Modelling of epithelial tissue impedance measured using three different designs of probe

Feasibility and effectiveness of endoscopic irreversible electroporation for the upper gastrointestinal tract: an experimental animal study

Irreversible electroporation (IRE) is a local non-thermal ablative technique currently used to treat solid tumors. Here, we investigated the clinical potency and safety of IRE with an endoscope in the upper gastrointestinal tract. Pigs were electroporated with recently designed endoscopic IRE catheters in the esophagus, stomach, and duodenum. Two successive strategies were introduced to optimize the electrical energy for the digestive tract. First, each organ was electroporated and the energy upscaled to confirm the upper limit energy inducing improper tissue results, including bleeding and perforation. Excluding the unacceptable energy from the first step, consecutive electroporations were performed with stepwise reductions in energy to identify the energy that damaged each layer. Inceptive research into inappropriate electrical intensity contributed to extensive hemorrhage and bowel perforation for each tissue above a certain energy threshold. However, experiments performed below the precluded energy accompanying hematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays showed that damaged mucosal area and depth significantly decreased with decreased energy. Relevant histopathology showed infiltration of inflammatory cells with pyknotic nuclei at the electroporated lesion. This investigation demonstrated the possibility of endoscopic IRE in mucosal dysplasia or early malignant tumors of the hollow viscus.

Evaluation of Esophageal Mucosal Integrity in Patients with Gastroesophageal Reflux Disease

BACKGROUND

Impaired esophageal mucosal integrity plays a role in causing symptoms of gastroesophageal reflux disease (GERD). Recently, the assessment of esophageal baseline impedance (BI) using the multichannel intraluminal impedance-pH (MII-pH) test was suggested as a surrogate technique for the study of esophageal mucosal integrity and was reported to be useful in distinguishing GERD from non-GERD. However, measuring BI requires a 24-h testing period, is complicated, and causes considerable patient discomfort.

SUMMARY

Recently, endoscopy-guided catheters that can measure mucosal impedance (MI) and mucosal admittance (MA), which is the inverse of impedance, were developed, and their usefulness in measuring MI and MA for the diagnosis of GERD has been reported. In these studies, esophageal MI values were significantly lower in patients with GERD than in those without GERD. In contrast, esophageal MA was significantly higher in patients with GERD than in those without. Furthermore, we reported that MA is inversely correlated with BI and correlated with acid exposure time. Key Messages: Endoscopy-guided real-time measurement of MI and MA may allow the estimation of mucosal integrity and may be a useful diagnostic tool for patients with GERD in a manner similar to 24-h MII-pH monitoring.

Mechanistic Multilayer Model for Non-invasive Bioimpedance of Intact Skin

An approximate semi-analytical solution based on a Hankel transform of a mechanistic model for electrical impedance spectroscopy (EIS) is derived for a non-invasive axisymmetric concentric probe with m electrodes measuring the response of n layers of human skin. We validate the semi-analytical solution for the case when the skin is treated as a three-layer entity - (i) stratum corneum, (ii) viable skin comprising living epidermis and dermis and (iii) adipose tissue - on the volar forearm in the frequency range 1 kHz to 1 MHz with experimental EIS measurements of 120 young subjects. Overall, we find good agreement for both the mean magnitude and phase of the impedance as well as the natural variability between subjects. Finally, the semi-analytical solution is verified with the full set of equations solved numerically: Good agreement is found for the point-wise potential distribution in the three skin layers.

Disease activity in eosinophilic esophagitis is associated with impaired esophageal barrier integrity

In eosinophilic esophagitis (EoE), the esophageal barrier integrity is impaired. Integrity can be assessed with different techniques. To assess the correlations between esophageal eosinophilia and various measures of mucosal integrity and to evaluate whether endoscopic impedance measurements can predict disease activity, endoscopies and mucosal integrity measurements were performed in adult EoE patients with active disease (≥15 eosinophils/high-power field) at baseline (n = 32) and after fluticasone (n = 15) and elemental dietary treatment (n = 14) and in controls (n = 19). Mucosal integrity was evaluated during endoscopy using electrical tissue spectroscopy (ETIS) measuring mucosal impedance and transepithelial electrical resistance (TER) and transepithelial molecule-flux through biopsy specimens in Ussing chambers. We included 61 measurements; 32 of patients at baseline and 29 after treatment, 3 patients dropped out. After treatment, 20 patients were in remission (≤15 eosinophils/high-power field) and these measurements were compared with 41 measurements of patients with active disease (at baseline or after failed treatment). All four mucosal integrity measures showed significant impairment in active EoE compared with remission. Eosinophilia was negatively correlated with ETIS and TER and positively with transepithelial molecule flux (P ≤ 0.001). The optimal ETIS cutoff to predict disease activity was 6,000 Ω·m with a sensitivity of 79% [95% confidence interval (CI) 54-94%], specificity of 84% (95% CI 69-94%), positive predictive values of 89% (95% CI 77-95%) and negative predictive values of 71% (95% CI 54-84%). In EoE patients, markers of mucosal integrity correlate with esophageal eosinophilia. Additionally, endoscopic mucosal impedance measurements can predict disease activity.NEW & NOTEWORTHY In adult patients with eosinophilic esophagitis (EoE), the mucosal integrity, measured by making use of four different parameters, correlates strongly with esophageal eosinophilia. The accuracy of endoscopically measured mucosal impedance to distinguish active disease from remission was acceptable with moderate specificity and sensitivity. Mucosal impedance measurements can predict disease activity in adult EoE patients.

Esophageal and Small Intestinal Mucosal Integrity in Eosinophilic Esophagitis and Response to an Elemental Diet

OBJECTIVES

The esophageal mucosal integrity is impaired in eosinophilic esophagitis (EoE) and it has been suggested that the duodenal permeability is increased. The absence of food allergens may restore the integrity. The aims of this study were to assess duodenal permeability in EoE and to evaluate the effect of an elemental diet on the esophageal and duodenal integrity.

METHODS

In this prospective study 17 adult EoE patients and 8 healthy controls (HC) were included. Esophageal biopsy specimens were sampled before and after 4 weeks of elemental diet to measure eosinophil counts and gene expression of tight junction and barrier integrity proteins. Esophageal and duodenal impedance were measured by electrical tissue impedance spectroscopy and Ussing chambers were used to measure transepithelial resistance (TER) and transepithelial molecule flux. Small intestinal permeability was measured using a test, measuring lactulose/mannitol (L/M) ratios.

RESULTS

In EoE patients, the esophageal but not the duodenal integrity was impaired, compared with HC. We observed no significant difference between L/M ratios of HC and EoE patients. After diet, eosinophil counts decreased significantly, which was paralleled by normalization of esophageal impedance and transepithelial molecule flux. The esophageal TER improved significantly, but did not reach values seen in HC. Esophageal expression of genes encoding for barrier integrity proteins filaggrin and desmoglein-1 was impaired at baseline and restored after diet.

CONCLUSIONS

An elemental diet restores esophageal integrity, suggesting that it is at least partly secondary to allergen exposure. Duodenal integrity seems not to be affected in EoE, and possibly plays a minor role in its pathophysiology.

The kidney tight junction (Review)

The tight junction is an important subcellular organelle which plays a vital role in epithelial barrier function. Claudin, as the integral membrane component of tight junctions, creates a paracellular transport pathway for various ions to be reabsorbed by the kidneys. This review summarizes advances in claudin structure, function and pathophysiology in kidney diseases. Different claudin species confer selective paracellular permeability to each of three major renal tubular segments: the proximal tubule, the thick ascending limb of Henle’s loop and the distal nephron. Defects in claudin function can cause a wide spectrum of kidney diseases, such as hypomagnesemia, hypercalciuria, kidney stones and hypertension. Studies using transgenic mouse models with claudin mutations have recapitulated several of these renal disease phenotypes and have elucidated the underlying biological mechanisms. Modern recording approaches based upon scanning ion conductance microscopy may resolve the biophysical nature of claudin transport function and provide novel insight into tight junction architecture.

Electrical tissue impedance spectroscopy: a novel device to measure esophageal mucosal integrity changes during endoscopy

BACKGROUND

Patients with gastroesophageal reflux disease (GERD) have impaired esophageal mucosal integrity. Measurement of the mucosal integrity is complex and time-consuming. Electrical tissue impedance spectroscopy (ETIS) is a device that measures impedance of tissue in vivo during endoscopy. In this study, we aimed to validate ETIS as a measure of esophageal mucosal integrity.

METHODS

Electrical tissue impedance spectroscopy measurements were performed during upper endoscopy in 12 GERD patients and 11 healthy controls after cessation of proton pump inhibition. During endoscopy biopsies of the distal esophagus were obtained for transmission electron microscopy to determine dilation of intercellular spaces (DIS) and for Ussing chamber experiments to determine transepithelial permeability and transepithelial electrical resistance.

KEY RESULTS

Extracellular impedance measured in vivo by ETIS was significantly lower in GERD patients compared to controls [mean (SD) 5621 (3299) Ω.m and 8834 (2542) Ω.m, respectively, P < 0.05]. We found a strong inverse relation between extracellular impedance determined by ETIS and DIS (r = -0.76, P < 0.05), and between extracellular resistance in vivo and transepithelial permeability of esophageal biopsies (r = -0.65, P < 0.01).

CONCLUSIONS & INFERENCES

Electrical tissue impedance spectroscopy is a new tool that can be used to evaluate esophageal mucosal integrity changes during endoscopy.

Numerical sensitivity modeling for the detection of skin tumors by using tetrapolar probe

The measurement of electrical impedance of skin using surface electrodes permits the assessment of changes in local properties of the skin and can be used in the detection of tumors. The sensitivity of this technique depends mainly on the geometry of the probe and the size of the tumor. In this article, the impedance method was used to estimate the sensitivity of a tetrapolar probe in detecting small regions of increased conductivity in a stratified model of human skin. The impedance method was used to model the potential distribution using fasorial analysis to solve the node equations of the equivalent circuit. Interpolation was applied to reduce discretization error. The skin was modeled as a three-layer structure with different conductivity and permittivity obtained from the literature. A tumor was modeled as a small volume with admittivity four times higher than the normal tissue. Sensitivity calculation was made as a function of electrode diameter and separation, tumor size, and excitation frequency. The simulations indicated that by inserting a one square millimeter tumor in the epidermis, the load impedance to the current source varies about 1% while the transfer impedance varied 8%. The sensitivity also increases nonlinearly with increasing tumor area and thickness. Additionally, it was found that the sensitivity of the transfer impedance has a maximum value when the electrodes are separated by 1.8 mm. The results show that transfer impedance measurements of the skin may detect small skin tumors with a reasonable sensitivity by using an appropriate tetrapolar probe.

Bioimpedance spectroscopy: a new tool to assess early esophageal changes linked to gastroesophageal reflux disease?

Bioimpedance spectroscopy can identify pathological changes related to precancerous lesions of the cervix uteri and esophagus. It therefore has the potential to detect early reflux-related changes in the esophageal mucosa, such as dilated intercellular spaces. The reliable detection of dilated intercellular spaces at the time of endoscopy would yield a significant diagnostic advantage for separating patients with functional heartburn from the large proportion of patients with gastroesophageal reflux symptoms but no macroscopic esophagitis or pathological acid exposure. The bioimpedance of the esophageal mucosa, measured with a small caliber probe, was evaluated in a series of preclinical experiments. First, sections of rabbit esophageal epithelium were mounted in Ussing chambers and exposed to solutions at pH 7.4 or pH 1.5 for 45 minutes. Impedance measurements were taken at varying probe pressures. Second, rabbit esophageal epithelia were perfused for 45 minutes in situ with pH 1.1 or control solutions and impedance measurements taken. Samples from both in vitro and in situ experiments were taken for morphological examination by light microscopy. Finally, esophageal bioimpedance was measured in awake dogs with permanent esophagocutaneous stoma. The in situ experiments demonstrated that morphological changes in the esophageal mucosa could be discerned by the use of bioimpedance spectroscopy. The variability in resistivity was species-independent but was affected by the pressure applied to the probe. The results suggest that evaluation of bioimpedance spectroscopy for use in a clinical setting is warranted. Small morphological differences in the esophageal mucosa may be detected by the use of bioimpedance spectroscopy.

Theoretical considerations of tissue electroporation with high-frequency bipolar pulses

This study introduces the use of high-frequency pulsed electric fields for tissue electroporation. Through the development of finite element models and the use of analytical techniques, electroporation with rectangular, bipolar pulses is investigated. The electric field and temperature distribution along with the associated transmembrane potential development are considered in a heterogeneous skin fold geometry. Results indicate that switching polarity on the nanosecond scale near the charging time of plasma membranes can greatly improve treatment outcomes in heterogeneous tissues. Specifically, high-frequency fields ranging from 500 kHz to 1 MHz are best suited to penetrate epithelial layers without inducing significant Joule heating, and cause electroporation in underlying cells.

The role of cervical Electrical Impedance Spectroscopy in the prediction of the course and outcome of induced labour

Background

Previous work by us and others had suggested that cervical electrical impedance spectroscopy (EIS) may be predictive of the outcome of induced labour. We sought to determine which probe configuration of the EIS device is predictive of the outcome of induced labour and compare this to digital assessment by the Bishop score.

Methods

In a prospective cohort of 205 women admitted for induction of labour, we used four probes of diameter 3, 6, 9 and 12 mm connected to an impedance meter to measure cervical resistivity (CR) in Ohm.meters at 14 electrical frequencies and compared their values to digital assessment of the cervix by the Bishop score for the prediction of the outcome of induced labour. We tested the association of labour characteristics and outcomes with CR and Bishop score by stepwise multilinear regression analyses, and the accuracy of prediction of categorical clinical outcomes by analysis of the area under the curves (AUC) of derived Receiver Operator Characteristic (ROC) curves.

Results

Of the four CR probe dimensions studied, only the 12 mm probe was predictive of any labour indices. In the frequency range 19 - 156 kHz, CR obtained with this probe was higher in women who delivered by caesarean section (CS) than those who delivered vaginally, and in labours lasting > 24 hrs. Cervical resistivity at 78.1 kHz best predicted vaginal delivery [optimal cut-off <2.25 Ohm.meter, AUC 0.66 (95% CI 0.59-0.72), sensitivity 71.0%, specificity 56.5%, LR+ 1.63, LR- 0.51, P < 0.01] and labour duration >24 hrs [optimal cut-off 2.27 Ω.m, AUC 0.65 (95% CI 0.58, 0.72), sensitivity 71%, specificity 59%, LR+ 1.72, LR- 0.50, P < 0.05]. In contrast digital assessment by the Bishop score neither predicted vaginal delivery nor the duration of labour. However, Bishop score predicted time to onset of labour > 12 hours and induction-delivery interval < 24 hrs [optimal cut-off ≤ 4, AUC 0.8 (95% CI 0.75, 0.86), sensitivity 77%, specificity 76%, LR+ 3.3, LR- 0.3, P < 0.05] whilst CR did not.

Conclusion

Cervical resistivity appears predictive of labour duration and delivery mode following induced labour. However the low predictive values obtained suggest that its current design proffers no immediate clinical utility.

Reproducibility and repeatability of measuring the electrical impedance of the pregnant human cervix-the effect of probe size and applied pressure

Background

The utility of cervical electrical impedance spectroscopy (EIS) as a diagnostic tool is being investigated in clinical trials. We sought to assess the reliability of two different sizes of tetrapolar probes used in measuring cervical impedance.

Methods

Cervical transfer impedance was measured at 14 frequencies between 76 and 625 000 Hz from 11 pregnant subjects at term. Repeated measurements were taken with two probes (3 mm and 12 mm diameter) applied softly (approximately 0.7 Newton of force), and firmly (approximately 2.2 Newton) to the surface of the cervix by two observers. The intra-class correlation coefficient (ICC), coefficient of variation (CV) and repeatability standard deviations (SD) were derived from these measurements and compared.

Results

Measurements taken by one observer were highly repeatable for both probes as demonstrated by high ICC and low CV values. Probe performance was improved further by firm application. Firm application of the 3 mm probe resulted in ICC values that ranged from 0.936 to 0.986 (p = 0.0001) and CV values between 1.0 and 3.4%. Firm pressure with the 12 mm probe resulted in ICC values that ranged between 0.914 and 0.988 (p = 0.0001) with CV values between 0.7 and 2.1%. In addition, the repeatability SD was low across all frequencies implying that there was low intra-observer variability. Measurements taken by 2 observers with firm application of the 12 mm probe demonstrated moderate reproducibility between 9.8 and 156 kHz, the frequency range in which previous clinical studies have shown predictive association between high cervical resistivity and vaginal delivery: ICC values ranged between 0.528 and 0.638 (p < 0.05), CV values were between 3.3 and 5.2% and reproducibility SD values were also low. In contrast the 3 mm probe demonstrated poor reproducibility at all study frequencies.

Conclusion

Measuring cervical resistivity by a single observer with both the 3 and 12 mm probes is highly repeatable whilst inter-observer reproducibility is poor with the 3 mm probe but moderately good when the 12 mm probe is firmly applied to the cervix in the frequency range 9.8 to 156 kHz, consistent with our observations of probe performance in clinical trials.

Impedance measurements for cervical cancer diagnosis

This article discusses using impedance measurements of body tissue in a diagnostic device. It then reviews the theory behind using these measurements to separate normal from diseased tissue. A small amount of time is devoted to discussing the meaning of sensitivity, specificity, and the receiver operating characteristic (ROC) curve, and their meanings. It also discusses the prospects of some new clinical devices using impedance measurements. One of the devices it focuses on is the TruScreen probe made by the Australian firm, Polartechnics.

Surface fluids effects on the bladder tissue characterisation using electrical impedance spectroscopy

The electrical impedance of the human urinary bladder in both benign and malignant areas can be measured using an electrical impedance spectroscopy system (EIS). Glycine is usually used in the bladder surgery in the theatre to make an insulation medium for electro-surgery and the extension of the mucosa. In addition, a saline solution is usually used to wash the inside of the bladder after bladder surgery and it is used to extend the bladder tissue mucosa. Therefore, the effect of glycine and the saline solution that fills the bladder is important, because it was expected that the application of common surface fluids (air, saline solution and glycine solution) in the bladder epithelium would affect the measured electrical impedance of the urothelium, to differentiate the malignant area from the normal bladder tissue. In this study, bladders were removed from the patients' bodies and then were moved from theatre to the histopathology department immediately after excision. These bladder samples were then opened and pinned to a corkboard to take the impedance readings, using the impedance spectroscopy system. Following this, the bladder and corkboard were completely submerged in a saline solution and readings were taken at about 1cm from the sutures. Subsequently, this procedure was repeated with the bladder submerged in glycine and then air, respectively. According to the statistical work, these fluids were found to have a significant effect on the measured impedance of the bladder tissue in benign and malignant areas. Furthermore, the best fluid between air, glycine and saline, to measure the impedance of the urinary bladder, is air (P<0.0001).

Measuring bioimpedance in the human uterine cervix: towards early detection of preterm labor

We have created a bioimpedance probe designed to detect subtle changes in human cervical tissue composition in vivo, and thereby detect the onset of cervical remodeling in a noninvasive manner sooner than existing clinical methods allow. Our cervical bioimpedance measurement device, which can be used during a routine pelvic examination, is composed of a contoured probe with disposable tip and, within the probe's handle, a bioimpedance sensor equipped with an integrated chip capable of generating sinusoidal voltage of varying frequencies. A constant force spring assures consistent measurements through a range of contact forces applied. An activation switch allows the operator to control the application of current. The sensor can be synchronized with a computer data storage and analysis system, which interfaces with the device. With the probe placed in contact with a collagen gels of varying concentration, the relationship between measured bioimpedance and collagen concentration is verified to be positive exponential (R/sup 2/=0.94) and repeatability in saline solution showed that measurements varied by less than +/-10% over 20 trials. Finally, a variety of user-applied forces showed that impedance values plateau when forces exceed 1N.

Electrical impedance spectroscopy of the cervix in non-pregnant and pregnant women

OBJECTIVES

We sought to validate and measure the electrical impedance of the uterine cervix in non-pregnant and pregnant women by spectroscopy.

STUDY DESIGN

Cervical stromal impedance (CSI) was measured in 50 non-pregnant, 20 1st, 20 2nd and 50 3rd trimester pregnant women. The technique was also validated by comparing in vivo data to a finite element (FE) model of cervical tissue.

RESULTS

CSI agreed well with the FE model and was highly reproducible in all study groups. Mean (S.E.) CSI at 4-819 kHz was higher in pregnant (2.78 +/- 0.09 Omega m) compared to non-pregnant (2.38 +/- 0.07, p < 0.01) women, and in the 3rd trimester (3.08 +/- 0.13) compared to non-pregnant (p < 0.01), 1st trimester (2.42 +/- 0.12, p < 0.001) and 2nd trimester (2.20 +/- 0.05, p < 0.001) pregnant women.

CONCLUSION

Measurement of CSI provides a non-invasive method of assessing cervical tissue characteristics. Cervical extracellular matrix synthesis and leukocyte infiltration may account for the increased tissue impedance noted in the 3rd trimester.

Comparison of human uterine cervical electrical impedance measurements derived using two tetrapolar probes of different sizes

Background

We sought to compare uterine cervical electrical impedance spectroscopy measurements employing two probes of different sizes, and to employ a finite element model to predict and compare the fraction of electrical current derived from subepithelial stromal tissue.

Methods

Cervical impedance was measured in 12 subjects during early pregnancy using 2 different sizes of the probes on each subject.

Results

Mean cervical resistivity was significantly higher (5.4 vs. 2.8 Ωm; p < 0.001) with the smaller probe in the frequency rage of 4–819 kHz. There was no difference in the short-term intra-observer variability between the two probes. The cervical impedance measurements derived in vivo followed the pattern predicted by the finite element model.

Conclusion

Inter-electrode distance on the probes for measuring cervical impedance influences the tissue resistivity values obtained. Determining the appropriate probe size is necessary when conducting clinical studies of resistivity of the cervix and other human tissues.

Impedance spectral measurements made through a membrane infection barrier

Impedance spectra of superficial tissues can be used to detect pre-malignant changes in the cervix but require electrical contact to be made between a probe and the tissue. Using a membrane which is permeable to ions but forms a barrier to agents of infection should enable impedance spectra to be measured without causing an infection risk to the patient. The properties required of such a membrane are considered and measurements on two suitable membranes are presented. It is shown that impedance spectra can be measured through a thin natural cellulose based membrane (Cuprophan) and that these are not significantly different from directly measured spectra. The ability of the membranes to block a virus is tested using expired polio virus vaccine.

Bioimpedance dispersion width as a parameter to monitor living tissues

In the case of living tissues, the spectral width of the electrical bioimpedance dispersions (closely related with the alpha parameter in the Cole equation) evolves during the ischemic periods. This parameter is often ignored in favor of other bioimpedance parameters such as the central frequency or the resistivity at low frequencies. The object of this paper is to analyze the significance of this parameter through computer simulations (in the alpha and beta dispersion regions) and to demonstrate its practical importance through experimental studies performed in rat kidneys during cold preservation. The simulations indicate that the dispersion width could be determined by the morphology of the extra-cellular spaces. The experimental studies show that it is a unique parameter able to detect certain conditions such as a warm ischemia period prior to cold preservation or the effect of a drug (Swinholide A) able to disrupt the cytoskeleton. The main conclusion is that, thanks to the alpha parameter in the Cole equation, the bioimpedance is not only useful to monitor the intra/extra-cellular volume imbalances or the inter-cellular junctions resistance but also to detect tissue structural alterations.

Modelling the electrical properties of bladder tissue—quantifying impedance changes due to inflammation and oedema

Electrical impedance spectroscopy has been developed as a potential method for the diagnosis of carcinoma in epithelial tissues. An understanding of the influence of structural changes in the tissue on the properties measured using this technique is essential for interpreting measured data and optimization of probe design. In contrast to other tissue types, carcinoma in situ of the bladder gives rise to an increase in electrical impedance over the kHz-MHz frequency range in comparison to normal tissue. Finite element models of the urothelium and the underlying superficial lamina propria have been constructed and solved in order to ascertain the influence of structural changes associated with malignancy, oedema and inflammation on the measured electrical properties of the tissue. Sensitivity analysis of results from a composite tissue model suggests that the increase in lymphocyte density in the lamina propria associated with an inflammatory response to the infiltration of urine into the tissue may explain these unusual electrical properties.

Impedance spectroscopy flow cytometry: On-chip label-free cell differentiation

BACKGROUND

The microfabricated impedance spectroscopy flow cytometer used in this study permits rapid dielectric characterization of a cell population with a simple microfluidic channel. Impedance measurements over a wide frequency range provide information on cell size, membrane capacitance, and cytoplasm conductivity as a function of frequency. The amplitude, opacity, and phase information can be used for discrimination between different cell populations without the use of cell markers.

METHODS

Polystyrene beads, red blood cells (RBCs), ghosts, and RBCs fixed in glutaraldehyde were passed through a microfabricated flow cytometer and measured individually by using two simultaneously applied discrete frequencies. The cells were characterized at 1,000 per minute in the frequency range of 350 kHz to 20 MHz.

RESULTS

Cell size was easily measured with submicron accuracy. Polystyrene beads and RBCs were differentiated using opacity. RBCs and ghosts were differentiated using phase information, whereas RBCs and fixed RBCs were differentiated using opacity. RBCs fixed using increasing concentrations of glutaraldehyde showed increasing opacity. This increased opacity was linked to decreased cytoplasm conductivity and decreased membrane capacitance, both resulting from protein cross-linking.

CONCLUSIONS

This work presents label-free differentiation of cells in an on-chip flow cytometer based on impedance spectroscopy, which will be a powerful tool for cell characterization.

The epitheliome: agent-based modelling of the social behaviour of cells

We have developed a new computational modelling paradigm for predicting the emergent behaviour resulting from the interaction of cells in epithelial tissue. As proof-of-concept, an agent-based model, in which there is a one-to-one correspondence between biological cells and software agents, has been coupled to a simple physical model. Behaviour of the computational model is compared with the growth characteristics of epithelial cells in monolayer culture, using growth media with low and physiological calcium concentrations. Results show a qualitative fit between the growth characteristics produced by the simulation and the in vitro cell models.