Poly(methyl methacrylate) - Palladium clusters nanocomposite formation by supersonic cluster beam deposition: a method for microstructured metallization of polymer surfaces

Nanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of palladium clusters on Poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd cluster are implanted in the polymer and form a continuous layer extending for several tens of nanometers beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared to metallic films obtained by thermal evaporation. These results suggest that SCBD is a promising tool for the fabrication of metallic microstructures on flexible polymeric substrates.Comment: 11 pages, 3 figure

Esplorare il territorio. Linee di ricerca socio-spaziali

Il volume nasce nell’ambito di un insegnamento di Sociologia urbana all’interno del quale era stata prevista un’attività seminariale che intendeva rispondere a un’esigenza didattica prioritaria: mostrare agli studenti la poliedricità di studi e ricerche che si collocavano nell’ambito della disciplina e al contempo evidenziarne la comune opzione euristica, andando oltre la prima impressione di un cumularsi magmatico di filoni di ricerca. Coinvolgendo giovani ricercatori, l’attività seminariale intendeva richiamare l’attenzione sulla valenza esplicativa della dimensione territoriale nella comprensione di una molteplicità di fenomeni sociali anche laddove questa non era immediatamente evidente e spesso non adeguatamente riconosciuta. Si trattava, per gli studenti coinvolti, di cogliere il filo rosso che univa i diversi contributi esposti nel seminario, pubblicati in questo volume. Le ricerche presentate hanno il pregio e il merito di concentrarsi sugli aspetti spaziali e territoriali delle diverse forme sociali studiate, cogliendone la dimensione materiale e contribuendo inoltre a una spazializzazione della teoria sociologica. Il territorio non emerge come mero sfondo e contenitore di un insieme di processi sociali ma come socialmente strutturato dalle forze in campo e strutturante le stesse. Nello spazio non si proietta semplicemente la vita sociale che su di esso si appoggia, ma esso stesso è “fattore attivo”

Nano-Stenciled RGD-Gold Patterns That Inhibit Focal Contact Maturation Induce Lamellipodia Formation in Fibroblasts

Cultured fibroblasts adhere to extracellular substrates by means of cell-matrix adhesions that are assembled in a hierarchical way, thereby gaining in protein complexity and size. Here we asked how restricting the size of cell-matrix adhesions affects cell morphology and behavior. Using a nanostencil technique, culture substrates were patterned with gold squares of a width and spacing between 250 nm and 2 µm. The gold was functionalized with RGD peptide as ligand for cellular integrins, and mouse embryo fibroblasts were plated. Limiting the length of cell-matrix adhesions to 500 nm or less disturbed the maturation of vinculin-positive focal complexes into focal contacts and fibrillar adhesions, as indicated by poor recruitment of α5-integrin. We found that on sub-micrometer patterns, fibroblasts spread extensively, but did not polarize. Instead, they formed excessive numbers of lamellipodia and a fine actin meshwork without stress fibers. Moreover, these cells showed aberrant fibronectin fibrillogenesis, and their speed of directed migration was reduced significantly compared to fibroblasts on 2 µm square patterns. Interference with RhoA/ROCK signaling eliminated the pattern-dependent differences in cell morphology. Our results indicate that manipulating the maturation of cell-matrix adhesions by nanopatterned surfaces allows to influence morphology, actin dynamics, migration and ECM assembly of adhering fibroblasts

Cell shape-dependent early responses of fibroblasts to cyclic strain

Randomly spread fibroblasts on fibronectin-coated elastomeric membranes respond to cyclic strain by a varying degree of focal adhesion assembly and actin reorganization. We speculated that the individual shape of the cells, which is linked to cytoskeletal structure and pre-stress, might tune these integrin-dependent mechanotransduction events. To this aim, fibronectin circles, squares and rectangles of identical surface area (2000μm(2)) were micro-contact printed onto elastomeric substrates. Fibroblasts plated on these patterns occupied the corresponding shapes. Cyclic 10% equibiaxial strain was applied to patterned cells for 30min, and changes in cytoskeleton and cell-matrix adhesions were quantified after fluorescence staining. After strain, megakaryocytic leukemia-1 protein translocated to the nucleus in most cells, indicating efficient RhoA activation independently of cell shape. However, circular and square cells (with radial symmetry) showed a significantly greater increase in the number of actin stress fibers and vinculin-positive focal adhesions after cyclic strain than rectangular (bipolar) cells of identical size. Conversely, cyclic strain induced larger changes in pY397-FAK positive focal complexes and zyxin relocation from focal adhesions to stress fibers in bipolar compared to symmetric cells. Thus, radially symmetric cells responded to cyclic strain with a larger increase in assembly, whereas bipolar cells reacted with more pronounced reorganization of actin stress fibers and matrix contacts. We conclude that integrin-mediated responses to external mechanical strain are differentially modulated in cells that have the same spreading area but different geometries, and do not only depend on mere cell size

Micro-beams with tunable stiffness and curvature for mechano-sensitive cell culture substrates

We present the complete fabrication of 3D microenvironments for single-cell culture. They are based on SiO2 cantilevers bending out-of-plane with radii as small as 20 um. By engineering the intrinsic stress of SiO2 thin films, we were able to tune the radii and the spring constant of cantilevers. Moreover micrometric Au dots were deposited onto the cantilevers, and functionalized in order to localize focal adhesions (FAs). Mouse fibroblasts were finally cultured and developed FAs on Au dots only

Single-Cell 3D Bio-Mems Environment With Engineered Geometry And Physiologically Relevant Stiffnesses

We present a three dimensional (3D) microenvironment for on-chip cell culture, with engineered geometrical and mechanical properties. The device, named mu-flower, is based on micorfabricated cantilever beams bent out of plane by the intrinsic stresses of a bilayer structure. The use of Ti-SiO2 bilayers with various thicknesses allows spanning a large range of rigidities while keeping the size nearly constant. The geometrical and mechanical properties of the devices are thus decoupled, and the degrees of stiffness of several physiological tissues are matched. These characteristics make mu-flowers a microfabricated cell-culture substrate designed to mimic essential physical properties of the in vivo environment (dimensionality, shape and rigidity) in a precisely controlled way, at the single-cell scale, and with a high degree of parallelization

Cell force measurements in 3D microfabricated environments based on compliant cantilevers.

We report the fabrication, functionalization and testing of microdevices for cell culture and cell traction force measurements in three-dimensions (3D). The devices are composed of bent cantilevers patterned with cell-adhesive spots not lying on the same plane, and thus suspending cells in 3D. The cantilevers are soft enough to undergo micrometric deflections when cells pull on them, allowing cell forces to be measured by means of optical microscopy. Since individual cantilevers are mechanically independent of each other, cell traction forces are determined directly from cantilever deflections. This proves the potential of these new devices as a tool for the quantification of cell mechanics in a system with well-defined 3D geometry and mechanical properties

Flexible and biocompatible microelectrode arrays fabricated by supersonic cluster beam deposition on SU-8

We fabricated highly adherent and electrically conductive micropatterns on SU-8 by supersonic cluster beam deposition (SCBD). This technique is based on the aerodynamical acceleration of neutral metallic nanoparticles produced in the gas phase. The kinetic energy acquired by the nanoparticles allows implantation in a SU-8 layer, thus producing a metal-polymer nanocomposite thin layer. The nanocomposite shows ohmic electrical conduction and it can also be used as an adhesion layer for further metallization with a metallic overlayer. We characterized the electrical conduction, adhesion and biocompatibility of microdevices obtained by SCBD on SU-8 demonstrating the compatibility of our approach with standard lift off technology on 4’’ wafer. A self-standing and flexible micro electrode array has been produced. Cytological tests with neuronal cell lines demonstrated an improved cell growth on the nanocomposite layer