BPS2026 – Thermal actuation drives hexagonal peptide domain formation in peptide polymer amphiphile-lipid hybrid membranes

Peptide-polymer amphiphile (PPA) and phospholipid (PL) hybrid membranes offer a promising platform for stimuli-responsive biomimetic systems with potential applications including drug delivery and biosensing. Determining the morphology of those two components’ hybridization remains challenging for achieving advantageous properties. Here, the self-assembly and temperature-dependent morphological behavior of multilamellar membranes formed from two lengths of poly( N -isopropylacrylamide)- block -poly(γ-benzyl- l -glutamate (PNIPAM- b -PBLG) PPAs and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) was systematically investigated. Morphological changes were evaluated by thermal actuation as a function of PPA length by using small angle X-ray scattering (SAXS), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM). The results show that hexagonal and lamellar phases coexist in short-peptide hybrid system, but rather than forming separate domains, the system features lamellar lipid layers that contain embedded regions of hexagonally packed PPA-pockets. As supported by X-ray scattering and microscopy data, hexagonal close packed (HCP) order of individual peptide pockets within an extended lamellar matrix was observed. Heating above PNIPAM's LCST causes thermal collapse of the PPA, as the domains became hydrophobic. Lipid layers unzip to accommodate the shrinking pockets, allowing considerable membrane restructuring. In contrast, the long-PPA hybrid has lamellar phases only for each component with minimal change upon thermal stimulation, since the longer PPA chains entangled and kinetically restrict insertion and reorganization within the bilayer, resulting in negligible lipid d -spacing changes and only minor compression of the PPA domains as obtained from SAXS data. This work advances the understanding of hybrid membrane system structures, which are critical for applications such as drug delivery and ion conductivity. The temperature responsiveness, polymer architecture, and hybridization conditions can yield diverse structures and morphologies, profoundly influencing the potential uses of these multilamellar membranes.