Polyamidoamine (PAMAM) dendrimers, a class of polymeric nanoparticles
(NPs) with highly-controllable sizes and surface chemistry, are promising
candidates for many biomedical applications, including drug and gene delivery,
imaging, and inhibition of amyloid aggregation. In circulation, binding of serum
proteins with dendritic NPs renders the formation of protein corona and alters
the biological identity of the NP core, which may subsequently elicit
immunoresponse and cytotoxicity. Understanding the effects of PAMAM size and
surface chemistry on serum protein binding is, therefore, crucial to enable
their broad biomedical applications. Here, by applying atomistic discrete
molecular dynamics (DMD) simulations, we first uncovered the binding of PAMAM
with HSA and Ig and detailed the dependences of such binding on PAMAM size and
surface modification. Compared to either anionic or cationic surfaces,
modifications with neutral phosphorylcholine (PC), polyethylene glycol (PEG),
and hydroxyls (OH) significantly reduced binding with proteins. The relatively
strong binding between proteins and PAMAM dendrimers with charged surface groups
was mainly driven by electrostatic interactions as well as hydrophobic
interactions. Using steered DMD (SDMD) simulations, we conducted a force-pulling
experiment in silico estimating the critical forces separating
PAMAM-protein complexes and deriving the corresponding free energy barriers for
dissociation. The SDMD-derived HSA-binding affinities were consistent with
existing experimental measurements. Our results highlighted the association
dynamics of protein-dendrimer interactions and binding affinities, whose
implications range from fundamental nanobio interfacial phenomena to the
development of “stealth NPs”.