Controlling Spatial Distribution of Functional Lipids in a Supported Lipid Bilayer Prepared from Vesicles

Conjugating biomolecules, such as antibodies, to bioconjugate moieties on lipid surfaces is a powerful tool for engineering the surface of diverse biomaterials, including cells and nanoparticles. We developed supported lipid bilayers (SLBs) presenting well-defined spatial distributions of functional moieties as models for precisely engineered functional biomolecular-lipid surfaces. We used quartz crystal microbalance with dissipation (QCMD) and atomic force microscopy (AFM) to determine how vesicles containing a mixture of 1,2-dipalmitoyl- sn - glycero -3-phosphatidylcholine (DPPC) and 1,2-distearoyl- sn - glycero -3-phosphoethanolamine-N-[azido(poly- ethylene glycol)-2000] (DSPE-PEG-N 3 ) form SLBs as a function of the lipid phase transition temperature ( T m ). Above the DPPC T m , DPPC/DSPE-PEG-N 3 vesicles form SLBs with functional azide moieties on SiO 2 substrates via vesicle fusion. Below this T m , DPPC/DSPE-PEG-N 3 vesicles attach to SiO 2 intact. Intact DPPC/DSPE-PEG-N 3 vesicles on the SiO 2 surfaces fuse and rupture to form SLBs when temperature is brought above the DPPC T m . AFM studies show uniform and complete DPPC/DSPE-PEG-N 3 SLB coverage of SiO 2 surfaces for different DSPEPEG-N 3 concentrations. As the DSPE-PEG-N 3 concentration increases from 0.01 to 6 mol%, the intermolecular spacing of DSPE-PEG-N 3 in the SLBs decreases from 4.6 to 1.0 nm. The PEG moiety undergoes a mushroom to brush transition as DSPE-PEG-N 3 concentration varies from 0.1 to 2.0 mol%. Via copper -free click reaction, IgG was conjugated to SLB surfaces with 4.6 nm or 1.3 nm inter-DSPE-PEG-N 3 spacing. QCM-D and AFM data show; 1) uniform and complete IgG layers of similar mass and thickness on the two types of SLB; 2) a higher -viscosity/ less rigid IgG layer on the SLB with 4.6 nm inter-DSPE-PEG-N 3 spacing. Our studies provide a blueprint for SLBs modeling spatial control of functional macromolecules on lipid surfaces, including surfaces of lipid nanoparticles and cells.