Research at Rensselaer

New sensors may revolutionize recoveries

Sensors implanted in orthopedic surgery patients provide up-to-date, accurate information

A biomedical research group at RPI is currently developing a sensor that could potentially revolutionize the recovery process following orthopedic operations. The team is comprised of Assistant Professor Eric Ledet, two graduate students, two undergraduate students, and members of Albany Medical College.

Currently, after orthopedic surgery, patients are given treatment based on the average time it takes a person to recover. Ledet used a broken arm as an example, mentioning that patients are often required to wear casts for approximately eight weeks because the average person requires that much time to heal. However, people recover at different rates; one person may be able to function normally after six weeks, while it could take another patient 10 weeks to get to that point. The sensor being developed by Ledet’s team could allow surgeons to make individualized, personal diagnoses that would address this issue.

The sensor—which is circular in shape, measuring four millimeters in diameter and having a thickness of 500 microns—can be inserted during surgery, particularly in cases where objects such as support rods are inserted into the patient. It would remain “passive” most of the time—that is, the sensor would not function and would not be powered during this period. When an external antenna is passed over the area containing the sensor, it provides the surgeon with information regarding the pressure, strain, temperature, and the like in that region of the patient’s body.

The technology required for such devices has existed for around 20 years, said Ledet. However, it had been prohibitively expensive to design such sensors due to their complexity. This cost is also why such devices have not moved into daily clinical practice. The sensor’s designed by Ledet’s team however could “cost less than $1 to produce.” Ledet stated that the sensors should be robust and stable enough to survive for the rest of the patient’s life.

Its strength is the result of its “extremely simple” design. Ledet explained that “the more complex something is, the more prone it is to failure.” By removing the complexity inherent in previous sensor designs, the research team was able to overcome this obstacle.

Having reached this stage in their research, the team shifted its attention to the design of the external components of the system, particularly the external antenna, which interacts directly with the sensor. The antenna emits radio frequencies that “energize” the sensor, allowing it to relay useful information to surgeons. Some areas of the body, such as a joint in the hip, are much deeper within the body than others, such as the wrist. Therefore, Ledet said, the research team has to figure out how to increase the reading range and power of the antenna, among other things. Additionally, the team has to tune the sensors such that they provide more accurate information to surgeons.

Ledet used a tuning fork and its user as an analogy for the sensor and the antenna. Essentially, the mechanical energy the user imparts on the fork is analogous to the radio frequencies sent from the antenna to the sensor. The vibrations of the tuning fork relate to the “energizing” of the sensor Ledet referred to before. The sound the user hears is equivalent to the information the antenna receiver takes in from the sensor and provides to the surgeon.

The original purpose of the research was to develop a “research tool,” added Ledet. However, early on in the process, the group recognized the potential of their work. From that point, the purpose became the “translation of technology to daily clinical practice.” Members of the team also saw potential for the sensors’ commercial success.

Ledet stressed the fact that the researchers at Rensselaer are “working very closely” with members of Albany Medical College, especially with the Head of the Division of Orthopedic Surgery Richard Uhl. Uhl received his bachelor’s degree from RPI.

Currently, each sensor developed by the team is built by hand. Despite the fact that they’re still devising a means by which the sensors can be mass produced, the research group is pursuing a patent for the devices. The sensors have already received attention, as Ledet has presented the progress of the team’s research at multiple conferences over the course of five years.

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