Microneedles permit transdermal delivery of a skin-impermeant medication to humans

Pretreatment of microneedles enhances passive transdermal administration of pilocarpine and pilocarpine-induced sweat production in humans

The development of an effective transdermal drug delivery protocol to eccrine sweat glands is important for the advancement of research on the human sweating response. We investigated whether microneedle treatment prior to the application of pilocarpine, a hydrophilic and sudorific agent that does not induce sweating due to a limited percutaneous passive diffusion by skin application alone, augments sweat production. We applied three microneedle arrays to forearm skin sites simultaneously (n = 20). Upon removal of the microneedles, 1 % pilocarpine was applied to each site for 5-, 15-, and 30-min for the assessment of sweat gland function. In parallel, pilocarpine was administered by transdermal iontophoresis (5-min) at a separate site. Sweat rate was assessed continuously via the ventilated capsule technique. Pilocarpine augmented sweat rate at the 15- and 30-min periods as compared to the application at 5-min. The sweating responses induced by the 15- and 30-min application of pilocarpine were equivalent to ∼ 80 % of that measured at the iontophoretically treated sites. Notably, we observed a correlation in sweat rate between these two transdermal drug delivery methods. Altogether, our findings show that pre-treatment of microneedle arrays can enhance transdermal delivery efficiency of pilocarpine to human eccrine sweat glands.

Long-acting transdermal drug delivery formulations: Current developments and innovative pharmaceutical approaches

Transdermal administration remains an active research and development area as an alternative route for long-acting drug delivery. It avoids major drawbacks of conventional oral (gastrointestinal side effects, low drug bioavailability, and need for multiple dosing) or parenteral routes (invasiveness, pain, and psychological stress and bio-hazardous waste generated from needles), thereby increasing patient appeal and compliance. This review focuses on the current state of long-acting transdermal drug delivery, including adhesive patches, microneedles, and molecularly imprinted polymeric systems. Each subsection describes an approach including key considerations in formulation development, design, and process parameters with schematics. An overview of commercially available conventional (adhesive) patches for long-acting drug delivery (longer than 24 h), the reservoir- and matrix-type systems under preclinical evaluation, as well as the advanced transdermal formulations, such as the core-shell, nanoformulations-incorporated and stimuli-responsive microneedles, and 3D-printed and molecularly imprinted polymers that are in development, is also provided. Finally, we elaborated on translational aspects, challenges in patch formulation development, and future directions for the clinical advancement of new long-acting transdermal products.

3D printing redefines microneedle fabrication for transdermal drug delivery

Microneedles (MNs) have emerged as an innovative, virtually painless technique for intradermal drug delivery. However, the complex and costly fabrication process has limited their widespread accessibility, especially for individuals requiring frequent drug administration. This study introduces a groundbreaking and cost-effective method for producing MNs utilizing fused deposition modeling (FDM) 3D printing technology to enhance transdermal drug delivery. The proposed fabrication process involves the elongation of molten polylactic acid (PLA) filaments to create meticulously designed conoid and neiloid MNs with smooth surfaces. This study underscores the critical role of printing parameters, particularly extrusion length and printing speed, in determining the shape of the MNs. Notably, the conoid-shaped MNs exhibit exceptional skin-penetrating capabilities. In order to evaluate their effectiveness, the MNs were tested on a polydimethylsiloxane (PDMS) skin model for skin penetration. The results highlight the high potential of 3D-printed MNs for transdermal drug administration. This novel approach capitalizes on the benefits of 3D printing technology to fabricate MNs that hold the promise of transforming painless drug administration for a variety of medical applications.

Impact of Formulation and Microneedle Length on Transdermal Metronidazole Permeation through Microneedle-Treated Skin

OBJECTIVE

This study aimed to determine the impact of formulation (gel vs cream) and microneedle characteristics (length, number) on permeation of metronidazole through excised microneedle-treated skin. The long-term goal is to apply these results towards a pharmacokinetic study in human subjects with diverse skin types, using in vitro flux data to determine dosing conditions and ultimately establish in vitro-in vivo correlations.

METHODS

Metronidazole release from 0.75% gel and cream was quantified with flow-through diffusion cells, using a cellulose membrane. Excised porcine skin was treated with stainless steel microneedles (500 or 800 μm length), to create 50 or 100 micropores. Metronidazole gel or cream was applied to microneedle-treated skin and replaced every 48 h for up to 7 days. Metronidazole permeation was quantified using HPLC. Intact skin (no microneedle treatment) served as controls.

RESULTS

Metronidazole release was faster from the gel vs cream. At 7 days there was no difference between gel vs cream in total metronidazole permeated through intact skin. For both formulations, metronidazole permeation was significantly higher (vs intact skin) following microneedle application, regardless of microneedle length or micropore number. Increasing microneedle length and micropore number enhanced MTZ permeation multiple fold for both gel and cream. The greatest enhancement in total permeation for both formulations was achieved with the 800 μm MN, 100 micropore condition.

CONCLUSIONS

Formulation and microneedle conditions both impacted metronidazole permeation. These data will be used to estimate in vivo serum concentrations after applying metronidazole to microneedle-treated skin in humans.

Thermosensitive biomaterial gels with chemical permeation enhancers for enhanced microneedle delivery of naltrexone for managing opioid and alcohol dependency

Naltrexone (NTX) can be transdermally delivered using microneedles (MN) to treat opioid and alcohol misuse disorders, but delivery is blunted by rapid in vivo micropore closure. Poloxamer (P407), a thermosensitive biocompatible hydrogel, sustains NTX delivery through MN-treated skin by generating a drug depot within the micropores. Optimizing P407 formulations could maintain sustained delivery after micropore closure while reducing required patch sizes, which would be more discreet and preferred by most patients. Here we developed NTX-loaded P407 gels with chemical permeation enhancers (CPEs) and used these novel formulations alongside MN treatment to enhance NTX permeation, utilizing parallel micropore and intact skin transport pathways. We analyzed physicochemical and rheological properties of CPE-loaded P407 formulations and selected formulations with DMSO and benzyl alcohol for further study. In vitro permeation tests demonstrated more consistent and sustained NTX delivery through MN-treated porcine skin from 16% P407 formulations vs. aqueous solutions. P407 with 1% benzyl alcohol and 10% DMSO significantly, P < 0.05, increased flux through MN-treated skin vs. formulations with benzyl alcohol alone. This formulation would require a smaller size patch than previously used to deliver NTX in humans, with half the NTX concentration. This is the first time poloxamer biomaterials have been used in combination with CPEs to improve MN-assisted transdermal delivery of an opioid antagonist. Here we have demonstrated that P407 in combination with CPEs effectively sustains NTX delivery in MN-treated skin while requiring less NTX than previously needed to meet clinical goals.

Transformative Materials for Interfacial Drug Delivery

Drug delivery systems (DDS) are designed to temporally and spatially control drug availability and activity. They assist in improving the balance between on-target therapeutic efficacy and off-target toxic side effects. DDS aid in overcoming biological barriers encountered by drug molecules upon applying them via various routes of administration. They are furthermore increasingly explored for modulating the interface between implanted (bio)medical materials and host tissue. Herein, an overview of the biological barriers and host-material interfaces encountered by DDS upon oral, intravenous, and local administration is provided, and material engineering advances at different time and space scales to exemplify how current and future DDS can contribute to improved disease treatment are highlighted.

Design, analysis and fabrication of solid polymer microneedle patch using CO2 laser and polymer molding

Microneedle-based transdermal drug delivery into the skin has gained attraction for the past few years. An affordable and effective fabrication methodology is required for the development of micron size needle. Manufacturing cost-effective microneedle patches in batch production is a challenging process. In this work, we proposed a cleanroom-free technique for fabrication of conical and pyramidal geometry of microneedle array for transdermal drug delivery. Using the COMSOL Multiphysics tool, the mechanical strength of the designed microneedle array under axial, bending, and buckling loads for the geometries during skin insertion was investigated. A CO2 laser and polymer molding technique are used to fabricate 10 × 10 designed microneedle array structure. On an acrylic sheet, a designed pattern is engraved to produce a 20 mm × 20 mm sharp conical and pyramidal shape master mold. We successfully created a biocompatible polydimethylsiloxane (PDMS) microneedle patch with an average height of 1200 µm, base diameter of 650 µm, and a tip diameter of 50 µm using acrylic master mold. According to structural simulation analysis, the microneedle array will experience resultant stress that is within a safe range. The mechanical stability of the fabricated microneedle patch was investigated using hardness test and universal testing machine. The depth of penetration studies were performed in an in vitro Parafilm® M model by manual compression tests and its detailed insertion depth was reported. The developed master mold is efficient to replicate several polydimethylsiloxane microneedle patches. The proposed combined method of laser processing and molding mechanism is simple and low-cost for rapid prototyping of microneedle array.

Quantification methods comparing in vitro and in vivo percutaneous permeation by microneedles and passive diffusion

Microneedles (MNs) are needles with a tip diameter ranging from 10 to 100 um and a length ranging up to 1 mm. The first patent for drug delivery device for percutaneous administration filed by Alza corporation dates back to 1976 (Gerstel and Place, 1976), and in between 1989 and 2021 the filed patents for MNs are more than 4500 (Banks et al., 2010). These devices can potential overcome some drawbacks of traditional needles, such as the pain generated during insertion, requirement for trained personnel to manipulate syringes, and difficulty of performing injections in elderly and obese patients. MNs and MNs arrays are emerging as a convenient method to deliver compounds and extract blood without causing any pain. A promising application is the use of MNs as alternative solution to topical creams (TC) and transdermal patches (TP) for transdermal drug delivery. The external layer of human skin, the epidermis, offers a major barrier to transdermal drug delivery, thanks to the stratum corneum (SC). Exposed to the external environment, SC ultimately protects the human body from UV light radiation, heat, water loss, bacteria, fungi and viruses, and it is the barrier that controls diffusion rate for almost all compounds. TC and TP applications are limited by the skin permeability to lipophilic compounds and small molecules, and by the slow delivery rate of some compounds. MNs have been around for more than 35 year now, and it is a general opinion that MN increase delivery compared to passive diffusion, thanks to the feature of penetrating the SC and reaching the dermis. This review recollects the existing studies that compare MNs delivery of drugs with passive diffusion of the same drugs in alive organisms, giving an overview of what are the type of MNs, the chemical delivered and the methods employed to quantify drug delivery into skin and/or in the bloodstream. The final aim is to quantify the enhancement factor of MNs with respect to passive diffusion, and establish a possible standard on how tests can be performed in order to compare different data.

Dissolving Microneedles Loaded with Gestodene: Fabrication and Characterization In Vitro and In Vivo

Background

Gestodene (GEST) is widely used in female contraception. It is currently being used as an oral contraceptive. However, unfortunately, oral contraceptives are often associated with several bothersome side effects and poor compliance. Therefore, a sustained delivery system for GEST to overcome these shortcomings is highly desirable.

Objectives

The present study successfully developed a kind of novel dissolving microneedles (DMNs) with a potential for sustained release and a minimally invasive intradermal treatment of GEST.

Methods

The dissolving microneedles containing GEST were fabricated using polyvinylpyrrolidone as the base material. The characteristics in vitro and pharmacokinetics in vivo of GEST-loaded DMNs were investigated.

Results

The results showed that the microneedle could pierce the porcine skin and release the drug at an average dose of 20µg/cm2 daily for seven days. The pharmacokinetic experiment of the microneedles indicated that the plasma level of GEST in rats increased with increasing drug dosage, and the plasma drug concentration-time curves were much flatter compared with subcutaneous injection and oral administration. In addition, no cutaneous irritation was observed.

Conclusions

GEST-loaded DMNs may be a promising intradermal sustained delivery system for contraceptive use.

Metallic Microneedles for Transdermal Drug Delivery: Applications, Fabrication Techniques and the Effect of Geometrical Characteristics

Current procedures for transdermal drug delivery (TDD) have associated limitations including poor administration of nucleic acid, small or large drug molecules, pain and stress for needle phobic people. A painless micro-sized device capable of delivering drugs easily and efficiently, eliminating the disadvantages of traditional systems, has yet to be developed. While polymeric-based microneedle (MN) arrays have been used successfully and clinically as TDD systems, these devices lack mechanical integrity, piercing capacity and the ability to achieve tailored drug release into the systemic circulation. Recent advances in micro/nano fabrication techniques using Additive Manufacturing (AM), also known as 3D printing, have enabled the fabrication of metallic MN arrays, which offer the potential to overcome the limitations of existing systems. This review summarizes the different types of MNs used in TDD and their mode of drug delivery. The application of MNs in the treatment of a range of diseases including diabetes and cancer is discussed. The potential role of solid metallic MNs in TDD, the various techniques used for their fabrication, and the influence of their geometrical characteristics (e.g., shape, size, base diameter, thickness, and tip sharpness) on effective TDD are explored. Finally, the potential and the future directions relating to the optimization of metallic MN arrays for TDD are highlighted.

Microneedle-Mediated Permeation Enhancement of Chlorhexidine Digluconate: Mechanistic Insights Through Imaging Mass Spectrometry

PURPOSE

Chlorhexidine digluconate (CHG) is a first-line antiseptic agent typically applied to the skin as a topical solution prior to surgery due to its efficacy and safety profile. However, the physiochemical properties of CHG limits its cutaneous permeation, preventing it from reaching potentially pathogenic bacteria residing within deeper skin layers. Thus, the utility of a solid oscillating microneedle system, Dermapen®, and a CHG-hydroxyethylcellulose (HEC) gel were investigated to improve the intradermal delivery of CHG.

METHODS

Permeation of CHG from the commercial product, Hibiscrub®, and HEC-CHG gels (containing 1% or 4% CHG w/w) was assessed in intact skin, or skin that had been pre-treated with microneedles of different array numbers, using an Franz diffusion cells and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

RESULTS

Gels containing 1% and 4% CHG resulted in significantly increased depth permeation of CHG compared to Hibiscrub® (4% w/v CHG) when applied to microneedle pre-treated skin, with the effect being more significant with the higher array number. ToF-SIMS analysis indicated that the depth of dermal penetration achieved was sufficient to reach the skin strata that typically harbours pathogenic bacteria, which is currently inaccessible by Hibiscrub®, and showed potential lateral diffusion within the viable epidermis.

CONCLUSIONS

This study indicates that HEC-CHG gels applied to microneedle pre-treated skin may be a viable strategy to improve the permeation CHG into the skin. Such enhanced intradermal delivery may be of significant clinical utility for improved skin antisepsis in those at risk of a skin or soft tissue infection following surgical intervention.

Core-shell microneedle patch for six-month controlled-release contraceptive delivery

There is a tremendous need for simple-to-administer, long-acting contraception, which can increase access to improved family planning. Microneedle (MN) patches enable simple self-administration and have previously been formulated for 1-2 months' controlled release of contraceptive hormone using monolithic polymer/drug MN designs having first-order release kinetics. To achieve zero-order release, we developed a novel core-shell MN patch where the shell acts as a rate-controlling membrane to delay release of a contraceptive hormone, levonorgestrel (LNG), for 6 months. In this approach, LNG was encapsulated in a poly(lactide-co-glycolide) (PLGA) core surrounded by a poly(l-lactide) (PLLA) shell and a poly(D,l-lactide) (PLA) cap that were fabricated by sequential casting into a MN mold. Upon application to skin, the core-shell MNs utilized an effervescent interface to separate from the patch backing within 1 min. The core-shell design limited the initial 24 h burst release of LNG to 5.8 ± 0.5% and achieved roughly zero-order LNG release for 6.2 ± 0.1 months in vitro. A monolithic MN patch formulated with the same LNG and PLGA core, but without the rate-controlling PLLA shell and PLA cap had a larger LNG burst release of 22.6 ± 2.0% and achieved LNG release for just 2.1 ± 0.2 months. This study provides the first core-shell MN patch for controlled months-long drug release and supports the development of long-acting contraception using a simple-to-administer, twice-per-year MN patch.

In-Plane Si Microneedles: Fabrication, Characterization, Modeling and Applications

Microneedles are getting more and more attention in research and commercialization since their advancement in the 1990s due to the advantages over traditional hypodermic needles such as minimum invasiveness, low material and fabrication cost, and precise needle geometry control, etc. The design and fabrication of microneedles depend on various factors such as the type of materials used, fabrication planes and techniques, needle structures, etc. In the past years, in-plane and out-of-plane microneedle technologies made by silicon (Si), polymer, metal, and other materials have been developed for numerous biomedical applications including drug delivery, sample collections, medical diagnostics, and bio-sensing. Among these microneedle technologies, in-plane Si microneedles excel by the inherent properties of Si such as mechanical strength, wear resistance, biocompatibility, and structural advantages of in-plane configuration such as a wide range of length, readiness of integration with other supporting components, and complementary metal-oxide-semiconductor (CMOS) compatible fabrication. This article aims to provide a review of in-plane Si microneedles with a focus on fabrication techniques, theoretical and numerical analysis, experimental characterization of structural and fluidic behaviors, major applications, potential challenges, and future prospects.

Microneedles in Action: Microneedling and Microneedles-Assisted Transdermal Delivery

Human skin is a multilayered physiochemical barrier protecting the human body. The stratum corneum (SC) is the outermost keratinized layer of skin through which only molecules with less or equal to 500 Da (Dalton) in size can freely move through the skin. Unfortunately, the conventional use of a hypothermic needle for large therapeutic agents is susceptible to needle phobia and the risk of acquiring infectious diseases. As a new approach, a microneedle (MN) can deliver therapeutically significant molecules without apparent limitations associated with its molecular size. Microneedles can create microchannels through the skin’s SC without stimulating the proprioceptive pain nerves. With recent technological advancements in both fabrication and drug loading, MN has become a versatile platform that improves the efficacy of transdermally applied therapeutic agents (TAs) and associated treatments for various indications. This review summarizes advanced fabrication techniques for MN and addresses numerous TA coating and TA elution strategies from MN, offering a comprehensive perspective on the current microneedle technology. Lastly, we discuss how microneedling and microneedle technologies can improve the clinical efficacy of a variety of skin diseases.

Microneedle-Based Natural Polysaccharide for Drug Delivery Systems (DDS): Progress and Challenges

In this focused progress review, the most widely accepted methods of transdermal drug delivery are hypodermic needles, transdermal patches and topical creams. However, microneedles (MNs) (or microneedle arrays) are low-invasive 3D biomedical constructs that bypass the skin barrier and produce systemic and localized pharmacological effects. In the past, biomaterials such as carbohydrates, due to their physicochemical properties, have been extensively used to manufacture microneedles (MNs). Due to their wide range of functional groups, carbohydrates enable the design and development of tunable properties and functionalities. In recent years, numerous microneedle products have emerged on the market, although much research needs to be undertaken to overcome the various challenges before the successful introduction of microneedles into the market. As a result, carbohydrate-based microarrays have a high potential to achieve a future step in sensing, drug delivery, and biologics restitution. In this review, a comprehensive overview of carbohydrates such as hyaluronic acid, chitin, chitosan, chondroitin sulfate, cellulose and starch is discussed systematically. It also discusses the various drug delivery strategies and mechanical properties of biomaterial-based MNs, the progress made so far in the clinical translation of carbohydrate-based MNs, and the promotional opportunities for their commercialization. In conclusion, the article summarizes the future perspectives of carbohydrate-based MNs, which are considered as the new class of topical drug delivery systems.

Products for Monitoring Glucose Levels in the Human Body With Noninvasive Optical, Noninvasive Fluid Sampling, or Minimally Invasive Technologies

BACKGROUND

Conventional home blood glucose measurements require a sample of blood that is obtained by puncturing the skin at the fingertip. To avoid the pain associated with this procedure, there is high demand for medical products that allow glucose monitoring without blood sampling. In this review article, all such products are presented.

METHODS

In order to identify such products, four different sources were used: (1) PubMed, (2) Google Patents, (3) Diabetes Technology Meeting Startup Showcase participants, and (4) experts in the field of glucose monitoring. The information obtained were filtered by using two inclusion criteria: (1) regulatory clearance, and/or (2) significant coverage in Google News starting in the year 2016, unless the article indicated that the product had been discontinued. The identified bloodless monitoring products were classified into three categories: (1) noninvasive optical, (2) noninvasive fluid sampling, and (3) minimally invasive devices.

RESULTS

In total, 28 noninvasive optical, 6 noninvasive fluid sampling, and 31 minimally invasive glucose monitoring products were identified. Subsequently, these products were characterized according to their regulatory, technological, and consumer features. Products with regulatory clearance are described in greater detail according to their advantages and disadvantages, and with design images.

CONCLUSIONS

Based on favorable technological features, consumer features, and other advantages, several bloodless products are commercially available and promise to enhance diabetes management. Paths for future products are discussed with an emphasis on understanding existing barriers related to both technical and non-technical issues.

Passive and iontophoretic transport of pramipexole dihydrochloride across human skin microchannels created by microneedles in vitro

Skin microchannels (MCs) created by microneedles (MNs) provide a promising route for enhancing transdermal drug delivery. This study investigated passive and iontophoretic transport of pramipexole dihydrochloride (PXCl) across skin MCs created by polymer MN patches made of 1:2 polymethyl-vinyl-ether-co-maleic acid (PMVEMA) to polyvinyl alcohol (PVA) ratio. Permeation studies were performed in vitro using excised human skin under the conditions of (i) "poke-and-patch" and "poke-and-release" delivery approaches with varying concentration of PXCl in the formulations, (ii) drug-loaded dissolving MN (DMN) and hydrogel-forming MN (HGMN) type patches and (iii) combination of MNs and iontophoresis. The results showed that DMN patch greatly enhanced transdermal delivery of PXCl for both "poke-and-patch" and "poke-and-release" approaches as compared with the conventional delivery method. PXCl flux mainly resulted from the contribution of MC pathway created in skin and increased with increasing drug amounts in the formulations. Compared to DMN patch, HGMN patch provided more linear sustained drug delivery over 72 h. Electromigration was the main mechanism of PXCl iontophoresis through MCs and flux enhancement was found to be larger for HGMN patch than DMN patch. These results demonstrated the potential application of MN patches individually or combined with iontophoresis as an alternative method for PXCl administration.

Microneedle patch designs to increase dose administered to human subjects

Microneedle (MN) patches are being developed for many different kinds of drugs, but are often limited to delivering sub-milligram doses. This is because larger patches can be more difficult to apply to the skin, and acceptability of larger MN patches by human subjects has received limited study. Here, we fabricated 18 different large MN patch designs by laser microfabrication with different MN length (800-1500 μm), number of MNs (225 to 900 MNs per patch), space between MNs (600-1100 μm), and MN base diameter (200-250 μm). After manual application of these patches to human participants, we assessed dose delivery efficiency, total dose delivered, dose delivered per MN, depth of MN penetration and whole-MN delivery efficiency. We found that all of these parameters generally increased with decreased MN length, increased number of MNs (among those ≤1000 μm in length) and increased MN-MN spacing. All MN patch designs caused less pain than a pin prick sensation and were generally considered acceptable by the study participants. The MN patches induced mild, or sometimes moderate, transient erythema on skin. Study participants showed higher preference for MN patches for long-acting contraception compared with conventional options, indicating strong interest and acceptability of MN patches in this study.

Electro-Mechanochemical Gating of a Metal-Phenolic Nanocage for Controlled Guest-Release Self-Powered Patches and Injectable Gels

Recent advances have led to the development of intelligent drug-delivery systems such as microchips, micropumps, and soft devices with sensors; however, the facile preparation of transdermal and implantable systems modulable to various stimuli remains elusive. In addition, the use of a battery limits their wearable and implantable applications. Therefore, to overcome these disadvantages, we herein suggest a facile strategy to prepare electro-mechanochemically responsive soft gel composites with molecular gatekeeper-based nanocontainers. We found that a metal-phenolic coordination network can act as an efficient self-healable and adaptive gatekeeper in response to electrical and mechanical stimuli owing to the reversible dynamic bonds and adhesiveness to the silica surface. The porous channels of mesoporous silica nanoparticles are filled with guest molecules, and the exterior is wrapped with metal-tannic acid (TA) networks. Owing to the robustness of metal-phenolic network, the guest molecules are efficiently entrapped in the channels but released by electrical and ultrasound input. Voltage-dependent changes in the guest release rate provide control over the dosage on demand. The combination of hydrogel matrixes with the responsive nanocapsules enables the construction of a series of adaptive gel composites capable of successive guest release in response to electrical, ultrasound, electromechanical, and triboelectric stimuli. The Korsmeyer-Peppas model revealed that the release mechanism is non-Fickian, which indicates the presence of boundaries around the guest-loading channels (n = 0.739, R² = 0.9574 when 2 V is applied). This study realized efficient platforms for active-type drug-delivery applications based on transdermal patches and implantable gels with remotely controllable release characteristics.

A Combined Approach for Fast Nanofat Microneedling

Background

Lipofilling is currently a fundamental component of rhytidoplasty and fat harvesting has become a common procedure. Tonnard introduced the concept of nanofat grafting, a revolutionary milestone, in which adipocytes are mechanically separated from the stromal vascular fraction and the latter is injected, adding the possibility of cellular therapies to the surgical field. Later, Verpaele et al. published a report using a new device to apply this nanofat in a uniform manner, which they termed nanofat needling. The device has 24 microneedles of 1.5 mm length and is applied as a stamp, in a tapping motion. The same manufacturer offers a similar model with 64 microneedles, 1.0 mm length, and available as a roller.

Objectives

We sought to evaluate the combination of the above-mentioned microneedling devices to achieve faster nanofat delivery.

Materials and Methods

A prospective evaluation of patients undergoing a combined nanofat microneedling approach for skin rejuvenation and scar revision, using both a stamp device as well as a roller, was performed in a private practice setting, from January 2019 to January 2020. Patient satisfaction, complications, and surgical time were evaluated.

Results

We applied this combination treatment to over 100 treatment areas in 86 patients over a 12-month period, with a short operative time, no increase in complications, consistent results, and good patient satisfaction.

Conclusions

We recommend the use of this new device in association with the original one, in order to decrease the procedure time. We designate this strategy "fast nanofat microneedling."

Micropore Closure Rates following Microneedle Application at Various Anatomical Sites in Healthy Human Subjects

INTRODUCTION

The continuous availability of open micropores is crucial for a successful microneedle (MN) drug delivery strategy. However, micropore lifetime depends on intrinsic skin functional and anatomical characteristics, which vary significantly at different anatomical sites.

OBJECTIVE

This pilot study explored if differences exist in micropore closure timeframes at 3 anatomical sites - upper arm, volar forearm, and abdomen.

METHODS

Healthy subjects (n = 35) self-identifying as Asian (n = 9), Bi-/multiracial (n = 2), Black (n = 9), Latino (n = 6), and White (n = 9) completed the study. The upper arm, volar forearm, and abdomen were treated with MNs; skin impedance and transepidermal water loss (TEWL) were measured at baseline and post-MN to confirm micropore formation. Impedance was measured for 3 days to evaluate micropore lifetime. Measurements of L*, which quantifies the skin lightness/darkness, were made using a tristimulus colorimeter. Micropore lifetime was determined by comparing baseline and post-MN impedance measurements, and micropore closure half-life was predicted using mathematical modeling.

RESULTS

Post-MN increase in TEWL and decrease in impedance were significant (p < 0.05), confirming successful micropore formation at all anatomical sites. When data were analyzed according to subject self-identified racial/ethnic groups, the mean micropore closure time at the abdomen (63.09 ± 13.13 h) was longer than the upper arm (60.34 ± 14.69 h) and volar forearm (58.29 ± 16.76 h). The predicted micropore closure half-life at anatomical sites was the abdomen (25.86 ± 14.96 h) ≈ upper arm (23.69 ± 13.67 h) > volar forearm (20.2 ± 11.99 h). Differences were not statistically significant between groups. Objective categorization by L* showed that the darker skin may be associated with longer micropore closure time at the abdomen site.

CONCLUSIONS

Our results suggest that anatomical site of application may not be a source of significant variability in micropore closure time. These findings may help reduce the number of physiological parameters that need to be explicitly considered when developing drug products to support MN-assisted drug delivery strategies.

Thermosensitive Gels Used to Improve Microneedle-Assisted Transdermal Delivery of Naltrexone

Transdermal delivery of naltrexone (NTX) can be enhanced using microneedles, although micropores generated this way can reseal by 48 h in humans, which prevents further drug delivery from a formulation. Poloxamer 407 (P407) is a thermosensitive polymer that may extend microneedle-assisted NTX delivery time by creating an in situ gel depot in the skin. We characterized gelation temperature, drug release, and permeation of P407 gels containing 7% NTX-HCl. To investigate microneedle effects on NTX-HCl permeation, porcine skin was treated with microneedles (600 or 750 μm length), creating 50 or 100 micropores. The formulations were removed from the skin at 48 h to simulate the effect of micropores resealing in vivo, when drug delivery is blunted. Gelation temperature increased slightly with addition of NTX-HCl. In vitro NTX-HCl release from P407 formulations demonstrated first order release kinetics. Microneedle treatment enhanced NTX-HCl permeation both from aqueous solution controls and P407 gels. Steady-state flux was overall lower in the P407 conditions compared to the aqueous solution, though ratios of AUCs before and after gel removal demonstrate that P407 gels provide more sustained release even after gel removal. This may be beneficial for reducing the required application frequency of microneedles for ongoing treatment.

2D and 3D inkjet printing of biopharmaceuticals - A review of trends and future perspectives in research and manufacturing

There is an ongoing global shift in pharmaceutical business models from small molecule drugs to biologics. This increase in complexity is in response to advancements in our diagnoses and understanding of diseases. With the more targeted approach coupled with its inherently more costly development and manufacturing, 2D and 3D printing are being explored as suitable techniques to deliver more personalised and affordable routes to drug discovery and manufacturing. In this review, we explore first the business context underlying this shift to biopharmaceuticals and provide an update on the latest work exploring discovery and pharmaceutics. We then draw on multiple disciplines to help reveal the shared challenges facing researchers and firms aiming to develop biopharmaceuticals, specifically when using the most commonly explored manufacturing routes of drop-on-demand inkjet printing and pneumatic extrusion. This includes separating out how to consider mechanical and chemical influences during manufacturing, the role of the chosen hardware and the challenges of aqueous formulation based on similar challenges being faced by the printing industry. Together, this provides a review of existing work and guidance for researchers and industry to help with the de-risking and rapid development of future biopharmaceutical products.

Emerging era of microneedle array for pharmaceutical and biomedical applications: recent advances and toxicological perspectives

Background

Microneedles (MNs) are the utmost unique, efficient, and minimally invasive inventions in the pharmaceutical field. Over the past decades, many scientists around the globe have reported MNs cautious because of their superb future in distinct areas. Concerning the wise use of MNs herein, we deal in depth with the present applications of MNs in drug delivery.

Main text

The present review comprises various fabrication materials and methods used for MN synthesis. The article also noted the distinctive advantages of these MNs, which holds huge potential for pharmaceutical and biomedical applications. The role of MNs in serving as a platform to treat various ailments has been explained accompanied by unusual approaches. The review also inculcates the pharmacokinetics of MNs, which includes permeation, absorption, and bioavailability enhancement. Besides this, the in vitro/in vivo toxicity, biosafety, and marketed product of MNs have been reviewed. We have also discussed the clinical trials and patents on the pharmaceutical applications of MNs in brief.

Conclusion

To sum up, this article gives insight into the MNs and provides a recent advancement in MNs, which pave the pathway for future pharmaceutical and biomedical applications.

Graphical abstract

Pharmaceutical and biomedical applications of MNs

A crossover clinical study to evaluate pain intensity from microneedle insertion in different parts of the oral cavity

The objective of the present study was to evaluate discomfort and safety of microneedle (MN) insertion in several intraoral regions. A device was developed to standardize MN insertions. MNs were inserted in the following regions of the oral cavity: gingiva, palatine alveolar process, buccal mucosa, dorsum of the tongue and inner portion of the lower lip. Perforations from MNs post insertion were confirmed with topical gentian violet stain. Pain was evaluated in a randomized, double-blinded, crossover study in 30 volunteers. Each volunteer received a MN patch, a 30G hypodermic needle (positive control) and an identical MN patch with its needles laying flat in the plane of the patch (negative control). Adverse events were visually evaluated immediately after (0 h) and 24 h post MN application. The application device developed a consistent application force (10 N) and promoted perforation of all individual MNs on a patch. At all sites, insertion of the hypodermic needle promoted more pain when compared to the negative control (p < 0.001). Application of the MNs promoted less pain than the hypodermic needle (p < 0.05), but slightly more pain as compared to the negative control (p < 0.05) at all sites except the tongue, where the MN did not differ from the negative control (p > 0.05). Hypodermic needle caused bleeding at all insertion sites. In contrast, MNs did not cause bleeding at most sites except in some cases of insertion into the hard gingiva and the palatine alveolar process where tiny blood spots appeared immediately after MN application for few of the MNs on the patch. There were no cases of bleeding at 24 h post MN application. In conclusion, MNs can perforate different sites of the oral cavity in a safe and significantly less painful manner as compared to the 30G hypodermic needle. Thus, analogous to the skin, MN-based approaches could be an attractive approach for drug delivery in the oral cavity.

Characterization of microneedles and microchannels for enhanced transdermal drug delivery

Microneedle (MN)-based technologies are currently one of the most innovative approaches that are being extensively investigated for transdermal delivery of low molecular weight drugs, biotherapeutic agents and vaccines. Extensive research reports, describing the fabrication and applications of different types of MNs, can be readily found in the literature. Effective characterization tools to evaluate the quality and performance of the MNs as well as for determination of the dimensional and kinetic properties of the microchannels created in the skin, are an essential and critical part of MN-based research. This review paper provides a comprehensive account of all such tools and techniques.

A microneedle platform for buccal macromolecule delivery

Alternative means for drug delivery are needed to facilitate drug adherence and administration. Microneedles (MNs) have been previously investigated transdermally for drug delivery. To date, drug loading into MNs has been limited by drug solubility in the polymeric blend. We designed a highly drug-loaded MN patch to deliver macromolecules and applied it to the buccal area, which allows for faster delivery than the skin. We successfully delivered 1-mg payloads of human insulin and human growth hormone to the buccal cavity of swine within 30 s. In addition, we conducted a trial in 100 healthy volunteers to assess potential discomfort associated with MNs when applied in the oral cavity, identifying the hard palate as the preferred application site. We envisage that MN patches applied on buccal surfaces could increase medication adherence and facilitate the painless delivery of biologics and other drugs to many, especially for the pediatric and elderly populations.

Biodegradable microneedles fabricated with carbohydrates and proteins: Revolutionary approach for transdermal drug delivery

There has been a surge in the use of transdermal drug delivery systems (TDDS) for the past few years. The market of TDDS is expected to reach USD 7.1 billion by 2023, from USD 5.7 billion in 2018, at a CAGR of 4.5%. Microneedles (MNs) are a novel class of TDDS with advantages of reduced pain, low infection risk, ease of application, controlled release of therapeutic agents, and enhanced bioavailability. Biodegradable MNs fabricated from natural polymers have become the center of attention among formulation scientists because of their recognized biodegradability, biocompatibility, ease of fabrication, and sustainable character. In this review, we summarize the various polysaccharides and polypeptide based biomaterials that are used to fabricate biodegradable MNs. Particular emphasis is given to cellulose and its derivatives, starch, and complex carbohydrate polymers such as alginates, chitosan, chondroitin sulfate, xanthan gum, pullulan, and hyaluronic acid. Additionally, novel protein-based polymers such as zein, collagen, gelatin, fish scale and silk fibroin (polyamino acid) biopolymers application in transdermal drug delivery have also been discussed. The current review will provide a unique perspective to the readers on the developments of biodegradable MNs composed of carbohydrates and protein polymers with their clinical applications and patent status.

Connecting the dots in drug delivery: A tour d'horizon of chitosan-based nanocarriers system

One of the most promising pharmaceutical research areas is developing advanced delivery systems for controlled and sustained drug release. The drug delivery system (DDS) can be designed to strengthen the pharmacological and therapeutic characteristics of different medicines. Natural polymers have resolved numerous commencing hurdles, which hindered the clinical implementation of traditional DDS. The naturally derived polymers furnish various advantages such as biodegradability, biocompatibility, inexpensiveness, easy availability, and biologically identifiable moieties, which endorse cellular activity in contrast to synthetic polymers. Among them, chitosan has recently been in the spotlight for devising safe and efficient DDSs due to its superior properties such as minimal toxicity, bio-adhesion, stability, biodegradability, and biocompatibility. The primary amino group in chitosan shows exceptional qualities such as the rate of drug release, anti-microbial properties, the ability to cross-link with various polymers, and macrophage activation. This review intends to provide a glimpse into different practical utilization of chitosan as a drug carrier. The first segment of the review will give cognizance into the source of extraction and chitosan's remarkable properties. Further, we have endeavored to provide recent literature pertaining to chitosan applications in various drug delivery systems via different administration routes along with current patented chitosan formulations.

Microneedle Technology: An Insight into Recent Advancements and Future Trends in Drug and Vaccine Delivery

Over the last decade, microneedle (MN) induced microporation multifunctional approaches to enhance the delivery of drugs through the skin. MN technology included micron-sized needles to create microchannels into the Stratum corneum of skin, the most significant protective layer. Delivery of drugs and vaccines through the transdermal route is an alternative route for hypodermic and oral. It overcomes the problems associated with gastrointestinal along with drug deterioration. It is affordable, noninvasive, painless, simple, and self-administered techniques that provide prolonged release of drugs to enhance patient compliance. The MN delivery focused on biopharmaceuticals like proteins or peptides. The novel concepts have drawn interest in using these techniques in tandem with other enhancement approaches. This review article discussed the latest advancements in MN technology. It emphasized types of MNs, methodology, mechanisms, strategies for delivery of several drugs and vaccines, and significant challenges in the marketing of biopharmaceuticals. Furthermore, relevant U.S. patents and clinical trials based on MNs are also accentuated. Therefore, MN techniques will play a pivotal role in promoting clinical applications and innovative research for scientists and researchers working in the pharmaceutical field.

Micropore closure time is longer following microneedle application to skin of color

Microneedles (MNs) allow transdermal delivery of skin-impermeable drugs by creating transient epidermal micropores, and micropore lifetime directly affects drug diffusion timeframes. Healthy subjects (n = 111) completed the study, self-identifying as Asian (n = 32), Bi-/multi-racial (n = 10), Black (n = 22), White (n = 23), Latino (n = 23), and Native American/Hawaiian (n = 1). L* was measured with tristimulus colorimetry to objectively describe skin lightness/darkness. MNs were applied to the upper arm; impedance and transepidermal water loss (TEWL) were measured at baseline and post-MN to confirm micropore formation. Impedance was repeated for 4 days to determine micropore lifetime. Post-MN changes in TEWL and impedance were significant in all groups (p < 0.05), confirming micropore formation regardless of skin type. Micropore lifetime was significantly longer in Blacks (66.5 ± 19.5 h) versus Asians (44.1 ± 14.0 h), Bi-/multi-racial (48.0 ± 16.0 h), and Whites (50.2 ± 2.6 h). Latinos (61.1 ± 16.1 h) had significantly longer micropore closure time versus Asians (44.1 ± 14.0 h). When categorizing data according to L*, micropore lifetime was significantly longer in darker skin. We report for the first time that micropore lifetime differences are present in human subjects of different ethnic/racial backgrounds, with longer micropore lifetime in skin of color. These results also suggest that objectively measured skin color is a better predictor of micropore lifetime than self-identified race/ethnicity.

Derma rollers in therapy: the transition from cosmetics to transdermal drug delivery

Derma roller, a device rolled onto the skin to form micropores, is extensively used for cosmetic purposes. The pores thus created are utilized to either result in the induction of collagen production, leading to glowing and wrinkle-free skin or for permeating the applied formulations to the site of action within the skin. Recent studies have shown the benefits of using derma rollers for transdermal delivery of drugs. In the nascent stage, this approach paves a way to successfully breach the stratum corneum and aid in the movement of medications directed towards the dermis and the hair follicles. The review essentially summarizes the evidence of the use of derma rollers in cosmetic setup, their designing, and the preclinical and clinical reports of efficacy, safety, and concerns when translated for pharmaceutical purposes and transdermal drug delivery.

Microneedle Mediated Transdermal Delivery of Protein, Peptide and Antibody Based Therapeutics: Current Status and Future Considerations

The success of protein, peptide and antibody based therapies is evident - the biopharmaceuticals market is predicted to reach $388 billion by 2024 [1], and more than half of the current top 20 blockbuster drugs are biopharmaceuticals. However, the intrinsic properties of biopharmaceuticals has restricted the routes available for successful drug delivery. While providing 100% bioavailability, the intravenous route is often associated with pain and needle phobia from a patient perspective, which may translate as a reluctance to receive necessary treatment. Several non-invasive strategies have since emerged to overcome these limitations. One such strategy involves the use of microneedles (MNs), which are able to painlessly penetrate the stratum corneum barrier to dramatically increase transdermal drug delivery of numerous drugs. This review reports the wealth of studies that aim to enhance transdermal delivery of biopharmaceutics using MNs. The true potential of MNs as a drug delivery device for biopharmaceuticals will not only rely on acceptance from prescribers, patients and the regulatory authorities, but the ability to upscale MN manufacture in a cost-effective manner and the long term safety of MN application. Thus, the current barriers to clinical translation of MNs, and how these barriers may be overcome are also discussed.

Evaluation of the clinical impact of repeat application of hydrogel-forming microneedle array patches

Hydrogel-forming microneedle array patches (MAPs) have been proposed as viable clinical tools for patient monitoring purposes, providing an alternative to traditional methods of sample acquisition, such as venepuncture and intradermal sampling. They are also undergoing investigation in the management of non-melanoma skin cancers. In contrast to drug or vaccine delivery, when only a small number of MAP applications would be required, hydrogel MAPs utilised for sampling purposes or for tumour eradication would necessitate regular, repeat applications. Therefore, the current study was designed to address one of the key translational aspects of MAP development, namely patient safety. We demonstrate, for the first time in human volunteers, that repeat MAP application and wear does not lead to prolonged skin reactions or prolonged disruption of skin barrier function. Importantly, concentrations of specific systemic biomarkers of inflammation (C-reactive protein (CRP); tumour necrosis factor-α (TNF-α)); infection (interleukin-1β (IL-1β); allergy (immunoglobulin E (IgE)) and immunity (immunoglobulin G (IgG)) were all recorded over the course of this fixed study period. No biomarker concentrations above the normal, documented adult ranges were recorded over the course of the study, indicating that no systemic reactions had been initiated in volunteers. Building upon the results of this study, which serve to highlight the safety of our hydrogel MAP, we are actively working towards CE marking of our MAP technology as a medical device.

Design and Characterization of Spray-Dried Chitosan-Naltrexone Microspheres for Microneedle-Assisted Transdermal Delivery

Naltrexone (NTX) hydrochloride is a potent opioid antagonist with significant first-pass metabolism and notable untoward effects when administered orally or intramuscularly. Microneedle (MN)-assisted transdermal delivery is an attractive alternative that can improve therapeutic delivery to deeper skin layers. In this study, chitosan-NTX microspheres were developed via spray-drying, and their potential for transdermal NTX delivery in association with MN skin treatment was assessed. A quality-by-design approach was used to evaluate the impact of key input variables (chitosan molecular weight, concentration, chitosan-NTX ratio, and feed flow rate) on microsphere physical characteristics, encapsulation efficiency, and drug-loading capacity. Formulated microspheres had high encapsulation efficiencies (70%-87%), with drug-loading capacities ranging from 10%-43%. NTX flux through MN-treated skin was 11.6 ± 2.2 µg/cm²·h from chitosan-NTX microspheres, which was significantly higher than flux across intact skin. Combining MN-assisted delivery with the chitosan microsphere formulation enabled NTX delivery across the skin barrier, while controlling the dose released to the skin.

Microneedle System for Transdermal Drug and Vaccine Delivery: Devices, Safety, and Prospects

Microneedle (MN) delivery system has been greatly developed to deliver drugs into the skin painlessly, noninvasively, and safety. In the past several decades, various types of MNs have been developed by the newer producing techniques. Briefly, as for the morphologically, MNs can be classified into solid, coated, dissolved, and hollow MN, based on the transdermal drug delivery methods of "poke and patch," "coat and poke," "poke and release," and "poke and flow," respectively. Microneedles also have other characteristics based on the materials and structures. In addition, various manufacturing techniques have been well-developed based on the materials. In this review, the materials, structures, morphologies, and fabricating methods of MNs are summarized. A separate part of the review is used to illustrate the application of MNs to deliver vaccine, insulin, lidocaine, aspirin, and other drugs. Finally, the review ends up with a perspective on the challenges in research and development of MNs, envisioning the future development of MNs as the next generation of drug delivery system.

Hydrogels: soft matters in photomedicine

Photodynamic therapy (PDT), a shining beacon in the realm of photomedicine, is a non-invasive technique that utilizes dye-based photosensitizers (PSs) in conjunction with light and oxygen to produce reactive oxygen species to combat malignant tissues and infectious microorganisms. Yet, for PDT to become a common, routine therapy, it is still necessary to overcome limitations such as photosensitizer solubility, long-term side effects (e.g., photosensitivity) and to develop safe, biocompatible and target-specific formulations. Polymer based drug delivery platforms are an effective strategy for the delivery of PSs for PDT applications. Among them, hydrogels and 3D polymer scaffolds with the ability to swell in aqueous media have been deeply investigated. Particularly, hydrogel-based formulations present real potential to fulfill all requirements of an ideal PDT platform by overcoming the solubility issues, while improving the selectivity and targeting drawbacks of the PSs alone. In this perspective, we summarize the use of hydrogels as carrier systems of PSs to enhance the effectiveness of PDT against infections and cancer. Their potential in environmental and biomedical applications, such as tissue engineering photoremediation and photochemistry, is also discussed.

Mesotherapy: Safety profile and management of complications

BACKGROUND

Mesotherapy is a procedure that involves the injection of active substances into the dermis and subcutaneous tissue in order to treat several local medical and cosmetic conditions. Despite being considered as a relatively safe method, a series of adverse reactions can occur due to its wide application and lack of standardization processes.

OBJECTIVES

The aim of this paper is to summarize all the mesotherapy-related complications published so far, and to provide an insight into their management.

PATIENT/METHODS

Articles derived from the databases, PubMed, EMBASE, and SCOPUS, and published between 1992 and 2018, were analyzed for this review. The study was conducted according to the PRISMA guidelines.

RESULTS

In this literature, there is a number of case series and isolated case reports describing various side effects of different severities. The therapeutic management of these complications is-in most cases-individualized.

CONCLUSIONS

Larger systematic studies are needed in order to adequately evaluate the safety profile of mesotherapy, and in order to determine standardized therapy parameters, so as to minimize the risk of potential adverse reactions.

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

Skin-targeting microscale medical devices are becoming popular for therapeutic delivery and diagnosis. We used cryo-SEM, fluorescence lifetime imaging microscopy (FLIM), autofluorescence imaging microscopy and inflammatory response to study the puncturing and recovery of human skin ex vivo and in vivo after discretised puncturing by a microneedle array (Nanopatch®). Pores induced by the microprojections were found to close by ~25% in diameter within the first 30 min, and almost completely close by ~6 h. FLIM images of ex vivo viable epidermis showed a stable fluorescence lifetime for unpatched areas of ~1000 ps up to 24 h. Only the cells in the immediate puncture zones (in direct contact with projections) showed a reduction in the observed fluorescence lifetimes to between ~518-583 ps. The ratio of free-bound NAD(P)H (α1/α2) in unaffected areas of the viable epidermis was ~2.5-3.0, whereas the ratio at puncture holes was almost double at ~4.2-4.6. An exploratory pilot in vivo study also suggested similar closure rate with histamine administration to the forearms of human volunteers after Nanopatch® treatment, although a prolonged inflammation was observed with Tissue Viability Imaging. Overall, this work shows that the pores created by the microneedle-type medical device, Nanopatch®, are transient, with the skin recovering rapidly within 1-2 days in the epidermis after application.

Recent development in biodegradable nanovehicle delivery system-assisted immunotherapy

A schematic illustration of BNDS biodegradation and release antigen delivery for assisting immunotherapy.