Douglas Hurd

Revolutionizing biodegradable metals

Development of biodegradable metal implants is a complex problem because it combines engineering and medical requirements for a material. This article discusses the development of sensing and corrosion control techniques that can help in the design of biodegradable metallic implants. Biodegradable metallic implants dissolve as new tissue is formed. One of the most important factors in the design of biodegradable implants is to study the active interface, which should be monitored and controlled to address the medical concern of biocompatibility. Thus miniaturized and nanotechnology-based sensors that measure the activities of the degradation process and the formation of tissue are discussed for use with in vitro and in vivo experiments. These sensors can monitor chemical components and also cell activity and can provide new knowledge about biodegradable interfaces and how to actively control the interface to provide the best bioactivity to regenerate new tissue in a short time. Development of new alloys, nano-materials, miniature sensors, corrosion control coatings, and auxiliary applications such as biodegradable drug delivery capsules is expected to open up a new era in the engineering of materials for medicine.

Development of novel single-wall carbon nanotube?epoxy composite ply actuators

This paper describes a carbon nanotube epoxy ply material that has electrochemical actuation properties. The material was formed by dispersing single-wall carbon nanotubes in a solvent and then solution casting a thin paper using a mold and vacuum oven. In order to take advantage of the high elastic modulus of carbon nanotubes for actuation, epoxy as a chemically inert polymer is considered. An epoxy layer was cast on the surface of the nanotube paper to make a two-layer ply. A wet electrochemical actuator was formed by placing the nanotube epoxy ply in a 2 M NaCl electrolyte solution. Electrochemical impedance spectroscopy and cyclic voltammetry were carried out to characterize the electrochemical properties of the actuator. The voltage–current relationship and power to drive the actuator material were also determined. Compared to previous single-wall carbon nanotube buckypaper tape actuators, which had poor adhesion between the nanotubes and tape, and other nanotube–thermal plastic polymer actuators, which could not provide high strength, the epoxy based actuator has a higher elastic modulus and strength, which will be useful for future structural applications. This demonstrates that a polymer layer can reinforce nanotube paper, which is an important step in building a new structural material that actuates. Further work is under way to develop a solid electrolyte to allow dry actuation. Finally, these actuator plies will be laminated to build a carbon nanocomposite material. This smart structural material will have potential applications that range from use in robotic surgical tools to use as structures that change shape.

Carbon Nanofiber Hybrid Actuators: Part II - Solid Electrolyte-based:

This two-part article describes a carbon nanofiber-polymethylmethacrylate (CNF-PMMA) composite material that has electrochemical actuation properties. Part I of the study considers use of a liquid electrolyte while Part II considers a solid electrolyte. Concerning Part I, a combination of solvent casting and melt mixing were used to disperse CNF in PMMA, and thin films of the material were cast. A liquid-based electrochemical actuator was formed by placing the CNF composite film in an electrolyte solution. Electrochemical impedance spectroscopy was carried out to characterize the electrochemical properties of the PMMA-CNF actuator. The actuator was tested at voltages up to 15V and the relationship between displacement and applied voltage was determined. Compared to previous single-wall carbon nanotube buckypaper actuators, the CNF-PMMA composite actuator is stronger and is two orders of magnitude lower in cost, but needs higher voltage to actuate. Because of the low cost of the CNF hybrid material, and the possibility for using stronger host materials, new smart structural materials that enable large components and structures to actuate may become feasible.

Study on Carbon Nano-Tube Spun Thread as Piezoresistive Sensor Element

Carbon nanotube spun threads are becoming growingly important for various technological and medical applications. Threads can be spun directly from carbon nanotube arrays using age old method of spinning. The process involves two rotations about two mutually perpendicular axes viz. spinning nanotubes into thread from array and winding the spun thread on spool. It is found that an array with properties of high uniform density, low amorphous carbon content and highly aligned nano-tubes are better spinnable. Piezoresistive property of spun thread is investigated through experiments. The change in resistivity of spun carbon nanotube thread with change in load will enable its use as force sensors. In a structural neural network system a network of sensors can pinpoint the location of damage in structure. If such network can be made of very small dimension it can detect crack initiation and crack propagation. Linearity of resistivity increase with increase in strain is observed for fine spun carbon nanotube threads. Upon unloading also this linearity is preserved with same slope.

Multifunctional carbon nanofiber/nanotube smart materials

This paper discusses the development of new multifunctional smart materials based on Carbon Nanofibers (CNF) and Multi-Wall Carbon Nanotubes (MWCNT). The material properties of CNF/MWCNT are a little lower than the properties of Single Wall Carbon Nanotubes (SWCNT). However, the CNF/MWCNT have the potential for more practical applications since their cost is lower. This paper discusses the development of four CNF/MWCNT-based sensors and actuators. These are: (i) an Electrochemical Wet Actuator for use in a liquid electrolyte, (ii) an Electrochemical Dry Actuator for use in a dry environment, (iii) a Bioelectronic sensor; and (iv) a MWCNT neuron for structural health monitoring. These materials are exciting because of their unique properties and many applications.

Responsive Biosensors for Biodegradable Magnesium Implants

A biosensor is an electronic device that measures biologically important parameters. An example is a sensor that measures the chemicals and materials released during corrosion of a biodegradable magnesium implant that impact surrounding cells, tissues and organs. A responsive biosensor is a biosensor that responds to its own measurements. An example is a sensor that measures the corrosion of an implant and automatically adjusts (slows down or speeds up) the corrosion rate. The University of Cincinnati, the University of Pittsburgh, North Carolina A&T State University, and the Hannover Medical Institute are collaborators in an NSF Engineering Research Center (ERC) for Revolutionizing Metallic Biomaterials (RBM). The center will use responsive sensors in experimental test beds to develop biodegradable magnesium implants. Our goal is to develop biodegradable implants that combine novel bioengineered materials based on magnesium alloys, miniature sensor devices that monitor and control the corrosion, and coatings that slow corrosion and release biological factors and drugs that will promote healing in surrounding tissues. Responsive biosensors will monitor what is happening at the interface between the implant and tissue to ensure that the implant is effective, biosafe, and provides appropriate strength while degrading. Corrosion behavior is a critical factor in the design of the implant. The corrosion behavior of implants will be studied using biosensors and through mathematical modeling. Design guidelines will be developed to predict the degradation rate of implants, and to predict and further study toxicity arising from corrosion products (i.e., Mg ion concentrations, pH levels, and hydrogen gas evolution). Knowing the corrosion rate will allow estimations to be made of implant strength and toxicity risk throughout the degradation process.Copyright

Building smart materials based on carbon nanotubes

The paper discusses the development of polymer composite materials based on carbon nanotubes. Carbon Nanotubes can be used to form polymer hybrid materials that have good elastic properties, piezoresistive sensing, and electrochemical actuation. Of particular interest are smart nanocomposite materials that are strong and self-sensing for structural health monitoring, or self-actuating to improve the performance and efficiency of structures and devices. Since nanoscale research is broad, challenging, and interdepartmental, undergraduate through Ph.D. level students and faculty have combined efforts to attack the special problems related to building nanoscale smart materials. This paper gives an overview of the work being performed to manufacture polymer nanocomposite materials starting from nanotube synthesis through to device fabrication and testing. Synthesis is performed using an EasyTube Nanofurnace, functionalization is done using plasma coating, dispersion using rotary mixing and ultrasonication, and processing using vacuum and pressure casting. Reinforced polymers, a carbon nanotube solid polymer electrolyte actuator, and piezoresistive sensors are being developed for several potential applications. The materials produced indicate that carbon nanotube hybrid smart materials may become a new class of smart material with unique properties and applications, but much work still needs to be done to realize their full potential.