Micropipette Aspiration Technique Revisited for Quantifying Mechanical Properties of Biological Samples

Jacques Ohayon, PhD

Laboratory TIMC-IMAG/DyCTiM, UJF, CNRS UMR 5525, In³S
Faculty of Medicine  of Grenoble - 38706 La Tronche Cedex, France
Email: Jacques.Ohayon@imag.fr

An Extended Modeling of the Micropipette Aspiration Experiment for the Characterization of the Young’s Modulus and Poisson’s Ratio of Adherent Thin Biological Samples - Journal of Biomechanics, 39:1677-85, 2006 -  Biorheology, 43(6) : 721-8, 2006 - Biorheology, 46(3):191-205, 2009 - The micropipette aspiration (MA) experiment remains a quite widely used micromanipulation technique for quantifying the elastic modulus of cells and, less frequently, of other biological samples. However, moduli estimations derived from MA experiments are only valid if the probed sample is non-adherent to the rigid substrate. This study extends this standard formulation by taking into account the influence of the sample adhesion. Using a finite element analysis of the sample aspiration into the micropipette, we derived a new expression of the aspirated length for linear elastic materials. Our results establish that -(i) below a critical value, the thickness h of the probed sample must be considered to get an accurate value of its Young’s modulus -(ii) this critical value depends both on the Poisson’s ratio and on the sample adhesivity. Additionally, we propose a novel method which allows the computation of the intrinsic Young’s modulus of the adherent probed sample from its measured apparent elasticity modulus. Thanks to the set of computational graphs we derived from our theoretical analysis, we successfully validate this method by experiments performed on polyacrylamide gels. Interestingly, the original procedure we proposed allows a simultaneous quantification of the Young’s modulus and of the Poisson’s ratio of the adherent gel. Thus, our revisited analysis of MA experiments extends the application domain of this technique, while contributing to decrease the dispersion of elastic modulus values obtained by this method.

Fig. 1 : Two video snapshots recorded during the aspiration of a polyacrylamide gel. The left images A and B were taken at dP = 0 kPa and dP = 4.52 kPa, respectively. Axial intensity curves (right) were obtained along the line centred about the pipette axis (dash line). From these curves, the distances between the gel/glass interface (arrows 1A and 1B) and the free gel surface (arrows 2A and 2B) were precisely measured and the aspiration length d was calculated.

Selected Publications

• Ohayon J, Mesnier N, Broisat A, Toczek J, Riou L, Tracqui P. Elucidating atherosclertic vulnerable plaque rupture by modeling cross substitution of ApoE-/- mouse and human plaque component stiffnesses. Biomechanics and Modeling in Mechanobiology. (in press), 2011.

•  Ohayon J, Gharib AM, Garcia A, Heroux J, Yazdani SK, Malvè M, Tracqui P, Martinez MA, Doblare M, Finet G, Pettigrew RI. Is arterial wall-strain stiffening and additional process responsible for atherosclerosis in coronary bifurcations? in vivo Study Based on Dynamic CT and MRI. Am J Physiol Heart Circ Physiol. 301(3):H1097-106, 2011.

• Broisat A, Toczek J, Mesnier N, Tracqui P, Ghezzi C, Ohayon J, Riou L. Assessing the low levels of mechanical stress in aortic atherosclerosis lesions from ApoE-/-mouse . Arterioscler Thromb Vasc Biol. 31(5):1007-10, 2011.

• Tracqui P, Broisat A, Toczek J, Mesnier N, Ohayon J, Riou L. Mapping elasticity moduli of atherosclerotic plaque in situ via atomic force microscopy . Journal of structural Biology 174(1):115-23, 2011.

• Heroux J, Gharib AM, Danthi NS, Cecchini S, Ohayon J, Pettigrew RI. High Affinity avb3 Integrin Targeted Optical Probe as a New Imaging Biomarker for Early Atherosclerosis: Initial Studies in Watanabe Rabbits. Mol Imaging Biol., 12(1):2-8, 2010.

•  Soloperto G, Keenan NG, Sheppard MN, Ohayon J, Wood N, Pennell DJ, Mohiaddin RH, Xu XY. A combined imaging, computational and histological analysis of a ruptured carotid plaque. Artery Research, 4(2):59-65, 2010.

•  Le Floc'h S, Cloutier G, Finet G, Tracqui P, Pettigrew RI, Ohayon J. On the potential of a new IVUS elasticity modulus imaging approach for detecting vulnerable atherosclerotic coronary plaques: in vitro vessel phantom study. Phys. Med. Biol., 55:5701-5721, 2010.

•  Finet G., Huo Y, Riouffol G, Ohayon J, Guerin P, Kassab GS.  Structure-function relation in the coronary artery tree: from fluid dynamics to arterial bifurcations. EuroIntervention, 6:J10-J15, 2010.

•  Le Floc'h S, Ohayon J, Tracqui P, Finet G, Gharib AM, Maurice R, Cloutier G, Pettigrew RI. Vulnerable Atherosclerotic Plaque Elasticity Reconstruction Based on a Segmentation-Driven Optimization Procedure Using Strain Measurements: Theoretical Framework. IEEE Trans Med Imaging, 28(7):1126-37, 2009.

•  Kotys MS, Herzka DA, Vonken EJ, Ohayon J, Heroux J, Gharib AM, Stuber M, Pettigrew RI. Profile order and time-dependent artifacts in contrast-enhanced coronary MR angiography at 3T: origin and prevention. Magn Reson Med., 62(2):292-9, 2009.

•  Eskandari H, Salcudean SE, Rohling R, Ohayon J. Viscoelastic characterization of soft tissue from dynamic finite element models. Physics in Medicine and Biology, 53(22):6569-90, 2008.

•  Ohayon J, Finet G, Gharib AM, Herzka DA, Tracqui P, Heroux J, Rioufol G, Kotys MS, Elagha A, Pettigrew RI. Necrotic core thickness asnd positive arterial remodeling index: emergent biomechanical factors for evaluating the risk of plaque rupture. Am J Physiol Heart Circ Physiol., 295(2):H717-27, 2008.

•  Ohayon J, Dubreuil O, Tracqui P, Le Floc'h S, Rioufol G, Chalabreysse L, Thivolet F, Pettigrew RI, Finet G. Influence of residual stress/strain on the biomechanical stability of vulnerable coronary plaques: potential impact for evaluating the risk of plaque rupture. Am J Physiol Heart Circ Physiol., 293(3):H1987-96, 2007.

•  Boudou T., Ohayon J., Arntz Y., Finet G., Picart C., Tracqui P. An extended modeling of the micropipette aspiration experiment for the characterization of the Young’s modulus and Poisson’s ratio of adherent thin biological samples: Numerical and experimental studies. Journal of Biomechanics, 39:1677-85, 2006.

•  Boudou T., Ohayon J., Picart C., Tracqui P. Characterization of the Young’s modulus and Poisson’s ratio of polyacrylamide gels using micropipette aspiration technique. Biorheology, 43(6): 721-8, 2006.