Shenglin Mei

The influence of hierarchical hybrid micro/nano-textured titanium surface with titania nanotubes on osteoblast functions

Hierarchical hybrid micro/nano-textured titanium surface topographies with titania nanotubes were produced by simple acid etching followed by anodization to mimic the hierarchical structure of bone tissues. Primary rat osteoblasts were used to evaluate the bioactivity. The microtopography formed by acid etching of titanium induced inconsistent osteoblast functions with initial cell adhesion and osteogenesis-related gene expression being dramatically enhanced while other cell behaviors such as proliferation, intracellular total protein synthesis and alkaline phosphatase activity, collagen secretion, and extracellular matrix mineralization being depressed. In comparison, addition of nanotubes to the microtopography led to enhancement of multiple osteoblast functions. Nearly all the cell functions investigated in this study were retained or promoted. Compared to a microtopography, the enhancement of multiple cell functions observed from the hierarchical micro/nano-textured surfaces is expected to lead to faster bone maturation around the titanium implants without compromising the bone mass. In addition, the hierarchical micro/nano-textured surfaces still retain the mechanical interlocking ability of the microtopography thereby boding well for osseointegration. Our study reveals a synergistic role played by the micro and nanotopographies in osteoblast functions and provides insight to the design of better biomedical implant surfaces.

Antibacterial effects and biocompatibility of titanium surfaces with graded silver incorporation in titania nanotubes.

Most commercial dental implants are made of titanium (Ti) because Ti possesses excellent properties such as osseointegration. However, many types of Ti products still suffer from insufficient antibacterial capability and bacterial infection after surgery remains one of the most common and intractable complications. In this study, a dual process encompassing anodization and silver plasma immersion ion implantation (Ag PIII) is utilized to produce titania nanotubes (TiO₂-NTs) containing Ag at different sites and depths. The concentration and depth of the incorporated Ag can be tailored readily by changing the PIII parameters. The Ag-embedded TiO₂-NTs which retain the nanotubular morphology are capable of sterilizing oral pathogens as opposed to pure Ti plates and pristine TiO₂-NTs. Biological assays indicate that the in vitro and in vivo biocompatibility of the sample plasma-implanted at a lower voltage of 0.5 kV (NT-Ag-0.5) is significantly compromised due to the large amount of surface Ag. On the other hand, the sample implanted at 1 kV (NT-Ag-1.0) exhibits unimpaired effects due to the smaller surface Ag accumulation. Sample NT-Ag-1.0 is further demonstrated to possess sustained antibacterial properties due to the large embedded depth of Ag and the technique and resulting materials have large potential in dental implants.

The role of sterilization in the cytocompatibility of titania nanotubes.

Titiania nanotubes have large potential in medical implant applications but their tissue compatibility is still controversial. Since the sterilization methods may impact the biocompatibility of titania nanotubes and be the source of the controversy, we investigate the influence of three commonly used sterilization methods, autoclaving, ultraviolet irradiation and ethanol immersion, on the cytocompatibility of titania nanotubes. Two titania nanostructures, namely nanonets with an average pore diameter of 25 nm and nanotubes with an average diameter of 80 nm, are used in this study. The results show that the sterilization methods significantly affect the cytocompatibility of these titania surfaces. UV and ethanol sterilization give rise to a higher surface free energy inducing higher initial cell adhesion and proliferation compared to autoclaving, whereas UV irradiation produces the best cell functions including adhesion, proliferation, as well as differentiation represented by related gene expressions. The cytocompatibility results obtained from the nanoscale surfaces are compared to those acquired from the polished surface demonstrating the significant effects. Our results suggest that the sterilization process plays an important role in the observed cytocompatibility of titania nanotubes and may be the reason for the controversial results so far. UV sterilization is found to be the best method from the viewpoint of surface contamination elimination.

The role of integrin-linked kinase/β-catenin pathway in the enhanced MG63 differentiation by micro/nano-textured topography

Micro/nano-texturing is a promising approach to produce biomaterials with better tissue integration properties, but the underlying mechanisms are only partially understood. We propose that the integrin-linked kinase (ILK)/β-catenin pathway may play a role in mediating the signals of topographical cues to cells. To confirm the hypothesis, human MG63 osteoblasts are cultured on the micro/nano-textured topographies (MNTs) to assess the cell differentiation in terms of collagen secretion, extracellular matrix mineralization, and osteogenesis-related gene expression. The expression of β-catenin, ILK and integrin β1 and β3 is assayed by real-time polymerase chain reaction and the protein levels of β-catenin, phosphorylated glycogen synthase kinase 3β (p-GSK3β) and ILK are determined by western blot. The ILK silenced MG63 induced by small interfering RNA is cultured on the samples and the cell functions and the levels of β-catenin, GSK3β and p-GSK3β are determined. The results show that the MNTs enhance MG63 differentiation and it is related to the higher expression of integrin β1 and β3 and ILK, which activate the β-catenin signaling by initiating β-catenin expression and inhibiting its degradation by phosphorylating GSK3β. ILK silencing attenuates the β-catenin signaling activation and the enhanced MG63 differentiation by the MNTs. Our results explicitly demonstrate the role of the ILK/β-catenin pathway in mediating the signals from topographical cues to osteoblasts to tailor differentiation and provide new target points for biomaterials modification and biofunctionalization to attain better clinical performance.

Immobilization of Ag nanoparticles/FGF-2 on a modified titanium implant surface and improved human gingival fibroblasts behavior

The objective of this study was to form a rapid and firm soft tissue sealing around dental implants that resists bacterial invasion. We present a novel approach to modify Ti surface by immobilizing Ag nanoparticles/FGF-2 compound bioactive factors onto a titania nanotubular surface. The titanium samples were anodized to form vertically organized TiO(2) nanotube arrays and Ag nanoparticles were electrodeposited onto the nanotubular surface, on which FGF-2 was immobilized with repeated lyophilization. A uniform distribution of Ag nanoparticles/FGF-2 was observed on the TiO(2) nanotubular surface. The L929 cell line was used for cytotoxicity assessment. Human gingival fibroblasts (HGFs) were cultured on the modified surface for cytocompatibility determination. The Ag/FGF-2 immobilized samples displayed excellent cytocompatibility, negligible cytotoxicity, and enhanced HGF functions such as cell attachment, proliferation, and ECM-related gene expression. The Ag nanoparticles also exhibit some bioactivity. In conclusion, this modified TiO(2) nanotubular surface has a large potential for use in dental implant abutment.

Suppressed primary osteoblast functions on nanoporous titania surface

Titiania nanotubes have large potential in medical implant applications but their tissue compatibility is still controversial. Considering that the biological behavior of primary osteoblasts is closer to the in vivo situation than other common cell lines, we investigate the response of primary osteoblasts on anodized nanotextured titania surfaces. Two nanotextured surface morphologies, namely the 5 V anodized surface with a pore diameter of 25 nm and the 20 V anodized surface with a tube diameter of 80 nm are chosen for this study. Initial cell adhesion is not obviously affected by the anodized surfaces. With the exception of slightly higher intracellular alkaline phosphatase activity and more extracellular matrix deposition, cell growth, and cell differentiation represented by the expressions of osteogenesis-related genes are impaired on both anodized surfaces. This may be attributed to the compromised focal contact formation on the anodized surfaces. The difference in the phenotypes of the primary osteoblasts and the osteoblastic cell lines may partly account for the controversy in osteoblast cytocompatibility on titania nanotubes.

Concentration- and time-dependent response of human gingival fibroblasts to fibroblast growth factor 2 immobilized on titanium dental implants.

Background Titanium (Ti) implants are widely used clinically, but peri-implantitis remains one of the most common and serious complications. Healthy integration between gingival tissue and the implant surface is critical to long-term success in dental implant therapy. The objective of this study was to investigate how different concentrations of immobilized fibroblast growth factor 2 (FGF2) on the titania nanotubular surface influence the response of human gingival fibroblasts (HGFs). Methods Pure Ti metal was anodized at 20 V to form a vertically organized titanium dioxide nanotube array on which three concentrations of FGF2 (250 ng/mL, 500 ng/mL, or 1000 ng/mL) were immobilized by repeated lyophilization. Surface topography was observed and FGF2 elution was detected using enzyme-linked immunosorbent assay. The bioactivity changes of dissolvable immobilized FGF2 were measured by methyl-thiazolyl-tetrazolium assay. Behavior of HGFs was evaluated using adhesion and methyl-thiazolyl-tetrazolium bromide assays. Results The FGF2 remained for several days on the modified surface on which HGFs were cultured. Over 90% of the dissolvable immobilized FGF2 had been eluted by Day 9, whereas the FGF2 activity was found to diminish gradually from Day 1 to Day 9. The titania nanotubular surface with an optimal preparing concentration (500 ng/mL) of FGF2 immobilization exhibited improved HGF functions such as cellular attachment, proliferation, and extracellular matrix-related gene expression. Moreover, significant bidirectional as well as concentration- and time-dependent bioactivity was observed. Conclusion Synergism of the FGF2-impregnated titanium dioxide nanotubular surface revealed good gingival-implant integration, indicating that these materials might have promising applications in dentistry and other biomedical devices.

Fabrication and in vitro release behavior of a novel antibacterial coating containing halogenated furanone-loaded poly(L-lactic acid) nanoparticles on microarc-oxidized titanium.

Background Dental implants have become increasingly common for the management of missing teeth. However, peri-implant infection remains a problem, is usually difficult to treat, and may lead eventually to dental implant failure. The aim of this study was to fabricate a novel antibacterial coating containing a halogenated furanone compound, ie, (Z-)-4-bromo-5-(bromomethylene)-2(5H)-furanone (BBF)-loaded poly(L-lactic acid) (PLLA) nanoparticles on microarc-oxidized titanium and to evaluate its release behavior in vitro. Methods BBF-loaded PLLA nanoparticles were prepared using the emulsion solvent-evaporation method, and the antibacterial coating was fabricated by cross-linking BBF-loaded PLLA nanoparticles with gelatin on microarc-oxidized titanium. Results The BBF-loaded PLLA nanoparticles had a small particle size (408 ± 14 nm), a low polydispersity index (0.140 ± 0.008), a high encapsulation efficiency (72.44% ± 1.27%), and a fine spherical shape with a smooth surface. The morphology of the fabricated antibacterial coating showed that the BBF-loaded PLLA nanoparticles were well distributed in the pores of the microarc oxidation coating, and were cross-linked with each other and the wall pores by gelatin. The release study indicated that the antibacterial coating could achieve sustained release of BBF for 60 days, with a slight initial burst release during the first 4 hours. Conclusion The novel antibacterial coating fabricated in this study is a potentially promising method for prevention of early peri-implant infection.