Shear Induced Fiber Alignment and Acoustic Nanoparticle Micropatterning during Stereolithography

The stereolithograpy method, which consists of a light source to polymerize the liquid photocurable resin, can produce structures with complex shapes. Most of the produced structures are unreinforced neat pieces. The addition of reinforcement, such as fibers and particles are regularly utilized to improve mechanical properties and electrical conductivity of the printed parts. Added fibers might be chosen as short or continuous fibers and the properties of the reinforced composite materials can be significantly improved by aligning the fibers in preferred directions. The first aim of this dissertation is to enhance the tensile and flexural strengths of the 3d printed composites by using shear induced alignment of short fibers. The second aim is to print parts with conductive embedded microstructures by utilizing acoustic patterning of conductive particles. Both aims are utilized during the stereolithography process.A lateral oscillation mechanism, which is inspired by large amplitude oscillatory shear test, was designed to generate shear flow. The alignment method, which combines the lateral oscillation mechanism with 3d printed wall patterns, is developed to utilized shear flow to align the fibers in the patterned wall direction. Shear rate amplitude, fiber concentration, and patterned wall angle were considered as parameters during this study.The stereolithography device incorporated with oscillation mechanism was utilized to produce short fiber reinforced ceramic composites and short nanofiber reinforced polymer composites. Nickel coated short carbon fibers, alumina and silica short fibers were used to reinforce the ceramic matrix with different fiber contents. The printed walls were demonstrated to align the short fibers parallel to the wall which was different from the oscillation direction up to 45°. The flexural strength of the ceramic matrix was improved with the addition and alignment of the short fibers. The alumina nanofibers were used as reinforcement in the photocurable polymer resin. The alumina nanofibers were treated with a silane coupling agent to improve interfacial bond between alumina fibers and polymer resin matrix. The aligned specimen demonstrated improvement in tensile strength with increasing nanowire content and their alignment.A hexagon shaped acoustic tweezer was incorporated into the stereolithography device to pattern conductive micro- and nanoparticles. This new approach for particle microstructuring via acoustic aligning during the stereolithography was used to produce embedded conductive microstructures in 3d printed parts. The acoustic tweezer was used to pattern the conductive particles into horizontal, 60°, and 120° parallel striped lines. The influence of the particle percentage content onto the electrical resistivity and thickness of the patterned lines were also investigated for different materials such as copper, magnetite, and carbon fiber. The copper patterns show less resistance to electrical currents compare to magnetite and carbon nanofiber patterns. Additionally, the influence of the particle concentration to the height of the pattern was studied and the data was utilized to achieve conductivity along z-axis. Later, this approach was used to fabricate examples of embedded conductive complex 3D microstructures

Cutting Edge Nanotechnology

The main purpose of this book is to describe important issues in various types of devices ranging from conventional transistors (opening chapters of the book) to molecular electronic devices whose fabrication and operation is discussed in the last few chapters of the book. As such, this book can serve as a guide for identifications of important areas of research in micro, nano and molecular electronics. We deeply acknowledge valuable contributions that each of the authors made in writing these excellent chapters

Magnetically Driven Micro and Nanorobots

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells. Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility. This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as "MagRobots") as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement. These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields. Actuation mechanisms of flagella-inspired MagRobots (i.e., corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (i.e., surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi)spherical, helical, flexible, wire-like, and biohybrid MagRobots. Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed. Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed

Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application: Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application

Having conducted the research described in this thesis I found that there exists a possibility to produce polyelectrolyte nanostructures on hydrophobic surfaces by application of the moving contact line approach. It was demonstrated that the morphology of nanostructures displays a range of structure variations from root-like to a single wire structure with a high anisotropy and aspect ratio (providing diameters of several nanometers and the length limited by the sample surface dimensions). Such nanostructures can be produced exactly on the spot of interest or can be transferred from the surface where they were produced to any other surfaces by the contact printing technique. A model describing the polymer deposition during the moving contact line processes on hydrophobic surfaces has been proposed. The application of this model provides the ground for an explanation of all the obtained experimental data. Utilizing moving contact line approach aligned one-dimensional polycation structures were fabricated and these structures were used as templates for assembling amphiphile molecules. Quasiperiodic aligned and oriented nanostructures of polyelectrolyte molecules formed in moving droplets were utilized for fabrication of electrically conductive one-dimensional nanowires

OPTIMAL CONTROL OF OBJECTS ON THE MICRO- AND NANO-SCALE BY ELECTROKINETIC AND ELECTROMAGNETIC MANIPULATION: FOR BIO-SAMPLE PREPARATION, QUANTUM INFORMATION DEVICES AND MAGNETIC DRUG DELIVERY

In this thesis I show achievements for precision feedback control of objects inside micro-fluidic systems and for magnetically guided ferrofluids. Essentially, this is about doing flow control, but flow control on the microscale, and further even to nanoscale accuracy, to precisely and robustly manipulate micro and nano-objects (i.e. cells and quantum dots). Target applications include methods to miniaturize the operations of a biological laboratory (lab-on-a-chip), i.e. presenting pathogens to on-chip sensing cells or extracting cells from messy bio-samples such as saliva, urine, or blood; as well as non-biological applications such as deterministically placing quantum dots on photonic crystals to make multi-dot quantum information systems. The particles are steered by creating an electrokinetic fluid flow that carries all the particles from where they are to where they should be at each time step. The control loop comprises sensing, computation, and actuation to steer particles along trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. I address following aspects of this technology. First I explain control and vision algorithms for steering single and multiple particles, and show extensions of these algorithms for steering in three dimensional (3D) spaces. Then I show algorithms for calculating power minimum paths for steering multiple particles in actuation constrained environments. With this microfluidic system I steer biological cells and nano particles (quantum dots) to nano meter precision. In the last part of the thesis I develop and experimentally demonstrate two dimensional (2D) manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets, with a view towards enabling feedback control of magnetic drug delivery to reach deeper tumors in the long term. To this end, I developed and experimentally demonstrated an optimal control algorithm to effectively manipulate a single ferrofluid droplet by magnetic feedback control. This algorithm was explicitly designed to address the nonlinear and cross-coupled nature of dynamic magnetic actuation and to best exploit available electromagnetic forces for the applications of magnetic drug delivery

USE OF HIGH SURFACE NANOFIBROUS MATERIALS IN MEDICINE

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Modeling and Experimental Techniques to Demonstrate Nanomanipulation With Optical Tweezers

The development of truly three-dimensional nanodevices is currently impeded by the absence of effective prototyping tools at the nanoscale. Optical trapping is well established for flexible three-dimensional manipulation of components at the microscale. However, it has so far not been demonstrated to confine nanoparticles, for long enough time to be useful in nanoassembly applications. Therefore, as part of this work we demonstrate new techniques that successfully extend optical trapping to nanoscale manipulation. In order to extend optical trapping to the nanoscale, we must overcome certain challenges. For the same incident beam power, the optical binding forces acting on a nanoparticle within an optical trap are very weak, in comparison with forces acting on microscale particles. Consequently, due to Brownian motion, the nanoparticle often exits the trap in a very short period of time. We improve the performance of optical traps at the nanoscale by using closed-loop control. Furthermore, we show through laboratory experiments that we are able to localize nanoparticles to the trap using control systems, for sufficient time to be useful in nanoassembly applications, conditions under which a static trap set to the same power as the controller is unable to confine a same-sized particle. Before controlled optical trapping can be demonstrated in the laboratory, key tools must first be developed. We implement Langevin dynamics simulations to model the interaction of nanoparticles with an optical trap. Physically accurate simulations provide a robust platform to test new methods to characterize and improve the performance of optical tweezers at the nanoscale, but depend on accurate trapping force models. Therefore, we have also developed two new laboratory-based force measurement techniques that overcome the drawbacks of conventional force measurements, which do not accurately account for the weak interaction of nanoparticles in an optical trap. Finally, we use numerical simulations to develop new control algorithms that demonstrate significantly enhanced trapping of nanoparticles and implement these techniques in the laboratory. The algorithms and characterization tools developed as part of this work will allow the development of optical trapping instruments that can confine nanoparticles for longer periods of time than is currently possible, for a given beam power. Furthermore, the low average power achieved by the controller makes this technique especially suitable to manipulate biological specimens, but is also generally beneficial to nanoscale prototyping applications. Therefore, capabilities developed as part of this work, and the technology that results from it may enable the prototyping of three-dimensional nanodevices, critically required in many applications

Nanogenerators in Korea

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters

Embedded Energy Landscapes In Soft Matter For Micro-Robotics And Reconfigurable Structures

The ability to manipulate microscale objects with precision to form complex structures is central to the field of micro-robotics and to the realization of reconfigurable systems. Understanding and exploiting the forces that dominate at the microscale in complex environments pose major challenges and open untapped opportunities. This is particularly the case for micro-particles in soft milieu like fluid interfaces or nematic liquid crystalline fluids, which deform or reorganize around dispersed colloids or near bounding surfaces. These energetically costly deformations can be designed as embedded energy landscapes, a form of physical intelligence, to dictate emergent colloidal interactions. The fluid nature of these soft milieu allows colloids to move to minimize the free energy and externally forced robotic structures to re-write the embedded energy landscapes in the domain. Such physically intelligent systems are of great interest at the intersection of materials science and micro-robotics. Micro-particles on fluid interfaces deform the interface shape, migrate, and assemble to minimize the capillary energy. In the first part of my thesis, I design and fabricate a magnetic micro-robot as a mobile curvature source to interact with passive colloids on the water/oil interface. An analytical expression that includes both capillary and hydrodynamic interactions is derived and captures the main feature of experimental observations. I further demonstrate multiple micro-robotic tasks including directed assembly, cargo carrying, desired release and cargo delivery on the interface. Micro-particles in confined nematic liquid crystals (NLCs) distort the nematic director field, generating interactions. These interactions depend strongly on the colloids shape and surface chemistry, geometric frustration of director field and behavior of dynamic topological defects. To probe far-from-equilibrium dynamics, I fabricate a magnetic disk with hybrid anchoring. Upon controlled rotation, the disk’s companion defect undergoes periodic rearrangement, executing a complex swim stroke that propels disk translation. I study this new swimming modality in both high and low Ericksen number regimes. At high rotation rates, the defect elongates significantly adjacent to the disk, generating broken symmetries that allow steering of the disk. This ability is exploited in path planning. Thereafter, I design a four-armed micro-robot as a mobile distortion source to promote passive colloids assembly at particular sites via emergent interactions in NLCs whose strengths are characterized and found to be several orders of magnitude larger than thermal energies. While the strength of theses interactions allows colloidal cargo to be carried with the micro-robot during translation, it poses challenges for cargo release. We find that rotation of this micro-robot generates a complex dynamic defect-sharing event with colloidal cargo that spurs cargo release. Thereafter, I demonstrate the ability to exploit NLC elastodynamics to construct reconfigurable colloidal structures in a micro-robotics platform. At the colloidal scale, rotation dynamics are easier to generate, and this motivated me to exploit the topological swimming modality of the micro-robot. Using programmable rotating fields to direct the micro-robot’s motion, I achieve fully autonomous cargo manipulations including approach, assembly, transport and release. The ability to dynamically manipulate micro-particles and their structures in soft matter systems with embedded energy landscapes, as demonstrated in this thesis, creates new possibilities for micro-robotics and reconfigurable systems