Organ-on-chip (OOC) is becoming the alternative tool to conventional in vitro screening. Heart-on-chip devices including microstructures for mechanical and electrical stimulation have been demonstrated to be advantageous to study structural organization and maturation of heart cells. This paper presents the development of metal and polymeric strain gauges for in situ monitoring of mechanical strain in the Cytostretch platform for heart-on-chip application. Specifically, the optimization of the fabrication process of metal titanium (Ti) strain gauges and the investigation on an alternative material to improve the robustness and performance of the devices are presented. The transduction behavior and functionality of the devices are successfully proven using a custom-made set-up. The devices showed resistance changes for the pressure range (0-3 kPa) used to stretch the membranes on which heart cells can be cultured. Relative resistance changes of approximately 0.008% and 1.2% for titanium and polymeric strain gauges are respectively reported for membrane deformations up to 5%. The results demonstrate that both conventional IC metals and polymeric materials can be implemented for sensing mechanical strain using robust microfabricated organ-on-chip devices.

The high aspect ratio and the porous nature of spatially oriented forest-like carbon nanotube (CNT) structures represent a unique opportunity to engineer a novel class of nanoscale assemblies. By combining CNTs and conformal coatings, a 3D lightweight scaffold with tailored behavior can be achieved. The effect of nanoscale coatings, aluminum oxide (Al₂O₃) and nonstoichiometric amorphous silicon carbide (a-SiC), on the thermal transport efficiency of high aspect ratio vertically aligned CNTs, is reported herein. The thermal performance of the CNT-based nanostructure strongly depends on the achieved porosity, the coating material and its infiltration within the nanotube network. An unprecedented enhancement in terms of effective thermal conductivity in a-SiC coated CNTs has been obtained: 181% compared to the as-grown CNTs and Al₂O₃ coated CNTs. Furthermore, the integration of coated high aspect ratio CNTs in an epoxy molding compound demonstrates that, next to the required thermal conductivity, the mechanical compliance for thermal interface applications can also be achieved through coating infiltration into foam-like CNT forests.

We present a novel method to easily and reliably transfer highly porous, large area, thin microfabricated Polydimethylsiloxane (PDMS) porous membranes on Lab-on-Chip (LOC) and Organ-on-Chip (OOC) devices. The use of silicon as carrier substrate and a water-soluble sacrificial layer allows a simple and reproducible transfer of the membranes to any PDMS-based OOC and LOC device. The use of IC and MEMS compatible techniques reduces significantly the fabrication time and the need of manual handling. Our method is suitable for automatic assembling systems, such as pick-and-place, crucial to significantly increase the throughput of OOC and LOC devices assembling. Membranes with 8 μm pore size and as thin as 4 μm are successfully transferred. The viability and biocompatibility of the transfer was assessed by culturing two different cell lines on an OOC with transferred porous PDMS membranes.

A novel, simple, low-cost method for the void-free filling of high aspect ratio (HAR) through-silicon-vias (TSVs) is presented. For the first-time pure indium, a type-I superconductor metal, is used to fill HAR vias, 300 to 500 μm in depth and 50 to 100 μm in diameter. The low electrical resistivity achieved without sintering, its reproducibility and straightforward processing steps, and the short time required to fill large arrays of vias at wafer scale - all make this method one of the simplest and quickest options for filling HAR TSVs for MEMS 3D integration. Moreover, the low melting point (∼ 150 °C), malleability and superconductivity at 3.41 K make indium an interesting option in 3D interconnects for connecting quantum devices operating below 4 K.

We present a novel and highly reproducible process to fabricate transferable porous PDMS membranes for PDMS-based Organs-on-Chips (OOCs) using microelectromechanical systems (MEMS) fabrication technologies. Porous PDMS membranes with pore sizes down to 2.0 μm in diameter and a wide porosity range (2–65%) can be fabricated. To overcome issues normally faced when using replica moulding and extend the applicability to most OOCs and improve their scalability and reproducibility, the process includes a sacrificial layer to easily transfer the membranes from a silicon carrier to any PDMS-based OOC. The highly reliable fabrication and transfer method does not need of manual handling to define the pore features (size, distribution), allowing very thin (<10 μm) functional membranes to be transferred at chip level with a high success rate (85%). The viability of cell culturing on the porous membranes was assessed by culturing two different cell types on transferred membranes in two different OOCs. Human umbilical endothelial cells (HUVEC) and MDA-MB-231 (MDA) cells were successfully cultured confirming the viability of cell culturing and the biocompatibility of the membranes. The results demonstrate the potential of controlling the porous membrane features to study cell mechanisms such as transmigrations, monolayer formation, and barrier function. The high control over the membrane characteristics might consequently allow to intentionally trigger or prevent certain cellular responses or mechanisms when studying human physiology and pathology using OOCs.

Polymeric (PEDOT:PSS) strain gauges embedded in PDMS membranes fabricated using a full wafer-scale fabrication process capable of realizing reproducible small features, are reported. The devices are characterized using a customized setup, which provides mechanical stretch while dynamically reading the electrical resistance. Measurements show relative resistance changes of approximately 11% for applied pressure up to 4 kPa. The process described is tailored to fabricate pressure sensors and microelectrodes for a flexible substrate-based Organ-on-Chip platform.

An unprecedented enhancement in electrical conductivity of horizontally aligned carbon nanotube (HA-CNT) structures using a 10 nm conformal coating of alumina (Al₂O₃) or amorphous silicon carbide (a-SiC) is presented. By combining the capability to grow long vertically aligned CNTs (VA-CNTs) with a liquid-assisted flattening technique, dense arrays of HA-CNTs exhibiting a high degree of alignment are realized and integrated at wafer-scale. Suspended structures, ranging from large area membranes to narrow beams, can be fabricated. The impressive enhancement in electrical conductivity, approximately 209% for the Al₂O₃ coated HA-CNTs (Al₂O₃/HA-CNTs) and 2276% for the a-SiC ones (a-SiC/HA-CNTs), demonstrates the potential of CNT-based scaffolds as scalable and functional building blocks for suspended interconnects, heat spreaders and novel chemical and optical sensors.

Sensing and stimulating microstructures are necessary to develop more specialized and highly accurate Organ-on-Chip (OOC) platforms. In this paper, we present the integration of a conductive polymer, poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), on a stretchable membrane, core element of an Heart-on-Chip. The electrical conductivity along with its biocompatibility, high transparency (≈88%) and mechanical elasticity (≈1.2 GPa) make this material a candidate to develop novel microstructures for electrical monitoring and stimulation of cells in flexible-substrate based OOCs. Microstructures with different shapes and geometries of PEDOT:PSS embedded in a 9 μm-thick Polydimethylsiloxane (PDMS) membrane are developed following a wafer-level fabrication approach. PEDOT:PSS layers between 120 nm and 300 nm are obtained by varying the deposition conditions. The layers are successfully patterned and microstructures with lateral dimensions down to 2 μm. The obtained results indicate that this polymer is a suitable material for microfabrication of sensing and stimulating elements in OOC platforms.