Magnetic-responsive hydrogels for cartilage tissue engineering

The use of magnetic nanoparticles (MNPs) has been explored as an alternative approach to overcome current limitations of regenerative medicine strategies. Cell engineering approaches where MNPs are incorporated within three-dimensional constructs, such as scaffolds or hydrogels may constitute a novel and attractive approach towards the development of a magnetically-responsive system. These systems would enable remote controlled actions over tissue engineered constructs in vitro and in vivo. Moreover, growing evidence suggests that the application of a magnetic field may enhance biological performance over commonly used static culture conditions providing stimulation for cell proliferation, migration and differentiation.

In this work we analyze the role of magnetic stimulation on the behavior of human adipose derived stem cells (hASCs) laden in k-carrageenan hydrogels aiming at cartilage tissue engineering approaches. Thermo-responsive natural-based κ-carrageenan hydrogels were used as 3D templates since previous studies⁽¹⁾ report the adequate environment provided by these materials to support the viability and chondrogenic differentiation of several types of cells.

K-carrageenan (k-carr) was mixed with MNPs in different ratios, namely 2.5, 5 and 10%. Human ASCs previously isolated from surplus tissues from elective plastic surgery procedures, were encapsulated in these k-carr-MNP hydrogels and cultured in vitro for up to 21 days in chondrogenic culture medium either in the presence or absence of magnetic stimulation generated by a bioreactor device. The hASCs-laden constructs were assessed for cell viability, cell proliferation as well as deposition of a cartilaginous-like extracellular matrix.

Human ASCs appear to preferentially adhere to MNPs as they could be found in higher concentrations in regions enriched with the magnetic component. The presence of MNPs within the κ-carrageenan hydrogels did not significantly influence the viability or proliferation of encapsulated hASCs, whose values were similar to hydrogel MNP-free controls. Results also indicate that the formation of vacuoles typically observed in chondrocytic cells, was noticed in cell laden k-carr-MNP hydrogels supplemented with chondrogenic medium.

Stem cell performance on k-carr-MNP hydrogels can be modulated by the presence of MNPs stimulated by a magnetic field. Magnetic responsive hydrogels can stimulate hASCs towards chondrogenic differentiation, without affecting cell viability or cell proliferation rates. Therefore, magnetic-based systems may provide new opportunities in regenerative medicine applications towards cartilage engineered tissues.

 (1) Popa EG, Gomes ME, Reis RL, (2011) Biomacromolecules, 12 (11), 3952-61.