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.

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.

Illustration of the nanorobot concept

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.

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. Mangla and Dr. Shi in the MDL facility

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.

Master's student Regina Pynn

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.

Dr. Xiaojun Yu and Dr. Hongjun Wang of the Department of Chemistry, Chemical Biology and Biomedical Engineering at Stevens Institute of Technology are working with several different types of tissue engineering; including skin, bone, nerve and cardiac muscle. They utilize principles of nanotechnology and a “bottom-up” philosophy that may result in exponentially faster recovery times and improve patient integration, as well as enable the introduction of 3-dimensional multilayer tissue formation due to advanced scaffold techniques, which have been developed in their respective labs. This improved scaffold provides a better location for cells to attach and regenerate, and because it is biodegradable, only native cells remain. With the potential to help burn victims, congestive heart failure patients, peripheral nerve injuries, spinal cord injuries, broken bones and more, the medical and industrial implications of their work are tremendous.

How is Tissue Engineering research unique at Stevens?

Dr. Wang's student working in the lab

The traditional method of Tissue Engineering involves implanting a scaffold with cultured cells in a specific location. The difficulties in standard development methods result from the seeding and culture of cells in a preformatted porous scaffold, which is often inadequate in restoring the lost function of diseased tissues. This is due in part to the lack of structural integrity and non-uniformity of the porous scaffold implants. With current skin grafting techniques, the procedure can take up to three weeks. Comparatively, the research from Dr. Wang’s lab has proved so useful that the skin grafting process can be shortened from three weeks to just one day.

Professor Wang has been studying this field since 1995, and believes the main limitation of traditional techniques stems from “the inability to make a complex tissue as a result of a ‘top-down’ approach, leading to slow progress in tissue engineering.” His research has resulted in the development of a “bottom-up” methodology, using nanotechnology to enable development of scaffolds that match the biological properties of the patient. Researchers have adopted the philosophies of other engineering disciplines, and are now focusing major research efforts on these improvements. The idea is that by working on the smallest level possible and building upward, they are more likely to develop a scaffold and cell cultures that match the native extra cellular matrix (ECM), that is, the complex structural entity surrounding and supporting cells found within mammalian tissues. Professor Wang highlights his skin grafting improvement goals: