Tuning Rheology and Printability of Gelatin Methacryloyl/Sodium Alginate Bioinks: The Role of Sodium Alginate Molar Mass and Sterilization

Gelatin methacryloyl (GelMA)/sodium alginate (SA) bioinks are widely explored for various biomedical applications due to their favorable biocompatibility and tunable properties. However, the molar mass (MM) of SA, a critical factor influencing bioink properties, has not yet been systematically investigated in these systems. In this work, we highlight the importance of SA MM as a key parameter that governs the rheological behavior of GelMA/SA bioinks, directly impacting their printability and the structural and mechanical characteristics of the resulting hydrogels. Three types of SA used are characterized by very low (SA-VL), low (SA-L), and medium (SA-M) weight-average MM ranging between 38 and 260 kg·mol^-1. In addition, the variability in the MM of SA is included as a result of SA sterilization by autoclaving. MM exponentially decreases with sterilization time for all SA samples showing a 37% drop for SA-VL and about a 65% drop for SA-M and SA-L after 20 min of sterilization time. MM of SA significantly affects the viscoelasticity of GelMA/SA bioinks, which enables us to recognize the conditions suitable for bioprinting tested by employing various printing conditions. SA-VL did not provide the required quality of printed strands due to high elasticity. The compression analysis of hydrogels suggests that formation of the GelMA covalent network is independent of the MM of SA, as shown from stress relaxation measurements, and the differences in hydrogel mechanical properties can solely be attributed to the SA ionic network. Interestingly, the higher degree of ionic cross-linking is observed in the case of lower MM of SA; however, these differences gradually decrease as the stress relaxation equilibrium is reached. The permeability of hydrogels in saline shows no significant variation across different MMs of SA. This study thus recommends considering the MM of SA as the principal factor allowing for optimization of GelMA/SA bioink printability without compromising the key properties of the resulting hydrogel.