A micromechanical comparison of human and porcine skin before and after preservation by freezing for medical device development

The Histological and Mechanical Behavior of Skin During Puncture for Different Impactor Sizes and Loading Rates

PURPOSE

The hierarchical structure of skin dictates its protective function against mechanical loading, which has been extensively studied through numerous experiments. Viscoelasticity and anisotropy have been defined for skin in tensile loading, but most puncture studies utilized skin simulants, which lacked natural tension and varying skin thicknesses. The purpose of this study was to define the mechanical behavior and failure thresholds of skin during puncture with various blunt impactor sizes and loading rates.

METHODS

After determining natural tension of porcine skin, 232 isolated skin samples were loaded in puncture. Pre-conditioning, sub-failure, and failure trials were conducted with an electrohydraulic piston actuator loading pre-strained skin samples with a 3-, 5-, or 8-mm spherical impactor at rates of 5 to 1000 mm/s. Generalized linear mixed models were used to determine significant factors and predict probability of puncture.

RESULTS

Increased skin thickness significantly increased RIII stiffness (p = 0.002), failure force (p < 0.001), and strain energy at failure (p = 0.002) and significantly decreased displacement at failure (p = 0.002). Significantly greater force, displacement, strain energy, and stiffness (p < 0.05) at failure were observed with the 8-mm impactor. Loading at 1000 mm/s resulted in significantly greater force (p = 0.026) and stiffness (p < 0.001) at failure compared to 5 mm/s and significantly decreased displacement at failure (p < 0.001). 3D-DIC strain maps displayed anisotropic behavior, and larger elliptical wounds resulted from puncture with an 8 mm impactor (p < 0.001). Quantitative histological analyses revealed collagen re-alignment near the impactor from pre-conditioning and minimal structural damage during sub-failure trials. Initial structural failure occurred in the reticular dermis followed by the papillary dermis and epidermis.

CONCLUSION

The presented failure metrics, with support from histological findings, may be utilized in development of protective clothing, improvement of computational models, and advancement in forensic sciences.

Electrospun fiber patches for inflammatory skin diseases - Correlating in vitro drug release with ex vivo permeation

In this proof-of-concept study, we aimed to develop an anti-inflammatory patch that in contrast to the semi-solid standard therapy is dry and non-greasy, and only needs to be changed once a day due to continuous release of the active ingredient over 24 h. While fiber materials for the treatment of inflammatory skin diseases have been reported in the literature, the majority of studies focuses solely on material characterization including in vitro release studies; however, there is a lack of ex vivo permeation studies as well as comparison with standard therapy. However, such experiments are crucial to deduct the potential efficacy of the drug delivery system, as skin absorption of the drug may be the rate-limiting step and not the drug release. Therefore, we set out to investigate different types of electrospun fiber systems based on polycaprolactone, a polymer with a well-established safety profile widely used for fabricating electrospun patches. The electrospun fiber patches were loaded with the anti-inflammatory drug hydrocortisone and characterized not only for their drug release properties, but for the first time also for their skin permeation and retention as well as their cytocompatibility and anti-inflammatory properties on human skin. While in the release studies, the layer-by-layer fiber system proved to be best suited for an application time of 24 h, this was not reflected in the permeation studies, where all fiber systems showed a similar skin permeation and retention of the drug. In our study set-up, a comparison with standard cream formulations revealed that electrospun fibers offer an advantage in terms of the permeated amount of hydrocortisone. Overall, this study supports the importance of conducting comparisons with standard therapies and, additionally, confirms that electrospun fibers are a promising dosage form for the controlled release of anti-inflammatory drugs for the treatment of inflammatory skin diseases.

Influence of experimental conditions on some in-vitro biomechanical properties of the sow's perineum

The aim of this work was to develop an experimental protocol that takes into account the influence of experimental conditions on these perineal tissues, before determining their mechanical properties. Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS) and anal mucosa of freshly dead sows. They were tested in quasi-static uniaxial tension using the Mach-1 testing machine. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled by hyperelastic laws described by three coefficients: C1, C2, and C3 (Yeoh model). The influence of sample preparation conditions such as tissue freezing, hygrometry and sample orientation were evaluated, and the conditions under which the tests were performed such as the displacement velocity during testing were also evaluated by analysing C1-coefficient. This study suggested that sample preparation conditions such as tissue freezing for 24 h, storage in cellophane paper for two hours and the strain rate did not statistically affect the C1-hyperelastic coefficient for each perineal layer (p > 0.05). Samples should not be stored in saline for 2 h (p < 0.05). Sample orientation did not influence C1-hyperelastic coefficient (p > 0.05). This experimental protocol could be used to study in vitro biomechanical properties of perineal tissues in order to better understand perineal tears during delivery.

Retention of nickel, cobalt and chromium in skin at conditions mimicking intense hand hygiene practices using water, soap, and hand-disinfectant in vitro

BACKGROUND

During the COVID-19 pandemic, increased hand hygiene practices using water, soap and hand disinfectants, became prevalent, particularly among frontline workers. This study investigates the impact of these practices on the skin's ability to retain the allergenic metals nickel, cobalt, and chromium. The study constitutes three parts: (I) creating an impaired skin barrier, (II) exposing treated and untreated skin to nickel alone, and (III) in co-exposure with cobalt and chromium.

METHODS

Using full-thickness skin from stillborn piglets, in vitro experiments were conducted to assess retention of metals in skin at conditions mimicking intense hand hygiene practices. Treatment of skin with varying concentrations of sodium lauryl sulphate (SLS), to impair its barrier integrity was assessed. This was followed by exposure of treated and untreated skin to the metals, that were dissolved in Milli-Q water, 0.5% SLS, and ethanol respectively.

RESULTS

Results showed that pre-treatment with 5% SLS impaired the skin barrier with regards to the measure of trans epidermal water loss (TEWL). Metal amounts retained in the skin were generally higher in treated than untreated skin. The highest amounts of metal retained in skin were observed for exposure to nickel in ethanol. Co-exposure to nickel, cobalt, and chromium in 0.5% SLS resulted in the highest amounts of total metal retention.

CONCLUSIONS

The in vitro findings highlight the increased risk of metal retention in skin due to an impaired barrier. The SLS concentration used in the current study corresponds to those used in many hand hygiene products. Hence, occupational settings with frequent exposure to water, soap and disinfectants need to consider protective measures not only for the irritant exposures themselves but also simultaneous exposure to allergenic metals.

The Dreaded 3-Minute Wait: Does It Really Prevent Operating Room Fires? The IGNITE Trial

INTRODUCTION

Operating room fires can have devastating consequences and as such must be prevented. There exists a paucity of literature requiring further elucidation regarding manufacturer recommendations of a predefined waiting period prior to patient draping after using alcohol-based surgical antiseptics, in order to reduce the risk of operating room fires.

METHODS

This was further investigated by exposing two common alcohol-based surgical antiseptics to electrosurgery and open flames at various power settings and time intervals in an ex vivo porcine model. The simulated surgical site was prepped following manufacturer recommendations and exposed to monopolar electrosurgery at low and high power, using both PURE CUT and COAGULATION modes, and open flame, at 15-s increments after application.

RESULTS

While using PURE CUT mode at both low and high power, no ignition was observed on hairless surgical sites prepped with ChloraPrep® at any time point. However, use of COAGULATION mode at both low and high powers resulted in ignition consistently out to 1-min post-application. Additionally, if the prepped area subjectively appeared wet, especially with pooling of the antiseptic, both COAGULATION mode and open flame caused ignition. Dry time was found to be about 59 s for both prep solutions. It was also observed that the amount of pressure directly correlated with the amount of prep dispersed and increased dry times.

CONCLUSION

In conclusion, our data suggest an average dry time of less than 1-min, with ignition only observed when the antiseptic was visibly wet. Ignition did not occur on hairless skin with electrocautery on CUT mode using ChloraPrep at any time point. Additionally, ignition on hair-bearing skin was not observed past 3 min, with current manufacturer recommendations stating 1 h wait time for hair-bearing skin. Arbitrarily waiting a specific predetermined dry time until patient draping, as recommended by the manufacturers, may be unnecessary and lead to hours' worth of time wasted each year. Ongoing research will further investigate the utility of drying the antiseptic after application and its affect on not only preventing ignition but also antimicrobial efficacy.

3D Polymeric Lattice Microstructure-Based Microneedle Array for Transdermal Electrochemical Biosensing

Microneedles (MNs) or microneedle arrays (MNAs) are critical components of minimally invasive devices comprised of a single or a series of micro-scale projections. MNs can bypass the outermost layer of the skin and painlessly access microcirculation of the epidermis and dermis layers, attracting great interest in the development of personalized healthcare monitoring and diagnostic devices. However, MN technology has not yet reached its full potential since current micro- and nanofabrication methods do not address the need of fabricating MNs with complex surfaces to facilitate the development of clinically adequate devices. This work presents a new approach that combines 3D printing technology based on two-photon polymerization with soft lithography for cost-effective and time-saving fabrication of complex MNAs. Specifically, this method relies on printing complex 3D objects efficiently replicated into polymeric substrates via soft lithography, resulting in a free-standing polymeric lattice (PL) membrane that can be transferred onto gold-coated MNs and used for electrochemical biosensing. This platform shows excellent electrochemical performance in detecting metabolite (glucose) and protein (insulin) biomarkers with a dynamic linear range sufficient for detecting biomarkers in healthy individuals and patients. The approach holds great potential for fabricating next-generationMNs, including their transfer into clinically adequate devices.

Ex vivo SIM-AFM measurements reveal the spatial correlation of stiffness and molecular distributions in 3D living tissue

Living tissues each exhibit a distinct stiffness, which provides cells with key environmental cues that regulate their behaviors. Despite this significance, our understanding of the spatiotemporal dynamics and the biological roles of stiffness in three-dimensional tissues is currently limited due to a lack of appropriate measurement techniques. To address this issue, we propose a new method combining upright structured illumination microscopy (USIM) and atomic force microscopy (AFM) to obtain precisely coordinated stiffness maps and biomolecular fluorescence images of thick living tissue slices. Using mouse embryonic and adult skin as a representative tissue with mechanically heterogeneous structures inside, we validate the measurement principle of USIM-AFM. Live measurement of tissue stiffness distributions revealed the highly heterogeneous mechanical nature of skin, including nucleated/enucleated epithelium, mesenchyme, and hair follicle, as well as the role of collagens in maintaining its integrity. Furthermore, quantitative analysis comparing stiffness distributions in live tissue samples with those in preserved tissues, including formalin-fixed and cryopreserved tissue samples, unveiled the distinct impacts of preservation processes on tissue stiffness patterns. This series of experiments highlights the importance of live mechanical testing of tissue-scale samples to accurately capture the true spatiotemporal variations in mechanical properties. Our USIM-AFM technique provides a new methodology to reveal the dynamic nature of tissue stiffness and its correlation with biomolecular distributions in live tissues and thus could serve as a technical basis for exploring tissue-scale mechanobiology. STATEMENT OF SIGNIFICANCE: Stiffness, a simple mechanical parameter, has drawn attention in understanding the mechanobiological principles underlying the homeostasis and pathology of living tissues. To explore tissue-scale mechanobiology, we propose a technique integrating an upright structured illumination microscope and an atomic force microscope. This technique enables live measurements of stiffness distribution and fluorescent observation of thick living tissue slices. Experiments revealed the highly heterogeneous mechanical nature of mouse embryonic and adult skin in three dimensions and the previously unnoticed influences of preservation techniques on the mechanical properties of tissue at microscopic resolution. This study provides a new technical platform for live stiffness measurement and biomolecular observation of tissue-scale samples with micron-scale resolution, thus contributing to future studies of tissue- and organ-scale mechanobiology.

Retinol semisolid preparations in cosmetics: transcutaneous permeation mechanism and behaviour

Retinol is widely used to treat skin ageing because of its effect on cell differentiation, proliferation and apoptosis. However, its potential benefits appear to be limited by its skin permeability. Herein, we investigated the transcutaneous behavior of retinol in semisolid cosmetics, in both in vitro and in vivo experiments. In vitro experiments used the modified Franz diffusion cell combined with Raman spectroscopy. In in vivo experiments, the content of retinol in rat skin and plasma was detected with HPLC. Retinol in semisolid cosmetics was mainly concentrated in the stratum corneum in the skin of the three animal models tested, and in any case did not cross the skin barrier after a 24 h dermatologic topical treatment in Franz diffusion cells tests. Similar results were obtained in live mice and rats, where retinol did not cross the skin barrier and did not enter the blood circulation. Raman spectroscopy was used to test the penetration depth of retinol in skin, which reached 16 μm out of 34 μm in pig skin, whereas the skin of mouse and rat showed too strong bakground interference. To explore epidermal transport mechanism and intradermal residence, skin transcriptomics was performed in rats, which identified 126 genes upregulated related to retinol transport and metabolism, relevant to the search terms "retinoid metabolic process" and "transporter activity". The identity of these upregulated genes suggests that the mechanism of retinol action is linked to epidermis, skin, tissue and epithelium development.

Characterising Skin Electrical Impedance Using Tape Stripping Methods: A Bioelectrical Study of a Porcine Model

Background Recent advancements in ultra-low power electronics and wireless devices have facilitated the widespread adoption of wearable technology for fitness and health monitoring, paving the way for personalized medicine. Microneedle-based devices, comprising small epidermal patches that penetrate the skin's stratum corneum to potentially access biomarkers in the extracellular fluid of the viable epidermis, represent a promising innovation in this field. Objectives This project aimed to develop and validate a novel method to evaluate microneedle engagement in the skin in real-time. To our knowledge, there are no studies published to date that have characterized the electrical impedance of stratum corneum and epidermis using the tape stripping method to selectively remove cell layers. Additionally, no studies have been published comparing the electrical impedance of fresh to frozen-thawed porcine skin. The objective of this study was to develop and validate a novel method to evaluate microneedle engagement in skin, in real-time, that does not require processing of the tissue. Methods A tape stripping technique was employed to selectively remove the stratum corneum from fresh and frozen-thawed porcine skin samples which were then electrically characterized using an excitation frequency of 5 kHz with a peak Voltage of 1 V. Results This study demonstrated a mean impedance reduction of 97.08 ± 1.3 % for fresh porcine skin, and 98.04 ± 0.3 % for frozen-thawed porcine skin when transitioning from the surface stratum corneum to the viable epidermis. The correlation between the reduction of impedance and the number of tape strips across all 18 test sites was significant (r = 0.98, p < 0.00001). However, comparing the skin impedance of the fresh and frozen-thawed specimens showed poor equivalence, with the frozen-thawed sites approximately 5.5 times the impedance of the fresh sites before any tape stripping, and 4.19 times greater after 30 tape strips. Conclusions These findings suggest that monitoring for an interelectrode impedance decrease of greater than 95% between two projections of a microneedle device could provide a rapid and effective evaluation of skin engagement, crucial for advancing the development and clinical application of microneedle-based technologies in personalized medicine. The study also underscores the impact of the freeze-thaw process on the mechanical and electrical properties of skin, which is crucial for standardizing testing protocols.

Wireless and Battery-Free Sensor for Interstitial Fluid Pressure Monitoring

Congestive heart failure (CHF) is a fatal disease with progressive severity and no cure; the heart's inability to adequately pump blood leads to fluid accumulation and frequent hospital readmissions after initial treatments. Therefore, it is imperative to continuously monitor CHF patients during its early stages to slow its progression and enable timely medical interventions for optimal treatment. An increase in interstitial fluid pressure (IFP) is indicative of acute CHF exacerbation, making IFP a viable biomarker for predicting upcoming CHF if continuously monitored. In this paper, we present an inductor-capacitor (LC) sensor for subcutaneous wireless and continuous IFP monitoring. The sensor is composed of inexpensive planar copper coils defined by a simple craft cutter, which serves as both the inductor and capacitor. Because of its sensing mechanism, the sensor does not require batteries and can wirelessly transmit pressure information. The sensor has a low-profile form factor for subcutaneous implantation and can communicate with a readout device through 4 layers of skin (12.7 mm thick in total). With a soft silicone rubber as the dielectric material between the copper coils, the sensor demonstrates an average sensitivity as high as -8.03 MHz/mmHg during in vitro simulations.

In vitro biomechanical properties of porcine perineal tissues to better understand human perineal tears during delivery

INTRODUCTION

Data concerning the mechanical properties of the perineum during delivery are very limited. In vivo experiments raise ethical issues. The aim of the study was to describe some of the biomechanical properties of each perineal tissue layer collected from sows in order to better understand perineal tears during childbirth.

MATERIAL AND METHODS

Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS), and the anal mucosa of fresh dead sows. They were tested in quasi-static uniaxial tension using the testing machine Mach-1®. Tests were performed at a displacement velocity of 0.1 mm·s-1. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled using a hyperelastic Yeoh model described by three coefficients: C1, C2, and C3. Pearson correlation coefficients were calculated to measure the correlation between the C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture for each perineal tissue layer. Pearson correlation was computed between C1 and the number of microfailures before complete rupture for each tissue.

RESULTS

Ten samples of each perineal tissue layer were analyzed. Mean values of C1 and corresponding standard deviations were 46 ± 15, 165 ± 60, 27 ± 10, 19 ± 13, 145 ± 28 kPa for the perineal skin, the vagina, the EAS, the IAS, and the anal mucosa, respectively. According to this same sample order, the first microfailure in the population of 10 sows appeared at an average of 54%, 27%, 70%, 131%, and 22% of strain. A correlation was found between C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture (r = 0.7, p = 0.02) or the number of microfailures before complete rupture only for the vagina (r = 0.7, p = 0.02).

CONCLUSIONS

In this population of fresh dead sow's perineum, the vagina and the anal mucosa were the stiffest tissues. The IAS and EAS were more extensible and less stiff. A significantly positive correlation was found between C1 and the duration between the first microfailure and the complete rupture of the vagina, and the duration between the first microfailure and the complete rupture of the vagina.

Diagnostic, Therapeutic, and Theranostic Multifunctional Microneedles

Microneedles (MNs) have maintained their popularity in therapeutic and diagnostic medical applications throughout the past decade. MNs are originally designed to gently puncture the stratum corneum layer of the skin and have lately evolved into intelligent devices with functions including bodily fluid extraction, biosensing, and drug administration. MNs offer limited invasiveness, ease of application, and minimal discomfort. Initially manufactured solely from metals, MNs are now available in polymer-based varieties. MNs can be used to create systems that deliver drugs and chemicals uniformly, collect bodily fluids, and are stimulus-sensitive. Although these advancements are favorable in terms of biocompatibility and production costs, they are insufficient for the therapeutic use of MNs. This is the first comprehensive review that discusses individual MN functions toward the evolution and development of smart and multifunctional MNs for a variety of novel and impactful future applications. The study examines fabrication techniques, application purposes, and experimental details of MN constructs that perform multiple functions concurrently, including sensing, drug-molecule release, sampling, and remote communication capabilities. It is highly likely that in the near future, MN-based smart devices will be a useful and important component of standard medical practice for different applications.

Towards the biomechanical modelling of the behaviour of ex-vivo porcine perineal tissues

The perineum is a layered soft tissue structure with mechanical properties that maintain the integrity of the pelvic floor. During childbirth, the perineum undergoes significant deformation that often results in tears of various degrees of severity. To better understand the mechanisms underlying perineal tears, it is crucial to consider the mechanical properties of the different tissues that make up the perineum. Unfortunately, there is a lack of data on the mechanical properties of the perineum in the literature. The objective of this study is to partly fill these gaps. Hence sow perineums were dissected and the five perineal tissues involved in tears were characterized by uniaxial tension tests: Skin, Vagina, External Anal Sphincter, Internal Anal Sphincter and Anal Mucosa. From our knowledge, this study is the first to investigate all these tissues and to design a testing protocol to characterize their material properties. Six material models were used to fit the experimental data and the correlation between experimental and predicted data was evaluated for comparison. As a result, even if the tissues are of different nature, the best correlation was obtained with the Yeoh and Martins material models for all tissues. Moreover, these preliminary results show the difference in stiffness between the tissues which indicates that they might have different roles in the structure. These obtained results will serve as a basis to design an improved experimental protocol for a more robust structural model of the porcine perineum that can be used for the human perineum to predict perineal tears.

Diphoterine, an amphoteric rinsing solution, reduces hydrofluoric acid injuries in an ex vivo pigskin model

Hydrofluoric acid (HF) is a ubiquitous industrial chemical that is particularly hazardous because of the potential for systemic effects and the induction of severe cutaneous necrosis after contact with the skin. Minimizing skin injury requires decontaminating the affected area promptly with an emergency rinsing solution. Few experimental studies have objectively characterized rinsing solutions such as Diphoterine (DP). Here we develop an ex vivo pigskin model to study and compare the efficacy of rinsing solutions as initial decontaminating agents to stop the progression of skin lesions after HF splashing. The pigskin model shows an immediate local response to HF at varying concentrations and exposure times. We then exposed the pigskin biopsies to 3.75% HF for 1 min and rinsed them with different solutions, including water, 0.9% NaCl solution (saline), 10% calcium gluconate (CaG), Hexafluorine (HXF), and DP. We found DP to be a more effective agent for decontaminating HF lesions than water, saline, and CaG. DP had a similar efficacy as HXF, an emergency rinsing solution used specifically for decontaminating HF-exposed skin. This study shows that skin exposed to HF must be treated quickly from the first minute of exposure.

Wearable Microneedle Patch for Transdermal Electrochemical Monitoring of Urea in Interstitial Fluid

Microneedle-based wearable electrochemical biosensors are the new frontier in personalized health monitoring and disease diagnostic devices that provide an alternative tool to traditional blood-based invasive techniques. Advancements in micro- and nanofabrication technologies enabled the fabrication of microneedles using different biomaterials and morphological features with the aim of overcoming existing challenges and enhancing sensing performance. In this work, we report a microneedle array featuring conductive recessed microcavities for monitoring urea levels in the interstitial fluid of the skin. Microcavities are small pockets on the tip of each microneedle that can accommodate the sensing layer, provide protection from delamination during skin insertion or removal, and position the sensing layer in a deep layer of the skin to reach the interstitial fluid. The wearable urea patch has shown to be highly sensitive and selective in monitoring urea, with a sensitivity of 2.5 mV mM-1 and a linear range of 3 to 18 mM making it suitable for monitoring urea levels in healthy individuals and patients. Our ex vivo experiments have shown that recessed microcavities can protect the sensing layer from delamination during skin insertion and monitor changing urea levels in interstitial fluid. This biocompatible platform provides alternative solutions to the critical issue of maintaining the performance of the biosensor upon skin insertion and holds great potential for advancing transdermal sensor technology.

Multi-Modal Spectroscopic Assessment of Skin Hydration

Human skin acts as a protective barrier, preserving bodily functions and regulating water loss. Disruption to the skin barrier can lead to skin conditions and diseases, emphasizing the need for skin hydration monitoring. The gold-standard sensing method for assessing skin hydration is the Corneometer, monitoring the skin's electrical properties. It relies on measuring capacitance and has the advantage of precisely detecting a wide range of hydration levels within the skin's superficial layer. However, measurement errors due to its front end requiring contact with the skin, combined with the bipolar configuration of the electrodes used and discrepancies due to variations in various interfering analytes, often result in significant inaccuracy and a need to perform measurements under controlled conditions. To overcome these issues, we explore the merits of a different approach to sensing electrical properties, namely, a tetrapolar bioimpedance sensing approach, with the merits of a novel optical sensing modality. Tetrapolar bioimpedance allows for the elimination of bipolar measurement errors, and optical spectroscopy allows for the identification of skin water absorption peaks at wavelengths of 970 nm and 1450 nm. Employing both electrical and optical sensing modalities through a multimodal approach enhances skin hydration measurement sensitivity and validity. This layered approach may be particularly beneficial for minimising errors, providing a more robust and comprehensive tool for skin hydration assessment. An ex vivo desorption experiment was carried out on fresh porcine skin, and an in vivo indicative case study was conducted utilising the developed optical and bioimpedance sensing devices. Expected outcomes were expressed from both techniques, with an increase in the output of the optical sensor voltage and a decrease in bioimpedance as skin hydration decreased. MLR models were employed, and the results presented strong correlations (R-squared = 0.996 and p-value = 6.45 × 10-21), with an enhanced outcome for hydration parameters when both modalities were combined as opposed to independently, highlighting the advantage of the multimodal sensing approach for skin hydration assessment.

Design and Evaluation of a Spoke-Based Double-Lumen Pediatric Gastrostomy Tube

Gastrostomy tubes (G-tubes) are the gold standard for feeding assistance for children with feeding dysfunction. Current G-tubes pose complications that interrupt the delivery of feed, including tube displacement and difficulty of at-home use. This study details an alternative, spoke-based, double-lumen G-tube design and preliminary validation of its function and usability. Pull force testing was performed on spoke G-tube models across three sizes and two classifications (hard/soft). Preliminary models were evaluated against market standards. Though the pull force of the spoke model was found to be lower than that of both market standards, hard modifications to the spoke model improved retentive force. Ease of use was tested amongst users unfamiliar with G-tube placement. The spoke design required 12.3 ± 4.7 s to deploy, less than half the time required for market standards. However, balloon G-tubes were still perceived to be easiest to use by 70% of participants, with indications that a spoke design may be easier to use if sized similarly to current G-tubes, with auxiliary improvements to factors such as grip. While there is a need for improvements in the material properties and manufacturing of the proposed design, this study provides early validation of the potential to address complications of existing G-tubes.

Assessment of needle-tissue force models based on ex vivo measurements

Needle insertion is one of the most common procedures in clinical practice. Existing statistics reveal that success rates of needle insertions can be low, leading to potential complications and patient discomfort. Real-time imaging techniques like ultrasound and X-ray can assist in improving precision, but even experienced practitioners may face challenges in visualizing the needle tip. Researchers have proposed models of force interactions during needle insertions into biological tissue to enhance accuracy. This article presents an evaluation of the forces acting on intravenous needles during insertion into skin. The aim was to explore mathematical models, compare them with data from tests on animal specimens, and select the most suitable model for future research. The experimental setup involved conducting needle insertion tests on animal-originated cadavers, using the Brucker Universal Mechanical Tester device, which measured the force response during vertical movement of the needle. The research was divided into 2 stages. In Stage I, force measurements were recorded for both the insertion and extraction phases of the hypodermic needles. The measurements were conducted for several different needle sizes, speed and insertion angles. In Stage II, five different models were examined to determine how well they matched the experimental data. Based on the analysis of fit quality coefficients, the Gordon's exponential model was identified as the best fit to the measured data. The influence of needle size, insertion angle, and insertion speed on the measured force values was confirmed. Different insertion speeds revealed the viscoelastic properties of the tested samples. The presence of the skin layer affected the puncture force and force values for subsequent layers.

The morphology of the interfacial tissue between bighorn sheep horn and bony horncore increases contact surface to enhance strength and facilitate load transfer from the horn to the horncore

The horns of bighorn sheep rams are permanent cranial appendages used for high energy head-to-head impacts during interspecific combat. The horns attach to the underlying bony horncore by a layer of interfacial tissue that facilitates load transfer between the impacted horn and underlying horncore, which has been shown to absorb substantial energy during head impact. However, the morphology and mechanical properties of the interfacial tissue were previously unknown. Histomorphometry was used to quantify the interfacial tissue composition and morphology and lap-shear testing was used to quantify its mechanical properties. Histological analyses revealed the interfacial tissue is a complex network of collagen and keratin fibers, with collagen being the most abundant protein. Sharpey's fibers provide strong attachment between the interfacial tissue and horncore bone. The inner horn surface displayed microscopic porosity and branching digitations which increased the contact surface with the interfacial tissue by approximately 3-fold. Horn-horncore samples tested by lap-shear loading failed primarily at the horn surface, and the interfacial tissue displayed non-linear strain hardening behavior similar to other soft tissues. The elastic properties of the interfacial tissue (i.e., low- and high-strain shear moduli) were comparable to previously measured values for the equine laminar junction. The interfacial tissue contact surface was positively correlated with the interfacial tissue shear strength (1.23 ± 0.21 MPa), high-strain shear modulus (4.5 ± 0.7 MPa), and strain energy density (0.38 ± 0.07 MJ/m3). STATEMENT OF SIGNIFICANCE: The bony horncore in bighorn sheep rams absorbs energy to reduce brain cavity accelerations and mitigate brain injury during head butting. The interfacial zone between the horn and horncore transfers energy from the impacted horn to the energy absorbing horncore but has been largely neglected in previous models of bighorn sheep ramming since interfacial tissue properties were previously unknown. This study quantified the morphology and mechanical properties of the horn-horncore interfacial tissue to better understand structure-property relationships that contribute to energy transfer during ramming. Results from this study will improve models of bighorn sheep ramming used to study mechanisms of brain injury mitigation and may inspire novel materials and structures for brain injury prevention in humans.

Development of hyaluronic acid-silica composites via in situ precipitation for improved penetration efficiency in fast-dissolving microneedle systems

Fast-dissolving microneedles (DMNs) hold significant promise for transdermal drug delivery, offering improved patient compliance, biocompatibility, and functional adaptability for various therapeutic purposes. However, the mechanical strength of the biodegradable polymers used in DMNs often proves insufficient for effective penetration into human skin, especially under high humidity conditions. While many composite strategies have been developed to reinforce polymer-based DMNs, simple mixing of the reinforcements with polymers often results in ineffective penetration due to inhomogeneous dispersion of the reinforcements and the formation of undesired micropores. In response to this challenge, this study aimed to enhance the mechanical performance of hyaluronic acid (HA)-based microneedles (MNs), one of the most commonly used DMN systems. We introduced in situ precipitation of silica nanoparticles (Si) into the HA matrix in conjunction with conventional micromolding. The precipitated silica nanoparticles were uniformly distributed, forming an interconnected network within the HA matrix. Experimental results demonstrated that the mechanical properties of the HA-Si composite MNs with up to 20 vol% Si significantly improved, leading to higher penetration efficiency compared to pure HA MNs, while maintaining structural integrity without any critical defects. The composite MNs also showed reduced degradation rates and preserved their drug delivery capabilities and biocompatibility. Thus, the developed HA-Si composite MNs present a promising solution for efficient transdermal drug delivery and address the mechanical limitations inherent in DMN systems. STATEMENT OF SIGNIFICANCE: HA-Si composite dissolving microneedle (DMN) systems were successfully fabricated through in situ precipitation and conventional micromolding processes. The precipitated silica nanoparticles formed an interconnected network within the HA matrix, ranging in size from 25 to 230 nm. The optimal silica content for HA-Si composite MN systems should be up to 20 % by volume to maintain structural integrity and mechanical properties. HA-Si composite MNs with up to 20 % Si showed improved penetration efficiency and reduced degradation rates compared to pure HA MNs, thereby expanding the operational window. The HA-Si composite MNs retained good drug delivery capabilities and biocompatibility.

Ex vivo transdermal delivery of 3H-labelled atovaquone solid drug nanoparticles: a comparison of topical, intradermal injection and microneedle assisted administration

Inherent barrier properties of the skin impose significant challenges to the transdermal delivery of drugs to systemic circulation. Here, the ex vivo transdermal permeation and deposition of an anti-malarial prophylactic atovaquone solid drug nanoformulation is radiometrically evaluated following application of a solid microneedle format.

Liposome-loaded polymeric microneedles for enhanced skin deposition of rifampicin

Methicillin-resistant Staphylococcus aureus (MRSA) is a prevailing bacterial pathogen linked to superficial skin and soft tissue infections (SSTIs). Rifampicin (RIF), a potent antibiotic against systemic and localised staphylococcal infections, faces limitations due to its low solubility. This constraint hampers its therapeutic potential for MRSA-induced SSTIs. To address this, an advanced liposomal system was designed for efficient dermal RIF delivery. Rifampicin-loaded liposomes (LipoRIF) were embedded within polymeric dissolving microneedles (DMNs) to enable targeted intradermal drug delivery. A robust Design of Experiment (DoE) methodology guided the systematic preparation and optimisation of LipoRIF formulations. The optimal LipoRIF formulation integrated within polymeric DMNs. These LipoRIF-DMNs exhibited favourable mechanical properties and effective skin insertion characteristics. Notably, in vitro assays on skin deposition unveiled a transformative result - the DMN platform significantly enhanced LipoRIF deposition within the skin, surpassing LipoRIF dispersion alone. Moreover, LipoRIF-DMNs displayed minimal cytotoxicity toward cells. Encouragingly, rigorous in vitro antimicrobial evaluations demonstrated LipoRIF-DMNs' capacity to inhibit MRSA growth compared to the control group. LipoRIF-DMNs propose a potentially enhanced, minimally invasive approach to effectively manage SSTIs and superficial skin ailments stemming from MRSA infections.

Strengthening the Key Features of Volumizing Fillers: Projection Capacity and Long-Term Persistence

Volumizing fillers aim to create or restore facial volume in fat layers. To provide strong tissue lifting and long-term persistence, gels are generally designed with stiff properties, characterized by a high storage modulus (G'). However, clinical evidence shows a discrepancy between high G' and good lifting capacities, especially after skin tension has been exerted on the gel. To better explore the in vivo behavior of a gel, we first evaluated the elastic moduli of five commercial volumizers (RHA4, JUVVOL, RESVOL, RESLYFT, and BELVOL) in dynamic compression mode, E'. We further developed a Projection Index score based on the rheological assessment of creep in compression to mimic skin tension-induced stress relaxation (flattening). Finally, the ability of a gel to resist enzymatic degradation was analyzed with a multidose approach. Despite similar clinical indications, volumizers exhibited distinct behaviors. RHA4 and BELVOL showed the highest E' values (resistance to strain), RHA4, JUVVOL, and RESVOL exhibited the greatest projection capacities, while JUVVOL and RHA4 offered the largest persistence to enzymatic degradation. In this article, we introduce the use of the Projection Index to efficiently assess the ability of a gel to lift tissues, thus increasing preclinical models' efficiency and reducing the need for animal studies.

Amino acid buffered hypochlorite facilitates debridement of porcine infected burn wounds

INTRODUCTION

Removal of necrotic tissue is a vital step in the treatment of full-thickness burn wounds, with surgical debridement being the most effective method. Since minor burn wounds are typically treated on an outpatient basis where surgical capabilities can be limited there is a need for alternative treatment options. In this study we aim to evaluate the use of amino acid buffered hypochlorite (AABH) as a chemical enhancement for wound debridement in a porcine infected burn wound model.

METHOD

A total of 60 full-thickness burn wounds, 3 cm in diameter, were created on four pigs using a standardized burn device. The wounds were inoculated with 107 colony-forming units (CFU) of S. aureus. The experimental groups included wounds debrided with a plastic curette, wounds debrided after pretreatment with AABH, and control wounds wiped with gauze. Wounds were treated twice per week for three weeks. Debridement, healing, and infection parameters were evaluated over time.

RESULTS

After one week, but not after two and three weeks, the curette and AABH groups had higher debrided weights compared to control (p < 0.05). Percentage of wound area adequately cleared from necrotic tissue was higher in the AABH-group compared to the curette-group and control, after one week. The earliest healing was measured in the AABH group after two weeks (5 % of wounds), which also had the most healed wounds after three weeks (55 %). In both the AABH and the curette groups, bacterial load had fallen below 105 CFU/g after two weeks. No CFU were detectable in the AABH group after three weeks. The AABH-group was also the easiest to debride.

CONCLUSION

Our results indicate that AABH facilitates wound debridement and could be a helpful addition to an effective treatment modality for removal of necrotic tissue in full-thickness burns.

Distinguishing between stamping in blood from walking through blood using blood pattern analysis

Bloodstains are typically encountered in violent incidents involving the use of a weapon or physical actions, such as punching, kicking, or stamping. Bloodstain pattern analysis can provide inceptive evidence or intelligence about what happened in an alleged incident, the sequence of events, along with indicating possible suspects if blood is analysed through DNA profiling. This research project focused on the differences in patterns created on footwear during a violent action, such as stamping on a person, and a non-violent action, such as walking through a pool of blood. In this project, several experiments were designed to simulate the stamping and walking actions on a surface wet with blood: carpet, lino flooring, and belly pork meat. Two volunteers with varying body weights were recruited to perform the two actions, using a pair of trainers and a pair of Wellington boots. Defibrinated horse blood was used to simulate real human blood. It was found that the patterns created from stamping and walking through blood differed by the type of pattern and the number and size of stains. The footwear used in the stamping action was characterised by a larger contact stain on the sole than those used in the walking actions: ∼209 mm in length by ∼92 mm in width versus ∼65 mm in length by ∼60 mm in width. The stamping action produced a large number of impact spatters (∼435) on the sides of the footwear versus no impact spatters in the walking actions. The presence of impact spatters was found to be the most prominent feature that differentiated between the two actions. The findings were statistically significant (p < 0.05) and could assist in evaluating whether a defendant was actively involved in a stamping action, or the evidence found was due to innocent reasons.

The Development of Nonthermal Plasma and Tirapazamine as a Novel Combination Therapy to Treat Melanoma In Situ

Although melanoma accounts for only 5.3% of skin cancer, it results in >75% of skin-cancer-related deaths. To avoid disfiguring surgeries on the head and neck associated with surgical excision, there is a clear unmet need for other strategies to selectively remove cutaneous melanoma lesions. Mohs surgery is the current treatment for cutaneous melanoma lesions and squamous and basal cell carcinoma. While Mohs surgery is an effective way to remove melanomas in situ, normal tissue is also excised to achieve histologically negative margins. This paper describes a novel combination therapy of nonthermal plasma (NTP) which emits a multitude of reactive oxygen species (ROS) and the injection of a pharmaceutical agent. We have shown that the effects of NTP are augmented by the DNA-damaging prodrug, tirapazamine (TPZ), which becomes a free radical only in conditions of hypoxemia, which is often enhanced in the tumor microenvironment. In this study, we demonstrate the efficacy of the combination therapy through experiments with B16-F10 and 1205 Lu metastatic melanoma cells both in vitro and in vivo. We also show the safety parameters of the therapy with no significant effects of the therapy when applied to porcine skin. We show the need for the intratumor delivery of TPZ in combination with the surface treatment of NTP and present a model of a medical device to deliver this combination therapy. The importance of functional gap junctions is indicated as a mechanism to promote the therapeutic effect. Collectively, the data support a novel therapeutic combination to treat melanoma and the development of a medical device to deliver the treatment in situ.

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.

Physicochemical and in vitro biological evaluation of an injectable self-healing quaternized chitosan/oxidized pectin hydrogel for potential use as a wound dressing material

Injectable self-healing hydrogels are attractive materials for use as wound dressings. To prepare such hydrogels, the current study used quaternized chitosan (QCS) to improve the solubility and antibacterial activity and oxidized pectin (OPEC) to introduce aldehyde groups for Schiff's base reaction with the amine groups from QCS. Self-healing hydrogels were made by co-injection of polymer solutions at specific polymer concentrations and reagent ratios that optimized both Schiff's base reactions and ionic interactions. The optimal hydrogel displayed self-healing 30 min after cutting and continuous self-healing during continuous step strain analysis, rapid gelation (< 1 min), a storage modulus of 394 Pa, and hardness of 700 mN, and compressibility of 162 mN s. The adhesiveness of this hydrogel (133 Pa) was within a suitable range for application as a wound dressing. The extraction media from the hydrogel displayed no cytotoxicity to NCTC clone 929 cells and higher cell migration than the control. While the extraction media from the hydrogel was found not to have antibacterial properties, QCS was verified as having MIC50 of 0.04 mg/mL against both E. coli and S. aureus. Therefore, this injectable self-healing QCS/OPEC hydrogel has the potential use as a biocompatible hydrogel material for wound management.

Effect of massage on retinol skin penetration

Topical administration of active substances may be promoted by optimizing not only the vehicle formulation but also the application protocol. The formulation aspects are widely studied in the literature while a few works are dedicated to the development of application methods. In this context, we studied an application protocol usable as a part of skincare routine by investigating the effect of massage on the skin penetration of retinol. Retinol is a lipophilic molecule widely used as an anti-ageing firming agent in cosmetic formulations. Massage was applied to pig skin explants mounted to Franz diffusion cells after or before the deposit of the retinol-loaded formulation. Thetype of skin massage (roll or rotary type) and its duration were varied.The massage protocol had a significant influence on retinol skin penetration. Due to its highly lipophilic character, retinol accumulated into the stratum corneum but, depending on the massage protocol, a significant retinol concentration was obtained after 4 hours in epidermis and dermis layers. Results showed that the roll-type massage was significantly more efficient than the rotary process that exhibited little effect on retinol cutaneous penetration. Such results could be interesting for the development of massage devices in association with cosmetic formulations.

In vivo tests of a novel wound dressing based on agar aerogel

Aerogels, especially bio-based ones, present a promising option for wound dressing; specifically, because of their low toxicity, high stability, bio-compatibility, and good biological performance. In this study, agar aerogel was prepared and evaluated as novel wound dressing material in an in vivo rat study. Agar hydrogel was prepared by thermal gelation, after that the water inside the gel was exchanged with ethanol, and finally the alcogel was dried by supercritical CO₂. The textural and rheological properties of the prepared aerogel were characterized, showing that the prepared agar aerogels possess high porosity (97-98 %), high surface area (250-330 m²g^-1) as well as good mechanical properties and easiness of removal from the wound site. The results of the in vivo experiments macroscopically demonstrate the tissue compatibility of the aerogels in dorsal interscapular injured rat tissue and a shorter wound healing time comparable to that of gauze-treated animals. The histological analysis underpins the reorganisation and healing of the tissue for the injured skin of rats treated with agar aerogel wound dressing within the studied time frame.

Skin-Based Vaccination: A Systematic Mapping Review of the Types of Vaccines and Methods Used and Immunity and Protection Elicited in Pigs

The advantages of skin-based vaccination include induction of strong immunity, dose-sparing, and ease of administration. Several technologies for skin-based immunisation in humans are being developed to maximise these key advantages. This route is more conventionally used in veterinary medicine. Skin-based vaccination of pigs is of high relevance due to their anatomical, physiological, and immunological similarities to humans, as well as being a source of zoonotic diseases and their livestock value. We conducted a systematic mapping review, focusing on vaccine-induced immunity and safety after the skin immunisation of pigs. Veterinary vaccines, specifically anti-viral vaccines, predominated in the literature. The safe and potent skin administration to pigs of adjuvanted vaccines, particularly emulsions, are frequently documented. Multiple methods of skin immunisation exist; however, there is a lack of consistent terminology and accurate descriptions of the route and device. Antibody responses, compared to other immune correlates, are most frequently reported. There is a lack of research on the underlying mechanisms of action and breadth of responses. Nevertheless, encouraging results, both in safety and immunogenicity, were observed after skin vaccination that were often comparable to or superior the intramuscular route. Further research in this area will underlie the development of enhanced skin vaccine strategies for pigs, other animals and humans.

Assessment of penetration and permeation of caffeine by confocal Raman spectroscopy in vivo and ex vivo by tape stripping

OBJECTIVE

Tape stripping is an often-used non-invasive destructive method to investigate the skin penetration of a substance. In recent years, however, the suitability of confocal Raman spectroscopy (CRS) as a non-invasive method of non-destructive examination of the skin has become increasingly apparent. In this study, we compared invasion and depletion penetration and permeation kinetics of a 2% caffeine solution with and without 1,2-pentanediol as a penetration enhancer measured with CRS and tape stripping.

METHODS

Porcine skin was used for tape stripping and human skin for CRS. 2% caffeine solution was applied to the skin for different incubation times. Human skin was then examined by CRS while caffeine was extracted from porcine skin and quantified via reverse-phase HPLC. Fluxes were also measured and calculated by sum of the total amounts of caffeine penetrated into the skin.

RESULTS

Without penetration enhancers, there is hardly any difference between the penetration profiles of the two measurement methods for invasion, but the curves for depletion are different. Furthermore, the calculated flux values for the invasion are almost identical, but for the depletion the tape stripping values are about twice as high as the CRS values.

CONCLUSION

The relevance of conducting invasion and depletion studies became clear and was able to show the still existing problems in the comparability of CRS and tape stripping.

Ultrathin Hydrogel Films toward Breathable Skin-Integrated Electronics

On-skin electronics that offer revolutionary capabilities in personalized diagnosis, therapeutics, and human-machine interfaces require seamless integration between the skin and electronics. A common question remains whether an ideal interface can be introduced to directly bridge thin-film electronics with the soft skin, allowing the skin to breathe freely and the skin-integrated electronics to function stably. Here, an ever-thinnest hydrogel is reported that is compliant to the glyphic lines and subtle minutiae on the skin without forming air gaps, produced by a facile cold-lamination method. The hydrogels exhibit high water-vapor permeability, allowing nearly unimpeded transepidermal water loss and free breathing of the skin underneath. Hydrogel-interfaced flexible (opto)electronics without causing skin irritation or accelerated device performance deterioration are demonstrated. The long-term applicability is recorded for over one week. With combined features of extreme mechanical compliance, high permeability, and biocompatibility, the ultrathin hydrogel interface promotes the general applicability of skin-integrated electronics.

An Elastic and Damage-Tolerant Dry Epidermal Patch with Robust Skin Adhesion for Bioelectronic Interfacing

On-skin patches that record biopotential and biomechanical signals are essential for wearable healthcare monitoring, clinical treatment, and human-machine interaction. To acquire wearing comfort and high-quality signals, patches with tissue-like softness, elastic recovery, damage tolerance, and robust bioelectronic interface are highly desired yet challenging to achieve. Here, we report a dry epidermal patch made from a supramolecular polymer (SESA) and an in situ transferred carbon nanotubes' percolation network. The polymer possesses a hybrid structure of copolymerized permanent scaffold permeated by multiple dynamic interactions, which imparts a desired mechanical response transition from elastic recoil to energy dissipation with increased elongation. Such SESA-based patches are soft (Young's modulus ∼0.1 MPa) and elastic within physiologically relevant strain levels (97% elastic recovery at 50% tensile strain), intrinsically mechanical-electrical damage-resilient (∼90% restoration from damage after 5 min), and interference-immune in dynamic signal acquisition (stretch, underwater, sweat). We demonstrate its versatile physiological sensing applications, including electrocardiogram recording under various disturbances, machine-learning-enabled hand-gesture recognition through electromyogram measurement, subtle radial artery pulse, and drastic knee kinematics sensing. This epidermal patch offers a promising noninvasive, long-duration, and ambulant bioelectronic interfacing with anti-interference robustness.

Effect of microneedles shape on skin penetration and transdermal drug administration

Microneedle (MN) patches are highly efficient and versatile tools for transdermal drug administration, in particular for pain-free, self-medication and rapid local applications. Diffraction ultraviolet (UV) light lithography offers an advanced method in fabricating poly(ethylene glycol)-based MNs with different shapes, by changing both the UV-light exposure time and photomask design. The exposure time interval is limited at obtaining conical structures with aspect ratio < 1:3, otherwise MNs exhibit reduced fracture load and poor indentation ability, not suitable for practical application. Therefore, this work is focused on a systematic analysis of the MN's base shapes effects on the structural characteristics, skin penetration and drug delivery. Analyzing four different base shapes (circle, triangle, square and star), it has been found that the number of vertices in the polygon base heavily affects these properties. The star-like MNs reveal the most efficient skin penetration ability (equal to 40 % of -their length), due to the edges action on the skin during the perforation. Furthermore, the quantification of the drug delivered by the MNs through ex-vivo porcine skin shows that the amounts of small molecules released over 24 h by star-like MNs coated by local anesthetic (Lidocaine) and an anti-inflammatory (Diclofenac epolamine) drugs are 1.5× and 2× higher than the circular-MNs, respectively.

Injectable Hybrid-Crosslinked Hydrogels as Fatigue-Resistant and Shape-Stable Skin Depots

Injectable hydrogels have gained considerable attention, but they are typically mechanically weak and subject to repeated physiological stresses in the body. Herein, we prepared polyurethane diacrylate (EPC-DA) hydrogels, which are injectable and can be photocrosslinked into fatigue-resistant implants. The mechanical properties can be tuned by changing photocrosslinking conditions, and the hybrid-crosslinked EPC-DA hydrogels exhibited high stability and sustained release properties. In contrast to common injectable hydrogels, EPC-DA hydrogels exhibited excellent antifatigue properties with >90% recovery during cyclic compression tests and showed shape stability after application of force and immersion in an aqueous buffer for 35 days. The EPC-DA hydrogel formed a shape-stable hydrogel depot in an ex vivo porcine skin model, with establishment of a temporary soft gel before in situ fixing by UV crosslinking. Hybrid crosslinking using injectable polymeric micelles or nanoparticles may be a general strategy for producing hydrogel implants resistant to physiological stresses.

A 3D-printed transepidermal microprojection array for human skin microbiome sampling

Skin microbiome sampling is currently performed with tools such as swabs and tape strips to collect microbes from the skin surface. However, these conventional approaches may be unable to detect microbes deeper in the epidermis or in epidermal invaginations. We describe a sampling tool with a depth component, a transepidermal microprojection array (MPA), which captures microbial biomass from both the epidermal surface and deeper skin layers. We leveraged the rapid customizability of 3D printing to enable systematic optimization of MPA for human skin sampling. Evaluation of sampling efficacy on human scalp revealed the optimized MPA was comparable in sensitivity to swab and superior to tape strip, especially for nonstandard skin surfaces. We observed differences in species diversity, with the MPA detecting clinically relevant fungi more often than other approaches. This work delivers a tool in the complex field of skin microbiome sampling to potentially address gaps in our understanding of its role in health and disease.

Ciprofloxacin-loaded dissolving polymeric microneedles as a potential therapeutic for the treatment of S. aureus skin infections

Microneedles have been widely studied for many topical and transdermal therapeutics due to their ability to painlessly puncture the skin, thereby bypassing the stratum corneum, the main skin barrier. In this study, ciprofloxacin (CIP) was loaded into dissolving polymeric microneedles prepared by a two-layer centrifugation method as a potential treatment of skin infections such as cellulitis. The polymers used were polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). Two formulations were investigated, namely CIP_MN1, composed of 10 mg ciprofloxacin incorporated into a polymer matrix of PVA and PVP with a weight ratio of (9:1), and CIP_MN2, composed of 10 mg ciprofloxacin incorporated into PVA polymer. CIP_MN1 and CIP_MN2 showed a mean microneedle height of 188 and 179 µm, respectively. Since Parafilm has been proven as a model to examine the perforation of microneedles in skin, it was used to evaluate the ability of microneedles to perforate the skin. CIP_MN1 showed almost complete perforation of Parafilm, 190 pores, compared to CIP_MN2 which created only 85 pores in Parafilm, and therefore CIP_MN1 was used for subsequent studies. Examining CIP_MN1 on agarose gel as an in vitro model of human skin showed that the formula was able to fully perforate the agarose gel. Moreover, this formula showed significantly greater antimicrobial activity (p < 0.0001) compared to a free gel of ciprofloxacin against Staphylococcus aureus in an agarose gel-based model. This was evidenced by a zone of inhibition of 29 mm for the microneedle formulation of ciprofloxacin (CIP_MN1) compared to 2 mm for the free gel of ciprofloxacin. Furthermore, the CIP_MN1 showed complete dissolution in human skin after 60 min from application. Finally, the skin deposition of CIP_MN1 was investigated in ex vivo excised human skin. CIP_MN1 showed significantly more deposition of ciprofloxacin in deeper skin layers compared to the free gel of ciprofloxacin, and the released ciprofloxacin from the microneedles tends to migrate to deeper layers with time. Collectively, these results suggest that CIP_MN1 can be a potential delivery system for the treatment of S. aureus skin infections.

Super-swelling Hydrogel-forming Microneedle based Transdermal Drug Delivery: Mathematical Modelling, Simulation and Experimental Validation

Super-swelling hydrogel-forming microneedles (HFMNs) based transdermal drug delivery (TDD) is gaining significant interest due to their non-invasiveness and ability to deliver a wide range of drugs. The HFMNs swell by imbibing interstitial skin fluid (ISF), and they facilitate drug transport from the reservoir attached at the base into the skin without polymer dissolution. To develop HFMNs for practical applications, a complete understanding of the drug transport mechanism is required, allowing for controlled TDD and geometrical optimisation. A three-phase system consisting of a reservoir, microneedle, and skin is considered. A mathematical model is developed to incorporate the drug binding within the matrix of the compartment, which was not considered earlier. Super-swelling nature of the HFMNs is incorporated through the swelling ratio obtained experimentally for a polymer. The results are validated with in vitro diffusion studies of ibuprofen sodium (IBU) across excised porcine skin, showing that around 20% of the loaded IBU in lyophilised wafer was delivered in 24 hours. It was observed that increasing IBU solubility in reservoir can achieve high drug transport across the skin. The developed model is shown to be in good agreement with the experimental data. It is concluded that the proposed model can be considered a tool with predictive design and development of super-swelling HFMNs based TDD systems.

Transdermal Delivery of High Molecular Weight Antibiotics to Deep Tissue Infections via Droplette Micromist Technology Device (DMTD)

Wound infection by multidrug-resistant (MDR) bacteria is a major disease burden. Systemic administration of broad-spectrum antibiotics colistin methanesulfonate (CMS) and vancomycin are the last lines of defense against deep wound infections by MDR bacteria. However, systemic administration of CMS and vancomycin are linked to life-threatening vital organ damage. Currently there are no effective topical application strategies to deliver these high molecular weight antibiotics across the stratum corneum. To overcome this difficulty, we tested if high molecular weight antibiotics delivered by Droplette micromist technology device (DMTD), a transdermal delivery device that generates a micromist capable of packaging large molecules, could attenuate deep skin tissue infections. Using green fluorescent protein-tagged E. coli and live tissue imaging, we show that (1) the extent of attenuation of deep-skin E. coli infection was similar when treated with topical DMTD- or systemic IP (intraperitoneal)-delivered CMS; (2) DMTD-delivered micromist did not spread the infection deeper; (3) topical DMTD delivery and IP delivery resulted in similar levels of vancomycin in the skin after a 2 h washout period; and (4) IP-delivered vancomycin was about 1000-fold higher in kidney and plasma than DMTD-delivered vancomycin indicating systemic toxicity. Thus, topical DMTD delivery of these antibiotics is a safe treatment for the difficult-to-treat deep skin tissue infections by MDR bacteria.

Assessing the Dermal Penetration Efficacy of Chemical Compounds with the Ex-Vivo Porcine Ear Model

(1) Background: The ex vivo porcine ear model is often used for the determination of the dermal penetration efficacy of chemical compounds. This study investigated the influence of the post-slaughter storage time of porcine ears on the dermal penetration efficacy of chemical compounds. (2) Methods: Six different formulations (curcumin and different fluorescent dyes in different vehicles and/or nanocarriers) were tested on ears that were (i) freshly obtained, (ii) stored for 24 or 48 h at 4 °C after slaughter before use and (iii) freshly frozen and defrosted 12 h before use. (3) Results: Results showed that porcine ears undergo post-mortem changes. The changes can be linked to rigor mortis and all other well-described phenomena that occur with carcasses after slaughter. The post-mortem changes modify the skin properties of the ears and affect the penetration efficacy. The onset of rigor mortis causes a decrease in the water-holding capacity of the ears, which leads to reduced penetration of chemical compounds. The water-holding capacity increases once the rigor is released and results in an increased penetration efficacy for chemical compounds. Despite different absolute penetration values, no differences in the ranking of penetration efficacies between the different formulations were observed between the differently aged ears. (4) Conclusions: All different types of ears can be regarded to be suitable for dermal penetration testing of chemical compounds. The transepidermal water loss (TEWL) and/or skin hydration of the ears were not correlated with the ex vivo penetration efficacy because both an impaired skin barrier and rigor mortis cause elevated skin hydration and TEWL values but an opposite penetration efficacy. Other additional values (for example, pH and/or autofluorescence of the skin) should, therefore, be used to select suitable and non-suitable skin areas for ex vivo penetration testing. Finally, data from this study confirmed that smartFilms and nanostructured lipid carriers (NLC) represent superior formulation strategies for efficient dermal and transdermal delivery of curcumin.

Thermally damaged porcine skin is not a surrogate mechanical model of human skin

Porcine skin is considered a de facto surrogate for human skin. However, this study shows that the mechanical characteristics of full thickness burned human skin are different from those of porcine skin. The study relies on five mechanical properties obtained from uniaxial tensile tests at loading rates relevant to surgery: two parameters of the Veronda-Westmann hyperelastic material model, ultimate tensile stress, ultimate tensile strain, and toughness of the skin samples. Univariate statistical analyses show that human and porcine skin properties are dissimilar (p < 0.01) for each loading rate. Multivariate classification involving the five mechanical properties using logistic regression can successfully separate the two skin types with a classification accuracy exceeding 95% for each loading rate individually as well as combined. The findings of this study are expected to guide the development of effective training protocols and high-fidelity simulators to train burn care providers.

Biofabricating hollow microneedle array with controllable microstructure for cell transplantation

Microneedles improve upon the direct injection method by piercing the epidermis to create microchannels for drug delivery in a painless and minimally invasive way. With these microchannels, large macromolecules can penetrate the skin barrier to reach the underlying target tissue. In this study, poly(methyl methacrylate) (PMMA) hollow microneedles (HMN) arrays were fabricated to transplant cells. The result showed that HMN arrays have good biocompatibility. Human epidermal melanocytes and follicle dermal papilla cells were shown to be successfully delivered to acellular porcine skin tissue. Similarly, human corneal keratocytes and corneal epithelial cells were shown to be successfully delivered to acellular porcine corneal tissue. The delivered cells proliferated and penetrated into the tissue. This system may have the potential in the application of cell delivery or cell transplantation.

Light-regulated nitric oxide release from hydrogel-forming microneedles integrated with graphene oxide for biofilm-infected-wound healing

Nitric oxide (NO) is an antimicrobial agent that possesses tissue-regenerating ability. However, it also has a short half-life and storage difficulties as disadvantages to its application. To overcome these limitations, a new type of hydrogel-forming microneedle (HFMN) is proposed that can be fabricated by integrating polyvinyl alcohol (PVA) hydrogels (a highly biocompatible drug carrier) with S-nitrosoglutathione (GSNO, a NO releasing agent), and graphene oxide (GO) at freezing temperatures (GO-GNSO-HFMNs). Results show that GSNO-GO-HFMNs release NO gradually with increasing temperature and, more importantly, can be warmed up by mild infrared irradiation to accelerate subcutaneous release of NO from the heat-sensitive GSNO. Biofilm-infected wounds often present obstacles to drug delivery, whereas the microneedle (MN) structure disrupts the biofilm and directly releases NO into the wound. This inhibits bacterial growth and increases tissue regeneration while shortening the healing time of biofilm-infected wounds. Therefore, this type of patch can be regarded as a novel, heat-sensitive, light-regulated, NO-releasing MN patch.

Effect of collagen fibre orientation on the Poisson's ratio and stress relaxation of skin: an ex vivo and in vivo study

During surgical treatment skin undergoes extensive deformation, hence it must be able to withstand large mechanical stresses without damage. Therefore, understanding the mechanical properties of skin becomes important. A detailed investigation on the relationship between the three-dimensional deformation response of skin and its microstructure is conducted in the current study. This study also discloses the underlying science of skin viscoelasticity. Deformation response of skin is captured using digital image correlation, whereas micro-CT, scanning electron microscopy and atomic force microscopy are used for microstructure analysis. Skin shows a large lateral contraction and expansion (auxeticity) when stretched parallel and perpendicular to the skin tension lines, respectively. Large lateral contraction is a result of fluid exudation from the tissue, while large rotation of the stiff collagen fibres in the loading direction explains the skin auxeticity. During stress relaxation, lateral contraction and fluid effluxion from skin reveal that tissue volume loss is the intrinsic science of skin viscoelasticity. Furthermore, the results obtained from in vivo study on human skin show the relevance of the ex vivo study to physiological conditions and stretching of the skin during its treatments.

Fabrication and testing of polymer microneedles for transdermal drug delivery

Microneedle (MN) patches have considerable potential for medical applications such as transdermal drug delivery, point-of-care diagnostics, and vaccination. These miniature microdevices should successfully pierce the skin tissues while having enough stiffness to withstand the forces imposed by penetration. Developing low-cost and simple manufacturing processes for MNs is of considerable interest. This study reports a simple fabrication process for thermoplastic MNs from cycloolefin polymers (COP) using hot embossing on polydimethylsiloxane (PDMS) soft molds. COP has gained interest due to its high molding performance and low cost. The resin master MN arrays (9 × 9) were fabricated using two-photon polymerization (TPP). A previous gap in the detailed characterization of the embossing process was investigated, showing an average of 4.99 ± 0.35% longitudinal shrinkage and 2.15 ± 0.96% lateral enlargement in the molded MN replicas. The effects of bending, buckling, and tip blunting were then examined using compression tests and also theoretically. MN array insertion performance was studied in vitro on porcine back skin using both a prototype custom-made applicator and a commercial device. An adjustable skin stretcher mechanism was designed and manufactured to address current limitations for mimicking skin in vivo conditions. Finite element analysis (FEA) was developed to simulate single MN insertion into a multilayered skin model and validated experimentally using a commercial Pen Needle as a model for the thermoplastic MNs. Margins of safety for the current MN design demonstrated its potential for transdermal drug delivery and fluid sampling. Experimental results indicated significant penetration improvements using the prototype applicator, which produced array penetration efficiencies as high as >92%, depending on the impact velocity setting.