The three work packages of the action covered (i) the preparation of robust and biocompatible hydrogels through the thiol-yne click chemistry approach, (ii) their exhaustive general characterizations and, finally, (iii) their bioapplication as tissue engineering scaffolds.
Firstly, polymeric precursors based on polyethylene glycol (PEG) were satisfactorily synthesized with specific side-chain and end-group functionalities and cross-linked in situ under physiologically relevant conditions (cell culture media, pH at 7.4 37 °C). At this stage, two different hydrogel systems were developed. For the first one, the swelling properties of the hydrogels were finely tuned by varying the hydrophilic/hydrophobic ratio of the hydrogel polymeric chains (Figure 1). In doing so, we were able to slow down the degradation process of the hydrogels, which were then stable for more than 30 days, as well as retain their excellent mechanical performance for longer. For the second group, biopolymers (i.e. alginate, gelatin, chitosan, hyaluronic acid, and heparin) were also included in the chemical composition of the hydrogels (Figure 2). Specifically, the addition of alginate chains, crosslinked with calcium ions, not only rendered the hydrogels stretchable and with enhanced tensile performance, but also self-healing. Furthermore, in comparison to the PEG-only system, PEG/Alginate hydrogels exhibit much higher cell viability, suggesting they are ideal matrices for cell growth and proliferation. Overall, our strategy resulted in a simple but effective way to improve the properties of covalent synthetic hydrogel systems.
Regardless of the approach followed, hydrogels showed adequate gelation times (i.e. from 30 seconds to 10 minutes), which allowed their injectability, as well as high water content (86% - 95%) and gelation fraction values (74%-92%). In general, as a consequence of the nature of the chemistry exploited to prepare the hydrogels, all the systems tested displayed excellent mechanical properties. Results obtained in this part were extremely promising. The hydrogels prepared displayed a robust nature and mechanical features, in terms of compression strength and stiffness, which match those exhibited by native cartilage tissue.
Finally, adult stem cells were encapsulated within the different hydrogel systems, and their viability at specific time points was determined (Figure 3). All the systems tested were highly cytocompatible, which allowed for the growth and proliferation of the cells.
As specified in the action, Dr. Pérez-Madrigal has been actively disseminating the new knowledge generated by the DN-CARTILOGEL project, thus enhancing the quality and effectiveness of interactions between scientists, general media and the society. As a first action of dissemination, results have been (or will be soon) published in peer-reviewed journals to ease their diffusion among the international community of researchers, and always fulfilling the requirement of Horizon2020 to as open access [Polym. Chem. 2017, 8, 5082; Biomacromolecules 2017, 19, 1378; Biomater. Sci. 2018, Advance Article]. Also, the Dr. Pérez-Madrigal has attended several national and international symposia and conferences to ensure maximum diffusion of the action. Finally, Dr. Pérez-Madrigal has also been engaged with web-based and social media activities to disseminate the action, as well as events to outreach the general public and children. Most relevant, the fellow created a web-page dedicated to the project to maximize the diffusion of the action.
