To counter the undesired colloidal destabilization of nanoparticles in biologically-compatible media of high ionic strength (i.e. NaCl, phosphate buffer), polymers can be added to nanoparticle suspensions that will be used in biomedical applications. In these suspensions, polymers can promote high colloidal stability by manifestation of steric and/or depletion forces. However, little is known about the influence of these polymers on the interactions between nanoparticles and the biological components of the organism, such as proteins and cells. In this work, it was shown that the addition of the polymers (i) Pluronic-F127 (PF127), (ii) polyethylene glycol (PEG) of different molecular weights - 1.5, 12 and 35 kDa - and (iii) the protein bovine serum albumin (BSA) on colloidal silica nanoparticles (CSNPs; 135 nm) dispersed in phosphate-buffered saline (PBS) largely alter their colloidal stability through different mechanisms. Although all polymers were adsorbed on the CSNP surface, BSA maintained the CSNP dispersion in the medium by electrosteric stabilization mechanisms, while PEG and PF127 led to the occurrence of depletion forces between the particles. In addition, it was found that the interactions between polymers and CSNPs did not prevent proteins to access the nanoparticles' surface and have minimal effect on the formation of the protein corona when they were incubated in human blood plasma. On the other hand, BSA had a greater effect on the CSNP protein corona profile compared to other polymers (PEG and PF127). Together, these results confirm that biocompatible polymers PEG and PF127 can be used as colloidal stabilizing agents for nanoparticles since they preserve the accessibility of biomolecules to the nanoparticle surface, and they have little effect on the protein corona composition.