Scientific publications

Metallic filler particles form continuous paths in nonconductive elastomers and provide electrical conduction. The resulting conductive polymer composites (CPCs) are useful as flexible and stretchable conductors or strain sensors. Percolation theory accurately describes the changes in conductivity close to a critical loading φC but fails to predict conductivities above this transition. Here, we show that graph theory (GT) metrics can be used to correlate network structure and macroscopic electrical conductivity above φC. We used FIB-SEM tomography to reconstruct (31.5 μm)3 large CPC volumes with 2.5-μm-diameter silver spheres at loadings between 27 and 52 vol%. We find linear correlations between the number of nodes and edges and the average graph degree, length, efficiency, and current-flow betweenness with the conductivity of CPCs. We formulate a simple model that describes the increase in conductivity above φC in terms of network morphology. Kirchhoff circuit analysis reveals that the change in network topology alone cannot explain the experimentally observed conductivity. We show that the average particle–particle contact resistance scales reciprocally with degree. This suggests that the filler loading affects contact areas or tunneling widths, providing a link between mechanical and electrical network properties.

Electrofluids, concentrated suspensions of electrically conductive particles, have recently attracted attention for their potential as soft conductors. In this study, we investigated the influence of morphological differences in 2D filler materials (graphene-like) on the electromechanical properties of glycerol-based electrofluids. Plasma synthesized few-layer graphene (FLG), chemically exfoliated multi-layer graphene (MLG), and bulk graphite were used as 2D fillers, which differed in specific surface area, aspect ratio, and intrinsic stiffness. Results showed that both electrical and mechanical percolation thresholds decreased with increasing filler aspect ratio. The high aspect ratio of the FLG promotes network formation at low filler concentrations, conferring its electrofluids with the lowest electrical (0.16 wt%) and mechanical (0.63 wt%) percolation threshold. Rheological amplitude sweeps revealed a larger linear viscoelastic region for electrofluids containing few-layer graphene, caused by their reduced internal stiffness and higher aspect ratio. This large capacity for storing elastic energy of FLG-electrofluids makes them almost insensitive to uniaxial tensile strain when encapsulated in elastomers, leading to gauge factors below 1, ideal for soft electrical resistors. In contrast, MLG-electrofluids exhibited good sensing properties as strain gauges. The presented study on structure-property relationships helps for rational design of electrofluids with tailored electromechanical properties that can be tuned for different use cases.

Most (bio)resins for volumetric printing (VP) are based on (meth)acrylated polymer precursors mixed with gelatine or Pluronic as thermoreversible thickening agents. Here we investigate if fast photocrosslinking reactions, like the thiol-ene, allow VP of low viscosity bioresins without the need of viscosity modifiers. We used a 4% w/v hyaluronic acid norbornene (HA-NB) resin with viscosity <0.1 Pa s, a frequently used matrix for encapsulation of cells. Using light doses in the range of 150–200 mJ cm−2, stable 8 × 5 × 2 mm3 crosslinked scaffolds with internal bifurcated channels down to ∼200 µm dimensions were printed in <30 s. At this concentration, HA methacrylate (HA-MA) resins with comparable viscosity and functionalization degree did not form stable structures. RGD-functionalized HA-NB scaffolds were printed in the presence of fibroblasts and showed homogeneous cell distribution across the scaffold, with cell viability >90%. Encapsulated cells spread and showed fibroblast-like morphology in 7 d cultures. We demonstrate volumetric bioprinting of low molecular weight HA-based bioresins without viscosity modifiers and in the absence of post-printing steps.

Lacticaseibacillus rhamnosus strains are widely recognized for their probiotic potential and relevance in urogenital and gut health. However, their genetic tractability and genetic tools remain limited, hindering functional microbiome research and synthetic biology applications. In this study, we expanded the genetic toolbox for the widely used probiotic strains, L. rhamnosus GR-1 and L. rhamnosus GG, by implementing direct plasmid cloning and testing of a set of genetic elements earlier validated in Lactiplantibacillus plantarum. Among five constitutive promoters (PtlpA, Ptec, Pcpg, P48 and P23), PtlpA showed strong promoter activity in L. rhamnosus GR-1. We further characterized this promoter's functionality by incorporating a repressor and assessing its native thermo-responsiveness and stability over time, enhancing its potential for industrial applications. Using these tools, we engineered L. rhamnosus GR-1 with constitutive fluorescence of mCherry, mScarlet3 and sfGFP. The functionality of these fluorescent L. rhamnosus GR-1 strains was shown in a proof-of-concept growth competition experiment with a fluorescent pathogenic Staphylococcus aureus strain. These constitutively fluorescent L. rhamnosus strains, along with the expanded genetic toolkit, offer valuable resources for studying functional properties, such as adhesion, microbe–microbe and host–microbe interactions, and advancing Lactobacillaceae as a chassis for synthetic biology.

The functional integration of biological switches with synthetic building blocks enables the design of modular, stimulus-responsive biohybrid materials. By connecting the individual modules via diffusible signals, information-processing circuits can be designed. Such systems are, however, mostly limited to respond to either small molecules, proteins, or optical input thus limiting the sensing and application scope of the material circuits. Here, a highly modular biohybrid material is design based on CRISPR/Cas13a to translate arbitrary single-stranded RNAs into a biomolecular material response. This system exemplified by the development of a cascade of communicating materials that can detect the tumor biomarker microRNA miR19b in patient samples or sequences specific for SARS-CoV. Specificity of the system is further demonstrated by discriminating between input miRNA sequences with single-nucleotide differences. To quantitatively understand information processing in the materials cascade, a mathematical model is developed. The model is used to guide systems design for enhancing signal amplification functionality of the overall materials system. The newly designed modular materials can be used to interface desired RNA input with stimulus-responsive and information-processing materials for building point-of-care suitable sensors as well as multi-input diagnostic systems with integrated data processing and interpretation.

Background: Intima proliferation and in-stent restenosis is a challenging situation in interventional treatment of small vessel obstruction. Al/Al2O3 nanowires have been shown to accelerate vascular endothelial cell proliferation and migration in vitro, while suppressing vascular smooth muscle cell growth. Moreover, surface modification of Al/Al2O3 nanowires with poly[bis(2,2,2-trifluoromethoxy)phosphazene (PTFEP) coating enables further advantages such as reduced platelet adhesion. Therefore, the study's goal was to compare the biocompatibility of novel Al/Al2O3 + PTFEP coated nanowire bare-metal stents to uncoated control stents in vivo using optical coherence tomography (OCT), quantitative angiography and histomorphometric assessment. Methods: 15 Al/Al2O3 + PTFEP coated and 19 control stents were implanted in the cervical arteries of 9 Aachen minipigs. After 90 days, in-stent stenosis, thrombogenicity, and inflammatory response were assessed. Scanning electron microscopy was used to analyse the stent surface. Results: OCT analysis revealed that neointimal proliferation in Al/Al2O3 + PTFEP coated stents was significantly reduced compared to control stents. The neointimal area was 1.16 ± 0.77 mm2 in Al/Al2O3 + PTFEP coated stents vs. 1.98 ± 1.04 mm2 in control stents (p = 0.004), and the neointimal thickness was 0.28 ± 0.20 vs. 0.47 ± 0.10 (p = 0.003). Quantitative angiography showed a tendency to less neointimal growth in coated stents. Histomorphometry showed no significant difference between the two groups and revealed an apparent inflammatory reaction surrounding the stent struts. Conclusions: At long-term follow-up, Al/Al2O3 + PTFEP coated stents placed in peripheral arteries demonstrated good tolerance with no treatment-associated vascular obstruction and reduced in-stent restenosis in OCT. These preliminary in vivo findings indicate that Al/Al2O3 + PTFEP coated nanowire stents may have translational potential to be used for the prevention of in-stent restenosis.

Supercapacitors are efficient and versatile energy storage devices, offering remarkable power density, fast charge/discharge rates, and exceptional cycle life. As research continues to push the boundaries of their performance, electrode fabrication techniques are critical aspects influencing the overall capabilities of supercapacitors. Herein, we aim to shed light on the advantages offered by dry electrode processing for advanced supercapacitors. Notably, our study explores the performance of these electrodes in three different types of electrolytes: organic, ionic liquids, and quasi-solid states. By examining the impact of dry electrode processing on various electrode and electrolyte systems, we show valuable insights into the versatility and efficacy of this technique. The supercapacitors employing dry electrodes demonstrated significant improvements compared with conventional wet electrodes, with a lifespan extension of +45% in organic, +192% in ionic liquids, and +84% in quasi-solid electrolytes. Moreover, the increased electrode densities achievable through the dry approach directly translate to improved volumetric outputs, enhancing energy storage capacities within compact form factors. Notably, dry electrode-prepared supercapacitors outperformed their wet electrode counterparts, exhibiting a higher energy density of 6.1 Wh cm−3 compared with 4.7 Wh cm−3 at a high power density of 195 W cm−3, marking a substantial 28% energy improvement in the quasi-solid electrolyte.

A low-temperature sintering mechanism of silver microparticles is established and used to enable the design-for-recycling of printed electronics. The formation of necks during the initial phase sintering of precipitated and atomized silver microparticles is studied. Temperature- and time-dependent in-situ analyses indicate the existence of a mobile silver species that provides efficient mass transport. The activation energy of neck formation identifies silver ion formation as the rate-limiting step of low-temperature silver sintering. It is demonstrated that resistivities of 271 times that of bulk silver can be attained after 40 minutes at 150°C. Low-temperature sintering not only reduces the energy required during thermal treatment but it yields layers that are suitable for recycling, too. The resulting layers have conductive necks that are mechanically weak enough to be broken during recycling. Printed layers are redispersed and the recycled silver powder is reused without loss of the electrical performance in new prints. Their conductivities are industrially relevant, which makes this recyclability-by-design approach promising for manufacturing more sustainable printed electronics.

Tunneling nanotubes (TNTs) are thin, dynamic, long membrane protrusions that allow intercellular exchanges of signaling clues, molecules and organelles. The presence of TNTs and their involvement as drug delivery channels have been observed in several types of cancer, including glioblastoma. Recently, increased attention has been directed toward nanoparticles (NPs) that can be transported in TNTs. However, few data are available on the role of physical parameters of nanoparticles, such as size, shape, charge and flexibility, in determining their transfer efficiency between cells by TNTs. Here, we focused our attention on NP shape, manufacturing spherical, discoidal and deformable negatively charged lipid-based NPs with sizes <120 nm and similar stiffness. The TNT-mediated transfer of NPs was investigated in 2D and 3D culture models of human glioblastoma cells. The permeability and biocompatibility of the blood–brain barrier (BBB) were also assessed. Results showed that discoidal NPs displayed the highest TNT-mediated transfer efficiency between cancer cells, with a maximum velocity of 69 nm s−1, and a higher endothelial permeability (1.29 × 10−5 cm min−1) across the BBB in an in vitro model. This depends on the NP shape because discoidal NPs have a larger surface area exposed to the flow along the TNT channel. Overall, the results suggest that the shape of NPs is the game-changer for more efficient TNT-mediated transfer between cancer cells, thus introducing a sustainable solution to improve the diffusion rate at which the NPs spread in the tumour microenvironment, opening the possibility of ameliorating drug distribution to difficult-to-reach cancer cell populations.

Currently, over 60% of the world's population lives in cities. Urban living has many advantages but there are also challenges regarding the need for smart urbanization. The next generation of tunable 2D nanomaterials, called MXenes, is the critical enabling technology that can bring the current urban thinking to the next level, called a smart city. The smart city is a novel concept based on a framework of self-sufficient technologies that are interactive and responsive to citizens’ needs. In this perspective, MXene-enabled technologies for sustainable urban development are discussed. They can advance self-sufficient, adaptive, and responsive buildings that can minimize resource consumption, solving the deficiency of essential resources such as clean energy, water, and air. MXenes are at the cutting edge of technological limitations associated with the Internet of Things (IoT) and telemedicine, combining diverse properties and offering multitasking. It is foreseen that MXenes can have a bright future in contributing to the smart city concept. Therefore, the roadmap is presented for demonstrating the practical feasibility of MXenes in the smart city. Altogether, this study promotes the role of MXenes in advancing the well-being of citizens by raising the quality of urban living to the next level.