Biotribology on the microscale and nanoscale

20 January 2009

Prof Ille C. Gebeshuber Universiti Kebangsaan Malaysia, Malaysia http://www.ille.com

Category:

Biochemistry, Genetics and Molecular Biology Biochemistry Engineering Engineering (miscellaneous), Mechanics of Materials Materials Science Biomaterials Physics and Astronomy Surfaces and Interfaces

Biotribologists gather information about biological surfaces inrelative motion, their friction, adhesion, lubrication, and wear, and apply this knowledge to technological innovation as well as to thedevelopment of environmentally sound products.

In micro- and nanotribology, at least one of the two interacting surfaces in relative motion has a relatively small mass, and the interaction occurs mainly under lightly loaded conditions. In this situation, negligible wear occurs and the surface properties dominate the tribological performance (Bhushan 2000). Biological systems also excel at this scale and might serve as templates for developing the next generation of tools based on nano- and micrometer scale technologies (Scherge and Gorb 2001).

A few examples of biological systems with amazing tribological properties at the micro- and nanoscale level are given below:

* Diatoms arealgae just a couple of micrometers in size (Round, Crawford and Mann 1990) that have rigid surfaces inrelative motion and have evolved self-healing adhesives, nanostructuredamorphous silica surfaces, and interconnected junctions (Gebeshuber 2007, Gebeshuber and Crawford 2006, Gebeshuber et al 2002).

* White blood cells serve as the police of the body's immune system. Theyflow in the blood stream and have to be stopped at the site of aninflammation. An exquisite arrangement of different, switchableadhesives enables controlled deployment of anti-inflammatory agents inour bodies (Orsello et al 2001).

* The Gecko can easily climb up walls and run on ceilings. The measurement of the adhesive force exerted by a single Gecko hair (Autumn et al 2000) has opened a new field of research: dry adhesives.

*Tough underwater adhesives produced by diatoms and the molecular mechanistic origin of the ‘glue’ responsible for the high fracture resistance of the abalone shell (Smith et al 1999) conclude the biological examples.

Current synthetic adhesives and lubricants are not perfect, and the low friction coefficients in many natural systems are yet to be achieved in artificial systems. Technological innovations, completely new ideas, and unconventional approaches can all be learned from nature. These approaches have been tested and improved upon for millions of years; they are continuously being optimized with respect to their function and environment. The perfect material is not pure, homogenous, and with constant parameters, but can be controlled over time, has the capacity to self-repair, and disintegrates after disposal. Living systems possess all these abilities.

Biomicro- and nanotribology, the investigation of micro- and nanoscale tribological principles in biological systems, may be a path to realizing simultaneously ‘smart’, dynamic, complex, environmentally friendly (nontoxic, biodegradable, able to be integrated in biogeochemical cycles without sinks), self-healing, and multifunctional lubricants and adhesives. A biomimetic and bioinspired approach to tribology should therefore be considered further (Gebeshuber and Drack 2008).