title: A portable extensional rheometer for measuring the viscoelasticity of pitcher plant and other sticky liquids in the field.
abstract: BACKGROUND
  Biological fluids often have interesting and unusual physical properties to adapt them for their specific purpose. Laboratory-based rheometers can be used to characterise the viscoelastic properties of such fluids. This, however, can be challenging as samples often do not retain their natural properties in storage while conventional rheometers are fragile and expensive devices ill-suited for field measurements. We present a portable, low-cost extensional rheometer designed specifically to enable in situ studies of biological fluids in the field. The design of the device (named Seymour) is based on a conventional capillary break-up extensional rheometer (the Cambridge Trimaster). It works by rapidly stretching a small fluid sample between two metal pistons. A battery-operated solenoid switch triggers the pistons to move apart rapidly and a compact, robust and inexpensive, USB 3 high speed camera is used to record the thinning and break-up of the fluid filament that forms between the pistons. The complete setup runs independently of mains electricity supply and weighs approximately 1 kg. Post-processing and analysis of the recorded images to extract rheological parameters is performed using open source software.
  
  
  RESULTS
  The device was tested both in the laboratory and in the field, in Brunei Darussalam, using calibration fluids (silicone oil and carboxymethyl cellulose solutions) as well as Nepenthes pitcher plant trapping fluids as an example of a viscoelastic biological fluid. The fluid relaxation times ranged from 1 ms to over 1 s. The device gave comparable performance to the Cambridge Trimaster. Differences in fluid viscoelasticity between three species were quantified, as well as the change in viscoelasticity with storage time. This, together with marked differences between N. rafflesiana fluids taken from greenhouse and wild plants, confirms the need for a portable device.
  
  
  CONCLUSIONS
  Proof of concept of the portable rheometer was demonstrated. Quantitative measurements of pitcher plant fluid viscoelasticity were made in the natural habitat for the first time. The device opens up opportunities for studying a wide range of plant fluids and secretions, under varying experimental conditions, or with changing temperatures and weather conditions.
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: Catherine
authors: C
authors: Collett
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: Alia
authors: A
authors: Ardron
authors: School of Biological Sciences, Life Sciences Building, 24 Tyndall Avenue, Bristol, BS8 1TQ UK ; Faculty of Science, Universiti Brunei Darussalam, Tungku Link, Gadong 1410, Bandar Seri Begawan, Brunei Darussalam.
authors: Ulrike
authors: U
authors: Bauer
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: Gary
authors: G
authors: Chapman
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK ; ESPCI ParisTech, 10 rue Vauquelin, 75005 Paris, France.
authors: Elodie
authors: E
authors: Chaudan
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: Bart
authors: B
authors: Hallmark
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: Lee
authors: L
authors: Pratt
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK ; Department of Chemical Engineering, University of Santiago de Compostela, Lope Gómez de Marzoa St, Santiago de Compostela, E-15782 Spain.
authors: Maria Dolores
authors: MD
authors: Torres-Perez
authors: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, Cambridge, CB2 3RA UK.
authors: D Ian
authors: DI
authors: Wilson
keywords: Biological fluids; Filament; Giesekus; Nepenthes; Pitcher plants; Polymer solution; Polysaccharide; Rheometry