Shaping the future of medical technology

New developments in materials are required so that ideas can find application and be brought to fruition in the form of products. And there is a great deal of activity in this area: the spectrum covers new and intelligent combinations of familiar materials, the development of functional methods of processing and working, functionalised plastics, innovative biomaterials and highly complex implants and neuroprostheses.

One example of intelligent combination and forward-looking processing is the patented structural diaphragm in the new microdiaphragm gas pump from KNF Neuberger GmbH in Freiburg. The sections of the pump in contact with the medium are made of different materials. The pumps are characterised by compact dimensions, simple installation, high resistance to steam and condensation and outstanding gas-tightness.

Sales Director Günter Emig explains how the product was developed: “The shape of the pump diaphragm was first brought right up-to-date and optimised on the basis of calculations; the traditional flat diaphragm was replaced by a tension-optimised structure.

This reduces the load on the diaphragm from the various work cycles significantly and results in a longer lifetime and lower lifecycle costs. “But,” he continues, “ in addition to the structural change, a new diaphragm fabric contributed to the crucial improvement. It looks like this: the side of the pump diaphragm that is in contact with the medium is coated with a universally media-resistant PTFE. The elastomer carrier layer next to it strengthens the interface with the PTFE and protects the diaphragm from overload. In the centre of the diaphragm is a metal insert tightly attached to the elastomer which is used to mechanically activate the pump.

As Günter Emig explains “By using materials to optimise the design and intelligently combining two familiar materials we have improved on the quality of our structural diaphragm.”

Dr Nils Hartmann from the Center for Nanointegation (CENIDE) at the University of Duisburg-Essen is working on thin polymer layers on solid surfaces. These could play an important part in many technical and medical applications in the future. Some examples include coatings for implants which release certain substances when stimulated from the outside.

Nils Hartmann says “In order to achieve these “switchable” surfaces, we need polymer layers which respond to an external stimulus as required.” The stimuli might be changes in temperature, the pH value or salinity. Thin polymer films can react to such stimuli with changes in their chain arrangement. The chains stretch or knot and thus alter the thickness of the film. Nils Hartmann explains in more detail: “However, one only refers to stimuli-responsive polymer layers when these changes are very pronounced and if the effect of switching the stimulus on and off is reversible and can be repeated sufficiently often.” The switching process must also be fast enough for the application in question.

A group of researchers working with Nils Hartmann showed in recently published study that certain polymer layers can indeed switch very quickly and that they are not damaged when this is repeated thousands of times, making them suitable for longterm use. Some examples of responsive and reactive polymers are Poly(N-isopropylacrylamide) (PNIPAM), polyacrylic acid (PAA) and sodium polystyrene sulphonate (PSS).

For many applications, the molecules of the polymer must attach themselves firmly to a surface. The polymer chains bond water and other fluids at temperatures below 32°C. If the temperature rises above this level, the tiny chains collapse, release the water and form a compact layer.

Thanks to special processes it is also possible to manufacture very thin layers of these polymers of less than 100 nanometres. Depending on the structure, the thickness of the layer can be reduced by at least half when it switches. According to Nils Hartmann, “This could allow the material to regulate small openings and channels in valves, for instance”. It would be of interest in diaphragm technology or microfluidics, as an example.

“Or,” he continues, “it could be used as a temperature or humidity sensor or this property could be exploited for the controlled release of medication inside the human body.” This immediately allows access to treatment methods with very different effects.

Dr. Christian Oehr from the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart is also interested in equipping surfaces with special properties. As Christian Oehr explains: “A range of plasma processes is already used in medical technology. They adjust the wettability of material surfaces and provide special anchor functions for biologically active molecules.” Christian Oehr’s research has shown how layers with various functions can be applied to surfaces. Summarising, he says “Plasmas can be used to manufacture thin layers to release active substances or to improve gliding properties or they can be used for their sterilising effect.”

The new microdiaphragm gas pump by KNF Neuberger GmbH in Freiburg.

The shape of the pump diaphragm was first brought right up-to-date and optimised on the basis of calculations; the traditional flat diaphragm was replaced by a tension-optimised structure.

Professor Thomas Hirth conducts research at the University of Stuttgart and at the Fraunhofer Institute for Interfacial Engineering and Biotechnology His work on plastics has shown, among other things, how important these materials have become in medical technology.

Plastics make up 50% of all the materials used in this area. The main applications are hygiene accessories, syringes and catheters, plus wound dressing materials and dialysis equipment. Disposable articles are primarily made of polyethylene, polypropylene, polystyrene and polyvinylchloride. They make up 80% of total usage.

However, according to Thomas Hirth, the use of functionalised plastics will grow above average in medical technology over the next few years. In his view, this is because “Plastics are easy to modify and therefore also functionalise as they are processed, by compounding, with additives and chemical reactions. Surface functionalisation can be carried out in the shaping process and also afterwards.”

In his research he starts with the material when looking at the modification and functionalisation of plastic surfaces for medical products in contact with biological matter. Its composition, processing and shape must result in surface properties which are easier to coat, modify and functionalise.

Thomas Hirth is convinced: “Medical technology needs functionalised plastics. However, the full bandwidth of options will only be available if key medical technologies such as biotechnology and cell technology interlink more closely with microelectronics and nanotechnology.” Researchers in new substances and materials, optical technologies, microsystems and IT must therefore synergise more when evaluating their results.

Bio-based plastics with bionic and biomimetic structures also have great potential for wetting, adhesion and friction functions inside the body. Prof. Klaus-Peter Hoffmann, is Head of the Department of Medical Engineering & Neuroprosthetics at the Fraunhofer Institute for Biomedical Engineering IBMT in St. Ingbert. This is also his field of expertise. “When the body’s own interfaces no longer function, due to disease or trauma for example, miniaturised electronic implants can modulate, bypass or even replace nerve structures or their functions.”

In-built sensors receive signals from the body and convert them to electronic stimuli which act on muscles or nerve cells or actuate technical systems such as an artificial hand. Innervation patterns are digitally processed, amplified and filtered to become control signals which move the prosthesis in an almost natural way. Klaus-Peter Hoffmann says “Even feedback is possible: sensors in a hand prosthesis can signal the temperature of the object it is gripping to a microprocessor implant in the lower arm, so that a sensation of temperature is produced in the relevant areas of the brain.” Basic research of this kind can also make an innovative contribution to limb prostheses. They function particularly well if the artificial joint can be controlled as simultaneously as possible and with a minimum of friction.

Fluid materials are being developed in which the flow properties are changed by electrical or magnetic fields, which means that mechanical components are not required to actuate valves and couplings, thereby making a significant improvement to the patient’s quality of life. These innovative prostheses follow the natural pattern of movement more closely.

Robert Wouters


German Summary

Damit aus Ideen auch anwendungstaugliche und marktreife Produkte werden können, sind zuerst Neuentwicklungen auf der Werkstoffseite nötig. Und die ist alles andere als untätig: Das Spektrum reicht von neuen, ‚intelligenten‘ Kombinationen bekannter Werkstoffe, der Entwicklung funktionsgerechteter Be- und Verarbeitungsmethoden, den funktionalisierten Kunststoffen, den innovativen Biomaterialien bis hin zu hochkomplex aufgebauten Implantaten oder Neuroprothesen. Der deutschsprachige Beitrag ist nachzulesen auf www.meditec-international.com/medi0511shap