INMdok (Leibniz Institute for New Materials)
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Synthetic cell-based tissues for bottom-up assembly of artificial lymphatic organs
Get PDFSynthetic cells have emerged as novel biomimetic materials for studying fundamental cellular functions and enabling new therapeutic approaches. However, replicating the structure and function of complete tissues as self-organized 3D collectives has remained challenging. Here, we engineer lymph node-mimicking 3D lymphatic bottom-up tissues (lymphBUTs) with mechanical adaptability, metabolic activity, and hierarchical microstructural organization based on individual synthetic cells. We demonstrate that primary human immune cells spontaneously infiltrate and functionally integrate into these synthetic lymph nodes to form living tissue hybrids. By tuning the lymphBUT micro-organization and metabolic activity, we induce the ex vivo expansion of therapeutic CD8+ T cells with an IL-10+/IL-17+ regulatory phenotype. Our study highlights the functional integration of living and non-living matter, advancing synthetic cell engineering toward 3D tissue structures
Data-driven analysis of surface roughness influence on weld quality and defect formation in laser welding of Cu–Al
Get PDFThe laser welding of Cu–Al alloys for battery applications in the automotive industry presents significant challenges due to the high reflectivity of copper. Inadequate bonding and low mechanical strength may occur when the laser radiation is directed toward the copper side in an overlap configuration welding. To tackle these challenges, a laser surface treatment technique is implemented to enhance the absorption characteristics and overcome the reflective nature of the copper material. However, elevating the surface roughness and heat-energy input over threshold values leads to heightened temperature and extreme weld. This phenomenon escalates the formation of detrimental intermetallic compounds (IMC), creating defects like cracks and porosity. Metallurgical analysis, which is time-consuming and expensive, is usually used in studies to detect these phases and defects. However, to comprehensively evaluate the weld quality and discern the impact of surface structure, adopting a more innovative approach that replaces conventional cross-sectional metallography is essential. This article proposes a model based on the image feature extraction of the welds to study the effect of the laser-based structure and the other laser parameters. It can detect defects and identify the weld quality by weld classification. However, due to the complexity of the photo features, the system requires image processing and a convolutional neural network (CNN). Results show that the predictive model based on trained data can detect different weld categories and recognize unstable welds. The project aims to use a monitoring model to guarantee optimized and high-quality weld series production. To achieve this, a deeper study of the parameters and the microstructure of the weld is utilized, and the CNN model analyzes the features of 1310 pieces of weld photos with different weld parameters
Contact mechanics of thin films, viscoelastic materials, and frictional interfaces via Green's function molecular dynamics
Get PDFThe theoretical framework of conventional contact mechanics is based on idealized as- sumptions that have shaped the field for more than 140 years. Unfortunately, these assumptions do not lend themselves to the modelling of thin films, viscoelastic materials and frictional interfaces. Therefore, the present thesis is concerned with the system- atic generalization of these assumptions and their GFMD implementation to simulate a variety of previously inaccessible, realistic contact problems. First, finite material thickness is considered in the design of film-terminated fibril struc- tures for skin adhesion. An elastic film resting on a hard foundation is effectively more stiff than its bulk counterpart, which reduces its ability to conform to counter-faces and therefore reduces the adhesion to roughness. Second, the velocity-dependence of soft, adhesive multi-asperity contacts is studied, revealing the importance of topographical saddle points and the initial configuration, from which detachment is initiated. Further- more, we identify a scaling relation describing how short-ranged microscopic interactions slow down the macroscopic relaxation of a contact. Finally, we explore the influence of interfacial friction, showing that it increases local stress concentrations and impedes the fluid flow through the interface. The reported results provide new insight into commonly neglected phenomena, whose practical significance is reinforced by direct comparisons to experiments.Der theoretische Rahmen der konventionellen Kontaktmechanik basiert auf idealisierten Annahmen, die das Fachgebiet seit über 140 Jahren prägen. Leider eignen sich diese nicht für die Modellierung von dünnen Filmen, viskoelastischen Materialien und reibungsbe- hafteten Oberflächen. Daher widmet sich die vorliegende Dissertation der systematischen Verallgemeinerung dieser Annahmen und ihrer Umsetzung in GFMD, um zuvor unzu- gängliche, realistische Kontaktprobleme zu simulieren. Zuerst wird die endliche Materialdicke berücksichtigt bei der Modellierung von filmter- minierten Fibrillenstrukturen für die Hautadhäsion. Ein dünner, eingeklemmter Film verhält sich effektiv steifer, was seine Anpassungsfähigkeit verringert und somit auch seine Haftung auf rauen Oberflächen. Anschließend wird die Zeitabhängigkeit von wei- chen, adhäsiven Multi-Asperitätskontakten untersucht, wobei topographische Sattel- punkte und die Anfangskonfiguration die Ablösung beeinflussen. Zudem identifizieren wir eine Skalierungsbeziehung für die Verlangsamung der makroskopischen Kontaktre- laxation durch kurzreichweitige mikroskopische Wechselwirkungen. Abschließend erfor- schen wir den Einfluss von Reibung, die lokale Spannungskonzentrationen erhöht und den Flüssigkeitsfluss durch die Grenzfläche beeinträchtigt. Die Ergebnisse bieten neue Einblicke in oft vernachlässigte Phänomene, deren praktische Relevanz durch direkte Vergleiche mit Experimenten verdeutlicht wird
Tuning the structure and conductivity of carbon-elastomer composites
Get PDFIn this work, I studied composites made of polydimethylsiloxane (PDMS) and carbon black (CB). This dissertation will focus on the fundamental issue of network formation of CB fillers with different size distributions. The percolation thresholds of composites using different sizes CB is compared to understand how the aggregate arrangement in agglomerates will affect the percolation and electrical conductivity of the composites. The influence of fillers’ structure on electrical conductivity is analyzed on multiple length levels. The fractal dimensions of filler agglomerates in composites change as a function of filler concentrations as shown via ultra-small-angle X-ray scattering. The microstructural changes caused by adding the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to PDMS-CB composites 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 and reduction of the cross-linking density of PDMS both globally and locally, which reduced the Young’s Moduli of the composites. 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 resistance changes consistent with IL’s presence at microscopic CB-CB interfaces.In dieser Arbeit untersuche ich Komposite aus Polydimethylsiloxan (PDMS) und Leitruß (Carbon Black, CB). Der Fokus liegt auf grundlegenden Fragen der Netzwerkbildung von CB Füllern unterschiedlicher Größenverteilungen. Die Perkolationsschwellen von Kompositen mit CB unterschiedlicher Größen werden verglichen, um zu verstehen, wie die Anordnung von Aggregaten Perkolation und elektrische Leitfähigkeit der Komposite beeinflusst. Der Einfluss der Füllstoffstruktur auf verschiedenen Längenskalen auf die elektrische Leitfähigkeit wird auf verschiedenen Längenskalen analysiert. Die fraktale Dimension von Füllstoffagglomeraten in den Kompositen ändert sich mit dem Füllgrad, wie Untersuchungen mittels Ultrakleinwinkelröntgenstreuung zeigen. Die Änderungen der Mikrostruktur durch Beigabe der -Ethyl-3-methylimidazolium-bis(trifluoreomethylsulfonyl)imid zu PDMS-CB Kompositen wird untersucht, um die elektrischen, mechanischen, rheologischen und optischen Eigenschaften der IL enthaltenden Vorstufen und Kompositen zu erklären. Experimente zur Quellung und optische Analysen deuten auf eine begrenzte Löslichkeit der IL in der PDMS-Matrix und eine lokale und globale Reduktion der Vernetzung des PDMS hin, die den Elastizitätsmodul der Komposite verringern. Die rheologische Analyse der Vorstufen zeigt, dass die IL die CB-CB und CB-PDMS Wechselwirkungen verringert und so die Kopplung zwischen Füllstoff und Matrix und die Dehnbarkeit erhöht. Elektromechanische Tests zeigen eine Mischung aus reversiblen und irreversiblen Widerstandsänderungen, die mit der Anwesenheit von IL an mikroskopischen CB-CB Grenzflächen konsistent sind. Elektromechanische Tests zeigen eine Mischung reversibler und irreversibler piezoelektrischer Antworten, die mit der Anwesenheit von IL an mikroskopischen CB-CB Grenzflächen konsistent sind
Structure–Property Relationships of Granular Hybrid Hydrogels Formed through Polyelectrolyte Complexation
Get PDFHybrid hydrogels are hydrogels that exhibit heterogeneity in the network architecture by means of chemical composition and/or microstructure. The different types of interactions, together with structural heterogeneity, which can be created on different length scales, determine the mechanical properties of the final material to a large extent. In this work, the microstructure–mechanical property relationships for a hybrid hydrogel that contains both electrostatic and covalent interactions are investigated. The hybrid hydrogel is composed of a microphase-separated polyelectrolyte complex network (PEC) made of poly(4-styrenesulfonate) and poly(diallyldimethylammonium chloride) within a soft and elastic polyacrylamide hydrogel network. The system exhibits a granular structure, which is attributed to the liquid–liquid phase separation into complex coacervate droplets induced by the polymerization and the subsequent crowding effect of the polyacrylamide chains. The coacervate droplets are further hardened into PEC granules upon desalting the hydrogel. The structure formation is confirmed by a combination of electron microscopic imaging and molecular dynamics simulations. The interpenetration of both networks is shown to enhance the toughness of the resulting hydrogels due to the dissipative behavior of the PEC through the rupture of electrostatic interactions. Upon cyclic loading–unloading, the hydrogels show recovery of up to 80% of their original dissipative behavior in less than 300 s of rest with limited plasticity. The granular architecture and the tough and self-recoverable properties of the designed hybrid networks make them good candidates for applications, such as shape-memory materials, actuators, biological tissue mimics, and elastic substrates for soft sensors
How to steer active colloids up a vertical wall
Get PDFAn important challenge in active matter lies in harnessing useful global work from entities that produce work locally, e.g., via self-propulsion. We investigate here the active matter version of a classical capillary rise effect, by considering a non-phase separated sediment of self-propelled Janus colloids in contact with a vertical wall. We provide experimental evidence of an unexpected and dynamic adsorption layer at the wall. Additionally, we develop a complementary numerical model that recapitulates the experimental observations. We show that an adhesive and aligning wall enhances the pre-existing polarity heterogeneity within the bulk, enabling polar active particles to climb up a wall against gravity, effectively powering a global flux. Such steady-state flux has no equivalent in a passive wetting layer
Membranes on the move: The functional role of the extracellular vesicle membrane for contact-dependent cellular signalling
Get PDFExtracellular vesicles (EVs), lipid-enclosed structures released by virtually all life forms, have gained significant attention due to their role in intercellular and interorganismal communication. Despite their recognized importance in disease processes and therapeutic applications, fundamental questions about their primary function remain. Here, we propose a different perspective on the primary function of EVs, arguing that they serve as essential elements providing membrane area for long-distance, contact-dependent cellular communication based on protein-protein interaction. While EVs have been recognized as carriers of genetic information, additional unique advantages that they could provide for cellular communication remain unclear. Here, we introduce the concept that the substantial membrane area provided by EVs allows for membrane contact-dependent interactions that could be central to their function. This membrane area enables the lateral diffusion and sorting of membrane ligands like proteins, polysaccharides or lipids in two dimensions, promoting avidity-driven effects and assembly of co-stimulatory architectures at the EV-cell interface. The concept of vesicle-induced receptor sequestration (VIRS), for example, describes how EVs confine and focus receptors at the EV contact site, promoting a dense local concentration of receptors into signalosomes. This process can increase the signalling strength of EV-presented ligands by 10-1000-fold compared to their soluble counterparts. The speculations in this perspective advance our understanding of EV-biology and have critical implications for EV-based applications and therapeutics. We suggest a shift in perspective from viewing EVs merely as transporters of relevant nucleic acids and proteins to considering their unique biophysical properties as presentation platforms for long-distance, contact-dependent signalling. We therefore highlight the functional role of the EV membrane rather than their content. We further discuss how this signalling mechanism might be exploited by virus-transformed or cancer cells to enhance immune-evasive mechanisms
Mechanically Robust, Inkjet-Printable Polymer Nanocomposites with Hybrid Gold Nanoparticles and Metal-like Conductivity
Get PDFHybrid core–shell nanoparticles with metal cores and conductive polymer shells yield materials that are sinter-free and highly conductive but mechanically weak. Conventional composites of such nanoparticles are electrically insulating. Here, we introduce microscale phase-separated nanocomposites of hybrid gold-PEDOT:PPS particles in insulating poly(vinyl alcohol) (PVA). They combine electrical conductivities of up to 2.1 × 105 S/m at 10 vol % PVA with increased mechanical adhesion on polyethylene terephthalate and glass substrates. We studied the effects of the PVA molecular weight, hydrolyzation degree, and volume fraction. Composites with 10 vol % highly hydrolyzed PVA at a MW of 89–98 kDa had the highest conductivities and stabilities; highly hydrolyzed PVA even increased the conductivity of the hybrid particle layers. We propose the formation of hydrogen bonds between PVA and PEDOT:PSS that lead to demixing and the formation of stable, structured composites. Finally, we demonstrated the inkjet-printability of inks containing PVA in water with viscosities of 1.6–2.0 Pa s at 50.1 s–1 and prepared bending-resistant electrical leads
Signal-amplifying Biohybrid Material Circuits for CRISPR/Cas-based single-stranded RNA Detection
Get PDFThe 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, we design a highly modular biohybrid material based on CRISPR-Cas13a to translate arbitrary single-stranded RNAs into a biomolecular material response. We exemplify this system by the development of a cascade of communicating materials that can detect the tumor biomarker microRNA miR19b in patient samples or sequences specific for COVID-19. 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, we developed a mathematical model. The model was 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
The effect of nanochannel length on in situ loading times of diffusion-propelled nanoparticles in liquid cell electron microscopy
Get PDFLiquid cell transmission electron microscopy is a powerful tool for visualizing nanoparticle (NP) assemblies in liquid environments with nanometer resolution. However, it remains a challenge to control the NP concentration in the high aspect ratio liquid enclosure where the diffusion of dispersed NPs is affected by the exposed surface of the liquid cell walls. Here, we introduce a semi-empirical model based on the 1D diffusion equation, to predict the NP loading time as they pass through the nanochannel into the imaging volume of the liquid cell. We show that loading of NPs into the imaging volume of the liquid cell may take several days if NPs are prone to attach to the surface of the mm-long nanochannel when using an industry-standard flat microchip. As a means to facilitate mass transport via diffusion, we tested a liquid cell incorporating a microchannel geometry resulting in a NP loading time in the order minutes that allowed us to observe the formation of a randomly oriented self-assembled monolayer in situ using scanning transmission electron microscopy