Collège de France, PSL University, 75231 Paris Cedex 05, France.
Sorbonne Université, CNRS, Collège de France, Laboratoire Chimie de la Matière Condensée de Paris (LCMCP), F-75005 Paris, France.
Proc Natl Acad Sci U S A. 2020 Jun 2;117(22):11947-11953. doi: 10.1073/pnas.2001178117. Epub 2020 May 18.
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.
活组织在微观尺度上通常是不均匀的，会散射光。强散射是导致骨骼、牙齿和大脑呈现白色的原因，并且已知严重限制了生物医学光学成像的性能。基于胶原蛋白的细胞外组织（如脱钙象牙、鱼鳞或角膜）也具有透明度。然而，其物理起源仍未得到很好的理解。在这里，我们揭示了在相图的浓度范围内存在一个透明性的间隙，该间隙存在于散射纤维状胶原蛋白基质中。这种前胆固醇相呈现出与天然组织相似的三维（3D）取向有序性。通过定量研究宏观基质中 3D 纤维网络与光学和机械性能之间的关系，我们表明透明度是由于结构部分有序抑制光散射，同时保持机械稳定性、刚度和非线性。合成材料和天然材料之间的惊人相似之处为更好地理解发生的透明度提供了线索。
