Bioprinting of hydrogel-based bioinks can allow for the fabrication of elaborate, cell-laden 3D structures. In addition to providing an adequate extracellular matrix mimetic environment and high cell viability, the hydrogels must offer facile extrusion through the printing nozzle and retain the shape of the printed structure. We demonstrate a strategy to incorporate cellulose oxalate nanofibrils in hyaluronan-based hydrogels to generate shear thinning bioinks that allowed for printing of free-standing multilayer structures, covalently cross-linked after bioprinting, yielding longterm stability. The storage modulus of the hydrogels was tunable between 0.5 and 1.5 kPa. The nanocellulose containing hydrogels showed good biocompatibility, with viability of primary human dermal fibroblasts above 80% at day 7 after seeding. The cells were also shown to tolerate the printing process well, with viability above 80% 24 h after printing. We anticipate that this hydrogel system can find broad use as a bioink to produce complex geometries that can support cell growth.
The often-forgotten astrocytes play an important role in the central nervous system, contributing to the development of and maintenance of synapses, recycling of neurotransmitters, and the pathophysiology of various neurodegenerative diseases. Hydrogels can provide improved support and attachment for the culture of astrocytes in 3D models, which could further be used to advance clinical in vivo like tissue models of numerous diseases. For full applicability, these gels must be of scalable and defined origin and with stable attachment elements, such as peptides. In this study, the generation of a functional 3D astrocyte model is presented using a hyaluronan-based hydrogel system conjugated with the peptide sequences cyclic RGD (cRGD) and IKVAV, known promoters of cell attachment. Encapsulation of the neuroblastoma cell line SH-SY5Y and glioblastoma cell line U87 is successfully demonstrated over a 6-day culture period. The presence of the peptides cRGD and IKVAV does not change the cells' viability. Human fetal primary astrocytes (FPA) are further tested for the 3D culture in these materials, similarly, showing that the peptides have no effect on the viability over a 6-day culture period. mRNA expression analysis reveals no biologically significant changes in the 3D cultures FPA or the U87 cells. Morphological analysis, on the other hand, revealed that FPA have a higher degree of interactions with the hyaluronan-based gels compared to the cell lines. This interaction is enhanced by peptide conjugation, in particular cRGD. Finally, we demonstrated that the peptide conjugated hydrogels could be used for bioprinting of FPA, opening up for defined neural astrocytic co-culture.
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