A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item MECHANICAL CHARACTERIZATION OF NORMAL AND CANCEROUS BREAST TISSUE SPECIMENS USING ATOMIC FORCE MICROSCOPY(2014) Roy, Rajarshi; Desai, Jaydev P.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Breast cancer is one of the most common malignancies among women worldwide. Conventional breast cancer diagnostic methods involve needle-core biopsy procedures, followed by careful histopathological inspection of the tissue specimen by a pathologist to identify the presence of cancerous lesions. However, such inspections are primarily qualitative and depend on the subjective impressions of observers. The goal of this research is to develop approaches for obtaining quantitative mechanical signatures that can accurately characterize malignancy in pathological breast tissue. The hypothesis of this research is that by using contact-mode Atomic Force Microscopy (AFM), it is possible to obtain differentiable measures of stiffness of normal and cancerous tissue specimens. This dissertation summarizes research carried out in addressing key experimental and computational challenges in performing mechanical characterization on breast tissue. Firstly, breast tissue specimens studied were 600 um in diameter, about six times larger than the range of travel of conventional AFM X-Y stages used for imaging applications. To scan tissue properties across large ranges, a semi automated image-guided positioning system was developed that can be used to perform AFM probe-tissue alignment across distances greater than 100 um at multiple magnifications. Initial tissue characterization results indicate that epithelial tissue in cancer specimens display increased deformability compared to epithelial tissue in normal specimens. Additionally, it was also observed that the tissue response depends on the patient from whom the specimens were acquired. Another key challenge addressed in this dissertation is accurate data analysis of raw AFM data for characterization purposes. Two sources of uncertainty typically influence data analysis of AFM force curves: the AFM probe's spring constant and the contact point of an AFM force curve. An error-in-variable based Bayesian Changepoint algorithm was developed to quantify estimation errors in the tissue's elastic properties due to these two error sources. Next, a parametric finite element modeling based approach was proposed in order to account for spatial heterogeneity in the tissue response. By using an exponential hyperelastic material model, it was shown that it is possible to obtain more accurate material properties of tissue specimens as opposed to existing analytical contact models. The experimental and computational strategies proposed in this dissertation could have a significant impact on high-throughput quantitative studies of biomaterials, which could elucidate various disease mechanisms that are phenotyped by their mechanical signatures.Item NEAR-GRAZING AND NOISE-INFLUENCED DYNAMICS OF ELASTIC CANTILEVERS WITH NONLINEAR TIP INTERACTION FORCES(2012) Chakraborty, Ishita; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within this dissertation work, numerical, analytical, and experimental studies are conducted with macro-scale and micro-scale elastic structures in the presence of nonlinear force interactions. The specific physical systems explored within this work are an atomic force microscope (AFM) micro-cantilever and a macro-scale cantilever experiencing similar tip interaction forces as the AFM cantilever operated in tapping mode. The tip sample forces in an AFM operation are highly nonlinear, with long-range attractive forces and short-range repulsive forces. In the macro-scale case, magnetic attractive forces and repulsive forces, which arise due to impacts with a compliant surface are used to generate similar nonlinear tip interaction forces. For elastic structures subjected to off-resonance base excitations, bifurcations close to grazing events are studied in detail, and the observed nonlinear phenomena are found to be common across the considered length scales. The dynamics of the considered systems are studied with a reduced-order computational model based on Galerkin projection with a single mode approximation. Along with studies on the bifurcation behavior, the effects of added Gaussian white noise on the system dynamics are also examined. Non-smooth system dynamics is studied by constructing local maps near the discontinuity. Period-doubling events are examined by using Poincaré maps and discontinuity mapping analysis. An important component of this dissertation research is the investigations into the effects of noise on the dynamics of these structures. Experimental and numerical efforts are used to examine the stochastic dynamics of the cantilever structures when a random component is added to the harmonic input. The noise effects are studied when the excitation frequency is close to a system resonance as well as when it is off-resonance. An analytical-numerical method with moment evolution equations is used to study the effects of noise. The effects of noise on contact and adhesion phenomena are explored. Through this dissertation work, the importance of considering noise-influenced dynamics in micro-scale applications such as AFM operations is illustrated. In addition, this work helps shed light on universality of nonlinear phenomenon across different length scales.Item DEVELOPMENT AND APPLICATIONS OF MULTIFREQUENCY IMAGING AND SPECTROSCOPY METHODS IN DYNAMIC ATOMIC FORCE MICROSCOPY(2011) Chawla, Gaurav; Solares, Santiago D; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Force spectroscopy and surface dissipation mapping are two of the most important applications of dynamic atomic force microscopy (AFM), in addition to topographical imaging. These measurements are commonly performed using the conventional amplitude-modulation and frequency-modulation dynamic imaging modes. However, the acquisition of the tip-sample interaction force curves using these methods can generally be performed only at selected horizontal positions on the sample, which means that a 3-dimensional representation of the tip-sample forces requires fine-grid scanning of a volume above the surface, making the process lengthy and prone to instrument drift. This dissertation contains the development of two novel atomic force spectroscopy methods that could enable acquisition of 3-dimensional tip-sample force representations through a single 2-dimensional scan of the surface. The force curve reconstruction approach in the first method is based on 3-pass scanning of the surface using the recently proposed single-frequency imaging mode called frequency and force modulation AFM. A second, more versatile method based on bimodal AFM operation is introduced, wherein the fundamental eigenmode of the cantilever is excited to perform the topographical scan and a simultaneously excited higher eigenmode is used to perform force spectroscopy. The dissertation further presents the development of a trimodal AFM characterization method for ambient air operation, wherein three eigenmodes of the cantilever are simultaneously excited with the objective of rapidly and quantitatively mapping the variations in conservative and dissipative surface properties. The new methods have been evaluated within numerical simulations using a multiscale simulation methodology, and experimental implementation has been accomplished for two multifrequency variants that can provide 2-dimensional surface property contrast.Item Quantitative Prediction of Tip-Sample Repulsive Forces and Sample Deformation in Tapping-Mode Frequency and Force Modulation Atomic Force Microscopy(2008-08-27) Crone, Joshua C; Solares, Santiago D; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to predict sample deformation and the resultant interaction forces is a vital component to preventing sample damage and acquiring accurate height traces in atomic force microscopy (AFM). By using the recently developed frequency and force modulation (FFM) control scheme, a prediction method is developed by coupling previously developed analytical work with numerical integration of the equation of motion for the AFM tip. By selecting a zero resonance frequency shift, the sample deformation is found to depend only on those parameters defining the tip-sample interaction forces. The results are represented graphically and through a multiple regression model so that the user can predict the tip penetration and maximum repulsive force with knowledge of the maximum attractive force and steepness of the repulsive regime in the tip-sample interaction force curve. The prediction model is shown to be accurate for a wide range of imaging conditions.