IMPROVING MEDICAL DEVICES WITH FORCE SENSING TECHNOLOGY

IMPROVING MEDICAL DEVICES WITH FORCE SENSING TECHNOLOGY SUMMARY

Design engineers integrate force sensors into medical devices to create smart tools that produce quantifiable and actionable data. These intelligent devices help to eliminate guesswork, create consistency, and improve patient outcomes. Force feedback is an increasingly valuable feature in the medical device market and a large array of products and applications use force feedback. 

MEDICAL DEVICE ADVANCEMENT 

The medical device market in the United States is a $60 billion industry and still growing significantly today. The main target demographic for the medical device market is not the patients themselves, but healthcare providers who are seeking new and innovative medical devices to improve basic procedural outcomes and patient quality of life. In the past, physicians relied heavily on simple tools and their own interpretations to best diagnose their patients. During these times, resources were scarce, and the variety of medical devices doctors have available to them today simply did not exist. 
Today, with the progressive nature of healthcare, the world of modern medicine is transforming. Over the past century, the innovative minds behind designing new medical devices have narrowed the focus toward designing tools that produce quantifiable data that in turn helps improve the integrity of the medical practice. In recent years, the growing partnership of the engineering and medical sciences has sparked numerous advances in medical devices and technologies across the board. 

THE IMPORTANCE OF QUANTIFIABLE DATA

Although there have been many significant advancements in the field of medicine in past decades, some medical examinations and diagnoses are still based solely on subjective interpretations and the studied knowledge of the physician. As the medical field continues to evolve, so does the need for a more systemic approach to treating patients efficiently and effectively. Engineers, alongside physicians, have learned that technology can help mimic the actions of doctors while also measuring the specific assessment variables. For example, in the case of physical therapy; specifically, manual evaluations, the amount of force applied by practitioners can vary as greatly as 500% and reach potentially dangerous levels. Therefore, consistency among therapists in order to obtain adequate feedback without harming their patients is crucial (Jacuinde, G. & Tuttle, N). This hands-on treatment involves skilled hand movements, taking into account both location and speed, applied by the therapist to improve the mobility and function of the targeted muscles and tissues. In recent years, medical researchers and therapists have sought after a device that would provide minimal interference to their techniques, while ensuring the proper amount of applied force to a patient. Design engineers were able to construct a glove incorporating small, thin force sensors, simple wiring, and custom software, to develop a way to measure the force applied between the user and the patient directly. When applying the glove to a surface, the sensors in the glove relay a signal that the custom software interprets and converts into a force value. The software displays a force reading as both an instantaneous value and time series graph. These outputs allow the user to not only feel, but also see the amount of force they are applying, and adjust appropriately. Doctors have become increasingly dependent on medical devices to assist them in their field studies and day-to-day practice. The design and function of these tools allow doctors and surgeons a clearer view of their patients’ health and progress. These medical devices are ultimately able to produce quantifiable data that leads to more supportive diagnoses and better data-driven adjustments. 
The overall quality of life improves as a direct result of studying the data yielded. 05/14/13 Improving Medical Devices with Force Sensing Technology (Rev A)


 4 SHIFT TOWARDS INTELLIGENCE 

The ability to integrate and apply electronics to simple medical tools has changed the face of the medical device industry dramatically. Adding intelligence to these devices increases the effectiveness of patient care and provides constant, consistent monitoring of a patient’s health. The growing field of biomedical engineering is a key attribute to these innovative advances in surgical tools, as well as assisted living and medical training devices. When it comes to designing a new product or tool, design engineers focus greatly on the most efficient, cost effective components to integrate into their medical device design. Whether using the tool for a diagnostic, therapeutic, or surgical purpose, the engineer must consider a variety of factors when constructing a new device. These factors include accuracy, size, cost, and more importantly to the medical world, safety and consistency. Doctors are looking for reliable tools with high accuracy, so design engineers must find a product that fits the needs of both the doctor and themselves. 

FORCE SENSING TECHNOLOGIES

 One of the most important elements of a medical device is the feedback it provides the person using the tool, whether it is a primary care physician, surgeon, or patient. The device design must support a flow of communication between the patient’s body, the tool used, and the doctor reading and analyzing the output. Force feedback has become an important focus in the design of new medical devices due to these factors. The human body is a sensitive object, so the amount of force applied by a doctor or medical instrument, whether it is the case of physical therapy or surgery is a key factor for consideration. There are a few ways that force can be measured, but depending on the context of the application, some force sensing technologies prove more ideal than others do. 

Figure 1: Load Cell Figure 2: Strain Gauge Measurement Load cells, strain gauges, and piezoresistive elements are devices used to measure force. The most well known device used to measure force amongst researchers and engineers is the load cell. Load cells can use a variety of technologies to sense loads, but are bulky in size; making them difficult to design into an application where lightweight and small size are priority. To obtain force measurements, engineers commonly use strain gauges. Strain gauges are smaller than load cells, but yield measurements that are a result of indirect force measurement drawn by correlating the strain of an assembly with a load. Both technologies also require expensive electronics to obtain accurate force readings. In recent years, a different approach to force sensing technology has become commercially available. The generic term for this device is the tactile force sensor. Typically built on a flexible circuit material, these sensors are sensitive to touch. Tactile sensors are thin, lightweight, and flexible; making them ideal for integrating into a variety of products, including medical devices. 05/14/13 Improving Medical Devices with Force Sensing Technology (Rev A) 5 

One example of a thin, tactile force sensor is the FlexiForce sensor manufactured by Tekscan, Inc. FlexiForce sensors consist of special, proprietary, piezoresistive material sandwiched between two pieces of flexible polyester. The polyester has printed silver conductors on each inner half. These conductive traces form electrical connections to external circuits. These force sensors are resistors that vary linearly in terms of conductance vs. force under an applied load. FlexiForce sensors come in off-the-shelf standard shapes for test and measurement, as well as proof of concept, but are also customizable for specific Original Equipment Manufacturer (OEM) applications. Tactile force sensors are easier to integrate into products and systems as compared to the other force sensing options due to their thin, flexible nature. 

THE ROLE OF FORCE SENSORS 

A broad range of medical device applications utilize force sensors. They can play a variety of different roles in the lives of both the patient and doctor. Medical tools monitor and control a patient’s key metrics, whether it is their blood pressure or the delivery of drugs to their body through a pump/IV. When designing a pressure sensor into a device, its main purpose is to measure the forces applied to a specific area, and then relay that message via selected output or electronics. Below are some examples of medical devices that incorporate thin and flexible force sensors, like FlexiForce, to enhance tool function and produce quantifiable data.

SURGICAL DEVICES

A key contributing factor to a successful surgery is sensory feedback. The interaction between a surgeon, their tools, and the patient’s body is a matter of life and death. In recent years, with the help of modern surgical tools, surgical procedures have become increasingly less invasive. With the introduction of laparoscopic surgery, the use of small incisions to the body and a camera at the end of a thin tube to capture visuals of a specific organ, minimally invasive surgery has become the desired standard. Small medical devices used for minimally invasive surgeries, such as catheters and endoscopes, depend greatly on force measurements relayed by force sensors integrated in their design. 

For example, cardiac catheters, used to diagnose cardiac disease, contain sensors that measure certain pressures within the heart. This provides surgeons with necessary information before performing a surgery. 
Endoscopes utilize pressure sensors for careful navigation through the studied area, ultimately to help detect cancers, polyps, and the organ’s overall health (Guziak, R., & Appel, L). 

The thin, miniature nature of these pressure sensors allows engineers to design medical devices that enhance surgical environments and help improve patient survival rates. Due to advances in electronics and technology, robotic surgery has become increasingly popular. 
Surgeons no longer have to operate directly on a patient, but instead can control a robot to carry out the procedure. 
Robotic surgery has benefits to both the surgeon and the patient. For the surgeon, robots display 3D visualization for enhanced viewing of the operative area and improve the control, precision, and range of motion of smaller instruments. 

In terms of the patient, a more precise and controlled surgery results in faster recovery time, less invasive surgery due to smaller incisions, and shorter hospitalization periods (Florida Hospital Global Robotics Institute). While robotic surgery may seem like the future of the medical industry, it still has its flaws. A significant disadvantage to robotic surgery is the lack of haptic technology and inability to provide force feedback. Figure 4: Robotic Surgery Procedure Figure 3: Construction of a FlexiForce Sensor 05/14/13 

Improving Medical Devices with Force Sensing Technology (Rev A) 6 This lack of feedback that is attainable by a human makes it more difficult for the robot to perform a successful surgery. Today, surgeons using the robotic controls must depend on tactile cues and visual confirmation to direct the robot. Design engineers are challenged with creating devices containing sensory force feedback that ultimately relay force measurements to the operator, so he or she can properly control the robot performing the surgery. The RIO surgical robot, used for hip and knee procedures, implements pressure sensors and force feedback to perform successful surgeries. Before a procedure, the RIO robot requires proper calibration based on CT scan results performed in preparation for operation. During the procedure, if the surgeon applies too much pressure to the specific section of the hip or knee, the robotic controls actively push back against the operator cueing them to ease up on the load (Sofge, Erik). The world of robotic surgery is slowly progressing and medical engineers are working to improve the already beneficial technologies some surgeons are using today. The rise of popularity in robotic surgery has sparked a growth in the market of haptic medical devices. 

Design engineers are working towards integrating tactile features into common medical tools to create a more engaging and efficient surgical environment. For example, surgical grippers are a modern tool often used by surgeons during invasive operations. The main advantage of grippers is the tool allows surgeons access into parts of the body not easily accessed by the operators themselves. The disadvantage is that the gripper does not relay any type of sensory element to the operator, making it difficult for the surgeon to recognize how much pressure or force they are applying to the operative area. Surgeons often use these grippers to hold very small and extremely sensitive parts of the body, such as veins and soft tissue. Today, medical device engineers are working to design grippers that include small, thin force sensors, like FlexiForce, to help detect force measurements throughout an operation. These types of sensors are flexible and easy to integrate into various designs while producing consistent data. By placing force sensors at the gripping area of the device, simple wiring and electronic feedback alert surgeons when a certain area is receiving too much pressure, avoiding a break or pull. Figure 5: Surgical Gripper Photo Courtesy of UCLA School of Medicine 

Figure 6: Drug Delivery Infusion Pump 

Assistive Living Devices Force sensing technology is also an important feature in medical devices used outside a hospital setting. After a diagnosis, a patient will most likely return to his or her everyday life with the assistance of medication or some form of medical device. An assistive living device helps monitor the patient’s health and status of progression. Because the patient usually carries around these types of medical devices, it is important for the device to be small, lightweight, and noninvasive. Small, thin, tactile force sensors provide a simple solution designed to receive accessible data with ease in devices such as these. 05/14/13 Improving Medical Devices with Force Sensing Technology (Rev A) 

7 Custom FlexiForce sensors, designed into wearable, drug-delivery infusion pumps, help detect potentially lifethreatening blockages. These automated pumps continuously deliver vital drugs to the patient on a daily basis. When designing the delivery system, engineers concluded that the detection of blockages and functional problems within the pump was critical. When a blockage occurs in the pump, the tubing within the pump expands. The custom sensor, located where the tubing meets the housing, in turn detects this expansion by monitoring the force applied to the sensor by a section of the tubing. The sensor then triggers an alarm to alert the user of a detected blockage, and to take the necessary steps to correct the problem in order to reduce any negative effects. This use of force sensors can apply to various medical devices in a variety of settings such as hospitals, hospices, and home-care. Monitoring systems are a way for doctors, patients, and their loved ones to keep constant track of a patient’s day-to-day activities in the comfort of their own natural environment. 

New medical devices are allowing doctors twenty-four hour access to this insightful information regarding a patient’s progression and everyday routine. Real-time monitoring systems are becoming increasingly popular in geriatrics, specifically keeping a close eye on elderly patients. For example, force sensors designed into non-invasive medical devices either worn or used by the patient. For instance, sensors designed into shoe insoles or integrated into furniture such as a bed frame. The force sensors designed into these products provide continuous data for relay to the doctor or the patient’s family members via a wireless hub. This data provides insight into the patient’s daily activity or lack thereof, which in turn would alert doctors or family members to check in on that patient. These medical devices allow doctors to stay informed and connected to their patients, resulting in more precise treatment methods.

 The above applications are examples of how medical devices use force sensors as a mode of communication to the patient or doctor in order to prevent further health issues and complications. Another type of assistive living device is one whose main purpose is to communicate with the patient’s body itself. Bioness is a company that designs medical devices that use Functional Electrical Stimulation (FES) to help those affected by muscle and nerve damage to regain mobility and improve their quality of life. Bioness manufactures a Foot Drop System, which is a device that senses when your foot is on or off the ground and helps the foot adjust to changes while walking. The device consists of a lightweight cuff worn below the knee, a gait force sensor attached to the inside of the shoe, and a portable, wireless control unit. The force sensor placed within the shoe relays wireless signals to the leg cuff, which then produces electrical stimulation to specific leg muscles. This stimulation of nerves and muscles signals the foot to lift off the ground and helps the user walk more naturally. The user also has the ability to adjust the level of stimulation with the hand-held portable unit, which is small enough to carry in a pocket or bag. The combination of this lightweight, flexible sensor and the wireless design results in a noninvasive device that can be used by the patient in their natural environment and easily integrate into their daily routine. This type of assistive device is liberating to its users because they have the ability to not only adjust the stimulation levels to meet their personal needs, but it gives them a sense of control, which they did not have before. 

Figure 7: Gait Analysis Device Photo Courtesy of Bioness 05/14/13 Improving Medical Devices with Force Sensing Technology (Rev A) 

8 MEDICAL TRAINING DEVICES

Many years of study and training are required in order to become a medical professional. Field experience is a key component for medical students in order to increase their skill sets and gain significant knowledge of their industry. Training medical devices have become increasingly important in establishing standards among medical professionals and trainees. For example, cardiopulmonary resuscitation (CPR) is a lifesaving technique performed by millions of people each year; however, it is often poorly executed and a significant percentage of CPR trainees lack the ability to perform successfully in life-threatening scenarios. Performing CPR can be very risky and involves a specific technique to avoid life-threatening injuries. 

Chest compressions are the primary focus and concern for those looking to perform CPR properly. A chest compression, which is the pumping of the chest, helps circulate blood throughout the body in turn returning blood to the heart and reviving the patient. Hand placement, depth of compression, and compression rate are three vital factors that affect the overall technique of CPR. If the person performing CPR starts compressions in the wrong location and with too much force, they can end up causing further injury such as a broken rib or even death. Self-guided and classroom-based CPR training programs use Interactive CPR manikins. These systems provide interactive features such as technique assessment and vital sign simulations. 

Figure 8: CPR Training Manikin 05/14/13 Improving Medical Devices with Force Sensing Technology (Rev A) 

Manikins with integrated force sensors help locate the pressure points of the hand compressions applied, ensuring proper hand placement. The relationship of force to depth estimates the proper compression depth. Manikins such as these provide students with quantifiable data, which helps the students adopt proper techniques. This gives students more confidence to perform chest compressions in life threatening situations. Another example of a medical training device that integrates ultra-thin force sensors is the MammaCare Palpation Proficiency and Assessment Device (PAD) used to detect palpable breast cancers, which are frequently undetected by imaging. To perform effective breast exams and reduce the incidence of missed diagnoses, healthcare professionals use this device. It consists of tactually accurate breast models, instrumented with FlexiForce sensors. 

These small tactile sensors relay over 1,000 levels of clinical examination pressure within each square centimeter of the device via a digital signal processor. The ability to quantify these force measurements has led MammaCare to certify with confidence clinicians that have demonstrated appropriate examination skill. This PAD system, developed with the support of the National Cancer Institute, is now recognized as the medical and scientific standard for clinical breast examination efficiency. 

Figure 9: MammaCare Palpation Proficiency and Assessment Device 

9 CONCLUSION

 Force-sensing technologies are now an integral component in a variety of medical devices. The capability of the device to maintain proper communication with its user is a desired function that has become standard. FlexiForce sensors are a thin, easy to integrate and customizable design option. If designed into a device, these tactile sensors help eliminate guesswork for the user by producing tangible and quantifiable data. The data produced by sensors and electronics allows doctors better insight into their patient’s health and recovery process. These smart force-sensing devices result in better treatment and understanding of the patient’s condition. FlexiForce sensors enhance medical devices by adding intelligence and broadening the scope of the tool’s capabilities. The data provided by force sensors not only improves patient outcomes, but also provides a standard of consistency, which is a common goal amongst medical practitioners. Although each patient’s case is different, consistency among treatments and therapies is critical. When a patient is under evaluation, being able to study quantifiable data and base treatment off concrete numbers and science is the ideal. Thin, tactile sensors, such as FlexiForce sensors, are durable, dependable, and cost-effective providing a solution to design engineers and healthcare providers by creating devices with intelligence that are both easy and practical to manufacture. 

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