Papers by Author: Xing Dong Zhang

Abstract: Hydroxyapatite (HA) ceramics is one of the most widely used bone substitute in clinics. Limited information is available concerning how HA ceramics may affect osteoprotegerin (OPG) and RANKL expression. In this study, osteoblastic-like SaOS-2 cells were grown on HA ceramics sintered at different temperature for 3 and 6 days, RANKL and OPG mRNA expression were analyzed with quantitative in situ hybridization (QISH) technique. Result showed that SaOS-2 grown on HA ceramics sintered at 800°C expressed higher RANKL mRNA than on other two HA ceramics after 3 days’ culture. No significant difference in OPG expression on different surfaces was detected after 3 days and 6 days culture. This result suggests that HA sintered at low temperature tend to induce more bone remodeling after implantation.

Abstract: This study investigated the utility of genetically modified cell line for fast and non-destructive cytotoxicity evaluation of biomaterials. The EGFP(enhanced green fluorescence protein)-expressing plasmid pcDNA-EGFP was constructed, and electroporated into ROS 17/28 osteoblastic cells to generate an EGFP-labeled stable cell line, ROS-EGFP. This genetically modified cell line provided two unique opportunities to qualitative and semi-quantitative evaluation of cell growth on biomaterials without destruction of samples. Firstly, utilizing the fluorescence of EGFP expressed in the cells, the viability state of cells on biomaterials was evaluated using a fluorescent light microscope. Secondly, the proliferation of cells on biomaterials, which was identified by MTT assay，was demonstrated according to the microscopically counted fluorescent cell numbers. From the results, it could be concluded that the ROS-EGFP cell line was an effective tool to trace the fate of cells on biomaterials and to evaluate the biocompatibility of biomaterials to cell growth in vitro.

Abstract: The mRNA expression of Cbfa1 and osteocalcin gene induced by calcium phosphate ceramics (Ca/P) were quantitative analyzed according to real-time RT-PCR method in this work. C2C12 cells were co-culture with four kinds of porous Ca/P ceramics for 2 and 5d without adding other growth factors. The four kinds of Ca/P ceramics were pure hydroxyapatite (HA) sintered at 1250°C and HA/TCP with a ratio of 60/40 sintered at 1100°C (HT1), 1200°C (HT2) and 1250°C (HT3) respectively. Real-time RT-PCR analysis found the Ca/P ceramics induced positive expression of Cbfa1 and osteocalcin in C2C12 cells, After 5 days culture, Cbfa1 and osteocalcin showed obvious higher expression compared with that in 2 days. Cbfa1 and osteocalcin expression in BCP was much higher than HA, and the expression level of osteocalcin was HT1>HT2>HT3>HA. Our results showed that Ca/P ceramics alone were sufficient to induce C2C12 cells to osteoblastic differentiation and the sinter temperature and phase composition of Ca/P ceramics could affect their osteoindctive capacity significantly.

Abstract: Porous HA/TCP bioceramics were immersed in pure dog serum to observe apatite formation. Deposited crystals were examined using SEM. Results showed that beamed sheet-like crystals formed on the surface of ceramics granules, and after postponement immersion time, crystals extended and became bigger. EDS and IR results suggested formed crystals were defect-calcium type carbonated hydroxyapatite. HRTEM photograph suggested formation process of new-formed crystals from non-crystal to crystal in serum. Directional organisms acted maybe as a template in process of crystals formation, so new crystals developed along certain direction.

Abstract: Protein adsorption is driven by various interactions. The contribution of surface charge to bovine serum albumin (BSA) adsorption on hydroxyapatite (HA) ceramic was investigated by adjusting the liquid environment in which the solid particles dispersed. Zeta potentials of HA and the adsorption of BSA on the surface were tested as a function of pH, ionic strength, Ca2+ and PO4 3- concentrations in the aqueous solutions, and the results showed that both of them were greatly affected by those experimental variations. Besides, the amount of adsorbed BSA was related to the variation of zeta potential of HA, as could be well understood in terms of electrostatic interactions.

Abstract: Collagenous molecule was successfully immobilized to hydroxyapatite (HA) surface through a molecular bridge (2-Hydroxyethyl acrylate, HEMA) that was grafted to the surface with covalent bond by gamma irradiation. Hydroxyapatite modified by atelocollagen had been characterized by several surface sensitive techniques, such as FT-IR, SEM, XPS. The investigations showed that the collagen, a bioactive macromolecule, was immobilized on the HA surface through covalent bond.

Abstract: The aim of this study was to optimize sintering aids and processing parameters for zirconia toughened alumina (ZTA) nano-ceramics with optimal properties as dental ceramics. Additive agents (TiO2, MgO, SiO2), dry pressing forces and sintering temperatures are very important for preparation of structural ceramics. In the present study, density and Vickers hardness measurement, SEM, and XRD analysis were employed to investigate the effects of these on the final products. The relevant results showed that higher pressing force led to an increase in the density and Vickers hardness of the sintered ceramics. Among the four groups of sintered nanoceramics with different ratios of alumina and zirconia, and combinations of additive agents, the best densification was achieved in the sample from Group 2# containing 1.05wt% MgO after sintered at 1450°C, as indicated by SEM observation. XRD analysis confirmed the formation of MgAl2O4 as an intermediate compound. The existence of TiO2 in the additive agents was in favor of the acquisition of high densification. The measured values for the density and Vickers hardness indicated that the sintered ZTA nano-ceramics would be a potential material for dental prosthetic applications.

Abstract: The purpose of this study was to evaluate biocompatibility of a new injectable root canal sealer. The cytotoxicity of zinc oxide-eugenol cements, CCQ and the new injectable root canal sealer were assessed by the MTT assays. These materials were filled into the root canals of the dog. One month later, the dog was sacrificed and the X-ray photos were taken. The histological response was observed through the microscope. The results show the new injectable root canal sealer showed better biocompatibility than the other two materials.

Abstract: Circumambient tissues infection is a common complication of implanted percutaneous and permucosal devices (PDs). In order to counter the infection, the titanium abutment surface of PDs was modified to achieve antibacterial and antiadhesive activities. Titanium discs were immersed into hydroxyapatite (HA) sol containing different mass fraction silver and thermally treated to get modified discs. The modified discs become more smoother and get crystal HA coatings containing silver. Silver ion release test demonstrate the release rate is very slow and the coating is a reservoir of silver. The antibacterial and antiadhesive effects of modified discs on Staphylococcus aureus and Porphyromonas gingivalis were evaluated. Modified titanium discs with silver significantly inhibited the growth of these two bacteria compared with both the polished titanium discs control and modified titanium discs without silver. And titanium discs modified with more silver have higher antibacterial activity and less bacteria adhesion in this study. These findings indicate that titanium surface modified with the HA sol-gel containing silver could achieve antibacterial and antiadhesive activities, and the abutments of PDs are promising to be modified by this method.

Abstract: After the Tantalum metal was subjected to the anodic oxidation at suitable voltage in 2M H2SO4 solution, tantalum oxide with rhombic or amorphous structure formed on the metal surface. The Oxide showed apatite formation ability in simulative body fluid at 6d. It meant the anodic oxidation treatment ia an effective method to accelerate the bioactivity of tantalum metal.