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

Integrated Micro/Nanoengineered Functional Biomaterials for Cell Mechanics and Mechanobiology: A Materials Perspective

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106681/1/adma201304431.pd

Lab on fiber technology: a nanospectroscopic approach for biochemical sensing

169 p.Hoy en día, gracias al uso de fibras ópticas, el desarrollo de sensores bioquímicos económicos y de altas prestaciones capaces de realizar medidas en tiempo real es posible, modificando esta tecnología por la tradicional basada en equipamientos caros, grandes y complejos. Por esta razón, en esta tesis hemos desarrollado un sensor mediante nanopartículas de oro inmovilizadas en la cara de una fibra óptica. El sensor que proponemos combina las ventajas de las fibras ópticas con el efecto plasmón de las nanopartículas, que proporcionan gran sensibilidad a cambios en el medio externo. Sin embargo, la mayor novedad que esta tesis proporciona es el uso de la nano-espectroscopia. Esta técnica se basa en hacer coincidir las frecuencias de resonancia de las nanopartículas con el elemento bioquímico que se quiera detectar, consiguiendo altos niveles de selectividad y sensibilidad, en contraposición con los métodos convencionales que se basan en medir cambios en longitud de onda de la frecuencia de resonancia de las nanopartículas. Para demostrar la validez de la nano-espectroscopia en la punta de una fibra óptica, se han realizado medidas para detectar iones de cobre (II) y Citocromo c, consiguiendo unos límites de detección varios órdenes de magnitud por debajo de los sensores basados en nano-espectroscopia mediante microscopios. Además, esta tesis contribuye también a un mayor entendimientodel proceso de inmovilización de las nanopartículas en la fibra óptica gracias a la amplia caracterizaciónque se ha realizado

Lab on fiber technology: a nanospectroscopic approach for biochemical sensing

169 p.Hoy en día, gracias al uso de fibras ópticas, el desarrollo de sensores bioquímicos económicos y de altas prestaciones capaces de realizar medidas en tiempo real es posible, modificando esta tecnología por la tradicional basada en equipamientos caros, grandes y complejos. Por esta razón, en esta tesis hemos desarrollado un sensor mediante nanopartículas de oro inmovilizadas en la cara de una fibra óptica. El sensor que proponemos combina las ventajas de las fibras ópticas con el efecto plasmón de las nanopartículas, que proporcionan gran sensibilidad a cambios en el medio externo. Sin embargo, la mayor novedad que esta tesis proporciona es el uso de la nano-espectroscopia. Esta técnica se basa en hacer coincidir las frecuencias de resonancia de las nanopartículas con el elemento bioquímico que se quiera detectar, consiguiendo altos niveles de selectividad y sensibilidad, en contraposición con los métodos convencionales que se basan en medir cambios en longitud de onda de la frecuencia de resonancia de las nanopartículas. Para demostrar la validez de la nano-espectroscopia en la punta de una fibra óptica, se han realizado medidas para detectar iones de cobre (II) y Citocromo c, consiguiendo unos límites de detección varios órdenes de magnitud por debajo de los sensores basados en nano-espectroscopia mediante microscopios. Además, esta tesis contribuye también a un mayor entendimientodel proceso de inmovilización de las nanopartículas en la fibra óptica gracias a la amplia caracterizaciónque se ha realizado

NASA Tech Briefs, June 2001

Topics covered include: Sensors; Electronic Components and Systems; Software Engineering; Materials; Manufacturing/Fabrication; physical Sciences; Information Sciences

Photonic Crystal Directional Coupler Based Optomechanical Sensor

An extremely small ($6.5\times6.5\mu$m) optomechanical sensor is proposed that utilizes a photonic crystal (PC) etched onto silicon-on-insulator (SOI) using adapted complimentary metal-oxide-semiconductor fabrication technology. The destructive interference of light with the periodic structure can forbid its propagation inside the crystal across a range of frequencies and can be used to confine light near edge of a PC slab. By placing two PC edges near each other, a directional coupler is formed where light is periodically exchanged between the two waveguides. Wet-etching away the buried oxide residing beneath the photonic crystal directional coupler (PCDC), a membrane is formed. Exerting force on the PCDC alters the separation between the two PC edges and modulates the observed transmission at the coupler outputs. Buckle-mitigating structures are also demonstrated here which relieve the unpredictable compressive stress built into the top silicon layer of SOI during wafer fabrication. The PCDC sensors attempt to overcome some of the shortcomings of existing micromechanical sensors such as area constraints, material restrictions, stiction, and EM interference. PCDC sensors are also highly parallelizable due to their small size and wide optical bandwidth. PCDC sensors are envisaged to be used in microfluidic integration and are capable of 149kPa full scale pressure measurement ranges

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators