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Neurotechnologies rely on long-term implantable technical systems, in which technical materials come into direct contact with brain tissue, which mainly consists of neurons and a permeating vasculature. Two questions are of central concern:

1 Do neurons permit intimate contact with the technical system?

2 Do the materials of the technical system disturb subsequent MRI?

The realization that carbon, despite its hardness, is readily accepted by many cell types, also by stem cells, led to the exploration of microstructurable carbon as a tissue scaffold for studies in cell migration, network formation, and cell response [37]. In this study, an aqueous cryogel was steadily cooled, causing ice nucleation and crystal growth with morphological control, which upon thawing remained separated so that after drying a 3D polymer network remained. The network was pyrolized to yield an interconnected 3D carbon lattice, which in turn could be populated by neuronal stem cells, which allowed medium- to long-term studies of cell viability, confirmed by gradient echo MRI, see Figure 1.8.

Figure 1.8 Porosity and connectivity analysis of a neuronal scaffold using magnetic resonance imaging microscopy, comparing a cryogel with its pyrolized and hence shrunk carbon counterpart. [37] Erwin Fuhrer et al. (2017), figure 02[p.03]/with permission from John Wiley & Sons, Inc.

Moreover, the low susceptibility to warping of the magnetic field caused by the carbon scaffold at 11.74 T opened the door for the exploration of carbon as a neuronal implant [38]. In this study, the authors produced carbon brain implant microelectrodes on Kapton foil, by lithographically structuring a photopolymer followed by pyrolysis and embedding in durimine before release. The implants were then investigated for their MR properties, including force-induced vibrations using a specially constructed dynamic force sensitive probe head [39]. Compared with platinum electrodes, which sufficiently warped the MRI signal coming from neighboring voxels, carbon electrodes permitted the acquisition of unwrapped images right up to the microelectrodes, thus paving the way for studies in postoperation tissue recovery and wound healing.