Piezoelectric materials for medical applications

Demands on components increase with the advancing miniaturisation in medical engineering.

An important prerequisite for this is, however, the choice of the matching drive.

Piezo-based drive solutions have proven themselves for a long time now in the semiconductor, biotechnology and metrology industries.

In addition, in medical engineering, piezo-based drives are increasingly being used.

Piezo elements and actuators are suitable for medical applications; they generate the linear motions required precisely and without detours and they can also be matched to the relevant application environment.

Their small size means that, along with laboratory applications, an increasing number of mobile solutions can be realised, be it in mobile measuring instruments, portable laboratories or infusion devices, as well as in therapeutic equipment.

Piezo ceramic actuators and drives feature many characteristics that make them suitable for a range of common methods in medical engineering.

They are fast, compact, vacuum compatible as a matter of principle and unaffected by magnetic fields.

Their reliability, long working life and low energy consumption make them the most suitable drives for this application.

Size and force, as well as actuator travel and position resolution, vary depending on what is required.

Further positive properties are also relevant on a practical level.

Piezo actuators are maintenance free because they have no moving parts in the conventional sense.

The motion is based on crystalline solid-state effects and so there are no mechanisms to rotate or produce friction.

Active ceramic components such as piezoceramic sensors and actuators are frequently being used in medical engineering, for example as ultrasonic generators in dentistry or for laser beam control in ophthalmology, dermatology or cosmetics.

PI Ceramic in Lederhose offers a range of piezoelectric components in a variety of shapes - standard as well as custom made - and piezo actuators with or without preload in different sizes, which have already been tried and tested in numerous applications.

The treatment of respiratory diseases often involves medication being directly applied with atomisers.

Conventionally, pressurised air atomises the inhalation solution into minute droplets.

An alternative method is to generate minute droplets with the aid of piezo technology.

Specially shaped piezo disks act as ultrasonic transducers here and excite a stainless steel diaphragm with several thousand holes to execute ultrasonic vibrations at more than 100kHz.

This produces particularly homogenous aerosols.

This is suitable for precise dosing - the administration of high-quality drugs can be better targeted, enabling access to new therapeutic concepts.

The risk of side effects is also reduced.

Piezo technology reduces the time required to atomise medications by up to 50 per cent compared with conventional systems, which means an increase in the quality of life, especially for patients with chronic respiratory diseases.

The special hygiene requirements that come with medical engineering applications are mastered by piezo ceramics; the aerosol generators can be professionally sterilised in autoclaves.

The ultrasonic operation is noiseless for humans, and the low power consumption of the piezo component also allows battery operation.

It is not easy to precisely target the dosing of miniscule amounts and volumes of a few microlitres or even nanolitres.

Micropumps or microvalves, also called microdispensers, are suitable here.

Piezo elements or actuators make good pump drives; they generate the linear motions required very precisely and can also be matched to the relevant application environment.

Microdiaphragm pumps are used to transport liquids or gases.

Here, the medium to be pumped is separated from the drive by a diaphragm.

Therefore, the drive cannot exert any adverse effects on the media pumped.

Highly dynamic, disk-shaped, piezo elements mounted directly onto a metal diaphragm lend themselves to the miniaturised version of this type of pump.

Typical specifications for such microdiaphragm pumps for the dosing of liquids are a flow rate of up to about 80ml/min at switching frequencies between 25Hz and 120Hz and a potential back pressure of between 200mbar and 500mbar.

When dosing gases, the values are between 0.1ml/min and 250ml/min, 100Hz to 500Hz and 100mbar.

Possible applications range from laboratory technology and medical engineering, where they can be used in analyses for the transport of reagents or also the removal of reaction gases, via chemistry and pharmaceuticals right through to mechanical engineering, where lubricants or coolants can be applied very accurately and in a decentralised way.

Their compact dimensions also make these dosing devices suitable for lab-on-a-chip applications.

Reliable analyses with tiny amounts, in research or routine onsite investigations, for example, can be carried out quickly and safely.

Dosing tasks cannot only be carried out with conventional diaphragm pumps; microvalves are the preferred solution where more viscous liquids requiring higher forces have to be dosed.

Depending on the drop size and therefore the diaphragm displacement required, they can be driven directly with piezo actuators or by means of levered systems.

As an alternative, piezo motors can take on this task: they offer all the advantages of piezo technology, such as low space requirement and energy consumption, and combine these with the longer travel range of a linear motor.

The drive does not need to be supplied with power to hold its position, so it does not produce heat and has no positional jitter.

Ultrasonic miniature motors measuring only a few millimetres or centimetres are especially suitable for microdosing.

Despite their small dimensions, they are tried-and-tested positioning systems whose moving parts are directly driven by an oscillating ceramic.

The motor fits into almost any installation space.

In addition to dosing tasks, this miniature motor is designed for mechanical manipulations of any type, the positioning of small objects and the operation of switches.