Three-dimensional bioprinting serves as an attractive platform to fabricate customized tissue-engineered substitutes from biomaterials and cells for the repair or replacement of injured tissues and organs. A common challenge for 3D bioprinting materials is that the structures printed from the biodegradable polymer hydrogels tend to collapse because of the poor mechanical stability. In this study, dual stimuli-responsive biodegradable polyurethane (PU) dispersions (PUA2 and PUA3) were synthesized from an eco-friendly waterborne process. Acrylate group was introduced in the PU chain end to serve as a photosensitive moiety for UV-induced cross-linking and improvement of the printability, while mixed oligodiols in the soft segment remained to be the thermosensitive moiety. The photo/thermal-induced morphological changes of PU nanoparticles were verified by dynamic light scattering, small-angle X-ray scattering, and rheological measurement of the dispersions. It was observed that these PU nanoparticles became more rod-like in shape after UV treatment and formed compact packing structures upon further heating. With the thermosensitive properties, these UV-cured PU dispersions underwent rapid thermal gelation with gel moduli in the range 0.5-2 kPa near body temperature. The rheological properties of the PU hydrogels including dynamic viscoelasticity, creep recovery, and shear thinning behavior at 37 °C were favorable for processing by microextrusion-based 3D printing and could be easily mixed with cells before printing to produce cell-laden constructs. The dual-responsive hydrogel constructs demonstrated higher resolution and shape fidelity as well as better cell viability and proliferation than the thermoresponsive control. Moreover, the softer hydrogel (PUA3) with a low modulus (<1 kPa) could offer neural stem cells a tofu-like, stable, and inductive 3D microenvironment to proliferate and differentiate. We expect that the photo/thermoresponsive biodegradable polyurethane ink may offer unique rheological properties to contribute toward the custom-made bioprinting of soft tissues.

In this study, silver-doped nickel oxide (NiO:Ag) was successfully synthesized by a sol-gel method and spin-coated on indium titanium oxide (ITO) as a hole-transport layer for polymer light-emitting diodes (PLED). After the calcination of the NiO:Ag/ ITO substrate at 300 C for 1 h, stable conductive regions and the mean workfunction on the NiO:Ag/ITO surface reached 89.43% and 5.53 eV, respectively, which were greater than those on a conventional poly [3,4-ethylenedioxythiophene] polystyrene sulfonate (PEDOT:PSS)/ITO surface. When NiO:Ag (300 C)/ITO was used as an anode window substrate for PLEDs, the enhancement factor for the average current efficiency in the current-density range of 20-50 mA/cm 2 and electroluminescence intensity at an applied bias of 8.0 V were 4.60 and 2.55 times, respectively, in comparison with those of PLED based on a conventional PEDOT: PSS/ITO anode. Highlights• NiO:Ag is synthesized by a sol-gel method and spin-coated on ITO as a HTL for PLED.• NiO:Ag/ITO calcined at 300 C for 1 h has the best microscopic electrical properties.• The performance for proposed PLED is much better than that for typical PLED.