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.

咖啡环效应（CRE）是基于液滴的处理技术的核心，在这种技术中，载有溶质的液滴的干燥过程会导致形成环状图案，而凝固的溶质分布不均匀，这是不希望的。尽管已经对CRE进行了深入研究，但文献中报道的预防CRE的实用策略仍然有限。在这项研究中，我们旨在开发一种简单实用的解决方案，通过向含有活性药物成分的药物溶液中添加聚合物赋形剂来最大程度地减少CRE。我们研究了粘度对含有聚合物（壳聚糖）和模型药物（对乙酰氨基酚）的多组分无柄液滴的影响。在玻璃上干燥后，显示出无数对乙酰氨基酚水溶液的液滴会重结晶为药物晶体的不良咖啡环图案，由于CRE。当用壳聚糖使制剂增稠时，结晶溶质的这种周边沉积被抑制。溶液粘度的增加通过将溶质固定在液滴内而阻止了CRE，从而防止了溶质径向流向液滴边缘。这项研究丰富了对抑制CRE的简单实用解决方案的机械理解，该解决方案可以在包括制药在内的许多工业领域得到广泛应用。