Fundamentals
What is Connected Barrier Modeling?
Biological barriers — such as the intestinal epithelium, blood-brain barrier (BBB), blood-cerebrospinal fluid barrier (BCSFB), and pulmonary epithelium — are not isolated structures. In the body, compounds cross multiple barriers sequentially, and their absorption, distribution, metabolism, and excretion (ADME) properties are shaped by this multi-step journey.
Connected barrier modeling recreates this physiological reality in vitro by linking two or more barrier tissues within a single experimental system, allowing researchers to study how drugs, toxins, or biologics traverse and interact with multiple barrier types in sequence.
This approach is critical for understanding CNS drug penetration, gut-to-brain signalling, pulmonary drug delivery, and systemic toxicity cascades that depend on multi-organ pharmacokinetics.
Physiological Relevance
Replicates the sequential barrier crossings a drug experiences in vivo
Dynamic Transport
Measures real-time flux across polarised epithelial and endothelial layers
CNS Access Prediction
Assesses BBB and BCSFB permeability for neurological drug programs
Barrier Integrity Monitoring
TEER measurements confirm barrier formation and compound-driven disruption
Key Systems
Major Barrier Axes in Drug Research
Each barrier axis presents unique challenges for drug developers. Understanding drug behaviour across these interfaces is essential for both efficacy and safety assessment.
Intestinal Epithelium
Gut–Blood Barrier
The primary absorption interface for orally administered drugs. Caco-2 and primary intestinal models assess passive and active transport, efflux pump activity, and first-pass metabolism.
Cerebrovascular Endothelium
Blood–Brain Barrier
A highly restrictive endothelial barrier protecting the CNS. Critical for neurology and oncology programs. NANOSTACKS™ enables human iPSC-derived BBB models with measurable TEER.
Choroid Plexus Epithelium
Blood–CSF Barrier
Often overlooked, the BCSFB regulates CSF composition and provides an alternative route for CNS drug access. Key for intrathecal drug programs and neuroinflammation studies.
Pulmonary Epithelium
Alveolar–Blood Barrier
Governs inhaled drug absorption and lung toxicity assessment. ALI (air–liquid interface) culture conditions are essential for physiologically relevant pulmonary barrier models.
Metabolite-Mediated Neurotoxicity
Liver–Brain Axis
Hepatic metabolism produces reactive metabolites that can cross the BBB and cause secondary neurotoxicity. Connecting liver and brain MPS reveals these systemic effects invisible to single-tissue assays.
Full Absorption-to-CNS Pathway
Gut–Liver–Brain Axis
The complete physiological journey for oral drugs. From gut absorption to hepatic metabolism and ultimately CNS exposure — this three-organ axis provides the most comprehensive oral drug ADME profile.
Scientific Rationale
Why Isolated Barrier Models Are Not Enough
Traditional Transwell-based barrier assays measure permeability in isolation — a single cell monolayer separating two compartments. While useful for screening, these systems miss critical inter-organ dependencies that determine real drug behaviour.
For example, a compound may appear BBB-impermeable in a standalone assay, but hepatic metabolism converts it to a metabolite with far greater CNS penetration. Without a connected liver-BBB system, this liability goes undetected until clinical trials.
Similarly, gut efflux pumps and intestinal metabolism fundamentally alter the compound profile reaching the liver and brain. Only connected multi-barrier models capture these compounding effects.
What connected barriers reveal that isolated assays miss:
Metabolite-driven barrier disruption from upstream organ processing
Active efflux interactions across sequential tissue layers
Concentration gradients that only emerge from multi-step transport
Barrier integrity changes induced by systemic inflammation signals
Species-relevant CNS exposure predictions using human iPSC cells
Compound-induced barrier leakiness as a toxicity endpoint
The NANOSTACKS™ Approach
Connected Barriers Without Microfluidic Complexity
NANOSTACKS™ achieves physiological fluid communication between barrier tissues using a passive gravity-driven flow system — no pumps, tubing, or specialised equipment required. Stacked modular inserts connect apical and basolateral compartments across multiple tissue layers, enabling true connected barrier biology with standard lab workflows.
Gravity-Driven Flow
Passive rocking platform creates directional fluid exchange between stacked barrier compartments without peristaltic pumps.
Modular Architecture
Add or remove barrier layers independently. Run intestine–liver–BBB in one system, or gut–liver–kidney in another — same platform, different configurations.
Standard Readouts
TEER, Lucifer Yellow permeability, LC-MS metabolite profiling, and imaging assays all compatible without system modifications.
Human Cell Sources
iPSC-derived endothelial cells, primary hepatocytes, Caco-2, and choroid plexus epithelial cells — all validated for NANOSTACKS™.
Scalable Format
96-well compatible format enables throughput appropriate for lead optimisation screening campaigns, not just mechanistic studies.
Validated Models
In-house validated IB–BBB–BCSFB triple barrier system with published TEER values and permeability data for reference compounds.
Applications
Research Applications
CNS Drug Penetration Profiling
Rank compounds by human BBB permeability using iPSC-derived endothelial monolayers. Predict free brain concentration and identify CNS-penetrant leads.
Oral CNS Drug ADME
Model the full oral absorption pathway from gut to liver to brain. Identify metabolites with enhanced or reduced CNS access compared to parent compound.
Neurotoxicity Mechanism
Detect whether neurotoxic effects arise from direct BBB permeation or from metabolite-driven mechanisms — critical for mechanism-of-toxicity studies.
Neuroinflammation & Barrier Disruption
Study how systemic inflammatory signals alter BBB tight junction integrity and increase CNS drug exposure under disease conditions.
Pulmonary Drug Delivery
Assess inhaled drug deposition, epithelial absorption, and systemic exposure using ALI-culture airway barrier models in NANOSTACKS™ format.
Regulatory ADME Packages
Generate human-relevant permeability and transport data for IND-enabling packages, replacing or supplementing rodent in vivo data.