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.

Secondary caries and microleakage

“…The reason is unclear, but dentin demonstrates form bifringence, which has been attributed to the micrometer size of the dentin tubules [88]. Moreover, collagen, which is abundant in dentin also displays form birefringence [89]. It is not unlikely that any or all of these confounders will cause or influence optical birefringence in the interface between a restoration and tooth when ground sections are observed in a PLM [57].…”

Supra-organization and optical anisotropies of the extracellular matrix in the amniotic membrane and limbal stroma before and after explant culture

“…It results from the material's difference in refractive indexes that leads to light propagation in different speeds and directions [20,23,24,[26][27][28][29][30]. Regarding ECM, birefringence informs us on the supraorganization of the fibrillary collagens (in terms of fiber spatial orientation and ordered aggregational state) and is formed of two fractions: intrinsic and form birefringence.…”

“…The incidence of polarized electromagnetic waves on anisotropic structures leads to measurable changes in phase or amplitude of the orthogonal components of the electric vector, known as birefringence and dichroism, respectively [20][21][22][23][24][25]. Studies on birefringence and dichroim (using polarized light microscope and image analysis) inform us as supramolecular organizations react with adaptation and flexibility to the morpho-functional or pathological requirements [26]. For example, several authors detected changes in supraorganization and anisotropical properties of ECM during wound healing, aging, endochondral ossification, inflammation and osteoarthritis, gelatinous drop-like corneal dystrophy, keratoconus, diabetes, floppy mitral valve syndrome and other.…”

“…It results from the electronic transitions of peptide bonds along the fiber axis [22,[26][27][28][29][30]. Form birefringence results from the compatibility of the photon's wavelengths and the nanometric dimensions of asymmetrical molecules in the fibrillary collagens [24][25][26][27][28][29][30][31][32]. It can be considered a nonlinear optical property [26][27][28][29][30].…”

“…Intrinsic birefringence is expressed by the equation n e -n o , where n e is the refractive index in the direction of propagation of the extraordinary ray and n o is the refractive index in the direction of the ordinary ray. It results from the electronic transitions of peptide bonds along the fiber axis [22,[26][27][28][29][30]. Form birefringence results from the compatibility of the photon's wavelengths and the nanometric dimensions of asymmetrical molecules in the fibrillary collagens [24][25][26][27][28][29][30][31][32].…”