Bio-inspired and microfabricated poly-amidoamine hydrogels : a novel smart material interfacing living systems

Recently available micro- and nanotechnologies applied to existing biomaterials may impart them novel properties and provide cutting-edge tools for the construction of clinically helpful micro- and nano devices. Poly(amidoamine)s (PAA) are highly hydrophilic synthetic polymers obtained by Michael-type poly-addition of amines to bisacrylamides. Crosslinked PAA in aqueous media form optically transparent hydrogels that in many cases proved to be fully biodegradable and biocompatible, warranting a definite potential for biomedical applications, such as for instance regenerative medicine. There is an increasing demand for new generation of biohydrogels to evolve from the present substrates to highly physiologic 3D environments adapted to live complexity. Accordingly, we report here the possibility of micro-designing and engineering a versatile PAA hydrogel named ISA23 to enhance and control major cell processes such as adhesion, proliferation, and tissue organization. In particular, we present the development of a direct-writing electron beam lithography method to pattern the surface of PAA hydrogels. The process is performed on the materials in the dry state before swelling them with water. The patterning is maintained after swelling. The computer assisted methodology enables to control physical and biochemical features, down to a lateral resolution of 500 nm. We demonstrated that the surfaces exposed to the e-beam could be coated with proteins or other biomolecules whose amount can be quantified by using fluorescent labels. The direct-writing approach on biohydrogels can be also used to manufacture larger microstructures, such as embedded microfluidic systems, or other miniaturized systems, easily integrated into cost-competitive biodevices. Finally we interfaced microfabricated hydrogels with cells lines such PC12, able to differentiate into neuronal cells. The cells and neurite recognized the electron beam modified area with strong preference (in terms of adhesion, proliferation and differentiation). The microfabrication allowed to precisely control the guidance of neurite outgrowth from single cell through microchannels (Fig. 1), thus eventually reconstituting neural networks. This technique applied to PAA hydrogels has the potential of creating low-cost biocompatible platforms accurately reproducing the physiological characteristics of cellular microenvironments or neuronal networks.