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Tissue engineering has undergone a great revolution in terms of the strategies, technologies and materials it uses (1). In this way, much more complex approximations have been proposed achieving a notorious improvement of the treatment of injuries as frequent as tendinopathies. In this sense, 3D bioprinting could help for the development of scaffolds whose biological or mechanical characteristics resemble those of the native tendon (2).
In this study, different materials of biological origin were analyzed with the aim of obtaining a new ink for 3D printing. The optimal concentrations of each of the materials were studied. The most appropriate protocol was established to guarantee the correct homogenization of the materials and the reproducibility of the ink. Once the final composition of the ink was established, its rheological characterization was carried out. Properties as important as the viscoelasticity and thixotropy of the developed product were analyzed. Next, a printability test was carried out on the 3D printer itself using the developed ink. Finally, tenocytes were incorporated into the ink and 3D bioprinted. The viability and metabolic activity of tenocytes in the scaffold were analyzed.
Hyaluronic acid, alginate, gelatin and fibrinogen were selected as natural materials for the development of the ink. The rotational test allowed establishing that the ink had non-Newtonian behaviour. Its shear thinning behaviour makes it ideal for 3D printing. The initial viscosity at low shear rates was 1020 Pa/s. This ink was not very thixotropic, since after applying and removing the force, the initial viscosity was not fully recovered. The oscillatory test made it possible to establish that the elastic modulus (G') of the ink was greater than the viscous modulus (G'') (elastic solid-like behaviour). As indicated by the rheological studies, the ink could be properly printed. The rheology tests made it possible to establish that the physical characteristics of the inks were dependent on temperature. Through the printability test, this dependency was confirmed and both the ideal temperature and pressure for printing the ink were established (24°C and 120kPa, respectively). After the incorporation of the tenocytes in the ink, the viability and activity of the cells within the scaffolds were analyzed. The viability of the cells at different times was good (no cell death was observed). This result was related to the one obtained for cellular activity in which an increase in activity could be seen over time.
The ink based on hyaluronic acid, alginate, gelatin and fibrinogen presented adequate rheological properties. The ink allowed reproducible designed structures to be printed. The scaffolds obtained were easily manageable and could be manipulated. The mechanical tensile strength was shown to be limited. The good results of cell viability and metabolic activity suggest that the developed scaffolds could have a positive effect on the regeneration of partial tendon injuries. In future studies, the incorporation of nanoparticles with growth factors will be analyzed.
(1) Moysidou, C. M. et al., Front Bioeng Biotechnol. 8:620962 (2021)
(2) Ruiz-Alonso, S. et al., J Control Release. 333:448-486 (2021)
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