It was Wilhelm von Siemens who, in 1860, started to look into developing a temperature sensor based on a copper resistor. The highresonance stability of single-crystal quartz, as well as its piezoelectric properties, is believed to have made a wide range of high-performance, affordable sensors possible. They have played an important role in everyday life ever since.

Since the days when Von Siemens started tinkering with quartz, sensors have crept into every single element of our lives. To define a sensor in medical settings is to deny part of its capabilities, but in the purest terms it can be said to be ‘an electronic component, module or subsystem the purpose of which is to detect events or changes in its environment and send the information to other electronics, frequently a computer processor’. A sensor is always used with other electronics, whether as simple as a light or as complex as a computer. Sensors have long been used in the medical world, but over the past decade there has been an explosion in new applications, to the level where they have become indispensable in modern medical device manufacturing.

The sixth sense

There are a host of new and exciting ways in which sensors are helping the medical world, some of them ingenious. Remember that, to viewers of the original 1960s Star Trek, automatic doors that opened without touch on the USS Enterprise were a complete fiction because they were hardly common. Urban legend has it that stage hands would stand on the side of the doors, out of sight of the camera, and open them for the actors as they walked through. (The more likely, but slightly less entertaining version, is that the sliding doors on all the Star Trek series were operated manually offscreen through either a pulley system or levers.)

Manufacturers are now realising that sensors can be used not only as monitoring medicine, but also as predictive systems.

And it was in 1954 that two friends, Dee Horton and Lew Hewitt, invented the sliding automatic door using a mat actuator when they decided the Texan town they lived in was too windy for revolving doors. They founded a company, Horton Automatics, that developed and sold the first automatic sliding door in the US in 1960. The automatic sliding door would become ideal for the shopping malls that soon blossomed across the country. After the invention of the motion sensor, automatic sliding doors would incorporate this technology for ease of implementation and better reliability. Now, of course, we’ve got completely used to the fact that supermarkets, shops and offices all have doors that sense motion and open automatically for us. But there was a time this wasn’t always the case. And in medical terms, it’s often the most simple ways in which they’ve been the most helpful.

Medical monitoring sensors include biosensors and mechanical sensors. The translating component of medical monitors is responsible for converting the signals from the sensors to a format that can be shown on the display device, or transferred to an external display or recording device. One example is an anaesthetic machine that has integrated systems for monitoring several vital parameters of the patient, including blood pressure and heart rate.

Sensing a change in the force

Sensors are now everywhere and are taking on a far larger part of the healthcare process than they did previously. Manufacturers are now realising that sensors can be used not only as monitoring medicine, but also as predictive systems that can relay a patient’s statistics back to a healthcare professional before anything has gone wrong.

One of these uses is the modern phenomenon of fitbits and heart rate monitors that can be worn by someone with a medical condition or someone who wants to monitor their activity or exercise regimen. The more serious uses for sensors, however, are far more intuitive. A conference talk given by Dr Mike Pinelis, from Rogue Valley MicroDevices, outlined some of the most exciting medical MEMS and sensor devices introduced to the marketplace and explained how they have been a boon to the healthcare market. Some of the devices are already in volume production and some are still being commercialised:

  • Smart contact lenses: these devices from Google consist of a tiny wireless chip and miniaturised glucose sensor that are embedded between two layers of soft contactlens material. It gives accurate glucose monitoring for diabetics using bodily fluids. Prototypes can generate one reading every second and the inventors are experimenting with LEDs to serve as an early warning for the wearer.
  • Non-invasive blood monitor: created by researchers from the University of California at San Diego, this is a digital tattoo that monitors blood flow from under the skin. The tattoos are needle-free, sensor-laden transdermal patches that are completely painless for the user. RogueValley says they have tiny sensors that can read blood levels for sodium, glucose, kidney function and electrolyte balance – all from a smartphone. Impressively, the prototypes also contain a wireless, battery-powered chip to continually test up to a hundred different samples.
  • Concussion sensor: Swiss electronics company ST Micro and US company X2Biosystems joined forces to create a wearable device that has an electronic head-impact monitoring sensor patch. The patch contains MEMs motion sensors, microcontrollers and a low-power radio transmitter, as well as a power mismanagement corsetry. On top of this, the device is connected to a cloud-based system that includes the patient’s concussion history, existing neurocognitive function and balance. It will be able to coordinate performance data to create a baseline for comparison after a suspected injury.
  • Ingestible drug delivery system: tech giant Phillips has created an electronic pill to help treat gastrointestinal cancer. The pill contains a drug reservoir, fluid pump, battery and pH sensor, and a microprocessor, thermometer and radio transmitter all tucked away in infinitesimal sizes to treat the tumour. In this smart device, the patient ingests the pill, which finds its way to the tumour, dispenses the drug and then harmlessly exits the body.
  • Wearable UV exposure sensor: developed by Sunfriend, this wristband is used for monitoring UV exposure. It allows the user to maximise vitamin D production – essential for good health – while it also reduces the risk of the wearer exposing themselves to skin cancer through spending too much time in the sun. An LED indicator lights up as UV exposure accumulates and then flashes once the safe limit has been reached.
  • Intraocular pressure sensor: while many of the devices are obvious from the start, this product, developed by Swiss companies Sensimed and STMicroelectronics, is somewhat less obvious. It’s a smart contact lens that the developers call Triggerfish. The contact lens can measure, monitor and control intra-ocular pressure level for patients and even catch the early cases of glaucoma. The sensor is a MEMS strain gauge pressure sensor, and this is then mounted on a flexible substrate. Though not for everyone, as it goes on the eye like a normal contact lens, this could be a great addition to the world of sensors.
  • Microneedle drug delivery system: Purdue University researchers have developed a micropump device that is based on skin-contact actuation for drug delivery. It’s a small box about the size of a fingernail and a few millimetres in depth, with a short needle. The actuation mechanism uses the patient’s body heat and no other external power source, meaning that it has sufficient strength through inducement to drive the liquid drug through the attached needle. The prototypes have low fabrication costs because they use biocompatible materials and do not rely on battery power for operation. The designers say that the system should be suitable for single or multiple-use transdermal drug dispensers.
Sensors have long been used in the medical world, but over the past decade there has been an explosion in new applications.

The new for the old

Many new sensor devices focus on geriatric care. While not a medical device per se, these types of sensors are offered by healthcare providers who are eager to respond to their older patients’ needs by helping them retain their independence and quality of life. They are also sought after as an easy-to-deliver solution.

One example of these types of devices is MedMinder, a collection of automatic medication dispensers. The dispensers first flash to remind users to take their medication. They then beep if the medicine is still not taken. Next, they call the user. After a certain period of time, a caregiver or family member will be notified. This is similar to many other devices currently being launched and making their way into management plans by doctors looking to ease the burden for elderly patients.

Most of these sensor application devices are focused on reminders, schedules or other ways of maintaining a medication routine. There are also the ubiquitous heart monitor bracelets that have been on the market for years. While less glamorous than other uses for the sensor technology that is continuing to develop, the rapidly ageing population means this application for the tech could be the most common, and most profitable, for medical device manufacturers.

Sensing the future

The development of new techniques for monitoring is an advanced, yet still developing, field in smart medicine. Biomedical-aided integrative medicine, alternative medicine, self-tailored preventive medicine and predictive medicine are all making their way into the public’s conscious and through regulatory frameworks.

In years to come, the list of devices that use new sensor technology will be vast and only outdated or budget devices will not have sensors that monitor a range of aspects. These new devices will emphasise the monitoring of comprehensive medical data of patients, as well as people at risk, through the use of biosensors, lab-ona- chip and advanced computerised medical diagnosis.

The global medical device sensor market boom

According to Transparency Market Research, the market for global sensor devices for mobile healthcare is expected to witness “robust growth during the forecast period owing to maturation of technology leading to miniaturisation of sensor devices”. Major factors propelling the market here include the low cost of sensors; integration of sensors into consumer devices; a surging geriatric population; a rise in awareness about health and fitness; an increase in remote patient monitoring; and the prevalence of chronic and lifestyle diseases, the report says.

The surge in the penetration rate of mobiles and smartphones, and reimbursement policies are the other factors likely to drive the global market from 2017 to 2025. However, “regulatory issues, privacy and security concerns, lack of clarity in health communication, and standard protocols are projected to restrain the global sensor devices for the mobile healthcare market during the forecast period”, the research states.

The market can be segmented by product type, application and region. In terms of product type, the global market can be divided into microphone sensors, camera sensors, accelerometer sensors and geolocation facilities, and others. Based on application, the market can also be segmented into health and wellness monitoring, safety monitoring, home rehabilitation, early diagnosis of disorders and efficacy assessment such as clinical trials. The health and wellness segment is expected to witness high growth owing to rise in public awareness in fitness, health and prevalence of chronic disease.

The growth of the market is attributed to rapid innovation of technology, a rise in enthusiasm in individuals about gathering quantified data about their health and the prevalence of unhealthy lifestyles.

Meanwhile, the disposable medical devices sensors market share will Increase more than $6 billion by 2022. The global disposable sensors market has an annual growth rate of 10.3% in the given forecast period.