Figure 4: Adhesion measurements.

(a) Shows the force-extension curves obtained by peeling the scaffolding discs (blue) and gumfoot discs (green) spun on a clean glass surface. Data are plotted as mean±s.d. from three measurements each. Inset emphasizes the initial region of the force-extension curve of the gumfoot disc. (b) Shows the force required to separate a gumfoot disc and a scaffolding disc from a clean glass surface. Gumfoot disc adhesion is an order weaker than scaffolding disc adhesion. The force required to break a dragline silk (MA silk) thread is also plotted. A dragline silk thread breaks when it is pulled to peel a scaffolding disc (hence thicker nylon threads were used to peel scaffolding discs). Gumfoot discs were peeled using the gumfoot silk threads (four intertwined MA threads). Data are plotted as mean±s.d. from five measurements each. In theory, however, gumfoot discs could be peeled using just one MA thread as the breaking force of MA thread is almost twice the pull-off force of gumfoot discs with glass. This indicates that scaffolding disc adhesion is much stronger than gumfoot disc adhesion. (c) Shows the energy of adhesion of a gumfoot disc and a scaffolding disc. Gumfoot discs adhere an order weaker than scaffolding discs adhere. The energy of adhesion is determined by subtracting the strain energy contribution of nylon threads (while peeling scaffolding discs) and gumfoot threads (while peeling gumfoot discs) from the total work done in peeling the discs. Data are plotted as mean±s.d, from five measurements each.