Mcr 302 wesp

The NIR-photorheology measurements were performed on an Anton Paar MCR 302 WESP with a P-PTD 200/GL Peltier glass plate and a disposable PP25 measuring system, which is hyphenated with a Bruker Vertex 80 FTIR spectrometer, equipped with NIR optics. A detailed description on the experimental set-up and the underlying method can be found in literature.^{9 (link)} For each measurement 150 μL of sample was applied between the glass and steel parallel plates at 20 °C with a gap of 200 μm. The formulations were oscillated with a strain of 1% and a frequency of 1 Hz. As UV light source an Exfo OmniCure LX 400 spot curing system was used and the light was projected via a dual-waveguide onto the glass plate with the sample (LED with 400 nm, 0.05 mW cm⁻² on the surface of the sample). During the experimental run, the storage modulus, loss modulus and normal force were measured via rheology. From NIR data collected during the measurements the double bond conversion (DBC) of the acrylate double bonds can be obtained in situ. The data were collected for 65 s in the dark and then during interrupted irradiation of the sample consisting of intervals with 6 s light impulses and 30 s periods in the dark. The data from the end of the 30 s intervals were plotted into a graph.

To characterize the photo‐crosslinking characteristics and viscoelastic properties of gelMA, oscillatory shear measurements were performed with aqueous solutions of gelMA with 5%, 7.5%, 10% as well as 12.5% (w/w) of gelMA (in the presence of 0.6 mM Li‐TPO as photo‐initiator) by means of a photorheometer (MCR 302 WESP, Anton Paar) with a light source of 320–500 nm wavelength and an intensity of 6 mW cm⁻² (Omnicure) (Gorsche et al., 2017 (link)). The samples were assayed using a parallel plate geometry setup, where 60 µL of gelMA precursor solution was loaded between the plates with a gap of 50 µm. Paraffin oil was applied at the edges to prevent drying of the gelMA film during measurements. A frequency of 10 Hz and a strain of 10% was applied via the parallel plates (d = 25 mm) at 37°C. The parameters were determined to be within the viscoelastic range of gelMA. The temperature was set at 37°C. Each sample was equilibrated for 20 s before the light source was turned on. Storage‐ (G′) and loss moduli (G″) were recorded in second intervals.