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Dynamic mechanical properties |E∗(f)| (a), δ(f) (b), E′(f) (c), and E″(f) (d) versus frequency for untreated and PG-depleted cartilage disks in PBS, using hydroxyl-functionalized spherical (R ∼ 2.5 μm) and pyramidal (R ∼ 50 nm, α ∼ 35°) probe tips at ∼4 nm z-piezo displacement amplitude (∼2 nm cartilage dynamic indentation depth amplitude), estimated using Eqs. 5–8 for n ≥ 6 different locations (mean ± SE).
