Biomechanics of Perfused Kidney-on-Chip Model: Effects of Shear Stress and Pressure 

Understanding the Role of Mechanical Forces in Kidney Disease  

Autosomal dominant polycystic kidney disease (ADPKD) affects 1 in 1,000-2,500 people worldwide, leading to kidney failure through the progressive formation of thousands of fluid-filled cysts (1).The earliest stage of cyst formation involves local dilation of kidney tubules, but the mechanisms driving this process remain poorly understood. While genetic mutations in PKD1 initiate the disease, emerging evidence suggests that mechanical forces play a decisive role in determining cysts formation. 

Kidney tubular cells constantly experience multiple mechanical cues:  

• flow shear stress: generated by urine flow, the tangential forces as fluid moves across cell surfaces, typically 0.2-2 dyn/cm² 

• intraluminal pressure: radial forces distending the tubule, ~10 mbar in the proximal nephron 

• interactions with the surrounding extracellular matrix 

These forces likely influence tubular deformation, but traditional cell culture systems cannot recreate them, and existing organ-on-chip platforms face a fundamental physics constrain flow and pressure are inherently coupled in small tubes. When you increase flow rate, you automatically increase pressure, making it difficult to determine which mechanical signal drives pathological changes. 

To address this challenge, researchers developed a perfused kidney-on-chip system with integrated microfluidic pressure control, designed to decouple shear stress and pressure while recreating key aspects of the kidney microenvironment. 

Pressure-Controlled Perfusion for Shear Stress Control in Kidney-on-Chip preparation 

Shear stress is the tangential force per unit area exerted by fluid flow on a surface, such as cells or extracellular matrix (ECM) within microfluidic channels. In ECM perfusion, controlling shear stress is critical to avoid structural damage (e.g., collagen collapse or delamination) while maintaining physiologically relevant conditions for cell adhesion, organization, and function. 

Fluigent Flow EZ pressure controllers were used for critical perfusions that conventional syringe pumps are insufficient: cell seeding, collagen channels coating and pressure control. The detailed protocol can be found at Methods in Molecular Biology (2023) (2) 

Controlled Cell Seeding  

The perfused kidney-on-chip resistive serpentines cause cells to accumulate in the lower-resistance collagen channels rather than flowing through. Pressure-based control enabled at ~50 mbar: 

• High-density, uniform cell deposition across all five parallel channels 

• Real-time adaptation as channels filled with cells (avoiding clogging) 

• Tunable seeding density by adjusting duration 

Gentle Laminin Coating  

The fragile collagen scaffolds required extremely gentle perfusion to coat channels with 50 µg/mL laminin without causing channel collapse, matrix delamination, or bubble formation. Pressure control delivered uniform coating while preserving delicate 3D structures. 

Post-Seeding Channel Flushing  

After cell adhesion, pressure-controlled perfusion removed non-adherent cells and created defined lumens. Gradual pressure increases (50+ mbar) cleared debris without damaging adhered cells through excessive shear stress. 

Pressure-based perfusion was essential at this stage, providing flow through fragile collagen structures without causing channel collapse or heterogeneous cell seeding across all channels.   v

Mechanical Drivers of Kidney Cyst Formation 

Adding 10 mbar intraluminal pressure to the flow amplified this effect. The dilation occurred in two distinct phases: 

• Initial phase (Day 0-1): Both parental and Pkd1⁻/⁻ tubules showed rapid dilation of 1.2-1.5 times due to the mechanical response to pressure application 

• Progressive phase (Day 1-5): Pkd1⁻/⁻ tubules continued dilating while parental tubules stabilized 

• By day 5, total dilation reached 2-fold for Pkd1⁻/⁻ tubules versus 1.6-fold for controls (Figure 2C). 

PCT dilation appears driven by intrinsic cellular overproliferation that mechanically pushes the tubule outward regardless of whether pressure, flow, or matrix stiffness changes. 

Figure 2:  Effect of intraluminal pressure on tubule morphology in PCT and mIMCD-3 cells. 

Representative confocal images of PCT (A, C) or mIMCD-3 (B, D) tubules cultured under two different conditions: unpressurized perfusion (A, B) and pressurized perfusion (C, D). Images were acquired on the day of confluency and at multiple time points thereafter to visualize morphological changes over time. Scale bars: 100 μm. 

The kidney-on-chip experiments revealed that mechanical forces have different effects depending on which part of the nephron is being studied: proximal tubules versus distal.  

PCT (proximal tubule) cells showed a consistent pattern across all mechanical conditions tested. Under flow alone (1 dyn/cm² shear stress, negligible pressure), Pkd1⁻/⁻ PCT tubules dilated significantly 1.38 times after 5 days, while parental control cells showed no dilation (Figure 2A). This excessive dilation mirrored what the team had observed previously in static conditions that are due to the pulling forces applied by the cell at confluency.  

Whereas mIMCD-3 (collecting duct) cells revealed different mechanical sensitivity. Under flow alone, the loss of Pkd1 was no longer sufficient to trigger tubular dilation (Figure 2B). Flow shear stress appeared to exert a protective effect, suppressing the pathological dilation that would otherwise occur. 

However, adding 10 mbar intraluminal pressure to the flow completely restored excessive dilation in Pkd1⁻/⁻ collecting duct tubules (Figure 2D). 

Unlike PCT cells, mIMCD-3 dilation was not driven by increased proliferation. Ki67 analysis showed no significant difference between Pkd1⁻/⁻ and parental cells at day 5 under flow+pressure conditions. Instead, the excessive dilation correlated with changes in cell shape: Pkd1⁻/⁻ cells adopted abnormally flat, squamous (flattened) morphology, with nuclei spreading farther apart (internuclear distance increased, p=0.0075) 

This cell flattening meant each cell covered more surface area, effectively stretching the tubule outward without requiring more cells. 

Intraluminal pressure is the decisive mechanical driver of early cyst formation in collecting ducts, the exact region where cysts preferentially initiate in ADPKD patients. Flow alone is insufficient and may even be protective; pressure is required to trigger the pathological response. the same genetic mutation (Pkd1 loss) triggers cyst formation through completely different mechanical pathways depending on nephron segment. For proximal tubule, the pathway is proliferation-dominant and mechanics-insensitive.  

References

1. Borghol AH, Bou Antoun MT, Hanna C, Salih M, Rahbari-Oskoui FF, Chebib FT. Autosomal dominant polycystic kidney disease: an overview of recent genetic and clinical advances. Ren Fail. 47(1):2492374. doi:10.1080/0886022X.2025.2492374 PubMed PMID: 40268755; PubMed Central PMCID: PMC12020221. 

2. Lapin B, Myram S, Nguyen ML, Gropplero G, Coscoy S, Descroix S. Construction of a Multitubular Perfusable Kidney-on-Chip for the Study of Renal Diseases. In: Hewitson TD, Toussaint ND, Smith ER, editors. Kidney Research: Experimental Protocols [Internet]. New York, NY: Springer US; 2023 [cited 2026 Mar 17]. p. 85–106. Available from: https://doi.org/10.1007/978-1-0716-3179-9_7 doi:10.1007/978-1-0716-3179-9_7