Suppression of the coffee-ring effect by tailoring the viscosity of pharmaceutical sessile drops

Janine Wilkinson, Chak Hin Tam, Alexandros Askounis, Sheng Qi

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)
7 Downloads (Pure)


The coffee ring effect (CRE) lies at the heart of droplet-based processing techniques where the drying process of the solute-laden droplet leads to the undesirable formation of a ring-like pattern with uneven distribution of the solidified solute. Although the CRE has been well studied, the practical strategies reported in the literature to prevent CRE are still limited. In this study, we aimed to develop a simple practical solution to minimise CRE by adding polymeric excipients to pharmaceutical solutions containing active pharmaceutical ingredients. We investigated the influence of viscosity on multicomponent sessile droplets containing a polymer (chitosan) and a model drug (paracetamol). When dried on glass, a sessile droplet of an aqueous paracetamol solution was shown to recrystallise into an undesired coffee-ring pattern of drug crystals, due to CRE. This peripheral deposition of crystalline solute was suppressed when the formulation was thickened with chitosan. Increasing the viscosity of the solution prevented the CRE by immobilising solute within the droplet, preventing the radial flow of the solute to the edge of the droplet. This study enriches the mechanistic understanding of a simple practical solution to the suppression of CRE which can have wide applications in many industrial sectors including pharmaceutical.
Original languageEnglish
Article number126144
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Early online date18 Jan 2021
Publication statusPublished - 5 Apr 2021


  • Chitosan
  • Coffee ring effect
  • Droplet casting
  • Drying suspensions
  • Paracetamol
  • Solid dispersion

Cite this