Polyimide/SU-8 catheter-tip MEMS gauge pressure sensor

This paper describes the development of a polyimide/SU-8 catheter-tip MEMS gauge pressure sensor. Finite element analysis was used to investigate critical parameters, impacting on the device design and sensing characteristics. The sensing element of the device was fabricated by polyimide-based micromachining on a flexible membrane, using embedded thin-film metallic wires as piezoresistive elements. A chamber containing this flexible membrane was sealed using an adapted SU-8 bonding technique. The device was evaluated experimentally and its overall performance compared with a commercial silicon-based pressure sensor. Furthermore, the device use was demonstrated by measuring blood pressure and heart rate in viv

Fluidic microstructuring of alginate hydrogels for the single cell niche

Controlling alginate gel formation by diffusion of Ca2+ ions through a filter barrier, a layer-by-layer deposition technique with resolution on the size scale of a single cell is presented. It offers the possibility of exposing cells under biocompatible conditions to microheterogeneous three-dimensional environments, mimicking the layered structure of extracellular matrix in tissues

Microcollimator for Micrometer-Wide Stripe Irradiation of Cells Using 20–30 keV X Rays

The exposure of subnuclear compartments of cells to ionizing radiation is currently not trivial. We describe here a collimator for micrometer-wide stripe irradiation designed to work with conventional high-voltage X-ray tubes and cells cultured on standard glass cover slips. The microcollimator was fabricated by high-precision silicon micromachining and consists of X-ray absorbing chips with grooves of highly controlled depths, between 0.5-10 mum, along their surfaces. These grooves form X-ray collimating slits when the chips are stacked against each other. The use of this device for radiation biology was examined by irradiating human cells with X rays having energies between 20-30 keV. After irradiation, p53 binding protein 1 (53BP1), a nuclear protein that is recruited at sites of DNA double-strand breaks, clustered in lines corresponding to the irradiated stripes

Nano-Stenciled RGD-Gold Patterns That Inhibit Focal Contact Maturation Induce Lamellipodia Formation in Fibroblasts

Cultured fibroblasts adhere to extracellular substrates by means of cell-matrix adhesions that are assembled in a hierarchical way, thereby gaining in protein complexity and size. Here we asked how restricting the size of cell-matrix adhesions affects cell morphology and behavior. Using a nanostencil technique, culture substrates were patterned with gold squares of a width and spacing between 250 nm and 2 µm. The gold was functionalized with RGD peptide as ligand for cellular integrins, and mouse embryo fibroblasts were plated. Limiting the length of cell-matrix adhesions to 500 nm or less disturbed the maturation of vinculin-positive focal complexes into focal contacts and fibrillar adhesions, as indicated by poor recruitment of α5-integrin. We found that on sub-micrometer patterns, fibroblasts spread extensively, but did not polarize. Instead, they formed excessive numbers of lamellipodia and a fine actin meshwork without stress fibers. Moreover, these cells showed aberrant fibronectin fibrillogenesis, and their speed of directed migration was reduced significantly compared to fibroblasts on 2 µm square patterns. Interference with RhoA/ROCK signaling eliminated the pattern-dependent differences in cell morphology. Our results indicate that manipulating the maturation of cell-matrix adhesions by nanopatterned surfaces allows to influence morphology, actin dynamics, migration and ECM assembly of adhering fibroblasts

Stencil Lithography and Inkjet Printing as New Tools for Life Sciences Research

This thesis work focuses on applying microtechnology to produce three toolkits for life-sciences research. The first technique presented is nanostencil lithography for patterning cell adhesions. Nanostencil lithography is a shadow-mask micro and nanopatterning technique that was adapted for patterning on silicone rubber (PDMS) in the course of this work. Once a specific material contrast is present on the substrate, the patterns can be functionalized using highly-selective surface modification techniques. In this work, Au micro and nanopatterns were rendered cell-adhesive by grafting a thiolated peptide (presenting an RGD moiety) to their surfaces. The micro and nanopatters were used to study whether geometric confinement could prevent a mammalian cell's primary 'focal contacts' from developing into mature 'focal adhesions'. Micro and nanopatters were successfully created on both PDMS, glass, and even polytetra fluoroethylene. The second part of this work focuses on 3D bioprinting. Recently, 3D printing has received attention as a possible means of assembling heterogeneous tissue mimetics (and ultimately entire organs). However, to date no one has shown true 3D printing of hydrogels in a manner analogous to an industrial rapid prototyping system. One of the main hurdles at this point remains the fact that printed hydrogels tend to show complete spreading on other printed hydrogels (or, like spreads on like). This work details how the materials properties of a hydrogel system can be optimized to get 3D hydrogel printing analogous to a rapid prototyping system. It goes on to show how an optimized printing process can permit the printing of branched vasculature – a key requirement in tissue engineering applications. The final part of this work focused on creating an X-ray microcollimator to study subcellular (and sub-nuclear) damage responses in cells. While many molecular biologists use ionizing radiation (commonly from X-ray tubes) to induce damage in cells, current X-ray microcollimators only work well with costly synchrotron radiation sources. During the course of this thesis, an x-ray microcollimator was developed that is compatible with conventional X-ray tube setups. The device collimates 20–30 keV X-rays into irradiation stripes between 0.5 and 10 µm in diameter. Results with the microcollimator show that it is effective in limiting IR damage to single stripe lengths. This work was initially funded by the SNF project: 205321-112323, and later by a SystemsX demonstration fund

Nanostencil and InkJet Printing for Bionanotechnology Applications

In this contribution we describe the application of Ink-Jet printing and Stencil Lithography in bionanotechnology. Both techniques are alternative patterning methods that can be used for the fabrication of biocompatible micro- and nanostructures out of the costly and restricted clean room environment. The applications presented in this contribution are 1) the cell patterning using Au dot arrays deposited on PDMS,by stencil lithography, 2) the fabrication of biosensors based on localized surface plasmon resonance in Au nanodots deposited by stencil lithography and 3) the printing of cells and biomolecules by InkJet printing

3D Patterning of Hydrogels and Cells by Multi-Component Inkjet Printing

Recapitulating the spatial and temporal complexity of tissues or organs represents one of the biggest challenges in engineering tissue-like living constructs in vitro. Inkjet printing with its high positioning precision (±1μm) and reliable droplet generation (<5% variation) should fulfill the requirements to pattern biomaterials into complex three-dimensional (3D) geometries. However, there exists no biologically relevant ink that could afford 3D shape retention after drop deposition and fast stabilization of a printed structure. To address this issue, we have been developing an alginate hydrogel-based inkjet printing platform. Alginate solutions can be reliably dispensed on a hydrogel substrate storing calcium ions that quickly diffuse into the alginate solution inducing rapid cross-linking. We characterized the crosslinking kinetics and optimized printing parameters towards homogeneous stacking of droplets. Since living tissues are multi-component entities comprised of several types of cells and extracellular environments, we then focused on optimizing the dispensing system for synchronized multi-component deposition. We successfully matched the ejection characteristics of multiple nozzles by evaluating droplet diameter, jet speed and jet angle of each nozzle for variable dispensing voltage and pulse length.. Finally, proof-of-concept experiments were conducted to successfully print living 3D structures in the form of a simplified blood vessel

An Oligomerized 53BP1 Tudor Domain Suffices for Recognition of DNA Double-Strand Breaks▿

53BP1, the vertebrate ortholog of the budding yeast Rad9 and fission yeast Crb2/Rhp9 checkpoint proteins, is recruited rapidly to sites of DNA double-strand breaks (DSBs). A tandem tudor domain in human 53BP1 that recognizes methylated residues in the histone core is necessary, but not sufficient, for efficient recruitment. By analysis of deletion mutants, we identify here additional elements in 53BP1 that facilitate recognition of DNA DSBs. The first element corresponds to an independently folding oligomerization domain. Replacement of this domain with heterologous tetramerization domains preserves the ability of 53BP1 to recognize DNA DSBs. A second element is only about 15 amino acids long and appears to be a C-terminal extension of the tudor domain, rather than an independently functioning domain. Recruitment of 53BP1 to sites of DNA DSBs is facilitated by histone H2AX phosphorylation and ubiquitination. However, none of the 53BP1 domains/elements important for recruitment are known to bind phosphopeptides or ubiquitin, suggesting that histone phosphorylation and ubiquitination regulate 53BP1 recruitment to sites of DNA DSBs indirectly