Multi-responsive hydrogel structures from patterned droplet networks

Thesis

Responsive hydrogels that undergo controlled shape changes in response to a range of stimuli are of widespread interest for use in microscale soft robotics and biomedical devices. However, existing fabrication methods cannot easily produce patterned multi-material structures. This thesis describes a novel approach for producing 2D- and 3D-patterned, multi-material, multi-responsive hydrogels, on a μm to mm scale, templated by droplet networks. Droplet networks are assemblies of aqueous droplets formed in a lipid-containing oil, and connected by droplet interface bilayers (DIBs). Within the compartmentalised structure of a droplet network, 3D patterning of multiple types of aqueous droplet is possible. Initially, nanolitre N-isopropylacrylamide (NIPAm) pre-gel droplets were assembled into networks in a range of 2D and 3D geometries. Polymerization across the lipid bilayers then resulted in continuous poly(N-isopropylacrylamide) (PNIPAm) hydrogel structures that reversibly contracted when heated and cooled. Exploiting the ability to modulate the temperature response of PNIPAm, and form multi-material structures using droplet networks, enabled the fabrication of structures capable of non-uniform shape changes, such as curling. Subsequently, additives were incorporated into the hydrogel structures that imparted additional functionality, including lightcontrolled shape change and magnetically controlled locomotion. By utilising a mechanism for dual temperature control, this would allow the fabrication of a magnetically controlled gripper-like device. Finally, the adaptation of a 3D droplet printer to automate the fabrication of PNIPAm hydrogel structures is described. With the droplet printer, networks composed of picolitre droplets were produced, which will allow higher resolution patterning. Furthermore, automated droplet generation enables the precise placement of hundreds to thousands of droplets. Successful implementation of this technology will allow the formation of multimaterial responsive hydrogels from networks composed of thousands of droplets, patterned to a resolution of tens of microns.

Authors: Downs, F

• DOI: 10.5287/ora-rd0x0zg6m
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English