2.2 Fabrication and characterization of PTMC/TPU scaffolds
Different amounts of PTMC and TPU at specific PTMC:TPU ratios were
homogeneously mixed in round-bottom flasks by mechanical stirring after
being heated in an oil bath to 170 ℃ under nitrogen protection.
Afterwards, PTMC/TPU mixtures were cut into pieces and then transferred
to a stainless steel cartridge in a 3D bioprinter (regenHU,
Switzerland). 4D printing was conducted using these printing parameters:
the inner diameter of the printing nozzle was 410 μm, the printing
temperature was 170 ℃, and the printing speed was 8 mm/s. Subsequently,
4D printed PTMC/TPU scaffolds were rolled up to tubular structures using
a stainless steel rod (rod diameter: 8mm) in an oven at 80℃ for 30min.
The tubular scaffolds were then flattened at room temperature for
further use.
A scanning electron microscope (SEM, Hitachi S-4800, Japan) was used to
observe the surface morphology and microstructure of 4D printed PTMC/TPU
scaffolds. Differential scanning calorimetry (DSC, Pyris 6, PerkinElmer,
USA) was conducted to analyze the glass transition temperature of
PTMC/TPU scaffolds, and thermogravimetric analysis (TGA, DZ-TGA101,
Nanjing Dazhan Testing Instrument CO., Ltd, China) was performed to
determine the real PTMC:TPU ratios for PTMC/TPU scaffolds. The
mechanical properties of PTMC/TPU scaffolds were studied via tensile
tests using a universal testing machine
(Model 5848, Instron Ltd., USA) at
room temperature and at 37 ℃, respectively. The surface wettability and
BSA adsorption of PTMC/TPU scaffolds were studied. Moreover, the shape
morphing behavior of PTMC/TPU scaffolds was investigated by immersing
scaffolds in a water bath at 37 ℃, with shape morphing processes being
recorded by a digital camera.