By Tom Henderson
Small Times Senior Writer
CLEVELAND, Oct. 8, 2001 — Small tech will soon lead to a “revolution” that “will change the ways in which neurosurgeons interact with the environment.”
That’s the conclusion reached by a group of collaborators at the Cleveland Clinic Foundation. They wrote of the coming changes in the October issue of the journal Neurosurgery.
Medical devices that contain MEMS — tiny
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| Researchers at the Cleveland Clinic Foundation have come up with this drawing of a possible device — a MEMS-based spinal system that attaches across four vertebras. Components include a strain gauge on the outside of the vertebra and a pressure sensor embedded in new bone that is attached to a tiny radio antenna. |
The article is both a primer on the history of MEMS and how MEMS devices are fabricated as well as a prediction of dramatic advances in the next five years. Neurosurgery is the official journal of the Congress of Neurological Surgeons.
The article was co-authored by Shuvo Roy and Aaron Fleischman, two bioengineers who specialize in MEMS fabrication; Lisa Ferrara, director of the spine research laboratory in the foundation’s Department of Neurosurgery; and Dr. Edward Benzel, a staff neurosurgeon and director of spinal disorders.
Benzel also gave a presentation on their work last week at the Congress of Neurological Surgeons in San Diego.
Recently, the Ohio Technology Action Fund awarded the four a $1.05 million grant to continue their research.
“We’re limited only by our imaginations,” said Benzel in an interview after his presentation. “MEMS and microsystems are very prevalent in aerospace and the auto industry. In medicine, we’ve been very limited by our imagination. We haven’t tried the ‘Star Wars’ creativity that the engineers have tried.”
The four have applied for a patent on MEMS-based orthopedic implants, including a combination pressure sensor/actuator that can be implanted in the spine to both monitor bone fusion and increase it through electrical stimulation.
Ferrara said that it’s currently very difficult to assess the degree of post-surgical bone fusion. For example, she said, when a hollow, threaded titanium tube is inserted into the spine, bone tissue is supposed to grow into and around the tube. But the process, she said, is often hit and miss.
“We need to be able to measure it,” Ferrara said. “Is the bone fusing? If it’s not fused, let’s go in and redo it.”
Ferrara said that many implantable devices are used in spinal medicine, including hooks, plates, rods and screws. “There are a ton of different implants, and MEMS will work with all of them.”
The clinic has come up with a drawing of one possible device. It’s a MEMS-based spinal system that attaches across four vertebras. Components include a strain gauge on the outside of the vertebra and a pressure sensor embedded in new bone that is attached to a tiny radio antenna.
Currently, the four are conducting a biocompatibility study using a goat at a pasture outside of Cleveland. The goat’s spine has been implanted with several sensors made of silicon carbide, a crystal that holds up well in the harsh chemical and saline environment of the body.
The sensors are coated with a polymer to make them more easily tolerated in the body.
The sensors will be removed in December, six months after they were implanted. They will be studied for degradation, and the goat’s tissues will be studied for signs of infection or other trouble.
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Benzel said that he expects recent presentations and the Neurosurgery article to generate substantial interest from makers of medical devices to incorporate MEMS into their products.
“Until now, companies haven’t been willing to make the investment, but I think there’s going to be a big push. Companies haven’t been hot on investing because they haven’t seen an advantage, but I think there will be a substantial change and soon,” he said.
The four researchers said they hope to either form a company or to license the technology to the private sector.
“We’re starting to get all kinds of interest,” said Ferrara.
Benzel said there are a number of MEMS-based applications for neurosurgeons, in addition to monitoring bone fusion. They include devices that:
- Monitor intracranial pressures in patients with acute head injuries or brain tumors.
- Detect and monitor tumor regeneration and help doctors decide when a follow-up operation is needed.
- Monitor whether hydrocephalus shunts are operating properly or are clogged, which can cause potential deadly cranial pressures to build up. A joint project testing shunt monitors, between the Cleveland Clinic and ISSYS Inc., of Ann Arbor, Mich., is being funding the Advanced Technology Program of the National Institute of Standards and Technology.
- Serve as neural prostheses, either to augment or to diminish certain brain functions, such as moderating motion in patients with movement disorders.
- Help build smarter operating tools. MEMS-based gyroscopic devices in surgical tools could eliminate the effects of tiny, but potentially significant, tremors in a surgeon’s hands during surgery, said Benzel. In minimally invasive surgery, where a doctor’s vision is limited, a smart tool could tell the doctor whether the tissue about to be cut into had the proper density. For example, was it the intended cartilage or a tendon grabbed by mistake?
COST STILL A BARRIER
Steve Griffith, vice president of research for Sulzer Spine-Tech Inc. of Minnesota, a maker of spinal implants and a wholly owned subsidiary of the Swiss-based Sulzer Medica Ltd., said there are major hurdles for MEMS devices to overcome.
“Let me quote from the journal article: ‘This merging of technologies requires money, and lots of it,’ ” he said. Prototypes are very expensive, and the market too unsure to justify the expense, he said.
Then there’s the difficulty in understanding the technology. “It’s an uphill curve to get people in the industry to understand it. And if we in the medical-devices industry have a hard time understanding it, you can understand the difficulty the end-user, the doctor, is going to have.”
Griffith said that while the current imaging technique of choice — doing X-rays while a patient goes through a range of motion — is “very, very crude, surgeons are pretty comfortable with it.”
“MEMS technology is fascinating and interesting but it may be ahead of its time. But even if it is ahead of its time, if it stimulates people to come up with other cheaper solutions, MEMS will have done its job. If it moves the scientific process ahead, more power to it.”
The bottom line? “We have chosen not to go down this path at this time. In five years, we may look back and kick ourselves.”
PEERS ARE ENTHUSIASTIC
The Neurosurgery article concluded with comments from those who had reviewed it.
“The potential of MEMS in neurosurgery is incredible . . . It clearly charts a path to the future,” said robotics scientist George Bekey of the University of Southern California.
“They are absolutely correct in their recognition of the pervasive, inexorable presence of MEMS in both the world at large and in the operating room,” wrote David Roberts, chief of the Section of Neurology of the Dartmouth Medical School.
“In the refinement of existing tools, such as intracranial pressure sensors, and in the facilitation of as yet unimagined intervention techniques, these miniaturized and relatively inexpensive devices will without question have a major influence on our profession.”
Dr. Richard Fessler, professor of neurological surgery at the Rush Medical School in Chicago and a member of the Chicago Institute for Neurosurgery and Neuroresearch, pointed out that surgeons will need significant retraining to use MEMS devices and operating tools.
But, he said, “MEMS could become one of the most exciting among the many revolutionary changes that are being observed in neurosurgery today, if the technological hurdles that the authors describe can be overcome.”
Those hurdles include:
- Proving the safety of MEMS devices inside the body.
- Improving wireless communications between implanted devices and receivers outside the body.
- Convincing insurance companies that the increased cost of implanting MEMS devices will ultimately save money.
- Funding the high cost of prototype development, which the authors say can range up to $1 million.
The authors predict the hurdles will be overcome within five years. “The opportunities are abundant, and the potential for future technological advances and applications is nearly endless,” they wrote.
Benzel and Ferrara said they first learned of MEMS technologies while on staff at the University of New Mexico in Albuquerque, through the work of MEMS researchers at nearby Sandia National Laboratories.
Benzel and Ferrara joined the Cleveland Clinic two years ago as part of the foundation’s thrust into MEMS-based bioengineering. Their prime focus at the foundation so far has been on spinal implants.
Benzel even envisions using MEMS devices to eventually regenerate spinal-cord tissue and treat paralysis by delivering growth-stimulation agents via microfluidic channels and subsequent electrical stimulation.
“I’m dreaming, now, but this is a perfect area to dream in, because it can happen,” he said.
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CONTACT THE AUTHOR:
Tom Henderson at [email protected] or call 734-528-6292.