Controlling cell adhesion via replication of laser micro/nano-textured surfaces on polymers.

The aim of this study is to investigate cell adhesion and viability on highly rough polymeric surfaces with gradient roughness ratios and wettabilities prepared by microreplication of laser micro/nano-textured Si surfaces. Negative replicas on polydimethylsiloxane as well as positive ones on a photocurable (organically modified ceramic) and a biodegradable (poly(lactide-co-glycolide)) polymer have been successfully reproduced. The final culture substrates comprised from forests of micron-sized conical spikes exhibiting a range of roughness ratios and wettabilities, was achieved by changing the laser fluence used to fabricate the original template surfaces. Cell culture experiments were performed with the fibroblast NIH/3T3 and PC12 neuronal cell lines in order to investigate how these surfaces are capable of modulating different types of cellular responses including, viability, adhesion and morphology. The results showed a preferential adhesion of both cell types on the microstructured surfaces compared to the unstructured ones. In particular, the fibroblast NIH/3T3 cells show optimal adhesion for small roughness ratios, independent of the surface wettability and polymer type, indicating a non-monotonic dependence of cell adhesion on surface energy. In contrast, the PC12 cells were observed to adhere well to the patterned surfaces independent of the roughness ratio and wettability. These experimental findings are correlated with micromechanical measurements performed on the unstructured and replicated surfaces and discussed on the basis of previous observations describing the relation of cell response to surface energy and rigidity.

Electrowetting properties of micro/nanostructured black silicon.

This paper reports on the electrowetting on dielectric (EWOD) properties of dual rough black silicon (Si) surfaces, produced by pulsed laser structuring of Si wafers and subsequently coating with a thermally grown oxide and a chloroalkylsilane layer. By varying the laser fluence, it was possible to tune the black Si wettability, from hydrophobicity to water repellence, through a systematic and reproducible variation of the surface roughness at micro- and nanoscales. It is shown that a liquid droplet on these surfaces can be readily switched between superhydrophobicity and hydrophilicity by applying moderate external electric fields. This behavior is reversible or irreversible depending on the geometry of the patterned structures and the water repellence characteristics of the different surfaces. The fundamental role of structural and dynamic wettability characteristics on the switching behavior during the EWOD process is investigated and discussed. The results indicate the potential use of dual rough black Si for EWOD applications.

From superhydrophobicity and water repellency to superhydrophilicity: smart polymer-functionalized surfaces.

pH-responsive surfaces, reversibly switching between superhydrophilicity and superhydrophobicity/water repellency, are developed by "grafting from" a pH-sensitive polymer onto a hierarchically micro/nano-structured substrate. We quantify the water repellency by investigating the restitution coefficient of water droplets bouncing off the surfaces. The water repellent state requires appropriate hydrophobicity of the functionalizing polymer as well as very low values of contact angle hysteresis.

Silicon scaffolds promoting three-dimensional neuronal web of cytoplasmic processes.

Primary neurons were grown on structured silicon (Si) substrates, in the absence of chemotropic factors or synthetic extracellular matrix. The Si substrates used for the study comprise hierarchical structures in the micro- and nanolength scales. The substrates were structured via femtosecond laser irradiation of the Si wafer, in a reactive SF(6) environment. Electron microscopy revealed that the neurons formed an elaborate web of cytoplasmic processes in the absence of glial elements. The neuronal cytoplasm autografted the depth of the spikes, and the neurite sprouting took place over the spikes surface. Here we demonstrate how microfabrication of a Si surface provides an excellent platform for multifaceted studies of neuronal specimens.

Generation of Al nanoparticles via ablation of bulk Al in liquids with short laser pulses.

Highly stable aluminum nanoparticles (NPs) are generated via ablation of bulk Al in ethanol using either femtosecond (fs) or picosecond (ps) laser sources. The colloidal NPs solutions obtained with fs pulses exhibit a yellow coloration and show an increased optical absorption between 300 and 400 nm, tentatively assigned to the plasmon resonance of nanosized Al. The corresponding solutions after ps ablation are gray colored and opalescent. The average size of the NPs formed ranges from 20 nm for the fs case to 60 nm for the ps case, while a narrower distribution is obtained using the shorter pulses. High Resolution Transmission Electron Microscopy (HRTEM) studies indicate that the NPs are mostly amorphous with single crystalline inclusions. Al NPs generated with short laser pulses slowly react with air oxygen due to the presence of a native oxide cladding, which efficiently passivates their surface against further oxidation.