Form birefringence as applied to biopolymer and inorganic material supraorganization

Abstract

I review here form, or textural, birefringence (Δ_F) in the context of advances in the field, as well as with regard to findings and applications in the physics of photonic devices, fibers maintaining polarization, photonic crystal fibers, and in biopolymers present in extracellular matrices and the myelin sheath. Some advantages of applying knowledge of Δ_F to biological fields involving biopolymers, especially collagen fibers, are considered in more detail. Tendon and cartilage collagen fibers have been regarded as a model of dense, highly aggregated biopolymers with preferential orientations. Owing to their supramolecular organization, such materials may be used to study molecular order by using anisotropic optical properties, especially Δ_F. Differences between collagen type I- and collagen type II-rich structures, and similarities between collagen crimp and second harmonic generation images are reported. Based on data reported here, it is possible to deduce that collagen type I supramolecular organization has nonlinear optical properties and that tendon segments can conduct red laser light. With respect to nerve fibers, the detection and measurements of Δ_F have allowed the myelin sheath to be considered a smectic liquid crystal.

Key words::

• biopolymers
• collagen fibers
• crimp
• form birefringence
• image analysis
• myelin sheath
• supraorganization

Acknowledgments

The support of the São Paulo State Research Foundation (FAPESP – grants no. 2003/04597-0 and 2007/058251-8) and of the Brazilian National Council for Research and Development (CNPq) is gratefully acknowledged. The author is indebted to Dr. Maria Luiza S. Mello (Unicamp, Brazil) for helpful discussion and suggestions.

Declaration of interest: The author report no conflicts of interest. The author alone is responsible for the content and writing of the paper.