Portable microstimulator for chronic deep brain stimulation in freely moving rats.

In the last decades, deep brain stimulation (DBS) has been widely used as a functional surgical strategy for the treatment of a variety of neurological and psychiatric disorders, including Parkinson's disease (PD), dystonia, epilepsy, depression or obsessive-compulsive disorder. While the therapeutic benefits of DBS are now recognized, experimental data on its mechanisms and impact at long term remain poor. This is mainly due to the lack of a microstimulation system adapted for chronic DBS in small laboratory animals. In this context, we have developed a microstimulator for DBS adapted to rat. This device, which has a size and weight compatible for use in freely moving rat, can be clipped to a support fixed on the animal's head. This easy "removal" property is crucial because it enables removing or even switching the microstimulator during the experiments without having to anaesthetize or to operate the animal, thus minimizing stress. The design of the microstimulator allows to set the DBS parameters easily (intensity, frequency and pulse width) and to replace the battery for long-term DBS. To validate our device, we performed continuous DBS of the subthalamic nucleus (known to improve motor deficits in clinic) in a classical rat model of PD during 5 weeks. We show that this long duration stimulation reduces significantly PD-induced akinesia without inducing animal discomfort and tissue damage. These first data demonstrated that long term DBS procedure in behaving rat is now workable.

Impact of chain length, temperature, and humidity on the growth of long alkyltrichlorosilane self-assembled monolayers.

In this work, we have studied the growth of self-assembled monolayers (SAMs) on silicon dioxide (SiO(2)) made of various long alkyltrichlorosilane chains (16, 18, 20, 24, and 30 carbon atoms in the alkyl chain), at several values of temperature (11 and 20 °C in most cases) and relative humidity (18 and 45% RH). Using atomic force microscopy analysis, thickness measurements by ellipsometry, and contact angle measurements, we have built a model of growth behaviour of SAMs of those molecules according to the deposition conditions and the chain length. Particularly, this work brings not only a better knowledge of the less studied growth of triacontyltrichlorosilane (C(30)H(61)SiCl(3)) SAMs but also new results on SAMs of tetracosyltrichlorosilane (C(24)H(49)SiCl(3)) that have not already been studied to our knowledge. We have shown that the SAM growth behaviour of triacontyltrichlorosilane at 20 °C and 45% RH is similar to that obtained at 11 °C and 45% RH for shorter molecules of hexadecyltrichlorosilane (C(16)H(33)SiCl(3)), octadecyltrichlorosilane (C(18)H(37)SiCl(3)), eicosyltrichlorosilane (C(20)H(41)SiCl(3)) and tetracosyltrichlorosilane (C(24)H(49)SiCl(3)). We have also observed that the monolayers grow faster at 45% than at 18% RH, and surprisingly slower at 20 °C than at 11 °C. Another important result is that the growth time constant decreases with the number of carbon atoms in the alkyl chain except for C(24)H(49)SiCl(3) at 11 °C and 18% RH, and for C(30)H(61)SiCl(3). To our knowledge, such a chain length dependence of the growth time constant has never been reported. The latter and all the other results are interpreted by adapting a diffusion limited aggregation growth model.

Functionalization of silicon dioxide surface with 3-aminopropyltrimethoxysilane for fullerene C60 immobilization.

Formation of self-assembled monolayers (SAM) of 3-aminopropyltrimethoxysilane (APTMS), chemically bonded to silicon dioxide surface, using a new solvent free process, has been studied by contact angle measurements, ellipsometry, ATR-FTIR spectroscopy and AFM imaging. The possibility of using as-obtained APTMS SAMs for anchoring functional molecular moieties is then studied with fullerene C60. In a first part we have analyzed the grafting kinetics of APTMS SAMs in order to control the formation of a single monolayer. Results show that about four hours are needed to obtain a complete APTMS single monolayer. In parallel, the ordering kinetics of the SAM has been monitored by ATR-FTIR spectroscopy, showing that the monolayer reaches its final order before grafting. We show that those APTMS SAMs can be used to graft C60 molecules deposited from a solution and forming about one monolayer anchored on amine terminal moieties. Such results could help paving the way to the preparation of hybrid C60-based molecular devices on silicon through a bottom-up approach.