Scientific publications

We study the stability of flexible transparent electrodes (FTEs) that were self-assembled from ultra-thin gold nanowires (AuNW) by direct nanoimprinting of inks with different particle concentrations (1 to 10 mg mL−1). The resulting lines were less than 3 μm wide and contained bundles of AuNW with oleylamine (OAm) ligand shells. Small-angle X-ray scattering confirmed a concentration-independent bundle structure. Plasma sintering converted the wire assemblies into lines with a thin metal shell that contributes most to electrical conductivity and covers a hybrid core. We studied the relative change in sheet resistance and the morphology of the FTEs with time. The sheet resistance increased at all concentrations, but at different rates. The metal shell aged by de-wetting and pore formation. The hybrid core de-mixed and densified, which led to a partial collapse of the shell. Residual organics migrated through the shell via its pores. Lines formed at low concentration (cAu = 2 to 3 mg mL−1) contained less residual organics and aged slower than those formed at high cAu ≥ 5 mg mL−1. We passivated the conductive shell with thin, adsorbed layers of PEDOT:PSS and found that it decelerated degradation by slowing surface diffusion and hindering further rupture of the shell. Thick capping layers prevented degradation entirely and stopped pore formation.

Abstract The microstructural changes caused by the addition of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to polydimethylsiloxane (PDMS) elastomer composites filled with carbon black (CB) are analyzed to explain the electrical, mechanical, rheological, and optical properties of IL-containing precursors and composites. Swelling experiments and optical analysis indicate a limited solubility of the IL in the PDMS matrix that reduces the cross-linking density of PDMS both globally and locally, which reduces the Young's moduli of the composites. A rheological analysis of the precursor mixture shows that the IL reduces the strength of carbon–carbon and carbon–PDMS interactions, thus lowering the filler–matrix coupling and increasing the elongation at break. Electromechanical testing reveals a combination of reversible and irreversible piezoresistive responses that is consistent with the presence of IL at microscopic carbon–carbon interfaces, where it enables re-established electrical connections after stress release but reduces the absolute conductivity.

Abstract The electron beam of an environmental scanning electron microscope is used to manipulate gold nanoparticles (AuNPs) at the liquid-vapor interface of their aqueous dispersion. Controlled motion and agglomeration of AuNPs into larger structures is achieved, enabling the writing of superstructures that float at the interface. AuNPs move toward the electron beam, independent of zeta potential, and the spatial range at which this attraction acts is much larger than what is possible for electrostatic interactions. The speed of agglomerate growth depends on the applied electron flux, and electron beam energy. The hypothesis that this electron beam-induced AuNP assembly process is caused by local liquid evaporation upon electron beam heating is presented.

Block copolymers (BCPs) are known to self-assemble into various structures. In particular, crystallization-driven self-assembly (CDSA) strategies revealed a high potential for expanding the scope of obtainable structures at the nanometer length scale. Herein, we report the characterization of different self-assembled structures of a series of amorphous-crystalline BCPs poly(dimethyl silacyclobutane)-block-poly(2-vinyl pyridine) (PDMSB-b-P2VP). The polymers and their structure formation in different solvents were analyzed, and their response toward different solvent vapors and temperatures in the deposited state was evaluated by transmission and scanning electron microscopy (TEM, SEM) and atomic force microscopy (AFM). The influence of additional solvents, temperature, and ultrasonication on colloidal dispersions was investigated with additional dynamic light scattering (DLS) and differential scanning calorimetry (DSC) experiments. Finally, the polymer was introduced to a colloidal confinement by employing the solvent evaporation method in the presence of cetyl-N,N,N-trimethylammoniumbromide (CTAB) or 16-hydroxycetyl-N,N,N-triethylammoniumbromide (CTEAB-OH) as surfactants, resulting in a plethora of additional colloidal structures.

Abstract Despite the progress in surgical techniques and antibiotic prophylaxis, opportunistic wound infections with Bacillus cereus remain a public health problem. Secreted toxins are one of the main factors contributing to B. cereus pathogenicity. A promising strategy to treat such infections is to target these toxins and not the bacteria. Although the exoenzymes produced by B. cereus are thoroughly investigated, little is known about the role of B. cereus collagenases in wound infections. In this report, the collagenolytic activity of secreted collagenases (Col) is characterized in the B. cereus culture supernatant (csn) and its isolated recombinantly produced ColQ1 is characterized. The data reveals that ColQ1 causes damage on dermal collagen (COL). This results in gaps in the tissue, which might facilitate the spread of bacteria. The importance of B. cereus collagenases is also demonstrated in disease promotion using two inhibitors. Compound 2 shows high efficacy in peptidolytic, gelatinolytic, and COL degradation assays. It also preserves the fibrillar COLs in skin tissue challenged with ColQ1, as well as the viability of skin cells treated with B. cereus csn. A Galleria mellonella model highlights the significance of collagenase inhibition in vivo.

Abstract Advances in optogenetics and the increasing use of implantable devices for therapies and health monitoring are driving demand for compliant, biocompatible optical waveguides and scalable methods for their manufacture. Molding, thermal drawing, and dip-coating are the most prevalent approaches in recent literature. Here the authors demonstrate that extrusion printing at room temperature can be used for continuous fabrication of compliant optical waveguides with polydimethylsiloxane (PDMS) core and crosslinked Pluronic F127-diacrylate (Pluronic-DA) cladding. The optical fibers are printed from fluid precursor inks and stabilized by physical interactions and photoinitiated crosslinking in the Pluronic-DA. The printed fibers show optical loss values of 0.13–0.34 dB cm–1 in air and tissue within the wavelength range of 405–520 nm. The fibers have a Young's Modulus (Pluronic cladding) of 150 kPa and can be stretched to more than 5 times their length. The optical loss of the fibers shows little variation with extension. This work demonstrates how printing can simplify the fabrication of compliant and stretchable devices from materials approved for clinical use. These can be of interest for optogenetic or photopharmacology applications in extensible tissues, like muscles or heart.

Stimuli-responsive hydrogels are smart materials that respond to variations caused by external stimuli and that are currently exploited for biomedical applications such as biosensing, drug delivery and tissue engineering. The development of stimuli-responsive hydrogels with defined user control is relevant to realize materials with advanced properties. Recently, our group reported firefly luciferin-inspired hydrogel matrices for 3D cell culture. This platform exhibited advantages like rapid gelation rate and tunability of mechanical and biological properties. However, this first molecular design did not allow fine control of the gelation onset, which restricts application as a cell-encapsulating matrice with injectable and processable properties. In this article, we endow the firefly luciferin-inspired hydrogels with redox-triggering capability, to overcome the limitations of the previous system and to widen its application range. We achieve this goal by introducing protected macromers as hydrogel polymeric precursors that can be activated in the presence of a mild reductant, to trigger gel formation in situ with a high degree of control. We demonstrate that the regulation of molecular parameters (e.g., structure of the protecting group, reductant type) and environmental parameters (e.g., pH, temperature) of the deprotection reaction can be exploited to modulate materials properties. This redox-triggerable system enables precise control over gelation onset and kinetics, thus facilitating its utilization as an injectable hydrogel without negatively impacting its cytocompatibility. Our findings expand the current toolkit of chemically-based stimuli-responsive hydrogels.

There is an increasing interest in coupling reactions for cross-linking of cell-encapsulating hydrogels under biocompatible, chemoselective, and tunable conditions. Inspired by the biosynthesis of luciferins in fireflies, here we exploit the cyanobenzothiazole-cysteine (CBT-Cys) click ligation to develop polyethylene glycol hydrogels as tunable scaffolds for cell encapsulation. Taking advantage of the chemoselectivity and versatility of CBT-Cys ligation, a highly flexible gel platform is reported here. We demonstrate luciferin-inspired hydrogels with important advantages for cell encapsulation applications: (i) gel precursors derived from inexpensive reagents and with good stability in aqueous solution (>4 weeks), (ii) adjustable gel mechanics within physiological ranges (E = 180–6240 Pa), (iii) easy tunability of the gelation rate (seconds to minutes) by external means, (iv) high microscale homogeneity, (v) good cytocompatibility, and (iv) regulable biological properties. These flexible and robust CBT-Cys hydrogels are proved as supportive matrices for 3D culture of different cell types, namely, fibroblasts and human mesenchymal stem cells. Our findings expand the toolkit of click chemistries for the fabrication of tunable biomaterials.

Endothelial cells play a central role in the vascular system, where their function is tightly regulated by both cell-extracellular matrix (e.g., via integrins) and cell–cell interactions (e.g., via cadherins). In this study, we incorporated cholesterol-modified integrin and N-cadherin peptide binding ligands in fluid supported lipid bilayers. Human umbilical vein endothelial cell adhesion, spreading and vinculin localization in these cells were dependent on ligand density. One composition led to observe a higher extent of cell spreading, where cells exhibited extensive lamellipodia formation and a qualitatively more distinct N-cadherin localization at the cell periphery, which is indicative of N-cadherin clustering and a mimic of cell–cell contact formation. The results can be used to reconstitute the endothelial-pericyte interface on biomedical devices and materials.

The opto-electronic properties of small-molecules and functional dyes usually differ when incorporated into solid matrices with respect to their isolated form due to an aggregation phenomenon that alters their optical and fluorescent properties. These spectroscopic modifications are studied in the framework of the exciton theory of aggregates, which has been extensively applied in the literature for the study of molecular aggregates of the same type of molecules (homoaggregation). Despite the demonstrated potential of the control of the heteroaggregation process (aggregation of different types of molecules), most of the reported works are devoted to intramolecular aggregates, complex molecules formed by several chromophores attached by organic linkers. The intramolecular aggregates are specifically designed to hold a certain molecular structure that, on the basis of the exciton theory, modifies their optical and fluorescent properties with respect to the isolated chromophores that form the molecule. The present article describes in detail the incorporation of Rhodamine 6G (Rh6G) and 800 (Rh800) into polymeric matrices of poly-(methyl methacrylate), PMMA. The simultaneous incorporation of both dyes results in an enhanced fluorescent emission in the near-infrared (NIR), originating from the formation of ground-state Rh6G–Rh800 intermolecular heteroaggregates. The systematic control of the concentration of both rhodamines provides a model system for the elucidation of the heteroaggregate formation. The efficient energy transfer between Rh6G and Rh800 molecules can be used as wavelength shifters to convert effectively the light from visible to NIR, a very convenient wavelength range for many practical applications which make use of inexpensive commercial detectors and systems.