As we see all too often, a cure that is considered state of the art in current medical practice may lead to future issues for the patient. Medical devices and biotech treatments may solve the immediate health issue and perhaps save the patient’s life, but unforeseen complications or technology life cycle limitations may lead to the need for future medical treatment or repair.
Such is the case for those who have had total hip replacement (THR) surgery, which over time, may result in osteolysis. Bone degradation of this type was identified as the most significant long‐term adverse effect associated with THR at the National Institutes of Health consensus conference on total hip joint replacements. The incidence of periprosthetic osteolysis in many studies is greater than the sum of all the rest of the complications. In the Swedish Total Hip Replacement Register, osteolysis accounted for over 75% of the patients undergoing revision hip surgery.
Current Treatment for Osteolysis
Bone degradation is a serious problem in the hip socket as it will cause the implant cup to loosen rendering the hip unstable. Walking becomes difficult, and falls are especially serious, as many in this treatment population are elderly. In many cases, a revision surgery is needed.
Osteolysis typically occurs due to wear of the polyethylene liner of the hip implant releasing particles that result in bone loss. In the less invasive treatment of osteolysis, surgeons conventionally use rigid tools to debride the resulting lesion, however with these inflexible instruments, complex lesion shapes account for about 50% of cases and are not completely treatable.
Johns Hopkins Engineering R&D
Researchers at the Laboratory for Computational Sensing and Robotics in the Mechanical Engineering Department at Johns Hopkins University are looking to replace the revision hip surgery with a procedure that combines advanced shape sensors with robotics. The main goal is to extend the areas of the hip socket that can be reached in order to remove lesions for a less invasive repair solution, and to extend the number of cases that are treatable.
The robot is a 35mm long tube-like structure with an interior diameter of 6mm. Its flexibility allows for c bending to the right or left, and even an S curve bend. A 4mm lumen inside is used to pass tools for the debriding process, as well as suction away removed material. Using a flexible tool brings with it the complication of controlling the robot. Ph.D. candidate Shahriar Sefati who is working on the next phase of development explains, “It becomes tricky when you want to do large curvatures. 137 degrees of bend in the flexible robot is a lot so the important part now, is the need to control the robot.”
Shahriar and the LCSR team realized specialized sensors were needed to determine where the robot is located & how the shape is configured in real time during the repair surgery. Two channels on the snake were designated for tiny fiber optic shape sensors, which required high precision fabrication. Since accuracy was key, Shahriar turned to Potomac to create 150-micron diameter notches in Nitinol wire that the structure required.
Laser Micromachining Tiny Structures in Nitinol
Since Potomac has worked in shape memory alloys such as Nitinol for many medical device customers over the years, we clearly understood the laser-material interaction required for the job. As Shahriar mentioned, accuracy was important for several reasons. The 150-micron diameter notches needed to hold tolerance over the 35 mm length of the structure. Plus, he adds, “Accuracy of these small parts was important as the entire assembly must sit well together.”
Potomac’s lasers can produce spot sizes as small as 1 micron, so the 150-micron diameter size was easy to produce. However, our expertise in manufacturing parts with high accuracy and holding tight tolerances is the result of extensive fixturing, tooling, laser beam control, and other sophisticated advanced manufacturing skills. Laser micromachining combines many processes to create small devices such as required for the robot shape sensor described here.
Although we enjoy manufacturing parts and devices for our customers in all industries from biotech to medical devices and displays to consumer products, there is special satisfaction in working with groups such as the Laboratory for Computational Sensing and Robotics to improve healthcare for mankind.
