Mechanics and Functionality of Extreme Mechanical Instabilities through Buckling Driven Delamination
Committee memberDarvish, Kurosh
Buckling Driven Delamination
Extremely Large Deformation
Thin Film/soft Substrate System
Permanent link to this recordhttp://hdl.handle.net/20.500.12613/3932
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AbstractMechanical instabilities such as wrinkling and buckling-driven delamination in thin film-substrate systems have historically been considered as one of structural failure mechanisms, which should be avoided. The past decade has witnesssed rapid growth in harnessing such surface instabilities for a wide range of tunable surface related properties and functionalities, especially in soft materials on small scales. Compared to extensively studied wrinkling on soft substrates and localized buckling driven delamination on stiff substrates, the fundamental mechanics underpinning ordered buckle-delamination on soft substrate over large area and its guidance for potential implications in engineering innovation remain largely to be explored. This thesis aims to partially bridging such a knowledge gap. In this thesis, I exploit how to generate the controllable and globally periodic delaminated buckling patterns in thin films on highly prestrained elastomeric substrates, and then explore the fundamental mechanics of this spontaneous extreme buckling driven periodic delamination, as well as its implications in design of extremely stretchable electronics and interfacial mechanical properties measurement. Compared to wrinkling, one of the benefits of extremely buckling driven delamination is the extraordinarily high aspect ratio of buckles. The large surface roughness and high local curvature could potentially enable extreme surface topographies related properties, such as adhesion, wetting, friction, and optics, as well as augment the extreme stretchability in stretchable optical and electronic devices. In the aim of harnessing this extreme buckling driven delamination, I first explore the formation and evolution of extraordinarily high-aspect-ratio delaminated buckles of thin films on 400% pre-strained elastomers, as well as uncovered the underlying deformation mechanism through combining quantitative theoretical analysis and experimental and numerical approaches. A theoretical framework is developed to describe the formation and evolution process of periodic delaminated buckles, which includes three deformation stages, i.e. onset of localized blisters (Stage I), growth and propagation of delamination (Stage II), and post-buckling after delamination arrest (Stage III). I show that under extreme large compressive strain, the profile of periodic blisters changes from sinusoidal shape to jig-saw-like shape with relative high aspect ratio, which have potential applications for design of extremely stretchable electronics. Equipped with the fundamental mechanics of buckle-delamination in thin films, I then exploit harnessing the spontaneous buckling driven periodic delamination to achieve high stretchability in both metal and silicon films. Experimentally I observe periodic buckle-delaminated patterns over large area, accompanied by highly ordered transversely cracking patterns, which can be theoretically predicted by simple crack fragments model. I hypothesize that when the width of ribbons is set to be equal or smaller than the theoretically predicted crack fragment width, there would be no cracking fragmentation. This criteria for designing crack-free micro-ribbons is further validated by related experiments. Guided by the validated criteria, I successfully design crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. I further extend the buckling instability-based metrology to systematically measure the mechanical properties of 2D organic conjugated polymer nano-films, which have tremendous promising applications in organic integrated circuits, solar cells, and stretchable devices. I develop a new fabrication strategy to generate buckle-delaminated free-standing organic conjugated polymeric (P3BT/C60) nanosheets. Through both experiments and theoretical analysis, I show that the free-standing buckle-delaminated organic P3BT/C60 nanosheets have significant advantages over the traditional spin-coated wrinkled nanosheets, including the enhanced mechanical properties, a higher level of stretchability with lower electrical resistance, and a wider range of controllable wettability modulation.
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Anti-cancer Functions and Mechanisms of a pRb2/p130 Peptide FragmentWaring, Richard B.; Giordano, Antonio, MD; Feitelson, Mark; Sang, Nianli (Temple University. Libraries, 2009)The spacer region of pRb2/p130 was reported to be able to inhibit the kinase activity of Cdk2. The region responsible for the inhibitory effect was further narrowed down to a 39-amino-acid sequence, which was named as Spa310. In this dissertation, the anti-cancer functions and mechanisms of Spa310 were studied. The synthesized Spa310 peptide was able to inhibit the kinase activities of Cdk2/Cyclin E/A complexes. In vitro kinase assays showed the inhibition occurred in a dose-dependent manner. The half maximal inhibition concentration of the Spa310 in the kinase assay was 1.67mM. In addition, it has been shown that Spa310 peptide is able to inhibit the kinase activities of both Cdk2/Cyclin E and Cdk2/Cyclin A. Intra-cellular distribution study using fluorescein-labeled Spa310 peptide showed that Spa310 was able to localize to the nuclei of A549 cancer cells. Some data indicated the endoplasmic reticulum might play a role in transporting Spa310 peptide from cytoplasm to the nucleus. At high concentration, the treatment of Spa310 peptide was able to arrest cells at the G0/G1 phase of the cell cycle and reduce the growth of xenografted tumors in nude mice. Further studies indicated Spa310 peptide is not a specific inhibitor for Cdk2/Cyclin E/A. It is also able to inhibit the kinase activities of Cdk1/Cyclin B, Cdk4/Cyclin D and Cdk9/Cyclin T/K. Result of a binding assay using GST-Spa310 and in vitro transcribed/translated Cdk2 did not support a direct binding between Spa310 and Cdk2. Additionally, GST-Spa310 was unable to bind to the in vitro transcribed/translated Cyclin E. At first, co-immunoprecipitation experiments indicated a weak binding between Spa310 peptide and Cdk2. However, later this weak binding was proven to be unspecific and only occurred when the concentration of Spa310 peptide was high. Thus, the hypothesized mechanism of the inhibitory effect of Spa310 was not supported. After noticing three classic Cdk phosphorylation sites present in Spa310, it was proven that Spa310 is a substrate for Cdk1, 2, 4 and 9. Results of kinase assays supported the inhibitory effect of Spa310 on the different Cyclin-dependent kinases was resulted from a substrate-competitive mechanism. Although the data generated from this study does not support Spa310 is a potent peptide inhibitor for the Cdks, knowledge gained from and the approach used in this research can be applied to design and develop more potent and specific Cdk2 peptide inhibitors, which have their potentials to work as powerful anti-cancer reagents.
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