Directing neuronal migration and growth has an important impact on potential post traumatic therapies. Magnetic manipulation is an advantageous method for remotely guiding cells. In the present study, we have generated highly localized magnetic fields with controllable magnetic flux densities to manipulate neuron-like cell migration and organization at the microscale level. We designed and fabricated a unique miniaturized magnetic device composed of an array of rectangular ferromagnetic bars made of permalloy (Ni80Fe20), sputter-deposited onto glass substrates. The asymmetric shape of the magnets enables one to design a magnetic landscape with high flux densities at the poles. Iron oxide nanoparticles were introduced into PC12 cells, making the cells magnetically sensitive. First, we manipulated the cells by applying an external magnetic field. The magnetic force was strong enough to direct PC12 cell migration in culture. Based on time lapse observations, we analysed the movement of the cells and estimated the amount of MNPs per cell. We plated the uploaded cells on the micro-patterned magnetic device. The cells migrated towards the high magnetic flux zones and aggregated at the edges of the patterned magnets, corroborating that the cells with magnetic nanoparticles are indeed affected by the micro-magnets and attracted to the bars' magnetic poles. Our study presents an emerging method for the generation of pre-programmed magnetic micro-'hot spots' to locate and direct cellular growth, setting the stage for implanted magnetic devices.

Raman scattering (RS) spectra and current-voltage characteristics at room temperature were measured in six series of small samples fabricated by means of electron-beam lithography on the surface of a large size (5x5 mm) industrial monolayer graphene film. Samples were irradiated by different doses of C${}^+$ ion beam up to $10^{15}$ cm${}^{-2}$. It was observed that at the utmost degree of disorder, the Raman spectra lines disappear which is accompanied by the exponential increase of resistance and change in the current-voltage characteristics.These effects are explained by suggestion that highly disordered graphene film ceases to be a continuous and splits into separate fragments. The relationship between structure (intensity of RS lines) and sample resistance is defined. It is shown that the maximal resistance of the continuous film is of order of reciprocal value of the minimal graphene conductivity $\pi h/4e^2\approx 20$ kOhm.Comment: 5 pages, 5 eps figures. As accepted for publication in PR

We present field effect measurements on discontinuous 2D thin films which are composed of a sub monolayer of nano-grains of Au, Ni, Ag or Al. Like other electron glasses these systems exhibit slow conductance relaxation and memory effects. However, unlike other systems, the discontinuous films exhibit a dramatic slowing down of the dynamics below a characteristic temperature T * . T * is typically between 10-50K and is sample dependent. For T < T * the sample exhibits a few other peculiar features such as repeatable conductance fluctuations in millimeter size samples. We suggest that the enhanced system sluggishness is related to the current carrying network becoming very dilute in discontinuous films so that the system contains many parts which are electrically very weakly connected and the transport is dominated by very few weak links. This enables studying the glassy properties of the sample as it transitions from a macroscopic sample to a mesocopic sample, hence, the results provide new insight on the underlying physics of electron glasses.PACS numbers: 75.75.Lf; 72.80.Ng; 72.20.Ee; 73.40.Rw Glassy behavior of the conductivity, σ, in strongly disordered systems that are characterized by strong electronic interactions were predicted by several groups [1][2][3][4][5]. Exciting such a system out of equilibrium leads to an increase in conductivity, σ, after which the relaxation towards equilibrium is characterized by extremely long times, memory phenomena and aging. Since the slow dynamics are related to their electronic properties these systems were termed electron glasses [4]. Experimentally, glassy features were observed in a verity of systems including granular Au [6], amorphous and poly-crystalline indium oxide films [7][8][9][10][11], ultrathin Pb films [12], granular aluminum [13,14] and thin beryllium films [15]. A standard way of excitation in these experiments is by applying a gate voltage, V g , in a MOSFET setup. Conductivity increases for both orientations of V g followed by very slow relaxation of σ which is found to follow an approximate logarithmic dependence on time and may be measured over time-scales of days. A typical feature which has been suggested as the hallmark of intrinsic electron glasses [16] is a "memory dip" (MD) which shows up as a minimum in the σ(V g ) curve when V g is scanned fast compared to the characteristic relaxation time. The dip is centered around the gate voltage at which the sample was allowed to equilibrate.The origin of the extremely slow relaxation and the memory dip as well as their dependence on parameters such as temperature, bias voltage, carrier concentration etc. are still under debate and more experimental information may help shedding light on the physics of electron glasses. In this letter we present results on the glassy properties of two dimensional discontinuous films. We find that these systems exhibit a dramatic slowing down of the dynamics below a characteristic temperature T * . For T < T * the conductance of the sample exhibits reproducible fluct...