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WBC meeting roundup

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The WBC2016 10th World Biomaterials congress held in Montreal, Canada, May 17-22 was a good meeting with respect to nanotubes. Actually, over a dozen papers were presented related to TiO2 nanotubes. There were as many presentations discussing nanotexturing as any other single topic.

This was good news for us and for nanotubes in general. The WBC papers presented positive results regarding improved fatigue properties, osseointegration cellular attachment, and antimicrobial biofilm reduction vs. other surface treatments. Here is a quick tour of four of the papers presented. I’ll summarize another set of papers in a subsequent post.

Could fatigue and fracture effects of TiO2 nanotubes be a titanium deal breaker?

I get asked this question nearly every time I talk to companies about nanotubes. While much effort is going into developing surface modification techniques that enhance implant fixation and biocompatibility, some researchers have reported that a large number of these techniques may be detrimental to fatigue performance of titanium and its alloys. Thanks to a study presented at WBC2016, the answer appears to be no.

To evaluate nanotube fatigue and fracture effects, researchers in Brazil performed fatigue testing on nanotubes that are very similar to ours, and examined the fracture behavior on self-organized TiO2 nanotubes on Ti-6Al-4V surface.

Using Ti-6Al-4V polished specimens by anodic oxidation in an aqueous electrolyte they performed fatigue tests using the staircase method in a physiological solution. They examined the tests of the nanotubes layer and the fracture surfaces by Scanning Electron Microscopy (SEM).

They found that the fatigue limit of TiO2 and the Ti-6Al-4V polished specimen was the same, calculated to be 845 megapascal (MPa). An examination of the SEM showed that, while cracks were observed, they concluded that because they only showed on the modified surface in the regions close to the fracture surface, they probably occurred with the rupture of the tested specimen. As a result they concluded that the cracks were irrelevant and that the fatigue behavior of Ti-6Al-4V was not affected by nanotubes formation mainly because of the nano scale thickness of the layer and the presence of a compact oxide layer at the interface with the substrate. View Lecture Notes

Soap meets nanotechnology to improve dental implants

Reducing the adhesion ability of bacteria is an idea as old as soap. The effort of a group of Hungarian researchers applied that simple idea to nanotechnology as a means to improving dental implants. The group’s approach was to develop nanostructures (nanotu¬bes or nanorods) onto microscopically flat, electropolished surfaces that markedly reduce bacterial adhesion while also having nanofeatures intended to stimulate the differentiation of bone forming cells that would eventually favor bone formation over bacterial adhesion.

In the study, they compared electropolished (EPOL), and electropolished and anodized (EPOLAN) approaches to the current gold standard for dental implants that uses sandblasted and acid-etched (SBAE) material. They used the bacterial adhesion of ability of streptococcus sanguinis to test three materials in petri dishes over a 24-hour period. The results showed a reduction in adhesion from 60 percent to between 16-18 percent for both electropolished surfaces.

For the experiment to see if the surfaces might stimulate bone-forming cells they used alkaline phosphatase (ALP) as well as deposited mineral as a marker for bone formation. The result showed the nanostructures provoked a positive impact on ALP activity and mineralization. They concluded that the implementation of nanostructures into microscopically flat surfaces is an efficient modification to reduce bacterial adhesion due to its microroughness while at the same time supported bone cell differentiation. View Lecture Notes

Milk-doping titania grows strong bones?

In another adhesion study aimed in this case at stimulating osteoblasts and bone formation, a collaboration of engineers and medical researchers from the U.S., Portugal, Belgium, and Brazil investigated the effect of of a calcium phosphorus (Ca/P) doped titania nanotubes on stimulating adhesion and proliferation of osteoblasts and human mesenchymal stem cells.

They used a two-step anodization that produced well-ordered Ca/P-NTs with diameter comprised between 60-85 nm and 4.9 0.5 μm length. After the anodization the water attraction, or hydrophilicity of the titanium (Ti) was enhanced with a significant decrease of water contact angle (WCA) from 45.4 3.1o to 5.7 2.3o (Ti vs. Ca/P-NTs; p<0.001). After 6 days of incubation, the osteoblasts cultured on the calcium phosphorus nanotubes showed similar viability as cultured on NT surfaces, and the viability of mesenchymal stem cells on the treated nanotubes was lower as compared to NT surfaces (p<0.05). Nevertheless the osteoblasts and stem cells strongly adhered presenting an elongated morphology with extensive filament forming (filopodia) adhesion points with NTs. In addition, the expression of osteogenic markers (Runx2, BMP-2, COL-1, ALP and OPN) was significantly higher on the treated nanotubes than on untreated nanotubes and titanium surfaces. This suggests that calcium phosphorus nanotubes induced the osteogenic differentiation of human mesenchymal stem cells.

This study, for first time, showed that biocompatible anodic Ca and P-doped titanium nanotubes has osteogenesis-inducing ability and may be a very attractive candidate for the development of new smart implant surfaces designed to produce better outcomes for dental implants. View Lecture Notes

Niobium may turn implants to bone

Niobium is named after Niobe, daughter of Tantalus in Greek mythology, who turned to stone while weeping for her slain children. Coincidentally, Brazil is the leading producer of niobium, which is used in various superconducting materials, so it may not be surprising that a Brazilian team presented results of a titanium and niobium alloy used in an anodizing technique with nanotubes to improve biocompatibility when compared to conventional materials.

Although rare, the titanium alloy (Ti-6Al-4V) frequently used to produce metallic biomaterials for orthopedic prostheses sometimes produces toxic effects due to the release of aluminum and vanadium ions. In their paper the Brazilian team investigated whether a titanium-niobium alloy nanotubes could prevent this.

The results on electron micrographs showed the anodized Ti-20Nb alloy, highly ordered titania nanotubes were produced. The resulting morphology demonstrated the potential to improve osseointegration and osteoblasts adhesion ability compared to metal implants without the surface treatment. View Lecture Notes

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Starting in the mid 2000’s, the founders of Nanovation Partners LLC sponsored research at the University of California at San Diego (UCSD) in the lab of Sungho Jin, PhD. This research showed enhanced osseointegration and reduced implant surface infection by forming thousands of rows of tiny metal oxide nanotubes

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