Browsing by Subject "cell"
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Item Continuum- based computational models of biological living cell(2009-05-15) Cheng, FeifeiAll living creatures, despite their profound diversity, share a common architectural building block: the cell. Cells are the basic functional units of life, yet are themselves comprised of numerous components with distinct mechanical characteristics. It is well established that cells have the ability to sense and respond to externally applied forces. However, the detailed mechanism of mechanosensation is still not clearly understood, and is an active area of research involving experimental and theoretical works. Mathematical modeling of the mechanical stimulus correlating to different experimental stimulation procedures forms the first step to understanding the mechanosensation in cellular system. In this thesis, a continuum -based computational model of living cells that explicitly incorporate the material properties of various cellular components are developed. In the constitutive modeling of cell, the continuum standard linear solid viscoelastic model (SLS), its natural extension for large scale deformation standard Neo-Hookean solid viscoelastic model (SnHS) as well as polymer mechanics- based dynamic shear modulus model was introduced. Finite element simulations of three widely used experiments- atomic force microscopy (AFM), magnetic twisting cytometry (MTC) and micropipette aspiration in the quantification of cell properties were carried out to verify the developed constitutive model. From the results of AFM finite element simulation, it was observed that the force-deformation and strain-relaxation curves obtained fit the experimental results very well. The influences of cytoplasm shear modulus which varies due to the formation of stress fiber, and cortex shear modulus which alters with the actin filament concentration factors and load frequency were systematically studied. Similarly, in magnetic twisting cytometry (MTC) simulation, the role of cytoplasm material properties, constant/sinusoidal forcing rates and various frequencies on the overall mechanical response of a cell was obtained. Numerical results are validated against experiments results. Micropipette aspiration simulation was also carried out in which the typical creep deformation test was carried out to study the viscoelastic behavior of the cell. Based on the results from finite element simulation, the effect of pipette radius, effect of cortex shear modulus and effect of pressure rate have been derived for the interpretation of the mechanical parameters from the micropipette aspiration.Item The use of Surface Enhanced Raman Spectroscopy (SERS) for biomedical applications(Texas A&M University, 2007-04-25) Chowdhury, Mustafa HabibRecent advances in nanotechnology and the biotechnology revolution have created an immense opportunity for the use of noble metal nanoparticles as Surface Enhanced Raman Spectroscopy (SERS) substrates for biological sensing and diagnostics. This is because SERS enhances the intensity of the Raman scattered signal from an analyte by orders of 106 or more. This dissertation deals with the different aspects involved in the application of SERS for biosensing. It discusses initial studies performed using traditional chemically reduced silver colloidal nanoparticles for the SERS detection of a myriad of proteins and nucleic acids. It examines ways to circumvent the inherent aggregation problems associated with colloidal nanoparticles that frequently lead to poor data reproducibility. The different methods examined to create robust SERS substrates include the creation of thermally evaporated silver island films on microscope glass slides, using the technique of Nanosphere Lithography (NSL) to create hexagonally close packed periodic particle arrays of silver nanoparticles on glass substrates as well as the use of optically tunable gold nanoshell films on glass substrates. The three different types of SERS surfaces are characterized using UV-Vis absorption spectroscopy, Electron Microscopy (EM), Atomic Force Microscopy (AFM) as well as SERS using the model Raman active molecule trans-1,2-bis(4-pyridyl)ethylene (BPE). Also discussed is ongoing work in the initial stages of the development of a SERS based biosensor using gold nanoshell films for the direct detection of b-amyloid, the causative agent for Alzheimer's disease. Lastly, the use of gold nanoshells as SERS substrates for the intracellular detection of various biomolecules within mouse fibroblast cells in cell culture is discussed. The dissertation puts into perspective how this study can represent the first steps in the development of a robust gold nanoshell based SERS biosensor that can improve the ability to monitor biological processes in real time, thus providing new avenues for designing systems for the early diagnosis of diseases.