title: Sensing surface morphology of biofibers by decorating spider silk and cellulosic filaments with nematic microdroplets.
abstract: Probing the surface morphology of microthin fibers such as naturally occurring biofibers is essential for understanding their structural properties, biological function, and mechanical performance. The state-of-the-art methods for studying the surfaces of biofibers are atomic force microscopy imaging and scanning electron microscopy, which well characterize surface geometry of the fibers but provide little information on the local interaction potential of the fibers with the surrounding material. In contrast, complex nematic fluids respond very well to external fields and change their optical properties upon such stimuli. Here we demonstrate that liquid crystal droplets deposited on microthin biofibers--including spider silk and cellulosic fibers--reveal characteristics of the fibers' surface, performing as simple but sensitive surface sensors. By combining experiments and numerical modeling, different types of fibers are identified through the fiber-to-nematic droplet interactions, including perpendicular and axial or helicoidal planar molecular alignment. Spider silks align nematic molecules parallel to fibers or perpendicular to them, whereas cellulose aligns the molecules unidirectionally or helicoidally along the fibers, indicating notably different surface interactions. The nematic droplets as sensors thus directly reveal chirality of cellulosic fibers. Different fiber entanglements can be identified by depositing droplets exactly at the fiber crossings. More generally, the presented method can be used as a simple but powerful approach for probing the surface properties of small-size bioobjects, opening a route to their precise characterization.
authors.affiliation: CENIMAT/I3N, Research Centre in Materials/Institute for Nanostructures, Nanomodelling and Nanofabrication, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal;
authors.forename: Luis E
authors.initials: LE
authors.lastname: Aguirre
authors.affiliation: CENIMAT/I3N, Research Centre in Materials/Institute for Nanostructures, Nanomodelling and Nanofabrication, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal;
authors.forename: Alexandre
authors.initials: A
authors.lastname: de Oliveira
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia; Adria Tehnik d.o.o., 4290 Tržič, Slovenia;
authors.forename: David
authors.initials: D
authors.lastname: Seč
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia;
authors.forename: Simon
authors.initials: S
authors.lastname: Čopar
authors.affiliation: CENIMAT/I3N, Research Centre in Materials/Institute for Nanostructures, Nanomodelling and Nanofabrication, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal; Área Departamental de Física, Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa, 1959-007 Lisbon, Portugal;
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Almeida
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia; Condensed Matter Physics Department, Jozef Stefan Institute, 1000 Ljubljana, Slovenia.
authors.forename: Miha
authors.initials: M
authors.lastname: Ravnik
authors.affiliation: CENIMAT/I3N, Research Centre in Materials/Institute for Nanostructures, Nanomodelling and Nanofabrication, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal; slobodan.zumer@fmf.uni-lj.si mhg@fct.unl.pt.
authors.forename: Maria Helena
authors.initials: MH
authors.lastname: Godinho
authors.affiliation: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia; Condensed Matter Physics Department, Jozef Stefan Institute, 1000 Ljubljana, Slovenia slobodan.zumer@fmf.uni-lj.si mhg@fct.unl.pt.
authors.forename: Slobodan
authors.initials: S
authors.lastname: Žumer
mesh_terms: D000818:Animals; D002482:Cellulose / Q000737:chemistry*; D015335:Molecular Probes; D047011:Silk / Q000737:chemistry*; D013112:Spiders; D013499:Surface Properties
chemical_list: D015335:Molecular Probes; D047011:Silk; D002482:Cellulose
keywords: biofibers; cellulose; nematic droplets; sensor; spider silk