Search

This paper presents the design and testing of a wrist-worn Wearable Health Device (WHD) with an integrated compliant Constant-Force Mechanism (CFM) as part of the wrist band, acting to keep the band tension constant. An integrated CFM can keep pressure on the wrist constant or near-constant, thereby solving one of the main difficulties (movement of and varying force on the sensor area) that wrist-worn WHDs face. The design requirements for a constant-force wristband were narrowed down to seven critical requirements. Multiple CFMs were explored with two main concepts (buckling beams and tape springs) prototyped and evaluated against the key requirements. The tape spring concept was chosen for human subject trials testing due to the mechanism’s better performance compared to the buckling beams concept. The human subject testing (IRB2020-268) compares pressure on the wrist for both a band with and without an integrated CFM for eight different movement activities. The band with the integrated CFM produced reduced variation in the pressure on the wrist, but the difference was not significant. In addition, it was found that, even with the CFM, the band’s sensor location shifted during human motion. Future work will focus on alternative ways of reducing pressure variation, including constant force mechanisms that apply force directly to the sensor package, rather than acting to keep band tension constant.

This paper presents the design and testing of a wrist worn health sensing band used to gather relationship data among band tension, sensor pressure, patient comfort, and measured pulsatile signal quality. It uses micromachined carbon-infiltrated carbon nanotube electrodes to detect a patient’s pulse using a bioimpedance approach. The micromachined electrodes experience no corrosion, and they are both strongly conductive and hypoallergenic. A simple mathematical model was developed to show the relationship between pressure on the wrist and tension in the wristband. The wristband was tested by being worn by 10 different research subjects over 15 tests. During each test, the tension in the band was varied, and the tension, pressure, and bioimpedance signal were measured and recorded. The test subject also reported a comfort and pain level score for each level of band tension. The results show that the model correctly predicts that tension varies linearly with pressure, and that the pressure vs. tension slope increases with increasing wrist width. There also exists a linear relationship between tension and patient pain/comfort, but pressure does not show an effect on the patient discomfort or pain experienced. Signal quality when measured in the range of 0–4 N of tension and 0–20 kPa of sensor pressure does not have a direct correlation to either tension or pressure.

This paper presents a novel approach to energy scavenging for a micro-electro-mechanical system (MEMS) device to convert the energy stored in pressurized gas into electrical power. The proposed design uses input pressure to move a piston and magnet through a set of coils while pulling on another mass through non-linear springs to open and close the input air valve. The model demonstrates that the design is capable of staying in motion with continual input pressure (up to at least a time stamp of 1 second), and that an average power output of 9.47 μW over 5 ms can be achieved. We suggest that further research be done to optimize the design parameters and that the optimized design be used to the test the system.

This paper describes the fabrication and testing of a system to inject DNA into plant leaves. Arrays of silicon lances were made using photolithographic and STS DRIE Bosch techniques. A nanoinjector device was also made to accept the silicon lance arrays and perform nanoinjections. Nanoinjections were performed on Arabidopsis and cotton cotyledons. Changes in the force applied during a nanoinjection and varying the number of repeated nanoinjections on the same cotyledon were observed. Too much force or too many repeated injections caused physical damage to the cotyledon. An optimal force and number of repeated injections can be performed without causing physical damage to the cotyledon. Several injections using DNA were performed without successful transfection of the leaves. Possible reasons for this failure to transfect were explored.

This work presents two novel support systems used to help mitigate flexible device buckling during insertion such as the insertion of medical device into the body. These systems are collapsible to accommodate the changing length of the flexible device as it is inserted. They use tension in wires or geometry to provide systems with lateral stiffness used to support the device. Through modeling, the performance of these systems can be predicted and they can be designed to a desired performance. This was validated in the geometry-based support system. They provide systems with small operating volumes and part counts.

This paper presents, for the first time, the process of growing a pattern of carbon nanotubes (CNT(s)) on 316L stainless steel. The data presented is preliminary and requires further investigation to detail the growth behaviors of CNTs on stainless steel in regards to producing a pattern. However, this article presents the viability of producing a pattern on a stainless steel surface that can be used in bio-surfacing and electronic applications, among others. The results show that producing a CNT pattern on stainless steel can be achieved in a similar manner to that of producing a CNT pattern on a silicon wafer, with some vital differences in the photolithography and growth processes. The results also show that long CNT growth can lead to partial overgrowth of the pattern.

Chronic Venous Insufficiency (CVI) is a disease of the lower limbs that affects millions of people in the United States. CVI results from incompetent venous valves. The purpose of venous valves is to prevent retrograde blood flow to the lower limbs. Valve failure can lead to edema, pain, and ulcers. One solution that has great potential is to create an implantable venous valve that could restore function of the venous system. No prosthetic venous valves are clinically used currently because of problems with biocompatiblility and thrombogenicity caused by high shear rates. This paper presents a prosthetic venous valve that could overcome these difficulties by using carbon-infiltrated carbon nanotubes (CI-CNTs). This material has been proven to be thrombo-resistant, biocompatible due to its non-reactive properties, and durable. The valve was designed to be initially open and to close with physiological pressures. Finite element modeling showed that, with a hydrostatic pressure of 20 mmHg (the minimum hydrostatic pressure in the common femoral vein), it fully closed with a maximum stress of 117 MPa, which is below the ultimate strength of CI-CNTs. A computational fluid dynamics analysis demonstrated the valve would cause a maximum shear rate of 225.1 s−1, which is less than the maximum shear rate in the body. Hence, this valve would be less likely than previous prosthetic valves to develop blood clots. Currently, this is the lowest shear rate reported for a prosthetic venous valve. These results demonstrate that a CI-CNT prosthetic venous valve has the potential to be an effective treatment for CVI.

This paper investigates the design of a nano-injection system that can deliver genetic material to cells within live tissue. The approach to creating such a system was to create candidate designs that meet all the requirements for successful in vivo injection and can be fabricated using silicon etching. The designs were tested through large-scale prototyping and through models that describe the systems’ behavior on the micrometer scale. One design consists of an array of lances on a rigid backing. The other design consists of an array of lances grouped in sets of three on a backing that can conform to the shape of the tissue being injected. Each design was prototyped in 3D printed ABS plastic. Preliminary results were qualitative and showed that the rigid and flexible designs performed similarly on mostly flat and irregular surfaces. On convex surfaces with a strong curvature (radius of curvature of about 2 cm), the flexible array gave slightly better results. Final testing gave a quantitative comparison of the two designs’ efficiencies on strongly curved convex surfaces. These results supported the preliminary results that the flexible array is more efficient in reaching points on the tissue than the rigid array is. As the applied force increased, each array performed more efficiently.Copyright © 2016 by ASME

This paper reports research in fabrication of cylindrical stents using carbon-infiltrated carbon nanotubes (CI-CNT), a material with good hemocompatibility. We demonstrate growth of CI-CNT forests in patterned lines on a 3 mm diameter stainless steel (SS) rod. Lines were patterned parallel, at 7°, at 45°, and perpendicular relative to the axis of the rod. Minimal cracking was seen in the parallel and angled lines. Significant cracking was seen in the perpendicular lines and we attempted to characterize the cracking in order to correlate it to width of the lines and height of the forest. No correlation was found but the average uncracked length was determined to be 414 μm with a standard deviation of 67 μm. We also demonstrate successful growth with minimal cracking of CI-CNT forests in a zig-zag type pattern in an effort to further the possibility of creating a coronary stent utilizing CI-CNT. Some of the patterned samples were also removed from the cylindrical substrate, resulting in free-standing, patterned, cylindrical patterns made from CI-CNT.

A new, compact 2 degree-of-freedom wrist mechanism suitable for robotically controlled surgical operations is presented. Current commercially available robotically controlled instruments achieve high dexterity defined by three degrees of freedom and relatively confined swept volume at just under 1 cm in diameter. Current smaller diameter instruments result in high part count and large swept volumes (less dexterity). A mesoscale rolling contact wrist mechanism is proposed as an alternative. The crossed cylinders wrist integrates two half-cylinders whose longitudinal axes are offset by 90°. The surfaces of the half cylinders have been populated with gearing that enables the two halves to roll in two directions while preventing slip. The manufacturing of the parts is demonstrated as feasible by a the layered assembly of Carbon Nanotube (CNT) structures, which can produce parts that are difficult to replicate with traditional manufacturing methods. The resulting wrist has only 2 parts and a small swept volume.

A new, compact 2 degree-of-freedom mechanism 4.1 mm in diameter suitable for robotically controlled surgical operations is presented. Current commercially available robotically controlled instruments achieve high dexterity defined by three degrees of freedom and relatively confined swept volume at just under 1 cm in diameter. Current smaller diameter instruments result in high part count and large swept volumes (less dexterity). A meso-scale rolling contact gripping mechanism is proposed as an alternative. The manufacturing of the parts is made feasible by Metal Laser Sintering, which can produce parts that are difficult to replicate with traditional manufacturing methods. The resulting instrument has only 6 parts and a small swept volume. Instrument actuation and control by a surgical robotic system is demonstrated.Copyright © 2015 by ASME

Being able to deliver molecular loads to the intracellular space of mammalian cells is a key initial step of genetic engineering. In the following work, experimentation with nanoinjection, a non-viral molecular load delivery technique, was examined in regards to transmembrane delivery of propidium iodide (PI), a dye that cannot penetrate the cell membrane and fluoresces when bound to genetic material. Investigation includes two environmental factors: peak pulse amplitude (1.5 to 3, 5, 7, or 9 V) and saline type (HBSS, PBS with potassium, and PBS without potassium). Results indicate that PBS with potassium has significantly higher PI uptake efficiency than the other two saline solutions for pulsed voltages of 3V, 5V, and 7V (with the peak value being 3.352 times greater than the positive control). Also, cell viability analysis indicates that there is a measureable reduction in cell viability for voltage protocol samples in comparison to non-voltage protocol samples. Cell viabilities range from 74.5% to 89.4% for voltage protocol samples. Findings suggest that a possible combination of physical/electrical variables work in concert with biological mechanisms to contribute to overall cell survival and PI uptake efficiency in nanoinjection.

This paper explores and demonstrates the potential of using pyrolitic carbon as a material for coronary stents. Stents are commonly fabricated from metal, which has worse biocompatibilty than many polymers and ceramics. Pyrolitic carbon, a ceramic, is currently used in medical implant devices due to its preferrable biocompatibility properties. It can be created by growing carbon nanotubes, and then filling the space between with amorpheous carbon via chemical vapor deposition. We prepared multiple samples of two different stent-like flexible geometry designs out of carbon infiltrated carbon nanotubes. Tension loads were applied to expand the samples and we recorded the forces at brittle failure. These data were then used in conjunction with a nonlinear FEA model of the stent geometry to determine Youngs modulus and maximum fracture strain for each sample. Additionally, images were recorded of the samples before, during, and at failure. These images were used to measure an overall percent elongation for each sample. The highest fracture strain observed was 1.4% and Youngs modulus values confirmed the the material was the similar to that used in previous carbon infiltrated carbon nanotube work. The average percent elongation was 86% and reached as high as 145%. This exceeds a typical target of 66%.Copyright © 2013 by ASME

This paper explores the effects of two parameters—operation voltage and the distance between the lance and electrode—on the repulsion process of a Stand-Alone Lance, a second-generation Nanoinjection tool used to inject DNA into egg cells for genetic purposes. Using a mathematical computer model to simulate the motion of the DNA during repulsion from the lance and into the cell, the results are quantified by the average DNA travel time and the electric field strength, which relates to the electroporation envelope. It is found that voltage has a very strong effect, while changing distance yields much less dramatic results. Specific ideal values are recommended for the magnitude and duration of the voltage pulse to successfully repel DNA into the cell.Copyright © 2012 by ASME

This paper introduces a metamorphic erectable cell restraint (MECR) to provide cell restraint in genetic research. A micro-electromechanical systems (MEMS) metamorphic mechanism with two phases of motion was designed to grasp individual embryos about their midplane. The first phase of motion lifts a compliant gripper approximately 40 μm (about half the diameter of an embryo). The gripper then closes in the second phase to grasp the embryo. The metamorphic mechanism includes compliant mechanism components which are analyzed here. A microscale prototype was fabricated from polysilicon and used to demonstrate the mechanism’s two phase motion.Copyright © 2012 by ASME

A nanoinjection lance array has been developed to inject foreign genetic material into thousands of cells at once using electrophoresis to attract and repel particles to and from the lances. A unique combination of isotropic and anisotropic etch processes are used to fabricate the four million 1 μm by 8 μm solid lances on a 2 cm by 2 cm chip. Initial studies show high cell viability when the lance array is used to pierce through a culture of HeLa cancer cells, often used for genetic research. A mathematical computer model simulating motion of attracted or repelled particles informs the design of the nanoinjection lance array system. The nanoinjection lance array provides an efficient, convenient, and quick way to simultaneously inject thousands of cells for a wide range of genetic research applications.Copyright © 2012 by ASME

Static balancing is an important contribution to compliant mechanisms enabling low operating force, thus allowing high mechanical efficiency. Preloading is generally needed in statically balanced compliant mechanisms, which at smaller scales presents a significant challenge. Physical handling of zero-force structures without causing damage also becomes difficult. This paper presents a solution to both of these issues. A novel compliant connection mechanism based on bistable beams was used to precisely preload the system in the direction of motion without backlash. Once this bistable mechanism is engaged by loading beyond its threshold, the system is in operating condition, i.e. the ON position. When the connection mechanism is disengaged (OFF position), it is much stiffer than it is in the statically balanced state and therefore more robust for handling purposes. As a demonstrator, we present the first statically balanced gripper with a fully compliant ON/OFF-connection mechanism allowing pre-loading collinear with the direction of motion. The combination of a pre-loaded bistable mechanism (i.e. negative stiffness) and a voluntary closing gripper (i.e. positive stiffness) is used for static balancing (i.e. zero stiffness and zero actuation force). The results show that the actuation force is reduced by at least 91% when the preload is engaged. The proposed ON/OFF connection shows a promising method for pre-loading compliant mechanisms or related devices.Copyright © 2012 by ASME

The comb-drive actuator is one of the main building blocks of microelectromechanical systems (MEMS). Its working principle is based on an electrostatic force that is generated between biased conductor plates as one moves relative to the other. Because of its capability of force generation, it finds wide application in micro-mechanical systems. Sample applications include polysilicon microgrippers [1], scanning probe devices [2], force-balanced accelerometers [3], actuation mechanisms for rotating devices [4], laterally oscillating gyroscopes [5], and RF filters [6]. Consequently, any improvement to this basic actuator could have far-reaching effects.

Bistable behavior is desirable for a variety of applications because power is applied only during switching, and the mechanism state remains the same regardless of any power interruptions. The low variability in the stable positions also makes accurate open-loop control of many systems possible, and the precise switching characteristics make them valuable in sensing arrays. In this paper, fully-compliant bistable micromechanisms were modeled using finite elements. This model was then coupled with an optimization program, allowing extensive exploration of the design space. Three designs within this space were generated by minimizing the layout size of the devices subject to force constraints. These designs were subsequently manufactured and tested to verify bistability, with each mechanism snapping as expected between the two stable positions. The design space was then further explored to determine the behavior of the device as the maximum force output increased. This study revealed that the minimum layout size increases with the maximum force output.

In many MEMS applications, it is desirable to amplify the force or displacement of an actuator or transducer. Devices that amplify force or mechanical advantage typically achieve this at the expense of displacement or geometric advantage. Likewise, devices that amplify geometric advantage do so at the expense of mechanical advantage. This paper proposes a device topology based on a four-link mechanism with compliant segments in place of hinges. Finite-element analysis and optimization were used to develop a Pareto set of solutions quantifying the force / displacement trade-off for a variety of loading conditions. Depending on these conditions, this device is capable of multiplying force inputs by as much as 23.7 and displacement inputs by as much as 588. Efficiency of these designs improves as the two objectives (mechanical and geometric advantage) are considered jointly in a multicriteria optimization problem rather than individually.

Bistable mechanisms, which have two stable equilibria within their range of motion, are important parts of a wide variety of systems, such as closures, valves, switches, and clasps. Compliant bistable mechanisms present design challenges because the mechanism’s energy storage and motion characteristics are strongly coupled and must be considered simultaneously. This paper studies compliant bistable mechanisms which may be modeled as four-link mechanisms with a torsional spring at one joint. Theory is developed to predict compliant and rigid-body mechanism configurations which guarantee bistable behavior. With this knowledge, designers can largely uncouple the motion and energy storage requirements of a bistable mechanism design problem. Examples demonstrate the power of the theory in bistable mechanism design.

This paper proposes a new class of bistable mechanisms: compliant bistable mechanisms. These mechanisms gain their bistable behavior from the energy stored in the flexible segments which deflect to allow mechanism motion. This approach integrates desired mechanism motion and energy storage to create bistable mechanisms with dramatically reduced part count compared to traditional mechanisms incorporating rigid links, joints, and springs. This paper briefly reviews bistable mechanism theory, introduces some additional bistable mechanism characteristics, and integrates this theory with compliant mechanism theory. The resulting theory of bistable compliant mechanisms is validated by measuring the force and motion characteristics of several test mechanisms and comparing them to predicted values.

A bistable mechanism has two stable states within its range of motion. Its advantages include the ability to stay in two positions without power input and despite small external disturbances. Therefore, bistable micro-mechanisms could allow the creation of MEMS with improved energy efficiency and positioning accuracy. This paper presents the first bistable MEMS which function within the plane of fabrication. These bistable mechanisms, known as “Young” bistable mechanisms, obtain their energy storage characteristics from the deflection of two compliant members, have two pin joints connected to the substrate, and can be constructed of two layers of polysilicon. The pseudo-rigid-body model overcomes problems with nonlinearities in the analysis and design of these mechanisms. This approach allows greater freedom and flexibility in the design process. Testing of the mechanisms demonstrated their bistable behavior and the repeatability of the stable positions.

Because of the difficulty of fabricating rigid-body joints and assembling parts in micro-electro-mechanical systems (MEMS), compliant mechanisms offer several advantages to MEMS designers. However, motion of compliant segments generally involves large, non-linear deflections which are difficult to predict using linear beam theory. This paper discusses MEMS design using the pseudo-rigid-body model. This model has been developed to permit simplified prediction of nonlinear deflections in compliant mechanisms, allowing traditional mechanism theory to be used in design. The design process is validated by testing MEMS structures designed using this model. The model successfully predicted the motion of the compliant MEMS, even for very large deflection paths. The mechanisms designed and tested achieved larger deflections and more complex motion than was previously possible.