Papers by Author: Zhi Qing Chen

Abstract: The aims of this study were to quantify the elements released from a Ni-Cr dental alloy in artificial saliva and saline solution and to test whether immersion time and different immersion media are factors influencing elemental release from a nickel-based dental alloy. Standard sized Ni-Cr alloy castings were put into different immersion media (saline solution or artificial saliva) randomly. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to test the elemental release of the alloy at 1, 3, 7, 30 and 82 days. The surfaces of alloy were observed by scanning electron microscope (SEM). It has been found that except Ni in the artificial saliva, all the other elements remained unchanged statistically in the first week after initial release. The accumulative elemental release showed Cr in both media and Ni in the artificial saliva increased statistically in 30-day period and Ni, Cr, Be, Al, Co increased significantly in 82 days, while Mo in both media and Co in artificial saliva were not yet detected. The total mass of elements released in saline solution was greater than that in artificial saliva. Conclusion: With the immersion time increasing，more kinds of elements were released and more amount of elements released was detected in solutions. The alloy was prone to corrosion in saline solution than in artificial Saliva.

Abstract: This study sought to compare the biocompatibility of four dental ceramics so as to provide indications useful for the further development of dental materials. Osteoblasts were obtained by culturing the cranial explant of SD rat and cultured in vitro when they were seeded onto four different materials: hydroxyapatite, bioactive glass ceramics, tricalciumphosphate-hydroxyapatite and nano-hydroxyapatite (nHA). The phase contrast microscope and scanning electron microscope were used to evaluate the cell morphology and attachment. The content of alkaline phosphatase was calculated by molecular biological methods. MTT method was performed to find the alteration of proliferation. Then by use of wash way method, the adhesion ability was tested. The results showed that all of the four bioceramics had good cytocompatibility. There were significant differences among them on the levels of cell growth, differation and adhesion in vitro. The biocompatibility of nHA is the best and of conventional HA is the worst.

Abstract: This research is aimed at the development and characterization of a novel bioceramic coating on the surface of pure titanium. Nano-TiO2/HA composite bioceramic coating was designed and developed on the surfaces of pure titanium discs by sol-gel route. The TiO2 anatase bioceramic coating was employed as the inner layer, which could adhere tightly to the titanium substrate. The porous HA bioceramic coating was employed as the outer layer, which has higher solubility and better short term bioactivity. Conventional HA coatings and commercially pure titanium (cpTi) were taken as control. XRD and SEM were employed to characterize the crystallization, surface morphology and thickness of the coatings. The bioactivities of the coatings were evaluated by the in vitro osteoblasts culture. Results show the nano-TiO2/HA composite bioceramic coating has good crystallization and homogeneous, nano-scale surface morphology. And it adheres tightly to the substrate. The in vitro osteoblasts culture exhibits satisfactory bioactivity.

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: 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: 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: The effect of Si doping on the bioactivity and characteristics of hydroxyapatite/TiO2 composite films was investigated. Pure titanium plates were treated to form Ca, P and Si enriched titania-based films by using micro-arc oxidation (MAO). Then, some specimens were undergone a further hydrothermal treatment to produce a thin outermost layer of hydroxyapatite (HA). Experiments revealed that that the film, which was about 10μm thick, was composed of amorphous silicon dioxide, amorphous calcium phosphate, rutile and anatase. The film was porous and uneven, with the pore size of 1-4μm. No obvious cracks exist on the surface. In order to investigate the cytocompatibility of the films, periodontal ligament (PDL) cells were seeded onto the surface of the films. It was concluded that the Si ion did not influence the characters of MAO film but Si enriched hydroxyapatite/ TiO2 composite coatings exhibited an effect on cell attachment.

Abstract: The aim of the present study is to evaluate the biomineralization behavior of silk fibroin. The biomimetic mineralization was carried out in an alternative calcium/phosphate soaking solution (ACPS). The formation of calcium phosphate deposits was identified by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). A quick formation of well-crystallized apatite on the surface of the silk fibroin film indicates that biomineralization may be an effective approach to obtaining fibroin/HAP composites.

Abstract: Sensory perception thresholds of implants were much higher than those of natural teeth. The purpose of this study was to evaluate the biocompatibility of TiO2/HA-biocoated dental implants for nerve regeneration using cultured Schwann cells. The nano-TiO2/HA composite bioceramic coating was developed on the surfaces of commercially pure titanium discs by sol-gel route, and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Using smooth titanium discs as a control, Schwann cell responses to the coating were evaluated by SEM, MTT assay, total protein content and leakage of cytosolic lactate dehydrogenase (LDH) activity. In addition, the amount of brain-derived neurotrophic factor (BDNF) secreted by Schwann cells was measured by Enzyme-Linked Immunosorbent Assay (ELISA). It was observed that the coating had fine crystallites and homogeneous micropores in the diameter of 5-10 um. The cell morphology, proliferation and function were unaffected. The results indicate that the TiO2/HA bioceramic coating developed on the surface of pure titanium by sol-gel route had good biocompatibility with Schwann cells for nerve regeneration around dental implants.

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.