Abstract
AbstractMicropatterning of hydrogel has brought innovative outcomes in fundamental and applied material sciences. Previous approaches have mainly been dedicated to fabricate arrays of bulk hydrogel beads, which have inherent challenges including loading ability, scalability, specificity, and versatility. Here, a methodology is presented to create hollow microcapsule arrays from sessile microdroplets. The difference in wettability between hydrophilic and hydrophobic surfaces enables self‐partitioning of liquid into microdroplet arrays, serving as microreservoirs to load complementarily functionalized host–guest polymers, cucurbit[8]uril‐threaded highly branched polyrotaxanes (HBP‐CB[8]) and naphthyl‐functionalized hydroxyethyl cellulose (HEC‐Np). The interfacial dynamic complexation between positively charged HBP‐CB[8] and HEC‐Np occurs in the presence of negatively charged surfactants, resulting in condensed supramolecular hydrogel skins. The hydrogel microcapsules are uniform in size and are developed to encapsulate target cargos in a robust and well‐defined manner. Moreover, the microcapsule substrates are further used for surface enhanced Raman spectroscopy sensing upon loading of gold nanoparticles. This facile assembly of microcapsule arrays has potential applications in controlled cargo delivery, bio‐sensing, high‐throughput analysis, and sorting.
Highlights
Micropatterning of hydrogel has brought innovative outcomes in fundamental and applied material sciences
They enable extremely small-volume, high-throughput and compartmental manipulations. Such hydrogel compartmentalization can be readily designed from various stimuli-responsive polymers, imparting the microarrays with responsiveness/adaptability to environmental changes. This fabrication process has been extensively investigated, considerable efforts are dedicated to bulk hydrogel beads or patterns for capturing chemical or biological samples.[17,18,19]
Complementarily-functionalized polymers in an aqueous phase accumulated at the water/oil interface with the presence of charged surfactants.[22]
Summary
On account of the electrostatic interactions between the positively-charged HBPCB[8] (microdroplets) and complementarily-charged perfluorinated dopant (oil phase), the polymer components preferentially accumulated at the droplet interface.[22,35] CB[8]-mediated host-guest complexation between HBP-CB[8] and HEC-Np promoted the formation of a hydrogel skin as well as the supramolecular capsule arrays (Figure 1b). In addition to providing the interface for complexation, the oil layer suppresses the capillary flow from the droplet centre to its edge, ensuring uniform distribution, other than the coffee-ring effect, of polymer components throughout the entire droplet during water evaporation.[36,37] Subsequently, supramolecular hydrogel skin formed at the micropatterned areas
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