SUNFEST at Penn
Developing Communication between the Leg and the Body of EduBot
Advisors: Dr. Daniel E. Koditschek, Dr. Jonathan Clark, Kevin Galloway, Bill Mather
APPLICATIONS OF THE ORGANIC THIN FILM TRANSISTOR: BIOLOGICAL SENSING AND FRAGILE X SYNDROME
Advisor: Dr. Cherie Kagan
ABSTRACT: This project aims to evaluate the suitability of the organic film transistor as a sensor, and more specifically, to help determine if the pentacene thin-film transistor may be used as a biological sensor for future research relevant to Fragile X Syndrome, a genetic disorder associated with congenital mental retardation. In Fragile X Syndrome, individuals do not produce Fragile X Mental Retardation Protein (FMRP), and although the overall effect of this absent production is known, the exact function of the FMRP is not. The transistor was exposed to biological and control environments representative of the environments that it will be exposed to in its potential application as a biological sensor; its potential future application will involve helping determine the function of the FMRP. These environments consisted of several components: water, bovine serum albumin (BSA), transfer RNA, a salt solution known as Moine buffer, RNase inhibitor, Fragile X Mental Retardation Protein (FMRP), and FMR1 RNA. The experiments performed involved exposing the transistor to each component individually, with the exception of the RNAse inhibitor, the FMR1 RNA, and the FMRP, as well as exposing the transistor to a combined solution of all the components (an RNA binding assay) and observing the transistor’s response through its current-voltage characteristics before and after the exposure. The experiments performed helped identify changes in fabrication that could be made for more optimal sensing as well as changes that could be made in the environment to ensure the transistor’s response was not largely due to a less important component of the solution. With these changes in mind, the organic thin film transistor may be able to contribute to research on the FMRP and to help us to understand more about the mechanism important in giving rise to Fragile X Syndrome. View Paper | View Slides
Advisor: Dr. Jay Zemel
ABSTRACT: Weight-bearing activity has recently been correlated with the growth and development of children's bone density. [1 ] In order to investigate the relationship, the Children's Hospital of Philadelphia (CHOP) wishes to analyze the kinetic activity of children. Although technology currently exists to perform human kinetic analyses, devices consist of expensive and obtrusive components. An inconspicuous and inexpensive mobile device that can accurately collect and store kinetic activity measurements is needed to advance research in childhood bone development.
Dr. Babette Zemel, CHOP, and Dr. Jay Zemel, ESE, have been developing an in-shoe physical activity dynamometer (Foot-PAD) in order to measure kinetic activities. The device uses piezoelectric polyvinylidene difluoride (PVDF) films as force sensors as the basis to continuously collect information for up to two weeks. Data would be stored and partially processed on board and appropriately accessed for subsequent activity analysis.
Previous projects confirmed that PVDF are appropriate mechanical force sensors and have optimized the circuitry and programming to successfully operate inside a child's shoe. However, the Foot-PAD still needs a PDVF sensor design that provides reproducible and calibrated force information compatible with the in-shoe requirements. After this summer's work, an appropriate device design has been created that collects data with acceptable accuracy while uet meet the requirement for being inconspicuous to the patient. View Paper | View Slides
THE EFFECT OF LEG DESIGN ON ROBOTIC RUNNING GAITS
Advisors: Dr. Clark and Kevin Galloway
ABSTRACT: Advances in legged robotics have led to the development of robots capable of running over rough terrain. Edubot, one such hexapedal robot, is a biologically inspired runner that mimics the cockroach in its alternating tripod gait and compliant legs. Most animals’ running gaits can be approximated by the Spring-Loaded Inverted Pendulum (SLIP) model, which treats an animal as a point mass on a linear spring. The SLIP model has been demonstrated to accurately model the center of mass motion of running animals, as well as the ground reaction forces associated with their gaits. While Edubot’s running behavior can also be viewed in terms of the SLIP model, the linear spring in the model fails to capture the complexity of the compliant C-shaped legs of the robot. These legs have shown superior performance over all previous designs. In this paper we attempt to isolate the characteristics of the C-legs and study their individual and combined effect on performance in hopes of understanding how to design better legs. We do this by decoupling and mathematically modeling the spring rest length and the effective stiffness of the leg as it rolls through stance. Using a SLIP model modified with our equations, we show evidence that both a decreasing stiffness and an increasing spring rest length during stance are important contributors to performance. We then describe legs designed to test our model’s predictions. View Paper | View Slides
MECHANOTRANSDUCTION IN MESENCHYMAL STEM CELLS FOR CARTILAGE TISSUE ENGINEERING
Advisor: Dr. Robert Mauck
ABSTRACT: Cartilage is a viscoelastic tissue that serves to withstand physiologic loads in the body. The prevalence of cartilage degeneration pathologies such as osteoarthritis in the United States coupled with the tissue’s poor native healing capacity call for a cell-based regenerative solution. Current attempts at using multipotent mesenchymal stem cells (MSCs) in a tissue-engineered approach have seen limited success, as MSCs have been shown to deposit extracellular matrix inferior to that produced by adult chondrocytes. In this study, we examine the effects of both short and long-term dynamic deformational loading on MSC extracellular matrix (ECM) production. We also use a novel photocrosslinkable hyaluronic acid (HA) scaffold for MSC seeding. Here, we report that the HA scaffold is capable of supporting MSC growth and chondrogenesis. Moreover, both short and long term dynamic deformational loading applied in conjunction with presence of the chemical morphogen TGF- β 3 increase the expression levels of four genes (GalNAc, C4st-1, C4st-2, XT-1) responsible for ECM biosynthesis. Interestingly, prolonged upregulation of the aforementioned genes does not translate to improved mechanical properties or increased proteoglycan content in the ECM. Further studies must therefore be made in order to elucidate the factors responsible for the observed discrepancy and to adjust the current loading regime for optimal ECM biosynthesis. View Paper | View Slides
DESIGN OF A VARIABLE COMPLIANCE LEG USING SHAPE DEPOSITION MANUFACTURING
Advisors: Dr. Daniel E. Koditschek, Dr. Jonathan Clark, Kevin Galloway
ABSTRACT: Biological studies have demonstrated that variable compliance legs in running animals respond to changes in terrain, running speed, and weight. Due to complexity and size limitations, no robot platform to date has been able to successfully integrate this capability. This paper describes the design and fabrication of variable compliance legs for the Edubot platform. The key design features of the major components are presented, followed by a discussion of the layered prototyping technique employed to fabricate the legs. Finally, some observations from initial leg prototypes are presented which demonstrate the design’s advantages and limitations. View Paper | View Slides
FABRICATION AND MODELING OF PIEZOELECTRIC RF MEMS RESONATORS
Advisor: Gianluca Piazza, PhD
Abstract: Resonators serve as essential components in radio-frequency (RF) electronics, forming the backbone of filters and tuned amplifiers. However, traditional solid state or mechanic implementations of resonators and filters tend to be bulky and power hungry, limiting the versatility of communications, guidance, and avionics systems. Micro-electro-mechanical systems (MEMS) are promising replacements for traditional RF circuit components. In particular Piazza, et al. has demonstrated high performance RF MEMS resonators utilizing thin film structures of piezoelectric aluminum-nitride (AlN) . These AlN films have been previously patterned using chemical wet-etching techniques, whose isotropic nature results in mask undercutting and sidewall sloping. This paper demonstrates that inductively coupled plasma (ICP) etching results in a cleaner, straighter etch profile. Furthermore, the effects of sloped sidewalls are investigated through finite element simulations for ordinary and high-mode resonator structures. It is shown that sidewall sloping degrades resonator efficiency and performance. View Paper | View Slides
ELECTROSPINNING NATURAL POLYMERS FOR TISSUE ENGINEERING APPLICATIONS
Advisor: Dawn M. Elliott, Ph.D.
ABSTRACT: Electrospinning is an efficient method by which to produce scaffolds composed of nanoscale to microscale fibers, which are comparable to the fiber diameters of native components of the extracellular matrix. In electrospinning, a polymer solution is pumped through a syringe that is connected to a high voltage source. As a droplet forms at the tip of the needle, electrostatic repulsions form long fibers that are collected onto a grounded metal plate in the form of a nanofibrous mat. These structures can be used in tissue engineering and drug delivery applications. Natural polymers are candidate materials to develop as electrospun scaffolds. Fibrinogen is one such protein that is present in blood plasma. Physiologically, the reaction between fibrinogen and thrombin leads to the assembly of fibrous structures that play a key role in wound healing. Collagen is another natural polymer that is an essential component of the extracellular matrix. It is largely responsible for the mechanical integrity of the extracellular matrix, making it ideal to be electrospun as a scaffold. The feasibility of electrospinning fibrinogen and collagen into viable nanofibrous scaffolds was explored in this study. Both proteins were produced as nanofibrous mats when certain electrospinning parameters were applied. While non-uniformities were observed in these structures, the presence of nanofibers throughout the mats and the versatility of the electrospinning process suggest that uniform nanofibrous scaffolds can be formed from these proteins. Finally, because fibrinogen and collagen are naturally occurring, these scaffolds have much potential to support cell adhesion and growth for use in tissue engineering applications. View Paper | View Slides
ASSEMBLY AND TESTING OF POLY(3,4-PROPYLENEDIOXYTHIOPHENE) BASED ELECTROCHEMICAL SUPERCAPACITORS
Advisors: Dr. Jorge Santiago-Avilés, Dr. Mariem Rosario-Canales
Abstract: Neither traditional capacitors nor batteries are capable of releasing high amounts of energy at high power. Supercapacitors represent a middle ground because they can hold and release considerable amounts of energy while doing so at a medium power. Continuous research in the supercapacitor area has been geared towards the testing of various active materials like metal oxides and electroactive polymers to probe their properties in this field. This paper presents the initial results for tests done with the electroactive polymer poly(3,4-propylenedioxythiophene) in an electrolyte system composed of the salt tetraethylammonium bis(trifluoromethylsulfonyl)imide, the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and propylene carbonate as solvent. View Paper | View Slides
RF-MEMS SWITCH ACTUATION AND TESTING
Advisor: Dr. Piazza
ABSTRACT: The first aluminum nitride based piezoelectric RF-MEMS switch is being developed at the Penn Nano and Micro Systems (PNaMS) Lab at the University of Pennsylvania. The RF-MEMS switch is one of the last RF-MEMS components to be successfully designed and fabricated utilizing piezoelectric aluminum nitride. The switch will eventually be integrated with other components to provide a single chip solution for communications.
The switch is expected to have high isolation, and low insertion losses, for frequencies up to 10 G Hz. AlN has strong piezoelectric forces, requiring lower actuation voltages than other piezoelectric materials. This paper focuses on the design and implementation of actuation and testing of the PNaMS switch, which a fixed-end, piezoelectric, ohmic, series switch. The piezoelectric actuation requires a high voltages low frequency square wave. A function generator creates the low frequency square wave, which is then amplified. An oscilloscope measures the dynamic response, while a network analyzer measures the static response of the switch. These instruments are controlled through the computer program LabVIEW. Initial testing has begun, although so far no successful actuation of the switch has occurred.