Dependence of aggrecan self-adhesion on Ca2+ concentration. (a) Maximum adhesion forces, Fad (open symbols), and (b) total adhesion energy, Ead (solid symbols), as a function of surface dwell time, t, between two opposing aggrecan layers in NaCl + CaCl2 solutions, [Cl−] = 0.154 M at varying [Ca2+], pH ≈ 5.6 (z ≈ 4 μm/s, Fmax ≈ 45 nN; mean ± SE, n ≥ 30 for each surface dwell time, t, at each IS). Statistically significant differences were observed for Fad and Ead at different [Ca2+] (two-way ANOVA test, p < 0.0001).