title: Housing tubes from the marine worm Chaetopterus sp.: biomaterials with exceptionally broad thermomechanical properties.
abstract: The housing tube material of the marine worm Chaetopterus sp. exhibits thermal stability up to 250°C, similar to other biological materials such as mulberry silkworm cocoons. Interestingly, however, dynamic mechanical thermal analysis conducted in both air and water elucidated the lack of a glass transition in the organic tube wall material. In fact, the viscoelastic properties of the anhydrous and undried tube were remarkably stable (i.e. constant and reversible) between -75°C and 200°C in air, and 5°C and 75°C in water, respectively. Moreover, it was found that hydration and associated-water plasticization were key to the rubber-like flexible properties of the tube; dehydration transformed the material behaviour to glass-like. The tube is made of bionanocomposite fibrils in highly oriented arrangement, which we argue favours the biomaterial to be highly crystalline or cross-linked, with extensive hydrogen and/or covalent bonds. Mechanical property characterization in the longitudinal and transverse directions ascertained that the tubes were not quasi-isotropic structures. In general, the higher stiffness and strength in the transverse direction implied that there were more nanofibrils orientated at ± 45° and ± 65° than at 0° to the tube axis. The order of the mechanical properties of the soft-tough tubes was similar to synthetic rubber-like elastomers and even some viscid silks. The complex structure-property relations observed indicated that the worm has evolved to produce a tubular housing structure which can (i) function stably over a broad range of temperatures, (ii) endure mechanical stresses from specific planes/axes, and (iii) facilitate rapid growth or repair.
authors.affiliation: Oxford Silk Group, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK darshil.shah@zoo.ox.ac.uk.
authors.forename: Darshil U
authors.identifier: http://orcid.org/0000-0002-8078-6802
authors.initials: DU
authors.lastname: Shah
authors.affiliation: Oxford Silk Group, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
authors.forename: Fritz
authors.initials: F
authors.lastname: Vollrath
authors.affiliation: Oxford Silk Group, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
authors.forename: David
authors.initials: D
authors.lastname: Porter
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA.
authors.forename: John
authors.initials: J
authors.lastname: Stires
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA ddeheyn@ucsd.edu.
authors.forename: Dimitri D
authors.initials: DD
authors.lastname: Deheyn
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D003460:Crystallization; D006358:Hot Temperature; D006859:Hydrogen / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D010100:Oxygen / Q000737:chemistry; D011077:Polychaeta / Q000502:physiology*; D011312:Pressure; D013314:Stress, Mechanical; D013696:Temperature; D013718:Tensile Strength; D013818:Thermogravimetry
chemical_list: D001672:Biocompatible Materials; D006859:Hydrogen; D010100:Oxygen
keywords: Chaetopterus; marine polychaete; parchment biomaterial; thermomechanical properties