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K Adatia, M Raja, P Vadgama Queen Mary, University of London

Electrochemical determination of diffusion coefficients: Observations at tissue matrix barriers and major anomalies in constrained channels. K Adatia, M Raja, P Vadgama Queen Mary, University of London. Fick’s Laws. Can we use molecular diffusion as a probe for water structure?.

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K Adatia, M Raja, P Vadgama Queen Mary, University of London

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  1. Electrochemical determination of diffusion coefficients: Observations at tissue matrix barriers and major anomalies in constrained channels K Adatia, M Raja, P Vadgama Queen Mary, University of London

  2. Fick’s Laws Can we use molecular diffusion as a probe for water structure? Jakubowski 2016

  3. Enzyme biosensorsDiffusion control membranes Enzyme Molecular concentration Current Flux

  4. d L Recessed tip voltammetry electrodes for biomatrix/H2O isolation Initial condition: C(0<x<L, t=0)=0 Boundary condition: C(x=L, t)=C0 100μm Cotterell Equation

  5. Bipartite analytical solution for cylindrical coordinate: Fick’s Laws Normalised time T≥ 0.063 T< 0.063

  6. Recessed Lactate electrode Increased recess length Effective enzyme Km D values as predicted for bulk water

  7. Tissue matrix • Signalling molecules • 3D scaffolds • Drug delivery Artificial membranes • Biosensors • Haemodialysis • Bioreactors Special case of the blood brain barrier Blood Brain Barrier

  8. Track etch polymer membranes 0.4µm polycarbonate (PC) 8.0µm polycarbonate (PC) c) 0.4µm polyethylene terephthalate (PET)

  9. 4b) 4a) Gaussian pore distribution – no tortuosity 8µm PC 0.4µm PC 4c) 0.4µm PET

  10. Planar electrochemical Cell

  11. Cotterell Randles-Sevcik equation

  12. Bulk water diffusion coefficients

  13. Dialysis membrane permeability ~ bulk water Catechol

  14. Pore normalised diffusion coefficients – track etched • PC – PET different –Cannot be wall effects at µm scale • Charge and MW dependent –Cannot be polymer charge ?Zeta potential Large pore PET Small pore PC

  15. Bulk H2O normalised diffusion coefficients

  16. Dpore/Dwater Ratios

  17. Artefact? Amperometryvs CV < PET PC Amp CV CV

  18. Surface geometry underestimates pore diameters

  19. Permeabiitydetermined by the material • Total pore area 0.4µm PC > 8µm PC > 0.4µm PET • Diffusivities: • 0.4µm PC > 0.4µm PET > 8µm PC PC imposes the greater constraint

  20. Pore constrained water - different properties

  21. ECM • Types I IV collagen, fibronectin, heparin and chondroitin sulphate • Collagen concentration effects • Charge selective? • Enantioselective? Tendon Cartilage

  22. Type I and Type IV Collagen: different roles I IV Sheets Fibres SEM Type IV collagen SEM Type I collagen (5mg/ml)

  23. Crosslinked Membrane mats Jakubowski

  24. Collagen I concentration effect *** *** ** *** ** *** ** ** *

  25. Collagen I vs Collagen IV I IV ** ** ** **

  26. Bulk water normalised diffusion - Collagen IModulated microsolute transport (cf track etched) Ratios should be the same for all molecules for a given collagen concentration

  27. Membrane charge effect only on ascorbate – Hep, CSO4 *** *** *** *** *** Hep CSO4

  28. Bulk water normalised charge selectivity with heparin (H) and chondroitin sulphate CSO4 Ratios all different H CSO4 H2O2 Ascorbate H CSO4

  29. Natural cartilage avascular : surprising open system: we cannot reproduce Cartilage 200mg/ml collagen D~10-6cm2 s-1 Dialysis membrane

  30. Tendon diffusion two orders lower: a physiological problem for cells 300mg/ml collagen D~10-8cm2 s-1 + Fibre orientation effect

  31. Track etched I IV Hep

  32. Is the data reliable? Two methods Dialysis membrane H2O Multipoint fit Simulation/data (Dialysis) Simulation/data (Track etch membrane)

  33. Conventional surface model A) Triple water phases : (i) Surfacefixed water (non-freezing) (ii) Loose bound ‘gel water’ (freezing) (iii) Bulk water Gel water determines biocompatibility: PEO augments gel water (Tanaka) Quasi-aqueous PEO cushion

  34. Conclusions • Porosity doesn’t predict permeability • Unknown effect • Double layer problem • Cell biology problem Acknowledgements: BBSRC - Flowers’ Scholarship (KA)

  35. Precision pore analysis possible

  36. Cylindrical pore membrane permeability:Simple? 0.4µm polycarbonate 8.0µm polycarbonate 0.4µmpolyethylene terephthalate (PET)

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