Mechanistic insights into the directed assembly of hydrogel blocks mediated by polyelectrolytes or microgels
Article [Accepted Manuscript]
Abstract(s)
In this study, we report the directed assembly of hydrogel blocks mediated by
electrostatic interactions. We compared two different assembly mechanisms, one
mediated by microgel particles and another mediated by direct interaction between
oppositely charged blocks. The system consisted of hydrogel blocks made of an
interpenetrated network of (hydroxyethyl)methacrylate-poly(ethylene
glycol)dimethacrylate (HEMA-PEGDMA) and either positively charged
polyethylenimine (PEI) or negatively charged hyaluronic acid (HA). Positively
charged hydrogel blocks were pretreated with negatively charged microgel
particles (MG) made of N-isopropylacrylamide-methacrylic acid. Both systems
(PEI/HA and PEI/MG) demonstrated spontaneous directed assembly, meaning that
positive blocks were systematically found in contact with oppositely charged
blocks. Directed assembly in water of PEI/HA blocks resulted in large and open
aggregates, while PEI/MG blocks exhibited more compact aggregates. Effects of
salt and pH were also assessed for both systems. Inhibition of blocks aggregation
was found to appear above a critical salt concentration (CSalt*) which was
significantly higher for the PEI/HA system (80 mM) compared to the PEI/MG system
(5-20 mM). The observed difference was interpreted in terms of the nanostructure
of the contact area between blocks. Blocks aggregation was also found to be
controlled by the content of negatively charged groups in the microgels as well
as the concentration of MG in the suspension (CMG) used to treat the hydrogel
block surfaces. Our results shine light on the subtle differences underlying the
adhesion mechanisms between hydrogel blocks and suggest new routes toward the
design of innovative complex soft materials.
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