Mechanically induced disorder-order transitions have been studied in fluid surfactant solutions or polymer thermotropic liquid crystals.H owever,i sothermally induced ordered phases do not persist after cessation of shear,w hich limits their technological applicability.M oreover,n os uch stimuli-responsive materials involving biomacromolecules have been reported although biopolymer liquids are gaining al ot of attention. Ab iological fluid system is introduced in which anionic polypeptides are complexed with cationic surfactants.T he resulting fluids exhibited very sensitive isotropic-nematic transition triggered by shear.T he formed liquid crystal was preserved after cessation of mechanical stimulus.S elf-ordering behavior of the material was achieved through water flowa nd finger pressing. The latter mechanical induction resulted in the formation of complex pattern that can be read out by birefringence,a llowing the recording of fingerprint information.Phase transitions of materials triggered by external stimuli, including application of electric fields, [1] magnetic fields, [2] light, [3] shear, [4][5][6] or temperature changes, [7] are of great interest because structural rearrangements within the materials result in abrupt changes of material properties.A mong them, shear-induced disorder-order transitions in soft polymeric materials have been extensively investigated because they are important for the optimization of processing conditions within the oil and plastic industry as well as for the function and properties of cell membranes and biological fibers in nature. [8][9][10][11][12][13][14] Forinstance,isotropic-nematic (I-N) and isotropic-smectic (I-S) transitions were realized in amphiphile micellar solutions [8][9][10][11] and thermotropic liquid crystals (LCs) [12,13] under steady shear flow.H owever,i ti sh ard to stabilize the resulting ordered phases after cessation of shear, [8][9][10][11][12][13] which may limit harnessing their favorable properties.Therefore,maintaining an ordered state induced from an isothermal disordered phase in polymer fluids in absence of an applied shear force remains an important challenge.Supramolecular self-assembly has attracted considerable interest for the fabrication of biomacromolecular soft materials. [15][16][17] Fori nstance,aseries of biopolymer LCs and disordered liquids made of nucleic acids, [18,19] polypeptides, [20,21] proteins, [22,23] and virus particles [24,25] have been reported. However,t ot he best of our knowledge,n o biological fluid that is characterized by shear-induced disorder-order transition has been disclosed. Such an ew type of stimuli-responsive soft biomaterial would be very appealing for several reasons.T hey would facilitate biophysical measurements for structure elucidation. [26] Cross-linking of building blocks of biological fibers in the ordered phase might result in biodegradable materials with appealing mechanical properties.I nb iocatalysis,s tructurally ordered enzymes might show improved catalytic properties on their biomacromo...
