Failure Modes in Capillary Self-Assembly

Capillary self-assembly is rapidly emerging as an innovative technique to enhance, complement and eventually replace pick-and-place assembly for the integration of heterogeneous microsystems. Vast literature and experimental data support such claim. Yet, the technique needs to overcome important limitations in order to earn wide industrial recognition. In this talk, we illustrate the challenges ahead for making part-to-substrate capillary self-assembly reliable and seriously competitive. We focus on the standard embodiment of capillary self-assembly, and we describe in details the often novel technological steps required for its effective and reproducible performance. This preludes to an outline of what are presently the major failure modes affecting the overall yield of the technique. Consequently, we propose solutions to face these challenges and foster the success of this technique

Micropositioning and microscopic observation of individual picoliter-sized containers within SU-8 microchannels

We describe the fabrication and application of a bioanalytical chip, made of SU-8 photoresist, comprising integrated, high aspect-ratio microfluidic channels, suitable to manipulate and investigate vesicles, cell fragments and biological cells. A central micrometer-sized aperture allows electrical particle counting and planar membrane experiments, microfluids allow (sub)micrometer-sized objects to be transported and addressed with different chemicals. Here we show how lipid vesicles are positioned with micrometer precision within the micro-channels by means of pressure and electrophoretic movement. Our approach is suited for controlling and investigating (bio)chemical synthesis and cellular signalling processes in ultrasmall individual vesicles by electro-optical technique

Drop-on-Demand Inkjet Printing of Functional Composites

Drop-on-Demand Inkjet printing can be used as an effective technique to deposit the sensing layer in chemical sensors. However, formulation of inks containing functional materials remains challenging due to rheological constraints imposed by the inkjet printer. Here, we show a systematic process to formulate and print functional inks containing polymer and carbon black (CB) particles. The functional ink is used for sensing different analytes considering the polarity of the polymer1,2. We formulated inks containing polyvinylpyrrolidone (PVP) with the molecular weight of 40 kDa and 360 kDa. We used high-structured carbon black as the conductive filler. Printing parameters were optimized and the polymer composite was printed on the sensor platform with screen printed interdigitated electrode (IDE). The ink showed good stability over time and no sedimentation was observed even weeks after the formulation. In the next step we characterize the sensing behavior of the printed campsites

Conduction in rectangular quasi-one-dimensional and two-dimensional random resistor networks away from the percolation threshold

In this study we investigate electrical conduction in finite rectangular random resistor networks in quasione and two dimensions far away from the percolation threshold p(c) by the use of a bond percolation model. Various topologies such as parallel linear chains in one dimension, as well as square and triangular lattices in two dimensions, are compared as a function of the geometrical aspect ratio. In particular we propose a linear approximation for conduction in two-dimensional systems far from p(c), which is useful for engineering purposes. We find that the same scaling function, which can be used for finite-size scaling of percolation thresholds, also applies to describe conduction away from p(c). This is in contrast to the quasi-one-dimensional case, which is highly nonlinear. The qualitative analysis of the range within which the linear approximation is legitimate is given. A brief link to real applications is made by taking into account a statistical distribution of the resistors in the network. Our results are of potential interest in fields such as nanostructured or composite materials and sensing applications

DOD Inkjet printing of functional polymers

Inkjet printing techniques have gained a lot of attention for the micro-structuring of functional materials. This is due to their low cost, low material consumption and relatively easy fabrication process. In this project, Drop-on-Demand (DOD) inkjet printing is used as a means of depositing gas-sensitive polymer nanocomposites on interdigitated electrodes. Different shapes and patterns (e.g. lines and films) can be printed by controlling the coalescence of the neighboring droplets. The final topography of the printed structure depends strongly on parameters such as ink formulation, surface properties of the substrate as well as printing parameters

Inkjet Printing of Functional Polymer Composites for Chemiresistive Gas Sensors

Drop-on-Demand Inkjet printing can be used as an effective technique to deposit the sensing layer in chemiresistive gas sensors. In this type of gas sensors, a composite containing an insulating polymer mixed with a conductive filler is used for sensing analytes. However, formulation of inks containing functional materials remains challenging due to rheological constraints imposed by the inkjet printer. Here, we show the process of ink formulation for functional inks containing polyvinylpyrrolidone (PVP), a polar polymer, and carbon black (CB). We formulated composite inks containing PVP with different molecular weights (40 and 360 kDa) and studied their inkjet-abilities based on their shear viscosity and particle size distribution. Composite inks were successfully printed onto the sensor platforms and their electrical properties were characterized

Individually actuated cantilever arrays for cell force spectroscopy

The design, fabrication and characterization of thermally actuated, parallelizable cantilevers is presented. Thermal simulations of operation in liquid give indications regarding displacement range in such an environment

Integrated long-range thermal bimorph actuators for parallelizable bio-AFM applications

AFM-based cell force spectroscopy is an emerging research method that already has enhanced our understanding of the structural changes that take place in a cell as it becomes cancerous. However, the method is limited as it is not time-efficient in its current state of development. This paper presents the fabrication of an integrated long-range thermal bimorph actuator that controls the z-position of an AFM cantilever in liquid. Multiplied in arrays, such individually actuated probes can parallelize cell force spectroscopy measurements, thereby drastically reducing the time per measured cell. The need to accommodate differences in tip-sample distance implies an individual device actuation range of ≥10 µm out of plane. In addition, any cross-talk, i.e. between actuators or between the actuator and the force sensor, must be minimized. To meet these requirements, we designed and fabricated a novel thermal bimorph actuator that was incorporated with force sensing cantilevers. In order to keep temperatures in a bio-friendly range, the design was optimized for high thermo-mechanical sensitivity. FEM simulations confirmed that the surrounding liquid constitutes a large thermal reservoir that absorbs the generated heat. Furthermore, given that a cell substrate material of high thermal conductivity is chosen, in our case silicon, the thermal coupling between the cell and the substrate dominates over that between the cell and the actuator. Suspended silicon nitride structures with platinum electrodes were micro-fabricated through standard techniques. The finalized actuator was able to displace the cantilever out of plane by 17 µm in air

Integrated MEMS actuation for force spectroscopy in liquid

This work aims to develop arrays of individually actuated cell force spectroscopy probes. Cross et al. (Nat. Nanotech. 2007) have shown that human cells undergo substantial mechanical changes as they become cancerous. Cell force spectroscopy using AFM has emerged as a promising candidate to measure those changes. It is believed that this method will lead to an increased understanding of the disease and potentially also to new diagnosis technologies. In order to collect a sucient amount of data, several cells must be measured. In the current state of the technology, iterations are very time-consuming. The PATLiSci project aims to parallelize these measurements by developing arrays of probes. Our task is to develop such arrays with the additional feature of individual actuation, allowing tuning of the applied force exerted by each probe