A central issue in implant success is integration with native tissue. Osseointegration is aided by a number of factors including implant material and surface qualities. It is not uncommon for implant manufacturers to treat the surface of an implant to give cells a more suitable interface for attachment. Nanoscale engineering is proving to simplify the process.
To achieve improved integration without complex post-processing, Biotanium™ can be used. This material was developed in a seemingly unlikely collaboration between US researchers at Los Alamos National Lab and Russian researchers at the Institute for Physics of Advanced Materials, and other institutes in Russia.
It works by increasing surface area (akin to roughness) through reduced grain size. Although compositionally identical to other biomedical titanium, the material exhibits a grain size about 100 times smaller than average titanium. The increased boundary area of the grains aids cell attachment and growth. The grain size reduction increases strength as well.
Biotanium™ is classified as an Ultra-fine Grained (UFG) metal. UFG materials have a grain size generally stated to be greater than 100 nm and less than a micron. The Hall-Petch relation predicts a dramatic rise in yield strength as grain size enters the nanoscale regime.
An increase in strength by grain size reduction is often associated with a concomitant decreased in ductility. For example, if you take a copper wire and bend it back and forth enough times you’ll notice that it gets harder to bend with each cycle.
Eventually it breaks. The metal has been severely deformed and becomes more brittle. There is a useful limit to grain size reduction, although multimodal grain size engineering is seeking to achieve the best of both worlds. UFG metals tend to retain good ductility for their strength.
Although the exact method for producing these materials is not described, severe plastic deformation (SPD) is a common route for reducing grain size. SPD amounts to little more than a forging or other forming operation taken to new (“severe”) extremes.
There are a variety of techniques for achieving a UFG metal through SPD. These include equal-channel angular extrusion (ECAE, or ECAP) and high-pressure torsion (HPT), neither of which is particularly good for large cross-sectional thickness. This is likely the reason Biotanium™ has been first adopted to relatively small dental implants.
The development of commercially viable micro- and nano-engineered materials is a clear indicator of the benefit these disciplines can deliver. By reducing and controlling grain size, a simple material can behave like or even outperform more complex components and processes.
Images courtesy of BASIC Dental Implants