The paradigm of Tissue Engineering and Regenerative Medicine is changing from a two dimensional perspective to three dimensional (3D), where the in vivo conditions are better mimicked. Natural-based hydrogels are one of the preferred tools to mimic such 3D environment. And their similarities to the extracellular matrix (ECM) regarding the mechanical properties, water content and diffusion rates, make them suitable matrices for therapeutic cell and drug delivery.

However, a lot of questions still remain unanswered about the stability and biodistribution of the hydrogels and cells, once inside the human body. The development and implementation of non-invasive monitoring tools capable of tracking the transplanted construct along time, would then pave the way for a better comprehension of those interactions.

Herein we explore the possibilities to develop a new cell laden 3D hydrogel construct capable of non-invasive in vivo tracking. Nanoparticles (NPs), as SPIONs or gold NPs, appear as an alternative method for non-invasive cell monitoring and tracking. As contrast agents, NPs can be detected by several imaging modalities, including the magnetic resonance (MRI) computed tomography (CT) and photoacoustic imaging. These NPs can be easily uptaken by different cell types, allowing their tracking in vitro and in vivo. Moreover, they can be further modified to include growth factor or drugs to improve cell survival/differentiation. The label of the hydrogel compartment is achieved by incorporating different contrast agents within the polymeric network. This new strategy can open new possibilities in the treatment of amyotrophic lateral sclerosis or other diseases.