The idea behind our bandage material was first to reformulate a medical question, solve it by mathematical novelty, and then realize it through the technical development of a smart textile.
To provide the pressure against a leg, a certain tensile force is required in the bandage being applied. The higher the stretching force that is used, the higher the sub-bandage pressure becomes. Different leg radii give different pressures at the same stretching force. The smaller the radius, the higher the sub-bandage pressure becomes.
By calculating these ratios precisely, one can get a specification of the optimal elastic properties of the bandage material. The basic principle of our bandage is that if we use the same amount of material for each turn around the leg, we need to stretch more if the radius is large (e.g. at the calf), but when the radius becomes less (eg. the ankle) we need to stretch less. Due to the specific elastic material properties our bandage, a constant pressure along the entire leg is delivered, invariant of changes in limb size and curvature. This elasticity characteristic can best be illustrated as a bandage material that provides a long and horizontal curve in the diagram.
Based on the Law of LaPlace
We have slightly extended the formulation of the Laplace’s Law to three (instead of two) factors. That is, the pressure obtained by a compression bandage depends on the following three factors: 1) the longitudinal tension in the bandage (i.e. how much you stretch the bandage), 2) the thickness (i.e. the amount of overlap between different turns of the bandage), and 3) the curvature of the profile of the object (i.e the curvature of a leg, for example).
Mechanism of action
The underlying idea is to make the tension and curvature work against each other. First, one makes sure both the overlap is constant (by adding a longitudinal guideline along the bandage - see picture below) and the amount of textile for each turn is also invariant (by making sure the shorter lines, perpendicular to the longitudinal overlapping line, are aligned – see the picture ot the right). This implies that the applicator must stretch more on the thicker parts of the limb in order for the tension to increase. At the same time, however, the curvature of the limb is less on the thicker regions of the leg. By controlling the elasticity property of the material, these two features – higher tension and less curvature – will completely compensate each other, resulting in a constant pressure.