Willi Schwotzer

Praxistauglichkeit und Trends

Um für den praktischen Einsatz geeignet zu sein, muss ein Klebsystem eine ganze Reihe an Kriterien erfüllen. Obwohl die Hafteigenschaften für technische Anwendungen eine wichtige Rolle spielen, garantieren sie noch lange keinen wirtschaftlichen Erfolg. Ebenso wichtig sind die Verfügbarkeit der Rohstoffe, die Reproduzierbarkeit bei der Produktion, eine gleichbleibende Qualität sowie das Preis-Leistungs-Verhältnis im Vergleich zu anderen Technologien. Im Medizinbereich kommen noch toxikologische und allergenrelevante Aspekte hinzu. Die wahrscheinlich größte Hürde, die es für einen biologischen Klebstoff auf dem Weg zur Vermarktung zu überwinden gilt, sind die Herstellkosten. Sie liegen vergleichsweise hoch, da die Natur ihre Ressourcen sehr effizient nutzt und die Hochleistungsklebstoffe nur in kleinsten Mengen punktgenau produziert. Dadurch wird die Extraktion größerer Mengen erschwert. Zudem handelt es sich in den seltensten Fällen um reine Stoffe, sondern in der Regel um komplexe Reaktivsysteme, deren Komponenten vom Organismus erst bei der Applikation gemischt werden. Angesichts des derzeitigen Stands der Technik ist eine Produktion mit Hilfe rekombinanter DNS offensichtlich zu komplex oder — mit anderen Worten — zu kostspielig. Für die Marktchancen biogener Klebstoffe gilt die Bedingung, dass deren Nutzen die hohen Kosten rechtfertigen muss.

Practicality and trends

To be practicable, an adhesive system must fulfil a wide range of criteria. While the technical adhesion profile plays a significant role, it does not constitute a guarantee for commercial success. Equally important criteria include the availability of raw materials, reproducibility in production, and consistent quality, as well as the price/performance ratio in comparison with alternative technologies. In medical applications, toxicological and allergy-relevant aspects must be considered as well. The most likely biggest obstacle that a biological adhesive must overcome en route to commercialization is manufacturing cost. It is comparatively high because nature is extremely resource-efficient: it produces high-performance adhesives only in very small amounts and only at precisely determined points. This limits the extraction of larger quantities. Moreover, such adhesives are rarely pure substances; as a rule, they are complex reactive systems whose components are not mixed by the organism until they are applied. So obviously, given the state of the art in technology, production via recombinant DNA would be arbitrarily complex, which is to say: expensive. There is a simple rule with respect to the market potential of biogenic adhesives: their benefits must justify the high cost.

Challenges and opportunities

Nature’s adhesion and bonding techniques are highly fascinating for laypeople and professionals alike. Fundamentally, all living organisms are glued together: most of their components are connected by adhesive bonds. Particularly among primeval life forms, there are many organisms for which gluing is vital in conjunction with procuring food, locomotion, affixation, and defense. Frequently cited examples include the prey-trapping structures of some carnivorous plants, the adhesion organs of insects and reptiles, the cements of mussels and barnacles, or the mucus of amphibians and snails. Many of these bioadhesives perform in ways that man-made products can hardly match, if at all. Some are reversible, others even work underwater, and many are universal in their performance to the substrates to which they can bond. For these reasons, it is not surprising that reports on adhesion in nature rank among the regularly recurring topics in the science sections of newspapers or in popular science journals. Such articles rarely omit the assumption that biogenic adhesives will soon revolutionize medical joining technologies and totally supplant classic surgical sutures, staples, or screws. Things look different in the real world, however. There, the deployment of biogenic or biomimetic systems is the exception rather than the rule.[1] Why is there such a disparity between vision and reality?

On-the-spot adhesives

In many applications, adhesive bonding is the preferred joining technology because it takes place almost exclusively on the material surface. Adhesive bonding is minimally invasive: the forces that build up between structural elements are distributed across the surface of the material boundaries. The materials themselves are neither mechanically compromised nor exposed to high thermal loads as is the case in welding. That has many advantages. Considerably fewer stress peaks occur in comparison with spot-type joints, for example. Additionally, adhesive bonds require no backfills, making it easily possible to join very thin substrates. Different coefficients of expansion between materials can be accommodated by the suitable selection of the joint material and the joint dimensions.