Cellular metabolism and pore lifetime of human skin following microprojection array mediation

NAD+ modulation with nicotinamide mononucleotide coated 3D printed microneedle implants

Nicotinamide adenine dinucleotide (NAD+) deficiency has been shown to cause pathogenesis of age-related functional decline and diseases. Investigational studies have demonstrated improvements in age-associated pathophysiology and disease conditions. However, invasive methods such as immunohistochemistry, metabolic assays, and polymerase chain reaction currently used to measure cell metabolism render cells unviable and unrecoverable for longitudinal studies and are incompatible with in vivo dynamic observations. We report a non-invasive optical technique to investigate the upregulation of nicotinamide adenine dinucleotide (NAD+) in keratinocytes (both in vitro and ex vivo) upon administration of nicotinamide mononucleotide (NMN) coated microneedle (μNDs) implants. Our technique exploits intrinsic autofluorescence of cells and tissues using multiphoton microscopy. Additionally, μND coating formulations to date have been evaluated using fluorescence microscopy to determine the coated amount, often an imprecise correlation between fluorescence intensity and the coated amount on the μND surface. We also show that rheomechanical attributes of the coating formulation (containing two different viscosity enhancers: sucrose and carboxy methyl cellulose) affect the flow mechanics of the coating formulation at micron scale, and thus the amount of drug coated on the μND surface. In vitro keratinocyte cells were investigated with four concentrations of NMN (50, 250, 500 and 1000 μg), and evaluated with time-dependent NMN (500 μg) treatment at 0, 5, 10, 30, 60, 360 and 1460 min. We demonstrate that intracellular keratinocyte fluorescence of the endogenous NADH shows a decreasing trend in both the average fluorescence lifetime (τm) and the free unbound NADH (τ1), with increasing dosage of NMN administration. A similar trend in the average fluorescence lifetime (τm) of endogenous NAD(P)H was also seen in mouse ear skin ex vivo skin upon administration of NMN. We show a promising, minimally invasive, alternative delivery system for the NAD+ precursor molecule that can enhance patient compliance and therapeutic outcomes.

Microneedle technology for enhanced topical treatment of skin infections

Skin infections caused by microbes such as bacteria, fungi, and viruses often lead to aberrant skin functions and appearance, eventually evolving into a significant risk to human health. Among different drug administration paradigms for skin infections, microneedles (MNs) have demonstrated superiority mainly because of their merits in enhancing drug delivery efficiency and reducing microbial resistance. Also, integrating biosensing functionality to MNs offers point-of-care wearable medical devices for analyzing specific pathogens, disease status, and drug pharmacokinetics, thus providing personalized therapy for skin infections. Herein, we do a timely update on the development of MN technology in skin infection management, with a special focus on how to devise MNs for personalized antimicrobial therapy. Notably, the advantages of state-of-the-art MNs for treating skin infections are pointed out, which include hijacking sequential drug transport barriers to enhance drug delivery efficiency and delivering various therapeutics (e.g., antibiotics, antimicrobial peptides, photosensitizers, metals, sonosensitizers, nanoenzyme, living bacteria, poly ionic liquid, and nanomoter). In addition, the nanoenzyme-based multimodal antimicrobial therapy is highlighted in addressing intractable infectious wounds. Furthermore, the MN-based biosensors used to identify pathogen types, track disease status, and quantify antibiotic concentrations are summarized. The limitations of antimicrobial MNs toward clinical translation are offered regarding large-scale production, quality control, and policy guidance. Finally, the future development of biosensing MNs with easy-to-use and intelligent properties and MN-based wearable drug delivery for home-based therapy are prospected. We hope this review will provide valuable guidance for future development in MN-mediated topical treatment of skin infections.

Skin microincision technique to enhance drug penetration for the treatment of keloid and hypertrophic scars

The synergistic effect of corticosteroids and 5-fluorouracil (5-FU) for the treatment of pathological scarring is widely documented. While topical administration can be a painless, convenient way to convey the two active ingredients, physical enhancement techniques such as microneedling are required to deepen their skin penetration and achieve the therapeutic effect. A novel approach to keloid and scar treatment is given by microincision, i.e., micrometric-sized columnar perforations which allow the drugs to diffuse into the skin and promote tissue proliferation in a more physiological structure. Combining the delivery of triamcinolone acetonide (TAC) and 5-FU with microincision is an innovative approach that could improve the speed and efficacy of regenerative treatments. This study evaluated the effectiveness of the skin treatment with a device combining microincisions and photobiomodulation, in the skin permeation of a combination of TAC and 5-FU. Increasing treatment times (4, 6, and 8 min) led to higher drug penetration compared to intact skin, with a more noticeable effect for 5-FU compared to TAC. Specifically, all treatment durations were significantly more effective (p < 0.05) than the control for 5-FU, while TAC showed less variation between treatments. Moreover, it was shown that in-vitro, the permeation improvement given by the red-light treatment was mainly due to the mechanical massage, which pushed the actives into the microchannels created by the treatment. The application of prolonged skin microincision times ensured much higher skin permeation of both TAC and 5-FU compared to microneedling on healthy excised skin.

Seeing through the skin: Optical methods for visualizing transdermal drug delivery with microneedles

Optical methods play a pivotal role in advancing transdermal drug delivery research, particularly with the emergence of microneedle technology. This review presents a comprehensive analysis of optical methods used in studying transdermal drug delivery facilitated by microneedle technology. Beginning with an introduction to microneedle technology and skin anatomy and optical properties, the review explores the integration of optical methods for enhanced visualization. Optical imaging offers key advantages including real-time drug distribution visualization, non-invasive skin response monitoring, and quantitative drug penetration analysis. A spectrum of optical imaging modalities ranging from conventional dermoscopy and stereomicroscopy to advance techniques as fluorescence microscopy, laser scanning microscopy, in vivo imaging system, two-photon microscopy, fluorescence lifetime imaging microscopy, optical coherence tomography, Raman microspectroscopy, laser speckle contrast imaging, and photoacoustic microscopy is discussed. Challenges such as resolution and depth penetration limitations are addressed alongside potential breakthroughs and future directions in optical techniques development. The review underscores the importance of bridging the gap between preclinical and clinical studies, explores opportunities for integrating optical imaging and chemical sensing methods with drug delivery systems, and highlight the importance of non-invasive "optical biopsy" as a valuable alternative to conventional histology. Overall, this review provides insight into the role of optical methods in understanding transdermal drug delivery mechanisms with microneedles.

3D Printed Microneedles for the Transdermal Delivery of NAD+ Precursor: Toward Personalization of Skin Delivery

3D printing of microneedles (μNDs) for transdermal therapy has the potential to enable patient personalization based on the target disease, site of application, and dosage requirements. To convert this concept to reality, it is necessary that the 3D printing technology can deliver high resolution, an affordable cost, and large print volumes. With the introduction of benchtop 4K and 8K 3D printers, it is now possible to manufacture medical devices like μNDs at sufficient resolution and low cost. In this research, we systematically optimized the 3D printing design parameters such as resin viscosity, print angle, layer height, and curing time to generate customizable μNDs. We have also developed an innovative 3D coating microtank device to optimize the coating method. We have applied this to the development of novel μNDs to deliver an established NAD+ precursor molecule, nicotinamide mononucleotide (NMN). A methacrylate-based polymer photoresin (eSun resin) was diluted with methanol to adjust the resin viscosity. The 3D print layer height of 25 μm yielded a smooth surface, thus reducing edge-ridge mismatches. Printing μNDs at 90° to the print platform yielded 84.28 ± 2.158% (n = 5) of the input height thus increasing the tip sharpness (48.52 ± 10.43 μm, n = 5). The formulation containing fluorescein (model molecule), sucrose (viscosity modifier), and Tween-20 (surface tension modifier) was coated on the μNDs using the custom designed microtank setup, and the amount deposited was determined fluorescently. The dye-coated μND arrays inserted into human skin (in vitro) showed a fluorescence signal at a depth of 150 μm (n = 3) into the skin. After optimization of the 3D printing parameters and coating protocol using fluorescein, NMN was coated onto the μNDs, and its diffusion was assessed in full-thickness human skin in vitro using a Franz diffusion setup. Approximately 189 ± 34.5 μg (5× dipped coated μNDs) of NMN permeated through the skin and 41.2 ± 7.53 μg was left in the skin after 24 h. Multiphoton microscopy imaging of NMN-coated μND treated mouse ear skin ex vivo demonstrated significantly (p < 0.05) increased free-unbound NADPH and reduced fluorescence lifetime of NADPH, both of which are indicative of cellular metabolic rates. Our study demonstrates that low-cost benchtop 3D printers can be used to print high-fidelity μNDs with the ability to rapidly coat and release NMN which consequently caused changes in intracellular NAD+ levels.

Development of solid lipid microparticles (SLMs) containing asiatic acid for topical treatment of acne: Characterization, stability, in vitro and in vivo anti-acne assessment

Solid lipid microparticles (SLMs) represent a promising approach for drug delivery in anti-acne applications. In this study, asiatic acid-loaded SLMs (AASLMs) were prepared by melt emulsification method in conjunction with freeze-drying. Comprehensive evaluations comprised particle size, %entrapment efficiency (%EE), %labeled amount (%LA), surface morphology, stability, %release, %skin permeation, and anti-acne activity. The AASLMs exhibited an average particle size ranging from 7.46 to 38.86 µm, with %EE and %LA falling within the range of 31.56 to 100.00 and 90.43 to 95.38, respectively. The AASLMs demonstrated a spherical shape under scanning electron microscopy, and maintained stability over a 3-month period. Notably, formulations with 10 % and 15 % cetyl alcohol stabilized with poloxamer-188 (specifically F6 and F12) displayed a minimum inhibitory concentration (MIC) value of 75 mg/ml against Cutibacterium acnes. Furthermore, F12 exhibited a higher %release and %skin permeation compared to F6 over 24 h. In a single-blind clinical trial involving fifteen participants with mild-to-moderate acne, F12 showcased its potential not only in reducing porphyrin intensity and enhancing skin barriers but also in significantly improving skin hydration and brightness. However, further investigations with larger subject cohorts encompassing diverse age groups and genders are necessary to thoroughly establish the performance of the developed AASLMs.

Assessing the risk of a clinically significant infection from a Microneedle Array Patch (MAP) product

Microneedle Array Patches (MAPs) are an emerging dosage form that creates transient micron-sized disruptions in the outermost physical skin barrier, the stratum corneum, to facilitate delivery of active pharmaceutical ingredients to the underlying tissue. Numerous MAP products are proposed and there is significant clinical potential in priority areas such as vaccination. However, since their inception scientists have hypothesized about the risk of a clinically significant MAP-induced infection. Safety data from two major Phase 3 clinical trials involving hundreds of participants, who in total received tens of thousands of MAP applications, does not identify any clinically significant infections. However, the incumbent data set is not extensive enough to make definitive generalizable conclusions. A comprehensive assessment of the infection risk is therefore advised for MAP products, and this should be informed by clinical and pre-clinical data, theoretical analysis and informed opinions. In this article, a group of key stakeholders identify some of the key product- and patient-specific factors that may contribute to the risk of infection from a MAP product and provide expert opinions in the context of guidance from regulatory authorities. Considerations that are particularly pertinent to the MAP dosage form include the specifications of the finished product (e.g. microbial specification), it's design features, the setting for administration, the skill of the administrator, the anatomical application site, the target population and the clinical context. These factors, and others discussed in this article, provide a platform for the development of MAP risk assessments and a stimulus for early and open dialogue between developers, regulatory authorities and other key stakeholders, to expedite and promote development of safe and effective MAP products.

Microneedle-assisted transdermal delivery of nanoparticles: Recent insights and prospects

Transdermal delivery of drugs offers an interesting alternative for the administration of molecules that present certain troubles when delivered by the oral route. It can produce systemic effects or perform a local action when the formulation exerts an optimal controlled drug release or a targeted delivery to the specific cell type or site. It also avoids several inconveniences of the oral administration such as the hepatic first pass effect, gastric pH-induced hydrolysis, drug malabsorption because of certain diseases or surgeries, and unpleasant organoleptic properties. Nanomedicine and microneedle array patches (MAPs) are two of the trendiest delivery systems applied to transdermal research nowadays. However, the skin is a protective barrier and nanoparticles (NPs) cannot pass through the intact stratum corneum. The association of NPs and MAPs (NPs@MAPs) work synergistically, since MAPs assist NPs to bypass the outer skin layers, and NPs contribute to the system providing controlled drug release and targeted delivery. Vaccination and tailored therapies have been proposed as fields where both NPs and MAPs have great potential due to inherent characteristics. MAPs conception and easy use could allow self-administration and therefore facilitate mass vaccination campaigns in undeveloped areas with weak healthcare services. Additionally, nanomedicine is being explored as a platform to personalize therapies in such an important field as oncology. In this work we show recent insights that prove the benefits of NPs@MAPs association and analyze the prospects and the discrete interest of the industry in NPs@MAPs, evaluating different limiting steps that restricts NPs@MAPs translation to the clinical practice. This article is categorized under: Nanotechnology Approaches to Biology > NA Therapeutic Approaches and Drug Discovery > NA.

Microneedle-Mediated Transdermal Delivery of Biopharmaceuticals

Transdermal delivery provides numerous benefits over conventional routes of administration. However, this strategy is generally limited to a few molecules with specific physicochemical properties (low molecular weight, high potency, and moderate lipophilicity) due to the barrier function of the stratum corneum layer. Researchers have developed several physical enhancement techniques to expand the applications of the transdermal field; among these, microneedle technology has recently emerged as a promising platform to deliver therapeutic agents of any size into and across the skin. Typically, hydrophilic biomolecules cannot penetrate the skin by passive diffusion. Microneedle insertion disrupts skin integrity and compromises its protective function, thus creating pathways (microchannels) for enhanced permeation of macromolecules. Microneedles not only improve stability but also enhance skin delivery of various biomolecules. Academic institutions and industrial companies have invested substantial resources in the development of microneedle systems for biopharmaceutical delivery. This review article summarizes the most recent research to provide a comprehensive discussion about microneedle-mediated delivery of macromolecules, covering various topics from the introduction of the skin, transdermal delivery, microneedles, and biopharmaceuticals (current status, conventional administration, and stability issues), to different microneedle types, clinical trials, safety and acceptability of microneedles, manufacturing and regulatory issues, and the future of microneedle technology.

Dual-Drug Loaded Separable Microneedles for Efficient Rheumatoid Arthritis Therapy

Although the inhibitors of the interleukin-6 receptor (IL-6R) and tumor necrosis factor-α (TNF-α) have achieved a certain success in the clinical treatment of rheumatoid arthritis (RA), great effort should be made to overcome side effects and to improve patient compliance. The present research aimed to address these problems by the co-delivery of tocilizumab (TCZ)—an inhibitor of IL-6R—and an aptamer Apt1-67, which specifically inhibits TNF receptor 1 via separable microneedles (MN). MN were featured with a sustained release of TCZ from needle tips and a rapid release of Apt1-67 from needle bodies by using methacrylate groups grafted hyaluronic acid as the fillings of needle tips and polyvinyl alcohol/polyvinyl pyrrolidone as the fillings of needle bodies. Our results demonstrated that TCZ and Apt1-67 were distributed in MN as expected, and they could be released to the surroundings in the skin. In vivo studies revealed that combined medication via MN (TCZ/Apt1-67@MN) was superior to MN loaded with a single drug. Compared with subcutaneous injection, TCZ/Apt1-67@MN was of great advantage in inhibiting bone erosion and alleviating symptoms of CIA mice. This study not only provides a novel approach for combined medication with different release properties but also supplies a strategy for improving drug efficacy.

Dissolvable polymer microneedles for drug delivery and diagnostics

Dissolvable transdermal microneedles (μND) are promising micro-devices used to transport a wide selection of active compounds into the skin. To provide an effective therapeutic outcome, μNDs must pierce the human stratum corneum (~10 to 20 μm), without rupturing or bending during penetration, then release their cargo at the predetermined area and time. The ability of dissolvable μND arrays/patches to sufficiently pierce the skin is a crucial requirement, which depends on the material composition, μND geometry and fabrication techniques. This comprehensive review not only provides contemporary knowledge on the μND design approaches, but also the materials science facilitating these delivery systems and the opportunities these advanced materials can provide to enhance clinical outcomes.

Design and characterization of polymeric microneedles containing extracts of Brazilian green propolis

Microneedles (MNs) are a means to break the protective skin barrier in a minimally invasive way. By creating temporary micropores, they make biologically active agents available in the skin layers. Propolis (PRP) is a gum resin with a complex chemical composition, produced by bees Apis mellifera L. and showing several therapeutic properties (i.e., antibacterial, antiviral, antifungal, anti-inflammatory, healing, and immunomodulatory properties). The administration of PRP extracts by conventional routes has some disadvantages, such as running off over the skin in liquid or emulsion form. When taken orally, the extracts have a strong and unpleasant taste. The aim of this work was to fabricate and characterize microneedles containing polyvinyl alcohol, polyvinylpyrrolidone, poloxamer P407, and an ethanolic or glycolic extract of PRP. Also, the obtained structures were microscopically and mechanically characterized. The results of the mechanical analysis showed that formulations containing 3% of P407 presented the highest compression values in a hard surface, which was also confirmed by the height and base values of the morphological analysis and by the microscopy images. It was possible to design MNs and select the best formulations for future tests. MNs containing an ethanolic extract of PRP showed to be better structured than MNs containing a glycolic extract of PRP. The MNs obtained in these studies proved to be a promising platform for the topical application of PRP.

Recent Advances in Microneedle Platforms for Transdermal Drug Delivery Technologies

In many clinical applications, the transdermal route is used as an alternative approach to avoid the significant limitations associated with oral drug delivery. There is a long history for drug delivery through the skin utilizing transdermal microneedle arrays. Microneedles are reported to be versatile and very efficient devices. This technique has spurred both industrial and scientific curiosity, due to its outstanding characteristics such as painless penetration, affordability, excellent medicinal efficiency, and relative protection. Microneedles possess outstanding properties for diverse biomedical uses such as the delivery of very large substances with ionic and hydrophilic physicochemical properties. Importantly, microneedles are applicable in numerous biomedical fields such as therapy, diagnosis, and vaccine administration. Microneedles are emerging tools that have shown profound potential for biomedical applications. Transdermal microneedle technologies are likely to become a preferred route of therapeutic substances administration in the future since they are effective, painless, and affordable. In this review, we summarize recent advances in microneedles for therapeutic applications. We explore their constituent materials and fabrication methods that improve the delivery of critical therapeutic substances through the skin. We further discuss the practicality of advanced microneedles used as drug delivery tools.

Optimization of Layered Dissolving Microneedle for Sustained Drug Delivery Using Heat-Melted Poly(Lactic-Co-glycolic Acid)

Dissolving microneedles (DMNs) have been used as an alternative drug delivery system to deliver therapeutics across the skin barrier in a painless manner. In this study, we propose a novel heat-melting method for the fabrication of hydrophobic poly(lactic-co-glycolic acid) (PLGA) DMNs, without the use of potentially harmful organic solvents. The drug-loaded PLGA mixture, which consisted of a middle layer of the DMN, was optimized and successfully implanted into ex vivo porcine skin. Implanted HMP-DMNs separated from the patch within 10 min, enhancing user compliance, and the encapsulated molecules were released for nearly 4 weeks thereafter. In conclusion, the geometry of HMP-DMNs was successfully optimized for safe and effective transdermal sustained drug delivery without the use of organic solvents. This study provides a strategy for the innovative utilization of PLGA as a material for transdermal drug delivery systems.

Microvascular effects of microneedles with subsequent histamin application in the skin prick test

BACKGROUND

Since decades, histamin applications are routinely performed in skin prick tests using a lancet. However, this technique is associated with various drawbacks.

MATERIALS AND METHODS

In healthy human subjects, we investigated the effects of microneedle-enhanced histamin delivery (wheal size, erythema size) in the skin microvasculature using polarized light spectroscopy imaging (Tissue Viability imaging, TiVi). Histamin was applied on microneedle-pretreated skin or on -untreated skin, to assess the microvascular response in the local skin.

RESULTS

In our results, histamin was delivered more rapidly into the skin after microneedle pretreatment compared to passive diffusion, visible as wheal and erythema.

CONCLUSION

The here presented technique might be useful for a personalized drug-testing system in the future.

Microvascular effects of microneedle application

BACKGROUND

The efficiency of transdermal drug delivery may be increased by pretreating the skin with microneedles, but distinct effects of microneedles and the microneedle-enhanced delivery of vasoactive drugs on the skin microvasculature are still not well investigated.

MATERIALS AND METHODS

In eight healthy human subjects, we measured the microvascular response to microneedle-induced microtraumas in the skin microvasculature using polarized light spectroscopy imaging (Tissue Viability imaging, TiVi). The microvascular response was assessed for up to 48 hours for three microneedle sizes (300 µm, 500 µm, and 750 µm) and for different pressures and application times.

RESULTS

In our results, microneedle application increased the local red blood cell (RBC) concentration for up to 24 hours dependent on the needle lengths, applied time, and force.

CONCLUSION

Optimization of microneedles size, pressure, and application time should be taken into account for future protocols for drug delivery and experimental provocations.

Using in vivo multiphoton fluorescence lifetime imaging to unravel disease-specific changes in the liver redox state

Multiphoton fluorescence lifetime microscopy has revolutionized studies of pathophysiological and xenobiotic dynamics, enabling the spatial and temporal quantification of these processes in intact organs in vivo. We have previously used multiphoton fluorescence lifetime microscopy to characterise the morphology and amplitude weighted mean fluorescence lifetime of the endogenous fluorescent metabolic cofactor nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) of mouse livers in vivo following induction of various disease states. Here, we extend the characterisation of liver disease models by using nonlinear regression to estimate the unbound, bound fluorescence lifetimes for NAD(P)H, flavin adenine dinucleotide (FAD), along with metabolic ratios and examine the impact of using multiple segmentation methods. We found that NAD(P)H amplitude ratio, and fluorescence lifetime redox ratio can be used as discriminators of diseased liver from normal liver. The redox ratio provided a sensitive measure of the changes in hepatic fibrosis and biliary fibrosis. Hepatocellular carcinoma was associated with an increase in spatial heterogeneity and redox ratio coupled with a decrease in mean fluorescence lifetime. We conclude that multiphoton fluorescence lifetime microscopy parameters and metabolic ratios provided insights into the in vivo redox state of diseased compared to normal liver that were not apparent from a global, mean fluorescence lifetime measurement alone.

Noninvasive in vivo human multiphoton microscopy: a key method in proving nanoparticulate zinc oxide sunscreen safety

We describe the contribution of our in vivo multiphoton microscopy (MPM) studies over the last ten years with DermaInspect^;® (JenLab, Germany), a CE-certified medical tomograph based on detection of fluorescent biomolecules, to the assessment of possible penetration of nanoparticulate zinc oxide in sunscreen through human skin. At the time we started our work, there was a strong movement for the precautionary principle to be applied to the use of nanoparticles in consumer products due to a lack of knowledge. The combined application of different MPM modalities, including spectral imaging, fluorescence lifetime imaging, second harmonic fluorescence generation, and phosphorescence microscopy, has provided overwhelming evidence that nanoparticle zinc oxide particles do not penetrate human skin when applied to various skin types with a range of methods of topical sunscreen application. MPM has also been used to study the viable epidermal morphology and redox state in supporting the safe use of topical zinc oxide nanoparticles. The impact of this work is emphasized by the recent proposed rule by the United States FDA on Sunscreen Drug Products for Over-the-Counter Human Use, which listed only zinc oxide and titanium dioxide of the currently marketed products to be generally recognized as safe and effective.