Controlled axonal outgrowth and cell reactions to nanostructures

Sammanfattning: The interface between living cells and artificial surfaces are highly relevant for biomedical applications such as implants and organized cell growth for tissue reconstruction as well as for basic science purposes. In the present thesis, we have studied axonal guidance on various nano-patterned surfaces such as polymethyl-meth-acrylate, porous silicon and on magnetically aligned Ni nanowires. Furthermore, the reaction of macrophages exposed to free nanowires made of Ni, Au, GaP and polystyrene was examined. The impact of porous silicon on the sciatic nerve regeneration was studied in an animal model. The overall aim was to study how neuronal processes grow and extend on nanopatterned surfaces and structures, intended for implantable electrodes or “lab on a chip” devices. 1) Axonal guidance was observed for grooves and ridges with dimensions between 100 nm and 800 nm. The axons were found to grow on the ridge edges and not in the grooves. Axonal guidance and cell guidance was also observed on Ni nanowires with a diameter of 200 nm, magnetically aligned on a glass cover slip. 2) Macrophages exposed to suspensions of nanowires. Nanowires made of Ni, Au, GaP and polystyrene, were studied. We found that the nanowires activated the macrophages, and nanowires composed of metal could induce cell death. 3) Porous silicon with different pore sizes was fabricated. We found that axons preferentially grow on porous silicon as compared to smooth silicon, but only if the pore size is between 150 and 500 nm. The integration with a regenerating nerve on porous silicon in vivo was also found to be better than for smooth silicon. Here, we found the encapsulation to be reduced on the porous silicon surface as compared to a smooth one. We conclude that axons are guided via contact guidance by structures as small as 100 nm and that magnetic nanowires can serve as such structures. This phenomenon may be used for in vitro applications such as lab on a chip or the creation of neuronal networks with high fidelity. Nanowires in suspension may be toxic to cells and we speculate that this is the case if the wires are too rigid e.g. metal wires, and/or if metal ions are released from the wires. Furthermore, porous silicon is a suitable material at the interface between electronics and living tissue due to its large area to volume ratio resulting in good anchoring of cells and tissue, a favorable situation for electrical recordings. Furthermore, in vivo there is less encapsulation of porous silicon. In vitro, such porous patterned chips supports axonal outgrowth and can be used for attracting axons to specific areas, a useful properties for many applications. Taken together, the present results show that nanomodification of surfaces is a promising avenue, when interfaces to the nervous system are considered.