buffer, a substantial recovery of the frequency and dissipation was observed in the case of BMP4, in agreement with the weaker binding and surface densities measured by SPR. Overall, surface densities extracted from QCM-D experiments for both BMP2 and BMP4 are aligned with SPR observations, indicating significantly higher adsorption levels with dense and thick HD-30 brushes, and significantly higher binding of BMP2 (Figure ). The higher surface densities quantified by QCM-D reflects the sensitivity of this technique to hydrated mass, although it is not clear whether this originates from the hydrated sphere of the proteins adsorbed alone, or whether this is also associated with conformational changes and swelling of the brushes too, as was evidenced during the binding of oligonucleotides to PDMAEMA brushes, via neutron reflectometry .