Interferometric Imaging of Solvent Vapor of Evaporating Liquid Films.

The liquid deposition of thin films requires a thorough understanding of the underlying drying process, as it is an essential subprocess, where many defects may arise. To complement experimental studies, the present study uses a laser Michelson interferometer to visualize the vapor cloud of evaporating liquid films. The recorded interferometric patterns are evaluated using windowed Fourier filtering and a novel phase-unwrapping algorithm to allow for a robust analysis. Thin solvent stripes of different lengths are combined to yield a quantitative two-dimensional distribution of the solvent vapor concentration along a thin liquid stripe. The results show a considerable influence of natural convection during evaporation.

Measuring isotropic subsurface light transport.

Subsurface light transport can affect the visual appearance of materials significantly. Measuring and modeling this phenomenon is crucial for accurately reproducing colors in printing or for rendering translucent objects on displays. In this paper, we propose an apparatus to measure subsurface light transport employing a reference material to cancel out adverse signals that may bias the results. In contrast to other approaches, the setup enables improved focusing on rough surfaces (e.g. uncoated paper). We derive a measurement equation that may be used to deduce the point spread function (PSF) of subsurface light transport. Main contributions are the usage of spectrally-narrowband exchangeable LEDs allowing spectrally-resolved measurements and an approach based on quadratic programming for reconstructing PSFs in the case of isotropic light transport.

A flatbed scanner for large-area thickness determination of ultra-thin layers in printed electronics.

Enabling solution-based printing techniques for sub-100 nm thin semiconductors for the application in large-area organic electronics is a challenging task. In order to optimize the process parameters, the layers have to be characterized on a large lateral scale while determining the nanometer thickness at the same time. We present a lateral and vertical resolving measurement method for large-area, semi-transparent thin films based on optical interference effects. We analyzed the RGB color images of up to 150 mm square-sized thin film samples obtained by a modified commercial flatbed scanner. Utilizing and comparing theoretical and measured color contrast values, we determined most probable thickness values of the imaged sample area pixel by pixel. Within specific boundary conditions, we found very good agreement between the presented imaging color reflectometry and reference methods. Due to its simple setup, our method is suitable to be implemented as part of a color vision inspection system in in-line printing and coating processes.

Device for measuring part adhesion in FFF process.

The adhesion of parts to the build surface plays a central role in the Fused Filament Fabrication (FFF) process. Without sufficient adhesion, the part will deform (so called warping) due to thermal shrinkage, so that no defined geometries can be created. Nevertheless, there is no established method to measure the adhesion of printed parts and therefore it is not possible to targeted improve it. This article presents a measurement method based on the DIN EN 28510-1 standard and a corresponding test device which makes it possible to identify the optimum build surface for a filament and also to improve the process parameters in a targeted manner. The test device combines a FFF printer with a measuring unit so that all common filaments can be tested close to the process up to a processing temperature of 400 °C in the nozzle and around 150 °C on the build platform. The test device uses only open-source parts and software and costs about 1700€.

Fabrication of biomimetic networks using viscous fingering in flexographic printing.

Mammalian tissue comprises a plethora of hierarchically organized channel networks that serve as routes for the exchange of liquids, nutrients, bio-chemical cues or electrical signals, such as blood vessels, nerve fibers, or lymphatic conduits. Despite differences in function and size, the networks exhibit a similar, highly branched morphology with dendritic extensions. Mimicking such hierarchical networks represents a milestone in the biofabrication of tissues and organs. Work to date has focused primarily on the replication of the vasculature. Despite initial progress, reproducing such structures across scales and increasing biofabrication efficiency remain a challenge. In this work, we present a new biofabrication method that takes advantage of the viscous fingering phenomenon. Using flexographic printing, highly branched, inter-connective channel structures with stochastic, biomimetic distribution and dendritic extensions can be fabricated with unprecedented efficiency. Using gelatin (5%-35%) as resolvable sacrificial material, the feasability of the proposed method is demonstrated on the example of a vascular network. By selectively adjusting the printing velocity (0.2-1.5 m s-1), the anilox roller dip volume (4.5-24 ml m-2) as well as the shear viscosity of the printing material used (10-900 mPas), the width of the structures produced (30-400 µm) as well as their distance (200-600 µm) can be specifically determined. In addition to the flexible morphology, the high scalability (2500-25 000 mm2) and speed (1.5 m s-1) of the biofabrication process represents an important unique selling point. Printing parameters and hydrogel formulations are investigated and tuned towards a process window for controlled fabrication of channels that mimic the morphology of small blood vessels and capillaries. Subsequently, the resolvable structures were casted in a hydrogel matrix enabling bulk environments with integrated channels. The perfusability of the branched, inter-connective structures was successfully demonstrated. The fabricated networks hold great potential to enable nutrient supply in thick vascularized tissues or perfused organ-on-a-chip systems. In the future, the concept can be further optimized and expanded towards large-scale and cost-efficient biofabrication of vascular, lymphatic or neural networks for tissue engineering and regenerative medicine.

In vitro Evaluation of a 20% Bioglass-Containing 3D printable PLA Composite for Bone Tissue Engineering.

Three-dimensional (3D) printing is considered a key technology in the production of customized scaffolds for bone tissue engineering. In a previous work, we developed a 3D printable, osteoconductive, hierarchical organized scaffold system. The scaffold material should be osteoinductive. Polylactic acid (PLA) (polymer)/Bioglass (BG) (mineral/ion source) composite materials are promising. Previous studies of PLA/BG composites never exceed BG fractions of 10%, as increase of bioactive BG component negatively affects the printability of the composite material. Here, we test a novel, 3D printable PLA/BG composite with BG fractions up to 20% for its biological activity in vitro. PLA/BG filaments suitable for microstructure 3D printing were spun and the effect of different BG contents (5%, 10%, and 20%) in this material on mesenchymal stem cell (MSC) activity was tested in vitro. Our results showed that all tested composites are biocompatible. MSC cell adherence and metabolic activity increase with increasing BG content. The presence of BG component in scaffold has only slight effect on osteogenic gene expression, but it has significant suppressive effect on the expression of inflammatory genes in MSC. In addition, the material did not provoke any significant inflammatory response in whole-blood stimulation assay. The results show that by increasing the BG content, the bioactivity can be further enhanced.

Carbohydrate binding module-fused antibodies improve the performance of cellulose-based lateral flow immunoassays.

Since the pandemic outbreak of Covid-19 in December 2019, several lateral flow assay (LFA) devices were developed to enable the constant monitoring of regional and global infection processes. Additionally, innumerable lateral flow test devices are frequently used for determination of different clinical parameters, food safety, and environmental factors. Since common LFAs rely on non-biodegradable nitrocellulose membranes, we focused on their replacement by cellulose-composed, biodegradable papers. We report the development of cellulose paper-based lateral flow immunoassays using a carbohydrate-binding module-fused to detection antibodies. Studies regarding the protein binding capacity and potential protein wash-off effects on cellulose paper demonstrated a 2.7-fold protein binding capacity of CBM-fused antibody fragments compared to the sole antibody fragment. Furthermore, this strategy improved the spatial retention of CBM-fused detection antibodies to the test area, which resulted in an enhanced sensitivity and improved overall LFA-performance compared to the naked detection antibody. CBM-assisted antibodies were validated by implementation into two model lateral flow test devices (pregnancy detection and the detection of SARS-CoV-2 specific antibodies). The CBM-assisted pregnancy LFA demonstrated sensitive detection of human gonadotropin (hCG) in synthetic urine and the CBM-assisted Covid-19 antibody LFA was able to detect SARS-CoV-2 specific antibodies present in serum. Our findings pave the way to the more frequent use of cellulose-based papers instead of nitrocellulose in LFA devices and thus potentially improve the sustainability in the field of POC diagnostics.

3D-Printing of Hierarchically Designed and Osteoconductive Bone Tissue Engineering Scaffolds.

In Bone Tissue Engineering (BTE), autologous bone-regenerative cells are combined with a scaffold for large bone defect treatment (LBDT). Microporous, polylactic acid (PLA) scaffolds showed good healing results in small animals. However, transfer to large animal models is not easily achieved simply by upscaling the design. Increasing diffusion distances have a negative impact on cell survival and nutrition supply, leading to cell death and ultimately implant failure. Here, a novel scaffold architecture was designed to meet all requirements for an advanced bone substitute. Biofunctional, porous subunits in a load-bearing, compression-resistant frame structure characterize this approach. An open, macro- and microporous internal architecture (100 µm-2 mm pores) optimizes conditions for oxygen and nutrient supply to the implant's inner areas by diffusion. A prototype was 3D-printed applying Fused Filament Fabrication using PLA. After incubation with Saos-2 (Sarcoma osteogenic) cells for 14 days, cell morphology, cell distribution, cell survival (fluorescence microscopy and LDH-based cytotoxicity assay), metabolic activity (MTT test), and osteogenic gene expression were determined. The adherent cells showed colonization properties, proliferation potential, and osteogenic differentiation. The innovative design, with its porous structure, is a promising matrix for cell settlement and proliferation. The modular design allows easy upscaling and offers a solution for LBDT.

Characterization and Inkjet Printing of an RNA Aptamer for Paper-Based Biosensing of Ciprofloxacin.

The excessive use of antibiotics in food-producing animals causes a steady rise of multiple antibiotic resistance in foodborne bacteria. Next to sulfonamides, the most common antibiotics groups are fluoroquinolones, aminoglycosides, and ß-lactams. Therefore, there is a need for a quick, efficient, and low-cost detection procedure for antibiotics. In this study, we propose an inkjet-printed aptamer-based biosensor developed for the detection of the fluoroquinolone ciprofloxacin. Due to their extraordinary high affinity and specificity, aptamers are already widely used in various applications. Here we present a ciprofloxacin-binding RNA aptamer developed by systematic evolution of ligands by exponential enrichment (SELEX). We characterized the secondary structure of the aptamer and determined the KD to 36 nM that allow detection of antibiotic contamination in a relevant range. We demonstrate that RNA aptamers can be inkjet-printed, dried, and resolved while keeping their functionality consistently intact. With this proof of concept, we are paving the way for a potential range of additional aptamer-based, printable biosensors.

Gravure printing for mesoporous film preparation.

This study presents gravure printing as a new strategy for rapid printing of ceramic mesoporous films and highlights its advantages over conventional mesoporous film preparation using evaporation induced self-assembly together with dip-coating. By varying the printing process parameters, the mesoporous coating thicknesses can be adjusted between 20 and 200 nm while maintaining a very high film homogeneity allowing the printing of ultrathin mesoporous films. Step gradients in film composition are accessible by consecutively printing two different "inks". Thereby, gravure printing is a much faster process than mesoporous single- and multilayer preparation using conventional dip-coating because lower amounts of solution are transferred and dissolution of previously deposited layers is avoided. The effect of printing process parameters on resulting film characteristics as well as the resulting mesoporous film's ionic accessibility is systematically investigated.

Printing Poly( p-phenyleneethynylene) PLEDs.

Gravure printing of functional thin-film layers of side-chain-substituted poly( para-phenyleneethynylene)s (PPEs) is reported. Rheological properties of PPEs in combination with the Hansen solubility model allowed the formulation of enhanced single-component inks. Layer evaluation is performed with reflectometric thin-film recordings in an optical setup for laterally resolved large-area investigation using imaging color reflectometry. An organic light-emitting diode in a simple glass/indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/PPE/LiF-Al stack was gravure-printed from the improved ink showing excellent luminance (542 cd m-2, U = 11.5 V) for this polymer class.

Peptide arrays with a chip.

Today, lithographic methods enable combinatorial synthesis of >50,000 oligonucleotides per cm(2), an advance that has revolutionized the whole field of genomics. A similar development is expected for the field of proteomics, provided that affordable, very high-density peptide arrays are available. However, peptide arrays lag behind oligonucleotide arrays. This is mainly due to the monomer-by-monomer repeated consecutive coupling of 20 different amino acids associated with lithography, which adds up to an excessive number of coupling cycles. A combinatorial synthesis based on electrically charged solid amino acid particles resolves this problem. A computer chip consecutively addresses the different charged particles to a solid support, where, when completed, the whole layer of solid amino acid particles is melted at once. This frees hitherto immobilized amino acids to couple all 20 different amino acids in one single coupling reaction to the support. The method should allow for the translation of entire genomes into a set of overlapping peptides to be used in proteome research.