Key Engineering Materials Vols. 330-332

Abstract: Poly 3-hydroxybutyrate (PHB) as a kind of polysaccharides has been proved promising for tissue engineering because of its biocompatibility and biodegradability. But its poor mechanical properties and hydrophilicity limit its application. In order to explore a new useful porch to improve the performance of PHB-based GTR membrane, membrane composed of nano-HA / PHB composite was manufactured through the air/jet electrospinning process which can potentially generate nanometer scale diameter fibers and enlarge surface area of materials while maintaining high porosity. Successively, the biomineralization behavior of the membrane in supersaturated calcification solution (SCS) was studied. The Results of this investigation show that the successfully manufactured porous nano-HA/PHB membrane has high activity in SCS and its ability of inducing the formation of mineral crystal in vitro than that of the unfilled PHB membrane. It can be concluded that the addition of nano-HA and the novel technology could improve the performance of the PHB-based GTR membrane.

Abstract: Non-woven silica fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. It was transferred to a syringe, which was connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica fibers containing calcium were spun under the electric field of 2 KV/cm. Their diameters were in the range from about 0.3 μm to 8 μm. It was heat-treated at 300 oC for 3 hours. After soaking in the SBF for 1 week, low crystalline apatite crystals were observed to occur on their surfaces. From the results, it can be concluded that the non-woven silica fabric containing calcium made by electro-spinning method and then heat-treated has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Abstract: The bioactivity of poled piezoelectric PLLA membrane was investigated by studying the calcium phosphate formation in vitro using a biomimetic method. Samples (φ10mm) were poled under DC electric field of 8~l0kV/cm at 70°C for 30 min followed by cooling under the electric field. Surface chemistry of the samples before and after poling treatment was studied by X-ray photoelectron spectroscopy (XPS). Poled/unpoled samples were immersed in supersaturated calcification solution (SCS) for periods up to 24 h (36.5°C). The surface morphology and composition of the soaked samples were evaluated by using scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). Poled samples showed two different charged surfaces, negatively-charged surface (N-PLLA) and positively-charged surface (P-PLLA). On the N-PLLA surfaces, SEM together with XRD showed a gradually formed calcium phosphate (Ca-P), while no obvious Ca-P on either P-PLLA or unpoled samples was observed. This study demonstrated that poled piezoelectric PLLA substrates induce substantially higher level of Ca-P formation than electrically neutral substrates and only N-PLLA, however, can improve Ca-P formation after immersion in SCS.

Abstract: Hydroxyapatite (HA) coatings were introduced onto Poly L-lactic Acid (PLLA) polymer in a controlled manner by immobilized urease method with a shortened precipitation time. Osteoblastic-like cellular responses to the composite were examined in terms of cell proliferation, differentiation and cell morphology, as well as the expression of bone-associated genes. The cells exhibited higher cellular proliferation at 2 and 4 days on the HA/PLLA composite compared to PLLA scaffold, while no significant difference was observed later at 6 days. The alkaline phosphatase (ALP) activity by cells at 7 days was statistically higher on HA/PLLA scaffold than on PLLA. Moreover, the gene expression of ALP and osteocalcin (OC) was up regulated on HA/PLLA composite by RT-PCR analysis. The preliminary study suggested that the use of the controlled modification of hydroxyapatite coating on PLLA scaffold to produce HA/PLLA composite might enhance cellular activity, indicating the potential use for bone substitute in tissue engineering.

Abstract: The surface charge of calcium phosphates in Simulated Body Fluid (SBF) may be one of the factors associated with the adhesion of cells and proteins, processes that are related with osteogenesis. For calcium phosphates in SBF, surface charge varies with solution pH due to the adsorption of positive ions and to the reactions that occur at the solid/biological fluid interface. In this work, the variation of the density of protons adsorbed and the surface charge as a function of pH were determined for Hydroxyapatite, CaHPO4, and Bone Mineral.

Abstract: The Pre-Ca procedure was applied to the titanium surfaces before immersion in the SBF to accelerate the apatite precipitation. The process of apatite formation on the titanium surfaces was investigated by using scanning electron microscopy (SEM). A QCM system was applied to quantitatively monitor the apatite formation process using biomimetic method in situ in real time and to estimate the effect of pre-calcification in the biomemetic process effectively combined with SEM technique.

Abstract: Phosphorylated chitosan (PCS) was used as the template to control hydroxyapatite(HAp) growth, a novel nanocomposite composed of PCS and HAp was synthesized by biomimetic method. Calcium phosphate (Ca 2+= 60mM, Ca/P = 1.67) solution in HCl was added dropwise into PCS solution in NaOH. The precipitate was lyophilized to obtain the composite. The biocompatibility of the PCS-HAp nanocomopite was evaluated by osteoblast culture in vitro. The results showed that low crystallized HAp nanocrystals was formed on the PCS fibers and its crystallographic c-axis were aligned preferentially parallel to the long axis direction of PCS; the composite have good biocompatibility in vitro. It is expected that the novel composite to be a potential material for bone repair.

Abstract: Simulated body fluid (SBF) solutions are widely used for in vitro bioactivity tests and to coat bioinert materials with biomimetic calcium phosphates. In this study SBF solutions with varying HCO3 - content were used to precipitate hydroxy carbonated apatite (HCA) on a bioactive titanium surface. XRD as well as cross-sectional TEM analyses revealed that the biomimetically derived crystallites show a preferred growth orientation in direction of their c-axis and perpendicular to the surface of the substrate. FTIR and Raman analyses revealed that, as long as the HCO3 - concentration in the testing solutions is below 20 mmol/l, only B-type HCA precipitates. Using SBF with a HCO3 - concentration equal to human blood plasma (27 mmol/l) leads to a AB-type substitution where, in accordance with bone mineral, CO3 2- substitutes PO4 3- as well as OH-.

Abstract: Ti-O film is a kind of potential biomaterial may be applied in medical devices. But the mechanism of its good biocompatility is not so clear. This study revealed that when Titanium oxide contact with macrophage and plasma, the activation, adhesion and secretion of inflammatory molecule MCP-1 of macrophage is lower than reference material. Ti-O film also show minor contact activation to plasma. So reducing the host reaction including contact activation and inflammation may be the important reason for the good biocompatibility of Ti-O film.

Abstract: AFM is used to study tooth surfaces (enamel and cementum) in order to compare the pattern of particle distribution and demineralization process in the two dissimilar tooth hard tissues. Our approach is focusing mainly on the qualitative observations of tooth surface morphology and quantitatively measuring the early stages of mineral loss. The native enamel presented globular particles tightly packed. After polishing the aprismatic layer, the particles observed were relatively larger and more organized than ones in the outmost enamel surface. The cementum had small grains arranged in some degree of ordered packing with varying crystallite orientations. After different time treatment with citric acid solution, all the sample surfaces became more irregular and had the deeper grooves. The maximum mineral loss was greatest for the cementum sample and lowest for the native enamel. The demineralization difference between the enamel and cementum shows the structure and component play important roles in the morphological changes of demineralization. These demonstrate that the microstructure and demineralized difference between enamel and cementum obtained with AFM are complementary to the usual SEM images and TEM data. AFM is suitable for measuring early stages of tooth surface demineralization.