A team of researchers from Spain and Italy have created a series of 3D hydrogel scaffolds for neuronal growth using a combination of aqueous graphene dispersions and acrylamide synthesized by in situ radical polymerization.
While this is not the first time acrylamide hydrogels have been synthesized for scaffold applications, they have commonly suffered from biocompatibility issues – a crucial flaw when it comes to implantable scaffolds. To address this issue, the researchers created a series of graphene-polyacrylamide hydrogels which support the growth of living primary neurons.
The incorporation of graphene into the hydrogels brought a remarkable and noticeable improvement to the properties of the hybrid hydrogel. The Researchers discovered that the graphene becomes an intrinsic component of the polymer network and not just an embedded nanomaterial. The hydrogel with a concentration of only 0.2 mgmL–1 was used as the support to grow the brain cells and develop synaptic activity.
Hippocampal neurons and astrocytes were efficiently developed on the hydrogel scaffolds, but only on the scaffold which contained graphene (pure polyacrylamide did not promote growth). In addition to the growth, the cultured cell networks produced active synaptic networks, which was observed directly by imaging techniques. The observation of the neuronal networks with the graphene incorporated networks is the most significant finding in this research.
In their work, the researchers prepared an aqueous dispersion of graphene by exfoliating graphite with melamine using a ball-milling method (Retsch PM100 planetary mill) and dispersing the mixture in water. The poorly exfoliated graphite was precipitated from solution and the melamine was removed through washing steps.
The researchers also prepared a polyacrylamide hydrogel using acrylamide, a N,N′- methylenebisacrylamide (MBA) crosslinker and a potassium peroxodisulfate (KPS) initiator. The Researchers homogenized the solution through a combination of mixing and sonication methods until polymerization took place. Unreacted monomers and initiator molecules were dialyzed to create a pure hydrogel.
A similar process was then followed to combine the polyacrylamide hydrogel with the graphene dispersion to create the graphene-hydrogel nanocomposite. The Researchers trialed graphene dispersion ranging between 0.05 and 2mgmL–1. Primary hippocampal cultures were adhered to the scaffold and cultured for 8-10 days.
The researchers measured the compressive moduli of the scaffolds and the values were much higher for the scaffolds containing graphene. The Researchers also found no obvious fatigue behavior in the scaffolds, even with the scaffolds containing the highest concentration of graphene.
It was deduced that the mechanical properties of the scaffold are not critical for neuronal growth in the presence of graphene, but more so that graphene plays a critical intrinsic role for the development of neurons.