Xuehui Zhang

Magnetic biodegradable Fe3O4/CS/PVA nanofibrous membranes for bone regeneration.

In recent years, interest in magnetic biomimetic scaffolds for tissue engineering has increased considerably. The aim of this study is to develop magnetic biodegradable fibrous materials with potential use in bone regeneration. Magnetic biodegradable Fe(3)O(4)/chitosan (CS)/poly vinyl alcohol (PVA) nanofibrous membranes were achieved by electrospinning with average fiber diameters ranging from 230 to 380 nm and porosity of 83.9-85.1%. The influences of polymer concentration, applied voltage and Fe(3)O(4) nanoparticles loading on the fabrication of nanofibers were investigated. The polymer concentration of 4.5 wt%, applied voltage of 20 kV and Fe(3)O(4) nanoparticles loading of lower than 5 wt% could produce homogeneous, smooth and continuous Fe(3)O(4)/CS/PVA nanofibrous membranes. X-ray diffraction (XRD) data confirmed that the crystalline structure of the Fe(3)O(4), CS and PVA were maintained during electrospinning process. Fourier transform infrared spectroscopy (FT-IR) demonstrated that the Fe(3)O(4) loading up to 5 wt% did not change the functional groups of CS/PVA greatly. Transmission electron microscopy (TEM) showed islets of Fe(3)O(4) nanoparticles evenly distributed in the fibers. Weak ferrimagnetic behaviors of membranes were revealed by vibrating sample magnetometer (VSM) test. Tensile test exhibited Youngs modulus of membranes that were gradually enhanced with the increase of Fe(3)O(4) nanoparticles loading, while ultimate tensile stress and ultimate strain were slightly reduced by Fe(3)O(4) nanoparticles loading of 5%. Additionally, MG63 human osteoblast-like cells were seeded on the magnetic nanofibrous membranes to evaluate their bone biocompatibility. Cell growth dynamics according to MTT assay and scanning electron microscopy (SEM) observation exhibited good cell adhesion and proliferation, suggesting that this magnetic biodegradable Fe(3)O(4)/CS/PVA nanofibrous membranes can be one of promising biomaterials for facilitation of osteogenesis.

Lower extent but similar rhythm of osteogenic behavior in hBMSCs cultured on nanofibrous scaffolds versus induced with osteogenic supplement.

Nanotopographic cues from biomaterials exert powerful effects on the osteogenic differentiation of mesenchymal stem cells because of their niche-mimicking features. However, the biological mechanisms underlying cell lineage determination by surface nanotopography have not been clearly elucidated. Here, we explored the osteogenic behavior of human bone marrow mesenchymal stem cells (hBMSCs) on poly-l-lactide nanofibers with different orientations and monitored the dynamic changes in global gene expression triggered by topographical cues. RT-PCR analysis of osteogenic marker genes and ALP activity assays demonstrated that hBMSCs cultured on random nanofibers showed enhanced osteogenic-specific fate compared with those on aligned nanofibers. Microarray analysis demonstrated a similar temporal change in gene expression patterns between hBMSCs cultured on random nanofibers and those induced with an osteogenic supplement (OS). However, the extent of osteogenic differentiation on the fibrous scaffold was much lower than that driven by chemical OS. In-depth pathway analysis revealed that focal adhesion kinase, TGF-β, Wnt, and MAPK pathways were involved in the activation of osteogenic differentiation in hBMSCs on random nanofibers. These findings suggested that a lower extent but similar rhythm of dynamic cellular behavior was induced on random nanofibers when compared with the OS condition and that mechanotransduction could trigger nonspecific and multilevel responses in hBMSCs. This study provides insight into the regulation of osteogenesis directed by substratum surfaces.

Cytotoxicity of silver nanoparticles in human embryonic stem cell-derived fibroblasts and an L-929 cell line

Consensus about the toxicity of silver nanoparticles (Ag-NPs) has not been reached, even though extensive attention has been paid to this issue. This confusion may be due to physicochemical factors of Ag-NPs and the cell model used for biological safety evaluation. In the present study, human embryonic stem cell-derived fibroblasts (EBFs), which have been considered a closer representative of the in vivo response, were used as a novel cell model to assess the cytotoxicity of Ag-NPs (∼20nm and ∼100 nm) in comparison with L-929 fibroblast cell line. Cell proliferation, cell cycle, apoptosis, p53 expression, and cellular uptake were examined. Results showed that Ag-NPs presented higher cytotoxicity to EBF than to L-929. EBF demonstrated a stronger capacity to ingest Ag-NPs, a higher G2/M arrest, and more upgraduated p53 expression after exposed to Ag-NPs for 48 h when compared with L-929. It could be concluded that EBF exhibited a more sensitive response to Ag-NPs compared with L-929 cells, indicating that EBF may be a valid candidate for cytotoxicity screening assays of nanoparticles.

Osteoconductive effectiveness of bone graft derived from antler cancellous bone: an experimental study in the rabbit mandible defect model.

The purpose of this study was to evaluate the properties of a novel inorganic xenogenic bone substitute, calcinated antler cancellous bone (CACB). Physicochemical properties of CACB including surface morphology, phase composition, chemical bond structure, Ca/P ratio and porosity were characterized by scanning electron microscopy, X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, inductively coupled plasma-atomic emission spectroscopy and nitrogen adsorption analysis, and were found to closely resemble calcinated human cancellous bone. The bone defect repair efficacy of CACB was evaluated in comparison with commercially available bone substitutes (Bio-Oss(®)) within rabbit mandible defects. The gross observation, micro-CT and histology analysis data demonstrated that CACB was efficacious for bone regeneration, and was comparable with Bio-Oss(®) bone substitute in inducing neovascularization and osteogenesis within the mandible defects. CACB can therefore serve as a safe, renewable, and sustainable source of bone graft material, but without the ethical issues pertaining to animal welfare.

Nanocomposite Membranes Enhance Bone Regeneration Through Restoring Physiological Electric Microenvironment

Physiological electric potential is well-known for its indispensable role in maintaining bone volume and quality. Although implanted biomaterials simulating structural, morphological, mechanical, and chemical properties of natural tissue or organ has been introduced in the field of bone regeneration, the concept of restoring physiological electric microenvironment remains ignored in biomaterials design. In this work, a flexible nanocomposite membrane mimicking the endogenous electric potential is fabricated to explore its bone defect repair efficiency. BaTiO3 nanoparticles (BTO NPs) were first coated with polydopamine. Then the composite membranes are fabricated with homogeneous distribution of Dopa@BTO NPs in poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix. The surface potential of the nanocomposite membranes could be tuned up to -76.8 mV by optimizing the composition ratio and corona poling treatment, which conform to the level of endogenous biopotential. Remarkably, the surface potential of polarized nanocomposite membranes exhibited a dramatic stability with more than half of original surface potential remained up to 12 weeks in the condition of bone defect. In vitro, the membranes encouraged bone marrow mesenchymal stem cells (BM-MSCs) activity and osteogenic differentiation. In vivo, the membranes sustainably maintained the electric microenvironment giving rise to rapid bone regeneration and complete mature bone-structure formation. Our findings evidence that physiological electric potential repair should be paid sufficient attention in biomaterials design, and this concept might provide an innovative and well-suited strategy for bone regenerative therapies.

Cell response of nanographene platelets to human osteoblast‐like MG63 cells

The biologic/cytotoxic effects of dispersed nanographene platelets (NGPs) on human osteosarcoma cells (MG63 cell line) were first studied by examining cell viability, cycle, apoptosis, change in morphology, lactate dehydrogenase (LDH) release, alkaline phosphatase (ALP) activity, and inflammation. The results shown that the cell cytotoxicity of the dispersed NGPs exhibited dose-dependent characters, which had no obvious cytotoxic effects to MG63 cells at the concentration less than 10 μg mL(-1), whereas could postpone cell cycle, promote cell apoptosis, damage cell microstructure, induce serious tumor necrosis factor-α expression and greatly reduce ALP activity of MG63 cells at higher concentration of NGPs (>10 µg mL(-1)). Besides, NGPs had little influence on the LDH leakage. The cytotoxic mechanism of NGPs to MG63 cells was speculated to be intracellular activity with no physical damage of plasma membrane.

Electrospun Gelatin/β-TCP Composite Nanofibers Enhance Osteogenic Differentiation of BMSCs and In Vivo Bone Formation by Activating Ca (2+) -Sensing Receptor Signaling.

Calcium phosphate- (CaP-) based composite scaffolds have been used extensively for the bone regeneration in bone tissue engineering. Previously, we developed a biomimetic composite nanofibrous membrane of gelatin/β-tricalcium phosphate (TCP) and confirmed their biological activity in vitro and bone regeneration in vivo. However, how these composite nanofibers promote the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) is unknown. Here, gelatin/β-TCP composite nanofibers were fabricated by incorporating 20 wt% β-TCP nanoparticles into electrospun gelatin nanofibers. Electron microscopy showed that the composite β-TCP nanofibers had a nonwoven structure with a porous network and a rough surface. Spectral analyses confirmed the presence and chemical stability of the β-TCP and gelatin components. Compared with pure gelatin nanofibers, gelatin/β-TCP composite nanofibers caused increased cell attachment, proliferation, alkaline phosphatase activity, and osteogenic gene expression in rat BMSCs. Interestingly, the expression level of the calcium-sensing receptor (CaSR) was significantly higher on the composite nanofibrous scaffolds than on pure gelatin. For rat calvarial critical sized defects, more extensive osteogenesis and neovascularization occurred in the composite scaffolds group compared with the gelatin group. Thus, gelatin/β-TCP composite scaffolds promote osteogenic differentiation of BMSCs in vitro and bone regeneration in vivo by activating Ca2+-sensing receptor signaling.

Improved performance of Bis-GMA/TEGDMA dental composites by net-like structures formed from SiO2 nanofiber fillers.

The major objective of this study was to explore the effects of silicon dioxide (SiO2) nanofibers on the performance of 2, 2-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA)/tri-(ethyleneglycol) dimethacrylate (TEGDMA) dental composites. At first, the mechanical properties of Bis-GMA/TEGDMA (50/50, w/w) resins containing different contents of SiO2 nanofibers were evaluated to identify the appropriate composition to achieve the significant reinforcing effect. Secondly, optimized contents (5 or 10wt.%) of SiO2 nanofibers were mixed into resins together with SiO2 microparticles, which was 60wt.% of the resin. Controls for comparison were Bis-GMA/TEGDMA resins containing only SiO2 microparticles (60wt.%) or with additional SiO2 nanoparticles (5 or 10wt.%). Properties including abrasion, polymerization shrinkage and mechanical properties were evaluated to determine the contribution of SiO2 nanofibers. In comparison with SiO2 nanoparticles, SiO2 nanofibers improved the overall performance of Bis-GMA/TEGDMA composite resins, especially in improving abrasion resistance and decreasing polymerization shrinkage. The explanations were that one-dimensional SiO2 nanofibers were able to shield particular fillers from being abraded off, and able to form a kind of overlapped fibrous network to resist polymerization shrinkage. With these approaches, SiO2 nanofiber-containing Bis-GMA composite resins were envisioned a promising choice to achieve long-term durable restorations in clinical therapies.

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

The aim of this work is to investigate the surface characteristics and corrosion behavior of NiTi (50.6 at.% Ni) shape memory alloy coated by a ceramic-like and highly biocompatible material, iridium oxide (IrO2). IrO2 coatings were prepared by thermal decomposition of H2IrCl6 · 6H2O precursor solution at the temperature of 300 °C, 400 °C and 500 °C, respectively. The surface morphology and microstructure of the coatings were investigated by scanning electron microscope (SEM) and glancing angle X-ray diffraction (GAXRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the surface elemental composition. Corrosion resistance property of the coated samples was studied in a simulated body fluid at 37±1 °C by electrochemical method. It was found that the morphology and microstructure of the coatings were closely related to the oxidizing temperatures. A relatively smooth, intact and amorphous coating was obtained when the H2IrCl6·6H2O precursor solution (0.03 mol/L) was thermally decomposed at 300 °C for 0.5 h. Compared with the bare NiTi alloy, IrO2 coated samples exhibited better corrosion resistance behavior to some extent.

Mechanical performance of polymer-infiltrated zirconia ceramics

OBJECTIVE The aim of this study was to evaluate the microstructure and mechanical behavior of polymer-infiltrated zirconia ceramics as a function of pre-sintering temperature (1000-1150°C). METHODS Polymer-infiltrated zirconia ceramics were prepared by combining the porous zirconia networks and polymer through infiltration and polymerization. XRD was employed to determine phase structure. The microstructure and fracture mechanism were observed by SEM. Flexural strength and fracture toughness were measured by three-point bending method and single-edge-notched beam method, respectively. A nanoindentation system was employed to determine elastic modulus and hardness. RESULTS Different porosities and polymer contents can be obtained by tuning the pre-sintered temperature of zirconia ceramic precursors. Zirconia network porosity varies from 46.3% to 34.7% and the relevant polymer content ranges from 18.4wt.% to 12.3wt.% when the pre-sintered temperature is set from 1000°C to 1150°C. The flexural strength, fracture toughness, hardness, and elastic modulus values of the specimen pre-sintered at 1150°C are 240.9MPa, 3.69MPam1/2, 3.1GPa, and 58.8GPa, respectively. CONCLUSION The pre-sintering temperature has a significant effect on the microstructure and mechanical properties of polymer-infiltrated zirconia ceramics and the optimal pre-sintering temperature is 1150°C. CLINICAL SIGNIFICANCE Specimen pre-sintered at 1150°C shows tooth-like mechanical properties, suggesting a promising restorative material in dental clinic. Moreover, the synthesis process is simple and can be easily performed in a prosthesis laboratory.