Noninvasive measurement of transdermal drug delivery by impedance spectroscopy

Equivalent Electrical Circuit Approach to Enhance a Transducer for Insulin Bioavailability Assessment

The equivalent electrical circuit approach is explored to improve a bioimpedance-based transducer for measuring the bioavailability of synthetic insulin already presented in previous studies. In particular, the electrical parameter most sensitive to the variation of insulin amount injected was identified. Eggplants were used to emulate human electrical behavior under a quasi-static assumption guaranteed by a very low measurement time compared to the estimated insulin absorption time. Measurements were conducted with the EVAL-AD5940BIOZ by applying a sinusoidal voltage signal with an amplitude of 100 mV and acquiring impedance spectra in the range [1-100] kHz. 14 units of insulin were gradually administered using a Lilly's Insulin Pen having a 0.4 cm long needle. Modified Hayden's model was adopted as a reference circuit and the electrical component modeling the extracellular fluids was found to be the most insulin-sensitive parameter. The trnasducer achieves a state-of-the-art sensitivity of 225.90 ml1. An improvement of 223 % in sensitivity, 44 % in deterministic error, 7 % in nonlinearity, and 42 % in reproducibility was achieved compared to previous experimental studies. The clinical impact of the transducer was evaluated by projecting its impact on a Smart Insulin Pen for real-time measurement of insulin bioavailability. The wide gain in sensitivity of the bioimpedance-based transducer results in a significant reduction of the uncertainty of the Smart Insulin Pen. Considering the same improvement in in-vivo applications, the uncertainty of the Smart Insulin Pen is decreased from [Formula: see text]l to [Formula: see text]l.Clinical and Translational Impact Statement: A Smart Insulin Pen based on impedance spectroscopy and equivalent electrical circuit approach could be an effective solution for the non-invasive and real-time measurement of synthetic insulin uptake after subcutaneous administration.

Nanocrystalline cellulose as a reinforcing agent for poly (vinyl alcohol)/ gellan-gum-based composite film for moxifloxacin ocular delivery

Nanocrystalline cellulose (NCC) is a star material in drug delivery applications due to its good biocompatibility, large specific surface area, high tensile strength (TS), and high hydrophilicity. Poly(Vinyl Alcohol)/Gellan-gum-based innovative composite film has been prepared using nanocrystalline cellulose (PVA/GG/NCC) as a strengthening agent for ocular delivery of moxifloxacin (MOX) via solvent casting method. Impedance analysis was studied using the capacitive sensing technique for examining new capacitance nature of the nanocomposite MOX film. Antimicrobial properties of films were evaluated using Pseudomonas aeruginosa and Staphylococcus aureus as gram-negative and gram-positive bacteria respectively by disc diffusion technique. XRD revealed the characteristic peak of NCC and the amorphous form of the drug. Sustained in vitro release and enhanced corneal permeation of drug were noticed in the presence of NCC. Polymer matrix enhanced the mechanical properties (tensile strength 22.05 to 28.41 MPa) and impedance behavior (resistance 59.23 to 213.23 Ω) in the film due to the presence of NCC rather than its absence (16.78 MPa and 39.03 Ω respectively). Occurrence of NCC brought about good antimicrobial behavior (both gram-positive and gram-negative) of the film. NCC incorporated poly(vinyl alcohol)/gellan-gum-based composite film exhibited increased mechanical properties and impedance behavior for improved ocular delivery of moxifloxacin.

Skin and Artificial Skin Models in Electrical Sensing Applications

Skin electrical properties play a significant role in recording biopotentials by using electrophysiological sensors. To test and evaluate sensor systems, it is commonly accepted to employ artificial skin models due to complications associated with testing on living tissues. The first goal of this Review is to provide a systematic understanding of the relation between skin structure and skin electrochemical behavior at an appropriate depth for electrophysiological sensing applications through a focus on skin structure, electrochemical properties of skin, and theoretical models (equivalent circuits) representing skin electrochemical behavior. The second goal is to review artificial skin models mimicking the electrochemical properties of skin and to give suggestions for future studies on relevant skin models based on a comparison between the behavior of skin and that of artificial skin models. The Review aims to help the reader to analyze the relation between the structure, elements of the equivalent circuits, and the resulting impedance data for both skin and artificial skin models.

Analytical study of gold-DNA nano core-shell cloaking characteristics for drug delivery and cancer therapy

The cloaking characteristics of biocells can be considered as a factor to determine drug absorption by the tissues. The metal-organic core-shell structure can act as a cloak around the molecules of tissue and can be used as a nanomachine for drug delivery. Thus, we define a ratio of drug absorption based on frequency red-shift and the effective permittivity in the optical spectrum. Here, a cylinder of molecules coated by plasmonic nano core-shells is proposed for measuring the cloaking characteristics of biocells. The overall bandwidth of the proposed cloak for reflectance less than -10 dB is 36%. We check the effect of the filling factors of nanoparticles on the reflection and the frequency response of the tissue. Besides the frequency red-shift and change in the level of reflection, the phase and impedance are extracted. We could obtain the normalized scattering cross-section of 5 dB lower than the cylinder without cloak for the cylinder with a gold-DNA core-shell cloak. Here, we modify the Maxwell-Garnett equation for a cylindrical structure to obtain the effective value of the permittivity for cancer and normal tissues. The results show that obtained permittivity from the simulation has a good match with the calculated permittivity from the Maxwell-Garnet equation. Therefore, this approach can be considered as an efficient method for drug absorption and diagnosis of cancer cells from normal cells.

Electrical Bioimpedance Analysis for Evaluating the Effect of Pelotherapy on the Human Skin: Methodology and Experiments

BACKGROUND

Pelotherapy is the traditional procedure of applying curative muds on the skin's surface-shown to have a positive effect on the human body and cure illnesses. The effect of pelotherapy is complex, functioning through several mechanisms, and depends on the skin's functional condition. The current research objective was to develop a methodology and electrodes to assess the passage of the chemical and biologically active compounds of curative mud through human skin by performing electrical bioimpedance (EBI) analysis.

METHODS

The methodology included local area mud pack and simultaneous tap water compress application on the forearms with the comparison to the measurements of the dry skin. A custom-designed small-area gold-plated electrode on a rigid printed circuit board, in a tetrapolar configuration, was designed. A pilot study experiment with ten volunteers was performed.

RESULTS

Our results indicated the presence of an effect of pelotherapy, manifested by the varying electrical properties of the skin. Distinguishable difference in the measured real part of impedance (R) emerged, showing a very strong correlation between the dry and tap-water-treated skin (r = 0.941), while a poor correlation between the dry and mud-pack-treated skin (r = 0.166) appeared. The findings emerged exclusively in the frequency interval of 10 kHz …1 MHz and only for R.

CONCLUSIONS

EBI provides a promising tool for monitoring the variations in the electrical properties of the skin, including the skin barrier. We foresee developing smart devices for promoting the exploitation of spa therapies.

Effect of Tamarind Gum on the Properties of Phase-Separated Poly(vinyl alcohol) Films

The current study aims to evaluate the effect of tamarind gum (TG) on the optical, mechanical, and drug release potential of poly(vinyl alcohol) (PVA)-based films. This involves preparing PVA-TG composite films with different concentrations of TG through a simple solvent casting method. The addition of TG has enhanced the phase separation and aggregation of PVA within the films, and it becomes greater with the increase in TG concentration. Brightfield and polarized light micrographs have revealed that aggregation is favored by forming crystalline domains at the PVA-TG interface. The interconnected network of PVA-TG aggregates influenced the swelling and drying properties of the films. Using Peleg’s analysis, the mechanical behavior of films was determined by their stress relaxation profiles. The addition of TG has made no significant changes to the firmness and viscoelastic properties of films. However, long-durational relaxation times indicated that the interconnected network might break down in films with higher TG concentration, suggesting their brittleness. The controlled release of ciprofloxacin in HCl solution (0.5% (w/v)) appears to decrease with the increase in TG concentration. In fact, TG has inversely affected the impedance and altered the ionic conductivity within the films. This seems to have directly influenced the drug release from the films as the mechanism was found to be non-Fickian diffusion (based on Korsmeyer–Peepas and Peppas–Sahlin kinetic models). The antimicrobial study using Escherichia coli was carried out to evaluate the activity of the drug-loaded films. The study proves that TG can modulate the properties of PVA films and has the potential to fine-tune the controlled release of drugs from composite films.

A personalized FEM model for reproducible measurement of anti-inflammatory drugs in transdermal administration to knee

A personalized model of the human knee for enhancing the inter-individual reproducibility of a measurement method for monitoring Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) after transdermal delivery is proposed. The model is based on the solution of Maxwell Equations in the electric-quasi-stationary limit via Finite Element Analysis. The dimensions of the custom geometry are estimated on the basis of knee circumference at the patella, body mass index, and sex of each individual. An optimization algorithm allows to find out the electrical parameters of each subject by experimental impedance spectroscopy data. Muscular tissues were characterized anisotropically, by extracting Cole-Cole equation parameters from experimental data acquired with twofold excitation, both transversal and parallel to tissue fibers. A sensitivity and optimization analysis aiming at reducing computational burden in model customization achieved a worst-case reconstruction error lower than 5%. The personalized knee model and the optimization algorithm were validated in vivo by an experimental campaign on thirty volunteers, 67% healthy and 33% affected by knee osteoarthritis (Kellgren-Lawrence grade ranging in [1,4]), with an average error of 3%.

Diabetic Foot Assessment using Skin Impedance in a Custom Made Sensor-sock

Diabetic peripheral neuropathy (DPN) may lead to several changes in the skin, and some of these may influence the skin impedance spectrum. In the present study we have developed a prototype solution for skin impedance spectroscopy at selected skin sites (big toe pulp, heel and toe ball) that was tested in a pilot study on five patients with DPN and five healthy controls. At the big toe, most of the controls had markedly lower impedance than the DPN group, especially in the range of 1-100 kHz. The separation between the groups seems to be weaker at the heel and weakest at the toeball. The results may indicate that monitoring of the skin impedance spectrum may be a method for detection of skin changes associated with DPN, encouraging further studies with the big toe sensor in particular.

Synthesis and characterization of novel tamarind gum and rice bran oil-based emulgels for the ocular delivery of antibiotics

In this study, we developed tamarind gum (TG) and rice bran oil (RBO)-based emulgels. The control formulation (TR0), did not contain RBO. The emulgels were named as TR1, TR2, TR3, and TR4, which contained 5% (w/w), 10% (w/w), 15% (w/w), and 20% (w/w/) of RBO, respectively. The microscopic studies showed that the emulgels were biphasic in nature. FTIR spectroscopy revealed the reduction in the hydrogen bonding with an increase in the RBO content. Impedance profiles suggested that the resistive component of the emulgels was increased as the RBO content was increased. The thermal analysis suggested that the addition of RBO reduced the water holding capacity of the emulgels. Stress relaxation studies revealed that the fluidic component was considerably higher in TG/RBO-based emulgels as compared to TR0. In vitro release study of the model drug (ciprofloxacin HCl; a hydrochloride salt of ciprofloxacin) suggested a significantly lower release from the emulgel matrices (TR1-TR4) in comparison to TR0. However, ex vivo corneal permeation of the drug increased with an increase in the RBO content. Since the emulgels were able to improve the corneal permeation of the model drug, the emulgels can be explored to deliver drugs to the internal structures of the eye.

A micro-bioimpedance meter for monitoring insulin bioavailability in personalized diabetes therapy

An on-chip transducer, for monitoring noninvasively the insulin bio-availability in real time after administration in clinical diabetology, is proposed. The bioavailability is assessed as insulin decrease in situ after administration by means of local impedance measurement. Inter-and-intra individual reproducibility is enhanced by a personalized model, specific for the subject, identified and validated during each insulin administration. Such a real-time noninvasive bioavailability measurement allows to increase the accuracy of insulin bolus administration, by attenuating drawbacks of glycemic swings significantly. In the first part of this paper, the concept, the architecture, and the operation of the transducer, as well as details about its prototype, are illustrated. Then, the metrological characterization and validation are reported in laboratory, in vitro on eggplants, ex vivo on pig abdominal non-perfused muscle, and in vivo on a human subject, using injection as a reference subcutaneous delivery of insulin. Results of significant intra-individual reproducibility in vitro and ex vivo point out noteworthy scenarios for assessing insulin bioavailability in clinical diabetology.

Current Strategies and Future Perspectives of Skin-on-a-Chip Platforms: Innovations, Technical Challenges and Commercial Outlook

The skin is the largest and most exposed organ in the human body. Not only it is involved in numerous biological processes essential for life but also it represents a significant endpoint for the application of pharmaceuticals. The area of in vitro skin tissue engineering has been progressing extensively in recent years. Advanced in vitro human skin models strongly impact the discovery of new drugs thanks to the enhanced screening efficiency and reliability. Nowadays, animal models are largely employed at the preclinical stage of new pharmaceutical compounds development for both risk assessment evaluation and pharmacokinetic studies. On the other hand, animal models often insufficiently foresee the human reaction due to the variations in skin immunity and physiology. Skin-on-chips devices offer innovative and state-of-the-art platforms essential to overcome these limitations. In the present review, we focus on the contribution of skin-on-chip platforms in fundamental research and applied medical research. In addition, we also highlighted the technical and practical difficulties that must be overcome to enhance skin-on-chip platforms, e.g. embedding electrical measurements, for improved modeling of human diseases as well as of new drug discovery and development.

Bioimpedance Sensor Array for Long-Term Monitoring of Wound Healing from Beneath the Primary Dressings and Controlled Formation of H2O2 Using Low-Intensity Direct Current

Chronic wounds impose a significant financial burden for the healthcare system. Currently, assessment and monitoring of hard-to-heal wounds are often based on visual means and measuring the size of the wound. The primary wound dressings must be removed before assessment can be done. We have developed a quasi-monopolar bioimpedance-measurement-based method and a measurement system to determine the status of wound healing. The objective of this study was to demonstrate that with an appropriate setup, long-term monitoring of wound healing from beneath the primary dressings is feasible. The developed multielectrode sensor array was applied on the wound area and left under the primary dressings for 142 h. The impedance of the wounds and the surrounding intact skin area was measured regularly during the study at 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. At the end of the follow-up period, the wound impedance had reached the impedance of the intact skin at the higher frequencies and increased significantly at the lowest frequencies. The measurement frequency affected the measurement sensitivity in wound monitoring. The skin impedance remained stable over the measurement period. The sensor array also enabled the administration of periodical low-intensity direct current (LIDC) stimulation in order to create an antimicrobial environment across the wound area via the controlled formation of hydrogen peroxide (H₂O₂).