title: Probing mechanical properties of living cells by atomic force microscopy with blunted pyramidal cantilever tips.
abstract: Atomic force microscopy (AFM) allows the acquisition of high-resolution images and the measurement of mechanical properties of living cells under physiological conditions. AFM cantilevers with blunted pyramidal tips are commonly used to obtain images of living cells. Measurement of mechanical properties with these tips requires a contact model that takes into account their blunted geometry. The aim of this work was to develop a contact model of a blunted pyramidal tip and to assess the suitability of pyramidal tips for probing mechanical properties of soft gels and living cells. We developed a contact model of a blunted pyramidal tip indenting an elastic half-space. We measured Young's modulus (E) and the complex shear modulus (G*= G' +i G" ) of agarose gels and A549 alveolar epithelial cells with pyramidal tips and compared them with those obtained with spherical tips. The gels exhibited an elastic behavior with almost coincident loading and unloading force curves and negligible values of G". E fell sharply with indentation up to approximately 300 nm , showing a linear regime for deeper indentations. A similar indentation dependence of E with twofold lower values at the linear regime was obtained with the spherical tip fitted with Hertz's model. The dependence of E on indentation in cells paralleled that found in gels. Cells exhibited viscoelastic behavior with G"/G' approximately 1/4 . Pyramidal tips commonly used for AFM imaging are suitable for probing mechanical properties of soft gels and living cells.
authors.affiliation: Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona--IDIBAPS, Casanova 143, 08036 Barcelona, Spain.
authors.forename: Félix
authors.initials: F
authors.lastname: Rico
authors.forename: Pere
authors.initials: P
authors.lastname: Roca-Cusachs
authors.forename: Núria
authors.initials: N
authors.lastname: Gavara
authors.forename: Ramon
authors.initials: R
authors.lastname: Farré
authors.forename: Mar
authors.initials: M
authors.lastname: Rotger
authors.forename: Daniel
authors.initials: D
authors.lastname: Navajas
mesh_terms: D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods; D018929:Cell Culture Techniques / Q000295:instrumentation* / Q000379:methods; D002478:Cells, Cultured; D004548:Elasticity; D042783:Endothelial Cells / Q000166:cytology* / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006244:Hardness; D006801:Humans; D008846:Micromanipulation / Q000295:instrumentation* / Q000379:methods; D018625:Microscopy, Atomic Force / Q000295:instrumentation* / Q000379:methods; D010812:Physical Stimulation / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical; D014159:Transducers; D014783:Viscosity