Bioprinting large constructs with a good structural integrity is easy, however, it is significant and biologically relevant to select a material that, in addition to providing structural support, enables cells to proliferate, migrate and rearrange the matrix. Soft materials with high cell affinity, like collagen, have in the past been difficult to use for 3D bioprinting of stable complex structures due to their low viscosity. The structural element is an important part when building up different compartments for the fabrication of complex in vitro models for regenerative medicine applications. However, too stiff materials can hinder the movement of the embedded cells which can affect the function of the tissue. For example, the structure of the kidney proximal tubule is composed of a single-layered epithelium of renal proximal tubule epithelial cells (RPTECs) with an apical–basal polarity with a brush border on the apical side to absorb nutrients and to secrete waste products and xenobiotics. These types of structures need to be formed inside the bioprinted construct by a rearrangement of the extracellular matrix by the cells.
Methodology: Here we present two printable, high concentration collagens from Advanced BioMatrix which were bioprinted into stable grids using CELLINK’s BIO X. The collagens Lifeink 200 (35 mg/mL) and Lifeink 220 (70 mg/mL) were mixed with immortalized RPTECs before printing. The viability of the cells was assessed using live/dead fluorescent staining on day 1, 7 and 14 after bioprinting. Samples were also stained using immunohistochemistry (IHC).
Results: The viability of the renal cells was above 70% in both collagens after bioprinting and maintained throughout the culture period. There was a clear cell stretching at day 7 and day 14 in both conditions where the cells stretch in all directions. The similarities between Lifeink 200 and 220 in terms of viability and especially in cell stretching, demonstrated that neither of the high concentration collagens hinder the growth nor movement of the RPTECs. With IHC we detected that the cells were allowed to migrate to the boarders of the construct but also lined the natural voids inside both bioinks.
Conclusion: This work highlights the possibility of bioprinting stable structures using collagens that also enable the RPTECs to remodel and move through the matrix. This allows for the fabrication of more complex and representable in vitro kidney models.