Date Published: March 4, 2019
Publisher: Public Library of Science
Author(s): Augusto Zuluaga-Vélez, Diego Fernando Cómbita-Merchán, Robison Buitrago-Sierra, Juan Felipe Santa, Enrique Aguilar-Fernández, Juan C. Sepúlveda-Arias, Athanassia Athanassiou.
Hydrogel scaffolds are important materials in tissue engineering, and their characterization is essential to determine potential biomedical applications according to their mechanical and structural behavior. In this work, silk fibroin hydrogels were synthesized by two different methods (vortex and sonication), and agarose hydrogels were also obtained for comparison purposes. Samples were characterized by scanning electron microscopy, infrared analysis, thermo-gravimetrical analysis, confined compression test, and rheological test. The results indicate that nanofibers can be obtained via both silk fibroin and agarose hydrogels. The mechanical tests showed that the Young’s modulus is similar to those found in the literature, with the highest value for agarose hydrogels. All the hydrogels showed a shear-thinning behavior. Additionally, the MTT test revealed that silk fibroin hydrogels had low cytotoxicity in THP-1 and HEK-293 cells, whereas the agarose hydrogels showed high toxicity for the THP-1 cell line. The results indicate that silk fibroin hydrogels obtained from a Colombian silkworm hybrid are suitable for the development of scaffolds, with potential applications in tissue engineering.
A general strategy used in tissue engineering is to replace damaged tissue with polymeric scaffolds containing specialized populations of viable cells . The scaffolds may have different forms and incorporate signals or growth factors to stimulate the expansion of a desirable cellular population. Once the platform is implanted, the polymeric scaffold must degrade so it can be replaced by healthy and functional tissue . Hydrogels are useful materials for tissue regeneration due to their compatibility with bioactive agents such as cells and proteins . They also have the ability to transport substances by diffusion to reach physiological concentrations similar to those of the target tissue .
Fig 1 shows the SEM images of silk fibroin- and agarose-obtained hydrogels. The diameter of the fibers of the hydrogels was measured at the end of each fiber. Fibers from silk fibroin-based hydrogels had an average diameter of 20 ± 5 nm when they were processed by the vortex method and 21 ± 6 nm by the sonication method. On the other hand, for agarose hydrogels, the fibers had an average diameter of 31 ± 8 nm.
Hydrogels are composed of cross-linked nanostructured fibers. The values of the diameters of the hydrogels’ fibers were in agreement with some reports available in the literature, where the diameters of the fibers vary from 3 to 30 nm depending on the experimental conditions [42,43]. Some authors have proposed the use of weak electric fields as a mechanism for the induction of nanofilaments, with similar values of fiber diameters, between 10 and 80 nm . Hydrogels made by annealing using a modulated water/methanol ratio were reported to have nanofibers 10–20 nm in diameter . Besides, the formation of silk fibroin hydrogels by self-assembled nanofiber networks produced fibers with larger diameters (253.2 ± 34.2 nm) .