Fabrication, Flow Assembly, and Permeation of Microscopic Any-Shape Particles.

Today, millimeter-sized nonspherical any-shape particles serve as flexible, functional scaffold material in chemical and biochemical reactors tailoring their hydrodynamic properties and active surface-to-volume ratio based on the particle's shape. Decreasing the particle size to smaller than 100 µm would be desired as it increases the surface-to-volume ratio and promotes a particle assembly based on surface interactions, allowing the creation of tailored self-assembling 3D scaffolds. This study demonstrates a continuous high-throughput fabrication of microscopic 3D particles with complex shape and sub-micron resolution using continuous two-photon vertical flow lithography. Evolving from there, in-channel particle fabrication into a confined microfluidic chamber with a resting fluid enables the precise fabrication of a defined number of particles. 3D assemblies with various particle shapes are fabricated and analyzed regarding their permeability and morphology, representing convective accessibility of the assembly's porosity. Differently shaped particles highlight the importance of contact area regarding particle-particle interactions and the respective hydraulic resistance of an assembly. Finally, cell culture experiments show manifold cell-particle interactions promising applicability as bio-hybrid tissue. This study pushes the research boundaries of adaptive, responsive, and permeable 3D scaffolds and granular media by demonstrating a high throughput fabrication solution and a precise hydrodynamic analysis method for micro-particle assemblies.

Mimicking the Natural Basement Membrane for Advanced Tissue Engineering.

Advancements in the field of tissue engineering have led to the elucidation of physical and chemical characteristics of physiological basement membranes (BM) as specialized forms of the extracellular matrix. Efforts to recapitulate the intricate structure and biological composition of the BM have encountered various advancements due to its impact on cell fate, function, and regulation. More attention has been paid to synthesizing biocompatible and biofunctional fibrillar scaffolds that closely mimic the natural BM. Specific modifications in biomimetic BM have paved the way for the development of in vitro models like alveolar-capillary barrier, airway models, skin, blood-brain barrier, kidney barrier, and metastatic models, which can be used for personalized drug screening, understanding physiological and pathological pathways, and tissue implants. In this Review, we focus on the structure, composition, and functions of in vivo BM and the ongoing efforts to mimic it synthetically. Light has been shed on the advantages and limitations of various forms of biomimetic BM scaffolds including porous polymeric membranes, hydrogels, and electrospun membranes This Review further elaborates and justifies the significance of BM mimics in tissue engineering, in particular in the development of in vitro organ model systems.

Formation of Single Micro- and Nanowires with Extreme Aspect Ratios in Microfluidic Channels.

Shown here is the site-specific formation of single extraordinarily long metal-organic micro- and nanowires using a microfluidic device made of poly(dimethylsiloxane) (PDMS). This approach exploits two concepts, i) the diffusion of organic precursor molecules through PDMS and ii) the use of microfluidic channels as a growth template. To initiate wire formation, metal and organic precursor solutions are filled into different supply channels that are separated by PDMS. As the precursor diffuses through PDMS, and thereby infiltrates the adjacent channel, the growth of micro- and nanowires starts at the side walls of this adjacent channel. The formation yields single wires with sizes ranging from several hundreds of micrometers to millimeters at diameters of 0.5-2 µm. The principles of this formation pathway are demonstrated with the reaction of tetrathiafulvalene (TTF) and gold(III) ions that yields Au-TTF wires. The influence of various reaction parameters including the choice of solvents and the chip fabrication protocol on the reaction are evaluated. Based on these findings, a further microfluidic device design with orthogonally arranged channels is developed, and the formation of single wires in a channel-defined pattern is demonstrated. Moreover, the possibility of pulsed precursor supply allows for advanced control over the growth of the wires.

The Effects of Shear Force Transmission Across Vesicle Membranes.

We report a comprehensive study on mechanotransmission of shear forces across lipid bilayer membranes of giant unilamellar vesicles (GUVs). GUVs containing fluorescent tracer particles were immobilized on a microfluidic platform and exposed to shear flows. A method was developed for the visualization of three-dimensional flows at high precision by defocusing microscopy. We quantify the symmetry of external flow around the GUV and show its effects on vortex flows and luminal dynamics. With increasing asymmetry, luminal vortices merged while liquid exchange in between them increased. The effect of membrane composition was studied through addition of cholesterol. Mechanotransmission efficacy, quantified by the ratio of luminal flow to external flow, ranged from ε = 0.094 (0 mol % cholesterol) to ε = 0.043 (16 mol % cholesterol). Our findings give new cues to the mechanisms underlying the sensing of strength and spatial distribution of shear forces by cells and the impact of membrane composition.

How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?

Dynamic sorption of ethanol and toluene vapor into ultrathin supported films of polymer of intrinsic microporosity PIM-1 down to a thickness of 6 nm are studied with a combination of in situ spectroscopic ellipsometry and in situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphology. For ethanol below 20 nm, three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to that of thicker films. Second, at low penetrant activities (below 0.3p/p0), films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite a similar swelling magnitude. Third, for the ultrathin films, the onset of the dynamic penetrant-induced glass transition Pg has been found to shift to higher values, indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the superglassy PIM-1 at the substrate surface leads to an arrested, even more rigid, and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics, and two distinct penetrant-induced relaxation phenomena, probably associated with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion, the surface seems to plasticize earlier than the bulk, and the two relaxations remain well separated down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.

Stable and Simple Immobilization of Proteinase K Inside Glass Tubes and Microfluidic Channels.

Engyodontium album proteinase K (proK) is widely used for degrading proteinaceous impurities during the isolation of nucleic acids from biological samples, or in proteomics and prion research. Toward applications of proK in flow reactors, a simple method for the stable immobilization of proK inside glass micropipette tubes was developed. The immobilization of the enzyme was achieved by adsorption of a dendronized polymer-enzyme conjugate from aqueous solution. This conjugate was first synthesized from a polycationic dendronized polymer (denpol) and proK and consisted, on average, of 2000 denpol repeating units and 140 proK molecules, which were attached along the denpol chain via stable bis-aryl hydrazone bonds. Although the immobilization of proK inside the tube was based on nonspecific, noncovalent interactions only, the immobilized proK did not leak from the tube and remained active during prolonged storage at 4 °C and during continuous operation at 25 °C and pH = 7.0. The procedure developed was successfully applied for the immobilization of proK on a glass/PDMS (polydimethylsiloxane) microchip, which is a requirement for applications in the field of proK-based protein analysis with such type of microfluidic devices.