Abstract
Hydrogels are key components in several biomedical research areas such as drug delivery, tissue engineering, and biofabrication. Here, a novel ABA-type triblock copolymer comprising poly(2-methyl-2-oxazoline) as the hydrophilic A blocks and poly(2-phenethyl-2-oxazoline) as the aromatic and hydrophobic B block is introduced. Above the critical micelle concentration, the polymer self-assembles into small spherical polymer micelles with a hydrodynamic radius of approx 8-8.5 nm. Interestingly, this specific combination of hydrophilic and hydrophobic aromatic moieties leads to rapid thermoresponsive inverse gelation at polymer concentrations above a critical gelation concentration (20 wt %) into a macroporous hydrogel of densely packed micelles. This hydrogel exhibited pronounced viscoelastic solid-like properties, as well as extensive shear-thinning, rapid structure recovery, and good strain resistance properties. Excellent 3D-printability of the hydrogel at lower temperature opens a wide range of different applications, for example, in the field of biofabrication. In preliminary bioprinting experiments using NIH 3T3 cells, excellent cell viabilities of more than 95% were achieved. The particularly interesting feature of this novel material is that it can be used as a printing support in hybrid bioink systems and sacrificial bioink due to rapid dissolution at physiological conditions.
Highlights
Thermosensitive water-soluble polymers undergo phase separation due to temperature changes
The scattering curves of the hydrogel were obtained by azimuthal integration and corrections taking the sample thickness, X-ray transmission, detector accuracy, setup geometry, and solvent scattering into account, by following the standard procedures described in the literature.[47]
Via Gel permeation chromatography (GPC), the number average molar mass Mn and the dispersity Đ (Mw/Mn) of both batches were compared after completion of every single block and purification of the final polymer product
Summary
Thermosensitive water-soluble polymers undergo phase separation due to temperature changes. In 2016, an inverse thermogelling ABA-type block copolymer comprising a poly(poly(ethylene glycol) methyl ether methacrylate) middle block and thermosensitive poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) outer blocks was described.[21] The temperature-dependent sol/gel properties were investigated in the temperature range of 8−80 °C and low polymer concentrations of 3 and 5 wt %. The SAXS data, which were obtained at the two largest distances, were calibrated in terms of absolute intensities using glassy carbon as a secondary calibration standard.[45,46] The scattering curves of the hydrogel were obtained by azimuthal integration and corrections taking the sample thickness, X-ray transmission, detector accuracy, setup geometry, and solvent scattering into account, by following the standard procedures described in the literature.[47] A detailed description of the fitting procedure using a hard sphere model can be found in the Supporting Information.
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