Visualization of the structure of native human pulmonary mucus

Area of Science:

• Biophysics
• Materials Science
• Respiratory Medicine

Background:

• Human respiratory mucus presents a significant barrier to inhalation therapeutics.
• Understanding mucus structure is vital for efficient drug delivery development.
• Conventional electron microscopy techniques may alter mucus structure due to vacuum conditions and sample preparation.

Purpose of the Study:

• To investigate the impact of dehydration on human respiratory mucus structure.
• To analyze the native structure of mucus in its hydrated state.
• To visualize the nano-scale organization of mucins within hydrated mucus.

Main Methods:

• Cryo-scanning electron microscopy (Cryo-SEM) to observe structural changes during sublimation.
• Environmental scanning electron microscopy (ESEM) to analyze hydrated mucus structure under varying pressures.
• Stimulated emission depletion (STED) microscopy to resolve nano-scale mucin patterns.
• Confocal laser scanning microscopy (CLSM) to assess the general structural organization of mucus components.

Main Results:

• Cryo-SEM revealed that mucus transforms from a non-porous to a porous structure during sublimation.
• ESEM demonstrated a non-porous structure for hydrated mucus, significantly altered by dehydration.
• STED microscopy successfully visualized the nano-scale patterns of MUC5B mucin in hydrated mucus.
• CLSM indicated a heterogeneous and composite structure of mucus components.

Conclusions:

• Hydrated mucus possesses an essentially pore-free structure, challenging conventional microscopy.
• Dehydration significantly alters mucus structure, impacting its native state.
• Advanced microscopy techniques provide novel insights into mucus's native structure, essential for drug delivery advancements.