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The focus of this dissertation is on refining atomic force micrscopy (AFM) methods and data analysis routines to measure the viscoelastic mechanical properties of soft polymer and biological materials in relevant fluid environments and in vivo using a range of relevant temperatures, applied forces, and loading rates. These methods are directly applied here to a several interesting synthetic and biological materials. First, we probe poly(n-butyl methacrylate) (PnBMA), above, at and below its glass transition temperature in order to verify our experimental procedure. Next, we use AFM to study the viscoelastic properties of coating materials and additives of silicone-based soft contact lenses in a tear-like saline solution. Finally, a major focus in this dissertation is determining the fundamental mechanical properties that contribute to the excellent sensitivity of the strain sensing organs in a wandering spider (Cupiennius salei) by probing under in vivo conditions. These strain-sensing organs are known to have a significant viscoelastic component. Thus, the cuticle of living spiders is directly investigated in near-natural environments (high humidity, temperatures from 15-40 °C). The main achievements of these studies can be summarized through the following findings: We suggest that full time-temperature-modulus relationships are necessary for the understanding of soft materials systems, and present a practical method for obtaining such relationships. These studies will have a direct impact on both scientists in the metrology field by developing practical experimental procedures and data analysis routines to investigate viscoelastic mechanical properties at the nanoscale, and future materials scientists and engineers by showing via spider mechanosensory systems how viscoelasticity can be applied for functional use in sensing technology.

<p> With the increasing concern about pollution the need has arisen for accurate trace analysis of hazardous or toxic trace elements such as cadmium. While the modern analytical chemist has at his disposal a great many different techniques for analysis, surveys of inter-laboratory analyses have often produced serious discrepancies among results done by different methods and/or workers. The purpose of this thesis will be to review the different methods for trace analysis of cadmium in biological samples and to experimentally compare two of these, atomic-absorption spectrometry and neutron-activation analysis.</p> / Thesis / Master of Science (MSc)

Yes

Fish scales can be considered as a laminated composite based on collagen fibrils arranged in a cross-plywood structure. This collagen-based composite is often partially mineralized (primarily hydroxyapatite) in the scale exterior in order to resist penetration and hence to enhance protection. Together with the overlapping assembly, the fish scales offer an excellent model system for developing fiber composite materials and flexible armor systems. The primary objective of this thesis is to characterize the distribution of the mineral phase within individual scale and to investigate the corresponding mechanical consequences of the scale as a whole and its different fields through experimental and computational approaches. In this thesis, we chose the scales from the black drum (Pogonias cromis) fish as a model system. First of all, the exterior surface morphology of individual scales was systematically studied, from which several distinct structural regions are identified, including focus field (central), lateral field (dorsal and ventral), rostral field (anterior), and caudal field (posterior). In the focus field, the classic two-layer design, i.e., mineralized exterior layer and collagen-based interior layer, was observed, and nanoindentation results revealed that the high mineral exterior layer results in a much higher hardness (800 vs 450 MPa). Moreover, macroscopic tensile tests indicate that the mechanical removal of mineralized layer did not lead to reduction in strength values, whereas acid-treated demineralized scales showed reduced mechanical properties. Finally, we identified a previously unreported mineral distribution pattern in the rostral field, in which the mineral phase is segregated into long strips along the anterior-posterior direction (width, ~300 μm). In addition, towards the interior of the scale, it appears that the mineral deposition is highly correlated with the collagen orientation, resulting a unique mineralized-unmineralized collagen-based composite structure. We built finite element models to compare this unique structure to two other mineral phases in different fields at the individual scale. This unique structure demonstrates a larger deformation displacement when load was applied, indicating that it provides further flexibility in anterior end of an individual scale. The mineralized phases and structures of various fields within a single scale provide different mechanical characteristics and properties. The structural and mechanical analysis of the various regions of the fish scale can further investigate the flexibility and protective capacity of the individual scale. / Master of Science / There are many protective systems that attracted scientists' attention, and the typical examples include the nacre, crustacean exoskeletons, and teleost fish scales. Fish scales can be considered as the most common flexible bio-inspired armor system, because they consist of mostly collagen fiber and a highly mineralized hydroxyapatite external layer. Due to the need for swimming and effective protection from predators, fish scales need to have excellent flexibility and penetration resistance. In the previous studies on fish scales, researchers usually focused on the entire scale as a multilayered composite, looking at their response against tension and fracture. The primary objective of this thesis is to characterize the distribution of the mineral phase within individual scale and to investigate the corresponding mechanical consequences of the scale as a whole and its different fields through experimental and computational approaches. In this thesis, we chose the scales from the black drum (Pogonias cromis) fish as a model system. First of all, the exterior surface morphology of individual scales was systematically studied, from which several distinct structural regions were identified, including the focus field (central), lateral field (dorsal and ventral), rostral field (anterior), and caudal field (posterior). In the focus field, the classic two-layer design, i.e., mineralized exterior layer and collagen-based interior layer, was observed, and nanoindentation results revealed that the high mineral exterior layer results in a much higher hardness (800 vs 450 MPa). In addition, we identified a previously unreported unique mineralized-unmineralized collagen-based composite structure in the rostral field, in which the mineral phase is segregated into long strips along the anterior-posterior direction (width, ~300 μm). We built finite element models to compare this unique structure to two other mineral phases in different fields at the individual scale. This unique structure demonstrates a larger deformation displacement when load was applied, indicating that it provides further flexibility at the anterior end of an individual scale, implying that the flexibility is more important at the anterior end of scales where the multi-scales overlap and are covered. The structural and mechanical analysis of the various regions of the fish scale can further investigate the flexibility and protective capacity of the individual scale, and provide further design inspiration for flexible armor designs.

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