Fabrication of Acoustically Micropatterned Coacervate-Based Hydrogels

  • Maddy Nichols

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


The central theme of this thesis is to exploit the non-contact technique of acoustic trapping for the manipulation of complex coacervate microdroplets in the construction of micropatterned hydrogels and gelatinous films for biological applications. Recently, the move towards interdisciplinary research has blurred the boundaries between engineering, chemistry, physics and biology. This overlap has created exciting opportunities to combine different expertise in the construction of functional materials for desired applications.
Ordered hydrogels are achieved through in-situ coacervation followed by hydrogel transformation within an acoustic trapping device in the presence of an applied acoustic standing wave field. The higher density of the coacervate droplets compared with their surrounding aqueous phase resulted in the droplets migrating to pressure minima of the acoustic field. Coacervates preferentially sequester guest molecules, such as dyes, enzymes and other biomolecules, on their interiors and this behaviour was exploited to reveal and explore the droplet behaviours within the acoustic field and the spatially organised hydrogel networks formed using fluorescence microscopy. Significantly upon initiating the hydrogelation transformation within an applied acoustic field, the droplets transformed at their trapped positions to form self-supporting hydrogel monoliths, with patterning fixed into the hydrogel network following removal from the acoustic device in both 1D lines and 2D gridded arrays.
The ordered self-supporting hydrogels fabrication process was then adapted to produce gelatinous thin films. Through removal of the unordered material comprising the majority of the hydrogel net- work, ordered gelatinous thin films in both 1D and 2D were produced. Layering of these films enabled pursuit of higher ordered structures and more complex gel architectures. Significantly, the thin films enabled better site-specific studies of behaviours of transformed coacervate populations with different guest molecules encapsulated within the spatially fixed network, particularly cascades such as the enzymatic reactions of urease and coupled glucose oxidase and horseradish peroxidase. Further, an alternative enzymatically driven hydrogelation route was demonstrated, from the evolution of the acidic product as glucose oxidase breaks down the substrate glucose, and used in achieving more distinct layered thin films. Layering of these enzymatically gelated thin films produced convincing 3D gel structures.
Finally, a coacervate hydrogel system comprising more biologically relevant molecules was developed. Through combining adenosine monophosphate with poly-L-lysine the resulting coacervate system was shown to hydrogelate via metal coordination upon mixing with zinc chloride. For this nucleotide- based coacervate system, trapping of the droplets within the acoustic field was demonstrated and protocols were developed for transformation into both ordered hydrogels and thin films. The successful patterning of this system shows the versatility of the acoustic trapping technique across different coacervate based hydrogel systems for fabrication of micro-patterned, soft viscoelastic materials.
Date of Award23 Jan 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAdrian C Barnes (Supervisor), Avinash J Patil (Supervisor), Bruce W Drinkwater (Supervisor) & Stephen Mann (Supervisor)

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