Figure 4.

Aggrecan self-adhesion specifically requires Ca²⁺. The probabilities of the adhesion energies, as measured under different saline solution conditions, are plotted as histograms. (a) Measurement in 100 mM sodium chloride solution leads to a low binding probability of ∼3%. (b) Measurement after supplementing with 10 mM Mg²⁺ (binding probability ∼2%). (c) Measurement in original calcium binding solution increases the binding probability clearly to ∼10%. A typical force-versus-distance curve with a sawtooth profile, which leads to higher adhesion energies when measuring in calcium-binding solution, is observed only in panel c.