Polymerization from Lipid Membranes

In living cells, lipid bilayer membranes can be asymmetrically functionalized with brush-like layers of macromolecules. Here, we describe a lipid membrane-initiated polymerization reaction for the growth of thick and dense polymer brushes directly from one side of lipid membranes. By incorporating a novel lipid-based polymerization initiator into lipid bilayers, we grew poly(N-isopropylacrylamide) (PNIPAM) brushes from supported lipid bilayers (SLBs), small unilamellar vesicles (SUVs), and giant unilamellar vesicles (GUVs), via aqueous atom transfer radical polymerization (ATRP). We used quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS) to quantify growth kinetics from SLBs and SUVs. The resulting polymer brushes were up to 70 nm thick. Growth from GUVs led to the spontaneous transformation of spheroidal vesicles into dense, bush-like networks of "strings of pearls". Broadly speaking, this approach could offer improved performance for biomedical applications and a valuable in vitro model for the biophysics of asymmetric lipid membranes.