Organ-on-Chip Fabrication with Integrated Electrodes for TEER | Protocol Preview

The Tissue Engineering Laboratory at API Geneva has developed an integrated system that measures trans-epithelial/endothelial electrical resistance (TEER) in real-time and non-invasively to assess the quality of biological barriers, with applications in toxicology testing and pharmacological studies such as drug discovery, addressing the challenge that only one in nine drugs receives regulatory approval due to inability to reach targeted sites.

Trans-epithelial electrical resistance (TEER) measurement is a fundamental technique for assessing the integrity and barrier function of epithelial cell monolayers in vitro. This method applies a small electrical current across a cell layer and measures the resulting voltage drop to calculate resistance, which correlates with how tightly cells are connected. TEER is essential for studying cellular barrier properties in various applications including drug permeability testing, toxicity assessment, and understanding physiological barriers like the blood-brain barrier. The technique requires specialized electrodes and instruments designed to deliver minimal current while providing accurate, repeatable measurements that reflect true cellular barrier function without disrupting the monolayer.

Before permeability testing, monolayer integrity is verified using Transepithelial Electrical Resistance (TEER) measurement with a multimeter and electrodes in each compartment. High TEER values indicate functional tight junctions. The assay procedure involves washing cells with HBSS, measuring TEER, decanting HBSS from the apical side, adding fresh HBSS to collection wells, and introducing test compounds to the apical compartment. Samples are collected separately from both compartments. Analytical methods include liquid chromatography and microplate readers, especially for fluorescent compounds. Results yield the apparent permeability coefficient (Papp), calculated from compound concentrations in both compartments over time. This coefficient correlates with reference compounds to predict human intestinal absorption fractions, enabling informed decisions in drug development programs.

Transepithelial Electrical Resistance (TEER) is a well-established technique used to assess the barrier function and integrity of epithelial and endothelial cell layers by applying a small AC current to the cell monolayer and measuring the resistance to ion flow, providing valuable insights into tight junction integrity and cell-cell interactions; WPI's EVOM family of meters, including manual and automated systems for 24-well and 96-well plates, serves as the gold standard in TEER technology, having been trusted for nearly 40 years and cited in thousands of peer-reviewed publications for applications in drug absorption studies, tissue engineering, disease modeling, and quality control.

Advanced organ-on-a-chip platforms integrate multiple sensors for comprehensive monitoring: optical sensors for oxygen, CO2, and pH; electrochemical sensors for specific molecule capture; bubble traps; and continuous measurement of temperature, glucose, and lactate. Fully automated systems with MATLAB-based data acquisition can monitor experiments running for days, weeks, or months. Such platforms represent the future direction of the field, though they remain technically challenging to implement.

Modern wearable sensors integrate multiple physiological monitoring modalities within single devices. Advanced systems combine electrochemical sensors for biomarkers like lactate and glucose with acoustic sensors for blood pressure monitoring, or integrate ECG electrodes with chemical sensors for simultaneous cardiac and metabolic assessment. Microfluidic channels integrated with flexible substrates enable continuous sweat sampling and removal, with natural sweat gland activity providing the pumping mechanism. For security applications, printed electrodes on elastic textiles enable flexible biosensors for nerve agent detection, gunshot residue identification, and explosive trace detection. Microneedle arrays penetrate the outer skin layer minimally while delivering sensors into interstitial fluid for detection of multiple biomarkers including glucose, ketones, lactate, and alcohol. Wound healing monitoring uses flexible sensors integrated into dressings to track pH levels and uric acid. For melanoma screening, sensors detect tyrosinase enzyme activity by measuring conversion of substrate catechol to benzoquinone, providing rapid preliminary screening at the point of care.

Modern health monitoring devices can simultaneously measure multiple physiological parameters through integrated sensors. The system measures body temperature (36.5-37.5°C normal range), blood oxygen saturation, blood pressure, and heart electrical activity (ECG). Each measurement requires specific user positioning and technique, with the application providing real-time feedback on correct placement. Results are color-coded for quick interpretation and stored for longitudinal health tracking.

Flexible biochemical sensing platforms combine optical and electrochemical sensing capabilities. The optical patch measures heart rate and oxygenation, while the electrochemical patch detects lactate, cortisol, glucose, pH, and temperature. Multi-analyte electrochemical patches enable simultaneous sensing of multiple biomarkers. For wound monitoring, bi-enzymatic systems for uric acid detection are printed on gauze bandages with spatially distributed sensors to measure changes near and away from the wound, tested in clinical studies at University of Miami Health System.

Comprehensive physiological monitoring requires detecting both chemical parameters and electrophysiological signals simultaneously. Combined sensors integrate ECG monitoring electrodes with chemical sensing electrodes (like lactate sensors) on a single PCB. This allows real-time collection of both types of signals simultaneously, providing complete information about underlying physiology rather than isolated measurements. Such integrated systems can be attached to appropriate body regions (like chest for ECG) for comprehensive health monitoring.

Multi-organ chips can simulate complete drug disposition pathways including absorption, distribution, metabolism, and excretion (ADME). Using Chip 4 with intestine, liver, kidney, brain, and blood-brain barrier models, researchers demonstrated that haloperidol excretion matched patient data (only 1% excreted), while carbamazepine oral application showed expected absorption and metabolism patterns. An antibiotic study revealed that at therapeutic concentrations, the drug was properly metabolized and excreted, but at 1000x higher concentrations, 100% was excreted through the kidney compartment, demonstrating dose-dependent toxicity prediction.

An integrated human body-on-chips system connects multiple organ chips (gut, liver, kidney, heart, lung, blood-brain barrier, brain neuronal networks, skin, bone marrow, pancreas) through robotic sampling and shared medium. Drugs pass sequentially through the system to model absorption, metabolism, distribution, and excretion. Computational scaling from chip measurements to in vivo parameters enables prediction of key pharmacokinetic values like Cmax and t1/2. For oral nicotine, predictions matched clinical data from Swedish studies with three formulations. For intravenous cisplatin, predictions matched clinical studies with two infusion protocols, demonstrating potential to shortcut clinical trial design.

Advanced human-on-a-chip platforms integrate multiple organ systems including blood-brain barrier (BBB), gastrointestinal tract (GIT), kidney, and skin tissues within a single system. These multi-organ models enable study of drug absorption, distribution, metabolism, and excretion (ADME) properties in physiologically relevant contexts. BBB models incorporate tight junction proteins and transporters (glucose transporters and P-glycoprotein), while GIT inserts allow study of oral versus intravenous dosing differences. Recirculating immune system models generate both restorative and inflammatory macrophages within the same system, enabling study of immune responses and immunomodulatory drug effects. Pharmacokinetic-pharmacodynamic (PK-PD) relationships created in these systems correlate well with in vivo data across species, from guinea pigs to non-human primates.

Organ-on-a-chip technology enables patient-specific drug testing by using cells from individual patients. Since people respond differently to the same drugs due to genetic and physiological differences, testing drugs on patient-derived cells can predict individual responses. This supports precision medicine, which tailors treatment to individual patients—different patients may respond to different doses or require different drugs entirely. Major challenges include scalability (devices are made artesially and cannot be produced at scale), complexity (incorporating immune cells, microbiota, and multiple organ systems), standardization (lack of consistent protocols), cost, and regulatory pathways. Multi-organ-on-a-chip systems connect multiple organ chips (liver, kidney, intestine, heart, bone marrow) to simulate systemic drug effects—for example, testing absorption in intestine, metabolism in liver, excretion in kidney, and systemic toxicity in bone marrow.

Organ chips of virtually every organ have been created, including lymph node, liver, and kidney chips. The vision is connecting multiple organ chips through blood vessel channels to create a human body-on-chips system. A simpler version with gut, liver, and kidney connected by a mixing chamber allows samples to be taken as if from peripheral blood. Computational modeling combined with measurements at every point in linked chips can scale from chip volumes to the human body. When oral nicotine and intravenous cisplatin were tested, predicted levels precisely matched patient observations, demonstrating the system's predictive power.