Lipogels: single-lipid-bilayer-enclosed hydrogel spheres

Area of Science:

• Materials Science
• Biophysics
• Polymer Chemistry

Background:

• Hydrogel microparticles offer tunable properties for various applications.
• Lipid bilayers are fundamental structures in cell membranes and drug delivery systems.
• Thermoresponsive polymers, like poly(N-isopropylacrylamide) (pNIPAM), change volume with temperature.

Purpose of the Study:

• To fabricate and characterize novel Lipogels.
• To investigate the thermoresponsive behavior of lipid bilayers on hydrogel supports.
• To explore potential applications in drug delivery and biophysical studies.

Main Methods:

• Fabrication of hydrophobically modified (HM) pNIPAM-co-AA hydrogel spheres.
• Assembly of a single 1,2-dioleoyl-3-phosphatidylcholine (POPC) lipid bilayer onto HM microgels via liposome binding and freeze-thaw cycles.
• Characterization using fluorescence studies to confirm bilayer integrity and fusion.
• Observation of structural changes above the pNIPAM volume phase transition (VPT) temperature (~32 °C).

Main Results:

• Successfully fabricated Lipogels with a single POPC lipid bilayer on HM hydrogel spheres.
• Confirmed the presence of the pNIPAM VPT (~32 °C) in the core hydrogel, even after modification and bilayer coating.
• Observed that hydrogel volume decrease above the VPT induced highly curved lipid bilayer obtrusions.
• Demonstrated the integrity of the lipid bilayer during temperature-induced structural changes.

Conclusions:

• Lipogels exhibit temperature-dependent structural rearrangements of the lipid bilayer.
• The coupled volume change of the hydrogel and lipid bilayer creates unique membrane morphologies.
• These findings suggest potential for Lipogels in controlled drug delivery and as model systems for membrane biophysics.