For many of us, life is complicated enough without having to be constantly reminded about our medical situations. Living with a disease that requires frequent doctor visits and rigorous treatment processes does not just take a physical toll on the patient — making significant lifestyle changes can be a mental battle itself. This is why medical device design engineers are all faced with a challenging but noble task: to develop effective, minimally invasive treatment technologies that allow patients to live a normal life.
As recent trends in therapeutic and drug-delivery devices have shown, patients generally prefer treatment methods that give them more control and freedom. According to a 2017 “Markets and Markets” medical device report, home-use insulin delivery devices are expected to reach $17.85 billion (USD) by 2021 — exceeding the current market by around 9.1 percent. A major reason for this projected growth comes from technological advancements in insulin-delivery devices, many of which now put patient experience at the forefront of the design.
However, devices to treat diabetes only represent one category of the grander therapeutic and drug-delivery device market. More and more patients with medical conditions ranging from arthritis to multiple sclerosis are electing to use self-injectors, wearable auto-injectors, and other home-use therapies for their treatments. Device simplicity, convenience, and portability are key attributes that often factor into a patient’s decision to choose one treatment method over another.
The Role of Force in Therapeutic and Drug-delivery Devices
Most therapeutic and drug-delivery devices, in some way, require a change in force to function. This change in force is either made manually by the patient, or made automatically by the device. For some devices, having the ability to capture and/or monitor these changes in force can streamline or automate certain processes and make the device smarter. Therefore, embedding force-sensing technology into therapeutic and drug-delivery devices can go a long way in addressing patient needs.
As with embedding any kind of new technology into an already compact device, embedding force-sensing technology into a medical device requires striking a balance between functionality and flexibility. The challenge then becomes selecting the right force-sensing technology to innovate the device without adding more burden to the end user.
A Comparison of Force-Sensing Technologies
Ease of integration, sensing component size, and power efficiency are always top of mind for medical device design engineers. However, depending on the type of force feedback the device is capturing, some embedded force-sensing technologies may be better choices than others.
Load cells, strain gauges, and piezoresistive sensors are the most common force-measuring technologies used in medical devices today. Load cells are the most well-known force sensor and offer the highest precision among the other force sensor types. Due to their large size, weight, and significant power requirements, load cells may not be as practical to embed as other options.
Strain gauges yield measurements that are the result of an indirect force measurement drawn by correlating the strain of a small wire to an assembly load. Although strain gauges are a small and thin force-sensing alternative, they are often powered with complex, expensive electronics, which can add difficulty to the design-in process.
Piezoresistive sensors — or touch sensors — consist of semiconductive material sandwiched between two flexible polymer substrates. A touch sensor acts as a force-sensitive resistor in an electrical circuit. When a force is applied to the sensor, its resistance decreases. This resistance change can be customized to trigger another action by the device.
Touch sensors may not have the precision of a load cell or a strain gauge, but they are effective methods to measure force or contact between nearly any two surfaces. They are thin, flexible, and require less power to function than load cells or strain gauges. Also, touch sensors are quite customizable to conform to, or around, specific areas of a device to capture force changes wherever needed.
Examples of Touch Sensors Embedded in Therapeutic and Drug-Delivery Devices
Application Example 1: Monitoring Performance of Automated Pumps. Even the slightest change in force can be an indicator of a significant performance issue within a drug-delivery system. For automated drug-delivery pumps, it is extremely important to design for a way to detect potentially life-threatening blockages that can build up over time. When blockages occur, there is typically an increase in pressure within the delivery tube that causes the tubing to expand.
Embedding touch sensors into specific areas where the infusion pump’s tubing meets the housing can be used to help detect expansions. If the sensor captures a change in pressure on the tubing, an alarm on the device would be triggered to alert the patient to a possible blockage, and to seek assistance. These same principles can also be applied to other infusion pumps or devices designed for operation by medical professionals in settings such as hospitals or hospices.
Application Example 2: Aiding Administration of Micro-Needle Therapy. Naturally, drug-delivery methods that cause less pain to the patient will certainly factor into their willingness to accept treatment. Transdermal micro-needle drug-delivery methods are beginning to emerge as a viable alternative to deliver complex biologics or vaccines for patients who may be uncomfortable giving themselves injections.
Embedding touch sensors into a high-pressure micro-needle drug-delivery device can enhance the device in a few different ways. In one application, sensors designed around the delivery areas of the micro-needle could help ensure complete and thorough administration of the micro-needle patch onto the patient. Sensors can also detect occlusion and measure the position of the device in relation to the subject. As this category of drug-delivery devices continues to grow, devising ways to make micro-needle administration devices smarter will be critically important.
Application Example 3: Ensuring Safe and Accurate CPR Treatment. Accuracy and consistency are vital to all types of therapeutic treatment — no matter whom or what is delivering the therapy. Touch sensors can be used to mediate human error and confirm a successful therapeutic administration process.
It is always a chaotic situation whenever a patient is struggling to breathe and needs CPR. When a life is on the line, there’s little time for CPR administrators to consider whether they are applying too much or too little compression force to the patient. Because of this, a force-sensitive CPR assistive device was developed to help quantify that force is applied in a safe, consistent manner. Force sensors embedded into pads and connected to a small digital monitor could measure the amount of force made by the administrator, instantly alerting the administrator if adjustments need to be made. This type of application can also be used to train emergency personnel on proper CPR technique.
Application Example 4: Providing Actionable Data for Connected Devices. The term Internet of Things (IoT) is a hot topic within most engineering communities, and especially so in the medical device market. The term is broadly defined as a Web-based network of smart devices effectively communicating with one another with little or no direct human interaction. Sensors of all kinds function as the touchpoint to provide data that can be used to trigger communication among other smart devices.
From a medical device perspective, embedding capabilities for physicians to monitor their patient’s health and treatment while they are on the go is an important IoT-style concept that touch sensors can help make a reality. Embedding sensors onto devices to count the amount of dosages made by a patient, or to monitor the amount of medicine available in the device, could be a driver for a powerful wireless communication system between the patient and their physician.
With each force impact — either done automatically by the delivery device, or made manually by the patient — a digital, real-time signal could be sent to the physician to review exactly how the patient is using the device. Based on the data, the physician could then make suggestions to increase or decrease the patient’s dosage frequency, or even automatically schedule a medicine refill with the patient’s pharmacist, all without needing to schedule an office visit.
Questions to Consider When Embedding Force-Sensing Technology
Considering how challenging and time-consuming it is to advance a medical device through the regulatory approval process, it is important to be efficient while in the prototyping and design-in process. Making the right investment in a force-sensing technology, and using third-party resources to ensure a successful integration process, will keep your device design on a clear path to success. Here are a few questions for design engineers to ask themselves when considering embedding force-sensing technology:
What patient usability challenges can we solve by capturing changes in force, or force impacts on the device?
Will the chosen force-sensing technology require too much power or space to keep the device functional?
Is there a specific force range, or is there some leeway in how precise the sensing technology needs to be?
Is the force sensor supplier a qualified, ISO 13485-certified company with a history of working with medical device companies?
Today more than ever, patient preference should to be top of mind when developing therapeutic and drug-delivery devices. As this article has shown, touch sensors offer many different applications to answer patient demands for simple, smart methods that can be used by the broadest population of users. Now, how will your device deliver?
This article was written by Mark Lowe, Vice President of Sensors for Tekscan, South Boston, MA. For more information, visit here.