Yao Wu

Hydroxyapatite coatings deposited by liquid precursor plasma spraying: controlled dense and porous microstructures and osteoblastic cell responses

Hydroxyapatite coatings were deposited on Ti-6Al-4V substrates by a novel plasma spraying process, the liquid precursor plasma spraying (LPPS) process. X-ray diffraction results showed that the coatings obtained by the LPPS process were mainly composed of hydroxyapatite. The LPPS process also showed excellent control on the coating microstructure, and both nearly fully dense and highly porous hydroxyapatite coatings were obtained by simply adjusting the solid content of the hydroxyapatite liquid precursor. Scanning electron microscope observations indicated that the porous hydroxyapatite coatings had pore size in the range of 10-200 µm and an average porosity of 48.26 ± 0.10%. The osteoblastic cell responses to the dense and porous hydroxyapatite coatings were evaluated with human osteoblastic cell MG-63, in respect of the cell morphology, proliferation and differentiation, with the hydroxyapatite coatings deposited by the atmospheric plasma spraying (APS) process as control. The cell experiment results indicated that the heat-treated LPPS coatings with a porous structure showed the best cell proliferation and differentiation among all the hydroxyapatite coatings. Our results suggest that the LPPS process is a promising plasma spraying technique for fabricating hydroxyapatite coatings with a controllable microstructure, which has great potential in bone repair and replacement applications.

The Influence of Bovine Serum Albumin on the Biomimetic Calcium Phosphate Coating of Bioactivated Titanium

In this study, bovine serum albumin protein (BSA) was introduced to investigate the co-precipitation process of calcium phosphate and BSA on bioactivated Ti. Commercially pure titanium were bioactivated firstly, and then immersed in a highly supersaturated stable calcium phosphate (Ca-P) solution at three different conditions. The samples designated as Ti-C, Ti-C-CB, and Ti-C-B for control. The samples were evaluated by SEM with EDX, XRD and XPS. The co-precipitation of BSA protein and Ca-P influenced the morphology of the crystals of Ti-C-CB significantly. In terms of the immersion in the Ca-P solution containing BSA, the co-precipitation of Ca-P with BSA on the surface of Ti-C-CB was a chemical process rather than simple physical adsorption, which was most possibly achieved by the linkage of –COO− groups to Ca-P. Such coprecipitated interaction led to the formation of a tight, dense and uniform Ca-P coating.

Tissue Responses to Titanium with Different Surface Characteristics after Subcutaneously Implanted in Rabbits

The objective of this study was to investigate the soft tissue responses to titanium with different surface characteristics. Titanium bars with three kinds of surface were available to be anchored in the femur bone of rabbits and then penetrated into the soft t issue just under the skin: hydroxyapatite (HA) coated Ti, anode-oxidized Ti and sandblasted Ti a s control. After 4 weeks and 8 weeks, the implants with surrounding soft tissue were retrieved a nd processed mechanically and histologically. All samples were encapsulated with quite thin f ibrous capsules and little inflammatory reaction was observed except the sandblasted bars. At 4 weeks postoperation, the histological reaction and the attachment strength of the anode oxidi zed group was similar to the HA coated group. But at 8 weeks postoperation, the histological response arou nd the HA coated group was better than at the anode oxidized group and the attachment stren g h was almost three times more. The sandblasted bars attached the soft tissue so weakly that it was too difficult to test the push-out strength. The SEM-EDX micrographs showed that a layer of calcium phosphate emerged at the interfaces between soft tissue and implants except sandbl aste Ti, so we can infer that the layer of calcium phosphate plays a very important role in impr oving the soft tissue integration with the titanium. Introduction For percutaneous devices (PD) anchored in bone, the major failure mod s are marsupialization and infection, which are resulted from skin downgrowth and mechanical dam age [1]. In order to avoid these phenomena occurring, the implant’s surface could be bioactivated to facilitate its firm attachment and bonding with the soft tissue under the skin, which is one of th main methods to inhibit the epithelial downgrowth. [2,3] Titanium and titanium alloys a re increasingly being used as PD implants as a result of their excellent bulk properties and bi ocompatibility. [3,4] But up to now, there are few reports available concerning soft tissue response s to the bioactivated surface of Ti. In this paper, three kinds of titanium bars with different surfaces cha ra teristics were subcutaneously implanted in rabbits to study their soft tissue responses, including the attachment strength of implant-tissue interface. Materials and Methods Commercially pure titanium was cut into cylinder bars 3 x12mm. Half part of the bar along the long axis was screwed and the other part was modified with two di fferent bioactivation methods or sandblasted. The first group of bars, defined as HAC group, was plasma sprayed with Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 725-728 doi:10.4028/www.scientific.net/KEM.254-256.725

Apatite Formation on Porous HA/TCP in Animals’ Serums In Vitro

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.

In Vivo Evaluation of Nano-HA/PDLLA Composite

The purpose of this study was to evaluate the behavior of nano-hydroxyapatite/ poly(D,L)lactide (n-HA/PDLLA) composite in vivo. The composite rods containing about 40wt% n-HA and control HA rods with a diameter of 2mm and a length of 6mm were implanted into the femora of 16 New Zealand rabbits. Composite wafers with a diameter of 5mm and a thickness of 1mm were implanted into the dorsal subcutis of 18 Wistar Albino rats. After definite intervals, the histological analysis was completed by light microscopy and the degradation behavior was observed by scanning electron microscopy. The histological analysis showed no obvious difference between n-HA /PDLLA composite and pure HA that had good biocompatibility and osteoconductivity. SEM analysis of the surface and cross section of the samples showed that the degradation of the composite started from surface, then into the inner gradually and formed multiple pores at surface. The pore size and porosity gradually increased along with time and a porous network may be formed.

The Effect of Bovine Serum Albumin on the Crystalline Characteristics of the CaP Biomimetic Coating

It is very necessary to develop a real biomimetic compound coating of CaP with organic component and investigate quantitatively the effects of different bovine serum albumin (BSA) concentration on the crystallite properties of the coprecipitated CaP layer. Bioactivated Ti was immersed in Ca-P solution with different BSA contents to obtain different biomimetic coating. The coatings were analyzed with scanning electron microscopy (SEM) and X-ray diffraction (XRD). With the increase of BSA, the crystals on the coating grew more slowly but packed more closely. The preferential crystallographic direction of 002 of hydroxyapatite became less distinguishable and the crystallinity of the deposited hydroxyapatite decreased gradually. The crystallite sizes reduced with the addition of BSA proteins. Accordingly, when a certain content of BSA protein was added to the Ca-P solution, Ti surface would form a real biomimetic coating with the crystal size and crystallinity similar to the natural bone.

In Vivo and In Vitro Studies on the Bioactivity of Anodic Oxidized Titanium Metal

In this study, the bioactivity of a new kind of anodic oxidized titanium metal was investigated in vitro and in vivo. After immersed in SBF solution for 7 days in vitro, apatite formed and covered almost all the surfaces of the anodic oxidized samples. In vivo animal experiment, the apatite was also tested precipitated on the interface of tissue/materials after 12 weeks post-operation, and there were no any fibrous capsule formed around the materials. The materials bonded with the bone very tightly and attached to the skin very closely, which would result in the achievement of the biological sealing for the bone-anchored percutaneous implants. These positive results might be contributed to the precipitated apatite layer formed on the surface of the bioactive oxidized titanium. Thus, Anodic oxidation treatment might be an effective way to prepare bioactive Ti both for bone replacement and percutaneous implant.

Preparation of Bioactive Nanophase Titania Ceramics by Alkali-Heat Treatment

In this study, alkali-heat treatment in NaOH solution and heat treatment, which could form amorphous sodium titanate on nanophase titania ceramics surface by conditioning the process, was employed to modify the structure and bioactivity of biomedical titania ceramics. After the nanophase titania ceramics was subjected to alkali-heat treatment, thin film X-ray diffraction and scanning electron microscopy results showed the titania ceramics surfaces were covered by porous sodium titanate. In fast calacification solution (FCS), the alkali-heat treated titania ceramics could induce bonelike apatite formation on its surface. Our results showed that induction of apatite-forming ability on titania ceramics could be attained by alkali-heat treatment. So it was an effective way to prepare bioactive titania ceramics by combining sintering and alkali-heat treatment.

The Study of Human Epithelium Cell Attachment to the Surface of Anode-Oxidized Titanium

The achievement of biological sealing is determined by the quality of the skin attachment on the surface of the percutaneous implant in the area where the implant penetrates the skin. It has been known that certain surface features of the implants can significantly influence the interactions between cells and substrate. In this study, titanium plates were bioactivated through anode-oxidization firstly, and then cultured with human epithelium cells for 72h. Untreated Ti plates were used as control. After the samples were dehydrated, the morphology of the cultured epithelium cells was tested with Scanning electron microscopy (SEM). The surfaces of control group did not enhance epithelium cell attachment and growth, while the bioactivated microporous surface of anode-oxidized group would be beneficial to induce the formation of the pseudopod of epithelium cell, and then interlock the human epithelium cells through the pseudopod, which imply that the surface modification method of anode oxidization may be one of the most effective methods to resolve the biological sealing.

Improvement and FEA of New Type of Osteointegrated Implant for Higher Amputated Leg Attachment

Stress concentration is one of the main mechanical problems leading to the failure of clinical application for osteointegrated implant of percutaneous osteointegrated prosthesis, which is especially marked for higher amputated leg prosthesis. Traditionally design was composed of only the distal part. To improve the biomechanical safety, a new design with the lag part similar to the lag screw was introduced. Based on CT scan data, relatively accurate model of femur for finite element analysis (FEA) were obtained. The FEA results with the new implant demonstrated that compared to traditional design, the declination of bone stress peak ranged from 15.68% to 28.67%, perpendicular deformation from 34.73% to 72.16%, and maximal stress of implant from 14.51% to 23.36% with the increasing of loads from 3750N to 2000N. So the new design of osteointegrated implant would be more secure mechanically, in the case of higher amputated leg attachment.