Water-matrix interaction at the drop-drop interface during drop-on-demand printing of hydrogels

Hydrogel-based soft materials have been used in numerous applications in healthcare, food, pharmaceutical, and cosmetic industries. Manufacturing hydrogels whose functional properties and compositions are voxelized at superior spatial resolutions can significantly improve current applications as well as will enable a new generation of soft materials. However, it remains challenging to control the structure and composition of soft materials reliably. In this context, the drop-on-demand (DOD) printing of hydrogels shows excellent potential to address this manufacturing challenge. Despite this potential, a lack of mechanistic understanding of the behavior of printed hydrogel drops makes it challenging to design and optimize DOD printing protocols for a wide variety of hydrogels. In particular, the curing of hydrogel drops, which requires dehydration of printed hydrogel drops, is poorly understood. In this study, thus, a hypothesis was postulated and tested that water-matrix interaction at drop-drop interfaces during curing processes determine the quality of hydrogels printed. Both computational and experimental studies were performed to establish a mechanism of the water-matrix interaction within printed hydrogel drops. The results were further discussed to establish a dimensionless similarity parameter that can characterize water transports during the hydrogel dehydration process. (C) 2020 Elsevier Ltd. All rights reserved.