teaching
Evolutionary Biomaterials Group

 

FrictionAdhesionMaterial

The construction of the head-prothorax articulation in adult dragonflies (Odonata) has no analogies in other groups of insects. Because of the weak mechanica strength of the head, the arresting system serve for the head stabilisation in some particular behavioural situations (figure: SEM picture of the neck part of the dragonfly arrester)

Snakes possess scales adapted for friction optimisation in various directions in different behavioural situations (figure: SEM picture of the ventral skin surface in a snake)

Fruits and seeds of many plants possess hooking structures promoting diaspore dispersal by animals. The hooks contact animal hairs, interlock, and are transported by the animals for some distance from the parent plant. The mechanical and frictional properties of the huge variety of plants employing the hook principle remain unknown (figure: SEM picture of the hooks of the Galium aparine fruit)

In joints of vertebrates and invertebrates, complementary surfaces are optimised for reduction of the contact area and friction minimisation. Underlying tissues are penetrated with canals responsible for delivering lubricants to the area of contact (figure: SEM picture of the contacting surface in a beetle leg joint)

 

Any movement involving contact between two surfaces or between a surface and a medium, deals with the resistance of the surfaces or medium. This resistance is called friction, a phenomenon which has a complex nature and great influence on the biological contact structures.

Living creatures have developed highly elaborate systems for decreasing friction (anti-frictional systems), and vice versa, for increasing it (frictional systems). Interestingly, in both cases the purpose of such a system is to save energy. One always needs friction to generate force for overcoming the drag caused by friction elsewhere. For example, in the case of terrestrial locomotion, for effective propulsive movements, high friction is necessary in contact to the substratum, and lower friction within the joints. Surface microsculpture and mechanical properties of biological surfaces are important parameters for the understanding of the resulting friction on various substrata.