AFM Colloidal Probe Measurements Implicate Capillary Condensation in Punch-Particle Surface Interactions during...

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Surface Chemistry

Background:

• Powder adhesion to tableting tools (sticking) is a critical issue affecting tablet quality and manufacturing costs.
• Predicting powder-tablet interactions before scale-up is essential for efficient pharmaceutical manufacturing.
• Surface-surface adhesive interactions primarily govern a powder's propensity to adhere to tooling.

Purpose of the Study:

• To model punch-particle surface interactions during tableting using atomic force microscopy (AFM).
• To characterize the adhesive forces between key pharmaceutical ingredients (ibuprofen, MCC, lactose) and a steel surface.
• To elucidate the mechanisms behind material-specific adhesion during the tableting process.

Main Methods:

• Atomic force microscopy (AFM) with a steel colloidal probe was employed.
• Measurements quantified adhesive interactions between ibuprofen, microcrystalline cellulose (MCC), and lactose particles with a steel surface.
• Force-distance curves were analyzed to understand the nature and magnitude of adhesive forces over multiple contacts.

Main Results:

• Excipients (MCC, lactose) exhibited weak, constant van der Waals forces with the steel probe, indicating low adhesion.
• Ibuprofen showed significantly higher adhesion, characterized by capillary forces that increased with repeated contacts.
• Ibuprofen's smooth crystal surfaces facilitated moisture 'harvesting' and condensation, leading to increased capillary adhesion.

Conclusions:

• AFM colloidal probe measurements effectively differentiate the adhesive propensities of tableting materials.
• Ibuprofen's adhesion is driven by capillary forces, while excipients exhibit weaker van der Waals interactions.
• Understanding these surface interactions provides a mechanistic basis for predicting and mitigating tableting sticking issues.