Where δ is the penetration depth, f the resonating frequency (related to the overtone number i.e: f3 = f0 * 3) η is the viscosity and ρ the density of the film. PBS was applied as running buffer and NaCl (1M) was used to remove any residual BMP left on the brushes before the next injection. BMPs were injected rapidly (100 μL/min) for 90 s until a plateau was achieved with a peristaltic pump (IPC4, Ismatec), while buffer solutions were continuously injected (15 μL/min).