Frequency dependence of surface acoustic wave swimming.

This is the author accepted manuscript. The final version is available from The Royal Society.Surface acoustic waves (SAWs) are elastic waves that can be excited directly on the surface of piezoelectric crystals using a transducer, leading to their exploitation for numerous technological applications, including for example microfluidics. Recently, the concept of SAW streaming, which underpins SAW microfluidics, was extended to make the first experimental demonstration of 'SAW swimming', where instead of moving water droplets on the surface of a device, SAWs are used as a propulsion mechanism. Using theoretical analysis and experiments, we show that the SAW swimming force can be controlled directly by changing the SAW frequency, due to attenuation and changing force distributions within each SAW streaming jet. Additionally, an optimum frequency exists which generates a maximum SAW swimming force. The SAW frequency can therefore be used to control the efficiency and forward force of these SAW swimming devices. The SAW swimming propulsion mechanism also mimics that used by many microorganisms, where propulsion is produced by a cyclic distortion of the body shape. This improved understanding of SAW swimming provides a test-bed for exploring the science of microorganism swimming, and could bring new insight to the evolutionary significance for the length and beating frequency of swimming microbial flagella.Leverhulme Trust Research Projec

Acoustic Bubble Propulsion and Rotation for MEMS Devices

The goal of this thesis research is to investigate acoustic wave actuated devices’ abilities spatially in different media and with various designs. Self-trapped bubble oscillation generates cavitation at the open end of the micro channel under a continuous sound wave. The cavitation generates propulsion from the opening through to the end of the micro channel. Researchers generally have found bubbles undesirable because of their non-linear effect in many applications. Therefore, there has been much research conducted in the area of eliminating the bubbles in liquid media. However, the use of bubbles can be beneficial in some applications like bubble powered actuators, switchers, and so forth. This research ensures the availability and feasibility of the bubble powered actuator for future medical applications. In the current research, the actuator works with the principle of an oscillating bubble cavitation. The bubble cavitation and oscillation effect create a propulsion effect through the designed tubes. The captured bubbles generate force against to contact surface. The force against this force from the contact surface causes propelling. Different frequencies oscillate the bubbles in different lengths. Thus, the length of the bubble that is captured in the channel has an impact on the oscillation frequency by the sound wave, since the changes in lengths of the bubble also differ the oscillating frequency. In different oscillating frequencies can be used not only for a planar propulsion but also for bilateral and three dimensional propulsion. In addition, with various designs, a device has an ability to substantiate many kind of motion in liquid media which means that propulsion effect can also use for circular or vortex motion purposes. In this research, up to 400 RPM circular and 70 mm/s instantaneous propelling speed are achieved in several designs by self-trapped and blocked micro-bubbles’ oscillations under acoustic wave in water media. In this novel study, availability and feasibility of acoustically oscillated micro-bubble based propulsion is demonstrated in spatial and rotational movement for future MEMS applications

Acoustic Powered Micro Swimmer and Its Bidirectional Propulsion

Micro-robots have great potential in biomedical aspects. However, there are no detailed experiments results for micro-swimmer (a micro-channel contains an air bubble inside it) propelling into the human body environment. This thesis describes the micro-swimmer propelling in blood environments, and testing in real blood. Demonstrated through bubble vibration, micro-swimmer can push forward in the blood environment. Meanwhile, I found the phenomenon of the micro-swimmer moving backward in the blood environment. The velocity of stream speed and position of the bubble interface have effect on the micro-swimmer propulsion direction. One the other hand, I find out the micro-swimmer is harder to propel in the blood environment. In order to improve the efficiency of acoustic transmission, I also made the liquid lens to focus sound, which can improve the transfer efficiency of acoustic wave

Ultrasonic locating and tracking of small particles for biomedical applications

This dissertation focuses on the development of two novel ultrasound technologies with the idea of tracking and locating small particles: 1) Ultrasound tracking of the acoustically actuated microswimmers, 2) Super-resolution ultrasound (SRU) imaging by locating the microbubbles. Artificial microswimmers that navigate in hard-to-reach spaces and microfluidic environments inside human bodies hold a great potential for various biomedical applications. For eventual translation of the microswimmer technology, a capability of tracking the microswimmers in 3-D through tissues is particularly required for reliable navigation. In this work, after first proposing and demonstrating the proof-of-concept of ultrasound tracking of the microswimmer in a 2-D setup in vitro, we built a 3-D ultrasound tracking system using two clinical ultrasound probes. A reliable performance for tracking the arbitrary 3-D motions of the newly designed 3-D microswimmers in real-time was demonstrated in vitro. The developed 3-D ultrasound tracking strategy could be a strong motivation and foundation for the future clinical translation of the novel microswimmer technology. SRU that can identify microvessels with unprecedented spatial resolution is promising for diagnosing the diseases associated with abnormal microvascular changes. One of the potential applications is to assess the changes in renal microvasculature during the progressive kidney disease. In this work, we applied the developed deconvolution-based SRU imaging on the mouse acute kidney injury (AKI) model to show the capability of SRU for noninvasive assessment of renal microvasculature changes during the progression from AKI to chronic kidney disease (CKD). SRU that can identify microvessels with unprecedented spatial resolution is promising for diagnosing the diseases associated with abnormal microvascular changes. One of the potential applications is to assess the changes in renal microvasculature during the progressive kidney disease. In this work, we applied the developed deconvolution-based SRU imaging on the mouse acute kidney injury (AKI) model to show the capability of SRU for noninvasive assessment of renal microvasculature changes during the progression from AKI to chronic kidney disease (CKD). Future endeavors for integrating SRU locating technology with a reliable tracking capability of microparticles will provide a unique tool for various biomedical applications of the novel microdrones for diagnosis and drug delivery

Self-Propelled Micro/Nanomotors (MNMs) and Their Applications

The majority of the micro/nanomotors use the precious noble metal platinum for propulsion. However, platinum suffers from high-cost, scarcity, and possibility of deactivation in various media. In this thesis, we explored the MnO2 based materials for the fabrication of the high-performance and low-cost micro/nanomotors. These newly developed MnO2 based micromotors show great potential for replacing Pt and will greatly improves the applications of micro/nanomotors for biomedical science and environmental remediations areas

DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS

World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices