Shape-Memory Material Could Improve Prosthetics

Monday, February 01 2010

A shape-memory composite material developed for satellite antennas could prove useful in prosthetics and next-generation ski boots. The material, identified by the trade name TEMBO®, was developed by Composite Technology Development (CTD) of Lafayette, CO. The TEMBO concept grew out of government-funded research to develop elastic memory composite (EMC) hinges to deploy structures in space-based applications. This EMC hinge has been used in place of motor-driven or spring-actuated hinges to deploy devices such as a solar array. Such an approach relies on electrical heaters to activate the shape memory material in the hinges, which then deploys the packaged structure to the shape needed for operation on orbit.

CTD initially was funded by the Federal government to conceptualize elastic memory composite-based deployable satellite structures. These EMC materials were adapted into hinges, which were developed and tested under a Small Business Innovation Research (SBIR) Phase II contract from Missile Defense Agency (MDA) predecessor BMDO in 2000. Since that time, the use of EMC material in space has been validated through repeated deployment, reliability, and integrity tests aboard the International Space Station.

How it Works

To manufacture EMC components, CTD develops polymers using a proprietary combination of thermoset materials such as epoxies and cyanate esters — materials commonly used to make composites for aerospace applications. The polymers are heated to the glasstransition temperature, generally around 80-90 °C for satellite structures. (The glass-transition temperature is the point at which properties of polymers change quite significantly, with the stiffness or modulus dropping by as much as a hundredfold.) At this temperature, the material generally becomes soft and weak. CTD engineers and chemists are able to physically modify these materials above the glass transition temperature to enable the carbon-fiber-reinforced materials to withstand very high strain levels without damage or degradation.

The EMC material combines the structural properties of fiber-reinforced composites with shape-memory characteristics of shape-memory polymers. Components and structures fabricated with the material can be folded, rolled, or otherwise packaged to a different shape for storage and later returned to the original as-manufactured shape, without loss of performance. This shape change is affected by use of a thermomechanical process where heat and force are required to package the component; heat alone is needed to return the component back to its “as-fabricated” shape. EMC material is manufactured using most composite manufacturing processes including thermally cured fabrics, filament winding, and vacuum-assisted resin transfer molding.