"It is just not feasible to think of screwing on micro-level"

Thomas Gesang is an expert in micro-bonding at the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM). COMPAMED.de talked to the chemist about special aeroplanes, endoscopes and glueing in the crisis.

COMPAMED.de: Mister Gesang, in the nearer future there may be aeroplanes, whose separate parts are not fixed by rivetting but by sticking. Would you fly with such a plane?

Thomas Gesang: Yes, of course. If you glue professionally, it will be safe. However, the bonding process should be controlled carefully.

COMPAMED.de: So glueing is a solid joining technology. Or is it inferior to other technologies?

Gesang: Each joining technology has advantages and disadvantages. High punctiform stability cannot be obtained by glueing, for example. This is only possible by welding. That is why you will need bigger surfaces, if you bind something by glueing. The advantage of sticking is, that it connects different materials like glass, plastic, ceramic or metal. Furthermore, there is a miniaturisation trend. You are forced to glue since it is just not feasible to think of screwing on micro-level.

COMPAMED.de: Everything is getting smaller in technology, also in medical technology. I suppose that you, as head of Production Techniques and Adhesive Bonding for Microsystems and Medical Technology at the IFAM, are hardly able to cope with all the orders.

Gesang: That is safe to say. There are really a lot of orders in the field of micro-bonding, even in times of the finance crisis. There is only a little decrease in demand.

COMPAMED.de: In which medical fields is glueing especially demanded?

Gesang: It is being examined how human body tissues can be glued in order to replace sutures. In medical technology micro-bonding is especially important for endoscopes and intelligent implants.

COMPAMED.de: To glue endoscopes is a challenge. What is problematic?

Gesang: Mainly, we have problems with the optics. During sterilisation, the endoscope is heated to about 140 degrees and abruptly cooled down to room temperature again. The glasses expand unequally challenging the adhesive layers which are only five to ten micrometres thin.

COMPAMED.de: You have developed a solution for exactly this problem.

Gesang: Yes, the theory behind it is related to tension. An adhesive sealing has an internal tension and the temperature acts as external tension. We thought: the less internal tension exists, the more external the adhesive layer has to bare. We experimented and simulated and tested materials and hardening processes until we had a thermo shock stable adhesive sealing. That is a sealing whose internal tension was sufficiently decreased.

COMPAMED.de: Especially for medical applications special glues are needed, which can be used inside the body as well. Just think of insulin pumps, cochlea implants or internal pressure sensors for eyes. Are there enough biocompatible adhesives?

Gesang: Actually, it is difficult to find biocompatible adhesives. Glues have to fulfil diverse requirements: they may not be too liquid but also not too stiff, they have to be transparent and so on. Often, it is hard work to find a manufacturer that produces a suitable adhesive. And there are definitely too few manufacturers that produce biocompatible types. The demand exceeds the range of offers by far. There is still a huge market potential.

COMPAMED.de: What kind of future do you predict for micro-bonding?

Gesang: A gigantic one! The materials that have to be bonded are getting more and more manifold. The miniaturisation is gaining more and more in importance. In many cases, there is simply no other possibility to connect than by micro-bonding.

The interview was conducted by Wiebke Heiss.