This chapter discusses the use of rapid prototyping techniques in the fabrication of biosensors. First it discusses the use of micromoulding, extrusion, 3D printing, stereolithography, and xurography in the prototyping of microfluidic biosensors. This is followed by a discussion of functionalization and patterning methods for adding bioelement and transducer materials to biosensor surfaces. Finally, the chapter discusses future trends in biosensors and the continued yet evolving role of rapid prototyping methods in their fabrication.

BackgroundMalignant pleural mesothelioma (MPM) is an aggressive disease of the pleural lining with a dismal prognosis. Surgical treatments of MPM with a curative intent include extrapleural pneumonectomy and extended pleurectomy/decortication (P/D). This meta-analysis aimed to compare the perioperative and long-term outcomes of EPP and extended P/D for selected surgical candidates.MethodsA systematic review of the literature was performed on six electronic databases to identify all relevant data on comparative outcomes of extended P/D and EPP in a multimodality setting. Endpoints included perioperative mortality and morbidity, as well as long-term overall survival.ResultsSeven relevant studies with comparative data on EPP (n=632) versus extended P/D (n=513) were identified from the current literature. Comparison of these two groups demonstrated significantly lower perioperative mortality (2.9% vs 6.8%, p=0.02) and morbidity (27.9% vs 62.0%, p<0.0001) for patients who underwent extended P/D compared to EPP. Median overall survival ranged between 13–29 months for extended P/D and 12–22 months for EPP, with a trend favouring extended P/D.ConclusionsAlthough it must be emphasized that patient selection and treatment strategies differ between EPP and extended P/D, a number of comparative studies have recently been conducted to compare these two surgical techniques for patients with resectable MPM. The present study indicated that selected patients who underwent extended P/D had lower perioperative morbidity and mortality with similar, if not superior, long-term survival compared to EPP, in the context of multi-modality therapy. This may represent an important paradigm shift in the surgical management of MPM.

In this work nanocomposites based on organic-capped semiconductor nanocrystals formed of a core of CdSe coated with a shell of ZnS (CdSe@ZnS), with different sizes, and a semiconducting conjugated polymer, namely poly[(9,9-dihexylfluoren-2,7-diyl)-alt- (2,5-dimethyl-1,4-phenylene)] (PF-DMB) have been investigated. The nanocomposites are prepared by mixing the pre-synthesized components in organic solvents, thereby assisting the dispersion of the organic-coated nano-objects in the polymer host. UV–vis steady state and time-resolved spectroscopy along with (photo)electrochemical techniques have been performed to characterize the obtained materials. The study shows that the embedded nanocrystals increase the PF-DMB stability against oxidation and, at the same time, extend the light harvesting capability to the visible spectral region, thus resulting in detectable photocurrent signals. The nanocomposites have been dispensed by means of a piezo-actuated inkjet system. Such inks present viscosity and surface tension properties well suited for stable and reliable drop-on-demand printing using an inkjet printer. The fabrication of arrays of single-color pixels made of the nanocomposites and micrometers in size has been performed. Confocal and atomic force microscopy have confirmed that inkjet-printed microstructures present the intrinsic emission properties of both the embedded nanocrystals and PF-DMB, resulting in a combined luminescence. Finally, the morphology of the printed pixels is influenced by the embedded nanofillers.

Keywords: inkjet prining, MEMS Reference EPFL-CHAPTER-176184 Record created on 2012-04-13, modified on 2017-05-10

We have developed a conducting composite based on multi-walled carbon nanotubes and bisphenol A novolak epoxy resin (SU8) for inkjet printing purposes. We could deposit regular conducting stripes and arrays of 150 mu m spots on glass and on flexible polyethylene terephthalate ( PET) films. The UV and temperature processed structures show very good adhesion and reasonably good resistivity with a low concentration of carbon nanotubes. Our composite material for inkjet deposition is completely compatible with current MEMS fabrication processes.

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 vivo.

We provide a common theoretical framework reuniting specific models for the Ca(2+)-alginate system and general reaction diffusion theory along with experimental validation on a microfluidic chip. As a starting point, we use a set of nonlinear, partial differential equations that are traditionally solved numerically: the Mikkelsen-Elgsaeter model. Applying the traveling-wave hypothesis as a major simplification, we obtain an analytical solution. The solution indicates that the fundamental properties of the alginate reaction front are governed by a single dimensionless parameter λ. For small λ values, a large depletion zone accompanies the reaction front. For large λ values, the alginate reacts before having the time to diffuse significantly. We show that the λ parameter is of general importance beyond the alginate model system, as it can be used to classify known solutions for second-order reaction diffusion schemes, along with the novel solution presented here. For experimental validation, we develop a microchip model system, in which the alginate gel formation can be carried out in a highly controlled, essentially 1D environment. The use of a filter barrier enables us to rapidly renew the CaCl(2) solution, while maintaining flow speeds lower than 1 μm/s for the alginate compartment. This allows one to impose an exactly known bulk CaCl(2) concentration and diffusion resistance. This experimental model system, taken together with the theoretical development, enables the determination of the entire set of physicochemical parameters governing the alginate reaction front in a single experiment.

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 optimized 3D inkjet printing process is demonstrated for structuring alginate into a tissue-like microvasculature capable of supporting physiological flow rates. Optimizing the reaction at the single-droplet level enables wet hydrogel droplets to be stacked, thus overcoming their natural tendancy to spread and coalesce. Live cells can be patterned using this process and it can be extended to a range of other hydrogels.

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.

Controlling alginate gel formation by diffusion of Ca(2+) 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.

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.

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 mu m, along their surfaces. These grooves form Xray 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. (C) 2009 by Radiation Research Society

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.

Vascularization arguably poses the most significant hurdle for the success of most biomaterials-based tissue engineering therapies. In this work, we report two printing strategies that permit the 3D Inkjet printing of fluorescent alginate hydro gels into overhanging structures and closed lumens that could serve as vessel mimetics. The first is 4-Matrix printing, where the order of droplet printing in each printing layer is optimized so that new droplets do not coalesce with un-gelled droplets on the surface. The second is the use of incremental droplet spacing to print overhanging and closed structures in order to reduce the degree of down-wall flow.Printed 3D structures were examined by 3D confocal microscopy in order to determine the effectiveness of these printing strategies. The results are promising and might be applied to other rapidly gelling hydrogel systems.

Resistless processes to realize the pattern transfer of your designs into the substrate present some advantages, as the reduction in fabrication steps. Stencil Lithography (SL) is one of the most used resistless processes and, up to now, it has mainly been used to perform local selective deposition of materials. Here, the local etching of different substrates through a stencil hard mask is presented. The compatibility with different etching conditions, the scalability of the technique and the main challenges are described. Minimum feature dimensions of 500nm in polysilicon and 200nm in LS-SiN is presented.