Use of Atomic Force Microscopy (AFM) to monitor surface crystallization in caffeine-oxalic acid (CAFOXA) cocrystal compacts

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Abstract

Our objective was to monitor the surface crystallization in disordered caffeine-oxalic acid (CAFOXA) cocrystals following exposure to elevated water vapor pressure. This was accomplished using atomic force microscopy (AFM). Disorder was induced in the cocrystal particles by the common pharmaceutical unit operations of milling and compaction. The ‘activated’ solid, upon exposure to elevated water vapor pressure, had a high propensity to sorb water. This led to a rise in molecular mobility and the surface underwent rapid crystallization to form needle shaped crystals of CAFOXA. Using AFM height and phase imaging, we were able to directly visualize phase transformations on the compact surface. The milled compacts exhibited higher processing induced disorder than the unmilled compacts, thereby accelerating the surface recrystallization.

Original languageEnglish (US)
Article number121196
JournalInternational journal of pharmaceutics
Volume609
Early online dateOct 16 2021
DOIs
StatePublished - Nov 20 2021

Bibliographical note

Funding Information:
This work was supported by the William and Mildred Peters Endowment Fund. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.

Publisher Copyright:
© 2021 Elsevier B.V.

Keywords

  • AFM
  • Cocrystals
  • Phase transformation
  • Surface disorder

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