3D brain micro electrodes arrays are of great interest for neuroscience research and for the rehabilitation of sensory and/or motor functions in patients with neurological diseases. However, one important problem reported with all available microelectrodes to date, is long-term functionality and biocompatibility. Indeed Si and SiO2 are attractive choices as brain implants materials due to an interesting technology transfer from MEMS industry. Although it has been reported that silicon-based shafts, silicon oxide based surfaces and other glass based products are highly biocompatible [1], acute and chronic inflammatory reactions [2-4] have also been observed. These reactions often result in neurons and microelectrodes damages and in a degradation of the stimulus/ recorded signal [5].
The challenge is to improve significantly the long term biocompatibility of the implant by coating it in a proper way in order to suppress the immunological response, and optimise the neurone/ probe interface. One possible approach is to mislead the immunological system by coating the probe by a constituent of the cerebral fluid, namely hyaluronic acid (HYA). In this study HYA was chemically functionalised with reactive S-S-Pyridin groups. In parallel, three different types of silicon samples with different degree of oxidation were derivatized by merkaptopropyldimethoxysilane, terminated by thiol groups. The samples were then exposed to the modified hyaluronic acid. The anchoring proceeds via the SS-Py groups, which reacts with thiols on the sample surface and forms di-sulfides covalent bonds. The adsorption of the polymer was studied by means of XPS and AFM. Homogeneous polymer monolayers could be synthesised. However, their final aspect is heavily influenced by the degree of oxidation of the original substrate surface. The samples are now being tested in-vitro.
[1] W.L. Rutten, Annu Rev Biomed Eng,. 4 (2002) 407.
[2] P. Heiduschka, and S. Thanos, Prog. Neurobiol., 55 (1998) 433.
[3] B.J. Agnew, et al., J Cell Sci, 112:16 (1999) 2639.
[4] E. Fernandez, F. Pelayo,; S. Romero, M. Bongard, C. Marin, A. Alfaro, L. Merabet, J. Neural Eng 2 (2005) R1.
[5] J.W. Fawcet, and R.A. Asher, Brain Res Bull, 49 (1999) 377.
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