Shuxin Qu

TEM study of calcium phosphate precipitation on HA/TCP ceramics

This study focuses on phase identification of precipitation on bioactive calcium phosphate (BCP) surfaces in vitro and in vivo. The BCP used in this study consisted of 70 wt% hydroxyapatite (HA) and 30 wt% beta-tricalcium phosphate. Single crystalline precipitates of calcium phosphates on porous BCP bioceramics obtained after immersion in dynamic simulated body fluid (SBF) and after implantation in pig muscle were examined using electron diffraction in transmission electron microscope. The crystals formed in vitro in dynamic SBF were identified as octacalcium phosphate (OCP), instead of apatite. Most of the precipitated crystals in vivo samples had an HA structure; while OCP and dicalcium phosphate dihydrate were also identified. The evidence from single diffraction patterns indicates that apatite formation on bioactive ceramics is a complicated process, particularly in physiological environments where formation might include a transient stage of intermediate phases.

Silver/hydroxyapatite composite coatings on porous titanium surfaces by sol-gel method.

Hydroxyapatite (HA) coatings loaded with nanosilver particles is an attractive method to impart the HA coating with antibacterial properties. Producing Ag/HA coatings on porous Ti substrates have been an arduous job since commonly used line-of-sight techniques are not able to deposit uniform coatings on the inner pore surfaces of the porous Ti. In this study, porous Ti scaffolds with high porosity and interconnected structures were prepared by polymer impregnating method. A sol-gel process was used to produce uniform Ag/HA composite coatings on the surfaces of porous Ti substrates. Ca(NO(3) )(2) ·4H(2) O and P(2) O(5) in an ethyl alcohol based system was selected to prepare the sol, which ensured the homogeneous distribution of Ag in the sol. The characterization revealed that silver particles uniformly distributed in the coatings without agglomeration. High antibacterial ratio (>95%), against E. coli and S. albus was expressed by the silver-containing coatings (Ag/HA 0.8 and 1.6 wt %). The biocompatibility of the Ag/HA 0.8 surfaces was as good as that of pure HA surface, as revealed by culturing osteoblasts on them. The results indicated that Ag/HA 0.8 had the good balance between the biocompatibility and antibacterial properties of the coatings.

Nano-Ag-loaded hydroxyapatite coatings on titanium surfaces by electrochemical deposition

Hydroxyapatite (HA) coatings on titanium (Ti) substrates have attracted much attention owing to the combination of good mechanical properties of Ti and superior biocompatibility of HA. Incorporating silver (Ag) into HA coatings is an effective method to impart the coatings with antibacterial properties. However, the uniform distribution of Ag is still a challenge and Ag particles in the coatings are easy to agglomerate, which in turn affects the applications of the coatings. In this study, we employed pulsed electrochemical deposition to co-deposit HA and Ag simultaneously, which realized the uniform distribution of Ag particles in the coatings. This method was based on the use of a well-designed electrolyte containing Ag ions, calcium ions and l-cysteine, in which cysteine acted as the coordination agent to stabilize Ag ions. The antibacterial and cell culture tests were used to evaluate the antibacterial properties and biocompatibility of HA/Ag composite coatings, respectively. The results indicated the as-prepared coatings had good antibacterial properties and biocompatibility. However, an appropriate silver content should be chosen to balance the biocompatibility and antibacterial properties. Heat treatments promoted the adhesive strength and enhanced the biocompatibility without sacrificing the antibacterial properties of the HA/Ag coatings. In summary, this study provided an alternative method to prepare bioactive surfaces with bactericidal ability for biomedical devices.

Molecular dynamics simulations on the interaction between polymers and hydroxyapatite with and without coupling agents.

Molecular dynamics (MD) simulations were employed to study hydroxyapatite/biopolymer interface interactions in composites for biomedical applications. The study analyzed the binding energies between hydroxyapatite (HA) and three polymers: polyethylene (PE), polyamide (PA) and polylactic acid (PLA). The interactions of polymers on HA crystallographic planes (001), (100) and (110) were simulated. The effects of the silane coupling agent (A174) on interfacial binding energies were also examined. The results show that HA (110) has the highest binding energy with these polymers because of its higher planar atom density than that of HA (001) and (100). The binding energies of PA/HA and PLA/HA are much higher than that of PE/HA, which might be attributed to large number of polar groups in PA and PLA chains. The silane coupling agent A174 increases the binding energy between PE and HA, but not for the PA/HA and PLA/HA systems. The MD results can be used to guide the design of polymer/HA composites and to select proper coupling agents.

Micro/nanostructural porous surface on titanium and bioactivity.

Porous surfaces can improve both early fixation and long-term stabilization of implants by contrast with smooth surfaces. In this study, a microporous surface on titanium was prepared by acid etching and the size of micropores ranged from 1 to 60 microm. The micro/nanostructural porous layer on this microporous surface was obtained by acid etching and anodization. In this micro/nanostructural porous layer, the diameter of nanotubes was about 100 nm. After heat treatment at 450 degrees C for 6 h, the oxides on micro/nanostructural surface transformed into anatase crystals and the grain size of anatase was about 20 nm. The bioactivity of samples was investigated respectively in simulated body fluid and a bovine serum albumin (BSA) solution. The information of specimen surfaces was detected using scanning electron microscope, X-ray diffractometer, and attenuated total reflection Fourier transform infrared spectroscope. The results showed that the sample with micro/nanostructural porous surface and anatase had excellent bioactivity under nonpretreatment. It had more hydroxyapatite (HA) formation and faster BSA adsorption than other samples under the same conditions. Besides, the HA coating on the micro/nanostructure surface had larger range thickness, no microcrack, and no separated interface from substrate. Therefore, this micro/nanostructural porous surface may be an ideal modification layer for preparing bioactive implants.

Osteogenic responses to extraskeletally implanted synthetic porous calcium phosphate ceramics: an early stage histomorphological study in dogs

In this experiment, synthetic porous calcium phosphate ceramics (hydroxyapatite–tricalcium phosphate) were prepared and implanted in dorsal muscles of dogs. The purpose was to study the biological processes prior to and during the morphogenesis of bone in extraskeletally implanted porous calcium phosphate ceramics. Specimens were harvested after implantation for 7, 15, 30, 45, 60, 90 and 120 days. Decalcified and undecalcified sections were prepared for alkaline phosphatase (ALP) histochemical localization and comparative histological analysis. The results show that bone morphogenesis in the pore regions of the extraskeletally implanted ceramics follows a complex process involving clot formation, vascular invasion, granulation-like tissue formation, polymorphic cell aggregation, osteoblast differentiation and bone formation. The characteristic feature preceding bone formation was polymorphic cell aggregation on the pore inner surface and near the invading capillaries or small venules. These cells were of various sizes and shapes, and some of them were positive for ALP activity. ALP-positive cell aggregates were more numerous where capillaries or venules were close to the pore inner surface. Osteoblast differentiation occurred within the cell clusters aggregated on the pore inner surface and bone matrix was secreted in direct contact with the ceramics. During bone formation, capillaries or small venules were always found close to the developing fronts of the osseous nidi. It is suggested that those cells which first appeared near the invading vasculature, the cells which aggregated on the pore inner surface and those cells which finally differentiated into osteoblasts may be interrelated in some way.

Effects of aqueous environment and surface defects on Arg-Gly-Asp peptide adsorption on titanium oxide surfaces investigated by molecular dynamics simulation.

The interactions between Arg-Gly-Asp (RGD) peptides and titanium oxide (TiO(2) ) surfaces are of considerable interest to medical technological and fundamental researchers. In the present study, a molecular dynamics (MD) simulation was used to study the interfacial interaction between RGD and TiO(2) at an atomistic level. Four important factors affecting RGD adsorption were considered: the initial configuration of the RGD, the crystal structure of the TiO(2) materials, the presence of surface defects, and a water environment. Three types of RGD initial configurations were considered: lying and standing on the N or O end. First, RGD adsorptions on ideal rutile (110) and anatase (101) surfaces in a vacuum and in a water environment were studied; then the step edge effects were considered, and, finally, the synergistic effects of water and surface defects on RGD adsorption were investigated. The results from the vacuum indicated that the crystal structure of the surface was more important than the initial RGD configuration. The interaction between RGD and the anatase (101) surface was stronger than that between RGD and the rutile (110) surface according the energy analysis. Atomic step edges on TiO(2) surfaces could greatly affect the adsorption of the RGD peptide. Water limited the interaction between the RGD peptide and the TiO(2) substrate and helped to sustain the initial configuration of the former. These findings should be helpful in understanding the RGD-TiO(2) interaction mechanisms and should provide useful theoretical guidelines for titanium surface treatments in orthopedic applications.

Evaluation of the expression of collagen type I in porous calcium phosphate ceramics implanted in an extra-osseous site.

The aim of the present study is to demonstrate the newly formed tissue in calcium phosphate (Ca/P) ceramics after extra-osseous implantation by histological and immunohistochemistry (IHC) methods. Synthesis porous Ca/P ceramics without adding any growth factor and living cell were implanted in the dorsal muscle of dogs for 1 and 2 months. Undecalcified and decalcified sections were stained by hematoxylin and eosin (H&E), and IHC, respectively. The histological results showed the beginning of osteogenesis and angiogenesis after being implanted for 1 month and the obvious new bone formation after being implanted for 2 months. IHC were conducted via the avidin-biotin peroxidase complex (ABC) method and the primary antibody was collagen type I. IHC results indicated that collagen type I was expressed within osteoblast-like cells and newly formed bone-like tissue in Ca/P ceramics after 1 month, and in the mineralized matrix of newly formed bone and osteoblasts, some osteocytes and some lacunae after 2 months. No cartilage and chondrocytes were observed in the histological and IHC-stained sections. Evidence of intramembranous osteogenesis was confirmed.

A novel porous bioceramics scaffold by accumulating hydroxyapatite spherulites for large bone tissue engineering in vivo. II. Construct large volume of bone grafts.

In vivo engineering of bone autografts using bioceramic scaffolds with appropriate porous structures is a potential approach to prepare autologous bone grafts for the repair of critical-sized bone defects. This study investigated the evolutionary process of osteogenesis, angiogenesis, and compressive strength of bioceramic scaffolds implanted in two non-osseous sites of dogs: the abdominal cavity and the dorsal muscle. Hydroxyapatite (HA) sphere-accumulated scaffolds with controlled porous structures were prepared and placed in the two sites for up to 6 months. Analyses of retrieved scaffolds found that osteogenesis and angiogenesis were faster in scaffolds implanted in dorsal muscles compared with those placed in abdominal cavities. The abdominal cavity, however, can accommodate larger bone grafts with designed shape. Analyses of scaffolds implanted in abdominal cavities [an environment of a low mesenchymal stem cell (MSC) density] further demonstrated that angiogenesis play critical roles during osteogenesis in the scaffolds, presumably by supplying progenitor cells and/or MSCs as seed cells. This study also examined the relationship between the volume of bone grafts and the physiological environment of in vivo bioreactor. These results provide basic information for the selection of appropriate implanting sites and culture time required to engineer autologous bone grafts for the clinical bone defect repair. Based on these positive results, a pilot study has applied the grafts constructed in canine abdominal cavity to repair segmental bone defect in load-bearing sites (limbs).

The effects of hydroxyl groups on Ca adsorption on rutile surfaces: a first-principles study

Hydroxyl groups on titanium surfaces have been believed to play an important role in absorbing Ca in solution, which is crucial in the formation of bioactive calcium phosphates both in vitro and in vivo. CASTEP, a first-principles density functional theory (DFT) code, was employed to investigate Ca adsorption on various rutile (110) surfaces in order to clarify how hydroxyl groups effect Ca adsorption. The surfaces modeled in the present study include a bare rutile (110) surface, a hydroxylated rutile (110) surface, an oxidized rutile (110) surface, and a rutile (110) surface bonded with mixed OH groups and water. The results reveal that not all OH groups favors to attract Ca adsorption and loosely bonded OH and water on a rutile surface actually combine with Ca during adsorption. An oxidized rutile surface has the highest ability to attract Ca atoms, which partially explains that alkali-treated Ti surfaces could induce hydroxyapatite formation in alkaline environments.