Assessment of laser-synthesized Si nanoparticle effects on myoblast motility, proliferation and differentiation: towards potential tissue engineering applications.

Due to their biocompatibility and biodegradability and their unique structural and physicochemical properties, laser-synthesized silicon nanoparticles (Si-NPs) are one of the nanomaterials which have been most studied as potential theragnostic tools for non-invasive therapeutic modalities. However, their ability to modulate cell behavior and to promote proliferation and differentiation is still very little investigated or unknown. In this work, ultrapure ligand free Si-NPs of 50 ± 11.5 nm were prepared by femtosecond (fs) laser ablation in liquid. After showing the ability of Si-NPs to be internalized by murine C2C12 myoblasts, the cytotoxicity of the Si-NPs on these cells was evaluated at concentrations ranging from 14 to 224 µg mL-1. Based on these findings, three concentrations of 14, 28 and 56 µg mL-1 were thus considered to study the effect on myoblast differentiation, proliferation and motility at the molecular and phenotypical levels. It was demonstrated that up to 28 µg mL-1, the Si-NPs are able to promote the proliferation of myoblasts and their subsequent differentiation. Scratch tests were also performed revealing the positive Si-NP effect on cellular motility at 14 and 28 µg mL-1. Finally, gene expression analysis confirmed the ability of Si-NPs to promote proliferation, differentiation and motility of myoblasts even at very low concentration. This work opens up novel exciting prospects for Si-NPs made by the laser process as innovative tools for skeletal muscle tissue engineering in view of developing novel therapeutic protocols for regenerative medicine.

Generating liquid nanojets from copper by dual laser irradiation for ultra-high resolution printing.

When the energy of a short laser pulse is localized in a fluid material, a flow motion is induced that can lead to the generation of free-surface jets. This nozzle-free jetting process is exploited to print conductive materials, typically metal nanoparticle inks, but this approach remains limited to the transfer of low viscosity fluids with a minimum feature size of few micrometers. We introduce a dual-laser method to achieve reproducible high-aspect-ratio jets from thin solid films. A first laser irradiation induces the melting of copper thin films and a second synchronized short pulse irradiation initiates the jetting process. Using time-resolved microscopy, we investigate the influence of the film thickness on the flow motion mechanisms and the ejection dynamics. For a wide range of laser fluences, we present observations similar to those obtained when the jets are generated by a single laser pulse from liquid donor films. The use of a solid film allows reducing the film thickness and then the volume of transferred material. Finally, we analyze these results in the perspective of using this double pulse LIFT technique for additive manufacturing of nano-micro-structures. Stable jets are formed from the copper films over distances exceeding 50-µm and are exploited to demonstrate periodic printing of 1.5-µm diameter droplets.

High-speed multi-jets printing using laser forward transfer: time-resolved study of the ejection dynamics.

This paper extends the current understanding of the laser-induced forward transfer (LIFT) process to the multi-jets ejection problem. LIFT has already been used to print micrometer-sized droplets from a liquid donor substrate with single pulse experiments. Here we study the dynamics of the high-speed multi-jets formation from silver nanoparticles ink films with a time-resolved imaging technique. A galvanometric mirrors head controls the spacing between adjacent pulses by scanning the focused beam of a high repetition rate UV picosecond laser along an ink-coated donor substrate. The laser pulses interact with the liquid film and generate cavitation bubbles that propel the ink away from the substrate and form the jets. When the spacing between consecutive pulses is substantially higher than the maximum diameter of the bubbles, there is no interaction between adjacent jets, and these remain unperturbed. However, when the pulses are brought closer significant jet-jet interaction takes place, which results in a clear deviation from the single jet dynamics. Thus, the cavitation bubbles acquire different shapes, the ink is ejected faster and along different directions depending on the spacing between the pulses, and each bubble alters the evolution of the previous one and shifts away from it.

Pulsed-laser printing of silver nanoparticles ink: control of morphological properties.

Fine electrically-conductive patterns of silver nanoparticles ink have been laser printed using the laser-induced forward transfer (LIFT) technique. LIFT is a technique that offers the possibility of printing patterns with high spatial resolution from a wide range of materials in solid or liquid state. Influence of drying the ink film, previous to its transfer, on the printed droplet morphology is discussed. The laser pulse energy and donor-receiver substrate separation were systematically varied and their effects on the transferred droplets were analyzed. The use of an intermediate titanium dynamic release layer was also investigated and demonstrated the possibility of a better control of both the size and shape of the printed patterns. Conditions have been determined for printing flat-top droplets with sharp edges. 21 µm width silver lines with 80 nm thickness have been printed with a smooth convex profile. Electrical resistivities of the transferred patterns are only 5 times higher than the bulk silver.