Network formation of lipid membranes: Triggering structural transitions bychain melting

Phospholipids when dispersed in excess water generally form vesicular membr ane structures. Cryo-transmission and freeze-fracture electron microscopy a re combined here with calorimetry and viscometry to demonstrate the reversi ble conversion of phosphatidylglycerol aqueous vesicle suspensions to a thr ee-dimensional structure that consists of extended bilayer networks. Thermo dynamic analysis indicates that the structural transitions arise from two e ffects: (i) the enhanced membrane elasticity accompanying the lipid state f luctuations on chain melting and (ii) solvent-associated interactions (incl uding electrostatics) that favor a change in membrane curvature. The materi al properties of the hydrogels and their reversible formation offer the pos sibility of future applications, for example in drug delivery, the design o f structural switches, or for understanding vesicle fusion or fission proce sses.