Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Edited by Lia Addadi, Weizmann Institute of Science, Rehovot, Israel, and approved April 10, 2020 (received for review January 21, 2020)
Significance
Disordered materials with heterogeneities at scales ranging from nano- to micrometers usually scatter visible light and become opaque beyond a certain thickness. However, transparent materials are found in nature. The physical origin of transparency in natural and artificial biopolymer materials is still not fully understood. Here, a gap of transparency is found in synthetic fibrillar collagen matrices within a very narrow range of concentration. The transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The potential to produce biomimetic hydrogels with such striking optical properties by self-assembly opens an interesting route in the study of photonic materials and provides new elements in the understanding of the appearance of transparency in natural materials.
Abstract
Living tissues, heterogeneous at the microscale, usually scatter light. Strong scattering is responsible for the whiteness of bones, teeth, and brain and is known to limit severely the performances of biomedical optical imaging. Transparency is also found within collagen-based extracellular tissues such as decalcified ivory, fish scales, or cornea. However, its physical origin is still poorly understood. Here, we unveil the presence of a gap of transparency in scattering fibrillar collagen matrices within a narrow range of concentration in the phase diagram. This precholesteric phase presents a three-dimensional (3D) orientational order biomimetic of that in natural tissues. By quantitatively studying the relation between the 3D fibrillar network and the optical and mechanical properties of the macroscopic matrices, we show that transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The striking similarities between synthetic and natural materials provide insights for better understanding the occurring transparency.
Footnotes
↵1C. Salameh and F.S. contributed equally to this work.
↵2Present address: Institut Européen des Membranes (IEM), UMR 5635, Univ Montpellier, CNRS, Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), 34095 Montpellier, Cedex 5, France.
- ↵3To whom correspondence may be addressed. Email: nadine.nassif{at}sorbonne-universite.fr.
Author contributions: N.N. designed research; C. Salameh, F.S., E.B., M.L., J.-M.C., E.M., Y.W., M.R., A.B., M.S., A.M., M.F., and N.N. performed research; C. Salameh, F.S., E.B., M.L., J.-M.C., F.A., A.M., C. Sanchez, M.-M.G.-G., M.F., R.C., and N.N. analyzed data; and C. Salameh, F.S., M.L., J.-M.C., F.A., A.M., R.C., and N.N. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2001178117/-/DCSupplemental.
Published under the PNAS license.
Origin of transparency in scattering biomimetic collagen materials
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- Chemistry
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