  Protein brushes not only play a key role in the functionality of
neurofilaments but also have wide applications in biomedical materials. Here,
we investigate the effect of ionic strength on the morphology of protein
brushes using a continuous-space self-consistent field theory. A coarse-grained
multi-block charged macromolecular model is developed to capture the chemical
identity of amino acid sequences. For neurofilament heavy (NFH) brushes at pH
2.4, we predict three morphological regimes: swollen brushes, condensed
brushes, and coexisting brushes which consist of both a dense inner layer and a
diffuse outer layer. The brush height predicted by our theory is in good
agreement with experimental data for a wide range of ionic strengths. The
dramatic height decrease is a result of the electrostatic screening-induced
transition from the overlapping state to the isolated state of the coexisting
brushes. We also study the evolution of the scattering and mechanical responses
accompanying the morphological change. The oscillation in the reflectivity
spectra characterizes the existence and microstructure of the inner condensed
layer, whereas the shoulder in the force spectra signifies the swollen
morphology.
