Note: This is the third article of a three-part series covering smart polymer (1) trends, (2) material/process advances and (3) applications.
Properties inherent in shape memory polymers (SMP) and other smart polymers have the potential to be game-changers across many industries. In the automotive field, these advanced materials may eventually lead to vehicle subsystems that can self-heal in the event of damage, or that can be designed to change color or appearance.
In the medical field, smart polymers are being chemically formulated that electroactively sense specific environmental changes in biological systems and adjust in a predictable manner, making them useful tools for drug delivery or other metabolic control mechanisms. Smart fabrics and intelligent textiles that make use of smart polymers and clever electronics currently in embryonic stages are poised for tremendous growth.
Let's start by taking a look at SMPs in automotive applications. SMPs open new opportunities for variable features in vehicles. The novel materials add new high-tech features while improving vehicle performance at lower cost.
SMP actuators and sensors can replace small electric motors or hydraulics. Though the mechanical behavior of such actuators is often unimpressive in isolation, the ability to use a simple device to produce specific mechanical action in response to specific conditions or signals can dramatically improve the overall performance of a device.
Shape-changing materials in place of motors can:
- Reduce vehicle mass and component size/complexity
- Increase reliability/improve vehicle performance
- Improve fuel economy
SMPs also improve design flexibility. Designers can use these materials to simplify products, add features, improve performance or increase reliability with relatively little mechanical complexity. The new materials permit functionality to be "programmed in" to facilitate inventive designs, enhance efficiency, and provide new and advanced features.
They allow the addition of movable elements in applications impractical for motors. They also enable new functionality and convenience/comfort features. SMPs/alloys are among smart materials in development by the General Motors Corporation (GMC).
Looking to revolutionize their car design, GMC refers to the new shape memory polymers and alloys as promising "game-changers" in automotive advanced materials. These new materials have the potential to change the look and feel of GMC cars and trucks and even eventually lead to automotive subsystems that can self-heal when damaged, or can be designed to change color.
GMC's use of smart materials builds upon their previous material advances including polymer nanocomposites that provide superior mechanical properties at lower cost. The company is currently testing and validating smart materials on prototype vehicles. GMC holds approximately 250 U.S. patents and patents pending for "smart" materials for its automobiles.
GMC is targeting the 2017 model year to introduce smart materials applications in its vehicles. The company is collaborating with HRL Laboratories LLC, a corporate R&D lab owned by GMC/Boeing; the University of Michigan; and the Smart Vehicle Concepts Center at Ohio State University to develop potential vehicle applications for new smart materials.
Smart Vehicle Concept Center — Ohio State University Chevy Volt SMP air louver concept part.
One possible application is in air dams and louvers that adjust to govern airflow, improving aerodynamics and performance. The air louver concept on the Chevy Volt that controls airflow into the engine compartment is a good example. Using shape memory material, the air louvers adjust to govern airflow, remaining closed to speed warmup during cold starts and opening wider to let in more air as the engine heats up.
The heat-activated smart material operating the louver uses the under-the-hood temperature as the basis for the vents opening. Heat contracts the shape memory material causing the louver blades to rotate to an open position when the under-the-hood temperature reaches a predetermined temperature.
Shape memory material "first generation" applications being tested include:
- Automatically adjusting air vents that let in more air as the engine heats up
- Aerodynamic front air dams that retract when not required
- On-demand rear spoiler
- Interior grab handle that automatically unfolds to facilitate vehicle entry
- More accessible engine hood, door latch, glove compartment releases
- Smart emergency brake release
- Rain-activated automated wipers
- SMP and alloy stiffening panels
- Self-healing panels/bumpers
Next, turning to medical smart materials there are emerging polypyrrole (PPy) biomedical micro actuators in R&D. Biomedical and life science products based on proprietary PPy electroactive polymers (EAP) technology are being developed by Creganna-Tactx Medical to build electroactive mechanical micromuscle devices.
The current focus is on medical device applications in microrobotics, drug delivery and cardiovascular areas such as a novel method to surgically reconnect blood vessels using an electroactive blood vessel connector.
PPy polymer actuators have unique properties well suited as actuators for biomedicine. These are:
- Demonstrated biocompatibility/sterilizability
- Reversible/repeatable volume change
- Small driving voltages (1-2 Volt) and low currents (µA, or microamps, to mA, or milliamps) are required
- Functions in liquid environments (saline solutions, urine, blood and cell culture media)
- Design flexibility (a wide variety of shapes/sizes are possible)
Specialty connectors can dramatically simplify reconnection of two ends of divided small blood vessels during hand, heart, brain and transplantation surgery. Developed for 1-3 mm (millimeter) blood vessels, the connector is an implantable tube with contractible and expandable features achieved by applying small voltages (approximately 1 Volt).
The multilayered tube is contracted (in less than a minute) and inserted into the vessel ends to be joined. When the connector has been properly placed, it is expanded by normalizing the applied potential to form a tight connection with the vessel walls. The multilayers of the connector tube equivalent to a thin foil can roll and unroll to cause expansion and contraction of the tube.
An electrical microsteerable implantable catheter in development makes use of EAP for steering. A prototype demonstrated in a vessel system allowed active steering of a common guide wire modified with EAP coating. Applying a small potential to the guide wire allowed the position of the tip to be controlled. Time to move from one extreme position to the other was a few seconds.
Finally, in smart impact absorbing sportswear, D3O Labs has been working with leading sportswear designer brands such as Spyder, Quicksilver head gear, Japanese Motorcycle Racing brand HYOD, Armadillo Scooter Wear and others to create intelligent wear. These items would incorporate D3O smart materials to provide normal flexibility during wear, yet impact absorption as needed in direct contact areas.
The material is washable at 40 degrees C and performs to minus-20 C without reduction in performance or negative impact on wearer comfort. It can be heat-bonded to fabrics using film adhesives or bonded to fabrics during parts molding.
Spyder pioneered the use of the material in ski apparel when it was added to base-layer tops and slalom suits worn by U.S. and Canadian alpine ski teams during recent Winter Olympics. The Capulet ballet shoe manufacturer significantly enhanced ballerinas' comfort using D3O smart materials, which essentially encompasses the entire shoe with thickness varying between 1 and 4 millimeters in different sections.
Quicksilver's incorporation of D3O smart materials into their range of beanies has been received within the recreational ski market with unprecedented success. SIXSIXONE teamed with D3O incorporating intelligent foam technology to create a new approach to the tough demands of 21st century Mountain trail bike riding for their mountain bike knee pads.
In an industry first, Equetech is using D3O smart materials in equestrian apparel to produce "Intelligent Competition" shirt and breeches. The new competition shirt contains 7mm D3O components, invisible beneath the rider's jacket and positioned in the shoulders to protect the rider's shoulders from impacts with the ground and other objects. Likewise, the "Intelligent Breeches" contain D3O components in the lower back and coccyx region to reduce the likelihood of injury to these areas.
In partnership with the D3O Labs, Cat Footwear is launching the first flexible external metatarsal guard work boot featuring D3O technology. The ERGO FlexGuard has an anatomically molded D3O metatarsal guard that can bend and flex as the wearer moves about. The metatarsal guard protects the instep and metatarsal areas when the foot is exposed to "drop" hazards. Upon impact, D3O, which is encased in leather, absorbs the shock and resists the impact, protecting the wearer from injury.
Beyond consumer goods, D3O Labs has been awarded a UK Minister for Defense funding contract to develop the use of their shock-absorbing material in military helmet liners.
D3O D3O impact absorbing smart material applications (from left) — ballet shoes, headgear, knee brace, ski padding, sportswear.
