Eric Lebraud

Laser-assisted bioprinting for creating on-demand patterns of human osteoprogenitor cells and nano-hydroxyapatite.

Developing tools to reproduce and manipulate the cell micro-environment, including the location and shape of cell patterns, is essential for tissue engineering. Parallel to inkjet printing and pressure-operated mechanical extruders, laser-assisted bioprinting (LAB) has emerged as an alternative technology to fabricate two- and three-dimensional tissue engineering products. The objective of this work was to determine laser printing parameters for patterning and assembling nano-hydroxyapatite (nHA) and human osteoprogenitors (HOPs) in two and three dimensions with LAB. The LAB workstation used in this study comprised an infrared laser focused on a quartz ribbon that was coated with a thin absorbing layer of titanium and a layer of bioink. The scanning system, quartz ribbon and substrate were piloted by dedicated software, allowing the sequential printing of different biological materials into two and/or three dimensions. nHA printing material (bioink) was synthesized by chemical precipitation and was characterized prior and following printing using transmission electron microscopy, Fourier transformed infrared spectroscopy and x-ray diffraction. HOP bioink was prepared using a 30 million cells ml(-1) suspension in culture medium and cells were characterized after printing using a Live/Dead assay and osteoblastic phenotype markers (alcaline phosphatase and osteocalcin). The results revealed that LAB allows printing and organizing nHA and HOPs in two and three dimensions. LAB did not alter the physico-chemical properties of nHA, nor the viability, proliferation and phenotype of HOPs over time (up to 15 days). This study has demonstrated that LAB is a relevant method for patterning nHA and osteoblastic cells in 2D, and is also adapted to the bio-fabrication of 3D composite materials.

Solid-state graphene formation via a nickel carbide intermediate phase

Direct formation of graphene with a controlled number of graphitic layers on dielectric surfaces is highly desired for practical applications but still challenging. Distinguished from the conventional chemical vapor deposition methods, a solid-state rapid thermal processing (RTP) method can achieve high-quality graphene formation on dielectric surfaces without transfer. However, little research is available to elucidate the graphene growth mechanism in the RTP method (heating rate ∼15 °C s−1). Here we show a solid-state transformation mechanism in which a metastable nickel carbide (Ni3C) intermediate phase plays a critical role in transforming amorphous carbon to two dimensional crystalline graphene and contributing to the autonomous Ni evaporation in the RTP process. The formation, migration and decomposition of Ni3C are confirmed to be responsible for graphene formation and Ni evaporation. The Ni3C-assisted graphene formation mechanism expands the understanding of Ni-catalyzed graphene formation and provides insightful guidance for controlled growth of graphene through the solid-state transformation process.

Bis(1,1-dimethyl­guanidinium) tetra­aqua­dimethyl­tin(IV) bis­(sulfate)

Single crystals of the title salt, (C3H10N3)2[Sn(CH3)2(H2O)4](SO4)2, formed concomitantly with the already known [Sn(CH3)3]2SO4·2H2O. In the title structure, the SnIV atom displays a slightly distorted octahedral coordination geometry defined by four O water atoms in the equatorial positions and two methyl groups in the axial positions. In the crystal, various O—H⋯O and N—H⋯O hydrogen-bonding interactions between the organic cation and the coordinated water molecules as donors and the sulfate O atoms as acceptors result in a three-dimensional structure. The SnIV atom is located on an inversion centre, resulting in half of the complex metal cation being in the asymmetric unit.