The Role of Leg Differentiation in Hexapedal Running

Advisors: Dr. Jonathan Clark and Joel Weingarten

ABSTRACT: Designing a robot that can autonomously traverse a variety of terrain types is difficult. For this reason, one may refer to nature for inspiration and produce robots that mimic biological organisms. RHex is one such device, a six-legged breadbox-sized robot whose design resembles that of a cockroach. Building a robot that mimics a living creature carries additional advantages beyond locomotive stability. For instance, mathematical models that describe animal walking and running can be applied to the device, so an entire existing body of analysis can be used to characterize the robot’s movement, saving time and increasing intuitive understanding. One such model, the spring-loaded inverted pendulum (or SLIP) model for animal running and hopping, has been successfully applied to RHex’s forward motion. However, like many animals, RHex deviates from this model in that it exhibits an oscillatory side-to-side motion. The goal of the current research is to characterize this swaying motion, describe it with a simple model, and use the model to explain how to compensate for the transverse motion. To characterize the swaying motion, a force plate sensor will be used to measure the ground reaction forces from each of the robot’s legs and high-speed video of the robot’s gait will be recorded. Following this, a simple mathematical model of the motion will be created. Then, using information from the model, aspects of the robot’s gait and leg composition will be altered to compensate for the swaying motion, ideally eliminating it entirely. Finally, observations will record the effect that this modification has had on the efficiency and stability of the robot’s motion. View Paper | View Slides

Micro-combustor

Advisor: Jorge Santiago

ABSTRACT: The micro-combustor is a compact, sub-millimeter device that burns hydrocarbon fuels homogeneously as a source of power. It efficiently converts heat generated by combustion into electric power. We want to design a cylindrical structure, using the FemLab simulation program it demonstrates that doing this geometry can reduce impedance fluid, and several gas inputs can be placed under and several outputs can be placed around the mixing chamber so it can be more efficient. The materials to be used for the construction of this device are fundamentally Low Temperature Co-Fired Ceramic (LTCC) and Graphite. The fabrication of this device will rely essentially on a thermal process (sintering of the LTCC tapes). The instruments that will be used for the fabrication include: a furnace for sintering the ceramics, a heated press for the ceramics lamination, a thermal laser and a numerically controlled milling machine for the patterning and machining of the tape. It is hoped that the combustor fabrication will be completed as designed. The parameters that characterize its combustion and power are expected to be consistent with its application as an electrical generator by means of the thermoelectric effect. View Paper | View Slides

Forming Vesicles from Carbon Nanotubes

ABSTRACT: Carbon nanotubes (CNTs), essentially layers of graphite seamlessly wrapped into cylinders, have shown great potential in a wide variety of applications. One prospect in bioengineering is to utilize CNTs for drug delivery by forming micelles or vesicles from aligned tubes. These structures would essentially be spherical nanocontainers with short carbon nanotube arrays forming the wall of the chamber. The nanotubes can be made amphiphilic by functionalizing only one end of the tube with a hydrophilic molecule, since CNTs are naturally hydrophobic. Amphiphilic molecules naturally configure so that their nonpolar ends are away from aqueous solution (in the core of the structure) while the polar ends are next to the aqueous solution (on the outside surface). Nanotubes that have been functionalized with a polar molecule on one end could be influenced to aggregate into such arrangements by altering the dimensions of the tubes themselves, since short and straight amphiphilic nanotubes would have a good chance of forming micelles spontaneously. The nanotubes would essentially mimic the behavior of phospholipids in water, self-assembling into micelles under the right conditions. If successfully developed, these micelles could be used for transport of poorly soluble drugs, such as many anticancer agents. Vesicles, with a bilayer membrane of nanotubes, could also be formulated, which would allow the transport of water-soluble drugs since both the inner and outer walls will be hydrophilic.

The first goal of the project is to obtain nanotubes that have been functionalized on just one end with a hydrophilic molecule, such as carboxylic acid (COOH). Ideally, this can be accomplished by simply finding a vendor from whom the CNTs can be purchased with the molecules already attached to one extremity. If such a vendor is not found, ordinary CNTs will need to be acquired, and the functionalization procedure will then be incorporated into the research project. Once the appropriate CNTs are available, they will be observed using an optical microscope and most likely also electron microscopy since the scales are very minute. The functionalized carbon nanotubes will be analyzed under diverse conditions, for instance, with different amounts of surfactant present in the water and with nanotubes of different dimensions. This type of assay will illustrate which, if any, circumstances allow the nanotubes to form micelles, vesicles, bilayers, or other such aggregates most readily. View Paper | View Slides

Quantitation of Oxygen Concentration

Advisor: Dr. Britton Chance, Ph. D, Sc. D, M.D

ABSTRACT: Many studies today are executed with the goal of inventing a non-invasive method to measure blood oxygen levels in the brain. The current methods include taking blood samples during surgery or using a pulse oximeter. Yet, neither of these methods yields direct or immediate data about brain oxygen levels. The goal of this project was to measure the concentration and saturation of hemoglobin with oxygen and associate this with how Near Infrared Light Spectroscopy (NIRS) can be used in a non-invasive way to measure brain activity. The protocol of this experiment was transfer methods of measuring oxygen concentration levels in yeast to using the same methods for hemoglobin, an animal’s brain, and finally the human brain. The brain probe invented by Dr. Britton Chance, which uses NIRS to correlate changes in oxygen levels to measure brain activity, was used during the hemoglobin experiment. During all of these experiments, levels of oxygen concentration were measured and plotted respectively. The results of these experiments were used to correlate the methods used on the aforementioned brain probe. This information could yield to developing a low-cost, non-invasive method to measuring oxygen concentration and saturation of hemoglobin in the brain. View Paper | View Slides

Electrochemical Methods for the Measurement of Electrical Properties in Thiol-Terminated Single Molecules

Advisor: Alan T. Johnson

ABSTRACT:Molecular electronics, or the use of single molecules in electrical components, is an exciting field due to its small size scale and promise for high speed. Although no one has created a single molecular electronic device, many advances have been made. Because of the length scale of these devices, however, both experimentation and implementation of single molecular electronic devices are very difficult.

Here we investigate the electrical properties of molecules which will be used in single molecular circuits. An electrochemical setup for measuring molecule conductance has already been developed; it has been used for measuring the conductance of DNA as well as thiol- and amine-terminated molecules. Adapting this method to create a steady current flow through a single molecule with a gold working electrode, we hope to obtain the IV characteristic of organic molecules with thiolated ends. Additionally, we hope to determine the most effective electrochemical setup for these measurements. Future work will refine and integrate this setup with other studies. View Slides

Fabrication of PVA Micropolarizer Arrays for CMOS Image Sensor

Advisors: Jan Van der Spiegel, Viktor Gruev

ABSTRACT: Most image sensors ignore the polarity of light signals, primarily because the human eye is not sensitive to polarization. However, it is possible to gather valuable information about geometry and composition based on the polarity of light reflecting off of an object. A polarization sensor has been designed combining a CMOS image sensor with micropolarizers fabricated out of polarizing polyvinyl alcohol (PVA) sheets. This project is focused on fabricating these micropolarizers using photolithography and etching. In order to obtain complete characterization for each pixel, it is necessary to obtain the intensity of light polarized at 0 degrees, 45 degrees, and in total. As a result, the micropolarizer array must contain two layers of 10-micron PVA structures oriented 45 degrees to each other. A single layer of micropolarizers has been created, but exhibits significant etching underneath the structures created in the photoresist by lithography. The future goals of the project are to refine the process for creating a single layer and to develop a technique to create a multi-layer array of micropolarizers. Two etching methods, plasma etching and reactive ion etching, will be evaluated based on the amount of underetching in each method. A mask will be designed with the proper alignment marks to allow layers of micropolarizers to be aligned relative to each other and to the CMOS chip. Procedures for gluing layers of micropolarizers together and for removing the remaining photoresist will be developed. Finally, a complete polarization image sensor will be assembled using these techniques and a previously developed CMOS image sensor. View Paper | View Slides

Pediatric Dynamometer

Advisor: Dr. Jay Zemel

ABSTRACT: The medical field has recently expressed interest in the possible correlation between weight-bearing activities during childhood and the bone density of children. Acquiring quantitative information about the magnitude and duration of force on children’s feet has posed a challenge, as surveys serve only to collect qualitative information about exercise. While the equipment necessary to perform human kinetic analyses exists, devices used for directly monitoring the activities of a child can be large, awkward, and obtrusive. A small, inconspicuous, self-contained mobile device that could collect and store data about the physical activity of the individual wearing it would facilitate the collection of data used for medical research in the field of pediatric bone health studies.

The pediatric dynamometer proposed by Dr. Zemel of the Moore School of Electrical engineering conforms to both the space and power consumption constraints characteristic of a portable data acquisition device. It uses a strip of piezoelectric plastic to generate a voltage proportional to the change in force applied to it. This piezoelectric strip is cut to fit conveniently inside of a shoe along with circuitry capable of taking measurements and storing data that may be useful for medical research. A small button-cell battery supplies power to the pediatric dynamometer over the course of its use. Upon completion, information can easily be uploaded to a computer for archival purposes.

While much of the groundwork has been laid for a working prototype, there is still plenty of research and design to be done before the device can be used by children participating in the study. The final stages of development for the pediatric dynamometer involve programming a microcontroller to sample the piezoelectric sensor, make calculations based on these readings, storing relevant data in a small memory bank, and extracting this information, uploading it to a personal computer after the acquisition has finished. View Paper | View Slides

Testing of a Novel Custom Made CMOS Imaging Sensor

Advisors: Jan Van Der Spiegel and Viktor Gruev

In the world today CMOS image sensors are used everywhere. These imagers are so commonly used because they have low power consumption, have a 2 mega-pixel capability, and can be put in very small devices. It is projected that about 700 million cell phones with these devices will be sold by 2008. In this project our objective is to test a custom made CMOS image sensor. Our image sensor, unlike the conventional image sensors, consists of only two transistors. This enables our image sensor to have a greater pixel capacity, fit in smaller places, and have less power consumption. In such a growing field of technology as imaging systems, the possibilities for new innovations could prove to be a very lucrative business. My goals for the rest of the summer are to complete a modular program for the CMOS imager and begin more intensive testing of our image sensor. View Slides

Electromechanical Modeling of a New Class of Contour-mode AlN MEMS RF Resonators

Advisor: Prof. Gianluca Piazza

ABSTRACT: This work deals with the electromechanical modeling of a new class of contour-mode AlN MEMS RF resonators. In the attempt to provide design guidelines for the resonator layout, fully understand the resonator electrical response and improve its performances, a thorough electrical characterization of the contour-mode RF resonators is performed using a Desert Cryogenics high frequency probe station. The equivalent electrical parameters of the resonator are extracted from the obtained plots of admittance versus frequency. Specific attention is placed in modeling any external parasitic capacitances and resistive losses due to the layout configuration, the silicon substrate or the resonator design itself. The cryogenic probe station also permits the characterization of these devices versus temperature (4.5 K to 400 K) and pressure (1e-6 Torr to ambient) and provides further insight in the resonator behavior. An extended Butterworth Van Dyke (BVD) model that thoroughly models the electromechanical response of the resonator in the frequency range of interest is proposed. View Slides

Design ofa “Ferro-Wax” Valve/Pump for Microfluidic Devices

Advisor: Dr. Haim Bau

ABSTRACT: Integrated pumps and valves make up an essential part of most microfluidic devices and produce increased control of the device. Some existing micro-pumps and valves utilized in microfluidics involve electrical, pneumatic, and thermal actuation. However, electrical micro pumps and valves generally entail a complicated and expensive fabrication process, and are limited to samples free of any ions or charges. We attempt to create a phase-changing pump/valve out of a mixture of ferrofluid and paraffin wax that is operated by magnetic force. We utilize oil based ferrofluid solution, which is made up of magnetic iron nanoparticles and surfactant. These immiscible ferrofluid slugs are able to separate water based samples in a hydrophilic modified polycarbonate channel without leaving noticeable film. We treat different polycarbonate samples using oxygen plasma, spin on glass, and polyvinylpyrrolidone (PVP) to find the optimal procedure on conditions of producing low contact angles with water, duration of maintaining high surface energy, and resistance with heat. Melting the “ferro-wax” allows simple manipulation of the pump by shifting the liquid form by application of a moving magnet. This same procedure allows the “ferro-wax” to operate as a valve, by directing the fluid across a branching side channel. We work on finding the most effective ratio of ferrofluid to wax, what properties the substrate require for this pump/valve to function appropriately, and how to create such a microfluidic device that integrates these “ferro-wax” pumps/valves. View Paper | View Slides

Spatial Resolutionof Chondrocyte Response to Mechanical Signals for Cartilage Tissue Engineering

Advisors: Dr. Robert L. Mauck, Alice H. Huang

ABSTRACT: Cartilage is a supportive structure able to transmit and distribute loads within the body, as a result of its composition of chondrocytes and extracellular matrix (ECM). Damage to cartilage associated with osteoarthritis and injury is difficult to repair because of the tissue’s avascular nature. Growth and maintenance of cartilage tissue in vivo result from the synergistic effects of biochemical molecules and mechanical stimulation. Specifically, the chondrocyte functions as a biological sensor that detects and transduces extracellular mechanical signals (mechanotransduction). However, many of the fundamental mechanisms of chondrocyte mechanotransduction remain unclear. The mitogen-activated protein kinases (MAPKs) are a family of molecules involved in responding to extracellular stimuli and regulating subsequent intracellular activities, a series of events known as the MAPK signaling cascade. In this study, a bioreactor capable of dynamic compression was used to stimulate ECM gene transcription in chondrocyte-laden agarose disks (2.25 mm × 5 mm Ø, 30×106 cells/mL) cultured in chondrogenic medium with or without TGFb-3 for one- and four-hour loading periods. After loading, disks were divided into inner core (2 mm Ø) and outer annulus regions and analyzed for ECM gene expression (aggrecan, type II collagen) by real-time PCR, and for active MAPK signaling molecules (ERK 1/2, SAPK/JNK, p38 MAPK) by Western blotting. In the future, this characterization of specific MAPK signaling cascades involved in chondrocyte mechanotransduction will be valuable in efforts to repair damaged cartilage tissue through functional tissue engineering solutions and in further understanding the role of the chondrocyte as a sensor. View Paper | View Slides