WEB Conductive, micro-channeled EG/Polyacrylamide 3D networks as scaffolds for tissue engineering
For the fabrication of artificial cardiac tissue materials are needed that fulfil certain requirements: mechanical properties matching the cardiac tissue, stability during cyclic contractions, electrical conductivity for the transmission of signals between cells and permeability for transport of nutrients or drug delivery. For the accomplishment of all these requirements we have prepared an exfoliated graphene (EG)/polyacrylamide (PAAm) micro-channeled composite, which can be tailored in terms of electrical conductivity and mechanical properties. The approach initially employs a highly porous (up to 98%) sacrificial template of interconnected tetrapodal zinc oxide (t-ZnO) microparticles.  By infiltration of the template with an aqueous dispersion of EG the 2D nanomaterial sheets are assembled into a 3D network structure forming electrically conductive pathways along the interconnected ZnO tetrapods.  In a next step, the free volume of the template is filled with polyacrylamide. Subsequent dissolution of the ZnO results in a conductive and micro-channeled hydrogel.  The approach allows for the preparation of EG/PAAm composites exhibiting conductivities (0.34 S/m) that exceed the DC conductivity of the heart at very low EG concentrations (0.16 vol%). In contrast to other approaches the composite matrix is not filled with graphene and thus, a much smaller amount of the conductive filler material is necessary. Due to the very low EG content, the mechanical properties are not altered by the incorporation of graphene. Thereby, the material can be tailored in its mechanical properties by simply modifying the hydrogel matrix. The presented work reveals the potential of EG/PAAm networks as scaffold material for cardiac tissue engineering including appropriate conductivity, mechanical properties and microchannels for nutrient transport and drug delivery.
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