Xianchun Chen

Localized delivery of growth factors for angiogenesis and bone formation in tissue engineering

Angiogenesis is a key component of bone formation. Delivery of growth factors for both angiogenesis and osteogenesis is about to gain important potential as a future therapeutic tool. This review focuses on these growth factors that have dual functions in angiogenesis and osteogenesis, and their localized application. A major hurdle in the clinical development of growth factor therapy so far is how to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity. It is now firmly established from the available information that the type, dose, combinations and delivery kinetics of growth factors all play a decisive role for the success of growth factor therapy. All of these parameters have to be adapted and optimized for each animal model or clinical case. In this review we discuss some important parameters associated with growth factor therapy and present an overview of selected preclinical studies, followed by a conceptual description of both established and proposed delivery strategies meeting therapeutic needs.

Preparation and in vitro bioactivity of novel merwinite ceramic

The ceramic of merwinite (Ca3MgSi2O8) was prepared by sintering sol-gel-derived merwinite powder compacts. The mechanical properties and the coefficient of thermal expansion (CTE) of the merwinite ceramic were determined. In vitro bioactivity of the merwinite ceramics was evaluated. Our results showed that the sintered body was single-phase merwinite ceramic, and that its bending strength, fracture toughness and Youngs modulus were approximately 151 MPa, 1.72 MPa m(1/2) and 31 GPa, respectively. The CTE of the ceramic was 9.87 x 10(-6) degrees C(-1) and close to that for the Ti-6Al-4V alloy (9.80 x 10(-6) degrees C(-1)). Immersion of the sintered body in simulated body fluid induced surface precipitation of Ca-P rich layers. Cell culture experiment results confirmed that soluble ionic products from merwinite dissolution significantly stimulated osteoblast proliferation, and osteoblasts adhered and spread well on merwinite ceramic surfaces.

Synergistic and sequential effects of BMP-2, bFGF and VEGF on osteogenic differentiation of rat osteoblasts

In the present study, the effects of bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) on regulation of rat osteoblast (ROB) maturation in vitro were investigated. It was found that the proliferation, differentiation and mineralization of ROBs were all dose-dependently increased at particular times in the case of treatment with only one growth factor. To investigate the effects of combined treatment, ROBs were treated with either a single application of a relatively high dose of each growth factor, or binary/triple combined applications of relatively low doses of the growth factors. Osteogenic differentiation was significantly promoted in the triple combination treatment of BMP-2, VEGF and bFGF compared with the single or binary combination treatments. The optimal timing of the triple combination to enhance osteogenesis was also tested. When bFGF and VEGF were added in the early stage, and BMP-2 and VEGF were added in the late stage, osteogenic differentiation of ROBs could be enhanced more effectively. These results could be used to construct bone tissue engineering scaffolds that release growth factors sequentially.

Cellular Compatibility of Biomineralized ZnO Nanoparticles Based on Prokaryotic and Eukaryotic Systems

Zinc oxide nanoparticles (NPs) with the size of ∼100 nm were prepared via a facile biomineralization process in the template of silk fibroin (SF) peptide at room temperature. These ZnO NPs have shown the remarkable behavior of low toxicity to gram-positive bacteria (Staphylococcus aureus, Staphylococcus agalactiae), gram-negative bacteria (Escherichia coli), and eukaryotic cells (mouse L929 fibroblasts). Bacteriological testing indicated that ZnO NPs presented a 50% inhibitory effect on Streptococcus agalactiae at the concentrations of >100 mM, whereas at the same concentrations, the growth of Staphylococcus aureus and Escherichia coli were hardly inhibited. On the other hand, a remarkable proliferation of Staphylococcus aureus or Escherichia coli was observed at the concentrations of ZnO NPs <50 mM. Moreover, the cytotoxicity test demonstrated that ZnO NPs mineralized with SF peptide possessed a low toxicity to mouse L929 fibroblasts. The SF peptide coated on the surface of ZnO NPs permitted greater adhesion and consequently greater proliferation of mouse L929 fibroblasts. Besides, from TEM micrographs of the cell ultrastructure, endocytosis of NPs into the cytoplasm can be detected and the ultrastructure of the cell underwent few changes. The cell membrane retained integrity, euchromatin dispersed homogenously inside the cytoplasm, the mitochondrial architecture remained intact, and no intracellular vacuoles were observed. High-resolution transmission electron microscopy images and selected area electron diffraction patterns of ultrathin cell sections indicated that the crystal structure of NPs was not damaged by the organelle or cytoplasm. All these observations indicated that ZnO NPs mineralized with the SF peptide possess good cytocompatibility.

Preparation, characterization, in vitro bioactivity, and osteoblast adhesion of multi-level porous titania layer on titanium by two-step anodization treatment

To combine the advantages of different electrolytes in anodic oxidation, pure titanium samples were anodized in CH(3) COOH electrolyte according to a novel anodizing treatment regime and then in H(2) SO(4) electrolyte in potentialstatic mode. The in vitro bioactivity of the as-prepared titanium samples was evaluated by simulated body fluid (SBF) test. In addition, MG63 osteoblast-like cells were cultured on surfaces of the as-prepared titanium samples to evaluate osteoblast adhesion ability. The titanium samples after the two-step anodization treatment were covered by titania layers of anatase and/or rutile with several micrometres thickness and presented a multi-level porous surface morphology consisting of interlaced grooves about 20-μm wide overlaid with submicron scale pores. The SBF test results showed that the crystal titania layers prepared at appropriate conditions were able to induce apatite-forming in 7 days, indicating that the abundance of surface Ti-OH groups and (101)-oriented rutile structure both played important roles in in vitro bioactivity of titania layers. The cell experiment results showed that the macroscopic grooves could effectively promote osteoblast adhesion and growth and submicron scale pores might be beneficial to osteoblast adhesion. The two-step anodization treatment might be a promising candidate for surface modification of titanium implant.

Synthesis and characterization of novel multiphase bioactive glass-ceramics in the CaO-MgO-SiO2 system

Three new chemical compositions based on the CaO-MgO-SiO(2) system were designed first, and then three novel glass-ceramics (M1, M2, and M3) were prepared by sol-gel method. X-ray diffraction analysis confirmed that they were predominantly composed of akermanite, wollastonite, and dicalcium silicate crystalline phases. The coefficient of thermal expansion (CTE) of M2 was 10.79 x 10(-6) degrees C(-1), closest to that of Ti-6Al-4V alloy, and the Youngs modulus of M2 was 29.73 GPa, similar to that of the cortical bone. The bioactivity in vitro of M2 was evaluated by investigating its bonelike hydroxyapatite (HA)-formation ability in simulated body fluid (SBF), and the biocompatibility in vitro was detected by osteoblast proliferation, differentiation, and adhesion assay. The results revealed that M2 possessed bonelike carbonated hydroxyapatite (CHA)-formation ability in SBF and could significantly stimulate cell proliferation and differentiation. Furthermore, osteoblasts adhered and spread well on M2, indicating good bioactivity and biocompatibility in vitro.

Synthesis and cellular compatibility of biomineralized Fe3O4 nanoparticles in tumor cells targeting peptides

Fe3O4 nanoparticles (NPs) coated with WSG-peptide were prepared via a facile biomineralization technique at room temperature. The concentration of the peptides and the mixing time could substantially influence the morphology of as-prepared particles. The saturation magnetization of WSG-coated Fe3O4 particles were 35.92 emu/g, slightly higher than that of Fe3O4 without WSG peptides. Cell viability assay revealed that WSG-coated Fe3O4 particles had a good cellular compatibility. In addition, compared with Fe3O4 NPs, the mineralized Fe3O4 NPs coated with WSG peptides could more easily assemble into the cancer cell, indicating that the WSG-Fe3O4 NPs possess cancer targeting property. Thus, the WSG-coated Fe3O4 NPs could be used in cancer diagnosis and treatment fields.

In vitro screening of ovarian tumor specific peptides from a phage display peptide library

To develop more biomarkers for diagnosis and therapy of ovarian cancer, a 12-mer phage display library was used to isolate peptides that bound specifically to the human ovarian tumor cell line SK-OV-3. After five rounds of in vitro screening, the recovery rate of phages showed a 69-fold increase over the first round of washings and a group of phage clones capable of binding to SK-OV-3 cells were obtained. A phage clone named Z1 with high affinity and specificity to SK-OV-3 cells was identified in vitro. More importantly, the synthetic biotin-labeled peptide, ZP1 (=SVSVGMKPSPRP), which corresponded to the sequence of the inserted fragment of Z1, demonstrated a high specificity to SK-OV-3 cells especially when compared to other cell lines (A2780 and 3T3). ZP1 might therefore be a biomarker for targeting drug delivery in ovarian cancer therapy.

Fabrication of conductive NGF-conjugated polypyrrole–poly(l-lactic acid) fibers and their effect on neurite outgrowth

In order to fabricate a tissue scaffold with the neurotrophic and electrical activities, conductive nerve growth factor (NGF)-conjugated polypyrrole-poly(l-lactic acid) (PPy-PLLA) composite fibers were prepared by oxidation polymerization and EDC chemistry with poly-l-lysine. PPy nanoparticles (∼70nm diameter) accumulated on PLLA fiber surface to form a rough thick shell (∼200nm thickness). These NGF-conjugated PPy-PLLA fibers could support PC12 neurite outgrowth and extension. Especially, 40% and 74% increase in PC12 neurite outgrowth and extension, respectively, could be obtained under electrical stimulation of 100mV/cm voltages through the composite fibers. A mechanism for the interaction between neurite extension and the NGF-conjugated PPy-PLLA fibers under electro-stimulation was proposed, to explain the synergistic effect of the rough PPy shell, conjugated NGF and electricity on neurite outgrowth and elongation.

A facile approach to synthesize rose-like ZnO/reduced graphene oxide composite: fluorescence and photocatalytic properties

Rose-like ZnO/reduced graphene oxide composites are synthesized by a simple, scalable, and facile route without using any surfactants. The well-defined ZnO microstructure has a hexagonal hierarchical rose-like architecture, which is composed of densely packed uniform thin flakes. The N,N-dimethylformamide/water system employed here acts as an organic solvent as well as a reagent, and two competing reactions give rise to the formation of the hexagonal hierarchical rose-like ZnO architecture. Compared with bare ZnO, the rose-like ZnO/reduced graphene oxide composite displays the fluorescence quenching property. Finally, the as-prepared products possess considerable photocatalytic property under visible light for the degradation of methylene blue.