Shedding light on biomaterials

20 Jul 2006

Researchers in Germany believe that the ability of some biomaterials to guide light is due to light scattering, and not fiber-optic effects as previously thought.

Biophysicists have known for a long time that polar-bear fur and other biological materials with an ordered microstructure can guide light, but this has always been assumed to be because of fiber-optic effects. Now, however, physicists in Germany have shown that the light-guiding effect in a component of teeth called dentin is due to light scattering (Phys. Rev. Lett. 97 018104).

"This light-guiding effect could be important for therapeutic and diagnostic applications of light in medicine because many tissues exhibit a similar elongated, cylindrical microstructure as dentin -- for example, muscle, skin, tendon, bone, enamel and ligaments," explains Alwin Kienle of the University of Ulm. The researchers say that the finding could also be relevant to other biomaterials, and call for all light-guiding effects in nature to be reviewed.

Scattering from dentin

The team came to its surprising conclusion after looking at how laser light scatters off the faces of cubes of dentin varying in thickness from 20 µm to 1 mm. Using an optical microscope, the researchers observed that almost all of the light was transmitted from one of the faces perpendicular to the first face but that very little light was transmitted from the other faces (see figure).

Tubules

According to the team, this anisotropic light propagation is due to multiple scattering from the microstructure of dentin, which is made up of "tubules" -- cylindrical channels that run from the pulp to the enamel-dentin junction in a tooth. The team confirmed this result by studying exactly how the light was transmitted using a CCD camera and comparing these measurements to computer simulations of light propagation through dentin.

Kienle also thinks that this effect could be seen in biomaterials other than human tissue. For example, nature could be using it as an "inexpensive" way to harvest light in seeds, leaves, or plants. The researchers even believe that the effect could be used to focus sunlight and generate solar power.