Mengfei Yu

Light-induced cell detachment for cell sheet technology.

The phenomenon of light-induced cell detachment is reported. Mouse calvaria-derived, pre-osteoblastic (MC3T3-E1) cells were cultured on a TiO(2) nanodot-coated quartz substrate. After 20 min of UV365 illumination, over 90% of the cells would detach from the surface. Moreover, intact cell sheets could be obtained in the same way. It was found that the as-obtained cells showed good viability, and could be used for further culture processes and other applications. Also, biocompatibility and safety characterizations indicated that the use of TiO(2) nanodots and UV365 illumination was safe for such cell detachment. It is suggested that adsorbed extracellular matrix proteins play key roles in developing cell sheets and ensuring biocompatibility. The present light-induced cell detachment method demonstrates a promising way for rapid cell/cell sheet harvesting.

Preparation and antibiotic drug release of mineralized collagen coatings on titanium

In this study, a mineralized collagen coating was electrolytically deposited onto titanium. The results showed that the mineralized collagen coatings with dense or porous morphology could be obtained. The mineral phase was mainly hydroxyapatite. In vitro evaluation showed the mineralized collagen coatings were stable in Kokubo’s simulated body fluid, and displayed a good cytocompatibility in the cell multiplication test. The mineralized collagen coatings loaded with vancomycin hydrochloride showed an inhibitory effect on the growth of S.aureus. The present mineralized collagen coating demonstrates good suitability for surface modification of orthopedic metal implants.

Incorporation of chitosan nanospheres into thin mineralized collagen coatings for improving the antibacterial effect.

It is desired that the coatings on metallic implants have both excellent biological responses and good loading-release capacities of biological factors or drugs. So far, the challenge still remains, because the morphology and composition of the bioactive coatings are usually not favorable for accommodating drug molecules. In this study, we adopted an approach of incorporating chitosan nanospheres into a thin mineralized collagen coating; this approach is based on the good loading-release behavior of the nanospheres and the good cytocompatibility of the thin coating. The incorporation of chitosan nanospheres into the mineralized collagen coatings was realized by electrolytic co-deposition. The morphologies and microstructures of the resulting coatings were characterized by SEM, and the phase and chemical compositions of the coatings were measured by XRD and FTIR. The loading-release capacity for vancomycin hydrochloride (VH) was determined by ultraviolet spectrophotometry. MTS assay was used to evaluate cytocompatibility, and in vitro bacterial adhesion was tested for assessing the antibacterial effects of the VH-loaded coatings. The chitosan nanospheres adhered tightly to collagen fibrils. The incorporated coatings facilitated the sustained release of VH, and had a clear antibacterial effect. The incorporation of chitosan nanospheres into mineralized collagen coatings demonstrates an effective way to improve the drug loading-release capacity for the thin coatings. This formulation had a highly effective biological response.

Surface hydroxyl groups direct cellular response on amorphous and anatase TiO2 nanodots

In this study, we investigated the differences between amorphous and anatase TiO2 at the biomolecular level which could explain differences in the osteoblast response on these surfaces. The number of surface hydroxyl groups in the TiOHT form on amorphous and anatase TiO2 was found to be the most important factor, resulting in adsorption of bovine serum albumin as a monolayer on amorphous TiO2 nanodots but as a multilayer on anatase TiO2 nanodots. The reason for this is that the presence of more TiOHT groups on amorphous TiO2 nanodots attracts more -NH3+ groups on BSA molecules, causing the conformation of surface-bound BSA molecules to differ from those adsorbed on anatase TiO2 nanodots. Fibronectin which is subsequently adsorbed on anatase TiO2 nanodots then retains a more active conformation for osteoblast adhesion and mineralization.

Weakly nonlinear analysis on the Kelvin-Helmholtz instability

A weakly nonlinear model is proposed for the Kelvin-Helmholtz instability in two-dimensional incompressible fluids. The second- and third-harmonic generation effects of single-mode perturbation, as well as the nonlinear correction to the exponential growth of the fundamental modulation are analyzed. An important resonance in the mode-coupling process is found. The nonlinear saturation time depends on the initial perturbation amplitude and the density ratio of the two fluids, but the nonlinear saturation amplitude depends only on the initial perturbation amplitude. The weakly nonlinear result is supported by numerical simulation. The practical system of boundary layer containing thermal conductivity is analyzed. Their nonlinear saturation amplitude can be predicted by our weakly nonlinear model.

Improvement of drug elution in thin mineralized collagen coatings with PLGA‐PEG‐PLGA micelles

A mineralized collagen (MC) coating on metallic implants has shown great potential as orthopedic material due to high biological responses. However, their drug delivery capacity remains unsatisfactory since a serious burst release may occur and long-term release is hard to be achieved. Aiming to improve the drug-eluting capability, we incorporated drug-loaded PLGA-PEG-PLGA (PPP) micelles into the thin coating. The in vitro release profiles showed that the burst release in the initial 8 h of the modified coating decreased from 81% to 58% compared to MC coating alone; meanwhile, the release duration was prolonged from 3 days to 1 week. Additionally, the release kinetics of vancomycin hydrochloride (VH, the model drug) could be adjusted by changing the size and concentration of PPP micelles. Interestingly, less initial release of VH caused by micelle immobilization did not affect the antibacterial activity in the early stage of implantation according to the antimicrobial test. The cytocompatibility assay demonstrated that the VH-loaded PPP micelles did not have negative effect on the bioactivity of coating which greatly enhanced cell activity compared to bare Ti substrates. Thus, the MC coatings with PPP micelles could be an effective implant route for bone repair.

Controlled Release of Naringin in Metal-Organic Framework-Loaded Mineralized Collagen Coating to Simultaneously Enhance Osseointegration and Antibacterial Activity

Two important goals in orthopedic implant research are to promote osseointegration and prevent infection. However, much previous effort has been focused on the design of coatings to either enhance osseointegration while ignoring antibacterial activity or vice versa, to prevent infection while ignoring bone integration. Here, we designed a multifunctional mineralized collagen coating on titanium with the aid of metal-organic framework (MOF) nanocrystals to control the release of naringin, a Chinese herbal medicine that could promote osseointegration and prevent bacterial infection. The attachment, proliferation, osteogenic differentiation, and mineralization of mesenchymal stem cells on the coating were significantly enhanced. Meanwhile, the antibacterial abilities against Staphylococcus aureus were also promoted. Furthermore, release kinetics analysis indicated that the synergistic effect of a primary burst release stage and secondary slow release stage played a critical role in the performance and could be controlled by the relative concentrations of MOF and naringin. This work thus provides a novel strategy to engineer multifunctional orthopedic coatings that can enhance osseointegration and simultaneously inhibit microbial cell growth.

Modulation of protein behavior through light responses of TiO2 nanodots films.

In this work, the behavior of protein molecules adsorbed on TiO2 nanodots films are modulated through the light responses of the nanodots. TiO2 nanodots films are first prepared through phase separation induced self assembly. Then, bovine serum albumin (BSA) is adsorbed on TiO2 nanodots films and exposed to ultraviolet (365 nm) illumination. It is found the conformation of surface-bound BSA molecules changes with ultraviolet illumination. Moreover, the BSA molecules conjugate to the surface-bound molecules, which are in the overlayer, are released. The reason is ascribed to that TiO2 nanodots absorb ultraviolet and result in the increase of surface hydroxyl groups on nanodots. Such increase further leads to intensified attraction of -NH3 groups in the surface-bound BSA molecules. That not only changes the conformation of the surface-bound BSA molecules, but also weaken the conjugation between surface-bound molecules and other BSA molecules in the overlayer. Eventually, the overlayer of BSA molecules is released. It is believed that such protein conformation variation and release behavior induced through light responses of TiO2 nanodots are crucial in understanding the biomedical performance of TiO2 nanostructures. Also, it could be widely utilized in tailoring of the materials-protein interactions.

Surface hydroxyl groups regulate the osteogenic differentiation of mesenchymal stem cells on titanium and tantalum metals

Titanium (Ti) and tantalum (Ta) metals have been widely used as implants for their favorable mechanical features and good biocompatibility. However, the results on their osteogenic capacity have been conflicting due to the synergistic effects of complex and multiple material surface features (such as topography, surface chemistries etc.) on cellular behaviors. Here, we directly compare the osteogenic response of mesenchymal stem cells (MSCs) to Ti and Ta metal surfaces with alterable surface hydroxyl groups. Although no difference was found on both surface topographies, cellular adhesion, proliferation, and the expression of osteogenic-related markers were upregulated with the increasing amount of surface hydroxyl groups (-OH) after ultraviolet (UV) light treatment. Moreover, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment. These results might be attributed to the comparative quantity of the distinct type of surface hydroxyl groups (bridging-OH and terminal-OH), which regulated the conformation of the initial protein adsorption and subsequent cellular behaviors. Our results demonstrate the central role of the surface hydroxyl groups in mediating cell-material interactions and implicate this interface as helping in optimizing osteointegration of Ti and Ta based orthopaedic and dental implants.

Mesenchymal stem cells in response to exposed rod-heights of TiO2 nanorod films

Cellular responses are strongly sensitive to surface structure, so the optimization of the structures is essential in biomaterial research. In this work, the exposed nanorod-heights in TiO2 nanorod films were adjusted for enhancing cellular responses. The adjustment was realized by incorporating mesoporous bioactive glass (MBG) into the nanorod films via a sol–gel method. The exposed nanorod-heights in the films could be changed from the original ∼300 nm to ∼200 nm and ∼100 nm. The cellular responses on the nanostructured surfaces were evaluated through culturing mesenchymal stem cells (MSCs). The results showed that the films with shortened nanorod-heights had better cellular responses and could accelerate osteogenic differentiation and mineralization, and the films with 100 nm nanorod-height provided the best surface for cell growth. This is attributed to the nanostructure with the shortened nanorod-heights being well recognized by the cells, consequently the cells grew with a faster osteogenic differentiation through a strengthened BMP-smads signal pathway.