Modeling and simulation of a wirelessly-powered thermopneumatic micropump for drug delivery applications

This paper presents modeling and finite element analysis of a thermopneumatic micropump with a novel design that does not affect the temperature of the working fluid. The micropump is operated by activating a passive wireless heater using wireless power transfer when the magnetic field is tuned to match the resonant frequency of the heater. The heater is responsible for heating an air-heating chamber that is connected to a loading reservoir through a microdiffuser element. The solution inside the reservoir is pumped through a microchannel that ends with an outlet hole. The thermal and pumping performances of the micropump are analyzed using finite element method over a low range of Reynold’s number ⩽ 10 that is suitable for various biomedical applications. The results demonstrate promising performance with a maximum flow rate of ∼2.86 μL/min at a chamber temperature of 42.5 ºC, and a maximum pumping pressure of 406.5 Pa. The results show that the developed device can be potentially implemented in various biomedical areas, such as implantable drug delivery applications

Design and Simulation of a Novel Magnetic Microactuator for Microrobots in Lab-On-a-Chip Applications

This article presents the design of a magnetic microactuator comprising soft magnetic material blocks and flexible beams. The modular layout of the proposed microactuator promotes scalability towards different microrobotic applications using low magnetic fields.  The presented microactuator consists of three soft magnetic material (Ni-Fe 4750) blocks connected together via two Polydimethylsiloxane (PDMS) semi-circular beams. A detailed design approach is highlighted giving considerations toward compactness, range of motion and force characteristics of the actuator. The actuator displacement and force characteristics are approximately linear in the magnetic field strength range of 80-160 kA/m. It can achieve maximum displacements of 111.6 µm (at 160 kA/m) during extension and 10.7 µm (at 80 kA/m) during contraction under no-load condition. The maximum force output of the microactuator, computed through a contact simulation, was 404.3 nN at a magnetic field strength of 160 kA/m. The microactuator achieved stroke angles up to 18.4 in a study where the microactuator was integrated with a swimming microrobot executing rowing motion using an artificial appendage, providing insight into the capabilities of actuating untethered microrobots

Frequency-controlled wireless passive microfluidic devices

Microfluidics is a promising technology that is increasingly attracting the attention of researchers due to its high efficiency and low-cost features. Micropumps, micromixers, and microvalves have been widely applied in various biomedical applications due to their compact size and precise dosage controllability. Nevertheless, despite the vast amount of research reported in this research area, the ability to implement these devices in portable and implantable applications is still limited. To date, such devices are constricted to the use of wires, or on-board power supplies, such as batteries. This thesis presents novel techniques that allow wireless control of passive microfluidic devices using an external radiofrequency magnetic field utilizing thermopneumatic principle. Three microfluidic devices are designed and developed to perform within the range of implantable drug-delivery devices. To demonstrate the wireless control of microfluidic devices, a wireless implantable thermopneumatic micropump is presented. Thermopneumatic pumping with a maximum flow rate of 2.86 μL/min is realized using a planar wirelessly-controlled passive inductor-capacitor heater. Then, this principle was extended in order to demonstrate the selective wireless control of multiple passive heaters. A passive wirelessly-controlled thermopneumatic zigzag micromixer is developed as a mean of a multiple drug delivery device. A maximum mixing efficiency of 96.1% is achieved by selectively activating two passive wireless planar inductor-capacitor heaters that have different resonant frequency values. To eliminate the heat associated with aforementioned wireless devices, a wireless piezoelectric normally-closed microvalve for drug delivery applications is developed. A piezoelectric diaphragm is operated wirelessly using the wireless power that is transferred from an external magnetic field. Valving is achieved with a percentage error as low as 3.11% in a 3 days long-term functionality test. The developed devices present a promising implementation of the reported wireless actuation principles in various portable and implantable biomedical applications, such as drug delivery, analytical assays, and cell lysis devices

Integration of shape memory alloy for microactuation

Shape memory alloy (SMA) actuators in microelectromechanical system (MEMS) have a broad range of applications. The alloy material has unique properties underlying its high working density, simple structures, large displacement and excellent biocompatibility. These features have led to its commercialization in several applications such as micro-robotics and biomedical areas. However, full utilization of SMA is yet to be exploited as it faces various practical issues. In the area of microactuators in particular, fabricated devices suffer from low degrees of freedom (DoF), complex fabrication processes, larger sizes and limited displacement range. This thesis presents novel techniques of developing bulk-micromachined SMA microdevices by applying integration of multiple SMA microactuators, and monolithic methods using standard and unconventional MEMS fabrication processes. The thermomechanical behavior of the developed bimorph SMA microactuator is analyzed by studying the parameters such as thickness of SMA sheet, type and thickness of stress layer and the deposition temperature that affect the displacement. The microactuators are then integrated to form a novel SMA micromanipulator that consists of two links and a gripper at its end to provide three-DoF manipulation of small objects with overall actuation x- and y- axes displacement of 7.1 mm and 5.2 mm, respectively. To simplify the fabrication and improve the structure robustness, a monolithic approach was utilized in the development of a micro-positioning stage using bulk-micromachined SMA sheet that was fabricated in a single machining step. The design consisted of six spring actuators that provided large stage displacement range of 1.2 mm and 1.6 mm in x- and y-axes, respectively, and a rotation of 20° around the z-axis. To embed a self-sensing functionality in SMA microactuators, a novel wireless displacement sensing method based on integration of an SMA spiral-coil actuator in a resonant circuit is developed. These devices have the potential to promote the application of bulk-micromachined SMA actuator in MEMS area

Optimization studies of thermal bimorph cantilevers, electrostatic torsion actuators and variable capacitors

In this dissertation, theoretical analyses and optimization studies are given for three kinds of MEMS devices: thermal bimorph cantilevers, electrostatic torsion actuators, and variable capacitors. Calculation, simulation, and experimental data are used to confirm the device behavior and demonstrate the application of the design approaches. For thermal bimorph cantilevers, an analytical model is presented which allows theoretical analysis and quantitative optimization of the performance based on material properties and device dimensions. Bimorph cantilevers are divided into two categories for deflection optimization: either the total thickness is constant, or the cantilever has one constant and one variable layer thickness. The optimum equations are then derived for each case and can be used as design rules. The results show that substantial improvements are possible over existing design approaches. Other parameters like static temperature distribution, power consumption, and dynamic behavior are also discussed, as are design tradeoffs such as feature size, application constraints, fabrication feasibility, and cost. The electrostatic torsion actuator studies are conducted for two device types: round and rectangular. The first case describes an analytical study of the pull-in effect in round, double-gimbaled, electrostatic torsion actuators with buried, variable length electrodes, designed for optical cross-connect applications. It is found that the fractional tilt at pull-in for the inner round plate in this system depends only on the ratio of the length of the buried electrode to the radius of the plate. The fractional tilt at pull-in for the outer support ring depends only on the ratio of the length of the buried electrode to the outer radius of the ring and the ratio of the ring\u27s inner and outer radii. Expressions for the pull-in voltage are determined in both cases. General relationships are also derived relating the applied voltage to the resulting tilt angle, both normalized by their pull-in values. Calculated results are verified by comparison with finite element MEMCAD simulations, with fractional difference smaller than 4% for torsion mode dominant systems. For the second case, a fast, angle based design approach for rectangular electrostatic torsion actuators based on several simple equations is developed. This approach is significantly more straightforward than the usual full calculation or simulation methods. The main results of the simplified approach are verified by comparing them with analytical calculations and MEMCAD simulations with fractional difference smaller than 3% for torsion mode dominant actuators. Also, good agreement is found by comparison with the measured behavior of a micro-fabricated full-plate device. In the last topic, ultra-thin silicon wafers, SU-8 bonding and deep reactive ion etching technology have been combined for the fabrication of folded spring, dual electrostatic drive, vertical plate variable capacitor devices with displacement limiting bumpers. Due to the presence of the bumpers, the variable capacitor with parallel plate drive electrodes has two tuning voltage regimes: first a parabolic region that achieves roughly a 290% tuning range, then a linear region that achieves an additional 310%, making the total tuning range about 600%. The variable capacitor with comb drive electrodes has a parabolic region that achieves roughly a 205% tuning range, then a linear region that achieves an additional 37%, making its total tuning range about 242%. The variable capacitors have Q factors around 100 owing to the use of silicon electrodes other than lower resistivity metal

Towards smart self-clearing glaucoma drainage device.

For patients who are unresponsive to pharmacological treatments of glaucoma, an implantable glaucoma drainage devices (GDD) are often used to manage the intraocular pressure. However, the microscale channel that removes excess aqueous humor from the anterior chamber often gets obstructed due to biofouling, which necessitates additional surgical intervention. Here we demonstrate the proof-of-concept for smart self-clearing GDD by integrating magnetic microactuators inside the drainage tube of GDD. The magnetic microactuators can be controlled using externally applied magnetic fields to mechanically clear biofouling-based obstruction, thereby eliminating the need for surgical intervention. In this work, our prototype magnetic microactuators were fabricated using low-cost maskless photolithography to expedite design iteration. The fabricated devices were evaluated for their static and dynamic mechanical responses. Using transient numerical analysis, the fluid–structure interaction of our microactuator inside a microtube was characterized to better understand the amount of shear force generated by the device motion. Finally, the anti-biofouling performance of our device was evaluated using fluorescein isothiocyanate labeled bovine serum albumin. The microactuators were effective in removing proteinaceous film deposited on device surface as well as on the inner surface of the microchannel, which supports our hypothesis that a smart self-clearing GDD may be possible by integrating microfabricated magnetic actuators in chronically implanted microtubes

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

Stepper microactuators driven by ultrasonic power transfer

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

Development of a light-powered microstructure : enhancing thermal actuation with near-infrared absorbent gold nanoparticles.

Development of microscale actuating technologies has considerably added to the toolset for interacting with natural components at the cellular level. Small-scale actuators and switches have potential in areas such as microscale pumping and particle manipulation. Thermal actuation has been used with asymmetric geometry to create large deflections with high force relative to electrostatically driven systems. However, many thermally based techniques require a physical connection for power and operate outside the temperature range conducive for biological studies and medical applications. The work presented here describes the design of an out-of-plane bistable switch that responds to near-infrared light with wavelength-specific response. In contrast to thermal actuating principles that require wired conductive components for Joule heating, the devices shown here are wirelessly powered by near -infrared (IR) light by patterning a wavelength-specific absorbent gold nanoparticle (GNP) film onto the microstructure. An optical window exists which allows near-IR wavelength light to permeate living tissue, and high stress mismatch in the bilayer geometry allows for large actuation at biologically acceptable limits. Patterning the GNP film will allow thermal gradients to be created from a single laser source, and integration of various target wavelengths will allow for microelectromechanical (MEMS) devices with multiple operating modes. An optically induced temperature gradient using wavelength-selective printable or spinnable coatings would provide a versatile method of wireless and non-invasive thermal actuation. This project aims to provide a fundamental understanding of the particle and surface interaction for bioengineering applications based on a “hybrid” of infrared resonant gold nanoparticles and MEMS structures. This hybrid technology has potential applications in light-actuated switches and other mechanical structures. Deposition methods and surface chemistry are integrated with three-dimensional MEMS structures in this work. The long-term goal of this project is a system of light-powered microactuators for exploring cells\u27 response to mechanical stimuli, adding to the fundamental understanding of tissue response to everyday mechanical stresses at the molecular level