Introduction: Due to their biocompatibility, biodegradability and cell-interactivity, gelatins are widely used in the biomedical and tissue engineering fields. Gelatin can be chemically crosslinked to originate constructs that are stable at body temperature. However, if modified gelatins cannot be produced with consistent molar mass and degree of modification (DoM), these advantageous biomaterials cannot be used in a reliable manner. To achieve predictable hydrogel strengths, consistent GelMA molar mass, degree of modification and the associated photo-kinetics need and can be tightly controlled.
Methodology: Six GelMA types (90 kDa and 160 kDa at DoM of 40, 60 and 80 %), were dissolved at concentrations of 5, 10 and 15 w/v% in PBS. The photo-initiator LAP was added to the GelMA resins. The photo-crosslinking kinetics of the GelMA resins were studied at 20 °C using a TA Discovery Hybrid Rheometer HR-2 (TA Instruments, the Netherlands) that was equipped with an Hönle - Bluepoint 4 - UV-A light (7.4 mW cm-2). The samples were in situ irradiated from the bottom through the quartz plate using a parallel plate setup (Ø 20 mm, gap 0.300 mm). A shear frequency of 1 Hz and an amplitude (strain) of 1 % were selected as they were within the linear visco-elastic range of the GelMA materials. The storage moduli (G’) were monitored over time.
Results: The herein presented data confirm that with increasing degree of modification (DoM) the storage modulus of the GelMA hydrogels will increase too. The increase in DoM can be correlated to an increase in storage modulus with an exponential component of e~0.6x for the 160 kDa GelMAs and an exponential component of e~0.54x for the 90 kDa GelMAs. With increasing GelMA concentrations (w/v%) the storage modulus of the hydrogel will increase. This statement was confirmed for the 90p GelMAs with a near perfect power-correlation (x~3.3). Interestingly, the 160 kDa GelMAs do not show a power correlation, but a linear one, between hydrogel strength and GelMA concentration. As a result of these different correlations, a convergence is seen between molar mass affected storage modulus, and concentration (w/v%) affected storage modulus. At low GelMA concentrations a clear difference is seen between molar mass and storage modulus, but as concentration increase this difference in storage moduli becomes smaller and smaller.
Conclusion: With consistent GelMA molar mass and degree of modification, hydrogel strength becomes predictable, as evidenced by the exponential-correlations found for the 160 kDa GelMA (e~0.6x) and 90 kDa GelMA (e~0.54x). Regarding hydrogel strength in function of GelMA concentration, a power-correlation was evinced (x~3.3) for 90 kDa GelMAs and a linear correlation for 160 kDa GelMAs, showing a convergence in hydrogel strength across GelMA molar mass and GelMA concentration.
Acknowledgement: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 964497.