Active Nanofiber Control - The Key to Next Generation Technology
November 17, 2009
Advances in nanotechnology are leading to dramatic new devices that can fundamentally improve our quality of life in fields ranging from healthcare to energy harvesting. While the potential applications are easily understood, the truly unique aspect about Dr. Yong Shi's research is his unparalleled ability to develop and control these materials.
Dr. Shi at the Active Nanomaterials and Devices Lab is a nanotechnology expert who works towards introducing new materials that have unparalleled precision and efficiency. He has introduced patented piezoelectric (PZT) nanofibers consisting of lead zirconate titanate and is also advancing the study of piezoresistive or conductive (indium tin oxide or ITO), thermal electric (both bismuth telluride and complex oxides) and photovoltaic materials (titanium oxide or TiO2).
The applications of these nanofibers are tremendous, and can potentially lead to improvements in health care, renewable energy sources, portable devices, diagnostics and sensing techniques. What is truly special about these piezoelectric nanofibers is their ability to efficiently convert vibration or acoustic energy into electricity (sensors), or to do the exact opposite – convert electricity into movement (actuators).
PZT nanofibers: a) randomly distributed b) partially aligned c) TEM image of a single fiber
Working in the Micro Devices Lab, a shared facility at Stevens, Dr. Shi was the first to fabricate and control PZT fibers on the nanoscale – a process that results in unique mechanical and electrical properties.
By manipulating these principles, he creates devices that are both tiny (Nanotechnology refers to development on the atomic level – a sheet of paper is about 100,000 nanometers thick) and can be maneuvered with precision, thus enabling amazing new technologies such as: tiny robots that navigate to the site of a blood clot in stroke therapy procedures, or harness the power of vibration and solar energy to produce electricity, and even monitor the vibrations involved in chemical bonding to detect cancer cells – all made possible through the application of Dr. Shi's nanofibers and their specification as a sensor or actuator to determine functionality.
Active Nanofibers as Actuators
Propulsion and Power Subsystem for the Micro Biosystem
In this process, Dr. Shi and his team are exploring the use of piezo nanomaterials for the development of biomimetic (the use of biological methods and systems found in nature to the study and design of engineering systems and modern technology) nanoscale robots. Science has long speculated a nanoscale biomimetic robot could usher in an entirely new era of medical care and the challenge has been development of an efficient and effective propulsion system.
Dr. Shi's proposed device consists of a nanorobot that utilizes the undulatory propulsion mechanism enabled by PTZ composite actuators and known as Planar Wave Propulsion.Changes in the electrical charge can create vibration energy (actuations) within the PZT device, a unique property which enables controlled movement through electrical input. This nanorobot consists of a control system placed inside the head and a tail made of PZT nanofiber actuators embedded in silicone rubber and driven by sinusoid signals.
The successful fabrication and controllability of these devices can usher in a new era of medical technology. Nanorobots can be used for accessing currently unreachable areas inside the human body, resulting in minimally invasive surgery, highly localized drug delivery, screening for diseases at very early stages and fighting implant related infections.
Stroke Therapy and the MEMS Umbrella-Shaped Actuator
Strokes are the third leading cause of death in the United States, claiming over 143,000 lives per year. Caused by a blood clot which blocks an artery, or by the breakage of a blood vessel, strokes result in a lack of oxygen, blood, and nutrients to the brain, and can invoke brain damage and even death.
Dr. Shi is particularly interested in assisting stroke victims and has worked collaboratively with Dr. Sundeep Mangla and Dr. Ming Zhang of SUNY Downstate Medical Center in the development of a blood clot retriever using his patented PZT fibers that have unique piezoelectric properties resulting in movement (actuation) as a response to electrical stimuli.
This principle allows for creation of a "MEMS Umbrella-shaped Actuator" that is inserted via catheter into the lower body of a stroke patient. The operator (in most cases a medical doctor) can control the device through the application of varying electrical signals and the location can be monitored with MRI and CAT SCAN technology.
Navigating up and through the arteries, the device will ultimately reach the location of the blood clot and proceed by "applying a fine-tuned shear force to facilitate the separation of the blood clot from the wall of the vascular artery due to the shearing-thinning phenomenon, thus enabling complete retrieval while minimizing the risk of damage to the arteries." Dr. Shi and his group which includes Master's students Regina Pynn and Swathi Vallala also study the effects of cooling the brain. Regina further explains that cooling "can prevent much of the serious brain damage that may occur during the onset of strokes and give the doctors a longer window for treatment." They are also working with other groups to develop bio-nanosensors for the prognostics of strokes. Their goal is to provide an all encompassing procedure which not only removes the clot from a patient's body, but most importantly predicts, prevents and reduces the potential for any damage.
Active Nanofibers as Sensors
Acoustic Emission Sensors for Structural Monitoring
Acoustic emission (AE) sensors rely on the unique properties of PZT nanofibers. Dr. Shi is applying these fibers in the creation of AE sensors composed of Nanoscale Active Fiber Composites which enable advanced self-powered sensing devices for the monitoring of structures such as aircrafts, buildings and bridges.
Upon fabrication, the PZT nanofibers become the building blocks of advanced AE sensors with high sensitivity and excellent conformability. These AE sensors can be embedded into or attached to the surface of structures such as aircrafts, bridges, dams, towers and roads. Due to their cost-effectiveness and convenience they will be conjoined into advanced networks which can monitor structural degradation, detect cracks, as well as delamination and debonding of various composite components.
This work has been the subject of significant interest and provides structural integrity and monitoring solutions for many of our most critical civil and military systems.
Energy Harvesting for Wireless Devices and Networks
As technology continues to be miniaturized, there is an increased need for more efficient power generation. In many cases, the advancements of battery power sources have not progressed as quickly as new devices thereby creating a need for alternate energy solutions.
In response, Dr. Shi and his lab are once again exploring the properties of micro scale PZT materials in the creation of vibration, thermal and radiation energy scavenging opportunities. The application of PZT nanofibers creates ways to capture energy that ultimately can be converted into electrical power, resulting in an on-chip power source for various MEMS scale devices.
This research is particularly important when dealing with scenarios that require enhanced mobility and as undergraduate student Natalie Schloeder explains, "this project hopes to harness mechanical energy which can then be converted into electrical energy." Natalie's work with Dr. Shi involves the optimization and micro-fabrication of such devices. They hope to exploit the unique characteristics enabled by micro/nano-fabrication in creating safe, efficient and portable power sources that will be used in portable systems such as cell phones and radio equipment.
As the second leading cause of death in the United States, early detection of cancer is a critical step in recovery. The Active Nanomaterials and Devices Lab aims to distinguish between a cancer cell and a normal cell through the use of high frequency ultrasound. The PZT materials once again play a critical role in their ability to detect vibration patterns and disseminate critical knowledge. By monitoring the absorption and attenuation of the cells using a specific frequency ultrasound, Dr. Shi will be able to distinguish cancer cells from normal cells.
Yong Shi is involved in vital research with Dr. Jian Cao of Stony Brook University which will introduce novel diagnostics that improve existing diagnostic methods resulting in early detection and the ability to save lives. Dr. Shi brings an expert understanding of Nanotechnology device engineering, while Dr. Cao is a leader in molecular and cellular biology of cancer. According to Dr. Cao, "this synergistic collaboration will bridge the gap between basic science and translational research."
Their collaboration has led to recent government funding for the development of a device that will be used to detect the spread of breast cancer cells in circulation. This device will eventually be used for clinical diagnostics to determine the possible spread of breast cancer.
In addition to improving the medical care for cancer diagnostics, technology innovations led by Dr. Shi and Dr. Cao will drastically reduce medical costs and enable greater care for a larger majority of patients.
Ultra Sensitive Nano Gas and Bio Sensors
While PZT nanofibers are a core technology of some applications, Dr. Shi also makes use of Indium Tin Oxide (ITO) nanofibers for the advancement of Nano Gas and Bio Sensors. This field is known as Chemical Sensing and has attracted enormous attention and is widely perceived as one of the most promising areas of nanotechnology.
This process begins with the creation of ITO nanofibers which are developed using a method known as electrospinning. Once fabricated, he applies a conductive silver paste which acts as a contact location for wiring and measurements. The device then runs through a testing chamber, which was designed and built for the characterization and optimization of the gas sensor. By recording changes in resistance, Dr. Shi is able to extract information based upon the presence of gases such as NO2.
This work has incredible potential and creates exciting applications in the firefighting, biomedical, and chemical industries.
Thermal Energy Scavenging
The development of cobalt-based nanostructures enables the conversion of thermal energy to electricity using integrated micro and nano fabrication methods. Thermal Energy Scavenging research studies a complex oxide thermoelectrical material known as Perovskite La1–xSrxCo03.
Dr. Shi suspects that the fabrication of Perovskite La1–xSrxCo03 at the nano-level will result in dramatically enhanced ZT — figure of merit of thermoelectrical conversion and high conversion efficiency. The enhanced functionality of thermoelectrical properties is a fundamental benefit of development at the nano level and the primary reason advancements in this field can lead to such dramatic technology improvements.
Dante Smiriglio is an undergraduate student of Dr. Shi's who works with graduate student Weihe Xu in the development of thermoelectric nano fibers. He states, "nanomaterial applications in power generation will play a large part in improving efficiencies and reducing the size of power generation systems."
Successful fabrication of this material at the nano level will lead to thermal/electric properties that enable Dr. Shi's research to be used as an energy harvesting device – working as a wireless energy source and a large scale energy converter.
Dye Sensitized Solar cells
Dr. Shi investigates Dye sensitized solar cells (DSSCs) which improve upon silicon based Photovoltaic (PV) cells by offering a lower cost, more simple fabrication process, and the potential for higher energy conversion efficiency.
Traditional solar energy conversion involves a process using silicon based cells which are usually very expensive.
Typical DSSCs have a sintered film of TiO2 nanoparticles which have a large surface area for the absorption of dyes. The electron transport in TiO2 nanoparticles in a DSSC rely on trap-limited diffusion process in which photo-generated electrons repeatedly interact with a distribution of traps before they can reach the collecting electrode, resulting in a very low energy conversion efficiency. Dr. Shi is exploring ways to enhance this electron transport and improve efficiency through the use of a one-dimensional nanostructure such as TIO2 nanofiber.
As the first to fabricate and control PZT nanofibers as well as introduce further advancements in ITO nanofibers, Dr. Shi has uncovered an incredibly effective method of operating and powering mechanical devices. He does this through the application of an electrical potential, which creates movement (actuators) or receives information based on vibration, thermal or acoustic energy (sensors). This technology is dramatically increasing the efficiency of many groundbreaking disciplines including:
- The development of a device that can actually remove a blood clot in the case of a stroke;
- Acoustic emission sensors for monitoring building integrity;
- Using the unique properties of PZT fibers to extract energy from sources such as vibration, thermal and radiation;
- The use of PZT technology to monitor and diagnose cancer like never before, and with dramatically reduced costs to the patient;
- Enlistment of ITO nanofibers to act as Nano Gas and Bio Sensors;
- Thermoelectric nanostructures which enable improvements in power generation systems;
- Revolutionary advancements in the solar energy field;
- Using PZT nanofibers to propel systems for use in drug delivery.
Dr. Shi is also an innovator at bringing technology to the marketplace. He has instilled an environment consistent with the Technogenesis™ mission and encourages the application of research ideas to commercial solutions.
One of Dr. Shi's graduate students, Shiyou Xu, explains further, "Nanotechnology is currently a 'hot' research area, and most of it is on the scientific level. The unique aspect of our lab is Dr. Shi's willingness to develop working devices that have the potential to be commercialized. We have seen this with nano piezoelectric generators and sensing devices, and are excited about future prototype developments."
It is amazing to consider how something developed on the atomic level can have a global impact and advance so many of the technologies integral in human health, communications, and the preservation of our environment.