(616e) Lateral Segregation in Polymer Nanocarriers

Nanocarriers, such as polymeric nanoparticles, micelles and liposomes show great possibilities in biomedical applications, for example for drug delivery or as imaging agents for biodetection and biolabeling. Direct biological applications of most nanoparticles for imaging or pharmaceutics are hindered by the hydrophobicity of the particles. To improve their solubility and biocompatibility the nanoparticles can be tethered with hydrophilic polymers or similarly embedded in the core of a polymer micelle. Experimental relevant examples of nanocarriers involve nanometer sized micelles made of short diblock copolymers of polyethylene glycol and phospholipids. An important feature of these 'nano' micelles is that the polymers are mobile. They have a liquid-like disorder similar to the positional disorder found in lipid bilayers. We used a molecular theory, that explicitly include the size, shape, and conformations of all molecules, to investigated the effect of the mobility on the structure of the polymers and on the binding of nanocarriers to a cell surface. The effect of two types of polymers of two different molecular weights is also investigated. A nanocarrier containing several types of polymers can have multiple functions, e.g. simultaneous selective targeting, imaging and drug delivery. In micelles that contain chains of different molecular weights, the long and short polymer chains segregate upon approaching a surface. The short chains are preferentially located near the surface, whereas the longer chains are located at the opposing side of the nanocarrier. The extent of the segregation is controlled by the total number of polymers, the relative amount and length of short and long polymers. Combining surface mobility with binding of the end-segments to the surface can be used to control the attraction of the nanocariers to the surface. The segregation, allowed by the surface mobility of the polymers and absent for immobile chains, can potentially be used to enhance the strength and selectivity of the binding of nanocarriers to a cell.