'Smart fluids' could improve medical rehab devices

'Smart fluids' could improve medical rehab devices

A mechanical engineering project at Northeastern University in Boston is bringing "smart fluids" to orthotic devices that will be used for rehabilitation of damaged knees, creating resistance to help the injured joints build strength.

Professor Constantinos Mavroidis and Brian Weinberg, a research engineer and a mechanical engineering graduate student, lead the project, using electro-rheological fluids, or ERFs, which are a type of smart fluid that change viscosity in an electric field. Applying electricity to the ERFs used in the Northeastern lab makes the fluids more viscous, so they have higher resistance to external loads. ERFs are suspensions of particles in a viscous nonconducting oil.

Smart fluids are used in automotive technology, as well as in various other industrial segments and by the U.S. National Aeronautics and Space Administration, but potential applications have mushroomed in recent years. Scientists have proposed that smart fluids could be used in structures in earthquake-prone regions because their main application is as vibration absorbers, Mavroidis said.

In the case of knee braces, a doctor could determine how much resistance a particular patient needs to help gain strength in an injured joint. Resistance could then be set with a battery-powered actuator, wirelessly controlled by computer and attached to the side of the brace, similar at least in look to knee braces now on the market. Changing the voltage applied to the actuator would alter the resistance created in the smart fluid contained in the actuator.

The researchers hope that the device will be tested by patients at Spaulding Rehabilitation Hospital in Boston in the near future, and meanwhile they are developing braces for the hand and elbow, while they also work on a second-generation knee brace prototype. The idea is essentially the same as exercise machines that help people build strength and muscle through increased resistance. As different levels of strength are achieved, resistance is increased.

"Picture someone who has very little use of their leg," Weinberg said, to describe the sort of patient who will benefit from a brace that uses smart-fluids technology. "It can adjust to the needs of the patient."

The same will be true for the hand and elbow braces, though the actuators used to control resistance will be smaller. The first knee brace design has an actuator that is larger than what is preferable because "we were just focused on making sure it worked," Weinberg said. The second-generation design is focused on miniaturizing the actuator. That redesign incorporates feedback from physicians at Spaulding and includes the ability of the device to push back against the injured joint, so that resistance comes from two directions.

"The first question they asked was can it "push back," said Mavroidis, who came to Northeastern six months ago from Rutgers University in New Jersey. Weinberg moved from Rutgers then, too.

They also are working on a smart-fluids force feedback knob for a project funded by General Motors Corp., which wants future vehicle interiors to have one control knob rather than many different knobs for air conditioning, the radio, and other functions. For that project, the researchers have built a device with ERF inside a cylinder that contains multiple flat copper plates that serve as the electrodes. The fluid is activated with 300 to 3,000 volts of electricity, though in this case the voltage is usually 1,500. The more voltage that is applied, the more viscous the fluid becomes.

A knob on the top of the experimental device simulates different feelings when touched, so someone driving a vehicle would be able to tell by those feelings the control they are altering using the single knob. Weinberg tapped some commands into a computer linked to the device to demonstrate how the knob is changed. "It's purely virtual," Mavroidis said, explaining that the feeling of the knob changes according to computer commands. "It's not mechanical at all."

"The end goal is to see how many different things we can simulate," Weinberg said.

They have yet to patent their intellectual property, so the pair cannot provide many more technical details related to the rehabilitation devices until they have protected it through Northeastern's Tech Transfer Office. Meanwhile, they continue work on the prototypes with fluid donated by Lord Corp. in Cary, North Carolina, and braces from DJ Orthopedics Inc., a medical device company based in San Diego that specializes in rehabilitation and regenerative products, including those for athletes.

A three-year, US$220,000 National Science Foundation (NSF) grant is supporting their work to develop hybrid actuators, one using ERF and the other to develop the active component for push back. They also are participating in an NSF Research Experience for Teachers grant to Northeastern. That program allows science teachers to spend time in actual research labs, learning about real-world applications of what they teach.

Geetika Diddee, an eighth grade physical science teacher at Clarke Middle School in Lexington, Massachusetts, is spending part of her school break working in the mechanical engineering lab. Weinberg suggested they teach her how molecular-based smart fluids work, and so they are building a demonstration model for that in Northeastern's mechanical engineering machine shop that she can take to her school. "The kids will be able to feel the resistance," created in the model, and so get a better understanding of how the smart fluid works and what it can be used for, she said.

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