ATOMIC FORCE MICROSCOPY : ARTIFACTS AND APPLICATIONS3.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSEILECTURE 7: SINGLE CELL MECHANICSOutline :LAST TIME : AFM IMAGING II : ARTIFACTS AND APPLICATIONS..........................................................2THE NANOMANIPULATOR ......................................................................................................................3SINGLE CELL AFM IMAGING....................................................................................................................4SINGLE 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)13.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSEATOMIC 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(q) = � (q)+ (q)= + (q)xtan x =wtanwwr* = wtan2r * 1tanw 23 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 DOPCHiggens, et al. Biophys. J. 2006 91, 2532.23.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSETHE NANOMANIPULATOR (NC STATE)A 3D virtual reality visual interface is provided to themicroscope that is similar to looking at a real human-scalephysical surface (essentially magnifying the object under studyup to a million times) with a "haptic" display (a Phantomforcefeedback device) or "touch" interface similar to operatingon 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 thesurface and can increase the force used in order to modifythe sample. Haptic feedback guides the progress of anexperiment. This system allows the scientist to see, touch, andmanipulate it directly.- More intuitive data interpretation (sense of touch) to allowscientists to more readily understand data, better control overnanomanipulation. Remote experimentation - MIT iLabs: Internet access to real labs - anywhere, anytime (http://icampus.mit.edu/ilabs/) : 33.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSESINGLE CELL AFM IMAGING43.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSESINGLE 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/strainswhich are a critical determinant of remodeling. Nonphysiological stress states result in cellular dysfunction producingdiseased states (i.e. ACL tear→osteoarthritis).-Circulatory System : Human red blood cell (RBC's) (diameter ~ 8 m) experience 100% elastic deformation as bloodflows through narrow capillaries, must deform repeatedly reversibly ~half million times- deformability is critical to RBCcirculation!! 120 day lifetime; aged and defective RBCs with decreased deformability are detected and removed fromcirculation 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 deathwhile slow stretching of the axon promotes neural cell growth.53.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSEEXPERIMENTAL METHODS FOR SINGLE CELL MECHANICS (Bao, et al 2003 Nature Materials.)A, B a localized area of the cell is deformedC,D mechanical loading of an entire cellE, F, G simultaneous mechanical loading of a population of cellsGCell force monitor : (B. Harley, L.J. Gibson, After Freyman 2001)63.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSEMECHANICS 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 area73.052 Nanomechanics of Materials and Biomaterials Tuesday 02/29/07 Prof. C. Ortiz, MIT-DMSEMECHANICS OF SINGLE CELLS (Dao, et al 2003 J. Mech. Phys. Solids.)Constitutive Law : stress vs. strain relationship that describes a particular materialSingle macromolecule Gaussian linear elastic Hookean spring F=kr→summing over a network of random coil molecules [1]Mohandas, Narla; Evans, Evan: Mechanical properties of the red cell membrane inrelation to molecular structures and genetic defects. Annu. Rec. Biophys. Struct. 1994.23:787-818{( ) ( )l +l +l + l +l +ll1 4 4 442 4 4 4 431 4 4 442 4 4 4 4332 3 2 2 3 2o1 2 3 3 1 2 3Strain energy of a 3D rubber elastic networknonGaussian Nonlinear Strain Hardening