Zirconia has been established as a promising material for dental implants. Various surface treatment methods have been utilized to promote better osseointegration and improve the success rate of dental implants. However, a better understanding of the influences of topographic characteristics on cell attachment, proliferation, and differentiation is needed. Different surface topographic zirconia specimens, As sintered, Mild rough, Moderate rough, and Rough zirconia groups were fabricated with sandblasting method in various distances and stages. The surface texture, microstructure, and wettability were inspected with the optical profiler, SEM, and contact angle measurement respectfully. Human primary osteoblast cells were cultured on the four groups of zirconia with different surface modifications in 24 well plates and on plates without test material as control. Crystal violet and triton X-100 solution were used to evaluate cell attachment efficiency at 9 hours and proliferation rate at 7, 14, and 21 days after seeding. ALP activity was measured with fluorometric assay. The expression of osteocalcin was measured with an ELISA kit. Alizarin red staining was conducted to evaluate the mineralization. The cell morphologies were inspected under SEM after cell fixation and critical point drying process. The data were analyzed with one-way ANOVA for experiment on each time interval and two-way ANOVA for all time points. Tukey post hoc test was used for pairwise comparison. P value < 0.05 was considered statistically significant. Topographic parameters and contact angle measured in As sintered, Mild rough, Moderate rough, and Rough surface groups were as follow: Sa = 0.23, 0.50, 2.13, 5 µm, Sal = 49.88, 21.20, 30.42, 49.87 µm, Sdq = 64.64, 248.60, 511, 734.66 µm/mm, Sk = 0.7, 1.54, 4.19,16 µm, Spk = 0.31, 0.64, 1.47, 5.13 µm, Svk = 0.35, 0.71, 5.96, 6.18 µm respectively, and contact angle = 64.6°, 55.2°, 43.5°, 38.6° respectively. The result showed that Rough zirconia group induced the highest cell attachment efficiency at 9 hours (p<.001). As sintered zirconia group promoted significant cell proliferation rate at 21 days (p<.001) while Rough zirconia group drastically down-regulated cell proliferation (p<0.001). The most elevated levels of ALP, osteocalcin, and mineralization expressions at 21 days were found in the Moderate rough group with significant differences (p<.001, p<.001, p<.001 accordingly) Within the limitations of this in vitro study, it can be concluded 1) the modified microroughened zirconia surfaces of Sa 5 µm would promote human osteoblast attachment but down-regulate cell proliferation, 2) the As sintered zirconia surface would stimulate cell proliferation, and 3) the microroughened surfaces of Sa 2 µm would up-regulate osteoblast differentiation. These findings could be incorporated into designing and fabricating the dental implant surfaces for optimal osseointegration.

<p dir="ltr">There is a plethora of applications that require chemical patterning on the molecular scale. While the surface science community has made tremendous progress in achieving this level of control on hard, crystalline interfaces, significant challenges are associated with extending this progress to less “perfect” systems such as soft, amorphous interfaces. Applications ranging from soft robotics and wearable electronics to regenerative medicine often utilize polymeric materials such as polydimethylsiloxane (PDMS) and hydrogels. These materials have advantageous properties, including biocompatibility and mechanical tunability. Biological applications, for example, often require the display of functional groups with precise spatial resolution. Cellular behavior is dictated by biochemical and biophysical cues in the extracellular matrix; therefore, substrate properties, including stiffness and ligand density, must be independently tunable. Soft, polymeric materials are highly heterogenous with pore sizes ranging from 10 nm to 1 µm and hence, particularly difficult to pattern below the length scale of substrate heterogeneity. Furthermore, deconvolving mechanical properties such as elastic modulus from the density of surface-active functional groups is especially challenging, with softer materials typically corresponding is lower ligand densities. Additionally, many traditional surface science characterization and patterning methods are incompatible with soft interfaces (e.g. amorphous surface structure, low mechanical strength, hydrated environment). Recently, we have reported a method capable of achieving high-resolution chemical patterning of PDMS and hydrogels. Long studied within the scanning probe community, amphiphiles with long alkyl chains self-assemble into lying down stripe phases on highly ordered pyrolytic graphite (HOPG), generating 1-nm-wide stripes of functional headgroups between 5-nmwide stripes of exposed alkyl chains. Stripe phases of functional diacetylenes (DA) are photopolymerized, producing a polydiacetylene backbone that tethers together adjacent molecules, generating a PDA film on HOPG (sPDA). We have shown that PDA films on HOPG can be transferred to PDMS as well as polyacrylamide hydrogels. When PDMS is cured in contact with sPDAs, the PDA backbones can act as a site for hydrosilylation, the same reaction responsible for PDMS curing, covalently linking sPDAs to the PDMS mesh. Careful exfoliation reveals nm-scale functional patterns on the surface layer of PDMS. 10 Here, we examine the impact of PDMS structural components on the efficiency of interfacial reactions between sPDAs and the PDMS network. We also illustrate the impact of PDAfunctionalized PDMS on the adhesion and spreading behavior of C2C12 murine myoblasts.</p>

In the past several years, the Defense Advanced Research Projects Agency (DARPA) has sponsored two Grand Challenges, races among autonomous ground vehicles in rural environments. These vehicles must follow a course delineated by Global Positioning System waypoints using no human guidance. Airborne LIDAR data and GIS can play a significant role in identifying barriers and least cost paths for such vehicles. Least cost paths minimize the sum of impedance across a surface. Impedance can be measured by steepness of slope, impenetrable barriers such as vegetation and buildings, fence lines and streams, or other factors deemed important to the vehicle's success at navigating the terrain. This research aims to provide accurate least cost paths for those vehicles using airborne LIDAR data. The concepts of barrier identification and least cost path generation are reviewed and forty-five least cost paths created with their performance compared to corresponding Euclidean paths. The least cost paths were found superior to the corresponding Euclidean paths in terms of impedance as they avoid barriers, follow roads and pass across relatively gentler slopes. / Master of Science

Geometrical modeling is a crucial aspect of simulations involving manufactured objects. Apart from the pure construction of curves and surfaces, the analysis of their quality is equally important in the design and manufacturing process. In computer-aided simulation, the original freeorm surfaces need to be tessellated into triangulated surfaces before the simulation procedure. To concurrently and interactively visualize the results from both simulation and surface interrogation in a virtual environment, I propose two novel surface interrogation algorithms for triangulated surfaces instead of the traditional freeorm surfaces. The novel algorithms are interactive and immersive versions of two well-established surface interrogation techniques ? reflection lines and generalized focal surfaces. These two algorithms have been designed to overcome some limitations of the traditional approaches and make them available for interactive and immersive applications. For reflection lines, the new algorithm maps the triangulated surface onto the light plane so that the computation of distance between reflection ray and light line in three dimensions can be reduced to computation of intersections between light lines and triangle edges in two dimensions, simplifying the computation. For generalized focal surfaces, the new algorithm estimates curvature by simple computation of the derivatives of a3rd degree triangular Bézier patch on each triangle and removes the requirement for a minimum number of neighbor points and implicit requirements on how the neighbor points are distributed. Proposed future work on real-time rendering of surface interrogation using a texture mapping technique is discussed.

Despite the effort to optimize soft contact lens performance, almost half of the 140 million contact lens wearers worldwide experience symptoms of ocular dryness and discomfort, especially towards the end of the day. These symptoms are attributed to reduced compatibility between the contact lens and the ocular surface and are the main reason for contact lens discontinuation. As the interactions of the contact lens-eye interface are dynamic, the surface properties play a key role in improving ocular compatibility, comfort and overall performance of contact lenses. One promising method to reduce adverse interfacial interactions between the contact lens and the ocular surface is to modify the contact lens surface with a biomimetic layer inspired by the ocular surface and the tear film. Hyaluronic acid (HA) is a non-sulfated glycosaminoglycan naturally found in the ocular environment providing ocular hydration and lubrication. Proteoglycan 4 (PRG4), a mucin-like glycoprotein naturally produced at the ocular surface contributes to natural lubrication during blinking and to tear film stability. Surface modification with HA or PRG4 has been shown to result in improved wetting, lubricating and antifouling properties. Moreover, HA and PRG4 have been previously found to interact and synergistically reduce friction further. In the current work, novel HA and PRG4-grafted soft contact lens surfaces were prepared, and the impact of the surface tethered layer on important contact lens properties was assessed. Furthermore, the potential synergistic effect between HA and rhPRG4 on the examined properties was evaluated. Surface immobilization of HA on model conventional (pHEMA) and silicone (pHEMA-co-TRIS) hydrogel contact lenses was achieved by thiol-ene “click” chemistry, while full-length recombinant human PRG4 (rhPRG4) was surface grafted via carbonyldiimidazole (CDI) linking chemistry respectively. The chemical structure after each modification step was determined by attenuated total reflectance FTIR (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) analyses. HA-grafted model soft contact lenses were characterized by improved surface wettability, antifouling and water retentive properties, while a decreasing trend in boundary friction was observed but only for the HA-grafted pHEMA-co-TRIS materials. Surface-tethering of rhPRG4 was found to effectively enhance the surface wettability and boundary lubricating properties of pHEMA-co-TRIS hydrogels only, whereas both rhPRG4-grafted pHEMA and pHEMA-co-TRIS materials exhibited lower protein sorption and dehydration rate. Overall, the surface immobilization processes followed herein did not alter the optical transparency of the model soft contact lenses or their in vitro compatibility with human corneal epithelial cells. Finally, there was evidence that HA and rhPRG4 synergistically interacted, further improving the contact lens properties. However, the degree of HA/rhPRG4 synergy was found to be dependent on the configuration of the formed HA/rhPRG4 complex as well as the composition of the substrate hydrogel material, with the noted improvement being more significant for the model silicone hydrogels. This is the first study to examine surface grafted full-length rhPRG4 and the effect of this modification on contact lens properties. Moreover, the study is the first to investigate the interactions between covalently tethered rhPRG4 and solutions containing HA. The results of this thesis demonstrate that HA and rhPRG4 are good candidates for the development of novel biomimetic surfaces, especially for silicone hydrogel contact lenses. The potential for using these compounds in synergy was also demonstrated, with wetting solutions of HA showing promise for modifying rhPRG4 modified materials to improve symptoms of discomfort. These naturally occurring ocular agents have the potential to improve the management of ocular dryness and discomfort, thus optimizing the overall soft contact lens performance. / Thesis / Doctor of Philosophy (PhD)

No / Three-dimensional (3D) representations of com- plex geometric shapes, especially when they are recon- structed from magnetic resonance imaging (MRI) and com- puted tomography (CT) data, often result in large polygon meshes which require substantial storage for their handling, and normally have only one fixed level of detail (LOD). This can often be an obstacle for efficient data exchange and interactive work with such objects. We propose to re- place such large polygon meshes with a relatively small set of coefficients of the patchwise partial differential equation (PDE) function representation. With this model, the approx- imations of the original shapes can be rendered with any desired resolution at interactive rates. Our approach can di- rectly work with any common 3D reconstruction pipeline, which we demonstrate by applying it to a large reconstructed medical data set with irregular geometry.

Yes / Titanium alloy Ti-6Al-4V is known for both its excellent mechanical properties and its low surface hardness. This study explores a two-step process for depositing a hard nanocrystalline coating onto the surface of the Ti-alloy, followed by surface melting, which embeds hard nanoparticles into a thin surface layer of the alloy. The treated surface layer was studied using X-ray diffraction, scanning electron microscopy, and Vicker's micro-hardness testing. The results of the study show that the surface of the Ti-6Al-4V alloy can be successfully hardened by embedding nanosized Al2O3 particles into the surface using gas tungsten arc welding to melt the surface of the material. Surface melting the Ti-6Al-4V alloy with a 50A welding current produced the maximum microhardness of 701 HV0.2kg. The micro-hardness of the treated surface layer decreased with the increasing size of the nanoparticles, while the roughness of the surface increased with the increasing welding current. The heat input into the surface during the surface melting process resulted in the formation of various intermetallic compounds capable of further increasing the hardness of the Ti-6Al-4V surface.

A study of the stability of bicontinuous nanoporous metals is presented. Atomic scale simulations are used to probe the dominant mechanisms of geometric relaxation in these materials. A method is presented for generating model bicontinuous metal / void structures for use in atomistic simulations of bicontinuous nanoporous solids. The structures are generated with periodic boundary conditions using a phase-field model to simulate the spinodal decomposition of an ideal system. One phase in the model is then associated with the pore volume while the other phase is associated with the metal ligaments. Small angle neutron scattering was used to quantitatively compare experimental samples to those generated by the phase field method. EAM results using model structures with experimentally accessible length scales are presented which demonstrate the potential of such simulations in understanding the behavior of nanoporous metals. Simulated relaxations of these structures, as well as the relaxation of model spherical clusters, indicate that the surface relaxation effect dominates the overall dimensional relaxation of np-metals post processing. Capillary effects play a secondary role in the overall relaxation. The simulation results presented also identify a maximum surface area to volume ratio necessary to maintain mechanical stability beyond which the pore structure collapses. / Ph. D.

The aerodynamic flow and fluctuating surface pressure of a plane, turbulent, two-dimensional wall jet flow into still air over smooth and rough surfaces has been investigated in a recently constructed wall jet wind tunnel testing facility. The facility has been shown to produce a wall jet flow with Reynolds numbers based on the momentum thickness, Re<SUB>&delta</SUB> = &deltaU<SUB>m</SUB>/&nu, of between 395 and 1100 and nozzle exit Reynolds numbers, Re<SUB>j</SUB> = U<SUB>m</SUB>b/&nu, of between 16000 and 45000. The wall jet flow properties (&delta, &delta<SUP>*</SUP>, &theta, y<SUB>1/2</SUB>, U<SUB>m</SUB>, u<SUP>*</SUP>, etc.) were measured and characterized over a wide range of initial flow conditions and measurement locations relative to the wall jet source. These flow properties were measured for flow over a smooth flow surface and for flow over roughness patches of finite extent. The patches used in the current study varied in length from 305 mm to 914 mm (between 24 and 72 times the nozzle height, b) and were placed so that the leading edge of the patch was fixed at 1257 mm (x/b = 99) downstream of the wall jet source. These roughness patches were of a random sand grain roughness type and the roughness grain size was varied throughout this experiment. The tests covered roughness Reynolds numbers (k<SUP>+</SUP>) ranging from less than 2 to over 158 (covering the entire range of rough wall flow regimes from hydrodynamically smooth to fully rough). For the wall jet flows over 305 mm long patches of roughness, the displacement and momentum thicknesses were found to vary noticeably with the roughness grain size, but the maximum velocity, mixing layer length scale, y<SUB>/2</SUB>, and the boundary layer thickness were not seen to vary in a consistent, determinable way. Velocity spectra taken at a range of initial flow conditions and at several distinct heights above the flow surface showed a limited scaling dependency on the skin friction velocity near the flow surface. The spectral density of the surface pressure of the wall jet flow, which is not believed to have been previously investigated for smooth or rough surfaces, showed distinct differences with that seen in a conventional boundary layer flow, especially at low frequencies. This difference is believed to be due to the presence of a mixing layer in the wall jet flow. Both the spectral shape and level were heavily affected by the variation in roughness grain size. This effect was most notable in overlap region of the spectrum. Attempts to scale the wall jet surface pressure spectra using outer and inner variables were successful for the smooth wall flows. The scaling of the rough wall jet flow surface pressure proved to be much more difficult, and conventional scaling techniques used for ordinary turbulent boundary layer surface pressure spectra were not able to account for the changes in roughness present during the current study. An empirical scaling scheme was proposed, but was only marginally effective at scaling the rough wall surface pressure. / Ph. D.

The self-assembly blends of cellulose propionate (CP) and fluorine (F)-containing cellulose derivatives was examined on a model system of solvent cast films. The F-containing derivatives were either high molecular weight statistical cellulose esters with a number of F-containing substituent evenly distributed along the backbone (F-esters), or F-terminated CP-segments with exactly one F-containing endgroup. The F-esters were synthesized in a homogeneous phase and identified by 19F-NMR. Thermal analysis showed improved thermal stability of the F-esters when compared to F-free derivatives. 1-monohydroxy functionalized CP-segments were synthesized by HBr depolymerization using either a commercially available CP with residual OH-groups or a perpropionylated CP (CTP). The hydrolysis using the commercial CP yielded only segments of a minimum DP of 50 and the Mark-Houwink constant declined from 1 to 0.6. The results indicate that in the presence of free hydroxyls branches are formed by transglycosidation. The hydrolysis from perpropionylated CP resulted in segments with a minimum DP of 7, which is in accordance to previous studies. F-terminated CP segments were synthesized by coupling of the appropriate F-containing alcohol to the CP segment via toluene diisocyanate. Solutions containing F-terminated CP-segments showed typical critical micelle behavior. The critical micelle concentration depended on the molecular weight of the CP segment and the type of F-containing endgroup. The micelles are thought to consist of a core of the F-endgroups and a corona made-up of CP. Films containing the oligomers cast from micellar solution revealed a linear decrease in wetting force according to the blend composition of the oligomer, i.e. behavior according to the rule of mixing. This indicated the absence of surface segregation of the F-endgroup and it is explained with the fact that the micellar structure is retained in the solid state, suppressing surface segregation. The solid state micelles were visualized as dome-like protrusions by height image atomic force microscopy. In systems blended with CP the distance between the protrusions was found to increase with increasing CP content which was explained by a dilution process. Films containing F-esters were characterized by wetting force measurements and x-ray photoelectron spectroscopy (XPS). The wetting force decreased dramatically at low blend content of the F-ester and at the same time an F surface-concentration higher then expected from the blend composition was found by XPS. This indicated self-assembly by surface segregation of the F-containing species during film formation. The extent of surface segregation was found to depend on the type of the F-ester group as well as on the blend concentration of the F-ester. Dynamic wetting force measurements revealed hysteresis in films containing either F-esters or F-terminated CP segments. The hysteresis was found to be both kinetic (water sorption and reorganization) and thermodynamic (surface roughness and surface coverage with F-moieties) in nature. Consecutive force loops revealed an increase in the wetting force (advancing and receding) with increasing loop number, indicating the increased hydrophobicity of the surface. The force increase was determined to be due to water sorption as well as due to surface reorganization. An increase in the size of the F-groups signified a decrease in reorganization rate due to a decreased mobility of the group. The process of reorganization was fully reversible, a behavior which is congruent with the definition of smart behavior. / Ph. D.