heat treatment, and the polarization curve was determined. The result shows that pH of the solution varied during the 60 h immersion of the coating in the simulated body fluid. This related to the fact that TiO2.CaTi4O9.NaTiO2 etc were dissolved and precipitated in the coating. With different immersion time, the coating weight increased first, and then decreased. The self-corrosion potential and morphology of the coating were influenced by different polarization corrosion rate. When the polarization corrosion rate was low, it contributed to the growth of bone-like apatite, and then the corrosion was restrained. In simulated body fluid, absorption, dissolution, and the formation and growth of new phases took place in the coating. Bone-like apatite may form on the coating surface, which indicates the excellent biocompatibility of 8Ti2G bio-composite coating.

Abstract: A polyelectrolyte complex (PEC) composed of chitosan (CS) and phosphorylated chitosan (PCS) was used to encapsulate a calcium phosphate by a biomimetic method. An acidic CS (polycation) solution containing calcium and phosphate ions (Ca2+: 6mM, Ca/P = 1.67) was added into PCS (polyanion) solution leading to the formation of a polyelectrolyte complex (PEC) with nanoscopic carbonate-containing, low-crystallinity hydroxyapatite (HA) distributed evenly in the fibrils of the PEC by controlled crystal growth. The resulting composite material, PEC-HA, has a complicated, hierarchical porous structure that is expected to have high bio-compatibity and that may be of use as a carrier for controlled-release therapetic agents.

Abstract: A three-dimensional biomimetic electrospun scaffold was prepared from a nanohydroxyapatite/ polymer blend in the present study. Viscosity of n-HA/PEA compound solution determined by PEA concentration and additives of n-HA was investigated while other parameters were fixed in the electrospinning process. The fiber diameter increased with the increasing viscosity of solution. 20wt% n-HA in the composite ultrafine fibrous scaffold was proved to be a preferable ratio. The n-HA/PEA scaffold was characterized by XRD, SEM and EDX. The fibrous electrospun scaffold, which is made up of ultrafine fibers with average diameter 400±50 nm and well-interconnected pores, was characterized with high surface–to-volume ratio, which is conducive to cell and tissue growth. A comparatively uniform distribution of n-HA crystals in a single fiber even in the whole scaffold was confirmed by EDX. The biocompatibility of the composite was investigated by culturing osteobalsts on the scaffold. Good cell adhesion and proliferation manner was observed on the fibrous scaffold by SEM and MTT assay. It could be expected that the electrospun HA/PEA composite scaffold would be a potential biomimetic extracellular matrix biomaterial for bone tissue engineering.

Abstract: To study the biomimetic mineralization behaviour of piezoelectric pulp-cap films, bioelectret chitosan films were prepared by polarization in an electric field and soaked in PBS with lysozyme for piezoelectricity attenuation testing. The results showed that comparing these with samples stored in an exsiccator, the films soaked in PBS had accelerated d33 loss. Calcium phosphate crystals nucleated and grew on the surfaces of samples soaked in supersaturated calcification solution at 37
for 1, 6, 12 and 24 h. OCP and HA were found to co-precipitate on the surfaces within 24 h of immersion. This novel piezoelectric inorganic-organic pulp-cap has the potential to be applied in dental pulp capping.

Abstract: This study is to investigate the method of pamidronate modifying HA bioceramics and the effect of pamidronate modifying HA bioceramics on the osteoblastic cells. Pamidronate was immobilized on the surface of porous HA bioceramics for bone scaffold by chelating. The outermost layer of the specimens was analyzed by XPS and FT-IR. The depth profile was investigated by the argon-ion sputtering method. The MC3T3-E1 osteoblastic cells were inoculated and cultured on the scaffolds. SEM and phase contrast microscope observation of the cells, MTT test and ALP activity test evaluated the cell attachment, proliferation and activity on the scaffolds. Characteristic peaks in XPS and FT-IR spectra indicated pamidronate being immobilized on the surface of the bioceramics. The cell culture test indicated that the cells actively proliferated on the scaffolds. There was no significant difference between the ALP activity of the cells cultured for 1d, 3d and 7d on PAM-HA and that of the controls. The result indicated that PAM-HA bioceramics had favorable cytocompatibility to be used as bone scaffold with potential ability to improve osteogenesis.

Abstract: Hydroxyapatite (HA)/titanium (Ti) composites were successfully fabricated by hot isostatic pressing at 850°C. The microstructure of 7T2HB (70Ti+20HA+10Bioglass, Vol. %) composites were systematically investigated. The main constituents of the composites are hydroxyapatite and titanium. A simulated body fluid (SBF) with the same ion concentrations as those of human plasma and pH value of 7.4 is selected to evaluate the in vitro biological properties of the composites. After 2-week immersion in SBF, the bioactive apatite formed a very dense film on the surface of the composites. The dissolution of CaO and Ca-P compounds in SBF improves the growth of apatite on the surface of the composites.

Abstract: Due to some inferior performance of Chemical Vapor Deposition (CVD) diamond dosimeters, their applications are somewhat limited. The quality of diamond films was improved using Microwave Plasma CVD (MWPCVD) by the modified processes such as cyclic deposition and in-situ plasma post-treatment. The simple radiation dosimeters were fabricated in a sandwich configuration. Influence of purity and orientation of the diamond films on the sensitivity of the dosimeters was studied. The results indicate that the radiation dosimeters have high sensitivity to X-ray and the response of the devices is linear with the X-ray flux. The higher the purity of films is, the higher the resistivity and sensitivity are. The dosimeter based on [100] film has higher sensitivity than that based on [111] film. The dosimeter based on films prepared by cyclic deposition has higher sensitivity than that based on films prepared by the conventional deposition. The characterization of the response to X-ray also shows that in-situ oxygen plasma post-treatment leads to the higher sensitivity of dosimeters compared with in-situ nitrogen, hydrogen plasma post-treatments.