Magnetic Tweezers as a Tool for Biological Physics and the Viscoelastic Characterisation of Fibrin

  • David Pearce

Student thesis: Phd


Rheology is a discipline of continuum mechanics that is concerned with the mechanical properties of matter as it flows. Key to the study of rheology is the concept that materials do not behave as Newtonian liquids of as heterogenous, homogenous mateirials, but as a combination of the two. This combination and blurring of the line between liquid and solid peoperties is knows as viscosity. Furthermore, the viscosity of a material or liquid will not necessarily remain constant when it is subjected input forces or stresses at different frequencies. This consideration brings with it the idea of viscoelasticity which can account for the variations in the characteristics of a sample medium.Magnetic tweezers are tools that allow examination of and investigation into the viscoelastic properties of a sample on the mesoscopic scale. Magnetic matter can be inserted into and bound onto a sample. This magnetic matter can then be manipulated using an external magnetic or electromagnetic field. Calibrated magnetic tweezers apparatus can be used to investigate the mechanical and viscoelastic properties of a material with the novel application of time-variant forcesand stresses. The resultant behaviour, or response, of the sample can be observed using a microscope and analysed further.Fibrin is the highly extensible, fibre-like protein that makes up blood clots. Its particularly high levels of extensibility combined with interesting material properties such as viscoelasticity can strain-hardening make it an ideal test sample for magnetic tweezers experiments. The high elastic limit of fibrin ensures that plastic deformation does not usually occur under the range of input forces and stresses exerted by magnetic tweezers. This allows non-destructive and repeatable tests to be performed.Magnetic tweezers have been developed and used in a series of experiments on fibrin to produce a viscoelastic characterisation of the fibrous networks. The key results in this work are the design of high-sensitivity apparatus for the experiments and associated techniques for high-frequency analysis, use of the tweezers with a high-speed CCD attached to a microscope and the analysis of the viscoelastic properties of fibrin over a several decades of frequency.
Date of Award1 Aug 2013
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorThomas Waigh (Supervisor)


  • Viscoelastic
  • Fibrin
  • Tweezers
  • Magnetic

Cite this