Blood-Brain Barrier Chips

The blood-brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents most substances in the blood from crossing into the brain. It protects the brain from toxins, pathogens, and fluctuations in blood composition while allowing essential nutrients to pass. The BBB is formed by specialized brain endothelial cells connected by tight junctions, supported by astrocytes, pericytes, and a basement membrane.

Most drugs cannot cross the BBB, making it extremely difficult to treat brain diseases. Over 98% of small molecules and nearly 100% of large molecules (antibodies, proteins) are blocked. This means promising drug candidates often fail in clinical trials because they cannot reach their target in the brain. BBB-on-chip models help identify drugs with brain penetration potential early in development.

Human BBB chips using iPSC-derived cells express human-specific transporter proteins and tight junction properties that differ significantly from rodents. P-glycoprotein and other efflux transporters have different substrate specificities between species. Human BBB chips provide more predictive permeability data, reduce animal use, and enable patient-specific disease modeling impossible with animals.

Many neurological conditions involve BBB breakdown including Alzheimer's disease (early BBB leakage correlates with cognitive decline), multiple sclerosis (immune cells crossing the barrier), stroke (BBB disruption causes brain edema), brain tumors (abnormal BBB allows tumor growth), and traumatic brain injury. BBB chips model these dysfunctions to study disease mechanisms and test protective therapies.

Trans-endothelial electrical resistance (TEER) measures the tightness of the barrier by quantifying electrical resistance across the cell layer. Higher TEER indicates stronger tight junctions and better barrier function. Human BBB in vivo has extremely high TEER values. Advanced BBB chips achieve TEER values approaching physiological levels, validating their barrier integrity for permeability studies.

Yes, BBB chips can model inflammatory conditions by exposing the endothelium to cytokines like TNF-alpha and IL-1beta, which disrupt tight junctions and increase permeability. Immune cells can be added to study their migration across the inflamed barrier, modeling conditions like multiple sclerosis. These models help develop anti-inflammatory therapies to protect BBB integrity.

BBB chips evaluate novel drug delivery systems like nanoparticles, liposomes, and exosomes designed to cross the barrier. Researchers test surface modifications (targeting ligands, stealth coatings), particle sizes, and drug payloads. Real-time imaging tracks particle transport, while mass spectrometry quantifies drug accumulation on the brain side. This accelerates development of brain-targeted therapeutics.

Receptor-mediated transcytosis is a pathway exploited to deliver drugs across the BBB. Molecules bind to receptors on the blood side (like transferrin or LRP1 receptors), are internalized, transported across the cell, and released on the brain side. BBB chips test antibodies and peptides targeting these receptors to shuttle therapeutic payloads into the brain.