Force-Film: A Digital Sense of Touch for Minimally Invasive Surgery

What it does

Medical error is the 3rd leading cause of death, with an estimated 12% due to improper force. The ForceFilm is a thin add-on for minimally invasive surgical (MIS) instruments that provides surgeons with a digital sense of touch to help improve surgical safety

Your inspiration

My PhD in mechanical engineering was spent in the Hospital for Sick Children. One of the early projects I was involved with was from a general surgeon who noticed that new minimally invasive surgeons were being too heavy handed and damaging tissue when tying surgical knots and wanted to look at the force in knot tying. We originally developed ForceFilm to solve this problem. I was also involved in developing a blood oxygen sensor, to tell if tissue was being grabbed too hard, and 3 surgical procedure-specific, mechanically-accurate tissue models. All these projects were trying to solve the same fundamental issue – force control.

How it works

MIS instruments enter the body through a number of artificial holes in the body know as trocars. To have a stiffness and biocompatibility required to do surgery, the shafts of these instruments need to be made of stainless steel and the trocars also come in standard sizes. Having a hollow shaft of known dimensions and material makes it possible to design a system to turn any MIS instrument into a force sensor. ForceFilm uses between 2 and 4 strain gauges to capture one to all of the two bending moments, axial force, and torsion depending on what is most important for a specific surgical instrument. These strain gauges are embedded on a flexible circuit board (FPC) to form our film. The FPC electrically connects the strain gauges to the electronics module at the handle of the surgical instrument. There is an analog circuit and a Bluetooth transceiver in the electronics module to read and transmit raw strain gauge data onto a surgical monitor.

Design process

The proof-of-concept used strain gauges attached to a standard FPC by soldered single strands of copper from a flex-rated wire. The FPC was rolled onto the surgical instrument like a sushi roll with super glue as the adhesive; the result was fragile, uneven and relatively thick and the process was very inconsistent. Using a precision Multimeter, the sensor was shown to work. The first prototype went to a thinner FPC material, a medical grade epoxy, and integrated strain gauges directly onto the FPC. The system was applied to the instrument by forcing the FPC and instrument into a non-stick PTFE mould. This system gave a more robust, thinner, and repeatable result. Electrical measurement was moved onto the instrument and Bluetooth was added to eliminate noise-conducting wires and make the device portable. Ultimately, the device was used in a 19 participant surgical knot tying study; however, the electronics were sensitive to the environment and couldn’t be sterilized. The second prototype added the piston-style case to seal the electronics. This resulted in a stable, sterilizable instrument. This prototype was shown to 40 surgeons, researchers, and educators at the Surgical Education Week conference, design changes are being made based on their feedback.

How it is different

The ForceFilm design is unique in that it allows retrofitting of existing surgical instruments without modifying or interfering with the surgeons’ or hosptial’s instruments, setup, or workflow. This is accomplished through the unique combination of wireless operation, compact design, and full sterilizability. ForceFilm uses a Bluetooth Low Energy transceiver powered from a high temperature carbon monofluoride lithum coin cell. Then the unique piston-style case protects the components from direct corrosion of steam so that the automotive-grade components can stay on the instruments during sterilization; no need to disassemble the instruments to clean them. Current designs, although none are commercially available yet, either require a completely new instrument with the force sensor built in, a bulky add-on that adds another tube around the surgical tool shaft, or damages the original instrument by cutting groves, slots, or holes to install force sensors.

Future plans

After creating a working first prototype and receiving positive feedback from surgeons, I created a startup, with my co-founder, around the ForceFilm, focused on getting the technology into the clinic. The next steps are to get ForceFilm into surgical education to shorten the learning curve for new surgeons as well as continue to work on our user experience. We also want to expand the models of surgical instruments the ForceFilm attaches to, so that every force-applying instrument in the surgical tray can be augmented. After that we ultimately want to get regulatory approval to use the ForceFilm clinically.

Awards

Heffernan Entrepreneurship Fellowship National Technology and Business Conference - Veteran Pitch Competition (1st) UofT Collaboration Fellowship Ontario Brain Institute - ONtrepreneurs UofT Hatchery - Lacavera Prize UofT Health to Innovation Hub Fellowship Ontario Bioscience Innovation Organization CAAP