Interaction of poly(N-isopropylacrylamide) (pNIPAM) based nanoparticles and their linear polymer precursor with phospholipid membrane models

Poly(N-isopropylacrylamide) (pNIPAM) is a thermoresponsive polymer which has promising applications in nanomedicine for drug delivery. The cross-linking of pNIPAM based copolymer using the chain collapse method leads to the synthesis of pNIPAM based polymer nanoparticles. This study looks at the interaction of pNIPAM polymers and pNIPAM nanoparticles with biomembrane models of, (i) a dioleoyl phosphatidylcholine (DOPC) monolayer on a mercury (Hg) electrode and (ii) DOPC and dimyristoyl phosphatidylcholine (DMPC) vesicles. The following techniques were used to follow the interactions: Dynamic light scattering (DLS), differential scanning calorimetry (DSC), rapid cyclic voltammetry (RCV) and electrochemical impedance spectroscopy (EIS). Results showed that the polymers interacted more extensively than the nanoparticles with the phospholipid. The interaction of the polymer was more rapid and led to a polymer-phospholipid conjugate whereas the nanoparticle adsorbed on the phospholipid monolayer surface and penetrated the monolayer at longer contact times. The association of the linear polymer with the phospholipid can be related to the larger molecular area available with the pendant -Cl groups and the inherent polymeric flexibility compared to the nanoparticle structure. The apparent dissociation constant for nanoparticles-DOPC complex was K-d,K-app = 1.67(*)10(-5) +/- 1.2(*)10(-6) mol dm(-3). The apparent kinetic constant of nanoparticle penetration through the DOPC monolayer was k(2,app) = 1.054(*)10(-2) +/- 9.1(*)10(-4) s(-1). It can be concluded therefore that the pNIPAM nanoparticle because of its lower affinity for phospholipids is more appropriate for medical applications. (c) 2011 Elsevier B.V. All rights reserved.