Key Engineering Materials Vols. 330-332

Abstract: The process of dental caries is dynamic and continuous, with periods of de- and remineralization of the tooth structure occurring over time. When the remineralization potential is superior to demineralization, the caries process can be stopped and early caries lesions can recover. Moreover, the remineralization potential will be increased if active components are added to a dentifrice. Therefore, the aim of this study was to re-evaluate the remineralizaton potential of a dentifrice containing nano-sized carbonated apatite using pH cycling, which simulates the oral environment. Artificial incipient caries was induced on bovine tooth specimens, which were treated with 4 dentifrices containing several concentrations of nano carbonated apatites with pH cycling. The remineralization effect was evaluated at each step by measuring the Vickers Hardness Number, and obtaining SEM and CLSM images of the enamel surface. The micro hardness of the enamel surface increased after the pH cycling treatment of the dentifrices. The dentifrice containing 5% n-CAPs showed the highest level of remineralization followed by 0%, 15% and 30%. One-way ANOVA indicated a significant difference in remineralization between the dentifrice containing 5% and 30% n-CAPs. SEM and CLSM also demonstrated observable differences in each step. From this study, the fluoride dentifrice containing 5% n-CAPs was effective in remineralizing an artificial incipient caries lesion. In conclusion, the dentifrice containing 5% nano carbonated apatites and 25% silica was the most effective in remineralizing early caries lesion.

Abstract: The aim of this study was to synthesize yttrium/hydroxyapatite(Y/HA) nanoparticles and submit to a structural, chemical and biological characterization. The microstructure, shape and size, concentration of yttrium released in water were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Inductively coupled plasma (ICP). The biological actions were evaluated by the cell cultivation method and oral bacterial colony counting method. The results showed that yttrium can be incorporated into the hydroxyapatite structure. Sizes of the nanocrystals were less than 100nm. The shape was needle-like. The human periodontal fibroblast growth was accelerated and oral bacterial growth was lightly restricted. The data indicate that the hydrothermally synthetized approach can be successfully used to prepare yttrium/hydroxyapatite nanocrystals with crystallinity, crystal dimensions, structure and stability close to those characteristic of biological apatite and with better biological activity, bacteriostasis.

Abstract: Since bacterial accumulation surrounding biomaterials has pathogens known to cause the biomaterials centered infection, it may be important to develop some kind of biomaterial with antibacterial activity as well as biocompatibility. This study focused on evaluating the antibacterial activity of silver-hydroxyapatite/ Titania nanoparticles (Ag-nHA/nTiO2) against oral bacteria with agar dilution method. Bacteria were seeded on agar plate containing antibacterial material with different concentrations after incubation of 48 hours. The antibacterial activity was demonstrated by MICs. The MICs of Ag-nHA/nTiO2 ranged between 1000μg/ ml and 7500μg /ml under anaerobic conditions. And it also exhibited remarkable antibacterial activity to all the aerobe bacteria (MIC≤500μg/ml). On the other hand, the antibacterial activities of Ag-nHA/nTiO2 differentiate to some extent with the bacterial strains. This Ag-nHA/nTiO2 exhibited remarkable antibacterial activity to anaerobic and aerobe bacteria. This antibacterial effect may reduce the potential for bacterial colonisation of oral biomaterials with Ag-nHA/nTiO2.

Abstract: In order to solve the problems on synthesizing carbonated hydroxyapatites (CHA) by the conventional heating precipitation method, such as long reaction and large particle size, poor crystallinity of CHA etc, the nanosized CHA particles have been synthesized by microwave heating method using phosphoric acid (H3PO4), calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3 ) as starting materials in the present paper. The influences of power level and time of microwave irradiation on synthesis of CHA have been investigated. The X-ray diffraction (XRD) analysis has indicated that microwave heating will reduce CHA crystallization time and improve crystallinity of CHA. Scanning electron microscope (SEM) analysis has showed that CHA particles are of rod like morphology with about 60nm width and 200nm length respectively. Infrared spectroscopy (IR) analysis has confirmed the B-type CHA precipitate can be formed under microwave irradiation. The microwave irradiation plays an important role to promote the reaction and the synthesis of nanosized CHA particles.

Abstract: To investigate nanoparticles’ antitumor effect, a globose 30~35nm Ce(IV) doped Titanium dioxide nanoparticles (CDT) were prepared by impregnation method and characterized by X-ray diffraction (XRD) and transmission electron microscopy(TEM). Proliferation of BEL7402 human Hepatoma cells was studied in vitro by using fluorescence microscopy and Flow Cytometry. The results show that cerium elements doping enhanced thermal stability of nano-size titanium dioxide to 800°C. With UV irradiated for 8min, BEL7402 were induced a dose-dependent apoptosis by CDT, about 28.2% , 41.5% and 88.3% cells were induced apoptosis after 24h at concentration of 60, 120 and 180ug/ml respectively, relative to 3.9% of that of control group cell just only in the presence of UV.

Abstract: The hydroxyapatite/collagen (HAp/Col) nanocomposite membrane was prepared from the HAp/Col nanocomposite fibers. The HAp/Col membrane crosslinked by a vacuum heating showed 14±2 (dry) and 1.0±0.1 (wet) MPa in tensile strengths that were enough strength to operate in both cell culture and surgical operations. Histological observation and total DNA amount analysis demonstrated that human osteoblastic cells, MG63, derived from osteosarcoma on the HAp/Col membrane adhered and proliferated well as the same as those on tissue culture polystyrene (TCPS). Real-time polymerase chain reaction analyses indicated that alkaline phosphatase gene expression on the HAp/Col membrane was 1.4 times greater than that on TCPS. These results suggested that the HAp/Col nanocomposite membrane can be utilized in bone tissue engineering scaffold as well as bone filler.

Abstract: The purpose of this study is to analyze osteogenic activity of human osteoblastic MG63 cells on the bone-like self-organized hydroxyapatite/collagen (HAp/Col) nanocomposite sponge cultured by a pressure/perfusion technique using collagen sponge as a control. Histological analyses, alkaline phosphatase (AlkP) protein analysis and real-time polymerase chain reaction (PCR) analyses for AlkP and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to evaluate the osteogenic activity of MG63. The MG63 cells were attached well and showed good proliferation on the HAp/Col sponge as well as in the control. The MG63 cells on HAp/Col sponge demonstrated higher osteogenic activity than those on the control. The results suggested that the HAp/Col sponge is expected to be a good scaffold for bone tissue engineering.

Abstract: Using nano-hydroxyapatite/polyamide66 composite (n-HA/PA66) and a special foamer as start materials, a porous species for bone defect repair was successfully developed by thermal-pressing method. The resulting material presented: (1) high compressive strength which reached 13~46MPa; (2) excellent porous structure, the average diameter of pores in the matrix was in range of 280μm to 500μm and porosity of 36% to 57%. The porous architecture could be adjusted by the combination of processing parameters such as the weight of start mixture used per mold and the ratio of composite to foamer as well as n-HA content in the composite. No apparent change in composition and structure of n-HA/PA66 composite was found by XRD and IR determination before and after formation of porous species. According to Sherrer equation, the value of D(002) of n-HA crystals in porous material and start powder were about 70nm, indicating no occurrence of change in size of n-HA during the thermal-pressing procedure. Additionally, no foamer residual was detected in porous species.

Abstract: In this experiment, un-dried silver-hydroxyapatite-titania nanoparticles slurry was used to make membrane with Polyamide-66 by co-polymerization method. The morphology, chemical components and structures of the membrane were characterized by AAS, XRD, SEM and EDX. S. aureus, E. eoli, P.gingivalis, F.nucleatum and S.mutans were utilized to test the antibacterial effect. XRD results demonstrated that the membrane have characteristic diffraction peaks of pure HA. A homogeneous distribution of the Ca, P, Ti, and Ag element in the membrane was confirmed by EDX. Both surface and section showed porous structure which was confirmed by SEM and the holes size was average 20-30μm. The bacteria assay reflects to the antibacterial effect, 56.31 % of S. aureus and 50.10 % of E. eoli were killed after 24 hours incubation. However, 91.84 % of P. gingivalis, 90.64 % of F. nucleatum and 90.49 % of S. mutans were killed and pictures of SEM showed obviously fewer cells on the surface. So the nanocomposite membrane could be one of the bioactive materials with antibacterial properties for oral GBR technique.