Mechanical characterization of microspheres - capsules, cells and beads: a review.
ABSTRACT Microspheres, including microcapsules and cells or beads, are widely used to produce many functional products. Information about their mechanical properties is essential to understanding their performance during manufacturing, processing and end-use applications. The mechanical characterization of microspheres requires applying a mechanical load onto single microspheres and measuring the corresponding deformation, and theoretical modelling of the force-deformation relationship, which allows the determination of mechanical property parameters of the materials such as the elastic modulus, yield stress or failure stress/strain. This review presents the techniques developed for the characterization of microspheres, but focus is on the two most common techniques: atomic force microscopy and compression testing by micromanipulation. The merits and limitations of these techniques and their future developments required are discussed along with the four key aspects to mechanically characterize single microspheres: (i) elastic regime, (ii) plasticity, (iii) rupture behaviour and (iv) time-dependent effects, such as viscoelasticity and permeation.
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ABSTRACT: We present a novel approach to probe elastic properties of polyelectrolyte multilayer microcapsules. The method is based on measurements of the capsule load-deformation curves with the atomic force microscope. The experiment suggests that at low applied load deformations of the capsule shell are elastic. Using elastic theory of membranes we relate force, deformation, elastic moduli, and characteristic sizes of the capsule. Fitting to the prediction of the model yields the lower limit for Young's modulus of the polyelectrolyte multilayers of the order of 1-100 MPa, depending on the template and solvent used for its dissolution. These values correspond to Young's modulus of an elastomer.The Journal of Chemical Physics 03/2004; 120(8):3822-6. · 3.16 Impact Factor
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ABSTRACT: We have studied the mechanical properties of encapsulated Saccharomyces cerevisiae yeast cells by performing AFM force measurements. Single living cells have been coated through the alternate deposition of oppositely charged polyelectrolyte layers and mechanically trapped into a porous membrane. Coated and uncoated cells in presence/absence of bud scars, i.e. scars resulting from previous budding events, have been investigated. No significant differences between encapsulated and bare cells could be inferred from AFM topographs. On the other hand, investigation on the system elasticity through the acquisition and analysis of force curves allowed us to put in evidence the differences in the mechanical properties between the hybrid cell/polyelectrolyte system and the uncoated cells. Analysis of the curves contact region indicates that the polyelectrolyte coating increases the system rigidity. Quantitative evaluation of the cell rigidity through the Hertz-Sneddon model showed that coated cells are characterized by a Young's modulus higher than the value obtained for uncoated cells and similar to the value observed on the bud scar region of uncoated cells.Journal of Biotechnology 09/2006; 124(4):723-31. · 3.18 Impact Factor
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ABSTRACT: This paper reports a monolithic, force-feedback MEMS (microelectomechanical systems) microgripper and its application to micro-scale compression testing of swollen hydrogel microcapsules at wet state during manipulation. The single-chip microgripper integrates an electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5 nN) and the other for gripping force measurements (force resolution: 19.9 nN). With the capability of resolving gripping forces down to 19.9 nN and material deformations with a 20.5 nm resolution, the system quantified Young's modulus values and viscoelastic parameters of alginate microcapsules (15-25 microm), demonstrating an easy-to-operate, accurate compression testing technique for characterizing soft, micrometer-sized biomaterials.Biomedical Microdevices 12/2008; 11(2):421-7. · 2.72 Impact Factor