Poly(l-glutamic acid)-g-poly(ethylene glycol) external layer in polyelectrolyte multilayer films: Characterization and resistance to serum protein adsorption

Formation of protein-resistant surfaces is a major challenge in the design of novel biomaterials and an important strategy to prevent protein adsorption is the formation of protein-resistant coatings. It can be achieved by proper modification of surfaces, e.g., by immobilization of hydrophilic polymers such as poly(ethylene glycol) (PEG). An appropriate method to immobilize PEG at charged surfaces is the adsorption of copolymers with PEG chains grafted onto polyelectrolyte backbone. The growing interest in the use of polyelectrolyte multilayer coatings in biomedical applications to improve biocompatibility and/or to prepare coating with antiadhesive properties has been the main reason for these studies. Therefore the aim was to produce protein resistant polyelectrolyte multilayer films. They were formed via the layer-by-layer approach, while their pegylation by the deposition of pegylated polyanion, PGA-g-PEG, as an external layer. The influence of PEG chain length and grafting density of PGA-g-PEG copolymers on the protein antiadhesive properties of pegylated polyelectrolyte multilayer films was investigated. To monitor the formation of pegylated and non-pegylated multilayer films, adsorption of the following proteins: HSA, Fibrinogen, and FBS were measured by quartz crystal microbalance (QCM - D). We found that protein adsorption onto all pegylated polyelectrolyte multilayers was significantly reduced in comparison to non-pegylated ones. Long-term performance tests confirmed the stability and the durability of the protein resistant properties of the pegylated multilayers. Antiadhesive properties of tested surfaces pegylated by PGA-g-PEG were compared to the available data for pegylated polycation PLL-g-PEG.

Formation of biocompatible nanocapsules with emulsion core and pegylated shell by polyelectrolyte multilayer adsorption

The aim of this work was to develop a novel method of preparation of loaded nanosize capsules based on liquid core encapsulation by biocompatible polyelectrolyte (PE) multilayer adsorption, with or without pegylated outermost layer. Using AOT (docusate sodium salt) as emulsifier, we obtained cores, stabilized by an AOT/PLL (poly-L-lysine hydrobromide) surface complex. These positively charged cores were encapsulated by layer-by-layer adsorption of polyelectrolytes, biocompatible polyanion PGA (poly-L-glutamic acid sodium salt), and biocompatible polycation PLL. We used the saturation method for formation of consecutive layers, and we determined the optimal conditions concerning concentration of surfactant and polyelectrolytes to form stable shells. The average size of the obtained capsules was 60 nm. Pegylated external layer were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). The capsules were stable for at least a period of 3 months. These nanocapsules were biocompatible when tested for cytotoxicity in a cellular coculture assay and demonstrated no or very low nonspecific binding to peripheral blood mononuclear cells when tested by flow cytometry. In order to study drug effects on leukemia cells, beta-carotene and vitamin A have been encapsulated as model drugs.