Xiao Yu Li

Basic research Cyclic tensile stretch modulates osteogenic differentiation of adipose-derived stem cells via the BMP-2 pathway

Introduction Mechanical forces play critical roles in the development and remodelling process of bone. As an alternative cell source for bone engineering, adipose-derived stem cells (ASCs) should be fully investigated for their responses to mechanical stress and the mechanisms responsible for osteogenic induction in response to mechanical signals. Material and methods We hypothesized that appropriate application of uniaxial cyclic tensile strain to ASCs could increase bone morphogenetic protein-2 (BMP-2) expression and improve osteogenesis of ASCs. To test our hypothesis, ASCs from the same flask of the same donor were subjected to tensile strain with different patterns in order to eliminate the difference of donor site and passage. After surface markers investigation, the osteo-induced ASCs were subjected to uniaxial cyclic tensile stretch with the following two loading patterns: long duration continuous pattern (6 h, 1 HZ, 2000 µɛ) and short duration consecutive pattern (17 min every day for 10 consecutive days, 1 HZ, 2000 µɛ). Then osteogenic related genes were analysed by real-time PCR. Results The ASCs were positive for the markers STRO-1, CD90 and CD44 and negative for CD34. Cyclic tensile strain of 6 continuous h’ duration significantly increased gene expressions of BMP-2 and Runx2, and depressed OCN mRNA expression. In contrast, mechanical loading of 17 min every day did not significantly affect gene expression of BMP-2, Runx2, OCN or ALP. Conclusions We indicate that ASCs may sense mechanical loading in a duration-dependent manner and cyclic tensile stretch may modulate the osteogenic differentiation of ASCs via the BMP-2 signalling pathway.

Auto-transplanted mesenchymal stromal cell fate in periodontal tissue of beagle dogs

BACKGROUND AIMSnMesenchymal stromal cells (MSC) possess multilineage differentiation potential and characteristics of self-renewal. It has been reported that MSC can acquire characteristics of cells in the periodontal ligament (PDL) in vitro. Moreover, the transplantation of MSC has been shown to be a promising strategy for treating periodontal defects. However, little is known about the fate of MSC in periodontal tissue in vivo. The aim of this study was to trace the paths of MSC after transplantation into periodontal tissues in vivo.nnnMETHODSnMSC labeled with bromodeoxyuridine (BrdU) were transplanted into periodontal defects of beagle dogs. Six weeks after surgery, the animals were killed and decalcified specimens were prepared. Migration and differentiation of MSC were detected by single/double immunohistochemistry and a combination of immunohistochemistry and in situ hybridization.nnnRESULTSnBrdU-labeled MSC were observed distributing into periodontal tissue that included alveolar bone, PDL, cementum and blood vessels and expressing surface markers typical of osteoblasts and fibroblasts.nnnCONCLUSIONSnCumulatively, our data suggest that MSC migrate throughout periodontal tissue and differentiate into osteoblasts and fibroblasts after transplantation into periodontal defects at 6 weeks in vivo, and have the potential to regenerate periodontal tissue.

Effect of implant surface microtopography on proliferation, neurotrophin secretion, and gene expression of Schwann cells.

The purpose of this study was to evaluate the effect of different implant surface properties on the morphology, proliferation, neurotrophin secretion, and gene expression of Schwann cells. Four types of implant surfaces, including ground (smooth surface), sandblasted and acid-etched (SLA), hydroxyapatite-coated (HA), and titanium plasma spray (TPS) surfaces were fabricated and photographed by a scanning electron microscopy (SEM). Schwann cells derived from neonatal rats were cultured on the implant surfaces and assessed via SEM observation and methylthiazol tetrazolium (MTT) colorimetric assay. The secretions and mRNA levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were measured by enzyme-linked immunosorbent assay (ELISA) and quantitative real time RT-PCR, respectively, on days 3 and 7. Tissue culture plastic was used as a control. The results demonstrated that Schwann cells exhibited typical bipolar spindle morphology on various surfaces, and proliferated faster than the control. Neurotrophin secretion and gene expression of both BDNF and NGF were also increased by implant surfaces. This study suggests that the function of Schwann cells can be enhanced by implant implants.

Biocompatibility of Nano-TiO2/HA Bioceramic Coating for Nerve Regeneration around Dental Implants

Sensory perception thresholds of implants were much higher than those of natural teeth. The purpose of this study was to evaluate the biocompatibility of TiO2/HA-biocoated dental implants for nerve regeneration using cultured Schwann cells. The nano-TiO2/HA composite bioceramic coating was developed on the surfaces of commercially pure titanium discs by sol-gel route, and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Using smooth titanium discs as a control, Schwann cell responses to the coating were evaluated by SEM, MTT assay, total protein content and leakage of cytosolic lactate dehydrogenase (LDH) activity. In addition, the amount of brain-derived neurotrophic factor (BDNF) secreted by Schwann cells was measured by Enzyme-Linked Immunosorbent Assay (ELISA). It was observed that the coating had fine crystallites and homogeneous micropores in the diameter of 5-10 um. The cell morphology, proliferation and function were unaffected. The results indicate that the TiO2/HA bioceramic coating developed on the surface of pure titanium by sol-gel route had good biocompatibility with Schwann cells for nerve regeneration around dental implants.

Development and Characterization of Nano-TiO2/HA Composite Bioceramic Coating on Titanium Surface

This research is aimed at the development and characterization of a novel bioceramic coating on the surface of pure titanium. Nano-TiO2/HA composite bioceramic coating was designed and developed on the surfaces of pure titanium discs by sol-gel route. The TiO2 anatase bioceramic coating was employed as the inner layer, which could adhere tightly to the titanium substrate. The porous HA bioceramic coating was employed as the outer layer, which has higher solubility and better short term bioactivity. Conventional HA coatings and commercially pure titanium (cpTi) were taken as control. XRD and SEM were employed to characterize the crystallization, surface morphology and thickness of the coatings. The bioactivities of the coatings were evaluated by the in vitro osteoblasts culture. Results show the nano-TiO2/HA composite bioceramic coating has good crystallization and homogeneous, nano-scale surface morphology. And it adheres tightly to the substrate. The in vitro osteoblasts culture exhibits satisfactory bioactivity.

Evaluation of Sodium Titanate Coating on Titanium by Sol-Gel Method In Vitro

In this study, an exclusive sodium titanate (Na2Ti6O13) coating on titanium was fabricated by sol-gel method and evaluated in vitro. The coating was characterized by SEM and XRD. The bioactivity of the Na2Ti6O13 coating was evaluated by the biomimetic growth of apatite on its surface after soaked in an acellular simulated body fluid (SBF) for a period of time. In vitro osteoblasts culture was carried out to determine cytocompatibility by the measurement of the proliferation and alkaline phosphatase (ALP) activity of the cells. XRD patterns showed that Na2Ti6O13 was well crystallized when the coating was heated at 800°C. SEM observation exhibited that the Na2Ti6O13 coated titanium had a homogeneous surface without any cracks. After immersion in SBF, the apatite layer can be formed on the coating. The cells culture showed that the osteoblasts grew well on the Na2Ti6O13 coated titanium. It can be concluded that Na2Ti6O13 coating on titanium obtained by sol-gel method is bioactive.

Evaluation of Osteoblast Responses to Silver-Hydroxyapatite/Titania Nanoparticles In Vitro

In the present in vitro study, osteoblasts proliferation, vitality and ultrastructure were investigated when cultured in the presence of silver-hydroxyapatite/titania nanoparticles (nAg_HA/TiO2) compared to HA nanoparticles (nHA) at various concentrations and cell culture without nanoparticles for up to 120 hours. Results confirmed the detrimental influences of both nAg_HA/TiO2 and nHA on osteoblast growth.Cell vitality was slightly higher during the earlier 24h, but after that was inhibited. Both cell proliferation and vitality by addition of nanoparticles were restricted with concentrations of nanoparticles increasing. However, the respiration rates by addition of nanoparticles were showed higher than that of the cell culture without nanoparticles. No remarkable ultrastructure changes were showed in the osteoblasts exposed nanoparticles. The difference in cell proliferation, vitality and ultrastructure between nAg_HA/TiO2 and nHA were insignificant. It was demonstrated that biocompatibility of nAg_HA/TiO2 is almost the same as nHA.

The Effect of Microarc Oxidation Ceramic Coating on Sensory Reconstruction around Implants Using Cultured Schwann Cells

Osseointegrated titanium implants have been widely used in clinics for replacement of missing teeth. However, sensory perception thresholds of implants were 10 to 100 times higher than those of natural teeth. The purpose of this study was to evaluate the effect of the ceramic coating generated by microarc oxidation (MAO) on sensory reconstruction around dental implants. The MAO coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning probe microscope (SPM). Moreover, the chemical composition was analyzed with an energy dispersive spectroscope (EDS). Using smooth titanium discs as a control, Schwann cell responses to the coating were evaluated by SEM, MTT assay, total protein content and leakage of cytosolic lactate dehydrogenase (LDH) activity. In addition, the amount of brain-derived neurotrophic factor (BDNF) secreted by Schwann cells was measured by Enzyme-Linked Immunosorbent Assay (ELISA). It was observed that the porous coating had separated and homogeneous micropores in the diameter of 1-2 μm. The concentrations of Ca and P in the layer were 8.63% and 5.23% respectively. The cell morphology, proliferation and secretion of BDNF were unaffected. The results indicated that the MAO ceramic coating developed on the surface of pure titanium had good biocompatibility with Schwann cells for sensory reconstruction around dental implants.

Structure and In Vitro Bioactivity of Si Enriched Hydroxyapatite/TiO2 Coatings on Pure Titanium by Micro-Arc Oxidation

The effect of Si doping on the bioactivity and characteristics of hydroxyapatite/TiO2 composite films was investigated. Pure titanium plates were treated to form Ca, P and Si enriched titania-based films by using micro-arc oxidation (MAO). Then, some specimens were undergone a further hydrothermal treatment to produce a thin outermost layer of hydroxyapatite (HA). Experiments revealed that that the film, which was about 10μm thick, was composed of amorphous silicon dioxide, amorphous calcium phosphate, rutile and anatase. The film was porous and uneven, with the pore size of 1-4μm. No obvious cracks exist on the surface. In order to investigate the cytocompatibility of the films, periodontal ligament (PDL) cells were seeded onto the surface of the films. It was concluded that the Si ion did not influence the characters of MAO film but Si enriched hydroxyapatite/ TiO2 composite coatings exhibited an effect on cell attachment.