WEB Rheological characterization of alginate and gelatine blends for 3d bioprinting
Hydrogels, such as alginate or gelatine, are polymeric networks that contain a high percentage of water and maintain their structure due to physical or chemical cross-linking. These materials are highly promising in regenerative medicine; indeed, if crosslinking agents are used to ensure biocompatibility and resorbable polymeric matrices, they can be used as inks in 3D bioprinting.
The design of a bioprinting ink should consider the rheological behaviour of the hydrogel as a function of the various stages of the 3D printing process. In recent years, several studies of gelatine and alginate blends have been reported looking for a model bio-ink. This model should have a gel point around room temperature and a viscosity between 0.1 and 1x106 Pa.s for extrusion bioprinting strain rates .
Following this goal in this contribution we present two blends of alginate and gelatine that fulfil these requirements: one with a gelatine of 150 Bloom (25-50 kg/mol) and the other with gelatine of 250 Bloom (50-100 kg/mol). We analyse how the molecular weight of the peptides of the gelatine (characterized by the Bloom number) affects the rheological properties of both inks.
Alginate and gelatine —one solution for each type of gelatine— were dissolved in PBS and mechanically mixed at 37°C, obtaining two inks, denoted 250B and 150B, according to Bloom number of the respective gelatine. Rotary and oscillatory tests were performed at 33°C in a Discovery HR-3 Rheometer (TA Instruments, USA) in the Small Amplitude Oscillatory Shear (SAOS) mode.
It was established that rising the Bloom number the viscosity increases (η 150B = 30-40Pa.s and η 250B = 35-60Pa.s, for a shear rate range between 10 and 35 1/s). Also, the gelling temperature is higher for the more viscous blend (tgel 150B = 19.8±0.2°C and tgel 250B = 25.1±0.3°C).
The evolution of the dynamic moduli as a function of frequency at the printing temperature (33°C) reveals a stable pre-gel like behaviour for both inks. Furthermore, it was observed that alginate provides a pseudoplastic behaviour to the inks, while gelatine imparts the temperature-dependent gelling mechanism, suitable for the 3D bioprinting process.
Finally, the non cytotoxic effect of the 250B ink was evidenced by the direct fibroblast attachment to the printed scaffolds after 24h.
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