Chapter Four · failure evidence
What In Vivo Microdialysis & Ex Vivo Probing got wrong, from 20 dissertations
The records describe various technical and biological failure modes encountered when using microdialysis sampling, retrodialysis delivery, and ex vivo tissue probing techniques. These studies show that probe-induced trauma, diffusion limitations, membrane recovery losses, and rapid ex vivo tissue degradation frequently impede accurate physiological measurement. These records come from PhD theses at 11 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Rapid tissue ischemia and structural degradation compromising ex vivo viability
Ex vivo tissue slices and preparations experience rapid ischemic death, loss of metabolic function, and geometric distortion compared to in vivo states. Extended handling or anoxic intervals between excision and processing further introduce artifactual ultrastructural changes and exceed physiological viability limits.
Tried and failed
fluorescence viability assay on ex vivo tissue slices applied to bovine liver tissue viability measurement. Outcome: no signal. Reason: control tissue slices underwent rapid ischemia, reaching zero viability within three hours of incubation
Predicting blast injury to the torso · Imperial
Tried and failed
capsaicin-induced epithelial permeability modulation applied to ex vivo tissue electrophysiology assays. Outcome: too slow. Reason: Action required tens of minutes, exceeding post-euthanasia ex vivo tissue viability limits
Detecting Tight Junction-Mediated Epithelial Barrier Dysfunction in Altered Gravity Environments · MIT
Considered and rejected
Considered and rejected: Rejected standard ex vivo immersion fixation because the anoxic period between excision and penetration induces artifactual ultrastructural alterations.
Ultrastructural Alterations in Canine Myocardium Persist after 96 Hours of Reperfusion · TXST Digital Repository
Considered and rejected
Considered and rejected: Rejected ex-vivo 3D LGE-CMR images for progression analysis due to irreversible loss of metabolic function, anatomical structure, and geometry relative to in-vivo space.
Image Processing Techniques for Analysis of Myocardial Fibrosis and Related Cardiomyopathies in Cardiac Magnetic Resonance Imaging · Carleton University Institutional Repository
Diffusion barriers and irregular mass transport in reverse microdialysis delivery
Retrodialysis and microdialysis substrate delivery fail when steep concentration gradients, diffusion limitations, and local substrate depletion prevent detectable extracellular shifts. In addition, physical factors such as membrane flaring, variable probe spacing, and non-specific adsorption produce irreproducible mass transport and baseline drift.
Tried and failed
microdialysis delivery of stable isotope labeled substrate applied to cerebral energy metabolism monitoring. Outcome: no signal. Reason: supplemented labeled glucose yielded no detectable downstream labeling or metabolic shifts in extracellular fluid
Understanding and ameliorating perturbations of human cerebral energy metabolism after major trauma · Cambridge
Considered and rejected
Considered and rejected: Single-catheter reverse micro-dialysis was rejected for drug delivery due to immediate equilibrium, steep concentration gradients, and inability to overcome molecular weight diffusion discrepancies.
Tried and failed
retrodialysis delivery in stationary solutions applied to enzyme activity quantification. Outcome: no signal. Reason: diffusion limitations, local substrate depletion, and background drift from enzyme adsorption to the probe membrane
Tried and failed
dual flexible microdialysis probe coupling applied to continuous biosensing and retrodialysis sampling. Outcome: unstable. Reason: inconsistent inter-probe spacing and membrane flaring caused irreproducible mass transport measurements
Probe size trauma and poor temporal resolution in microdialysis sampling
Conventional microdialysis probes possess large physical diameters that cause substantial tissue damage upon insertion into target structures. Furthermore, their minute-level temporal resolution is inadequate for resolving rapid neurochemical signaling dynamics.
Considered and rejected
Considered and rejected: Rejected microdialysis due to poor temporal resolution (minutes) and large probe size causing tissue trauma.
Concurrent neurochemical and neurophysiological investigation of fMRI signals · Publikationssystem UB Tuebingen
Considered and rejected
Considered and rejected: Rejected standard microdialysis probes due to large diameters (200-400 µm) causing tissue damage and semipermeable membranes causing analyte/extracellular vesicle loss
Monitoring and Treating Neurological Conditions Through Focal Interfacing with the Brain · MIT
Considered and rejected
Considered and rejected: Rejected microdialysis with HPLC for monitoring rapid dopamine and acetylcholine dynamics due to sub-minute temporal limitations and probe-induced tissue trauma.
Probing presynaptic regulation of dopamine release in health and disease · Oxford
Membrane pore constraints and extraction loss of large proteins
Semipermeable microdialysis membranes suffer from severe extraction loss when applied to large protein targets. Micro-capillary fluidic interfaces and cutoff restrictions cause analyte recoveries to drop as low as 7.3 to 20 percent.
Tried and failed
microdialysis sampling through micro-capillary fluidic interfaces applied to sampling of large proteins. Reason: extreme extraction loss with recovery dropping to 7.3-20% for large proteins
Tools for Monitoring and Modulating Cellular Communication · MIT
Tried and failed
membrane-based microdialysis sampling applied to large protein extraction in vivo. Outcome: worse than baseline. Reason: semipermeable membranes cause substantial extraction loss and low molecular weight recovery for large proteins
Monitoring and Treating Neurological Conditions Through Focal Interfacing with the Brain · MIT
Failure of ex vivo probing assays to reliably reflect dynamic physiological states
Fluorescent probes applied directly to dissected tissues can fail to produce reliable detection of oxidative targets ex vivo. Additionally, static post-mortem histology does not correlate with real-time dynamic spectroscopy measurements taken in living tissue.
Tried and failed
direct fluorescent ROS and oxidative damage probes applied to ex vivo dissected gut tissue. Outcome: no signal. Reason: probes failed to yield reliable detection in dissected tissue ex vivo
Exploring the effects of diet-induced obesity on the invasiveness of Drosophila tumours · Imperial
Tried and failed
correlating dynamic in vivo spectroscopy with ex vivo histology applied to tissue oxygenation monitoring in tumours. Outcome: no signal. Reason: dynamic real-time physiological measurements did not correlate with static post-mortem immunohistochemical staining
Sensing rectal cancer hypoxia for advanced prognostication and response monitoring · Imperial
Left open by the authors
Problems the authors named and did not get to.
Left open
Compare intravenous delivery of succinate to microdialysis delivery in larger traumatic brain injury patient cohorts. Blocker: Requires clinical trials, TBI patients, specialized microdialysis equipment, intravenous drug administration, and clinical MRI/MRS scanners.
Understanding and ameliorating perturbations of human cerebral energy metabolism after major trauma · Cambridge
Left open
Replicate cortical microdialysis experiments in mice to confirm endogenous cortical DMT biosynthesis. Blocker: Requires a wet lab, animal models (mice), and microdialysis surgical/analytical equipment.
Investigating Endogenous DMT Biosynthesis and VMAT2 Activity · UT Austin
Left open
Conduct a clinical study interrogating human brain metabolism kinetics using in-vivo 13C MRS following traumatic brain injury per the thesis protocol. Blocker: Requires clinical access to TBI patients, specialized MRI scanners with custom coils, and wet-lab/microdialysis equipment.
Understanding and ameliorating perturbations of human cerebral energy metabolism after major trauma · Cambridge
Left open
Measure sub-tissue metabolite levels and spatial heterogeneity using microdialysis or micro-invasive collection platforms in tumor models. Blocker: Requires wet lab facilities, tissue samples, and physical microdialysis or micro-invasive experimental platforms
The influence of nutrient availability on tumor metabolism · MIT
Left open
Analyze late-stage blood samples (>7 days post-injury) from microdialysis patients to evaluate the effect of catheter insertion on neurofilament light levels. Blocker: Requires access to longitudinal clinical patient blood samples and wet lab biomarker assay facilities
Left open
Investigate in vivo brain dialysate choline concentration dynamics during cardiac arrest and resuscitation using microfluidic biosensors. Blocker: Requires in vivo animal models of cardiac arrest, wet lab microdialysis sampling, and custom biosensor hardware
Left open
Evaluate the correlation between oxidative damage, depth of hypoglycaemia, and degree of post-hypoglycaemic hyperglycaemia using ex vivo or in vitro models. Blocker: Requires a wet lab and biological experimental models (ex vivo/in vitro tissue preparations)
Left open
Investigate whether diffusion limitations across dialysis membranes cause the biphasic protein synthesis rate in PURE cell-free systems. Blocker: Requires wet lab equipment, PURE cell-free expression reagents, and dialysis reaction setups
Proteins as sustainable and recyclable polymers for a circular economy in bioplastics · EPFL
Left open
Extend the counter-current dialysis computational model to incorporate membrane binding and absorption of protein-bound toxins. Blocker: Requires wet lab experimental data for characterizing membrane absorption and binding kinetics of other protein-bound toxins.
Experimental Validation of Computational Model for Circulating Albumin Dialysis and Optimization of Conditions · ResearchWorks
Left open
Evaluate total lithium migration efficiency in monovalent selective electrodialysis across lower lithium concentration regimes. Blocker: Requires a physical electrodialysis stack (PCCell ED 200), specific ion-exchange membranes, chemical brines, and analytical laboratory instrumentation
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