Weichang Xue

In vivo evaluation of plasma sprayed hydroxyapatite coatings having different crystallinity.

In this paper, hydroxyapatite (HA) coatings having the crystallinities of 56% and 98% were deposited by the plasma spraying and vapor-flame treatment process. The phase composition and crystallinity of the coatings were investigated by X-ray diffraction and infrared spectra. The dissolution behavior of the coatings in tris-buffer solutions was examined. The results obtained indicated that the coating having the high crystallinity showed the lower dissolution as compared to the low crystallinity coating. The bone bonding ability of HA coatings were observed in vivo by implanted in dogs femur. After 3 months implantation, the high crystallinity coating showed the higher shear strengths and remained integrated, whereas the separation of the coating fragments was clearly observed in the coating having low crystallinity.

Fabrication of compositionally and structurally graded Ti-TiO2 structures using laser engineered net shaping (LENS).

Novel structures with functional gradation in composition and structure were successfully made in Ti-TiO(2) combination using laser engineered net shaping. The addition of fully dense, compositionally graded TiO(2) ceramic on porous Ti significantly increased the surface wettability and hardness. The graded structures with varying concentrations of TiO(2) on the top surface were found to be non-toxic and biocompatible. In addition, the higher wettability of surfaces with TiO(2) can enhance their ability to form chemisorbed lubricating films, which can potentially lower the friction coefficient against ultrahigh molecular weight polyethylene liner, thus reducing its wear rate. These unitized structures with open porosity on one side and hard, low friction surface on the other side can eliminate the need for multiple parts with different compositions for load-bearing implants such as total hip prostheses.

Mesoporous calcium silicate for controlled release of bovine serum albumin protein

The purpose of this study is to synthesize mesoporous calcium silicate (CS or wollastonite, CaSiO(3)) and evaluate its possible application in protein/drug delivery. First, calcium silicate was synthesized by wet chemical method and then mesoporosity was created by acid modification of the synthesized CS particle using hydrochloric acid at pH 7, 4.5, and 0.5. The results showed that a hydrated silica gel with abundant Si-OH functional group formed on the surface of calcium silicate due to acid modification. This surface layer had mesoporous structure, with pore diameter between 4 and 5 nm. BET specific average surface area increased to 221, 333, and 356 m(2) g(-1) due to acid modification at pH 7, 4.5, and 0.5, respectively, whereas the surface area for unmodified CS particles was 65 m(2) g(-1). Protein adsorption studies indicated that mesoporous CS has higher ability to adsorb bovine serum albumin and lysozyme compared to unmodified particles. The release kinetics showed that proteins on mesoporous CS released sequentially over one week, whereas the proteins on unmodified particle followed burst release kinetics within a few hours. Human osteoblast cell-material interaction study showed that these materials were biocompatible and promoted excellent bone cell proliferation. In summary, this work has demonstrated the potential to produce mesoporous CS as a carrier for protein/drug delivery for bone regeneration and other biomedical applications.

Laser-assisted Zr/ZrO2 coating on Ti for load-bearing implants

Oxidized Zr alloys have been shown to exhibit lower friction and superior wear properties, suggesting that they could be used in hip and knee implants. However, conventional oxidation of Zr alloys above 500 degrees C, in dry air, for several hours has been shown to have detrimental effects on the substrates properties. In this work, we deposited pure Zr on Ti, then oxidized the coating using a continuous-wave Nd:YAG laser, which facilitated localized heating to elevated temperatures without affecting the substrate. Laser-assisted oxidation resulted in a 7microm thick fully dense ZrO(2) layer on Zr in which an increase in oxidation kinetics was evident due to an increase in the laser power and/or the oxygen partial pressure. Due to its high surface energy and wettability, the wear rate of laser-oxidized Zr was two orders of magnitude less compared to that of as-deposited Zr. The oxidized coatings showed comparable in vitro biocompatibility to that of pure Ti and excellent in vitro cell-material interactions. This article reports the processing of Zr/ZrO(2) coatings on Ti using lasers, and the influence of laser parameters and oxygen partial pressure on the coatings mechanical, microstructural, wear and in vitro biological properties using human osteoblast cells.