title: Study of the tensile properties of individual multicellular fibres generated by Bacillus subtilis.
abstract: Multicellular fibres formed by Bacillus subtilis (B. subtilis) are attracting interest because of their potential application as degradable biomaterials. However, mechanical properties of individual fibres remain unknown because of their small dimensions. Herein, a new approach is developed to investigate the tensile properties of individual fibres with an average diameter of 0.7 μm and a length range of 25.7-254.3 μm. Variations in the tensile strengths of fibres are found to be the result of variable interactions among pairs of microbial cells known as septa. Using Weibull weakest-link model to study this mechanical variability, we predict the length effect of the sample. Moreover, the mechanical properties of fibres are found to depend highly on relative humidity (RH), with a brittle-ductile transition occurring around RH = 45%. The elastic modulus is 5.8 GPa in the brittle state, while decreases to 62.2 MPa in the ductile state. The properties of fibres are investigated by using a spring model (RH < 45%) for its elastic behaviour, and the Kelvin-Voigt model (RH > 45%) for the time-dependent response. Loading-unloading experiments and numerical calculations demonstrate that necking instability comes from structural changes (septa) and viscoelasticity dominates the deformation of fibres at high RH.
authors.affiliation: Department of Engineering Mechanics, AML, Tsinghua University, Beijing 100084, China.|Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
authors.forename: Xuan
authors.initials: X
authors.lastname: Ye
authors.affiliation: Center for Synthetic and Systems Biology, Tsinghua University, Beijing 100084, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhao
authors.affiliation: Department of Engineering Mechanics, AML, Tsinghua University, Beijing 100084, China.|Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
authors.forename: Jiecun
authors.initials: J
authors.lastname: Liang
authors.affiliation: Department of Engineering Mechanics, AML, Tsinghua University, Beijing 100084, China.|Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.
authors.forename: Xide
authors.initials: X
authors.lastname: Li
authors.affiliation: Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China.|Center for Synthetic and Systems Biology, Tsinghua University, Beijing 100084, China.
authors.forename: Guo-Qiang
authors.initials: GQ
authors.lastname: Chen
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D055119:Elastic Modulus; D017353:Gene Deletion; D006813:Humidity; D008954:Models, Biological; D013718:Tensile Strength; D014783:Viscosity