2.2.7. Polyacrylic and Polyvinyl Polymers Synthetic polyacrylic and polyvinyl polymers bearing hydrophobic moieties have been prepared to coat liposomes. The hydrophobic function allows for the polymer anchoring on the particle surface.

Palmitoyl- or phosphatidylethanolamine- (PE-) terminated derivatives of poly(acryl amide) (PAA), poly(vinyl pyrrolidone) (PVP), and poly(acryloyl morpholine) (PAcM) have been found to exert comparable stealth effects on liposomes in vivo. This behaviour depends on the length of the hydrophobic Inhibitors,research,lifescience,medical alkyl function, the polymer molecular weight, and its surface density [88, 89]. Comparative studies performed with palmitoyl-or PE-functionalized 6–8kDa PAA, PVP, and PEG showed Inhibitors,research,lifescience,medical that the PEG derivative has slightly better performance as compared to the other polymers. Macromolecules containing shorter hydrophobic moieties than palmitoyl- or phosphatidylethanolamine-, namely, Inhibitors,research,lifescience,medical dodecyl alkyl chains, or higher polymer molecular weight (12–15kDa) showed a lower effect on circulation time of liposomes. Short hydrophobic moieties cannot efficiently anchor the polymer on the liposome surface as the energy of the polymeric chain motion is higher

than the energy of the anchoring alkyl chain interaction with the liposomal phospholipid bilayer [88, 90]. The Inhibitors,research,lifescience,medical higher the polymer molecular weight, the higher the free energy of the exposed polymer chains. Therefore, the polymer can detach in vivo inducing liposome opsonisation and removal by the RES [91]. The layer thickness of poly(vinyl Inhibitors,research,lifescience,medical alcohol)s (6, 9, and 20kDa PVA) derivatized with C16H33–S– as hydrophobic anchor (PVA-R) on the liposome surface was directly proportional to the polymer molecular weight and to the concentration of the polymer solution used

for the coating process. Furthermore, it was found that the PVA-R density on the liposome surface increased as the molecular weight of the polymer decreased. The PVA-R on liposomes was not detached by dilution or in presence of serum while preventing the adsorption of plasma proteins. In vivo the PVA-R-BIX 01294 supplier coated liposomes showed prolonged permanence Chlormezanone in the circulation, which increased as the PVA molecular weight increased. The circulation time of liposomes coated with 1.3% mol of 20kDa PVA-R was comparable to that of liposomes coated with 8% mol of 2kDa PEG-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (PEG-DSPE). Detailed investigations showed that the increased permanence in the bloodstream was strictly related to the PVA-R stability on the liposome surface that was higher compared to PEG-DSPE [92]. 2.3.