Injectable and magnetic responsive hydrogels with bioinspired ordered structures

Injectable hydrogels are particularly interesting for applications in minimally invasive tissue engineering and regenerative medicine strategies. However, the typical isotropic microstructure of these biomaterials limits their potential for the regeneration of ordered tissues. In the present work, we decorated rod-shaped cellulose nanocrystals with magnetic nanoparticles and coated these with polydopamine and polyethylene glycol polymer brushes to obtain chemical and colloidal stable nanoparticles. Then, these nanoparticles (0.1-0.5 wt %) were incorporated within gelatin hydrogels, creating injectable and magnetically responsive materials with potential for various biomedical applications. Nanoparticle alignment within the hydrogel matrix was achieved under exposure to uniform low magnetic fields (108 mT), resulting in biomaterials with directional microstructure and anisotropic mechanical properties. The biological performance of these nanocomposite hydrogels was studied using adipose tissue derived human stem cells. Cells encapsulated in the nanocomposite hydrogels showed high rates of viability demonstrating that the nanocomposite biomaterials are not cytotoxic. Remarkably, the microstructural patterns stemming from nanoparticle alignment induced the directional growth of seeded and, to a lower extent, encapsulated cells in the hydrogels, suggesting that this injectable system might find application in both cellular and acellular strategies targeting the regeneration of anisotropic tissues.Fundação para a Ciência e a Tecnologia for SFRH/BPD/112459/2015 (RD), EU’s H2020 programme for Marie Skłodowska-Curie grant agreement 706996 and for European Research Council grant agreement 772817 - MagTendon, project RECOGNIZE (UTAPICDT/CTM-BIO/0023/2014), project FOOD4CELLS (PTDC/CTM-BIO/4706/2014 - POCI-01- 0145-FEDER 016716) (PB), and project NORTE-01-0145-FEDER-000021