Parietal Structures of Escherichia coli Can Impact the D-Cateslytin Antibacterial Activity.

Bacterial resistance to conventional antibiotics is of major concern. Antimicrobial peptides (AMPs) are considered excellent alternatives. Among them, D-cateslytin (D-Ctl, derivative of a host defense peptide) has shown high efficiency against a broad spectrum of bacteria. The first target of AMPs is the outer membrane of the bacterium. However, the role of bacterial cell-wall structures on D-Ctl's mechanism of action has not yet been understood. In this study, we investigated the activity of D-Ctl on two isogenic strains of E. coli: one is devoid of any parietal structures; the other constitutively overexpresses only type 1 fimbriae. We studied the damage caused by D-Ctl at several initial concentrations of bacteria and D-Ctl, and exposure times to D-Ctl were examined using a combination of epifluorescence microscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy in attenuated total reflectance mode (ATR-FTIR). The analysis of nanomechanical and spectrochemical properties related to the antibacterial mechanism showed a concentration dependent activity. Whereas the membrane permeabilization was evidenced for all concentrations of D-Ctl and both mutants, no pore formation was observed. The bacterial stiffness is modified dramatically concomitantly to major membrane damage and changes in the spectral fingerprints of the bacteria. In the case of the occurrence of type 1 fimbriae only, an intracellular activity was additionally detected. Our results evidenced that D-Ctl activity is highly impacted by the cell-wall external structures and surface properties of the bacteria.

Integration of sharp silicon nitride tips into high-speed SU8 cantilevers in a batch fabrication process.

Employing polymer cantilevers has shown to outperform using their silicon or silicon nitride analogues concerning the imaging speed of atomic force microscopy (AFM) in tapping mode (intermittent contact mode with amplitude modulation) by up to one order of magnitude. However, tips of the cantilever made out of a polymer material do not meet the requirements for tip sharpness and durability. Combining the high imaging bandwidth of polymer cantilevers with making sharp and wear-resistant tips is essential for a future adoption of polymer cantilevers in routine AFM use. In this work, we have developed a batch fabrication process to integrate silicon nitride tips with an average tip radius of 9 ± 2 nm into high-speed SU8 cantilevers. Key aspects of the process are the mechanical anchoring of a moulded silicon nitride tip and a two-step release process. The fabrication recipe can be adjusted to any photo-processable polymer cantilever.

Phase masks for electron microscopy fabricated by thermal scanning probe lithography.

Nano-structured phase masks offer intriguing possibilities in electron-beam shaping. The fabrication of such phase masks is typically achieved by focused (Ga+-)ion beam milling of thin membranes. To overcome the problem of Ga implantation in the phase mask, we explore the fabrication of silicon-nitride phase masks using thermal scanning probe lithography combined with wet and dry etching. The functionality of the phase masks is demonstrated by generation of electron Vortex and Bessel beams. Major benefit of thermal scanning probe lithography in addition to the absence of ion implantation is the high accuracy and control over the patterned structure and depth.

A compressible scaffold for minimally invasive delivery of large intact neuronal networks.

Millimeter to centimeter-sized injectable neural scaffolds based on macroporous cryogels are presented. The polymer-scaffolds are made from alginate and carboxymethyl-cellulose by a novel simple one-pot cryosynthesis. They allow surgical sterility by means of autoclaving, and present native laminin as an attachment motive for neural adhesion and neurite development. They are designed to protect an extended, living neuronal network during compression to a small fraction of the original volume in order to enable minimally invasive delivery. The scaffolds behave as a mechanical meta-material: they are soft at the macroscopic scale, enabling injection through narrow-bore tubing and potentially good cellular scaffold integration in soft target tissues such as the brain. At the same time, the scaffold material has a high local Young modulus, allowing protection of the neuronal network during injection. Based on macroscopic and nanomechanical characterization, the generic geometrical and mechanical design rules are presented, enabling macroporous cellular scaffold injectability.