Piezoceramic materials are used in actuation and sensing applications across a variety of markets, and are key to some of the leading-edge technologies now used in the medical sector. From molecular diagnostics and microdosing to ultrasonic tartar removal from teeth, medical technologies require components that are fast and reliable, with low energy consumption. Piezoceramics combine all these characteristics, giving much higher accuracy and precision – and requiring less power – compared to traditional mechanical actuators and sensors. They are also friction free, so are less susceptible to wear and tear, keeping ongoing costs to a minimum.
The direct piezoelectric effect is based on the generation of charges through the application of force by a crystal, and this piezo technology is used in a range of everyday objects. The most widely recognised application of the piezoelectric effect is probably to provide the ‘spark’ for electronic cigarette or gas grill lighters, but it is just as frequently used in reverse – applying a voltage to a piezo crystal to cause it to change shape. This ability to convert electrical signal into motion is, if anything, even more commonly used in consumer goods – particularly for the speakers often used in cell phones and other compact devices – and the rise of advanced piezoceramic materials has further expanded their use. With no mechanical parts, piezoceramic actuators offer exceptional precision and speed combined with excellent reliability and low power consumption. They do not create, and are not affected by, magnetic fields, and work reliably under extreme conditions, for example at cryogenic temperatures and in vacuums, making them easily adaptable to different environments.
In vitro diagnostics (IVD) offer numerous possibilities to diagnose and detect diseases and other conditions at an early stage from samples of blood, saliva, urine or tissue. IVD is increasingly important in the fight against virus pandemics, such as COVID-19, where fast, easy and widely accessible testing methods open up the possibility to adapt therapeutic interventions for a personalised medicine approach to help cure, treat, and prevent diseases. Laboratory-based and portable point-of-care IVD testing devices require nano- and picolitre-level liquid handling, as well as high precision, shock-free dosing, fast mixing or separation of fluids and particles, and the generation of perfect droplets, taking into account the viscosity and surface tension of the media and the dosing speed. Often, contactless execution is also necessary to avoid sample contamination.
Piezoelectric components and actuators are ideal for several of these challenging IVD applications, and many clinical instruments take advantage of the incredible speed and accuracy that these technologies offer down to the nanometre level. In a lab setting, devices are getting more compact as we try to cram more capabilities into the same space, while the density of sampling is getting higher, creating a need for very small and fast drivers for the pipetting process. At the same time, these mechanisms must produce enough force to move the pipettes vertically, but with the accuracy to aspirate or dispense the right amounts of fluid. Small footprint piezomotors are perfect for this application, operating as a direct linear drive that can generate high forces. A ceramic that oscillates at ultrasonic frequencies generates a controllable forward motion with uniform speed and unparalleled accuracy.
Highly reliable PICMA stack multilayer piezo actuators are available in numerous designs with different displacement modes.
Piezo elements are also commonly used in micropumps to reliably and precisely move extremely small volumes of liquid or gas, ranging from a few hundred millilitres to a few nanolitres. Different types of pumps, such as membrane or peristaltic pumps, are actuated by different drive principles. The piezo elements can be adapted perfectly to each specific application and environment, from miniaturised lab-on-a-chip solutions for mobile analytical instruments, to microdiaphragm pumps that create continuous and variable flow rates down to the picolitre range. Essentially, any application that needs reliable metering of minute amounts of liquids and gases – from medical uses and biotechnology to chemical analytics and process engineering – can benefit from powerful and versatile piezo technology, and the more it is applied to this sector, the more device manufacturers will realise its potential.
Enhancing medical imaging
Another use of piezo motors is in conventional chip-on-the-tip video endoscopes. These instruments typically use fixed focus optics to provide imaging for a certain depth of field, but integration of a miniature piezo motor enables variable focusing, ensuring that an object can always be displayed optimally in sharp focus. Selection of the most appropriate drive technology for the specific task and boundary conditions will enhance the image quality and depth of focus without compromising reliability.
Piezo drives also offer benefits compared to traditional mechanical drives for ultrasound applications. By avoiding the need for mechanical components – such as clutches or gearheads – they offer lower weight, reduced costs and greater reliability. Oscillations of a piezoceramic actuator at ultrasonic frequencies are converted into linear motion along a moving rod, giving a uniform motion of theoretically unlimited travel range.
Miniaturised piezo elements can be used for many minimally invasive treatment procedures, such as ablation, intravascular lithotripsy, or even the controlled release of medication. For example, a non-contact ablation procedure using piezoceramics has recently been developed for the treatment of atrial fibrillation. The transcatheter technology uses tiny piezo elements to generate ultrasonic waves, and the mechanical energy that the target tissue area absorbs leads to heating, causing coagulation. Treatment can be monitored in real-time, allowing lesions to be created as seamless lines, an important criterion that is the basis for the success of the therapy. This technology, generated by ultrasound only, reduces the risk of injury during treatment, and solves the greatest limitations of current catheter ablation technologies.
As stated above, piezo elements are also used in intravascular lithotripsy, for minimally invasive reduction of atherosclerotic plaques in blood vessels or heart valves, as well as life-threatening stenoses. Here, ultrasound waves increase the permeability of the blood vessel wall through sonoporation, enabling better penetration of the medication used to induce plaque dissolution.
Piezoceramics bring versatility
As medical technology continues to develop at a rapid pace, the versatility of piezoceramics is becoming increasingly useful in providing solutions for more efficient instrumentation. The potential uses for piezoceramics is vast – from minimally invasive treatment for atrial fibrillation to IVD testing platforms. The flexibility of piezoceramic materials mean that they can be adapted for multiple different applications, offering reliability and precision, and continuing to support instrumentation development as technology advances even further.