Depth-resolved characterization of diffusion properties within and across minimally-perturbed skin layers

Masticatory system-inspired microneedle theranostic platform for intelligent and precise diabetic management

Integrated systems for diabetic theranostics present advanced technology to regulate diabetes yet still have critical challenges in terms of accuracy, long-term monitoring, and minimal invasiveness. Inspired by the feature and functions of animal masticatory system, we presented a biomimetic microneedle theranostic platform (MNTP) for intelligent and precise management of diabetes. The MNTP was supported by a miniatured circuit, which used microneedle arrays for on-demand skin penetration, enabling interstitial fluid exudation for simultaneous detection of glucose and physiological ions, and subcutaneous insulin delivery. Interstitial fluid exudation enabled sensing in oxygen-rich environment via the incorporated epidermal sensor functionalized with hybrid carbon nanomaterials. This feature addressed the biosafety issues due to implanted electrodes and the "oxygen-deficit" issues in vivo. The MNTP was demonstrated to accurately detect glucose and ions and deliver insulin to regulate hyperglycemia. The biomimetic and intelligent features of the MNTP endowed it as a highly advanced system for diabetes therapy.

Lateral Dermal Penetration is Dependent on the Lipophilicity of Active Ingredients

INTRODUCTION

With its large surface area skin facilitates a topical administration of active ingredients, and thus percutaneous delivery to a specific target site. Due to its high barrier function and different diffusion characteristics skin governs the efficacy of these active ingredients and a bioavailability in the epidermal and dermal tissue.

OBJECTIVE

In order to characterize the vertical and lateral movement of molecules into and inside the skin the diffusivity of active ingredients with different physico-chemical properties and their penetration ability in different dermal skin layers was investigated.

METHODS

A novel lateral dermal microdialysis (MD) penetration setup was used to compare the diffusion characteristics of active ingredients into superficial and deep implanted MD membranes in porcine skin. The corresponding membrane depth was determined via ultrasound and the active ingredients concentration via high-pressure liquid chromatography (HPLC) measurement.

RESULTS

The depth depended penetration of superficial and deep implanted MD membranes and the quantitative diffusivity of two active ingredients was compared. An experimental lateral MD setup was used to determine the influence of percutaneous skin penetration characteristics of an active ingredient with different lipophilic and hydrophilic characteristics. Therefore, hydrophilic caffeine and lipophilic LIP1, which have an identical molecular weight, but different lipophilic characteristics were tested for their penetration ability inside a propylene glycol (PG) and oleic acid (OA) formulation.

CONCLUSION

The vertical and lateral penetration movement of caffeine was found to exceed that of LIP1 through the hydrophilic dermal environment. The findings of this study show that the lipophilicity of active ingredients influence the penetration movement and that skin enables a conical increasing lateral diffusivity and transdermal delivery.

Developing a Stabilizing Formulation of a Live Chimeric Dengue Virus Vaccine Dry Coated on a High-Density Microarray Patch

Alternative delivery systems such as the high-density microarray patch (HD-MAP) are being widely explored due to the variety of benefits they offer over traditional vaccine delivery methods. As vaccines are dry coated onto the HD-MAP, there is a need to ensure the stability of the vaccine in a solid state upon dry down. Other challenges faced are the structural stability during storage as a dried vaccine and during reconstitution upon application into the skin. Using a novel live chimeric virus vaccine candidate, BinJ/DENV2-prME, we explored a panel of pharmaceutical excipients to mitigate vaccine loss during the drying and storage process. This screening identified human serum albumin (HSA) as the lead stabilizing excipient. When bDENV2-coated HD-MAPs were stored at 4 °C for a month, we found complete retention of vaccine potency as assessed by the generation of potent virus-neutralizing antibody responses in mice. We also demonstrated that HD-MAP wear time did not influence vaccine deposition into the skin or the corresponding immunological outcomes. The final candidate formulation with HSA maintained ~100% percentage recovery after 6 months of storage at 4 °C.

Finite Element Analysis for Predicting Skin Pharmacokinetics of Nano Transdermal Drug Delivery System Based on the Multilayer Geometry Model

Background

Skin pharmacokinetics is an indispensable indication for studying the drug fate after administration of transdermal drug delivery systems (TDDS). However, the heterogeneity and complex skin structured with stratum corneum, viable epidermis, dermis, and subcutaneous tissue inevitably leads the drug diffusion coefficient (Kp) to vary depending on the skin depth, which seriously limits the development of TDDS pharmacokinetics in full thickness skin.

Methods

A multilayer geometry skin model was established and the Kp of drug in SC, viable epidermis, and dermis was obtained using the technologies of molecular dynamics simulation, in vitro permeation experiments, and in vivo microdialysis, respectively. Besides, finite element analysis (FEA) based on drug Kps in different skin layers was applied to simulate the paeonol nanoemulsion (PAE-NEs) percutaneous dynamic penetration process in two and three dimensions. In addition, PAE-NEs skin pharmacokinetics profile obtained by the simulation was verified by in vivo experiment.

Results

Coarse-grained modeling of molecular dynamic simulation was successfully established and the Kp of PAE in SC was 2.00×10⁻⁶ cm²/h. The Kp of PAE-NE in viable epidermis and in dermis detected using penetration test and microdialysis probe technology, was 1.58×10⁻⁵ cm²/h and 3.20×10⁻⁵ cm²/h, respectively. In addition, the results of verification indicated that PAE-NEs skin pharmacokinetics profile obtained by the simulation was consistent with that by in vivo experiment.

Discussion

This study demonstrated that the FEA combined with the established multilayer geometry skin model could accurately predict the skin pharmacokinetics of TDDS.

Space- and time-resolved investigation on diffusion kinetics of human skin following macromolecule delivery by microneedle arrays

Microscale medical devices are being developed for targeted skin delivery of vaccines and the extraction of biomarkers, with the potential to revolutionise healthcare in both developing and developed countries. The effective clinical development of these devices is dependent on understanding the macro-molecular diffusion properties of skin. We hypothesised that diffusion varied according to specific skin layers. Using three different molecular weights of rhodamine dextran (RD) (MW of 70, 500 and 2000 kDa) relevant to the vaccine and therapeutic scales, we deposited molecules to a range of depths (0-300 µm) in ex vivo human skin using the Nanopatch device. We observed significant dissipation of RD as diffusion with 70 and 500 kDa within the 30 min timeframe, which varied with MW and skin layer. Using multiphoton microscopy, image analysis and a Fick's law analysis with 2D cartesian and axisymmetric cylindrical coordinates, we reported experimental trends of epidermal and dermal diffusivity values ranging from 1-8 µm2 s-1 to 1-20 µm2 s-1 respectively, with a significant decrease in the dermal-epidermal junction of 0.7-3 µm2 s-1. In breaching the stratum corneum (SC) and dermal-epidermal junction barriers, we have demonstrated practical application, delivery and targeting of macromolecules to both epidermal and dermal antigen presenting cells, providing a sound knowledge base for future development of skin-targeting clinical technologies in humans.

The hyperelastic and failure behaviors of skin in relation to the dynamic application of microscopic penetrators in a murine model

In-depth understanding of skin elastic and rupture behavior is fundamental to enable next-generation biomedical devices to directly access areas rich in cells and biomolecules. However, the paucity of skin mechanical characterization and lack of established fracture models limits their rational design. We present an experimental and numerical study of skin mechanics during dynamic interaction with individual and arrays of micro-penetrators. Initially, micro-indentation of individual skin strata revealed hyperelastic moduli were dramatically rate-dependent, enabling extrapolation of stiffness properties at high velocity regimes (>1ms^-1). A layered finite-element model satisfactorily predicted the penetration of micro-penetrators using characteristic fracture energies (∼10pJμm^-2) significantly lower than previously reported (≫100pJμm^-2). Interestingly, with our standard application conditions (∼2ms^-1, 35gpistonmass), ∼95% of the application kinetic energy was transferred to the backing support rather than the skin ∼5% (murine ear model). At higher velocities (∼10ms^-1) strain energy accumulated in the top skin layers, initiating fracture before stress waves transmitted deformation to the backing material, increasing energy transfer efficiency to 55%. Thus, the tools developed provide guidelines to rationally engineer skin penetrators to increase depth targeting consistency and payload delivery across patients whilst minimizing penetration energy to control skin inflammation, tolerability and acceptability.

STATEMENT OF SIGNIFICANCE

The mechanics of skin penetration by dynamically-applied microscopic tips is investigated using a combined experimental-computational approach. A FE model of skin is parameterized using indentation tests and a ductile-failure implementation validated against penetration assays. The simulations shed light on skin elastic and fracture properties, and elucidate the interaction with microprojection arrays for vaccine delivery allowing rational design of next-generation devices.

Recent trends in the transdermal delivery of therapeutic agents used for the management of neurodegenerative diseases

With the increasing proportion of the global geriatric population, it becomes obvious that neurodegenerative diseases will become more widespread. From an epidemiological standpoint, it is necessary to develop new therapeutic agents for the management of Alzheimer's disease, Parkinson's disease, multiple sclerosis and other neurodegenerative disorders. An important approach in this regard involves the use of the transdermal route. With transdermal drug delivery systems (TDDS), it is possible to modulate the pharmacokinetic profiles of these medications and improve patient compliance. Transdermal drug delivery has also been shown to be useful for drugs with short half-life and low or unpredictable bioavailability. In this review, several transdermal drug delivery enhancement technologies are being discussed in relation to the delivery of medications used for the management of neurodegenerative disorders.

Potent response of QS-21 as a vaccine adjuvant in the skin when delivered with the Nanopatch, resulted in adjuvant dose sparing

Adjuvants play a key role in boosting immunogenicity of vaccines, particularly for subunit protein vaccines. In this study we investigated the induction of antibody response against trivalent influenza subunit protein antigen and a saponin adjuvant, QS-21. Clinical trials of QS-21 have demonstrated the safety but, also a need of high dose for optimal immunity, which could possibly reduce patient acceptability. Here, we proposed the use of a skin delivery technology - the Nanopatch - to reduce both adjuvant and antigen dose but also retain its immune stimulating effects when compared to the conventional needle and syringe intramuscular (IM) delivery. We have demonstrated that Nanopatch delivery to skin requires only 1/100(th) of the IM antigen dose to induce equivalent humoral response. QS-21 enhanced humoral response in both skin and muscle route. Additionally, Nanopatch has demonstrated 30-fold adjuvant QS-21 dose sparing while retaining immune stimulating effects compared to IM. QS-21 induced localised, controlled cell death in the skin, suggesting that the danger signals released from dead cells contributed to the enhanced immunogenicity. Taken together, these findings demonstrated the suitability of reduced dose of QS-21 and the antigen using the Nanopatch to enhance humoral responses, and the potential to increase patient acceptability of QS-21 adjuvant.

Influenza nucleoprotein DNA vaccination by a skin targeted, dry coated, densely packed microprojection array (Nanopatch) induces potent antibody and CD8(+) T cell responses

DNA vaccines have many advantages such as thermostability and the ease and rapidity of manufacture; for example, in an influenza pandemic situation where rapid production of vaccine is essential. However, immunogenicity of DNA vaccines was shown to be poor in humans unless large doses of DNA are used. If a highly efficacious DNA vaccine delivery system could be identified, then DNA vaccines have the potential to displace protein vaccines. In this study, we show in a C57BL/6 mouse model, that the Nanopatch, a microprojection array of high density (>21,000 projections/cm(2)), could be used to deliver influenza nucleoprotein DNA vaccine to skin, to generate enhanced antigen specific antibody and CD8(+) T cell responses compared to the conventional intramuscular (IM) delivery by the needle and syringe. Antigen specific antibody was measured using ELISA assays of mice vaccinated with a DNA plasmid containing the nucleoprotein gene of influenza type A/WSN/33 (H1N1). Antigen specific CD8(+) T cell responses were measured ex-vivo in splenocytes of mice using IFN-γ ELISPOT assays. These results and our previous antibody and CD4(+) T cell results using the Nanopatch delivered HSV DNA vaccine indicate that the Nanopatch is an effective delivery system of general utility that could potentially be used in humans to increase the potency of the DNA vaccines.

Formulations for microprojection/microneedle vaccine delivery: Structure, strength and release profiles

To develop novel methods for vaccine delivery, the skin is viewed as a high potential target, due to the abundance of immune cells that reside therein. One method, the use of dissolving microneedle technologies, has the potential to achieve this, with a range of formulations now being employed. Within this paper we assemble a range of methods (including FT-FIR using synchrotron radiation, nanoindentation and skin delivery assays) to systematically examine the effect of key bulking agents/excipients - sugars/polyols - on the material form, structure, strength, failure properties, diffusion and dissolution for dissolving microdevices. We investigated concentrations of mannitol, sucrose, trehalose and sorbitol from 1:1 to 30:1 with carboxymethylcellulose (CMC), although mannitol did not form our micro-structures so was discounted early in the study. The other formulations showed a variety of crystalline (sorbitol) and amorphous (sucrose, trehalose) structures, when investigated using Fourier transform far infra-red (FT-FIR) with synchrotron radiation. The crystalline structures had a higher elastic modulus than the amorphous formulations (8-12GPa compared to 0.05-11GPa), with sorbitol formulations showing a bimodal distribution of results including both amorphous and crystalline behaviour. In skin, diffusion properties were similar among all formulations with dissolution occurring within 5s for our small projection array structures (~100μm in length). Overall, slight variations in formulation can significantly change the ability of our projections to perform their required function, making the choice of bulking/vaccine stabilising agents of great importance for these devices.

Nanoethosomes for Dermal Delivery of Lidocaine

PURPOSE

It is necessary for local anesthetics to pass through the stratum corneum to provide rapid pain relief. Many techniques have been reported to enhance intradermal penetration of local anesthetics such as vesicular lipid carriers. Ethosomes are lipid vesicles containing phospholipids, ethanol at relatively high concentration. We hypothesized that synergistic effects of phospholipids and high concentration of ethanol in formulation could accelerate penetration of nanoethosomes in deep layers of skin.

METHODS

Lidocaine-loaded nanoethosomes were prepared and characterized by size and zeta analyzer, scanning electron microscopy (SEM) and X-ray diffractometer (XRD). Furthermore, encapsulation efficiency (EE), loading capacity (LC), and skin penetration capability were evaluated by in vitro and in vivo experiments.

RESULTS

results showed that the particle size, zeta potential, EE and LC of optimum formulation were 105.4 ± 7.9 nm, -33.6 ± 2.4 mV, 40.14 ± 2.5 %, and 8.02 ± 0.71 respectively. SEM results confirmed the non-aggregated nano-scale size of prepared nanoethosomes. Particle size of ethosomes and EE of Lidocaine were depended on the phospholipid and ethanol concentrations. XRD results demonstrated the drug encapsulation in amorphous status interpreting the achieved high drug EE and LC values. In vitro and in vivo assays confirmed the appropriate skin penetration of Lidocaine with the aid of nanoethosomes and existence of deposition of nanoethosomes in deep skin layers, respectively.

CONCLUSION

The developed nanoethosomes are proposed as a suitable carrier for topical delivery of anesthetics such as Lidocaine.

Diffusion profile of macromolecules within and between human skin layers for (trans)dermal drug delivery

Delivering a drug into and through the skin is of interest as the skin can act as an alternative drug administration route for oral delivery. The development of new delivery methods, such as microneedles, makes it possible to not only deliver small molecules into the skin, which are able to pass the outer layer of the skin in therapeutic amounts, but also macromolecules. To provide insight into the administration of these molecules into the skin, the aim of this study was to assess the transport of macromolecules within and between its various layers. The diffusion coefficients in the epidermis and several locations in the papillary and reticular dermis were determined for fluorescein dextran of 40 and 500 kDa using a combination of fluorescent recovery after photobleaching experiments and finite element analysis. The diffusion coefficient was significantly higher for 40 kDa than 500 kDa dextran, with median values of 23 and 9 µm(2)/s in the dermis, respectively. The values only marginally varied within and between papillary and reticular dermis. For the 40 kDa dextran, the diffusion coefficient in the epidermis was twice as low as in the dermis layers. The adopted method may be used for other macromolecules, which are of interest for dermal and transdermal drug delivery. The knowledge about diffusion in the skin is useful to optimize (trans)dermal drug delivery systems to target specific layers or cells in the human skin.

Sample-free quantification of blood biomarkers via laser-treated skin

Surface modified microneedle (MN) arrays are being developed to capture circulating biomarkers from the skin, but inefficiency and unreliability of the current method limit its clinical applications. We describe here that illumination of a tiny area of the skin with hemoglobin-preferably absorbent laser increased the amount of circulating biomarkers in the upper dermis by more than 1000-fold. The hemoglobin-specific light altered the permeability of capillaries leading to extravasation of molecules but not blood cells beneath the skin involved. When specific probe-coated MN arrays were applied into the laser-treated skin, the biomarkers accumulated in the upper dermis were reliably, accurately, and sufficiently captured as early as 15 min of the assay. The maximal binding occurred in 1 h in a manner independent of penetration depth or a molecular mass of the biomarker. With anti-fluorescein isothiocyanate (FITC)-MNs, we were able to measure blood concentrations of FITC in mice receiving FITC intravenously. The sensitivity and accuracy were comparable to those attained by fluorescence spectrophotometer. Likewise, MNs containing influenza hemagglutinin (HA) could detect anti-HA antibody in mice or swine receiving influenza vaccines as effectively as standard immunoassays. The novel, minimally invasive approach holds great promise for measurement of multiple biomarkers by a single array for point-of-care diagnosis.

Formulation design for topical drug and nanoparticle treatment of skin disease

The skin has evolved to resist the penetration of foreign substances and particles. Topical therapeutic and cosmeceutical delivery is a growing field founded on selectively overcoming this barrier. Both the biology of the skin and the nature of the formulation/active ingredient must be aligned for efficient transcutaneous delivery. This review discusses the biological changes in the skin barrier that occur with common dermatological conditions. This context is the foundation for the discussion of formulation strategies to improve penetration profiles of common active ingredients in dermatology. Finally, we compare and contrast those approaches to recent advances described in the research literature with an eye toward the future of topical formulation design.

Microprojection arrays to immunise at mucosal surfaces

The buccal mucosa (inner cheek) is an attractive site for delivery of immunotherapeutics, due to its ease of access and rich antigen presenting cell (APC) distribution. However, to date, most delivery methods to the buccal mucosa have only been topical-with the challenges of: 1) an environment where significant biomolecule degradation may occur; 2) inability to reach the APCs that are located deep in the epithelium and lamina propria; and 3) salivary flow and mucous secretion that may result in removal of the therapeutic agent before absorption has taken place. To overcome these challenges and achieve consistent, repeatable targeted delivery of immunotherapeutics to within the buccal mucosa (not merely on to the surface), we utilised microprojection arrays (Nanopatches-110 μm length projections, 3364 projections, 16 mm2 surface area) with a purpose built clip applicator. The mechanical application of Nanopatches bearing a dry-coated vaccine (commercial influenza vaccine, as a test case immunotherapeutic) released the vaccine to a depth of 47.8±14.8 μm (mean±SD, n=4), in the mouse buccal mucosa (measured using fluorescent delivered dyes and CryoSEM). This location is in the direct vicinity of APCs, facilitating antigenic uptake. Resultant systemic immune responses were similar to systemic immunization methods, and superior to comparative orally immunised mice. This confirms the Nanopatch administered vaccine was delivered into the buccal mucosa and not ingested. This study demonstrates a minimally-invasive delivery device with rapid (2 min of application time), accurate and consistent release of immunotherapeutics in to the buccal mucosa-that conceptually can be extended in to human use for broad and practical utility.

Colocalization of cell death with antigen deposition in skin enhances vaccine immunogenicity

Vaccines delivered to the skin by microneedles – with and without adjuvants – have increased immunogenicity with lower doses than standard vaccine delivery techniques such as intramuscular (i.m.) or intradermal (i.d.) injection. However, the mechanisms behind this skin-mediated ‘adjuvant’ effect are not clear. Here, we show that the dynamic application of a microprojection array (the Nanopatch) to skin generates localized transient stresses invoking cell death around each projection. Nanopatch application caused significantly higher levels (~65-fold) of cell death in murine ear skin than i.d. injection using a hypodermic needle. Measured skin cell death is associated with modeled stresses ~1–10 MPa. Nanopatch-immunized groups also yielded consistently higher anti-IgG endpoint titers (up to 50-fold higher) than i.d. groups after delivery of a split virion influenza vaccine. Importantly, co-localization of cell death with nearby live skin cells and delivered antigen was necessary for immunogenicity enhancement. These results suggest a correlation between cell death caused by the Nanopatch with increased immunogenicity. We propose that the localized cell death serves as a ‘physical immune enhancer’ for the adjacent viable skin cells, which also receive antigen from the projections. This natural immune enhancer effect has the potential to mitigate or replace chemical-based adjuvants in vaccines.

Elongate microparticles for enhanced drug delivery to ex vivo and in vivo pig skin

The delivery of therapeutics and cosmaceuticals into and/or through the skin is hindered by epidermal barriers. To overcome the skin's barriers we have developed a novel cutaneous delivery method using high aspect ratio elongate microparticles (EMPs). Using ex vivo and in vivo pig skin we assess the penetration and delivery characteristics of the elongate microparticles. With reflectance confocal microscopy we observed that the elongate microparticles successfully penetrated the epidermis and upper dermis. Delivery was then assessed using two different length populations of EMPs, comparing their delivery profile to topical alone using sodium fluorescein and confocal microscopy. We observed a relatively uniform and continuous delivery profile in the EMP treated area within the upper layers of the skin--up to seven times greater than topical alone. Finally, we delivered two therapeutically relevant compounds (Vitamins A and B3), showing enhanced delivery using the EMPs. To our knowledge this is the first report using high aspect ratio elongate microparticles in this manner for enhanced topical delivery to the skin.