Hydrogels for neuroprotection and functional rewiring: a new era for brain engineering.

The neurological devastation of neurodegenerative and cerebrovascular diseases reinforces our perseverance to find advanced treatments to deal with these fatal pathologies. High-performance preclinical results have failed at clinical level, as it has been the case for a wide variety of neuroprotective agents and cell-based therapies employed to treat high prevalent brain pathologies such as stroke, Alzheimer's and Parkinson's diseases. An unquestionable reality is the current absence of effective therapies to neuroprotect the brain, to arrest neurodegeneration and rewire the impaired brain circuits. Part of the problem might arise from the lack of adequate in vitro and in vivo models and that most of the underlying pathophysiological mechanisms are not yet clarified. Another contributing factor is the lack of efficient systems to sustain drug release at therapeutic concentrations and enhance the survival and function of grafted cells in transplantation procedures. For medical applications the use of biomaterials of different compositions and formats has experienced a boom in the last decades. Although the greater complexity of central nervous system has probably conditioned their extensive use with respect to other organs, the number of biomaterials-based applications to treat the injured brain or in the process of being damaged has grown exponentially. Hydrogel-based biomaterials have constituted a turning point in the treatment of cerebral disorders using a new form of advanced therapy. Hydrogels show mechanical properties in the range of cerebral tissue resulting very suitable for local implantation of drugs and cells. It is also possible to fabricate three-dimensional hydrogel constructs with adaptable mesh size to facilitate axonal guidance and elongation. Along this article, we review the current trends in this area highlighting the positive impact of hydrogel-based biomaterials over the exhaustive control of drug delivery, cell engraftment and axonal reinnervation in brain pathologies.