Interdigitation in spin-coated lipid layers in air

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Phospholipid bilayers are fundamental to cell membranes.
• Understanding lipid phase behavior is crucial for biomaterials and drug delivery.
• Interdigitation is a known phase in hydrated lipid systems.

Purpose of the Study:

• To investigate the formation of interdigitated phases in dry phospholipid layers.
• To determine the conditions influencing interdigitation in spin-coated lipid films.
• To compare interdigitation in dry versus hydrated lipid systems.

Main Methods:

• Spin-coating technique for preparing dry phospholipid layers.
• Atomic Force Microscopy (AFM) for morphological characterization.
• Systematic variation of lipid chain length, alcohol presence, spinning velocity, and cholesterol.

Main Results:

• Dry saturated phosphocholine layers (DLPC, DMPC, DPPC, DSPC) can exhibit thinner regions resembling interdigitated phases.
• Interdigitation in dry films is influenced by different parameters than in hydrated samples.
• DPPC and DSPC showed structures similar in height to interdigitated regions, while DLPC and DMPC did not.
• Lateral tensions were identified as the cause of interdigitation, reducible by cholesterol addition.

Conclusions:

• Interdigitation is a general phenomenon observable in dry lipid bilayers.
• The presence of lateral tensions plays a key role in dry lipid interdigitation.
• Spin-coating and AFM are effective tools for studying dry lipid phase behavior.