Variations of skin thermal diffusivity on different skin regions

BACKGROUND AND OBJECTIVE

Skin thermal diffusivity plays a crucial role in various applications, including laser therapy and cryogenic skin cooling.This study investigates the correlation between skin thermal diffusivity and two important skin parameters, melanin content and erythema, in a cohort of 102 participants.

METHODS

An in-house developed device based on transient temperature measurement was used to assess thermal diffusivity at different body locations. Melanin content and erythema were measured using a colorimeter. Statistical analysis was performed to examine potential correlations.

RESULTS

The results showed that the measured thermal diffusivity values were consistent with previous reports, with variations observed among subjects. No significant correlation was found between thermal diffusivity and melanin content or erythema. This suggests that other factors, such as skin hydration or epidermis thickness, may have a more dominant influence on skin thermal properties.

CONLCUSION

This research provides valuable insights into the complex interplay between skin thermal properties and physiological parameters, with potential implications for cosmetic and clinical dermatology applications.

Integrated Device Based on a Sudomotor Nanomaterial for Sweat Detection

The compositions of sweat and blood are related. Therefore, sweat is an ideal noninvasive test body fluid that could replace blood for linear detection of many biomarkers, especially blood glucose. However, access to sweat samples remains limited to physical exercise, thermal stimulation, or electrical stimulation. Despite intensive research, a continuous, innocuous, and stable method for sweat stimulation and detection has not yet been developed. In this study, a nanomaterial for a sweat-stimulating gel based on the transdermal drug delivery system is presented, which transports acetylcholine chloride into the receptors of sweat glands to achieve the function of biological stimulation of skin sweating. The nanomaterial was applied to a suitable integrated sweat glucose detection device for noninvasive blood glucose monitoring. The total amount of evaporated sweat enabled by the nanomaterial is up to 35 μL·cm^-2 for 24 h, and the device detects up to 17.65 μM glucose under optimal conditions, showing stable performance regardless of the user's activity level. In addition, the in vivo test was performed and compared with several studies and products, which showed excellent detection performance and osmotic relationship. The nanomaterial and associated integrated device represent a significant advance in continuous passive sweat stimulation and noninvasive sweat glucose measurement for point-of-care applications.

Quantification of nanoparticles' concentration inside polymer films using lock-in thermography

Thin nanocomposite polymer films embedding various types of nanoparticles have been the target of abundant research to use them as sensors, smart coatings, or artificial skin. Their characterization is challenging and requires novel methods that can provide qualitative as well as quantitative information about their composition and the spatial distribution of nanoparticles. In this work, we show how lock-in thermography (LIT) can be used to quantify the concentration of gold nanoparticles embedded in polyvinyl alcohol (PVA) films. LIT is an emerging and non-destructive technique that measures the thermal signature produced by an absorbing sample illuminated by modulated light with a defined frequency. Films with various concentrations of gold nanoparticles of two different sizes have been prepared by evaporation from homogeneous aqueous PVA gold nanoparticle suspensions. When the thin films were illuminated with monochromatic light at a wavelength close to the plasmonic resonance signature of the nanoparticles, the amplitude of the thermal signature emitted by the nanoparticles was recorded. The measurements have been repeated for multiple modulation frequencies of the incident radiation. We have developed a mathematical method to quantitatively relate the concentration of nanoparticles to the measured amplitude. A discussion about the conditions under which the sample thickness can be determined is provided. Furthermore, our results show how LIT measurements can easily detect the presence of concentration gradients in samples and how the model allows the measured signal to be related to the respective concentrations. This work demonstrates the successful use of LIT as a reliable and non-destructive method to quantify nanoparticle concentrations.

BODIPY-Based Photothermal Agents with Excellent Phototoxic Indices for Cancer Treatment

Here, we report six novel, easily accessible BODIPY-based agents for cancer treatment. In contrast to established photodynamic therapy (PDT) agents, these BODIPY-based compounds show additional photothermal activity and their cytotoxicity is not dependent on the generation of reactive oxygen species (ROS). The agents show high photocytotoxicity upon irradiation with light and low dark toxicity in different cancer cell lines in 2D culture as well as in 3D multicellular tumor spheroids (MCTSs). The ratio of dark to light toxicity (phototoxic index, PI) of these agents reaches striking values exceeding 830,000 after irradiation with energetically low doses of light at 630 nm. The oxygen-dependent mechanism of action (MOA) of established photosensitizers (PSs) hampers effective clinical deployment of these agents. Under hypoxic conditions (0.2% O₂), which are known to limit the efficiency of conventional PSs in solid tumors, photocytotoxicity was induced at the same concentration levels, indicating an oxygen-independent photothermal MOA. With a PI exceeding 360,000 under hypoxic conditions, both PI values are the highest reported to date. We anticipate that small molecule agents with a photothermal MOA, such as the BODIPY-based compounds reported in this work, may overcome this barrier and provide a new avenue to cancer therapy.

Use of digital technologies to combat loneliness and social isolation: a cross-sectional study in Swiss outpatient care during COVID-19 pandemic

Background

There is limited data on the use of digital technologies in outpatient care in Switzerland. Our objectives were therefore to determine which digital technologies are used and whether they had an impact on loneliness and social isolation in the wake of the COVID-19 pandemic.

Methods

A cross-sectional survey design was used with a convenience sample of 1272 outpatient care providers in Switzerland. The questionnaire used is based on an unsystematic literature review and a previous qualitative study with six outpatient caregivers and two caring relatives, based on which the 30 items for this questionnaire were developed. Data were analyzed descriptively, and group comparisons were made using the Kruskal Wallis test. Changes over time were measured using Friedman test with Bonferroni post hoc tests and Wilcoxon test for paired samples.

Results

The impact of the COVID-19 pandemic was evident both on the part of the health care system, e.g., inadequate protective equipment; on the part of health care providers, e.g., increasing fatigue in keeping abreast of the virus as the pandemic progressed; and on the part of clients, who reduced services of care, e.g., out of fear of infection. According to the assessment of the outpatient caregivers, loneliness and social isolation of the clients was high in spring 2020 and increased strongly in the following winter. Alternative solutions, such as digital technologies, were hardly used or not used at all by the clients.

Conclusions

The results suggest that the pandemic is dramatically impacting clients. This highlights the urgent need to invest in the development of appropriate digital technologies reducing the impact of social isolation and loneliness and the associated long-term costs to the healthcare system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12912-022-00946-7.

A Naked Eye-Invisible Ratiometric Fluorescent Microneedle Tattoo for Real-Time Monitoring of Inflammatory Skin Conditions

The field of portable healthcare monitoring devices has an urgent need for the development of real-time, noninvasive sensing and detection methods for various physiological analytes. Currently, transdermal sensing techniques are severely limited in scope (i.e., measurement of heart rate or sweat composition), or else tend to be invasive, often needing to be performed in a clinical setting. This study proposes a minimally invasive alternative strategy, consisting of using dissolving polymeric microneedles to deliver naked eye-invisible functional fluorescent ratiometric microneedle tattoos directly to the skin for real-time monitoring and quantification of physiological and pathological parameters. Reactive oxygen species are overexpressed in the skin in association with various pathological conditions. Here, one demonstrates for the first time the microneedle-based delivery to the skin of active fluorescent sensors in the form of an invisible, ratiometric microneedle tattoo capable of sensing reactive oxygen species in a reconstructed human-based skin disease model, as well as an in vivo model of UV-induced dermal inflammation. One also elaborates a universal ratiometric quantification concept coupled with a custom-built, multiwavelength portable fluorescence detection system. Fully realized, this approach presents an opportunity for the minimally invasive monitoring of a broad range of physiological parameters through the skin.

A simple non-contact optical method to quantify in-vivo sweat gland activity and pulsation

OBJECTIVE

Most methods for monitoring sweat gland activity use simple gravimetric methods, which merely measure the average sweat rate of multiple sweat glands over a region of skin. It would be extremely useful to have a method which could quantify individual gland activity in order to improve the treatment of conditions which use sweat tests as a diagnostic tool, such as hyperhidrosis, cystic fibrosis, and peripheral nerve degeneration.

METHODS

An optical method using an infrared camera to monitor the skin surface temperature was developed. A thermodynamics computer model was then implemented to utilize these skin temperature values along with other environmental parameters, such as ambient temperature and relative humidity, to calculate the sweat rates of individual glands using chemically stimulated and unstimulated sweating. The optical method was also used to monitor sweat pulsation patterns of individual sweat glands.

RESULTS

In this preliminary study, the feasibility of the optical approach was demonstrated by measuring sweat rates of individual glands at various bodily locations. Calculated values from this method agree with expected sweat rates given values found in literature. In addition, a lack of pulsatile sweat expulsion was observed during chemically stimulated sweating, and a potential explanation for this phenomenon was proposed.

CONCLUSION

A simple, non-contact optical method to quantify sweat gland activity in-vivo was presented.

SIGNIFICANCE

This method allows researchers and clinicians to investigate several sweat glands simultaneously, which has the potential to provide more accurate diagnoses and treatment as well as increase the potential utility for wearable sweat sensors.

Development and Clinical Validation of the LymphMonitor Technology to Quantitatively Assess Lymphatic Function

Current diagnostic methods for evaluating the functionality of the lymphatic vascular system usually do not provide quantitative data and suffer from many limitations including high costs, complexity, and the need to perform them in hospital settings. In this work, we present a quantitative, simple outpatient technology named LymphMonitor to quantitatively assess lymphatic function. This method is based on the painless injection of the lymphatic-specific near-infrared fluorescent tracer indocyanine green complexed with human serum albumin, using MicronJet600^TM microneedles, and monitoring the disappearance of the fluorescence signal at the injection site over time using a portable detection device named LymphMeter. This technology was investigated in 10 patients with unilateral leg or arm lymphedema. After injection of a tracer solution into each limb, the signal was measured over 3 h and the area under the normalized clearance curve was calculated to quantify the lymphatic function. A statistically significant difference in lymphatic clearance in the healthy versus the lymphedema extremities was found, based on the obtained area under curves of the normalized clearance curves. This study provides the first evidence that the LymphMonitor technology has the potential to diagnose and monitor the lymphatic function in patients.

A comparative study of silver nanoparticle dissolution under physiological conditions

Upon dissolution of silver nanoparticles, silver ions are released into the environment, which are known to induce adverse effects. However, since dissolution studies are predominantly performed in water and/or at room temperature, the effects of biological media and physiologically relevant temperature on the dissolution rate are not considered. Here, we investigate silver nanoparticle dissolution trends based on their plasmonic properties under biologically relevant conditions, i.e. in biological media at 37 °C over a period of 24 h. The studied nanoparticles, surface-functionalized with polyvinylpyrrolidone, beta-cyclodextrin/polyvinylpyrrolidone, and starch/polyvinylpyrrolidone, were analysed by UV-Vis spectroscopy, lock-in thermography and depolarized dynamic light scattering to evaluate the influence of these coatings on silver nanoparticle dissolution. Transmission electron microscopy was employed to visualize the reduction of the nanoparticle core diameters. Consequently, the advantages and limitations of these analytical techniques are discussed. To assess the effects of temperature on the degree of dissolution, the results of experiments performed at biological temperature were compared to those obtained at room temperature. Dissolution is often enhanced at elevated temperatures, but has to be determined individually for every specific condition. Furthermore, we evaluated potential nanoparticle aggregation. Our results highlight that additional surface coatings do not necessarily hinder the dissolution or aggregation of silver nanoparticles.

Rapid and sensitive quantification of cell-associated multi-walled carbon nanotubes

Evaluating nanomaterial uptake and association by cells is relevant for in vitro studies related to safe-by-design approaches, nanomedicine or applications in photothermal therapy. However, standard analytical techniques are time-consuming, involve complex sample preparation or include labelling of the investigated sample system with e.g. fluorescent dyes. Here, we explore lock-in thermography to analyse and compare the association trends of epithelial cells, mesothelial cells, and macrophages exposed to gold nanoparticles and multi-walled carbon nanotubes over 24 h. The presence of nanomaterials in the cells was confirmed by dark field and transmission electron microscopy. The results obtained by lock-in thermography for gold nanoparticles were validated with inductively coupled plasma optical emission spectrometry; with data collected showing a good agreement between both techniques. Furthermore, we demonstrate the detection and quantification of carbon nanotube-cell association in a straightforward, non-destructive, and non-intrusive manner without the need to label the carbon nanotubes. Our results display the first approach in utilizing thermography to assess the carbon nanotube amount in cellular environments.

Ultra-simple wearable local sweat volume monitoring patch based on swellable hydrogels

Quantifiably monitoring sweat rate and volume is important to assess the stress level of individuals and/or prevent dehydration, but despite intense research, a convenient, continuous, and low-cost method to monitor sweat rate and total sweat volume loss remains an un-met need. We present here an ultra-simple wearable sensor capable of measuring sweat rate and volume accurately. The device continuously monitors sweat rate by wicking the produced sweat into hydrogels that measurably swell in their physical geometry. The device has been designed as a simple to fabricate, low-cost, disposable patch. This patch exhibits stable and predictable operation over the maximum variable chemistry expected for sweat (pH 4-9 and salinity 0-100 mM NaCl). Preliminary in vivo testing of the patch has been achieved during aerobic exercise, and the sweat rates measured via the patch accurately follow actual sweat rates.

Thermography: High sensitivity and specificity diagnosing contact dermatitis in patch testing

BACKGROUND

Patch testing of contact allergens to diagnose allergic contact dermatitis (ACD) is a traditional, useful tool. The most important decision is the distinction between allergic and irritant reactions, as this has direct implications on diagnosis and management. Our objective was to evaluate a new method of non-contact infrared reading of patch tests. Secondary objectives included a possible correlation between the intensity of the patch test reaction and temperature change.

METHODS

420 positive reactions from patients were included in our study. An independent patch test reader assessed the positive reactions and classified them as allergic (of intensity + to +++) or irritant (IR). At the same time, a forward-looking infrared (FLIR) camera attachment for an iPhone was used to acquire infrared thermal images of the patch tests, and images were analyzed using the FLIR ONE app.

RESULTS

Allergic patch test reactions were characterized by temperature increases of 0.72 ± 0.67 °C compared to surrounding skin. Irritant reactions only resulted in 0.17 ± 0.31 °C temperature increase. The mean temperature difference between the two groups was highly significant (p < 0.0001) and therefore was used to predict the type of contact dermatitis.

CONCLUSIONS

Thermography is a reliable and effective way to distinguish between allergic and irritant contact dermatitis.

Minimally invasive method for the point-of-care quantification of lymphatic vessel function

Current clinical methods for the evaluation of lymphatic vessel function, crucial for early diagnosis and evaluation of treatment response of several pathological conditions, in particular of postsurgical lymphedema, are based on complex and mainly qualitative imaging techniques. To address this unmet medical need, we established a simple strategy for the painless and quantitative assessment of cutaneous lymphatic function. We prepared a lymphatic-specific tracer formulation, consisting of the clinically approved near-infrared fluorescent dye, indocyanine green, and the solubilizing surfactant Kolliphor HS15. The tracer was noninvasively delivered to the dermal layer of the skin using MicronJet600 hollow microneedles, and the fluorescence signal decay at the injection site was measured over time using a custom-made, portable detection device. The decay rate of fluorescence signal in the skin was used as a direct measure of lymphatic vessel drainage function. With this method, we could quantify impaired lymphatic clearance in transgenic mice lacking dermal lymphatics and distinguish distinct lymphatic clearance patterns in pigs in different body locations and under manual stimulus. Overall, this method has the potential for becoming a noninvasive and quantitative clinical "office test" for lymphatic function assessment.

A lock-in-based method to examine the thermal signatures of magnetic nanoparticles in the liquid, solid and aggregated states

We propose a new methodology based on lock-in thermography to study and quantify the heating power of magnetic nanoparticles. Superparamagnetic iron oxide nanoparticles exposed to a modulated alternating magnetic field were used as model materials to demonstrate the potency of the system. Both quantitative and qualitative information on their respective heating power was extracted at high thermal resolutions under increasingly complex conditions, including nanoparticles in the liquid, solid and aggregated states. Compared to conventional techniques, this approach offers a fast, sensitive and non-intrusive alternative to investigate multiple and dilute specimens simultaneously, which is essential for optimizing and accelerating screening procedures and comparative studies.

Lock-in thermal imaging for the early-stage detection of cutaneous melanoma: a feasibility study

This paper theoretically evaluates lock-in thermal imaging for the early-stage detection of cutaneous melanoma. Lock-in thermal imaging is based on the periodic thermal excitation of the specimen under test. Resulting surface temperature oscillations are recorded with an infrared camera and allow the detection of variations of the sample's thermophysical properties under the surface. In this paper, the steady-state and transient skin surface temperatures are numerically derived for a different stage of development of the melanoma lesion using a two-dimensional axisymmetric multilayer heat-transfer model. The transient skin surface temperature signals are demodulated according to the digital lock-in principle to compute both a phase and an amplitude image of the lesions. The phase image can be advantageously used to accurately detect cutaneous melanoma at an early stage of development while the maximal phase shift can give precious information about the lesion invasion depth. The ability of lock-in thermal imaging to suppress disturbing subcutaneous thermal signals is demonstrated. The method is compared with the previously proposed pulse-based approaches, and the influence of the modulation frequency is further discussed.

A picosecond time-resolved vibrational circular dichroism spectrometer

We present an experimental setup to detect transient vibrational circular dichroism signals. A femtosecond laser system is synchronized to a photoelastic modulator to produce alternating left- and right-handed circularly polarized mid-IR pulses at 1 kHz repetition rate. Transient changes in the circular dichroism of the CH-stretch vibrations of a cobalt-sparteine complex were probed in a proof-of-principle experiment and are clearly distinct from conventional transient absorption changes.

3-D optical coherence tomography of the laryngeal mucosa*

Laryngeal carcinoma is one of the commonest primary head and neck malignancy and the need for early identification is very important for successful treatment. Outpatient fibreoptic examination of the larynx is unreliable in differentiating benign, pre-malignant and malignant lesions, and therefore surgeons have to rely on biopsies for a definitive diagnosis. This is an invasive procedure requiring general anaesthesia and may have a detrimental effect on the patient's voice. Conventional imaging modalities (ultrasound, computed tomography and magnetic resonance imaging) have a limited resolution and hence cannot give sufficient information on the extent or nature of laryngeal lesions. The aim of our study is to investigate the feasibility of optical coherence tomography (OCT) in imaging the normal larynx, to lay the foundations for an investigation of its ability to differentiate between benign and malignant disease. Ten tissue specimens from normal larynges were imaged with an 850 nm OCT system that was capable of providing both B-scan (longitudinal or cross-section) images as well as C-scan (en-face or images at constant depth). The en-face OCT mode allowed us to reconstruct 3-D OCT images of the tissue examined. Imaged specimens were processed with standard histopathological techniques and sectioned in the plane of the B-scan OCT images. Haematoxylin-eosin stained specimens were compared with the OCT images thus collected. Preliminary results showed good correlation between OCT images and histology sections in normal tissue.