Yu Mei Xiao

Preparation and Characterization of Nano Hydroxyapatite

The aim of this study is to prepare nano hydroxyapatite powder. Hydroxyapatite powder was prepared via co-precipitated method with the addition of citric acid at pH 9-11 in ambient environment. The precipitates were aged for 24hs, and then milled into powder after washed and dried. The particle morphology and particle size of as prepared HA powders were characterized. The results showed that hydroxyapatite powder with width of 10-30nm and length of 30-100nm was prepared by wet co-precipitation.

Fabrication of Porous Hydroxyapatite Ceramics by Microwave Sintering Method

Microwave processing of porous hydroxyapatite ceramics was investigated in a dual frequency microwave-sintering furnace. The results revealed that microwave-sintering process could get sintered ceramics at much shorter sintering time and at lower sintering temperature than that of the conventionally heat-sintering process. Further, the microwave-sintered samples showed much smaller grain size and more uniform microstructure and reached a comparable compressive strength. The mechanism of rapid heating behavior of hydroxyapatite ceramics in microwave was also discussed. The results revealed that microwave processing was a promising method for sintering porous hydroxyapatite ceramics.

Preparation and Cytocompatibility of Novel Nano-HA/PLA Composite

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.

A New Way to Prepare Porous Polylactide /Hydroxyapatite Scaffold at Room Temperature

A new way to prepare polymer/hydroxyapatite(HA) composite scaffolds with 3-D interconnected macro and micro pores at room temperature was established, basically based on solvent-casting and particle-leaching together with foaming technique. With this method, Polylactide (PLA) / HA composites of porous architecture with macro pores (50~300)m, average 200)m) and micro pores (~10)m) on the skeleton were obtained. The bending strength and the compressive strength of the composite scaffold were reached to 11.5 MPa and 7MPa respectively with the porosity of approximate to 90%. The study supplied a new short time, low energyexpending method to prepare polymer/ceramic composite with high porosity and interconnected porous structure at room temperature.

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.

A Novel Preparation Method for Nano-HA/PLA Composite with Grafted PLA

Good interfacial interaction is crucial for preparation of inorganic-organic materials at a nanometer level. Poly(α-methacrylic acid) (PMAA) was grafted on the PLA surfaces via photooxidization and subsequent UV induced polymerization in an attempt to synthesize nano-hydroxyapatite/poly(lactide) (n-HA/PLA) composites. Grafting of PMAA on the PLA surface was confirmed using FTIR analysis and the size distribution measurement of the grafted-PLA (g-PLA) particles. n-HA/g-PLA composites were in situ synthesized via dropwise addition of Ca2+- and g-PLA containing solution to PO4 3-- solution. The prepared composites were characterized by FTIR, XRD，SEM and TEM means. Analytical results indicated that the g-PLA acts as a template to manipulate the nucleation and growth of n-HA crystals and thereby to control the morphology, size and anisotropy of n-HA crystals and their distribution over the organic phase. Chemical linkages and/or interfacial interactions between the n-HA and the g-PLA in the n-HA/g-PLA composite were further discussed.

A Novel Way to Prepare Nano-Hydroxyapatite/Poly(D,L-Lactide) Composite

A composite of needle-like nano-hydroxyapatite (n-HA)/poly (D,L) lactide (PDLLA) was prepared. The n-HA crystals were poorly crystallized and uniformly distributed in the composite with a crystal size of 10–20 nm in diameter by 40–60nm in length，which was smaller than that of pure nano-HA. Molecular interactions and chemical bonds might present between n-HA and PDLLA in the composite, which were revealed by IR and XPS. The synthetic n-HA/PDLLA composite had a good homogeneity and could be a bioactive material for bone defect especially for load-bearing bone repair, which is more potential than pure HA or pure PDLLA.

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.

Improvement of Bioactivity of Collagen/Alginate Scaffolds by Hydroxyapatite for Tissue Engineering Cartilage

With good biocompatibility, collagen is often used in cartilage tissue engineering. Collagen/alginate composite was hoped to improve the poor mechanical property of pure collagen but the biocompatibity was decreased. In this study, hydroxyapatite (HA) particles were used to get collagen/alginate/HA (CAHA) composite film to enhance the bioactivity properties. The bioactivity of the composite was investigated by in vitro co-culture with chondrocytes. During the 6-day cell culture in vitro, the composite showed a significant improvement in promoting proliferation and maintaining morphology/phenotype of the chondrocytes over collagen/alginate composite by MTT, SEM, fluorescent and immunohistochemical assays. Cytocompatibility and cytoviablility of CAHA even come up to that of collagen film alone. The results indicated that the composite film may provide an appropriate environment for the proliferation and maintaining the morphology and phenotype of chondrocytes and have a potential clinical application in the cartilage tissue engineering field.

Effect of Solvent on Porous PLA/HA Scaffolds Preparation Using Novel Solid H2O2 Porogen

Hydroxyapatite/polymer scaffolds with proper biomechanical properties and stable 3-D porous structure were fabricated by combining gas foaming with solvent-casting/particle-leaching technique, in which novel solid H2O2 were used as a porogen. During the manufacturing process, we found that the porosity, compressive strength and microstructure of the composites are varied from each other while different solvents (dichloromethane, acetone, chloroform and 1,4-dioxane) were used. Porosities of the specimens increase from 72±5 to 87±5% in accordance with the increase of boiling point from 39.75 to 101.32 °C, while compressive strength decreased (4.8±0.7- 0.5±0.3 MPa). Interactions of HA/solvent and PLA/solvent together with evaporation dynamic tests of different solvents were investigated. The results show that the evaporation rate of the solvents is the most important factor affecting the final properties of the scaffolds.