Quanhe Bao

CHARACTERIZATION OF SOME METHODS OF PREPARATION FOR BIOACTIVE GLASS COATING ON IMPLANTS

Since the discovery of Bioglass® by Hench, bioactive glasses have been used in many medical applications, such as drug delivery systems, nonload-bearing implants, and bone cements because of their excellent bioactivity and biocompatibility. However, due to their poor mechanical properties, these glasses cannot be used in load-bearing applications, where the metallic alloys are still main materials. One useful approach to solving the mechanical limitations of bioactive glasses is to apply the glasses as the coating on mechanically tough substrates; it was also recognized early that bioactive glasses could be used as coatings for prosthetic metallic implants. In this paper, the mechanism, characterization, and current status of some methods of preparation for bioactive glass coating on implants are introduced. In the end, to get the homogeneous and compact coating with perfect bonding strength, some ideas of improving the performance of coatings are also presented.

ADVANCEMENT IN PREPARATION OF HYDROXYAPATITE/BIOGLASS GRADED COATINGS BY ELECTROPHORETIC DEPOSITION

Electrophoretic deposition is a good method in the preparation of hydroxyapatite/bioglass graded coatings. Its processing parameters are easy to be operated. As it is nonbeeline process, it can be used in the deposition of complex shape and porous surface. This paper reviewed the advancement of the graded coatings in recent years, concluded the principles, characters, steps of electrophoretic deposition of bioceramic coatings and analyzed influencing factors in detail, such as granularity of suspension, aging of suspension, dispersion media, PH of suspension, electricity, voltage, deposition time, pretreatment of substrate and sintering. The foreground of hydroxyapatite/bioglass graded coatings is expected.

Effects of technological parameters on the microstructure of laser remelted hydroxyapatite (HA) coatings

In this paper, the influence of different laser power and scanning speed on the microstructure of laser remelted as-sprayed hydroxyapatite (HA) coatings was studied and the optimum technological parameters were obtained. The morphologies, elements and phase analysis of both sprayed and remelted coatings were examined by means of electron probe microanalysis, x-ray diffraction and so on. The results show that the plasma sprayed coatings could be improved by laser remelting and the optimum technological parameters are that the laser power is 600 W and the scanning speed is 11.2 mm s−1. In the technological condition, the remelted coating which has compact columnar and cellular dendritic crystal consists of HA, α-TCP, CaO and TiO2 phases, and the Ca/P ratio of the coating is the most approximate to that of HA. When increasing the laser power and slowing the scanning speed, the structure of the coating will become much coarser and the Ca/P ratio will deviate more from that of HA. On the contrary, if the laser power is reduced and the scanning speed is accelerated, the influence of technological parameters of laser remelting on the sprayed coating will be weakened.

THE TARGET MORPHOLOGY DURING PULSED LASER DEPOSITION OF HYDROXYAPATITE THIN FILMS

A modified surface layer of hydroxyapatite (HA) target was observed before and after pulsed laser deposition. Two types of HA targets were used for laser ablation. We observed that the surface morphology of the target has a very fine compacted grain structure and presents many irregularities with some microroughness and microporosity before laser ablation. The laser ablated regions can be divided into two areas: one area is porous and rough but the other is dense and smooth. The percentage of particles in the films was high for the films produced with targets that were sintered at 1200°C.

APPLICATIONS OF ELECTROPHORETIC DEPOSITION IN THE COATING AND POROUS MATERIALS FABRICATIONS

Electrophoretic deposition (EPD) is a good method in the fabrication of the coating materials. Its processing parameters are easy to be operate. It is a nonbeeline process and can be used in the deposition on complex shape and porous surface. It has been widely used in many ways. This paper reviews the principles and fabrication steps of EPD and points out the influencing factors. The developments of EPD in the fabrication of materials, such as solid surface coatings, porous structure materials and gradient materials, are introduced in detail. The future of the application of EPD is also discussed.

Development Of Preparation Of The Functional Thin Films By Pulsed Laser Deposition

Pulsed laser deposition (PLD) exhibits unique advantages for the preparation of functional thin films which are widely used in microelectronics, photoelectrons, integrate circuits, superconductors and biomedical fields. The principle of and the characteristics of PLD are introduced, its applications in ferroelectrics, high-temperature superconductors, diamond-like and superlattices. The future application trend is reviewed.

BONDING ZONE MORPHOLOGIES CHARACTERISTICS OF LASER REMELTED HA COATINGS

The low bonding strength between plasma sprayed hydroxyapatite (HA) coatings and substrates is one of the problems, which should be solved. In this paper, the as-sprayed HA coatings were retreated by laser remelting. The microstructure and element analysis in coatings were studied by electron probe microanalyzer (EPMA) and the accessory of energy spectrum analyzer. The results show that the bonding state can be improved greatly after laser remelting and it is a metallurgical combination between transition layers and substrates. Generally, with the increase of laser power and the decrease of scanning speed, the bonding state between the surface and transition layer will be improved much more, but the value of Ca/P ratio will deviate much more from 1.67. In this experiment, the optimum technological parameter is that the laser power is 600 W and the scanning speed is 11.2 mm/s.

Solidification Mechanism Of Laser Remelted Bioactive Ha Coatings

In this paper, as-sprayed HA coatings were remelted by CW laser. The morphologies and the development of microstructures were analyzed by electron probe microanalysis. The solidification mechanism of laser remelted bioactive HA coatings is usually determined by the parameters of the temperature gradient G and the solidification velocity R. In the region of bottom pool, the G/R value is high which will result in the forming of planar crystal. With the decrease of G/R value, cellular and cellular dendrites will form. Near the surface, the coating can radiate heat to the atmosphere which will form a negative temperature gradient, consequently the structure is composed of dendrites.