Exploring the Versatility of MEMS Pressure Sensors

MEMS (microelectromechanical systems) pressure sensors in catheter

At a Glance

MEMS sensors are made of a piezoresistive diaphragm connected to a Wheatstone-bridge circuit
They respond to pressure change and generate a proportional electrical current
Compare MEMS sensors with fiber-optic and fluid-filled sensors

Advances in medical devices are helping transition the healthcare industry from a subjective mindset to that of a quantitative mindset. Smarter medical devices are enabling physicians and healthcare workers to produce quantifiable data that leads to more supportive diagnosis and better data-driven treatments, and as a result, these smarter devices are contributing to an overall improvement in patient quality of life. This transition is being largely enabled by advances in sensor technology, particularly medical devices that are integrated with MEMS (microelectromechanical systems) pressure sensors. These sensors offer unique capabilities that contribute to this transition toward data-driven healthcare.

Why MEMS in Medical Devices?

MEMS sensors play a pivotal role in medical devices by providing closed-loop feedback, which can then enhance device responsiveness and improve therapy outcomes. These high-performance sensors can seamlessly integrate into a wide range of medical devices and technologies that are driving the next wave of lifesaving medical innovation. Serving as switches, these sensors communicate with control units to make real-time decisions based on pressure data. This not only helps to reduce facility costs but can also increase the overall value proposition of the medical device. The sensors are constructed of a piezoresistive diaphragm connected to a Wheatstone bridge circuit. When mechanical strain is applied to the diaphragm, it alters its resistivity, resulting in changes in current flow through the sensor and generating an output voltage proportional to the applied force. The biocompatibility of MEMS devices, manufactured with materials like silicon, glass, titanium, gold, platinum, and parylene, makes them suitable for seamless integration with living cells and physiological structures in the human body.

Alternative Pressure Technologies in Medical Devices

While MEMS pressure sensors are the typical sensor of choice for medical applications, alternatives like fiber-optic sensors and fluid-filled sensors also exist.

Fiber-optic sensors shine laser light into an optical fiber. The end of the fiber is often equipped with a flexible membrane that flexes in relation to applied pressure and temperature. Changes in the membrane are sensed by shifts in wavelength of reflected light. This sensor requires a reasonably complex receiving electronics system that also has to correct for temperature effects. Integration of these sensors requires care such that the bending of the catheter does not add additional strain over the signal being measured. Fiber optic cables within the catheters are fragile and may be prone to cracking, increasing integration costs.
Fluid-filled sensors use an external transducer coupled with a fluid-filled catheter that communicates the pressure from the source. Problems associated with fluid-filled lines include viscous damping resulting from the long catheter and extension tubing. Further, dynamic pressure changes such as those produced in normal cardiac operation cause measured signals to peak much higher than the actual pressure. This results from resonance within the tubing system. Using fluid-filled systems is an art, and success depends on how the sensor is set-up and used.

MEMS (microelectromechanical systems) pressure sensors in catheter Catheter_device_with_sensor_(2).png

A sensor integrated into a catheter. MILLAR

Application Examples for MEMS-Enabled Devices

MEMS pressure sensors can be found in a variety of clinical applications and devices in both acute (<24 hours) and chronic (>5 years) durations. Some examples of clinical applications for MEMS-enabled medical devices include:

Cardiovascular Pressures
- MEMS sensors can be integrated into a wide range of cardiovascular devices that provide cardiovascular pressure measurements, such as left ventricular pressure, right ventricular pressure, valve gradients, and supply in-depth data to assess heart failure conditions and more.
Intracranial Pressure Monitoring for Traumatic Brain Injury
- Pressure data acquired by MEMS sensors during invasive monitoring for critical care patients can help physicians make life-saving decisions.
Airway Pressures
- MEMS sensors can record precise measurements within the airway to advance discovery in respiratory physiology. Signals are unaffected by patient position or movement during respiratory cycles of breathing events such as obstructive sleep apnea.

Additional examples of clinical applications for MEMS-enabled devices include compartment syndrome, tumor pressures, drug delivery systems, urology, oncology, ophthalmology, and emergency care.

Considerations for MEMS Sensor Integration

The optimal integration of MEMS pressure sensors is critical for the success of any project. An example of the comprehensive integration approach involved with this process includes a feasibility analysis, sensor selection, packaging design, prototype development, sensor coating, integration, validation, testing, manufacturing optimization, and eventual commercialization. Key considerations include:

Implant Time
- Acute: For durations up to 29 days, the sensor is typically integrated into a catheter, addressing short-term medical needs.
Sensor Size
- There is an increasing emphasis on enhancing medical devices through miniaturization. This shift highlights the importance of careful handling of small components, like 50 AWG wires, during integration, to prevent breakage and mitigate increased manufacturing costs.
Sensor Encapsulation and Integration
- The encapsulation and integration of the sensor play pivotal roles in both its performance and the efficacy of the device. Incorrect encapsulation can result in higher drift and lower accuracy in pressure measurements.
Accuracy
- Attention to detail during the integration process is necessary to meet the device’s requirements and application needs. Some factors influencing accuracy include:
  – Drift reduction
  – Zeroing
  – Operation in altitudes
  – Temperature range of operations
  – Light sensitivity
  – Proprietary algorithms to reduce time-varying drift
  
  Article Source: MDDI

Exploring the Versatility of MEMS Pressure Sensors

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