Table 2.

BBB-on-a-chip models to study neurological diseases.

Device characteristics						Barrier characterization methods			Supplementary information
Target disease	Chip type	Channel design	Culture type and ECM	Cell type(s)	Disease induction method	TEER Sensors	Permeability assessment	Immunostaining	Major on-chip disease phenotypes	Importance/Applications	Ref
AD	PDMS-based microfluidic chip (dynamic)	Parallel channels separated by post array	EC: 2D with Matrigel; Brain: 3D with Matrigel and collagen type I gel	EC: hCMEC/D3; Brain: ReN cells	ReN cell line with human familial AD mutations	NA	3kDa and 40kDa dextrans	Claudin-1, Claudin-5, VE-cadherin	Increased permeability; reduced TJ expression; in vivo like Aβ deposition patterns; Neuronal damage due to neurotoxins	Modeling of AD pathologies in vitro using BBB-on-a-chip model with genetically modified ReN cells	[170]
ALS	PDMS-based microfluidic chip (dynamic)	Custom design	EC: 2D with collagen type I gel; Motor unit: 3D with MN spheroids and collagen type I gel/Matrigel	EC: iPSC-ECs; Motor unit: patient-derived hESC- and iPSC-MNs, iPSC-skeletal muscle cells,	Addition of excess glutamic acid; patient-derived cells	NA	40kDa dextran	ZO-1, occludin, P-glycoprotein	Decreased muscle contraction; muscle function improved by cotreatment with rapamycin and bosutinib through BBB	ALS-on-a-chip using cells from ALS patients and demonstration of compromised muscle function in ALS vs. control model	[225]
GBM	PDMS-based microfluidic chip (dynamic)	Central chamber (brain) and outer channel (EC barrier)	EC & Brain: 2D with Matrigel/fibronectin	EC: HUVECs; Brain: CTX-TNA2 rat brain astrocytes, and Met-1 murine metastatic breast cancer cells	Mouse-derived primary cancer cells	NA	3kDa and 70kDa dextrans; Rho 123; sulforhodamine 101 Acid Chloride	NA	Increased permeability	One of the first BTB-on-a-chip platforms; demonstration of leakier barrier phenotype in BTB vs BBB model	[226]
	PDMS-based microfluidic + bioprinted chip (dynamic)	Central chamber (brain) and outer channel (EC barrier)	EC: 2D with fibronectin; Brain: 3D in GelMA-alginate and GelMA-fibrin hydrogels	EC: hCMEC/D3 or HUVECs; Brain: human GBM cells	Cancer cell line	NA	40kDa Texas Red-dextran	ZO-1	Decreased ZO-1 expression in hCMEC/D3; alteration of cell morphology and decreased expression of vinculin and active Yap1 in GBM cells with microgravity exposure	A dynamic, microfluidic GBM-on-a-chip with bioprinted GBM; elucidation of effects of mechanical cues on BTB and GBM cells	[178]
	PDMS-based microfluidic chip (dynamic)	Parallel channels separated by post array	EC & Brain: 3D with fibrinogen	EC: HUVEC; Brain: U-87, patient-derived GBM cells	Cancer cell line; patient-derived cells	NA	70 kDa dextran	Green fluorescent protein, VE-cadherin, vWF	Colocalization of GBM stem-like cells with perivascular niche; distinct migration trajectory profiles for different GBM cell lines with accompanying changes in gene expression	Recapitulation of 3D microvasculature in GBM; a new potential functional assay to assess the invasiveness of GBM cells for personalized medicine	[227]
	PDMS-based microfluidic chip (dynamic)	Central chamber (brain) and outer channel (EC barrier)	EC: 2D with Poly-D-Lysine; Brain: 3D with Matrigel and HA	EC: hBMECs; Brain: macrophages, microglia, CD8+ T-cells, and patient-derived GBM cells	Patient-derived cells	NA	NA	NA	Distinct profiles of T cell extravasation, cytotoxic activities, PD-1 expression, and inflammatory cytokine secretion between different GBM subtypes	Development of a patient-specific GBM model that differentiates different GBM subtypes; Enables personalized molecular assessment of effects of anti-PD1 therapy	[228]
HD	PDMS-based microfluidic chip (dynamic)	Sandwiched channels with top (brain) and bottom (vascular) chambers	EC: 2D with collagen IV and fibronectin; Brain: 3D with EZ-spheres and laminin	EC: iPSC-BMECs; Brain: iPSC-EZ spheres	Patient-derived cells	Integrated Au electrodes (AC resistance)	4, 20 or 70 kDa dextrans; 3,5,3'-triiodothyronine; 2-NBDG; retigabine; levetiracetam; colchicine	GLUT-1, PECAM-1, Caudin-5, Occludin, ZO-1	Increased permeability with inter-individual variations	Development of BBB-on-a-chip that captures in vivo like complexity of BBB and recapitulates patient heterogeneity in HD phenotype	[65]
PD	PDMS-based microfluidic chip (dynamic)	Sandwiched channels with top (brain) and bottom (vascular) chambers	EC & Brain: 2D with collagen type IV, fibronectin, and laminin	EC: iPSC-BMECs; Brain: primary human brain pericytes, primary human astrocytes, primary human brain microglia, iPSC-neurons	Treatment with αSyn fibril	NA	3 kDa dextran, and 0.5 kDa lucifer yellow	Claudin-1, Claudin-5, Occludin, PECAM-1	Phosphorylation of αSyn129, decreased mitochondrial activity and increase in ROS production, induction of caspase-3 activation and neuroinflammation; increased permeability	Recapitulation of PD pathologies induced by treatment with αSyn fibril in BBB-on-a-chip system	[229]
Stroke	PDMS-based microfluidic chip (dynamic)	Parallel channels separated by a smaller middle channel	EC:2D; Brain: 3D with Engelbreth–Holm–Swarm tumor (Cultrex)	EC: human primary BMECs; Brain: human primary astrocytes, human microglial cell line, human primary vascular pericytes, iPSC-NPCs	Treatment with low oxygen and deprivation of serum and glucose content	Chopstick silver chloride electrodes (DC resistance)	4kDa and 70kDa dextrans	PECAM-1, vWF, ZO-1, Claudin-5	Upregulation of inflammatory genes; increased activity of glutamate and decreased activity of GABA; irregular Ca2+ signaling patterns; increased VEGF; decreased TJ protein expression; pericyte and microglia activation; disruption of AQP4	Development of stroke-on-a-chip; assessed the neurorestorative effects of several stem cell-based therapies	[177]