Dr. Susan Allen receives patent for body limb movement limiter

July 31, 2008 -- Dr. Susan Allen, distinguished professor and director of the Arkansas Center for Laser Applications and Science at Arkansas State University, has been granted a personally owned patent for a body limb movement limiter. The patent, granted to Dr. Allen July 22, resulted from a rollerblading accident she sustained several years ago.

According to the patent abstract, a body limb movement limiter restrains the movement of a person’s arm to protect the person’s shoulder or restrains the movement of a person’s lower leg with respect to the upper leg to protect the person’s knee.

“Just like scientists are trained to think differently, inventors learn to look at the world a little differently,” said Dr. Allen. “I knew about non-Newtonian shear-thickening fluids from a conversation in graduate school with a colleague. He told me that a popular Mattel toy, “The Bee Says,” had a non-Newtonian switch in it.

“I remembered it because I thought it was really cool that Mattel was using high-tech materials in their toys. When I dislocated my shoulder trying to turn a corner while going a little too fast rollerblading, I also broke my pelvis. During my recovery, I had my immobilizer off at one point and was sitting down when I was startled by something and reached out instinctively for the nearest wall with my bad arm. It really hurt.”

Dr. Allen said she thought during her physical therapy that in order to get her range of motion back that it would have been better to keep that joint moving during the recovery period. She realized that she needed a tether with a “squishy brake” and the non-Newtonian fluid from graduate school came to mind.

Corn starch and water or sand near the tide line are the shear-thickening non-Newtonian fluids that most people will encounter, Dr. Allen explained.

“When you stir a thick paste of cornstarch and water slowly, it moves, but if you try to stir it fast, your spoon freezes up,” she said. “The same thing happens when you bury your feet in wet sand. You wiggle them in but if you try to pull them out fast, it’s hard to do. Properly designed, such a fluid would allow slow, deliberate movement but would prevent rapid starts and stops and the forces on the recovering joint that would accompany them.” 

As a result, the device aids in building strength and preventing the shortening of the affected tendon or ligament. Dr. Allen’s invention prevents rapid movement to a person’s shoulder, knee or other joint and allows the user to move normally without discomfort while preventing sudden acceleration of a person’s limb. Such hurried movement could cause reinjury, pain or damage to a person’s joint.

The movement limiter consists of a housing framework containing a fluid that thickens under acceleration and a reel. A tether is attached to the housing case with the free end placed around the person’s arm.  A strap attached to the housing is secured around the torso.  For a hinge joint like a knee or elbow, two pairs of arms are each secured to a case containing a similar fluid. This limits the movement of one pair of arms with respect to the other, attached above and below the knee or elbow.

By way of Dr. Allen’s invention, a thickening fluid is able to produce a body limb movement limiter that needs no external power source. However, a sensor and electrically driven clamps, or electrically or magnetically modified fluid viscosity, can also prevent the forces generated by rapid acceleration.

The next step for Dr. Allen’s invention is marketing and distribution. In addition, this marks the seventh patent issued to her, dating back to 1991. She said six more patents are currently under consideration at the United States Patent and Trademark Office as well as several disclosures pending with the ASU Office of Research and Technology Transfer.          
 

###