3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 1 I LECTURE 7: SINGLE CELL MECHANICS Outline : LAST TIME : AFM IMAGING II : ARTIFACTS AND APPLICATIONS ....................................................... 2 THE NANOMANIPULATOR .................................................................................................................... 3 SINGLE CELL AFM IMAGING ................................................................................................................. 4 SINGLE CELL MECHANICS : Motivation ................................................................................................ 5 Experimental Methods ................................................................................................................ 6 General Structure and Stiffness .................................................................................................. 7 Detailed Modeling ....................................................................................................................... 8 Objectives: To understand the fundamentals of single cell mechanics, in particular the structural components and how they are typically modeled Readings: Dao, et al. J. Mech. Phys. Solids 51 (2003) 2259-2280 (posted on stellar under "Supplementary Resources"-not in course reader). Multimedia : Listen to "Malaria" Podcast corresponding to journal article : Suresh, et al. Acta Biomaterialia 2005 1, 15, 2)3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 2 ATOMIC FORCE MICROSCOPY : ARTIFACTS AND APPLICATIONS ●Factors affecting spatial resolution; piezo amplifier, sensor, and control electronics, mechanical parameters; specimen deformation and thermal fluctuations, adhesion force, cantilever thermal noise, probe tip sharpness; tip deconvolution 2D Height Profilez x height would theoretically be accurate       xtan x = wtanwwr* = wtan2r * 1tanw2 3 Applications : ● AFM Imaging of Biological Macromolecules (DNA) ● Bone Implant Materials : AFM combined with HRFS : Spatially Specific Measurements ● Support Lipid Bilayers (Higgens, et al. Structured Water Podcast) DPPC DOPC Higgens, et al. Biophys. J. 2006 91, 2532.3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 3 THE NANOMANIPULATOR (NC STATE) A 3D virtual reality visual interface is provided to the microscope that is similar to looking at a real human-scale physical surface (essentially magnifying the object under study up to a million times) with a "haptic" display (a Phantom forcefeedback device) or "touch" interface similar to operating on a human-scale materials with a hand-tool such as a pencil, scalpel, or broom. The scientist can guide the tip directly in order to feel the surface and can increase the force used in order to modify the sample. Haptic feedback guides the progress of an experiment. This system allows the scientist to see, touch, and manipulate it directly. - More intuitive data interpretation (sense of touch) to allow scientists to more readily understand data, better control over nanomanipulation. Remote experimentation - MIT iLabs: Internet access to real labs - anywhere, anytime (http://icampus.mit.edu/ilabs/) :3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 4 SINGLE CELL AFM IMAGING Contact mode image of human red blood cells - note cytoskeleton is visible. blood obtained from Johathan Ashmore, Professor of Physiology University College, London. A false color table has been used here, as professorial blood is in fact blue. 15µm scan courtesy M. Miles and J. Ashmore, University of Bristol, U.K. Rat Embryo Fibroblast (*M. Stolz,C. Schoenenberger, M.E. Müller Institute, Biozentrum, Basel Switzerland)Height image of endothelial cells taking in fluid using Contact Mode AFM. 65 µm scan courtesy J. Struckmeier, S. Hohlbauch, P. Fowler, Digital Intruments/Veeco Metrology, Santa Barbara, USA.Red Blood CellsShao, et al., : http://www.people.virginia.edu/~js6s/zsfig/random.htmlRadmacher, et al., Cardiac Cellshttp://www.physik3.gwdg.de/~radmacher/3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 5 SINGLE CELL MECHANICS : MOTIVATION (Bao, et al 2003 Nature Materials.) Mechanical forces are essential to living cells! Examples : -Musculoskeletal Tissues : Cells in our tissues (e.g. cartilage, bone) are subjected to physiological stresses/strains which are a critical determinant of remodeling. Nonphysiological stress states result in cellular dysfunction producing diseased states (i.e. ACL tear→osteoarthritis). -Circulatory System : Human red blood cell (RBC's) (diameter ~ 8 m) experience 100% elastic deformation as blood flows through narrow capillaries, must deform repeatedly reversibly ~half million times- deformability is critical to RBC circulation!! 120 day lifetime; aged and defective RBCs with decreased deformability are detected and removed from circulation by the spleen. D. Kunkel Microscopy, Inc., http://nmhm.washingtondc.museum/news/imgs/red_blood_cells_lg.jpg, Biomechanics Fung, 1993 -Brain : Large fast strains of the axon of neuronal cells for example as a result of traumatic brain injury causes cell death while slow stretching of the axon promotes neural cell growth.3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 6 EXPERIMENTAL METHODS FOR SINGLE CELL MECHANICS (Bao, et al 2003 Nature Materials.) A, B a localized area of the cell is deformed C,D mechanical loading of an entire cell E, F, G simultaneous mechanical loading of a population of cells G Cell force monitor : (B. Harley, L.J. Gibson, After Freyman 2001)3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSE 7 MECHANICS OF SINGLE CELLS (Bao, et al 2003 Nature Materials, Dao, et al 2003 J. Mech. Phys. Solids.) • The cell is surrounded by a lipid bilayer that provides little mechanical strength. • The cell stiffness is largely determined by the cytoskeleton. • The composite is modeled as an isotropic, elastic, continuum, incompressible (constant volume), constant surface