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- ItemMelt Electrowriting of Graded Porous Scaffolds to Mimic the Matrix Structure of the Human Trabecular Meshwork(Washington, DC : ACS Publ., 2022) Włodarczyk-Biegun, Małgorzata K.; Villiou, Maria; Koch, Marcus; Muth, Christina; Wang, Peixi; Ott, Jenna; del Campo, AranzazuThe permeability of the human trabecular meshwork (HTM) regulates eye pressure via a porosity gradient across its thickness modulated by stacked layers of matrix fibrils and cells. Changes in HTM porosity are associated with increases in intraocular pressure and the progress of diseases such as glaucoma. Engineered HTMs could help to understand the structure-function relation in natural tissues and lead to new regenerative solutions. Here, melt electrowriting (MEW) is explored as a biofabrication technique to produce fibrillar, porous scaffolds that mimic the multilayer, gradient structure of native HTM. Poly(caprolactone) constructs with a height of 125-500 μm and fiber diameters of 10-12 μm are printed. Scaffolds with a tensile modulus between 5.6 and 13 MPa and a static compression modulus in the range of 6-360 kPa are obtained by varying the scaffold design, that is, the density and orientation of the fibers and number of stacked layers. Primary HTM cells attach to the scaffolds, proliferate, and form a confluent layer within 8-14 days, depending on the scaffold design. High cell viability and cell morphology close to that in the native tissue are observed. The present work demonstrates the utility of MEW for reconstructing complex morphological features of natural tissues.
- ItemMechanical Robustness of Graphene on Flexible Transparent Substrates(Washington, DC : Soc., 2016) Kang, Moon H.; Prieto López, Lizbeth O.; Chen, Bingan; Teo, Ken; Williams, John A.; Milne, William I.; Cole, Matthew T.This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend–relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium–tin oxide on PET. After 104 bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.
- ItemLight-Regulated Angiogenesis via a Phototriggerable VEGF Peptidomimetic(Weinheim : Wiley-VCH, 2021) Nair, Roshna V.; Farrukh, Aleeza; del Campo, AránzazuThe application of growth factor based therapies in regenerative medicine is limited by the high cost, fast degradation kinetics, and the multiple functions of these molecules in the cell, which requires regulated delivery to minimize side effects. Here a photoactivatable peptidomimetic of the vascular endothelial growth factor (VEGF) that allows the light-controlled presentation of angiogenic signals to endothelial cells embedded in hydrogel matrices is presented. A photoresponsive analog of the 15-mer peptidomimetic Ac-KLTWQELYQLKYKGI-NH2 (abbreviated PQK) is prepared by introducing a 3-(4,5-dimethoxy-2-nitrophenyl)-2-butyl (DMNPB) photoremovable protecting group at the Trp4 residue. This modification inhibits the angiogenic potential of the peptide temporally. Light exposure of PQK modified hydrogels provide instructive cues to embedded endothelial cells and promote angiogenesis at the illuminated sites of the 3D culture, with the possibility of spatial control. PQK modified photoresponsive biomaterials offer an attractive approach for the dosed delivery and spatial control of pro-angiogenic factors to support regulated vascular growth by just using light as an external trigger.
- ItemTowards hybrid one-pot/one-electrode Pd-NPs-based nanoreactors for modular biocatalysis(Amsterdam [u.a.] : Elsevier, 2021) Koch, M.; Apushkinskaya, N.; Zolotukhina, E.V.; Silina, Y.E.Here, fundamental aspects affecting template-assisted engineering of oxidase-associated peroxide oxidation co-catalysis of the modeled microanalytical system based on the hybrid palladium nanoparticles (Pd-NPs) with tailored functional properties were studied. By an accurate tuning and validation of the experimental setup, a modular Pd-NPs-doped one-pot/one-electrode amperometric nanobiosensor for advanced multiplex analyte detection was constructed. The specific operational conditions (electrochemical read-out mode, pH, regeneration procedure) of the modular one-pot/one-electrode nanobiosensor allowed a reliable sensing of L-lactate (with linear dynamic range, LDR = 500 µM – 2 mM, R2 = 0.977), D-glucose (with LDR = 200 µM – 50 mM, R2 = 0.987), hydrogen peroxide (with LDR = 20 µM – 100 mM, R2 = 0.998) and glutaraldehyde (with LDR = 1 – 100 mM, R2 = 0.971). In addition, mechanistic aspects influencing the performance of Pd-NPs-doped one-pot/one-electrode for multiplex analyte sensing were studied in detail. The designed one-pot/one-electrode amperometric nanobiosensor showed a thin layer electrochemical behavior that greatly enhanced electron transfer between the functional hybrid layer and the electrode. Finally, a specific regeneration procedure of the hybrid one-pot/one-electrode and algorithm towards its usage for modular biocatalysis were developed. The reported strategy can readily be considered as a guideline towards the fabrication of commercialized nanobiosensors with tailored properties for advanced modular biocatalysis.
- ItemEnhancing the Stabilization Potential of Lyophilization for Extracellular Vesicles(Weinheim : Wiley-VCH, 2021) Trenkenschuh, Eduard; Richter, Maximilian; Heinrich, Eilien; Koch, Marcus; Fuhrmann, Gregor; Friess, WolfgangExtracellular vesicles (EV) are an emerging technology as immune therapeutics and drug delivery vehicles. However, EVs are usually stored at −80 °C which limits potential clinical applicability. Freeze-drying of EVs striving for long-term stable formulations is therefore studied. The most appropriate formulation parameters are identified in freeze-thawing studies with two different EV types. After a freeze-drying feasibility study, four lyophilized EV formulations are tested for storage stability for up to 6 months. Freeze-thawing studies revealed improved colloidal EV stability in presence of sucrose or potassium phosphate buffer instead of sodium phosphate buffer or phosphate-buffered saline. Less aggregation and/or vesicle fusion occurred at neutral pH compared to slightly acidic or alkaline pH. EVs colloidal stability can be most effectively preserved by addition of low amounts of poloxamer 188. Polyvinyl pyrrolidone failed to preserve EVs upon freeze-drying. Particle size and concentration of EVs are retained over 6 months at 40 °C in lyophilizates containing 10 mm K- or Na-phosphate buffer, 0.02% poloxamer 188, and 5% sucrose. The biological activity of associated beta-glucuronidase is maintained for 1 month, but decreased after 6 months. Here optimized parameters for lyophilization of EVs that contribute to generate long-term stable EV formulations are presented. © 2021 The Authors. Advanced Healthcare Materials published by Wiley-VCH GmbH
- ItemBending as Key Mechanism in the Tactile Perception of Fibrillar Surfaces(Weinheim : Wiley-VCH, 2021) Gedsun, Angelika; Sahli, Riad; Meng, Xing; Hensel, René; Bennewitz, RolandThe touching of fibrillar surfaces elicits a broad range of affective reactions, which range from the adverse stinginess of a stiff bristle brush to the pleasant feel of velvet. To study the tactile perception of model fibrillar surfaces, a unique set of samples carrying dense, regular arrays of cylindrical microfibrils with high aspect ratio made from different elastomer materials have been created. Fibril length and material compliance are varied independently such that their respective influence on tactile perception can be elucidated. This work finds that the tactile perception of similarity between samples is dominated by bending of the fibrils under sliding touch. The results demonstrate that variations of material stiffness and of surface structure are not necessarily perceived independently by touch. In the case of fibrillar elastomer surfaces, it is rather the ratio of fibril length and storage modulus which determines fibril bending and becomes the dominant tactile dimension. Visual access to the sample during tactile exploration improves the tactile perception of fibril bendability. Experiments with colored samples show a distraction by color in participants’ decisions regarding tactile similarity only for yellow samples of outstanding brightness.
- ItemIncreasing Antibacterial Efficiency of Cu Surfaces by targeted Surface Functionalization via Ultrashort Pulsed Direct Laser Interference Patterning(Weinheim : Wiley-VCH, 2020) Müller, Daniel W.; Lößlein, Sarah; Terriac, Emmanuel; Brix, Kristina; Siems, Katharina; Moeller, Ralf; Kautenburger, Ralf; Mücklich, FrankCopper (Cu) exhibits great potential for application in the design of antimicrobial contact surfaces aiming to reduce pathogenic contamination in public areas as well as clinically critical environments. However, current application perspectives rely purely on the toxic effect of emitted Cu ions, without considering influences on the interaction of pathogenic microorganisms with the surface to enhance antimicrobial efficiency. In this study, it is investigated on how antibacterial properties of Cu surfaces against Escherichia coli can be increased by tailored functionalization of the substrate surface by means of ultrashort pulsed direct laser interference patterning (USP-DLIP). Surface patterns in the scale range of single bacteria cells are fabricated to purposefully increase bacteria/surface contact area, while parallel modification of the surface chemistry allows to involve the aspect of surface wettability into bacterial attachment and the resulting antibacterial effectivity. The results exhibit a delicate interplay between bacterial adhesion and the expression of antibacterial properties, where a reduction of bacterial cell viability of up to 15-fold can be achieved for E. coli on USP-DLIP surfaces in comparison to smooth Cu surfaces. Thereby, it can be shown how the antimicrobial properties of copper surfaces can be additionally enhanced by targeted surface functionalization. © 2020 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
- ItemHybrid Dielectric Films of Inkjet-Printable Core-Shell Nanoparticles(Weinheim : Wiley-VCH, 2021) Buchheit, Roman; Kuttich, Björn; González-García, Lola; Kraus, TobiasA new type of hybrid core-shell nanoparticle dielectric that is suitable for inkjet printing is introduced. Gold cores (dcore ≈ 4.5 nm diameter) are covalently grafted with thiol-terminated polystyrene (Mn = 11000 Da and Mn = 5000 Da) and used as inks to spin-coat and inkjet-print dielectric films. The dielectric layers have metal volume fractions of 5 to 21 vol% with either random or face-centered-cubic structures depending on the polymer length and grafting density. Films with 21 vol% metal have dielectric constants of 50@1 Hz. Structural and electrical characterization using transmission electron microscopy, small-angle X-ray scattering, and impedance spectroscopy indicates that classical random capacitor-resistor network models partially describe this hybrid material but fail at high metal fractions, where the covalently attached shell prevents percolation and ensures high dielectric constants without the risk of dielectric breakdown. A comparison of disordered to ordered films indicates that the network structure affects dielectric properties less than the metal content. The applicability of the new dielectric material is demonstrated by formulating inkjet inks and printing devices. An inkjet-printed capacitor with an area of 0.79 mm2 and a 17 nm thick dielectric had a capacitance of 2.2±0.1 nF@1 kHz .
- ItemEngineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications(Weinheim : Wiley-VCH, 2018) Hensel, René; Moh, Karsten; Arzt, EduardReversible adhesion is the key functionality to grip, place, and release objects nondestructively. Inspired by nature, micropatterned dry adhesives are promising candidates for this purpose and have attracted the attention of research groups worldwide. Their enhanced adhesion compared to nonpatterned surfaces is frequently demonstrated. An important conclusion is that the contact mechanics involved is at least as important as the surface energy and chemistry. In this paper, the roles of the contact geometry and mechanical properties are reviewed. With a focus on applications, the effects of substrate roughness and of temperature variations, and the long-term performance of micropatterned adhesives are discussed. The paper provides a link between the current, detailed understanding of micropatterned adhesives and emerging applications.
- ItemYields and Immunomodulatory Effects of Pneumococcal Membrane Vesicles Differ with the Bacterial Growth Phase(Weinheim : Wiley-VCH, 2021) Mehanny, Mina; Kroniger, Tobias; Koch, Marcus; Hoppstädter, Jessica; Becher, Dörte; Kiemer, Alexandra K.; Lehr, Claus-Michael; Fuhrmann, GregorStreptococcus pneumoniae infections are a leading cause of death worldwide. Bacterial membrane vesicles (MVs) are promising vaccine candidates because of the antigenic components of their parent microorganisms. Pneumococcal MVs exhibit low toxicity towards several cell lines, but their clinical translation requires a high yield and strong immunogenic effects without compromising immune cell viability. MVs are isolated during either the stationary phase (24 h) or death phase (48 h), and their yields, immunogenicity and cytotoxicity in human primary macrophages and dendritic cells have been investigated. Death-phase vesicles showed higher yields than stationary-phase vesicles. Both vesicle types displayed acceptable compatibility with primary immune cells and several cell lines. Both vesicle types showed comparable uptake and enhanced release of the inflammatory cytokines, tumor necrosis factor and interleukin-6, from human primary immune cells. Proteomic analysis revealed similarities in vesicular immunogenic proteins such as pneumolysin, pneumococcal surface protein A, and IgA1 protease in both vesicle types, but stationary-phase MVs showed significantly lower autolysin levels than death-phase MVs. Although death-phase vesicles produced higher yields, they lacked superiority to stationary-phase vesicles as vaccine candidates owing to their similar antigenic protein cargo and comparable uptake into primary human immune cells.