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As liposomes have been widely explored as drug delivery carriers over the past decades, they are one of the most promising platforms due to their biocompatibility and versatility for surface functionalization. However, to improve the specific design of liposomes for future biomedical applications such as nanovaccines, it is necessary to understand how these systems interact with cell membranes, as most of their potential applications require them to be internalized by cells. Even though several investigations on the cellular uptake of liposomes were conducted, the effect of the liposome membrane properties on internalization in different cell lines remains unclear. Here, we demonstrate how the cellular uptake behavior of liposomes can be driven towards preferential interaction with dendritic cells (DC2.4) as compared to macrophages (RAW264.7) by tuning the lipid composition with varied molar ratios of the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). Cellular internalization efficiency was analyzed by flow cytometry, as well as liposome-cell membrane co-localization by confocal laser scanning microscopy. The corresponding proteomic analysis of the protein corona was performed in order to unravel the possible effect on the internalization. The obtained results of this work reveal that it is possible to modulate the cellular uptake towards enhanced internalization by dendritic cells just by modifying the applied lipids and, thus, mainly the physico-chemical properties of the liposomes.

Biofouling is a severe problem of any water borne structure. Since the ban of tin-organic compounds and expected bans of other poisonous chemical formulations in the near future, replacement of these compounds are sought. This study investigates antibiofouling properties of micro- and nanostructured alginate layer films. Alginate is a natural product from brown algae and was in this study electro-sprayed and crosslinked with divalent calcium and copper ions to produce homogeneous micro- and nanoparticles. These calcium- and copper-alginate particles were assembled into micro- and nanostructured layer films and the antifouling properties of these low elastic modulus, hydrophilic, biodegradable system were evaluated with the microalgae chlorella. Comparison with pristine glass slides, smooth copper- and calcium alginate bulk films was performed. The comparison shows less biofouling for smooth bulk films compared to micro-nanostructured alginate, while all alginate systems are less bio-fouled on long timescales compared to pristine glass.

The combination of an efficient encapsulation method of small water-soluble substances with a stimuli-responsive release of defined quantity remains a challenging task. A novel drug delivery system (DDS) representing a free-standing PLLA microchamber arrays film and its application as the cover for implantable endovascular stent are reported in this work. The proposed DDS preparation method is consisting of a patterned polydimethylsiloxane (PDMS)-stamp dip-coated into a polymer solution followed by drug loading and sealing it by polymer pre-coated substrate. It was shown that using 1 wt% PLLA solution is optimal for obtaining microchamber arrays with an individual cargo capacity of 2.88 × 10−9 µg, which was successfully loaded by model drug substance Rhodamine B. Rhodamine B was completely released in vitro during 13 days in PBS at 37 °C by diffusion. It was demonstrated that low-frequency ultrasound (LFUS, 20 kHz) allows triggering RhB release due to microchamber damage and detachment of individual PLLA microchambers over time. LFUS exposure time up to 25 s led to RhB release of up to 8.4 × 10−4 µg (approximately 55%) from microchambers located on the flat substrate; up to 5.2 × 10−4 µg from microchambers located on the stent with using a simplified vessel model. Furthermore, the free-standing printed PLLA microchamber arrays were demonstrated to be applied as endovascular stent cover that can be used for complementary pharmacological effect, for example, triggered local delivery of anticoagulants.

Hydrogel capsules are a potential candidate for drug delivery and an interesting alternative to polyelectrolyte multilayer capsules which are under investigation since 20 years. Recently introduced polyelectrolyte complex capsules produced by spraying are non-biodegradable and not biocompatible, which limits their practical application, while biodegradable alginate capsules require complex coaxial electrospray ionization jetting. In this work, biodegradable alginate capsules cross-linked by calcium are successfully produced by hydrodynamic electrospray ionization jetting with the assistance of low frequency ultrasound. The size and shape of most capsules show significant differences with respect to different spraying distance, spraying mode, electrode shape and spraying concentration. Capsules in the shape of vase, mushrooms and spheres were successfully produced. Average capsule size can be adjusted from 10 μm to 2 mm. These capsules are used to encapsulate a model drug. Encapsulated paramagnetic particles enable defined directional motion under the propulsion of a rotating magnetic field, while model drugs can be released by ultrasound.

One of the most promising future applications of hydrogels is drug delivery. The hydrogels act as a biomedical cargo model to reach the target and release drugs to cure diseases. This application requires no side effects of the hydrogel and the ability to pass through porous media (e.g. membranes, interstitial tissue etc.) with nanoscaled channels. At the same time, the hydrogel must be mass-producible in an economic way. In this work, we show that hydrodynamic electrospray ionization jetting combined with ultrasound can fulfill these high requirements. This method can produce mucoadhesive micro-/nano-particles, which are small enough to pass through the gastrointestinal epithelium. The average size of the produced particles is exactly predictable by controlling the spraying distance, spraying mode, alginate concentration, ultrasound bath frequency and counter electrode shape. These micro-/nano-particles are loaded with biocompatible magnetite nanoparticles, and propelled by a rotating magnetic field between 5 to 20 m T and a frequency from 1 Hz to 100 Hz. These rotating micro-/nano-particle motors perform directional motion in solution, offering a promising possibility for magnetically controlled drug delivery.

Cellular, inter-organismal and cross kingdom communication via extracellular vesicles (EVs) is intensively studied in basic science with high expectation for a large variety of bio-technological applications. EVs intrinsically possess many attributes of a drug delivery vehicle. Beyond the implications for basic cell biology, academic and industrial interests in EVs have increased in the last few years. Microalgae constitute sustainable and renewable sources of bioactive compounds with a range of sectoral applications, including the formulation of health supplements, cosmetic products and food ingredients. Here we describe a newly discovered subtype of EVs derived from microalgae, which we named nanoalgosomes. We isolated these extracellular nano-objects from cultures of microalgal strains, including the marine photosynthetic chlorophyte Tetraselmis chuii, using differential ultracentrifugation or tangential flow fractionation and focusing on the nanosized small EVs (sEVs). We explore different biochemical and physical properties and we show that nanoalgosomes are efficiently taken up by mammalian cell lines, confirming the cross kingdom communication potential of EVs. This is the first detailed description of such membranous nanovesicles from microalgae. With respect to EVs isolated from other organisms, nanoalgosomes present several advantages in that microalgae are a renewable and sustainable natural source, which could easily be scalable in terms of nanoalgosome production., Journal of Extracellular Vesicles, 10 (6), ISSN:2001-3078

Safe, efficient and specific nano-delivery systems are essential for current and emerging therapeutics, precision medicine and other biotechnology sectors. Novel bio-based nanotechnologies have recently arisen, which are based on the exploitation of extracellular vesicles (EVs). In this context, it has become essential to identify suitable organisms or cellular types to act as reliable sources of EVs and to develop their pilot- to large-scale production. The discovery of new biosources and the optimisation of related bioprocesses for the isolation and functionalisation of nano-delivery vehicles are fundamental to further develop therapeutic and biotechnological applications. Microalgae constitute sustainable sources of bioactive compounds with a range of sectorial applications including for example the formulation of health supplements, cosmetic products or food ingredients. In this study, we demonstrate that microalgae are promising producers of EVs. By analysing the nanosized extracellular nano-objects produced by eighteen microalgal species, we identified seven promising EV-producing strains belonging to distinct lineages, suggesting that the production of EVs in microalgae is an evolutionary conserved trait. Here we report the selection process and focus on one of this seven species, the glaucophyte Cyanophora paradoxa, which returned a protein yield in the small EV fraction of 1 μg of EV proteins per mg of dry weight of microalgal biomass (corresponding to 109 particles per mg of dried biomass) and EVs with a diameter of 130 nm (mode), as determined by the micro bicinchoninic acid assay, nanoparticle tracking and dynamic light scattering analyses. Moreover, the extracellular nanostructures isolated from the conditioned media of microalgae species returned positive immunoblot signals for some commonly used EV-biomarkers such as Alix, Enolase, HSP70, and β-actin. Overall, this work establishes a platform for the efficient production of EVs from a sustainable bioresource and highlights the potential of microalgal EVs as novel biogenic nanovehicles.

Stimuli-responsive polymers have attracted increasing attention over the years due to their ability to alter physiochemical properties upon external stimuli. However, many stimuli-responsive polymer-based sensors require specialized and expensive equipment, which limits their applications. Here an inexpensive and portable sensing platform of novel microarray films made of stimuli-responsive polymers is introduced for the real-time sensing of various environmental changes. When illuminated by laser light, microarray films generate diffraction patterns that can reflect and magnify variations of the periodical microstructure induced by surrounding invisible parameters in real time. Stimuli-responsive polyelectrolyte complexes are structured into micropillar arrays to monitor the pH variation and the presence of calcium ions based on reversible swelling/shrinking behaviors of the polymers. A pH hysteretic effect of the selected polyelectrolyte pair is determined and explained. Furthermore, polycaprolactone microchamber arrays are fabricated and display a thermal-driven structural change, which is exploited for photonic threshold temperature detection. Experimentally observed diffraction patterns are additionally compared with rigorous coupled-wave analysis simulations that prove that induced diffraction pattern alterations are solely caused by geometrical microstructure changes. Microarray-based diffraction patterns are a novel sensing platform with versatile sensing capabilities that will likely pave the way for the use of microarray structures as photonic sensors.

Attaching targeting ligands on the surface of self-assembled drug delivery systems is the key request for a controlled transport of the drug to a desired location. Most commonly, the amphiphilic molecules (blockcopolymers, lipids etc.) are therefore pre-functionalized before the self-assembly takes place. However, this strategy cannot be applied, if it interferes with the self-assembly process, if the introduced functional groups react with loaded cargo or if natural carriers like extracellular vesicles should be functionalized. Here, we present the site-specific coupling of antibodies to the surface of amino group-terminated liposomes via bio-orthogonal copper-free click chemistry after liposome formation. The present primary amino groups were functionalized with a linker carrying a strained alkyne group for a bio-orthogonal strain-promoted alkyne–azide cycloaddition (SPAAC) reaction where Cu(I) as a catalyst can be avoided. Antibodies were site-specifically functionalized with azide moieties along the Fc region to avoid interference with the antigen binding sites. The liposome surface functionalization reaction was optimized by precisely analyzing the number of available functional groups (both amine and alkyne), which often represents a challenge for self-assembled systems. By finally confirming the successful antibody coupling, we provide a facile and robust functionalization strategy, which can be applied to a wide range of selfassembled systems and desired targeting antibodies maintaining physiological conditions throughout the procedure

Polyelectrolyte multilayers as well as Langmuir−Blodgett or layer-by-layer (LbL) assembled films are widely used as nanostructured coatings for chemical sensors, systems for drug delivery etc. The automated devices for fabricating planar films via dipping first appeared in the early 1990s and those for producing surface coatings via spraying in 2009−2010. However, an automated fabrication for dispersed micro-templates has remained non-developed until recently. In this publication the authors introduce an automated device suitable for coating of dispersed superparamagnetic microtemplates via LbL self-assembly.

An implantable ultrasound triggered controlled release micro-chamber (MC) array based on polylactic acid (PLA) sealed polyelectrolyte multilayers (PEM) is presented. In this work Rhodamine B (RhB) nano-precipitates are loaded as model cargo and sealed water tight within micro-air bubbles. Cargo release at low frequency (LFUS (37 kHz)) and high frequency ultrasound (HFUS (2 MHz, medical range)) is compared. The release speed and mechanism varies significantly between both ultrasound frequencies, allowing for a 60 times faster MC opening at HFUS. LFUS MC opening is based on material fatigue combined with thermo-acoustic effects while strong thermo-acoustic effects are responsible for MC opening at HFUS. The slower MC opening at LFUS allows for controlling the release amount and enables multiple release pulses compared to HFUS. Not PLA coated and no air bubble entrapping PEM thin films are in case of HFUS destroyed, while no interaction is determined at LFUS.

Controlled drug delivery and gene expression is required for a large variety of applications including cancer therapy, wound healing, cell migration, cell modification, cell-analysis, reproductive and regenerative medicine. Controlled delivery of precise amounts of drugs to a single cell is especially interesting for cell and tissue engineering as well as therapeutics and has until now required the application of micro-pipettes, precisely placed dispersed drug delivery vehicles, or injections close to or into the cell. Here we present surface bound micro-chamber arrays able to store small hydrophilic molecules for prolonged times in subaqueous conditions supporting spatiotemporal near infrared laser mediated release. The micro-chambers (MCs) are composed of biocompatible and biodegradable polylactic acid (PLA). Biocompatible gold nanoparticles are employed as light harvesting agents to facilitate photothermal MC opening. The degree of photothermal heating is determined by numerical simulations utilizing optical properties of the MC, and confirmed by Brownian motion measurements of laser-irradiated micro-particles exhibiting similar optical properties like the MCs. The amount of bioactive small molecular cargo (doxycycline) from local release is determined by fluorescence spectroscopy and gene expression in isolated C2C12 cells via enhanced green fluorescent protein (EGFP) biosynthesis.

Biofouling is a severe problem for many applied technical surfaces ranging from ships and piers to water inlets and medicine. Here we investigate the physical–chemical properties of divalent copper and divalent calcium alginate bulk films and their anti-biofouling properties on the example of Chlorella vulgaris and in a natural river water environment. Physical-chemical characterization includes mechanical characterization of different mixing ratios, oil contact angles, and equilibrium water contents, self-polishing properties and copper ion release of copper alginate and copper-calcium alginate compositions. The results prove highly composition dependent physical–chemical properties. This causes highly composition dependent antibiofouling properties against Chlorella vulgaris, which changes significantly over time due to copper ion release and self-polishing resulting into up to 100 times lower biofouling compared to glass slides. Extending the test to river water, less Chlorella vulgaris compared to pure Chlorella vulgaris solution were determined. The total biofouling, which reached however, saturation of 25% and 35% coverage for copper, and calcium alginate respectively, which is comparable to glass.

Efficient depot systems for entrapment and storage of small water-soluble molecules are of high demand for wide variety of applications ranging from implant based drug delivery in medicine and catalysis in chemical processes to anticorrosive systems in industry where surface-mediated active component delivery is required on a time and site specific manner. This work reports the fabrication of individually sealed hollow-structured polyelectrolyte multilayer (PEM) microchamber arrays based on layer-by-layer self-assembly as scaffolds and microcontact printing. These PEM chambers are composed out of biocompatible polyelectrolytes and sealed by a monolayer of hydrophobic biocompatible and biodegradable polylactic acid (PLA). Coating the chambers with hydrophobic PLA allows for entrapment of a microair-bubble in each chamber that seals and hence drastically reduces the PEM permeability. PLA@PEM microchambers are proven to enable prolonged subaqueous storage of small hydrophilic salts and molecules such as crystalline NaCl, doxicycline, and fluorescent dye rhodamine B. The presented microchambers are able to entrap air bubbles and demonstrate a novel strategy for entrapment, storage, and protection of micropackaged water-soluble substances in precipitated form. These chambers allow triggered release as demonstrated by ultrasound responsiveness of the chambers. Low-frequency ultrasound exposure is utilized for microchamber opening and payload release.

Polystyrene (PS) is currently mainly used as a sacrificial template during pattern release upon microcontact printing or for self-assembled flat free-standing films. We hereby present a method for creating 3D microstructured free-standing self-assembled polyelectrolyte multilayer (PEM) thin films. The approach presented utilizes a sacrificial microstructured PS template which can be coated with PEM thin films, whereby dissolution of the PS facilitates a free-standing 3D microstructured PEM film. The PS templating approach allows for omitting hot embossing on silicon masters, since PS templates can be prepared by drop casting on silicon masters. The prepared PEM film offers, if gold nanoparticles are incorporated, stimuli-responsive properties like light-induced chamber opening.

The collision phenomena of self-propelled micro-plate motors are significantly different from classical life-less particles. The Janus micro-plate motors used in this study are 5 and 10 μm in diameter and driven by catalytic decomposition of hydrogen peroxide. Periodically oscillating oxygen bubbles drive the motor in rugged straight or spiral motion. Since the inertia effect of mass is no longer important for slow motion in low Reynold number liquid, the momentum law of collision shows some new characteristics due to the constant self-propelling force. We found a bounce back collision and a linear collision between the bubbles of one motor and the micromotor plates as well as between 2 microplates and present a basic theoretical concept. In addition we show experimentally that these 2D particles are able to destroy emerging gas bubbles. More complex collision dynamics may exist for a higher concentration of self-propelled motors.

Photothermal therapies utilizing gold nanostructures are widely investigated and used within state-of-the-art noninvasive approaches. Single, isolated gold nanoparticles are unable to produce high enough temperatures to perform a sufficient wound closure, requiring therefore large amounts and concentrations to facilitate a therapeutic effect. In this proof of principle study we prepare composite micro-particles which contain near-infrared laser sensitive gold nanorods (GNRs) and Fe 3 O 4 superparamagnetic particles which are agglommerated in a layered polyelectrolyte multilayer (PEM) matrix. The GNRs-Fe 3 O 4 -PEM particles can be enriched in tissue incisions by applying a magnetic field. With this magnetic filed a targeted agglomeration is observed which is beneficial for near-infrared laser based wound sealing. Mechanical tests show that laser treated skin recovered closest to pristine samples and is comparable with nanoparicle gluing. The healing effect of this system is comparable with clinical sutures and nanoparticle gluing in in-vivo experiments. The observation that internal organs like liver can be welded with such composite particles opens new applications for laser tissue welding.

Synthetic microparticles present exciting features owing to their customizable light-matter interaction. We hereby report on the optical trapping of two artificial plasmonic microparticles: one with isotropic nanoparticles covering the surface (homogeneous particle) used as a hot Brownian particle and an anisotropic Janus microparticle, half coated with a gold nano-layer. The homogeneous particle decorated with plasmonic nanoparticles on the surface displays features of hot Brownian dynamics as well as photophoretic motion along z dimension in the optical trap. A dielectric particle was used as a reference particle because it acts as a cold particle with only the gradient force affecting it. In general, Janus particles orient in the trap with the dielectric part in the trap center. Plasmonic gold nanostructures absorb the light energy and produce heat; the photothermal forces significantly affect the optical trapping. These hot microspheres display temperature and Janus orientation dependent position distribution significantly different from cold (purely dielectric) microparticles. The developed method allows for the first time direct determination of the photophoretic (thermal force along light propagation direction) and thermophoretic force (light propagation direction independent force) acting on the respective particles, which opens new paths for analysis and control of micromachines.

Biofouling is defined by the adsorption of biomolecules or microorganisms on technical surfaces, which are causing adverse effects on the functionality (decrease of ship speed) and safety (infections of implants) of quite a number of industrial products. Conventional, anti-biofouling in marine environments is done by coating a technical surface with highly poisonous tin-organic, which have already been banned for environmental protection. Therefore, the developing of biologically benign coatings becomes a long-term pursue for the industry. Here, we study the Chlorella vulgaris settlement on self-disinfecting titanium dioxide surfaces with three different micro-structures: a flat surface, a light harvesting surface with nano-structure and a hierarchical surface structure, spanning over 5 orders of magnitude (from 0.1 nm to 10 μm). These titanium dioxide surfaces were prepared by Ostwald ripening. This sample manufacturing process gains new catalytic properties as a self-cleaning effect, especially for the light harvesting surface with nano-structure (bulk metallic glass). Chlorella vulgaris dispersions were growing in glass flasks together with the different surface samples over the full time of the experiments. Therefore, this study was made as part of a laboratory scale test. It was found, that bulk metallic glass structures made by Ostwald ripening are showing the highest catalytic and at the same time the best self-cleaning effects. Additionally, the Chlorella vulgaris settlement probability was found to depend on the Wenzel roughness. The surfaces with a high Wenzel roughness were the ones with the lowest Chlorella vulgaris settlement. A semi-field test is proving the comparable antibiofouling performance of our surfaces with existing polymeric or sharkskin like structures on the timescale of one month.

Photosensitive polymeric three-dimensional microstructured film (PTMF) is a new type of patterned polymeric films functionalized with an array of sealed hollow 3D containers. The microstructured system with enclosed chemicals provides a tool for the even distribution of biologically active substances on a given surface that can be deposited on medical implants or used as a cells substrate. In this work, we proposed a way for photothermally activating and releasing encapsulated substances at picogram amounts from the PTMF surface in different environments using laser radiation delivered with a multimode optical fiber. The photosensitive PTMFs were prepared by the layer-by-layer (LbL) assembly from alternatively charged polyelectrolytes followed by covering with a layer of hydrophobic polylactic acid (PLA) and a layer of gold nanoparticles (AuNPs). Moreover, the typical photothermal cargo release amounts were determined on the surface of the PTMF for a range of laser powers delivered to films placed in the air, deionized (DI) water, and 1% agarose gel. The agarose gel was used as a soft tissue model for developing a technique for the laser activation of PTMFs deep in tissues using optical waveguides. The number of PTMF chambers activated by a near-infrared (NIR) laser beam was evaluated as the function of optical parameters.

Encapsulation of small water soluble molecules is important in a large variety of applications, ranging from medical substance releasing implants in the field of medicine over release of catalytically active substances in the field of chemical processing to anti-corrosion agents in industry. In this work polylactic acid (PLA) based hollow-structured microchamber (MC) arrays are fabricated via one-step dip coating of a silicone rubber stamp into PLA solution. These PLA MCs are able to retain small water soluble molecules (Rhodamine B) stably entrapped within aqueous environments. It is shown, that degradation of PLA MCs strongly depends on environmental conditions like surrounding pH and follows first order degradation kinetics. This pH dependent PLA MC degradation can be utilized to control the release kinetics of encapsulated cargo.

This paper presents the synthesis of highly biocompatible and biodegradable poly(lactide- co-glycolide) (PLGA) microchamber arrays sensitive to low-intensity therapeutic ultrasound (1 MHz, 1-2 W, 1 min). A reliable method was elaborated that allowed the microchambers to be uniformly filled with epinephrine hydrochloride (EH), with the possibility of varying the cargo amount. The maximum load of EH was 4.5 μg per array of 5 mm × 5 mm (about 24 pg of EH per single microchamber). A gradual, spontaneous drug release was observed to start on the first day, which is especially important in the treatment of acute patients. Ultrasound triggered a sudden substantial release of EH from the films. In vivo real-time studies using a laser speckle contrast imaging system demonstrated changes in the hemodynamic parameters as a consequence of EH release under ultrasound exposure. We recorded a decrease in blood flow as a vascular response to EH release from a PLGA microchamber array implanted subcutaneously in a mouse. This response was immediate and delayed (1 and 2 days after the implantation of the array). The PLGA microchamber array is a new, promising drug depot implantable system that is sensitive to external stimuli.

Surface mediated drug delivery is important for a large variety of applications, especially in medicine to control cell growth, prevent blood platelet activation on implants or for self-disinfecting devices (e.g. catheters). In industrial applications, controlled release of substances from surfaces is needed in a broad range of applications from anti-corrosion systems to anti-biofouling. Polyelectrolyte multilayers (PEM) based microcontainers (MCs) require several days production time, while MCs composed out of polylactic acid (PLA) are entirely hydrophobic, offering no functionality. We hereby present an approach to fabricate PLA coated synthetic as well as biopolymer based biodegradable polyelectrolyte complex MCs able to encapsulate small hydrophilic cargo within less than one hour. The chambers facilitate laser controlled release of cargo within submerged conditions.

Hydrodynamic electrospray ionization jetting was applied for generating and characterizing calcium cross-linked alginate microparticles. These microparticles show different diameters and aspect ratios for three electrospray modes (dripping, conejet and multijet modes), four spraying distances (5, 10, 15 and 20 cm), and six spraying concentrations. Comparing the three different electrospray modes, we found that the conejet mode results in the smallest particle diameters, lowest aspect ratio and smallest variations over the parameter space mentioned above. For all spraying modes, the resultant particle diameters become independent of the spraying distance at a sprayed solute concentration ≥ 2.5%. The aspect ratio of microparticles varies significantly for different spraying modes and distances. An increasing aspect ratio of all spray modes was determined for sodium alginate spraying concentrations ≤ 1.5% and spraying distances of 20 cm; this phenomenon can be explained with the chain ejection effect. This systematic investigation offers a basic database for industrial applications of hydrodynamic electrospray ionization.

Micro and nano-patterned surfaces are important for many applications ranging from antibiofouling over tissue engineering to electronics. Often the incorporation of functional entities is of interest. Polymer coatings especially polyelectrolyte multilayer (PEM) films and patterns are materials offering a large variety of tuning and engineering. The PEM pattern printing quality bases not only on the surface force balance but also in the way the PEM is softened, which can be done by printing the PEM in water, using an ultrasound humidifier or by exposing the film to (hot) water vapor. In this publication it is shown, that cold water vapor from an ultrasound humidifier or direct printing in water is superior to steam evaporation onto PEM thin films as humidification method. In addition the capillary pressure of the patterns within the stamp and the glass–viscous flow transition point of the PEM thin film are the significant parameters for PEM printing. This is because the PEM can surpass the glass–viscous flow transition point due to the shear forces and be sucked into the stamp microwells (or holes) preventing a structure replication. Under high temperatures and in aqueous conditions, the PEM can be expelled from the microwells due to the osmotic pressure produced by the counter ions of PEM in glass–viscous flow state and dissolving polyelectrolyte if a PEM with counter ion based charge balance is used.

International audience; Polyelectrolyte multilayer (PEM) thin films are popular candidates for surface coating due to their versatility, tunability and simple production method. Often these films are used in a 2D structured manner for creating defined cell scaffolds or electronic applications. Although these films were successfully printed in the past, the conditions and energies necessary for a successful printing were only investigated as isolated parameters or as a function of the substrate but not the PEM surface energy and therefore the dominating forces remained controversial. We hereby present a theory and method for microcontact printing of condensed polyelectrolyte multilayer thin films, based on surface energies and the line tension. The theory relies on the surface energy of the substrate, stamp and PEM as well as the PEM line tension ratios to create the desired pattern. The presented theory is able to predict the printability, quality and resolution limit of a chosen system and was evaluated with experiments. A reduction of the production time from the beginning of PEM assembly to the final pattern from several hours down to 30 minutes was achieved while increasing reproducibility and resolution of the printed patterns at the same time. We would like to point out that this approach can generally be used for any kind of adsorbed thin film on substrates.

Long term encapsulation combined with spatiotemporal release for a precisely defined quantity of small hydrophilic molecules on demand remains a challenge in various fields ranging from medical drug delivery, controlled release of catalysts to industrial anti-corrosion systems. Free-standing individually sealed polylactic acid (PLA) nano- and microchamber arrays were produced by one-step dip-coating a PDMS stamp into PLA solution for 5 s followed by drying under ambient conditions. The wall thickness of these hydrophobic nano–microchambers is tunable from 150 nm to 7 μm by varying the PLA solution concentration. Furthermore, small hydrophilic molecules were successfully in situ precipitated within individual microchambers in the course of solvent evaporation after sonicating the PLA@PDMS stamp to remove air-bubbles and to load the active substance containing solvent. The cargo capacity of single chambers was determined to be in the range of several picograms, while it amounts to several micrograms per cm2. Two different methods for sealing chambers were compared: microcontact printing versus dip-coating whereby microcontact printing onto a flat PLA sheet allows for entrapment of micro-air-bubbles enabling microchambers with both ultrasound responsiveness and reduced permeability. Cargo release triggered by external high intensity focused ultrasound (HIFU) stimuli is demonstrated by experiment and compared with numerical simulations.

Polyelectrolyte complexes (PEC) are formed by mixing the solutions of oppositely charged polyelectrolytes, which were hitherto deemed “impossible” to process, since they are infusible and brittle when dry. Here, we describe the process of fabricating free-standing micro-patterned PEC films containing array of hollow or filled microchambers by one-step casting with small applied pressure and a PDMS mould. These structures are compared with polyelectrolyte multilayers (PEM) thin films having array of hollow microchambers produced from a layer-by-layer self-assembly of the same polyelectrolytes on the same PDMS moulds. PEM microchambers “cap” and “wall” thickness depend on the number of PEM bilayers, while the “cap” and “wall” of the PEC microchambers can be tuned by varying the applied pressure and the type of patterned mould. The proposed PEC production process omits layering approaches currently employed for PEMs, reducing the production time from ~2 days down to 2 hours. The error-free structured PEC area was found to be significantly larger compared to the currently-employed microcontact printing for PEMs. The sensitivity of PEC chambers towards aqueous environments was found to be higher compared to those composed of PEM.

Current wound sealing systems such as nanoparticle-based gluing of tissues allow almost immediate wound sealing. The assistance of a laser beam allows the wound sealing with higher controllability due to the collagen fiber melting which is defined by loss of tertiary protein structure and restoration upon cooling. Usually one employs dyes to paint onto the wound, if water absorption bands are absent. In case of strong bleeding or internal wounds such applications are not feasible due to low welding depth in case of water absorption bands, dyes washing off, or the dyes becoming diluted within the wound. One possible solution of these drawbacks is to use autonomously movable particles composing of biocompatible gold and magnetite nanoparticles and biocompatible polyelectrolyte complexes. In this paper a proof of principle study is presented on the utilization of thermophoretic Janus particles and capsules employed as dyes for infrared laser-assisted tissue welding. This approach proves to be efficient in sealing the wound on the mouse in vivo. The temperature measurement of single particle level proves successful photothermal heating, while the mechanical characterizations of welded liver, skin, and meat confirm mechanical restoration of the welded biological samples.

This communication sheds light on the production method and motion patterns of autonomous moving bubble propelled two dimensional micro-plate motors. The plate motors are produced by the well-known layer-by-layer self-assembly process in combination with micro-contact printing. The motion analysis covers instances of oscillating bubble development on one or more nucleation sites, which influence the motion speed and direction.

Cell transport is important to renew body functions and organs with stem cells, or to attack cancer cells with immune cells. The main hindrances of this method are the lack of understanding of cell motion as well as proper transport systems. In this publication, bubble-propelled polyelectrolyte microplates are used for controlled transport and guidance of HeLa cells. Cells survive attachment on the microplates and up to 22 min in 5% hydrogen peroxide solution. They can be guided by a magnetic field whereby increased friction of cells attached to microplates decreases the speed by 90% compared to pristine microplates. The motion direction of the cell-motor system is easier to predict due to the cell being opposite to the bubbles.

Biofouling is one of the biggest problems of water-borne systems. Since not only marine but also freshwater-based structures are affected, the biofouling in this environment is studied. The focus of this study lies on the antifouling properties of novel coating materials like polyelectrolyte multilayers (PEM) compared with currently used silicon rubber (PDMS) based fouling release coatings. The following article contains the results of a systematical screening of the mechanical, surface charge and surface nano-heterogeneous properties of the investigated PEM and PDMS systems. The results show that negatively charged non crosslinked and crosslinked PEM coated PDMS can surpass current PDMS based fouling release coatings. The PEM films are not only able to reduce the biofouling, but are additionally able to control the type of settled bacteria (gram positive or negative). The negative terminated surfaces inhibit the settlement of gram positive bacteria, whereby the positive terminated surfaces inhibit the settlement of gram negative bacteria.

Polyelectrolytes (PEs) find applications in many fields of modern life starting from food additives to flocculation and solubility enhancers, down to viscosity adjusting agents in cosmetics and subterranean gelling or drug delivery agents. Most of these properties are related to the PE charge density, structure, counterions, temperature or counter PE. This book chapter gives an overview of the current state of understanding of the thermodynamical properties of PEs in solution. The theoretical predictions and results are compared with current state of the art computer simulations (with a focus on molecular dynamics) as well as experiments on PE structure, complex formation and viscosity properties.