Ji Dong Li

Antibacterial Effect and Security Evaluation on Nano-Hydroxyapatite Bearing Cu2+ and Zn2+

Nano-hydroxyapatite (n-HA) slurry was synthesized at normal pressure, and (Cu2+, Zn2+)-bearing nano-hydroxyapatite (Cu-Zn-HA) was prepared by ion exchange reaction in water medium. The properties of n-HA and Cu-Zn-HA were characterized by AAS, TEM, XRD and FTIR. The results of XRD analysis indicate that Cu2+ and Zn2+ can occupy Ca2+ sites and enter the crystal lattice of hydroxyapatite. Through the antibacterial experiments, it was found that Cu-Zn-HA had better antibacterial ability on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). After heat treatment at 400°C for an hour, the materials still had good antibacterial effect. The accelerated aging method was employed to test antibacterial durability of the material and the results indicated that the durability was good. The results of the security assessment, including skin stimulation test of rabbit, acute toxicity test by stomach filling and the micronucleus test in bone marrow polychromatic erythrocytes of mice, showed that the security of the material was excellent.

Comparison of Hydroxyapatite Synthesized under Different Conditions

In this paper, using sodium phosphate and calcium nitrate as reagents, nano-hydroxyapatite (n-HA) was synthesised under 8 conditions. The morphology and crystallinity of these prepared HA were investigated by Transmission Electron Microscope (TEM) and X-ray diffraction pattern (XRD). The Ca/P molar ratio of n-HA was tested by chemical method. In order to find a better way to obtain purer nano-hydroxyapatite, the phases transition and purification of these 8 samples before and after sintering at 1000°C were compared. The results indicated that all these samples showed similar, poorly crystallized apatite structures before sintering. The adding order between calcium and phosphate would affect the crystallinity, structure and Ca/P molar ratio of hydoxyapatite significantly. XRD analysis showed that adding sodium phosphate into calcium nitrate could gain more HA phase after sintering at 1000°C. The pH of reaction system had obvious effects on the structure of hydroxyapatite. Besides the pH of reactants also affected the structure of hydoxyapatite.

Fabrication of Porous n-HA/PA66 Composite for Bone Repair

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.

Effects of γ-Ray Irradiation on the Properties of Nano-Hydroxyapatite/Polyurethane Composite Porous Scaffolds

To well understand the influence of the sterilization on the properties of biomaterials prior to application is pivotal. The effect of γ-ray irradiation on the mechanical and thermal properties of nanohydroxyapatite/polyurethane (n-HA/PU) porous scaffold for bone tissue engineering was studied in this paper. The mechanical testing, fourier transform infrared spectroscopy and thermal analysis were employed to determine the structure and properties change of these composite scaffolds after γ-ray irradiation with different doses.The results show that thermal stability, and mechanical properties of the composite scaffolds increase after γ-ray irradiation with doses of15 kGy to 25 kGy, especially the irradiation dose of 15kGy which imposed a remarkable effect on these properties. However, a reverse trend is found when the 50kGy irradiation dose was applied.In general, it can be concluded that sterilization using γ-ray irradiation with proper dose has no adverse effect on the properties of n-HA/PU composite scaffolds.

Effect of Compatibilizers on the Properties of Nano-Hydroxyapatite Reinforced Polyamide 66 and High Density Polyethylene Blends

The compatibility efficiency on different compatibilizer for nano-hydroxyapatite (n-HA) reinforced polyamide 66 (PA66) and high density polyethylene (HDPE) blends at a composition of 40/42/18 as functionalized biomaterial was investigated by mechanical properties testing and scanning electron microscopy (SEM). The results showed that mechanical properties of compatibilized blends were much improved by the compatibilizers of maleic anhydride grafted polyethylene (PE-g-MAH) and ethylene/methacrylic acid ionomer-sodium ion (ION) compared with the uncompatibilized blends. Blends had peak mechanical values of different compatibilizer. Both PE-g and ION formed adhesion during melt mixing and stabilized the morphology and significantly reduced the size of dispersed PE phase. PE-g gave the blends with PE spheres ranging from 1 to 4µm and ION with well-dispersed spheres with an average diameter of 1µm. The more enlarged interphase of the blends containing ION reduced the lower interfacial energy to increase the miscibiliy of the blends. Consequently, ION had better contribution to rigidity properties than PE-g for n-HA/PA/PE blends.

Antibacterial Properties Evaluation of a Novel Polyurethane-Based Root Canal Sealer

Elimination of microorganisms from the root canal system and the prevention of subsequent reinfection are of importance for long-term endodontic treatment. The application of a sealer with antibacterial properties may reduce the reinfection and improve the success rate of the root filling treatment. The aim of this paper is to evaluate the antibacterial properties of a novel root canal sealer based on injectable self-curing polyurethane with silver phosphate (PU/Ag3PO4). The antibacterial abilities were assessed by direct contact test, anti-bacterial adhesion assay and bacteriostatic rate test. The results show that the fabricated PU/Ag3PO4 sealer can completely inhibit the bacterial growth and prevent bacterial adhension effectively. The bacteriostatic rate is 93.6% and 98.1% when the bacteria incubated with PU/Ag3PO4 sealer for 7 and 24h respectively. The strong antibacterial abilities suggest that PU/Ag3PO4 sealer has great application potential in the field of root canal filling.Key words: Root canal sealer, polyurethane, silver phosphate, antibacterial properties, direct contact test

Preparation of Freestanding TiO2 Nanotube Arrays via Controlling the Anodizing Voltage

In order to assemble titania nanotubes arrays (TNTs) with better performance in solar cells application, hierarchical voltage-reduction was employed to reduce the thickness of barrier layer and acquire freestanding films simultaneously. Study of intratubular microenvironment and TiO2/Ti interface indicated that it might be H+ generated in anodizing process permeating into the Ti substrate that resulted in peeling off the whole tube layers. Our findings provide a promising way to fabricate freestanding TNTs membranes just by tailoring the applied voltage.

A Novel Antimicrobial Nano-Composite Porous Material for Bone Repair

In this paper, isoniazid (INH)-loaded poly (ε-caprolactone) microspheres with a special microporous surface and relatively high drug loading were fabricated by an oil-in-oil (O/O) solvent evaporation method. Meanwhile the microspheres were produced by an oil-in-water (O/W) method for comparison. The technological parameters such as the concentration of surfactant, the volume of continuous phase and the quantity of the drug were investigated systematically. The microspheres morphology, their size distribution and the viscosity of both the dispersed and continuous phase were characterized. The results indicate that the O/O solvent evaporation method is a feasible approach to encapsulate micromolecular and hydrophilic drugs in PCL. This opens the door for INH-loaded microspheres able to release drugs and thereby improve the therapy of tuberculosis of bones and joints in the future.

Study on Improving Stainless Steel Antibacterial Capability

A new method was studied for improving stainless steel antibacterial capability. The Na2FeO4 coating was prepared on steel surface throughout NaOH treatment, then steel samples were immersed into the solution coantaining Ag+, Zn2+ and TiO2. The antibacterial-ions were fixated firmly on the stainless steel with chemical bond. Scanning electronic microscopy(SEM), X-ray(XRD) and atomic absoption spectroscopy(AAS) were employed to analyze the materials, and the results showed that the antibacterial membrane included silver citrate and silver peroxide. Quinn test was also carried out, in which Staphylococus and E.coli. the results showed that the steel has a bacteriostasis rate of 99.48% to Staphylococus, and 99.09% to E.coli.