Application of Solid Lipid Nanoparticles for Delivery of Hydrophilic Drugs: PEG Coating
To avoid the uptake by phagocytic cells and to improve the biodistribution ofdrugs for a prolonged time, surface modification of SLNs using PEG polymers has been reported [69,70]. PEG polymers consist of hydrophilic and hydrophobic residues that help to incorporate the lipophilic SLN by shell formation surrounding it (Fig. 12.5) . Thus PEG attaches covalently to SLNs and sterically stabilizes them with formation of a hydrophilic protective layer. This prevents aggregation ofnanoparticles and improves the overall formulation stability. In a study, levothyroxine, a poorly soluble drug, was formulated into SLN by microemulsion technique. It was then coated using PEG-100-S. It was found that there was an increase in stability of SLN in varied pH of the gastrointestinal tract. There was a reduction in the zeta potential values from —40.0 to —23.0 mV for uncoated and PEG 100-S-coated SLN. This could be attributed to partial surface charge neutralization by PEG coating .
Figure 12.5 Polyethylene glycol (PEG)-coated solid lipid nanoparticle (SLN) and its molecular residues. (Modified from Uner M, Yener G. Importance of solid lipid nanoparticles (SLN) in various administration routes and future perspectives. Int J Nanomedicine 2007;2:289.)