The value of the global sensor market is projected to reach $287 billion by 2025. But with demand for reliable, high-performance, low-cost sensors increasing, and new technologies, such as microtechnology and nanotechnology being developed, there are numerous challenges throughout your development journey, which must be considered when implementing your sensor technology in to a marketable medical device or IVD.
There are numerous different types of sensor tech, ranging from optical and electromagnetic, to electrochemical and implantable, but unfortunately the benefits of novel or emerging sensor tech can often be outweighed by the many pitfalls found downstream in volume implementation.
So, what is the solution to effectively implementing sensor technology into a medical device? The answer is, there is no single solution. Risks are a major part of product development, specifically within products that are classified as medical devices. The key is to build your development programme in a way which not only front loads risk assessment, but incorporates it throughout the programme. I know we have said it before, but the sooner risks and potential pitfalls can be identified (and addressed!) the better. And it just so happens that we have extensive experience, not only in the design and development of medical devices, but also in the integration of a variety of sensor technologies.
In fact, eg Director and co-founder, Andrew Ede, recently delivered an industry lecture for students at the University of Cambridge on this very subject, so we thought we would share five of the key challenges and considerations that he has come across, when integrating sensor technology into the development of medical devices.
In order to provide some context to each of his key challenges, Andrew talked through a project we worked on with Sphere Medical, designing their Proxima; a multi-parametric measurement of drugs, physiological analytes, metabolites and disease markers in the blood in real time. The Proxima allowed real time monitoring of standard clinical parameters, giving the ability to titrate therapy and provide closed-loop control.
1. Integrating issues
Depending on what your medical device is used for and whether the sensors are providing feedback for self-adjustment or as a diagnostic aid, the sensors within will have different integration challenges. Andrew used the example of a sensor which was functionalised to detect a range of analytes in blood. The development team had to overcome a number of issues mainly stemming from the size constraints of the unit and the properties of blood. They had to ensure the blood continued to move over the sensor to avoid any trapped volumes, as well as ensuring that there were no bubbles introduced, which could not only provide erroneous readings but also cause harm if added to the patient’s system. The manufacturing assembly process needed to be viable; components such as glue (which may affect the sensor) had to be avoided and UV proof filters integrated to allow optical light through (enables nurses to see any bubbles), whilst blocking UV light which throws the sensor’s reading. Whilst these seem like very specific examples, these are fairly typical in many sensor applications within medical devices, especially when integrating into a fluid path.
2. Accuracy and Calibration
It is imperative that sensors used within medical devices offer accurate results and therefore in-situ calibration can be a critical requirement. There can be a huge amount of variability within the manufacturing process and sensor performance will vary over time. Sensors can be affected by temperature, short term drifts caused by, for example, protein build up and longer-term drifts. A sensor with drift requires frequent calibration and the process therefore needs to be automated. Calibration itself adds another hurdle in the development process and comes with its own risks. Calibration fluid is required for each analyte and must be stable itself. There is also a possibility in some devices that the calibrating fluid could be infused in to the patient, which brings complications such as safety and toxicity, sterility, particulates and good manufacturing practice in to play.
Depending on its function, medical devices can often be in direct contact with a patient for prolonged periods of time. Therefore, the biological effects of the device having prolonged contact must be considered and are actually outlined within ISO 10993 regulation (the FDA also requires some areas to have additional consideration). They also, in turn, detail which effects should be tested for, ranging from cytotoxicity, sensitization, irritation, acute systemic toxicity & chronic toxicity.
Other aspects which must be considered are within the manufacture process. Injection moulding plastics are often pre-tested (although additives such as pigment or UV block can affect the approval) and, in the case of Sphere Medical, the CMOS manufacturing process is fundamentally hazardous. It is imperative to assure that no residuals can be released when the device is in use and that the functionalisation chemicals have each been tested and approved. You may also need to conduct a sterilization validation batch of production devices before yours can be used clinically.
4. Electrical safety
Hazards are inherent when using a device for medical purposes, but this is more of an issue when the device is attached to the patient. The ISO 60601 defines standards for electrical safety, but the most exacting standard is for patient connected devices. Electrical leakage from the sensor to the patient (or even the clinician) could have serious implications. Therefore, electrical isolation is extremely important in your product design. With this in mind, if something does happen to go wrong with your device, failsafe measures must be in place. Considering failure modes will ensure your patient, and the clinician, are protected in the event that something goes wrong.
Consideration must also be given to potential electromagnetic interference and electrical noise (commonplace in a clinical setting), which will potentially affect the accuracy of the sensor and therefore the output of the device.
Sterilisation is obviously a regular occurrence when it comes to medical devices. However, sterilisation is an aggressive process, involving either gamma radiation or Ethylene Oxide which must come in to contact with every surface in order to ‘do its job’. Both of these methods have the potential to affect the sensor or its chemical technology. Therefore, the device must be designed so that the required sterilisation does not affect the performance of the sensor, but effectively cleans the device.
There are numerous regulatory requirements within the design and development of medical devices, but this increases vastly with the implementation of sensor technology. The necessity of identifying, assessing and overcoming the many risks in your development programme, as early as possible cannot be understated. If risks are identified, outlined and expected, solutions or mitigating factors can be incorporated in to your design.
Each development programme should factor in:
- Typical challenges in the development of your device, including issues with manufacturability, integration, consistency and longevity.
- Regulatory challenges and the need for positive & negative controls within your programme.
- A stringent risk assessment early in your programme to identify challenges such as those detailed.
- A plan to overcome these development challenges.
If these key considerations are implemented, your pathway to developing a medical device with integrated sensor technology is more likely to be paved with success.
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