Xiaoyi Chen

A new approach for toughening of ceramics

Abstract A new approach for the toughening of ceramics was proposed and investigated, in which a piezoelectric secondary phase was incorporated into the ceramic matrix as toughening phase, and energy dissipation by the piezoelectric effect was suggested as a new toughening mechanism. In a BaTiO3 toughened Al2O3 system, fracture toughness was significantly enhanced, and KIC reached 5.1 MPa m 1 2 for a composition of 0.05BaTiO3/0.95Al2O3.

Trace element-incorporating octacalcium phosphate porous beads via polypeptide-assisted nanocrystal self-assembly for potential applications in osteogenesis.

The promising future of calcium phosphates (CaP) as a group of biomedical materials with a wide range of functions, might ultimately depend on tuning their composition and microstructure. However, the disorderly growth and aggregation of CaP nanocrystals limit their practical application. This paper reports a strategy for designing polypeptide/trace elements (TE), dual mediating the self-assembly of octacalcium phosphate (OCP) nanocrystals, with multilayered porous cross section and TE dilute doping. Intriguing advantages such as bead morphology, mesoporous structure, tunable diameter (20-1,000 μm) and TE contents, biodegradability and bioactivity are obtained. The microcomputerized-tomography reconstruction reveals an interconnective macroporous architecture and a void volume of over 49.02% for the nearly close-packed bead scaffolds. The specific surface area and average mesopore size are 89.73 m(2)g(-1) and 2.75 nm for the 180 μm diameter bead group, and those of 500 μm diameter beads are 130.17 m(2)g(-1) and 3.69 nm, respectively. It is demonstrated that the bead production mechanism is a multistep process including liquid-like precursor formation, nanocrystal nucleation and aggregation, aggregate combination and bead growth. Such a multilayer structure of TE-OCP porous beads would have adequate physical strength to maintain their shape, in contrast to the physical weakness of pure OCP hollow shell. The beads exhibit good biocompatibility and degradability and encourage bone mineralization in the early stage in vivo. This study demonstrates the feasibility of developing highly porous calcium phosphate giant beads via biomimetic self-assembly for direct application in reconstructive surgery and other widespread applications such as tissue engineering and drug delivery.

Chitosan-modified, collagen-based biomimetic nanofibrous membranes as selective cell adhering wound dressings in the treatment of chemically burned corneas

Corneal chemical injury is a general but intractable ocular emergency, the sequelae of which are particularly challenging to treat. Human amniotic membrane (HAM) is one of the resources as a wound dressing for damaged corneal reconstruction, but the concerns related to the possible transmission of infectious diseases are the main drawbacks. Here we present a versatile method utilizing electrospinning and surface modification processes to develop optically highly transparent, microstructurally stable (>20 MPa in tensile strength in the wet state) biomimetic nanofibrous membranes. These membrane nanofibers, mainly consisting of a collagen-hyaluronate interior and a chitosan surface coating, showed superior mechanical and biological performances compared to HAM, and were favorable to the selective adhesion of epithelial cells (corneal, conjunctival) and fibroblasts. The alkali-burned corneal damage model in rats demonstrated that the biomimetic membranes could markedly improve re-epithelialization in corneal tissue within one week. Therefore, such bioactive multifunctional membranes may find widespread biomedical applications in wound healing and postoperative anti-adhesion in the near future.

The effect of five probiotic lactobacilli strains on the growth and biofilm formation of Streptococcus mutans

OBJECTIVE To compare the effects of five probiotic lactobacilli strains on the growth and biofilm formation of Streptococcus mutans (MS). MATERIALS AND METHODS Five probiotic lactobacilli bacteria (LB), Lactobacillus casei Shirota, Lactobacillus casei LC01, Lactobacillus plantarum ST-III, Lactobacillus paracasei Lpc-37, and Lactobacillus rhamnosus HN001, were used as test strains effecting on the Streptococci strain S. mutans UA159 in this study. The effect of LB strains and their supernatants on the viability of the MS was evaluated. Then, the effect of LB strains on the growth of MS biofilm formation was observed by fluorescence microscope. RESULTS All of the LB strains inhibited the growth of MS at concentrations of 1 × 10(8) and 3 × 10(8) CFU ml(-1) (P < 0.05). Untreated (without pH adjustment and ultrafiltration) LB supernatants from all of the LB strains inhibited the growth of MS (P < 0.05) as well. After pH adjustment and ultrafiltration (treated), only supernatants from L. casei Shirota and L. rhamnosus HN001 inhibited the growth of MS (P < 0.05). MS biofilm formation was also inhibited by all untreated supernatants and by the treated supernatants of L. casei Shirota and L. rhamnosus HN001 (P < 0.05). CONCLUSION All five probiotic lactobacilli strains inhibited the growth and biofilm formation of MS, likely through the production of an acid environment, bacteriocin-like poly peptides, or both, and the effects on MS were dependent on the LB strains used.

Enhancing in vitro bioactivity and in vivo osteogenesis of organic–inorganic nanofibrous biocomposites with novel bioceramics

Fabricating bioactive nanofibrous scaffolds from biodegradable polymers to mimic native tissue is an important approach in repairing bony defects. Silk fibroin (SF) may contribute to bone regeneration because of its excellent mechanical properties, slow degradability, and low osteoconductivity. A combination of bioceramic-polymer materials is generally used to provide an improved osteoconductive environment for bone healing. This study attempts developing for the first time an electrospun SF-based biocomposite system by introducing new bioceramics based on mesoporous bioactive glass/hydroxyapatite nanocomposite (MGHA). The addition of MGHA into the SF matrix could regulate the physicochemical properties and surface hydrophilicity, but induce weakened tensile properties as compared to pure SF. The excellent apatite-formation ability of a MGHA-introduced nanocomposite also improved the bioactivity of the composite. The biphasic composite increasingly degraded in PBS or enzyme solution in vitro compared with pure SF. In vivo evaluation of bone formation confirmed that SF/MGHA is more advantageous in bone reconstruction than the SF group for cranial bone defects. These results indicate the suitability of the SF/MGHA composite system in bone defects, demonstrating its potential application in bone tissue regeneration.

Bioactive glasses-incorporated, core-shell-structured polypeptide/polysaccharide nanofibrous hydrogels.

Although the synthetic hydrogel materials capable of accelerating wound healing are being developed at a rapid pace, achieving inorganic-organic hybrid at nanoscale dimension in nanofibrous hydrogels is still a great challenge because of its notorious brittleness and microstructural stability in wet state. Here, we developed a new nanofibrous gelatin/bioactive glass (NF-GEL/BG) composite hydrogel by phase separation method and followed by arming the nanofibers network with counterionic chitosan-hyaluronic acid pairs for improving microstructural and thermal integrity. We achieve this feature by carrying an optimal balance of charges that allows the inorganic ion release in aqueous solution without minimal structure collapse. Therefore, such NF-GEL-based, polysaccharide-crosslinked bioactive hydrogel could afford a close biomimicry to the fibrous nanostructure and constituents of the hierarchically organized natural soft tissues to facilitate chronic, nonhealing wound treatment.

Dielectric ceramics with TiO2 rich compositions in Bi2O3-TiO2 system

Abstract Dielectric ceramics with TiO 2 rich compositions in the system of Bi 2 O 3 ·TiO 2 were investigated in order to reduce the temperature coefficient of TiO 2 . It was observed that τ e became opposite in the composition of Bi 2 O 3 ·2TiO 2 while e r was near 120 and almost frequency independent. Bi 4 Ti 3 O 12 phase was observed in Bi 2 O 3 ·2TiO 2 and it played an important role in modifying the temperature coefficient of dielectric constant of TiO 2 based ceramics.

The Production and Comparative Evaluation of Native and Recombinant Antigens for the Fast Serodiagnosis of Cystic Echinococcosis with Dot Immunogold Filtration Assay

Clinical diagnosis and post‐surgery assessment of cystic echinococcosis depend on laboratory serodiagnosis and ultrasound examinations. This study aims to produce the recombinant antigen (rAgB) and compare its diagnostic effect with natural antigens (crude fluid antigen, protoscolex antigen). After rAgB, crude fluid antigen, protoscolex antigen were produced, and the diagnostic accuracy was evaluated with dot immunogold filtration assay (DIGFA) by the sera from the following groups: surgically confirmed cystic echinococcosis patients (n = 113), alveolar echinococcosis patients (n = 46), other parasitic diseases (n = 49), nonparasitic hepatic diseases (n = 63) and healthy people (n = 121). In diagnosing cystic echinococcosis, the sensitivity of recombinant AgB was 77·9% and the specificity was 98·3%. The crude fluid antigen B showed a sensitivity of 92·9% and specificity of 81·0%. The protoscolex antigen had sensitivity of 87·6% and specificity of 90·9%. The recombinant AgB indicates the advantage of no cross‐reaction with other parasite diseases or nonparasite hepatic diseases. Recombinant antigen B can improve the specificity but decrease the sensitivity. The combination of native and recombinant antigens will improve the overall performance of serodiagnosis of cystic echinococcosis.

Hybrid calcium phosphate coatings with the addition of trace elements and polyaspartic acid by a low-thermal process

Research in the field of orthopedic implantology is currently focused on developing methodologies to potentiate osseointegration and to expedite the reestablishment of full functionality. We have developed a simple biomimetic approach for preparing trace elements-codoped calcium phosphate (teCaP) coatings on a titanium substrate. The reaction proceeded via low-thermal incubation in trace elements (TEs)-added simulated body fluid (teSBF) at 90 and 120 °C. The x-ray photoelectron spectroscopy, x-ray diffraction and energy-dispersive x-ray analyses demonstrated that the teCaP coating was the composite of hydroxyapatite and whitlockite, simultaneously doped with magnesium, strontium, zinc and silicon. The addition of polyaspartic acid and TEs into SBF significantly densified the coating. The incubation temperature is another important factor controlling the coating precipitation rate and bonding strength. An incubation temperature of 120 °C could accelerate the coating precipitation and improve the interface bonding strength. The in vitro cell culture investigation indicated that the teCaP coating supported the adhesion and spreading of ovariectomized rat mesenchymal stem cells (rMSCs) and particularly, promoted rMSCs proliferation compared to the CaP coating prepared in SBF. Collectively, from such a biomimetic route there potentially arises a general procedure to prepare a wide range of bioactive teCaP coatings of different composition for osteoporotic osteogenic cells activation response.

3D printing of Mg-substituted wollastonite reinforcing diopside porous bioceramics with enhanced mechanical and biological performances

Mechanical strength and its long-term stability of bioceramic scaffolds is still a problem to treat the osteonecrosis of the femoral head. Considering the long-term stability of diopside (DIO) ceramic but poor mechanical strength, we developed the DIO-based porous bioceramic composites via dilute magnesium substituted wollastonite reinforcing and three-dimensional (3D) printing. The experimental results showed that the secondary phase (i.e. 10% magnesium substituting calcium silicate; CSM10) could readily improve the sintering property of the bioceramic composites (DIO/CSM10-x, x = 0–30) with increasing the CSM10 content from 0% to 30%, and the presence of the CSM10 also improved the biomimetic apatite mineralization ability in the pore struts of the scaffolds. Furthermore, the flexible strength (12.5–30 MPa) and compressive strength (14–37 MPa) of the 3D printed porous bioceramics remarkably increased with increasing CSM10 content, and the compressive strength of DIO/CSM10-30 showed a limited decay (from 37 MPa to 29 MPa) in the Tris buffer solution for a long time stage (8 weeks). These findings suggest that the new CSM10-reinforced diopside porous constructs possess excellent mechanical properties and can potentially be used to the clinic, especially for the treatment of osteonecrosis of the femoral head work as a bioceramic rod.