How piezoceramics are revolutionising medical diagnostics and treatment

Piezoceramics belong to the group of piezoelectric materials that can convert pressure into an electric charge or, conversely, deform (change shape) in response to an electric field. These are called the piezoelectric effect and the inverse piezoelectric effect, respectively, and have a variety of applications in commercial devices, medical equipment and research.

The most common commercial use of the piezoelectric effect is probably creating the spark in an electric cigarette lighter: the user presses a button making a spring-loaded hammer hit a piezoelectric crystal that in turn creates a high voltage, heating and igniting the gas. Another common application, which benefits from the piezoceramic’s ability to be deformed by an electric field, is cell mobile speakers, where piezoceramic pieces can move a metallic diaphragm, making the sounds.

Since piezoelectric actuators do not have any moving parts that are subjected to stiction or friction, they can provide accurate motion control without any delay. Piezoceramics are not affected by extreme conditions, like cryogenic temperatures or vacuum, and since they are also neither creating, nor being affected by a magnetic field, they can be trusted for use in different environments. Their properties have led to piezoceramics becoming increasingly popular for applications across the chemistry, medicine or biology fields, providing reliable and flexible handling of small amounts of liquids and gases.

Piezoceramics provide better diagnostics

Clinical laboratories routinely test blood, saliva, urine and other tissues to detect diseases, monitor a person’s overall health, or predict how a patient will respond to a certain treatment or therapy. The IVD devices used for this testing can either be made for stationary use in laboratories, or as portable point-of-care devices, and cover a vast array of technologies – from polymerase chain reaction (PCR), whole genome sequencing and other molecular diagnostic tests to immunodiagnostics, cytometry and lab-on-a-chip devices.

Almost all of these applications require devices to be able to handle fluids at low volume and extremely high precision – sometimes at a nano- and picolitre level – as well as offering features such as fast mixing or separation of fluids and particles, shock-free and accurate dosing, and generation of perfect droplets at different dosing speeds.

Piezoceramic plates and discs can be used to create lightweight, tiny and accurate micropumps for IVD. When an electric field is applied, the piezoceramic component will deform inwards or outwards, pumping the liquid through the fluid chamber in a shock-free manner to enable highly controlled, very low flow rates. These piezo disks and plates can also be used to mix fluids, operating in a similar way as speakers. The creation of acoustic waves, and the resulting turbulence, ensures that liquids are evenly mixed, even in thin capillary tubes, which was previously difficult to achieve in microfluidics applications. Using hard piezoceramic materials in this way, it is possible to produce a high-frequency acoustic wave to create a bubble, which will oscillate due to its interaction with the acoustic wave, enabling rapid flows and effective mixing.

With sizes down to a millimetre in diameter and just a few tenths of a millimetre thick, piezo components are particularly well suited to integration into portable point-of-care devices, as both pumps and valve actuators. Their very low mass minimises energy consumption – a particularly important consideration for devices operating on batteries – and a piezo-actuated valve does not need any energy to keep its nominal position, further reducing power requirements.

Piezo technology in medical imaging and treatment

Endoscopes are widely used in healthcare to observe internal organs or tissues, in order to investigate symptoms like difficulties swallowing or persistent pain in the stomach. The endoscope consists of a flexible tube with a camera and, to make the procedure as pleasant and effective as possible, this camera needs to be small and able to produce high quality images.

Chip-in-the-tip endoscopes obtain an image through a sensor situated on the tip of the endoscope but, until recently, they could only give sharp imaging at a certain distance (fixed focus). By integrating an actuator between the optics and the image processing chip, the focus can be easily shifted, enabling sharp imaging of, for example, the whole abdomen without reconfiguring the endoscope. Since the endoscope needs to be small, the actuator cannot be larger than 10mm, which makes a piezo motor – using a varying electric field to create linear or rotary motion – an ideal candidate.

Even better imaging quality can be achieved by high resolution scanning fibre endoscopes (SFE). SFEs provide more image information than regular endoscopes, through high quality laser-based images with an enlarged field of view and full colour. They use miniature piezo tubes to provide motion control in the xy plane, as well as radial and axial deflection, and are both flexible and only a couple of millimetres in diameter, making them less invasive for the patient.

This image quality is particularly important when performing minimally invasive surgeries such as laparoscopies, where two or three small incisions are made for insertion of the camera and medical instruments used in the procedure. Using this technique instead of open surgery minimises the risk of wound infections, and allows faster healing. Minimally invasive surgeries obviously require small, precise and reliable tools, and piezo technologies can help to scratch that itch by providing tiny, flexible solutions that are both versatile and easy to control.

Another procedure now benefitting from the use of compact piezoceramics is non-contact ablation for the treatment of atrial fibrillation. This condition causes fast and irregular heartbeats, reducing the flow rate through the heart and increasing the risk of blood clots, which in turn can lead to a stroke. Atrial fibrillation is caused by electrical conduction abnormalities in the heart, and can be cured by creation of lines of scar tissue that can prevent the ‘faulty’ electrical impulses from spreading. These scar tissue lesions are created using piezo-generated ultrasound waves, starting at the opening of the pulmonary veins and continuing into the atrium, making ultra-small, easy to control devices essential to success.

Conclusion

Medicine is constantly evolving, driven by the need for more effective and reliable diagnostic and treatment procedures. Piezo ceramics have proven to be of great use in many medical applications, providing better imaging and facilitating minimally invasive surgical procedures. The ability to create ultrasound waves or provide rapid and accurate management of small volumes of liquids – combined with a small size and low power consumption – has made piezoceramics irreplaceable in both IVD and surgical applications, but the same principles apply to a wide range of other areas, not only in medicine but also in chemistry, life sciences research and engineering. In summary, piezoceramics could be used in any field that needs tiny actuators, controlled through an electric current, to provide precise motion control.