3D printing shape-changing double-network hydrogels

  • Kate Oliver

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The technique of 3D printing enables the creation of
a vast range of shapes with no setup beyond design.
Printing materials which change shape once printed,
so-called 4D printing, opens up still more
possibilities. However,
Entry Details
much prior work in 4D printing uses proprietary
equipment and hard polymers. This work presents an
alternative route using thermoresponsive hydrogels
processed using accessible, low-cost techniques. The
working material
is a tough double network hydrogel comprised of the
thermoresponsive polymer poly-N-isopropyl
acrylamide (PNIPAM) and the polysaccharide alginate,
formed by UV-initiated and ionic crosslinking
respectively.
An open-source, low-cost printer suitable for
processing this hydrogel material is presented, which
is at least a factor of 4 cheaper than alternatives and
licensed such that others may replicate or modify it.
This machine has
been used to explore a new method for generating
shape change in printed hydrogel pieces. PNIPAMalginate hydrogels, initially printed flat, adopt a
curved configuration when equilibrated in both
ambient, and thermally
contracted, conditions. The degree of curvature in
these states differs in magnitude and direction
depending on the dimensions of the printed piece
and the angle of curing. This is demonstrated with 1D
beams and gripper
shapes. Potential origins for this effect including
crosslink density and porosity variation are explored.
While no conclusive evidence is found a theory based
on solvent flow towards the first areas crosslinked is
proposed.
These findings form a complete package of
technology and material to reproduce the results
seen.
An alternative approach to changing the properties of
PNIPAM-alginate gels was trialled with the addition of
1-6μg/ml concentration of gold nanorods. Despite
the low concentration, significant effects on swelling
ratio, elastic moduli, and thermoresponse were seen.
This indicates that even at low concentrations
nanoparticles can affect the hydrogel matrix
containing them, relevant for workers on soft matter
systems.
Date of Award25 Jun 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAnnela M Seddon (Supervisor) & Steve Eichhorn (Supervisor)

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