Abstract
The synthesis and characterization of an ABA triblock copolymer based on hydrophilic poly(2-methyl-2-oxazoline) (pMeOx) blocks A and a modestly hydrophobic poly(2-iso-butyl-2-oxazoline) (piBuOx) block B is described. Aqueous polymer solutions were prepared at different concentrations (1–20 wt %) and their thermogelling capability using visual observation was investigated at different temperatures ranging from 5 to 80 °C. As only a 20 wt % solution was found to undergo thermogelation, this concentration was investigated in more detail regarding its temperature-dependent viscoelastic profile utilizing various modes (strain or temperature sweep). The prepared hydrogels from this particular ABA triblock copolymer have interesting rheological and viscoelastic properties, such as reversible thermogelling and shear thinning, and may be used as bioink, which was supported by its very low cytotoxicity and initial printing experiments using the hydrogels. However, the soft character and low yield stress of the gels do not allow real 3D printing at this point.
Highlights
Thermoresponsive polymers are a type of “smart” material which change their appearance and physical properties upon a change in temperature [1]
This temperature is called the “cloud point”, and it may depend on the solvent quality and polymer concentration
Thermoresponsive polymer solutions may undergo thermogelling, which can be described as a significant change in agglomeration/aggregation and which significantly increases the viscosity upon thermal stimulation [7,8,9]
Summary
Thermoresponsive polymers are a type of “smart” material which change their appearance and physical properties upon a change in temperature [1]. One very prominent thermogelling polymer is Pluronic®F127, an ABA triblock copolymer bearing hydrophilic poly(ethylene glycol) as the A blocks and thermoresponsive poly(propylene glycol) as the B block. In a recent study [47], a small library of POx-based ABA triblock copolymers were synthesized based on 2-n-propyl-2-oxazoline and 2-methyl-2-oxazoline with the aim to mimic the behavior of Pluronic®F127. These polymers did not show any gelation, even at higher concentration (20–30 wt %) even though the materials exhibit cloud points depending on the ratio between individual blocks.
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