Re-designing materials for biomedical applications: from biomimicry to nature-inspired chemical engineering

Gathering inspiration from nature for the design of new materials, products and processes is a topic gaining rapid interest among scientists and engineers. In this review, we introduce the concept of natureinspired chemical engineering (NICE). We critically examine how this approach offers advantages over straightforward biomimicry and distinguishes itself from bio-integrated design, as a systematic methodology to present innovative solutions to challenging problems. The scope of application of the nature-inspired approach is demonstrated via examples from the field of biomedicine, where much of the inspiration is still more narrowly focused on imitation or bio-integration. We conclude with an outlook on prospective future applications, offered by the more systematic and mechanistically based NICE approach, complemented by rapid progress in manufacturing, computation and robotics. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’

Tandem actuation of legged locomotion and grasping manipulation in soft robots using magnetic fields

Untethered soft robots have the potential to impact a variety of applications, particularly if they are capable of controllable locomotion and dexterous manipulation. Magnetic fields can provide humansafe, contactless actuation, opening the gates to applications in confined spaces - for example, in minimally invasive surgery. To translate these concepts into reality, soft robots are being developed with different capabilities, such as functional components to achieve motion and object manipulation. This paper investigates the tandem actuation of two separate functions (locomotion and grasping) through multi-legged soft robots with grippers, actuated by magnetic fields. The locomotion and grasping functions are activated separately by exploiting the difference in the response of the soft robots to the magnitude, frequency and direction of the actuating magnetic field. Two robots capable of performing controllable straight and turning motions are demonstrated: a millipede-inspired robot with legs moving in a rhythmic pattern, and a hexapod robot with six magnetic legs following an alternating tripod gait. Two types of grippers are developed: one inspired by prehensile tails and another similar to flowers or jellyfish. The various components are fabricated using a composite of silicone rubber with magnetic powder, and analyzed using quasi-static models and experimental results. Fully untethered locomotion of the robots and independent gripper actuation are illustrated through experiments. The maneuverability of the robots is proven through teleoperated steering experiments where the robots navigate through the workspace while avoiding obstacles. The ability of the robots to manipulate objects by operating in tandem with the grippers is demonstrated through multiple experiments, including pick-and-place tasks where the robots grasp and release cargo at specific locations when triggered using magnetic fields. (C) 2020 The Authors. Published by Elsevier Ltd

Bioinspired Light Robots from Liquid Crystal Networks

Bioinspired material research aims at learning from the sophisticated design principles of nature, in order to develop novel artificial materials with advanced functionalities. Some of the sophisticated capabilities of biological materials, such as their ability to self-heal or adapt to environmental changes, are challenging to realize in artificial systems. Nevertheless, many efforts have been recently devoted to develop artificial materials with adaptive functions, especially materials which can generate movement in response to external stimuli. One such effort is the field of soft robots, which aims towards fabrication of autonomous adaptive systems with flexibility, beyond the current capability of conventional robotics. However, in most cases, soft robots still need to be connected to hard electronics for powering and rely on complicated algorithms to control their deformation modes. Soft robots that can be powered remotely and are capable of self-regulating function, are of great interest across the scientific community.In order to realize such responsive and adaptive systems, researches across the globe are making constant efforts to develop new, ever-more sophisticated stimuliresponsive materials. Among the different stimuli-responsive materials, liquid crystal networks (LCNs) are the most suited ones to design smart actuating systems as they can be controlled and powered remotely with light and thereby obviate the need for external control circuitry. They enable pre-programable shape changes, hence equipping a single material with multiple actuation modes. In addition to light, they can also be actuated by variety of stimuli such as heat, humidity, pH, electric and magnetic fields etc., or a combination of these. Based on these advantages of LCNs, we seek inspiration from natural actuator systems present in plants and animals to devise different light controllable soft robotic systems.In this thesis, inspired from biological systems such as octopus arm movements, iris movements in eyes, object detection and capturing ability of Venus flytraps and opening and closing of certain nocturnal flowers, we demonstrate several light robots that can be programmed to show pre-determined shape changes. By employing a proper device design, these light robots can even show the characteristics of selfregulation and object recognition, which brings new advances to the field of LCNbased light robots. For instance, octopod light robot can show bidirectional bending owing to alignment programming using a commercial laser projector; artificial iris is a fully light controllable device that can self-regulate its aperture size based on intensity of incident light; the optical flytrap can not only autonomously close on an object coming into its ‘‘mouth’’ but it can also distinguish between different kinds of objects based on optical feedback, and finally, integration of light and humidity responsiveness in a single LCN actuator enables a nocturnal flower-mimicking actuator, which provides an opportunity to understand the delicate interplay between different simultaneously occurring stimuli in a monolithic actuator.We believe that besides providing a deeper understanding on the photoactuation in liquid crystal networks, at fundamental level, our work opens new avenues by providing several pathways towards next-generation intelligent soft microrobots

Nature-inspired soft robotics: On articial cilia and magnetic locomotion

Inspired by micro-organisms in nature, people imagined using micro-scale soft robots to work inside the human body for therapeutic drug delivery, minimally invasive surgery, or diagnostic biochemical sensing. To create these robots is challenging due to their small size, viscosity environment, and soft constituting materials. In addition, the mechanisms of operation are quite different from the conventional rigid macro-scale robots that we are familiar with. In this PhD project, we focused on the computational analysis and design of micro-scale soft robots. Working closely with experimental groups, we studied artificial cilia and micro-swimmers that can realize particle manipulation, fluid transport, fluid mixing, or magnetic locomotion. Various cilia systems are considered, including soft inflatable cilia which could be controlled individually and programmable magnetic cilia featuring phase shifts and collective metachronal patterns. We also analyze micro-swimmers that are soft and adaptive in confined spaces. Driven by different external magnetic fields, the swimmer's motion can be changed between undulation crawling, undulation swimming, and helical crawling. By using computational modeling, we analyze the transport mechanisms of the soft robots and study the effect of different parameters to provide guidelines for the design of the robots in specific applications. By studying the physical mechanisms of micro-organisms in nature, we are not only able to understand more clearly their functional behaviour, it also opens the possibility of biomimetic design of soft robotic cilia and micro-swimmers

Non-inertial Undulatory Locomotion Across Scales

Locomotion is crucial to behaviors such as predator avoidance, foraging, and mating. In particular, undulatory locomotion is one of the most common forms of locomotion. From microscopic flagellates to swimming fish and slithering snakes, this form of locomotion is a remarkably robust self-propulsion strategy that allows a diversity of organisms to navigate myriad environments. While often thought of as exclusive to limbless organisms, a variety of locomotors possessing few to many appendages rely on waves of undulation for locomotion. In inertial regimes, organisms can leverage the forces generated by their body and the surrounding medium's inertia to enhance their locomotion (e.g., coast or glide). On the other hand, in non-inertial regimes self-propulsion is dominated by damping (viscous or frictional), and thus the ability for organisms to generate motion is dependent on the sequence of internal shape changes. In this thesis, we study a variety of undulating systems that locomote in highly damped regimes. We perform studies on systems ranging from zero to many appendages. Specifically, we focus on four distinct undulatory systems: 1) C. elegans, 2) quadriflagellate algae (bearing four flagella), 3) centipedes on terrestrial environments, and 4) centipedes on fluid environments. For each of these systems, we study how the coordination of their many degrees of freedom leads to specific locomotive behaviors. Further, we propose hypotheses for the observed behaviors in the context of each of these system's ecology.Ph.D

복합 미세 구조의 최적설계와 건식접착 시스템 응용

학위논문 (박사)-- 서울대학교 대학원 : 협동과정 바이오엔지니어링전공, 2014. 2. 전누리.In this thesis, we describe the bio-inspired design and fabrication methods to mimic scalable hierarchical structure in Nature and exploited 3 representative structureslotus life, geckos feet and extra cellular matrix (ECM). Multiscale, hierarchically patterned surfaces such as lotus leaves, butterfly wings, adhesion pads of gecko lizards are abundantly found in nature, where microstructures are usally used to strengthen the mechanical stability while nanostructures offer the main functionality, i.e., wettability, structural color, or dry adhesion. To emulate such hierarchical structures in nature, multiscale, multilevel patterning has been extensively utilized for the last few decades towards various applications ranging from wetting control, structural colors, to tissue scaffolds. In this thesis, we suggested simple yet robust fabrication method to scalable multiscale patterning to bring about improved functions that can even surpass those found in nature, with particular focus on the analogy between natural and synthetic architectures in terms of the role of different length scales. First, we present here an enhanced dry adhesive skin patch with composite micropillarsthe stem region of the pillars is formed by a relatively rigid material like hard polydimethylsiloxane (h-PDMS) (Youngs modulus: ~8.2 MPa) or PDMS with a higher amount of curing agent, e.g., 15% (Youngs modulus: ~2.8 MPa). The top layer is additionally integrated by transferring a soft PDMS layer with a lower amount of curing agent, e.g., 5% (Youngs modulus: ~0.8 MPa). In this way, monolithically integrated composite PDMS micropillars can be prepared with better adhesion strength and durability. Next, we present a simple method of fabricating robust dry adhesives by coating a soft polydimethyl siloxane (PDMS) thin layer on rigid backbone micropillars of polyurethane acrylate (PUA). These core-shell type micropillars demonstrated enhanced durability both in normal and shear adhesion over more than 100 cycles of attachment and detachment. Relatively strong normal (~11.4 N/cm2) and shear (~15.3 N/cm2) adhesion forces were observed, which were similar to or even larger than those of homogeneous PDMS micropillars. A simple theoretical model based on beam deflection theory was used to explain the experimental results. Finally, Inspired from exceptional climbing ability of gecko lizards, rtificial fibrillar adhesives have been extensively studied over the last decade both experimentally and theoretically. Therefore, a new leap towards practical uses beyond the academic horizon is timely and highly anticipated. To this end, we present a fibrillar adhesive in the form of bridged micropillars and its application to a transportation system with the detachment mechanism inspired by the climbing behaviour of gecko lizards. The adhesive shows strong normal attachment (~30 N/cm2) as well as easy and fast detachment within 0.5 sec without involving complex dynamic mechanisms or specific stimulus-responsive materials. The fabrication of the bridged micropillars consists of replica moulding of polydimethylsiloxane (PDMS) micropillars, transfer of the PDMS precursor to the heads of micropillars, and inverse placement on an inert Teflon-coated surface. Owing to spontaneous interconnections of low viscosity PDMS precursor, bridged micropillars with a uniform capping nanomembrane (~800 nm thickness) are formed over a large area. Interestingly, macroscopic adhesion in normal direction can be immediately switched between on and off states by changing the two detachment modes of pulling and peeling, respectively. To prove the potential of the fibrillar adhesive for practical use, an automated transportation system is demonstrated for lifting and releasing a mass of stacked glass slides over 1000 cycles of attachment and detachment.Chapter 1. Introduction 1 1-1. The role of multiscale, hierarchical structures in nature 2 Chapter 2. Enhanced skin adhesive patch with modulus-tunable composite micropillars 16 2-1. Introduction 16 2-2. Experimental 19 2-3. Results and Discussion 22 2-4. Summary 34 Chapter 3. Fabrication and analysis of enforced dry adhesives with core-shell micropillars 35 3-1. Introduction 35 3-2. Experimental 38 3-3. Results and Discussion 40 3-4. Supplemental 51 3-5. Summary 53 Chapter 4. Instantly switchable adhesion of bridged fibrillar adhesive via gecko-inspired detachment mechanism and its application to transportation system 54 4-1. Introduction 54 4-2. Experimental 58 4-3. Results and Discussion 61 4-4. Supplemental 80 4-5. Summary 84 Chapter 5. Bio-inspired design and fabrication for superhydrophobic metallic surface 85 5-1. Introduction 85 5-2. Experimental 90 5-3. Results and Discussion 92 5-4. Supplemental 107 5-5. Summary 111 Chapter 6. Bio-inspired design and fabrication for multiscale patterns by shape memory effect 112 6-1. Introduction 112 6-2. Experimental 116 6-3. Results and Discussion 120 6-4. Supplemental 136 6-5. Summary 139 References 140 국문초록 153Docto

Lateral bending liquid crystal elastomer beams for microactuators and microgrippers

With the rapid development of microsystems in the last few decades, there is a requirement for high precision tools for micromanipulation and transportation of micro-objects, such as microgrippers, for applications in microassembly, microrobotics, life sciences and biomedicine. Polymer based microgrippers and microrobots executing various tasks have been of significant interest as an alternative to the traditional silicon and metal based counterparts due to the advantages of low cost fabrication, low actuation temperature, biocompatibility, and sensitivity to various stimuli. The exceptional actuation properties of liquid crystal elastomers (LCE) have made these materials highly attractive for various emerging applications in the last two decades. Large programmable deformations and the benefits offered by the elastic, thermal and optical properties of LCEs are suitable for implementing stimuli-responsive microgrippers as well as various biomimetic motion in soft robots. In this thesis, a method and the associated processes for fabrication and molecular alignment in LCE were developed, which enabled new functionality and improved performance of the LCE based microactuators and microgrippers, providing controlled response by thermal and remote photothermal actuation, and allowing easy integration of the LCE end-effectors into robotic systems for automated operation. Lateral bending actuation has been demonstrated in LCE microbeams of 900 µm of length and 40 µm of thickness, owing to the new monolithic micromolding technique using vertical patterned walls for alignment. The effects of parameters such as the beam width, the size of the microgrooves, and the surface treatment method on the behavior of the microactuators were studied; the internal alignment pattern of liquid crystals in the structure was investigated by different microscopy methods. An efficient method for finite element modeling of the bending LCE actuators was developed and experimentally verified, based on the gradient of equivalent thermal expansion in the multi-layer structure, which was able to predict the bending behavior of the actuators in a large range of thicknesses as well as rolling behavior of the actuators of tapered thickness. The novel LCE microgripper with in-plane operation showed efficient thermal and photothermal actuation, achieving the gripping stroke of 64 µm under the light intensity of 239 mW/cm2 for the gripper length of 900 µm, which is more efficient than the typical SU-8 polymer based microgrippers of the same dimensions. The LCE gripper was successfully demonstrated for the application in manipulation of the objects of tens to hundreds of micrometers in size. Therefore, the novel LCE microgripper bridges the gap in the LCE-based gripper technologies for typical object size in applications for systems microassembly, biological and cell micromanipulation. The lateral bending functionality enabled by the proposed method expands design opportunities for thermal and photothermal LCE microactuators, providing an effective route toward realization of new modes of gripping, locomotion, and cargo transportation in soft microrobotics and micromanipulation