Papers by Author: Pan Jian Li

Abstract: In this study we explore the possibility of incorporating Sr into nano-apatite coatings prepared by a solution-derived biomimetic methodology for coating titanium based implants. The way this element is incorporated in the apatite structure and its effects on the stereochemistry and morphology of the resulting apatite layers were investigated, as well as the resulting mineralization kinetics. The presence of Sr in solution induced an inhibitory effect on mineralization, leading to a decrease in the thickness of the mineral layers. This ion was incorporated in the apatite structure through a substitution mechanism by replacing Ca in the crystal lattice. The obtained Sr-substituted biomimetic coatings are expected to enhance bone formation and osteointegration.

Abstract: Hydroxyapatite (HA) coated total hip joint device has caused concerns of generating wear particles after long-term implantation. We designed a pin-on-disk (POD) test to examine the morphological changes and wear particle generation of plasma sprayed HA coating in vitro. HA coatings were immersed in supplemented α-calf bovine serum for 48 hours. Serum soaked HA coating exhibited significant amount of weight loss due to dissolution of amorphous calcium phosphate (ACP). POD test demonstrated the serum soaked HA coatings presented many micronsized particles on the surface while the as-received HA coatings maintained good integrity. The generation of wear particles of the serum soaked HA coatings is related to the reduction of the cohesion/adhesion of HA coatings due to the preferential dissolution of ACP.

Abstract: The monoclinic zirconia content in clinically failed ceramic heads was investigated in order to identify the cause of the failure. High percentages of the monoclinic zirconia were associated with the fractured surface. In vitro, accelerated aging of some components shows that the monoclinic transformation is site related: the closer to the bore, the more the monoclinic transformation. This phenomenon may be associated with the composition and the manufacturing process.

Abstract: Ti-6Al-4V polished disks were immersed in a-calf-serum-solution and studied for resulting surface changes. The as-polished samples had more Ti2O3 close to the surface than titanium oxidizing in air – a result of low oxygen supply during polishing. Close to the interface with the metal, the TiO oxide is dominant. Immersion in serum caused the oxide thickness to become thicker, and to contain a higher concentration of the TiO2 component.

Abstract: Typical plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce consistent bioceramic coats of precise thickness on porous surfaces. The resultant “biomimetic” surface more closely mimics the trabecular pattern and biochemistry at the bone interface. This report compares bone response to porous surfaces with biomimetic hydroxyapatite coatings. Implants were manufactured as Ti6Al4V cylinders (5-mm diameter, 41-mm long) coated with c.p-Ti PorocoatÒ porous layer with a thickness of 750 (± 250 µm). Implants were divided into three groups based on surface treatments. The porous surfaces of control group implants did not receive any treatment. The porous surfaces of HA group implants were plasma sprayed with hydroxyapatite. The porous surfaces of BAp group implants were coated with a biomimetic apatite (BAp) coating using a lowtemperature solution-based process that mimics bone mineralization. BAp coating is pure apatite coating of uniform structure and composition, with a thickness of approximately 15 µm on the outer beads. Because of the reduced thickness, the BAp coating does not block the pores or alter the porous structure. Bilateral femurs in thirty-six rabbits were implanted with one of the above groups. Twelve rabbits each were euthanized at 2, 4, and 12 weeks. Osseointegration was measured by automated computerized histomorphometry of scanning electron microscopy images of sections taken through the implant. Bone ingrowth on the Control surface was 45 % at 2 weeks and 47% at 12 weeks. Bone ingrowth on the PS surface increased from 51% at 2 weeks to 67% at 12 weeks. Bone ingrowth on the BAp surface increased from 45 % at 2 weeks to 71% at 12 weeks. At both time points mean bone ingrowth on PS and BAp coated implants was significantly higher than the control uncoated implants (p < 0.01). By 12 weeks the PS hydroxyapatite coat began showing evidence of fragmentation and debris production on SEM. This was not evident in the BAp coat. This study supports the hypothesis that apatite coating benefits osseointegration. A biomimetic coat of solution deposited apatite may not show the disadvantages of coating delamination and particle generation. Biomimetic apatite coatings may be attractive alternatives for noncemented total hip arthroplasty.

Abstract: Hydroxyapatite (HA) coating applied on metallic orthopedic joint implants can improve bone apposition, presumably through selective protein adsorption from blood plasma. However, the detailed interaction mechanism of HA coating with serum proteins remains to be largely elucidated. Protein adsorption behavior of a biomimetic apatite (BAp) coating in bovine calf serum and alpha calf fraction was investigated in this study. Plasma sprayed HA (PSHA) coating was tested in alpha calf fraction. The microstructure and composition of the coatings before and after serum incubation were characterized and the proteins adsorbed during the incubation were extracted from the coatings and analyzed. Microstructural transformation of the BAp coating accompanied by selective serum protein adsorption was observed after incubation in both media. The total protein amount adsorbed by the BAp coating in alpha calf faction was about three times that of the PSHA coating. To test the potential use of BAp coating as a carrier of therapeutic agents, interaction between the BAp coating and transforming growth factor (TGF)-β1 was studied. The growth factor was successfully loaded onto the coating in a sodium acetate buffer. Because of its high affinity to the coating, TGF-β1 could not be easily eluted in a bovine serum albumin containing solution but could be recovered after coating dissolution in acid. The strong protein adsorption property of the BAp coating was found to be due mainly to its unique nanoporous structure. The BAp coating can serve as an ideal carrier of therapeutic agents for aiding in the healing of bone and soft tissues.