Papers by Author: Xing Dong Zhang

Abstract: 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.

Abstract: Synthesis of hydroxyapatite (HA) in organic solutions has received extensive attention in recent years with an attempt to obtain HA of a nanometer level. In this preliminary study, we demonstrated that organic-HA nanocomposites could also be achieved with one step method via in situ mineralization and subsequent crosslinking of organic species. This design was realized through in situ synthesis of hydroxyapatite in poly(vinyl alcohol) and acrylic acid aqueous solution as an organic template. The aforementioned organic-inorganic nanocomposites were analyzed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electrical microscopy, thermal analysis. The comparative structural measurements were also conducted with the synthesized HA with absence of the organic template. The results indicated that the existence of organic species effectively inhibits the growth of calcium phosphate and that relatively pure HA can be obtained in sintered composite products. The present study provides a direct and versatile route for fabrication of nanocomposite biomaterials.

Abstract: In order to develop a bone-filling material with osteoinductive potential, a composite micorspheres of collagen molecules and biphasic calcium phosphate (BCP) was prepared by utilizing emulsion polymerization and the intrinsic self-assembly of collagen. The prepared microspheres were analyzed by granularity test, scanning electron microscopy (SEM), infrared spectra (IR) and enzymatic digestion experiment. The results showed that the collagen matrix of fibrils was reconstituted in the droplets, and the native triple-helix structure of collagen was still maintained. The study provides an effective way to prepare microspheres of collagen and BCP composite.

Abstract: Collagen (Col) and chitosan (Chi) are both natural polymers and have received extensive investigation in recent years in the field of tissue engineering, but there are few reports on the introduction of hydroxyapatite (HA) into the Col-Ch system. In this study, based on the miscibility of these two polymers under proper condition, hydroxyapatite (HA) was synthesis in the Col-Chi system by in-situ co-precipitate method to give rise to a novel nanocomposite. The structural characterization of such Col-Ch-HA nano-materials was carried out by using FT-IR, XRD, SEM and TGA analyses with main components and Col-Chi samples used for comparison. It was found that there exist interactions between Col and Chi molecules. The nucleation and growth of inorganic phase occurs in the Col-Chi system and final products are uniform dispersion of nano-sized HA in the Col-Chi network without obvious phase separation. This novel nanocomposite would be a promising material for bone tissue engineering.

Abstract: In order to prepare nano-hydroxyapatite/poly(lactide) (n-HA/PLA) composite with good interfacial interaction, some groups which could bind with Ca ions in HA crystals need to be introduced onto PLA surface. Poly(α-methacrylic acid) (PMAA) was grafted on the PLA surfaces via photooxidization and subsequent UV induced polymerization. Suspension of PMAA-PLA microparticles with an average size as 133.1nm was prepared with solvent evaporation technique. Then utilizing the action of template manipulating of PMAA-PLA microparticles, n-HA/PLA composite were synthesized. Zeta potentials measurement and SEM indicated that there were good interfacial interactions between two phases of n-HA/PLA composite. The results of cell viability confirmed that n-HA/PLA composite possessed good cytocompatibility, so the n-HA/PLA composite scaffold obtained by electrospun technology might be used as bone tissue engineering scaffold.

Abstract: Hydroxyapatite/collagen composites were prepared in-situ synthesis. The composites were finally achieved by dehydration including air-drying and freeze-drying methods. FTIR, XPS and DSC were employed to investigate the composites dehydrated by two methods. The air-dried composites had better mechanical properties than those of the composites dried by freeze drying. Air-drying of the composite induced more bond formation and crosslink between collagen fibers and HA crystals compared with freeze-drying of the composite, as indicated by the shifting of amide A and I bands to the lower wavenumber and by the changes in the binding energy of O1s, Ca2p, and P2p, leading to the increase of the peak temperature of the composites. Collagen crosslink and bond formation in the air-dried composites were key factors to increase the bending strength of the composites. The results of this study confirm that in situ synthesis and air-dry method are effective ways to obtain nanoHA/COL composites with high mechanical properties.

Abstract: In this study, three kinds of photo-reactive polymers, namely positively charged azidophenyl-derived polyallylamine (AzPhPAAm), negatively charged azidophenyl-derived poly(acrylic acid) (AzPhPAAc) and neutral azidophenyl-derived poly(ethylene glycol) (AzPhPEG), were synthesized by introduction of photo-reactive group (-N3) into polyallylamine, poly(acrylic acid) and poly(ethylene glycol), respectively. The structure of the azidophenyl-derived polymers was confirmed by 1H-NMR measurement. All of the photo-reactive polymers can be pattern-grafted on the surface of cells culture plate, which was confirmed by the optical microscopy observation. The contact angle decreased after surface modification by the photo-reactive polymers. Human mesenchymal stem cells (MSC) cultured on the modified surfaces showed different morphology. The cells adhered and spread more on the PAAm- and PAAc-grafted surfaces than on the PEG-grafted surface. The pellets formed on PAAm- and PEG-grafted surfaces in condrogenic differentiation medium were positively stained by safranin O/ fast green. But the pellet formed on PAAc-grafted surface did not show obviously positive staining for safranin O/ fast green. These results indicate that the PAAm- and PEG-grafted surfaces promoted chondrogenic differentiation of MSC.

Abstract: Poly(vinyl alcohol) (PVA) was introduced during in situ synthesis of hydroxyapatite (HA) in neutral collagen (COL) solution and final PVA-COL-HA nanohybrids were achieved via sequential steps including gelation by fibrillogenesis, freezing-thawing physical crosslinking, removal of unreacted residues and dehydration. This method is expected to endow the pure PVA with good bioactivity and meanwhile the presence of elastic PVA would improve the properties of COL-HA composites. The phase, microstructure and possible molecular interactions of the achieved PVA-COL-HA nanohybrids were analyzed by using X-ray diffraction, Fourier transform infra-red spectroscopy and scanning electron microscopy. The results indicate that the inorganic phase is poorly crystallized apatite with a nanometer size due to the confinement of organic macromolecules which forms a network structure.

Abstract: The purpose of this study was to explore the feasibility of repairing massive bone defect with in vivo tissue engineering(TE) bone, and to provide experimental evidence for the application of in vivo TE bone into clinic in the future. Six calcium phosphate ceramics (Ca-P ceramics) columns were prepared, and then immersed in dynamic revised simulated body fluid (RSBF). 72 hours later, the bone-like apatite was formed on the surface and pore walls of ceramics. Three dogs were used in this study. Two ceramic columns were implanted bilaterally in the femoral muscles of each dog to construct living bone graft of in vivo TE bone. 6 weeks after implantation, they were transplanted to the box-like bone defects sites created in bilateral mandible of the same animals. The dogs were sacrificed at 8, 12 week after operation respectively. Samples were harvested for gross observation, X-ray examination, tetracycline fluorescence labeling, SPECT and histological observation. These results demonstrated that as a living bone graft, in vivo TE bone participated in the bone metabolism of host, and integrated with the host bone. It is feasible to reconstruct box-like bone defect of mandible with the in vivo TE bone.

Abstract: In order to solve the problems on synthesizing carbonated hydroxyapatites (CHA) by the conventional heating precipitation method, such as long reaction and large particle size, poor crystallinity of CHA etc, the nanosized CHA particles have been synthesized by microwave heating method using phosphoric acid (H3PO4), calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3 ) as starting materials in the present paper. The influences of power level and time of microwave irradiation on synthesis of CHA have been investigated. The X-ray diffraction (XRD) analysis has indicated that microwave heating will reduce CHA crystallization time and improve crystallinity of CHA. Scanning electron microscope (SEM) analysis has showed that CHA particles are of rod like morphology with about 60nm width and 200nm length respectively. Infrared spectroscopy (IR) analysis has confirmed the B-type CHA precipitate can be formed under microwave irradiation. The microwave irradiation plays an important role to promote the reaction and the synthesis of nanosized CHA particles.