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Updated: Jul 22, 2026
10:19
Three-Dimensionally Printed Microfluidic Cross-flow System for Ultrafiltration/Nanofiltration Membrane Performance Testing
Published on: February 13, 2016
Summary
Unstirred layer effects significantly underestimate epithelial osmotic water permeability (Posm). New methods are needed to accurately measure Posm, water flow pathways, and solute concentrations for a better understanding of epithelial transport.
Area of Science:
- Physiology
- Biophysics
- Epithelial Transport
Background:
- Solute-linked water transport is crucial for epithelial function.
- Current methods for measuring osmotic water permeability (Posm) are affected by unstirred layer (USL) effects.
- Controversies exist regarding water flow pathways and the standing-gradient theory.
Purpose of the Study:
- To review unsolved problems in solute-linked water transport in epithelia.
- To highlight the impact of unstirred layer effects on Posm measurements.
- To discuss challenges in determining water flow routes and the standing-gradient theory.
Main Methods:
- Review of existing literature and theoretical considerations.
- Analysis of unstirred layer effects (dissipation, sweeping-away, solute polarization).
- Discussion of time constants influencing osmotic transients.
Main Results:
- Unstirred layer effects cause significant underestimation of epithelial Posm, potentially by orders of magnitude.
- True Posm values for leaky epithelia likely exceed 10(-3) or 10(-2) cm/sec.osm.
- Difficulties in separating transcellular and transjunctional water flow are highlighted.
Conclusions:
- Accurate Posm determination requires accounting for unstirred layer effects and resolving osmotic transients.
- New methodologies are essential for resolving water flow pathways (transcellular vs. transjunctional).
- Direct measurement of solute concentrations in lateral intercellular spaces is needed to validate theories like the standing-gradient model.
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