In the past, surgeons relied on simple tools, training, and their own interpretations to perform their surgical procedures. The innovative minds behind designing new medical devices focused on developing tools that produced quantifiable data, which in turn improved the integrity of the surgical procedure.

Fig. 1 Common force sensing technologies include load cells, strain gauges, and tactile force sensors.

However, much like the rest of the world, the surgical field is becoming more automated by the day. Engineers have learned that technology can help mimic the actions of physicians and surgeons, while also measuring specific assessment variables. As a result, medical device companies have begun targeting healthcare providers who are seeking new and innovative tools to improve basic procedural outcomes and patient quality of life.

Robotic surgical systems and smart surgical tools are used in hospitals worldwide to make complex procedures safer and less invasive. In some of these types of procedures, the surgeon may not even need to be in the same room with the patient while the procedure is taking place. This has opened new opportunities for smarter surgical systems and devices to help set higher standards for conventional procedures.

While robotic systems may be the future of surgery, they still have their flaws. A significant disadvantage to robotic surgery is a lack of haptic technology and inability to provide force feedback data.

Force sensing technology is a key element to enhance robotic surgical systems and smart surgical devices by essentially embedding a sense of touch into their interfaces. Especially in surgery, where precision is critically important, embedding a surgical system or device with force sensing capabilities can help these systems capture quantifiable and potentially lifesaving force feedback.

Force Sensing Technologies

There are a few ways that force can be measured, but depending on the context of the application, some force sensing technologies prove more suitable than others. Load cells, strain gauges, and tactile force sensors are the most common force measuring technologies (see Figure 1).

Load cells are the most well-known force sensor type. They are highly accurate, but they have limitations as an embedded technology because of their large size and weight. Strain gauges are much smaller than load cells, but yield measurements that are a result of an indirect force measurement drawn by correlating the strain of an assembly with a load. This adds complexity to the electronics. In fact, load cells and strain gauges require expensive electronics to obtain accurate force readings.

Piezoresistive sensors — often referred to as tactile force sensors — consist of semiconductive material sandwiched between two pieces of flexible polyester. Tactile force sensors act as a force sensing resistor in an electrical circuit. When a force is applied to the sensor, this resistance decreases. The resistance change can be customized depending on the needs of the application.

Of the different types of force sensors, tactile force sensors offer several benefits that make them the ideal technology for embedding into surgical systems and devices. Tactile force sensors are thin, flexible, and minimally invasive. They can usually be designed in a variety of shapes and sizes to meet specific application and device needs. In applications where components need to be disposable, tactile force sensors also offer the benefit of being more economical from a material cost and electronics integration standpoint.

Surgical and Smart Medical Applications

The rise in popularity of robotic surgery has sparked growth in the market of haptic medical devices. A key contributing factor to a successful robotic surgery is sensor feedback. The interaction between surgeons, their tools, and the patient’s body is a matter of life and death. Integrating tactile force-capturing features into medical tools can create a more effective and efficient surgical environment.

The following examples showcase innovative ways embedded tactile force sensors are being used to enhance robotic surgical systems and other smart medical devices.

Application example 1: Surgical robots with quantifiable haptic feedback. One challenge with surgical robots is that many lack an ability to provide haptic feedback. As a result, Cambridge Research & Development (CRD) of Cambridge, MA led the charge in developing a noninvasive, haptic man-machine interface to overcome this challenge.

The CRD Neo interface uses linear actuation to provide force feedback and mimic the sensation of force through a device that can be worn anywhere on the surgeon’s body. Very sensitive, paper-thin tactile force sensors were placed in the front fenestration of a double-fenestrated gripper. The sensor-enabled grasper is connected to the haptic interface worn by the surgeon. The force sensor can then measure applied force, which is read by the haptic interface and translated into pressure applied by the device, using a mechanism that moves up and down in response to the force.

In this particular application, a surgeon wearing an apparatus on his or her head feels a tapping sensation that speeds up or slows down depending on the amount of force applied. This allows the surgical procedure to be performed remotely.

Application example 2: Endoscopic tools with enhanced awareness. Endoscopic surgery is used in many different types of procedures today. These procedures limit the size or amount of incisions that would typically be needed, which helps speed patient recovery and improve the efficiency of the surgery. Endoscopes are usually equipped with cameras for the surgeon to see the immediate environment they are working on, but force sensing technology can help surgeons also “feel” within the area the surgery is being performed.

Tactile force sensors can be important elements to help ensure endoscopic probes and tools are inserted and to help navigate through the patient’s body safely with regard to the surrounding tissue. Embedding ultrathin pressure sensors in critical positions on endoscopes provide force readings around the instrument at all times. This can be especially valuable to the surgeon when working in and around sensitive tissue.

This type of application may help provide opportunities for new types of minimally-invasive surgical procedures, especially from a robotic surgical system perspective.

Application example 3: Remote surgical stapling. Robots can play a major role in streamlining stapling processes. However, different parts of the body or types of tissue need specific, quantifiable amounts of force during surgical stapling applications. Tactile force sensors can help deliver force feedback that ensures a safe and proper stapling process.

In this application, tactile force sensors are embedded in the enclosures of the stapling mechanism to quantify the amount of force being applied with each action by the robot. The surgeon can acquire instant data on the amount of applied force, and make any necessary adjustments on the fly. This adds value to the robotic application by eliminating a lot of the guesswork the surgeon must consider during stapling procedures.

Application example 4: “Sensorized” prosthetics and implants. Precision is important any time prosthetics are introduced into the body. For example, a serious procedure like vertebral replacement surgery requires very careful placement of the vertebrae implant. The healing process itself can take over a year, which means there are significant complications that can occur during this time and beyond.

Embedding force-sensing capabilities into the vertebrae implant can deliver important information on vertebrae fit and contact, as well as feedback on whether the implant should be replaced due to wear and tear. Tactile force sensors offer the benefit of being able to work in paper-thin spaces to capture force data that cannot be acquired by any other method. This instant, actionable information can go a long way in improving the success rate of this high-risk procedure.

Design Considerations

The Cambridge Research & Development Neo interface uses linear actuation to provide force feedback. (Credit: Tekscan)

Medical device design engineers face lots of challenges when embedding new technology into products. Not only are there functionality challenges, but there are many other layers from a regulatory process that are involved. Therefore, here are some questions for design engineers to ask themselves as they go through the design process:

  • What force sensing technology can effectively and economically be integrated into the product design?
  • What mechanical or electrical requirements or obstacles may impact the choice of force sensing technology?
  • Does the product require capturing force within a specific sensitivity range?
  • Is the force sensor company a qualified, ISO 13485 certified supplier with a history of working with medical device companies?

Force sensing technology helps improve the quality of robotic surgical systems and smart surgical devices. As technology has evolved, physicians and their patients have become much more accepting and trusting of new technologies to perform medical procedures with a wider range of complexity. The thin, miniature nature of tactile force sensors allows engineers to design medical devices that enhance surgical environments and help improve patient survival rates.

Although each patient’s case is different, robotic surgical systems equipped with force sensing technology provide a level of consistency among treatments and therapies that is crucial to the advancement of the medical field.

This article was written by Mark Lowe, Vice-President of Sensors for Tekscan, South Boston, MA. For more information, Click Here .