Mechanism of fluid infusion during microneedle insertion and retraction

Targeting Diverse Wounds and Scars: Recent Innovative Bio-design of Microneedle Patch for Comprehensive Management

Wounds and the subsequent formation of scars constitute a unified and complex phased process. Effective treatment is crucial; however, the diverse therapeutic approaches for different wounds and scars, as well as varying treatment needs at different stages, present significant challenges in selecting appropriate interventions. Microneedle patch (MNP), as a novel minimally invasive transdermal drug delivery system, has the potential for integrated and programmed treatment of various diseases and has shown promising applications in different types of wounds and scars. In this comprehensive review, the latest applications and biotechnological innovations of MNPs in these fields are thoroughly explored, summarizing their powerful abilities to accelerate healing, inhibit scar formation, and manage related symptoms. Moreover, potential applications in various scenarios are discussed. Additionally, the side effects, manufacturing processes, and material selection to explore the clinical translational potential are investigated. This groundwork can provide a theoretical basis and serve as a catalyst for future innovations in the pursuit of favorable therapeutic options for skin tissue regeneration.

Diagnostic, Therapeutic, and Theranostic Multifunctional Microneedles

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

Integration of polysaccharide electrospun nanofibers with microneedle arrays promotes wound regeneration: A review

Utilizing electrospun nanofibers and microneedle arrays in wound regeneration has been practiced for several years. Researchers have recently asserted that using multiple methods concurrently might enhance efficiency, despite the inherent strengths and weaknesses of each individual approach. The combination of microneedle arrays with electrospun nanofibers has the potential to create a drug delivery system and wound healing method that offer improved efficiency and accuracy in targeting. The use of microneedles with nanofibers allows for precise administration of pharmaceuticals due to the microneedles' capacity to pierce the skin and the nanofibers' role as a drug reservoir, resulting in a progressive release of drugs over a certain period of time. Electrospun nanofibers have the ability to imitate the extracellular matrix and provide a framework for cellular growth and tissue rejuvenation, while microneedle arrays show potential for enhancing tissue regeneration and enhancing the efficacy of wound healing. The integration of electrospun nanofibers with microneedle arrays may be customized to effectively tackle particular obstacles in the fields of wound healing and drug delivery. However, some issues must be addressed before this paradigm may be fully integrated into clinical settings, including but not limited to ensuring the safety and sterilization of these products for transdermal use, optimizing manufacturing methods and characterization of developed products, larger-scale production, optimizing storage conditions, and evaluating the inclusion of multiple therapeutic and antimicrobial agents to increase the synergistic effects in the wound healing process. This research examines the combination of microneedle arrays with electrospun nanofibers to enhance the delivery of drugs and promote wound healing. It explores various kinds of microneedle arrays, the materials and processes used, and current developments in their integration with electrospun nanofibers.

Dermal tissue penetration of in-plane silicon microneedles evaluated in skin-simulating hydrogel, rat skin and porcine skin

Recently, microneedle-based sensors have been introduced as novel strategy for in situ monitoring of biomarkers in the skin. Here, in-plane silicon microneedles with different dimensions and shapes are fabricated and their ability to penetrate skin is evaluated. Arrays with flat, triangular, hypodermic, lancet and pencil-shaped microneedles, with lengths of 500-1000 μm, widths of 200-400 μm and thickness of 180-500 μm are considered. Fracture force is higher than 20 N for all microneedle arrays (MNA) confirming a high mechanical stability of the microneedles. Penetration force in skin-simulating hydrogels, excised rat abdominal skin and porcine ear skin is at least five times lower than the fracture force for all MNA designs. The lowest force for skin penetration is required for triangular microneedles with a low width and thickness. Skin tissue staining and histological analysis of rat abdominal skin and porcine ear skin confirm successful penetration of the epidermis for all MNA designs. However, the penetration depth is between 100 and 300 μm, which is considerably lower than the microneedle length. Tissue damage estimated by visual analysis of the penetration hole is smallest for triangular microneedles. Penetration ability and tissue damage are compared to the skin prick test (SPT) needle applied in allergy testing.

Microneedle-based cell delivery and cell sampling for biomedical applications

Cell-based therapeutics are novel therapeutic strategies that can potentially treat many presently incurable diseases through novel mechanisms of action. Cell therapies may benefit from the ease, safety, and efficacy of administering therapeutic cells. Despite considerable recent technological and biological advances, several barriers remain to the clinical translation and commercialization of cell-based therapies, including low patient compliance, personal handling inconvenience, poor biosafety, and limited biocompatibility. Microneedles (MNs) are emerging as a promising biomedical device option for improved cell delivery with little invasion, pain-free administration, and simplicity of disposal. MNs have shown considerable promise in treating a wide range of diseases and present the potential to improve cell-based therapies. In this review, we first summarized the latest advances in the various types of MNs developed for cell delivery and cell sampling. Emphasis was given to the design and fabrication of various types of MNs based on their structures and materials. Then we focus on the recent biomedical applications status of MNs-mediated cell delivery and sampling, including tissue repair (wound healing, heart repair, and endothelial repair), cancer treatment, diabetes therapy, cell sampling, and other applications. Finally, the current status of clinical application, potential perspectives, and the challenges for clinical translation are also highlighted.

Long-acting microneedle formulations

The minimally-invasive and painless nature of microneedle (MN) application has enabled the technology to obviate many issues with injectable drug delivery. MNs not only administer therapeutics directly into the dermal and ocular space, but they can also control the release profile of the active compound over a desired period. To enable prolonged delivery of payloads, various MN types have been proposed and evaluated, including dissolving MNs, polymeric MNs loaded or coated with nanoparticles, fast-separable MNs hollow MNs, and hydrogel MNs. These intricate yet intelligent delivery platforms provide an attractive approach to decrease side effects and administration frequency, thus offer the potential to increase patient compliance. In this review, MN formulations that are loaded with various therapeutics for long-acting delivery to address the clinical needs of a myriad of diseases are discussed. We also highlight the design aspects, such as polymer selection and MN geometry, in addition to computational and mathematical modeling of MNs that are necessary to help streamline and develop MNs with high translational value and clinical impact. Finally, up-scale manufacturing and regulatory hurdles along with potential avenues that require further research to bring MN technology to the market are carefully considered. It is hoped that this review will provide insight to formulators and clinicians that the judicious selection of materials in tandem with refined design may offer an elegant approach to achieve sustained delivery of payloads through the simple and painless application of a MN patch.

Microneedles and Their Application in Transdermal Delivery of Antihypertensive Drugs-A Review

One of the most cutting-edge, effective, and least invasive pharmaceutical innovations is the utilization of microneedles (MNs) for drug delivery, patient monitoring, diagnostics, medicine or vaccine delivery, and other medical procedures (e.g., intradermal vaccination, allergy testing, dermatology, and blood sampling). The MN-based system offers many advantages, such as minimal cost, high medical effectiveness, comparatively good safety, and painless drug application. Drug delivery through MNs can possibly be viewed as a viable instrument for various macromolecules (e.g., proteins, peptides, and nucleic acids) that are not efficiently administered through traditional approaches. This review article provides an overview of MN-based research in the transdermal delivery of hypertensive drugs. The critical attributes of microneedles are discussed, including the mechanism of drug release, pharmacokinetics, fabrication techniques, therapeutic applications, and upcoming challenges. Furthermore, the therapeutic perspective and improved bioavailability of hypertensive drugs that are poorly aqueous-soluble are also discussed. This focused review provides an overview of reported studies and the recent progress of MN-based delivery of hypertensive drugs, paving the way for future pharmaceutical uses. As MN-based drug administration bypasses first-pass metabolism and the high variability in drug plasma levels, it has grown significantly more important for systemic therapy. In conclusion, MN-based drug delivery of hypertensive drugs for increasing bioavailability and patient compliance could support a new trend of hypertensive drug delivery and provide an alternative option, overcoming the restrictions of the current dosage forms.

Recent advancements in the expedition of microneedles: from lab worktops to diagnostic care centers

Microneedle (MN) technology plays a significant role in bioengineering as it allows for minimally invasive exposure to the skin via the non-invasive procedure, increased drug permeability, and improved biological molecule detectability in the epidermal layers, all while improving therapeutic safety and effectiveness. However, MNs have several significant drawbacks, including difficulty scaling up, variability in drug delivery pattern regarding the skin's external environment, blockage of dermal tissues, induction of inflammatory response at the administration site, and limitation of dosing based on the molecular weight of drug and size. Despite these drawbacks, MNs have emerged as a special transdermal theranostics instrument in clinical research to assess physiological parameters. Bioimaging technology relies on microneedles that can measure particular analytes in the extracellular fluid effectively by crossing the stratum corneum, making them "a unique tool in diagnostics detection and therapeutic application inside the body." This review article discusses the recent advances in the applications especially related to the diagnostics and toxicity challenges of microneedles. In addition, this review article discusses the clinical state and commercial accessibility of microneedle technology-based devices in order to provide new information to scientists and researchers.

Single step fabrication of hollow microneedles and an experimental package for controlled drug delivery

Hollow microneedle arrays (HMNs) are an excellent choice for managing chronic diseases requiring the administration of multiple drug doses over a prolonged duration. However, HMNs have gained partial success due to limitations in their manufacturing capabilities, and cumbersome processes. In the present study, polymeric HMNs were fabricated using a novel single-step drop-casting process without needing cleanroom facilities, and sophisticated instrumentation. When drop casted on the pyramidal tip stainless steel needles, the optimized polymer solution allowed the reproducible formation of desired height HMMs on a detachable acrylic base. To enable broader applications, the base with HMNs was integrated into an experimental package built to deliver a dose of ∼ 5 µL per 30° clockwise rotation of the actuator, allowing multiple metered drug dose administrations. The fabricated HMNs were optically imaged, and tested for mechanical integrity and stability. The working and functional utility of the HMNs package in delivering metered drug doses was demonstrated by delivering vitamin B12 (ex vivo) and insulin (in vivo), respectively. The optimized process can be used for the large-scale manufacturing of HMNs and the experimental package shows the potential to be further developed into a wearable device.

Silk Fibroin Microneedles for Transdermal Drug Delivery: Where Do We Stand and How Far Can We Proceed?

Microneedles are a patient-friendly technique for delivering drugs to the site of action in place of traditional oral and injectable administration. Silk fibroin represents an interesting polymeric biomaterial because of its mechanical properties, thermal stability, biocompatibility and possibility of control via genetic engineering. This review focuses on the critical research progress of silk fibroin microneedles since their inception, analyzes in detail the structure and properties of silk fibroin, the types of silk fibroin microneedles, drug delivery applications and clinical trials, and summarizes the future development trend in this field. It also proposes the future research direction of silk fibroin microneedles, including increasing drug loading doses and enriching drug loading types as well as exploring silk fibroin microneedles with stimulation-responsive drug release functions. The safety and effectiveness of silk fibroin microneedles should be further verified in clinical trials at different stages.

Mechanistic modeling-guided optimization of microneedle-based skin patch for rapid transdermal delivery of naloxone for opioid overdose treatment

Naloxone, an FDA-approved opioid inhibitor, used to reverse opioid overdose complications has up till date faced challenges associated with its delivery. Limitations include the use of invasive delivery forms and the need for frequent redosing due to its short half-life. The goal of the current study was to design a transdermal rapidly dissolving polymeric microneedle (MN) patch with delivery and pharmacokinetic properties comparable to that seen with the commercially available NAL products, eliminating their delivery limitations. Patches of varying dimensions (500 µm; 100 array,800 µm; 100array, and 600 µm; 225 array) were fabricated to evaluate the effect of increasing MN length, and density (no. of needles/unit area) on drug release. Drug dose in each of these patches was 17.89 ± 0.23 mg, 17.2 ± 0.77 mg, and 17.8 ± 1.01 mg, respectively. Furthermore, the insertion efficiency of each of the MN patches was 94 ± 4.8%, 90.6 ± 1.69%, and 96 ± 1.29%, respectively. Compared to passive permeation, a reduced lag time of about 5-15 min was observed with a significant drug flux of 15.09 ± 7.68 g[Formula: see text]/cm²/h seen in the first 1 h (p < 0.05) with the array of 100 needles (500 µm long). Over 24 h, a four and ten-fold increase in permeation was seen with the longer length and larger density MN patch, respectively, when compared to the 500 µm (100 array) patch. Model simulations and analyses revealed the significance of needle base diameter and needle count in improving systemic pharmacokinetics of NAL.

Constant Pressure Convection-Enhanced Delivery Increases Volume Dispersed With Catheter Movement in Agarose

Convection-enhanced delivery (CED) has been extensively studied for drug delivery to the brain due to its inherent ability to bypass the blood-brain barrier. Unfortunately, CED has also been shown to inadequately distribute therapeutic agents over a large enough targeted tissue volume to be clinically beneficial. In this study, we explore the use of constant pressure infusions in addition to controlled catheter movement as a means to increase volume dispersed (Vd) in an agarose gel brain tissue phantom. Constant flow rate and constant pressure infusions were conducted with a stationary catheter, a catheter retracting at a rate of 0.25 mm/min, and a catheter retracting at a rate of 0.5 mm/min. The 0.25 mm/min and 0.5 mm/min retracting constant pressure catheters resulted in significantly larger Vd compared to any other group, with a 105% increase and a 155% increase compared to the stationary constant flow rate catheter, respectively. These same constant pressure retracting infusions resulted in a 42% and 45% increase in Vd compared to their constant flow rate counterparts. Using constant pressure infusions coupled with controlled catheter movement appears to have a beneficial effect on Vd in agarose gel. Furthermore, constant pressure infusions reveal the fundamental limitation of flow-driven infusions in both controlled catheter movement protocols as well as in stationary protocols where maximum infusion volume can never be reliably obtained.

The clinical and translational prospects of microneedle devices, with a focus on insulin therapy for diabetes mellitus as a case study

Microneedles have the clinical advantage of being able to deliver complex drugs across the skin in a convenient and comfortable manner yet haven't successfully transitioned to medical practice. Diabetes mellitus is a complicated disease, which is commonly treated with multiple daily insulin injections, contributing to poor treatment adherence. Firstly, this review determines the clinical prospect of microneedles, alongside considerations that ought to be addressed before microneedle technology can be translated from bench to bedside. Thereafter, we use diabetes as a case study to consider how microneedle-based-technology may be successfully harnessed. Here, publications referring to insulin microneedles were evaluated to understand whether insertion efficiency, angle of insertion, successful dose delivery, dose adjustability, material biocompatibility and therapeutic stability are being addressed in early stage research. Moreover, over 3,000 patents from 1970-2019 were reviewed with the search term '"microneedle" AND "insulin"' to understand the current status of the field. In conclusion, the reporting of early stage microneedle research demonstrated a lack of consistency relating to the translational factors addressed. Additionally, a more rational design, based on a patient-centred approach is required before microneedle-based delivery systems can be used to revolutionise the lives of people living with diabetes following regulatory approval.

Wearable microneedle-based electrochemical aptamer biosensing for precision dosing of drugs with narrow therapeutic windows

Therapeutic drug monitoring is essential for dosing pharmaceuticals with narrow therapeutic windows. Nevertheless, standard methods are imprecise and involve invasive/resource-intensive procedures with long turnaround times. Overcoming these limitations, we present a microneedle-based electrochemical aptamer biosensing patch (μNEAB-patch) that minimally invasively probes the interstitial fluid (ISF) and renders correlated, continuous, and real-time measurements of the circulating drugs' pharmacokinetics. The μNEAB-patch is created following an introduced low-cost fabrication scheme, which transforms a shortened clinical-grade needle into a high-quality gold nanoparticle-based substrate for robust aptamer immobilization and efficient electrochemical signal retrieval. This enables the reliable in vivo detection of a wide library of ISF analytes-especially those with nonexistent natural recognition elements. Accordingly, we developed μNEABs targeting various drugs, including antibiotics with narrow therapeutic windows (tobramycin and vancomycin). Through in vivo animal studies, we demonstrated the strong correlation between the ISF/circulating drug levels and the device's potential clinical use for timely prediction of total drug exposure.

Research progress on detachable microneedles for advanced applications

INTRODUCTION

Microneedles (MNs) have undergone great advances in transdermal drug delivery, and commercialized MN applications are currently available in vaccination and cosmetic products. Despite the development of MN technologies, common limitations of MN products still exist. Typical MN patches are applied to target tissues, where the substrate of an MN patch must remain until the drug is delivered, which reduces patients' compliance and hinders the applicability of the MN technique to many diseases in various tissues. MN research is ongoing to solve this issue.

AREAS COVERED

Most recent MNs developed by combining various biomaterials with appropriate fabrication processes are detachable MNs (DeMNs). Because of advances in biomaterials and fabrication techniques, various DeMNs have been rapidly developed. In this review, we discuss four types of DeMN: substrate-separable, multi-layered, crack-inducing, and shell DeMN. These DeMNs deliver various therapeutic agents ranging from small- and large-molecular-weight drugs to proteins and even stem cells for regeneration therapy. Furthermore, DeMNs are applied to skin as well as non-transdermal tissues.

EXPERT OPINION

It has become increasingly evident that novel MN technologies can be expected in terms of designs, fabrication methods, materials, and even possible application sites given the recent advances in DeMNs.

Skin optical clearing enabled by dissolving hyaluronic acid microneedle patches

Optical imaging and phototherapy are of great significance in the detection, diagnosis, and therapy of diseases. Depth of light in the skin tissues in optical imaging and phototherapy can be significantly improved with the assistance of optical clearing technology by weakening the scattering from the refractive indexes inhomogeneity among skin constituents. However, the barrier of the stratum corneum restricts the penetration of optical clearing agents into deep tissues and limits the optical clearing effects. Herein, we develop an optical clearing strategy by using dissolving microneedle (MN) patches made of hyaluronic acid (HA), which can effortlessly and painlessly penetrate the stratum corneum to reach the epidermis and dermis. By using the HA MN patches, the transmittance of skin tissues is improved by about 12.13 %. We show that the HA MN patches enhance the clarity of blood vessels to realize naked-eyes observation. Moreover, a simulated subcutaneous tumor cells experiment also verifies that the optical clearing effects of the HA MN patch efficiently boost the efficiency of the photodynamic killing of tumor cells by 26.8 %. As a courageous attempt, this study provides a promising avenue to improve the optical clearing effects for further clinical application of optical imaging and phototherapy.

Promising Strategies for Transdermal Delivery of Arthritis Drugs: Microneedle Systems

Arthritis is a general term for various types of inflammatory joint diseases. The most common clinical conditions are mainly represented by rheumatoid arthritis and osteoarthritis, which affect more than 4% of people worldwide and seriously limit their mobility. Arthritis medication generally requires long-term application, while conventional administrations by oral delivery or injections may cause gastrointestinal side effects and are inconvenient for patients during long-term application. Emerging microneedle (MN) technology in recent years has created new avenues of transdermal delivery for arthritis drugs due to its advantages of painless skin perforation and efficient local delivery. This review summarizes various types of arthritis and current therapeutic agents. The current development of MNs in the delivery of arthritis drugs is highlighted, demonstrating their capabilities in achieving different drug release profiles through different self-enhancement methods or the incorporation of nanocarriers. Furthermore, the challenges of translating MNs from laboratory studies to the clinical practice and the marketplace are discussed. This promising technology provides a new approach to the current drug delivery paradigm in treating arthritis in transdermal delivery.

Research progress of microneedles in the treatment of melanoma

Melanoma is an aggressive malignancy deriving from melanocytes, which is characterized by high tendency of metastases and mortality rate. Current therapies for melanoma, like chemotherapy, immunotherapy and targeted therapy, have the problem of systemic exposure of drugs, which will lead to many side effects and premature degradation of drugs. The resulting low drug accumulation at the lesion limits the therapeutic effect on melanoma and makes the cure rate low. As an emerging drug delivery system, microneedles (MNs) can efficiently deliver drugs through the skin, increase the drug distribution in deeper tumor sites and minimize the leakage of therapeutic drugs into adjacent tissues, thus improving the therapeutic effect. In addition, compared with traditional drug delivery methods, MN-based drug delivery system has the advantages of simplicity, safety and little pain. So MNs can be developed for the treatment of melanoma, which can relieve the pain of patients and improve the survival rate. This review aims to introduce an update on the progress of MNs as an innovative strategy for melanoma, especially when MNs combining with different therapies against melanoma, such as chemotherapy, targeted therapy, immunotherapy, photothermal therapy (PTT), photodynamic therapy (PDT) and synergic therapy.

The Relationship between the Drug Delivery Properties of a Formulation of Teriparatide Microneedles and the Pharmacokinetic Evaluation of Teriparatide Administration in Rats

PURPOSE

Teriparatide is an effective drug for the treatment of osteoporosis. This study examines the relationship between the drug delivery properties of the solid formulation with teriparatide and the pharmacokinetic properties of teriparatide in vivo.

METHODS

Teriparatide microneedles with different dissolution rates were prepared using sucrose and carboxymethylcellulose (CMC). There were three aspects of this study: (1) The dissolution rate of teriparatide from both formulations (sucrose and CMC) was measured in vitro. (2) After administration into porcine skin ex vivo, the diffusion rate of FITC-dextran was observed using a confocal microscope. (3) Pharmacokinetic studies were performed in rats and pharmacokinetic data compared with the release rate and the diffusion pattern.

RESULTS

In the in vitro dissolution experiment, 80% of teriparatide was released within 30 min from the CMC MNs, whereas 80% of teriparatide was released within 10 min from the sucrose MNs. After 30 min, the fluorescence intensity on the surface of the MNs was 40% of the initial intensity for sucrose MNs and 90% for CMC MNs. In the pharmacokinetic study, the C_max values of the CMC and sucrose MNs were 868 pg/mL and 6809 pg/mL, respectively, and the AUC_last values were 6771 pg*hr/mL for the CMC MNs and 17,171 pg*hr/mL for the sucrose MNs.

CONCLUSIONS

When teriparatide is delivered into the skin using microneedles, the release rate from the solid formulation determines the drug's pharmacokinetic properties. The diffusion pattern of fluorescence into the skin can be used to anticipate the pharmacokinetic properties of the drug.

Advances in the Novel Nanotechnology for the Targeted Tumor Therapy by the Transdermal Drug Delivery

Despite modern medicine advances greatly, cancer remains a serious challenge to world health for which effective methods of treatment have hardly been developed yet. However, throughout the recent years, the rapid-developing nanotechnology has provided a new outlook of cancer therapy by transdermal drug delivery. By disrupting the stratum corneum, drugs are delivered through the skin and navigated to the tumor site by drug delivery systems such as nanogels, microneedles, etc. The superiorities include the improvement of drug pharmacokinetics as well as reduced side effects. This paper reviews the reported novel development of transdermal drug delivery systems for targeted cancer therapy. Advanced techniques for penetrating the skin will be discussed as well.

Development and characterization of a dry reservoir-hydrogel-forming microneedles composite for minimally invasive delivery of cefazolin

Cefazolin (CFZ) is one of the most extensively used cephalosporins. This antibiotic exerts its bactericidal activity by interfering with bacterial cell wall formation, leading to bacteriolysis. CFZ is highly polar, resulting in the drug having poor oral bioavailability. Accordingly, the antibiotic is administered via intramuscular or intravenous injections, which are both painful and invasive. Due to these limitations, there is an impetus to explore alternative drug delivery platforms which offer a minimally invasive approach to delivery CFZ into and across the skin. The current work presents the development of a composite pharmaceutical system composed of hydrogel-forming microneedles (MNs) in tandem with CFZ dry reservoirs. The hydrogel system was fabricated from Gantrez® S-97 and Carbopol® 974P NF crosslinked with PEG 10,000. Swelling kinetic studies showed that the hydrogel system developed was capable of achieving 4000% swelling in PBS pH 7.4. In addition, results from a solute diffusion study showed that CFZ was able to achieve ≈100% cumulative permeation across the swollen hydrogel film. When formulated into MNs, the hydrogel system was capable of breaching the stratum corneum, resulting in intradermal insertion of the hydrogel forming MNs into ex vivo neonatal porcine skin, as evidenced from optical coherence tomography. In addition, two different CFZ loaded dry reservoirs consisting of directly compressed tablets (DCT) and lyophilised (LYO) wafers were formulated and characterised. These dry reservoir systems showed fast dissolution, dissolving in phosphate buffer saline pH 7.4 in less than one minute. In vitro permeation studies, using full thickness ex vivo neonatal porcine skin were conducted. HPLC analysis demonstrated the dry reservoir combination consisting of DCT with hydrogel-forming MNs was capable of achieving up to 80 µg CFZ delivery into the epidermis within 2 hours of application. In addition, DCT reservoir coupled with hydrogel-forming MNs were able to deliver CFZ up to 1.8 mg into and across the skin at 24 hours. Should this system be translated into clinical practice, it may provide a minimally invasive strategy to administer CFZ for the treatment of infections such as septic arthritis, osteomyelitis and cellulitis.

Angled Insertion of Microneedles for Targeted Antigen Delivery to the Epidermis

Peanut and tree nut allergies account for most food-induced anaphylactic events. The standard allergy immunotherapy approach involves subcutaneous injection, which is challenging because severe adverse reactions can occur when antigens spread systemically. Allergen localization within the epidermis (i.e., the upper 20–100 µm of skin) should significantly reduce systemic uptake, because the epidermis is avascular. Microneedle (MN) patches provide a convenient method for drug delivery to the skin, but they generally target both epidermis and dermis, leading to systemic delivery. In this study, we adapted MN technology for epidermal localization by performing angled insertion of 250 µm–long MNs that limits MN insertion depth mostly to the epidermis. We designed a biplanar insertion device to aid the repeatability of angled insertions into porcine skin ex vivo at specified angles (90°, 45°, and 20°). When compared to 90° insertions, MN application at 20° decreased mean insertion depth from 265 ± 45 µm to 97 ± 15 µm. Image analysis of histological skin sections revealed that acute-angle insertion increased epidermal localization of delivery for antigen-coated MNs from 25% ± 13% to 70% ± 21%. We conclude that angled insertion of MNs can target antigen delivery to epidermis.

Advances of microneedles in hormone delivery

The skin is recognized as a potential target for local and systemic drug delivery and hormone. However, the transdermal route of drug administration seems to be limited by substantial barrier properties of the skin. Recently, delivering hormone via the skin by transdermal patches is a big challenge because of the presence of the stratum corneum that prevents the application of hormone via this route. In order to overcome the limitations, microneedle (MN), consisting of micro-sized needles, are a promising approach to drill the stratum corneum and release hormone into the dermis via a minimal-invasive route. This review aimed to highlight advances in research on the development of MNs-based therapeutics for their implications in hormone delivery. The challenges during clinical translation of MNs from bench to bedside are also discussed.

Insights into the mechanics of solid conical microneedle array insertion into skin using the finite element method

In order to develop optimum microneedle designs, researchers must first develop robust, repeatable and adaptable test methods which are representative of in vivo conditions. However, there is a lack of experimental tools which can accurately comparatively interrogate functional microneedle penetration of tissue. In this study, we seek to develop a state of the art finite element model of microneedle insertion into and penetration of human skin. The developed model employs a 3D hyperelastic, anisotropic pre-stressed multi-layered material which more accurately reflects in vivo skin conditions, while the microneedle is modeled as an array, which can capture the influence of adjacent microneedles on the overall response. Using the developed finite element model, we highlight the importance of accurate computational modeling which can decipher the mechanics of microneedle insertion, including the influence of its position within an array and how it correlates well with experimental observations. In particular, we have concluded that, for our model microneedle array, increasing skin pretension from 0 to 10% strain reduces the penetration force by 13%, ultimate local deformation about the microneedle by 22% and the ultimate penetration efficiency by 15%. We have also concluded that the presence of a base plate limits the penetration efficiency by up to 24%, while the penetration efficiency across a 5 × 1 microneedle array may vary by 27%. This model elucidates, for the first time, the combined effects of skin tension and needle geometry on accurately predicting microneedle penetration efficiency. STATEMENT OF SIGNIFICANCE: Microneedles arrays (MNAs) are medical devices with microscale protrusions, typically designed to penetrate the outermost layer of the skin, that upon optimisation, could lead to disruptive minimally-invasive disease management. However, the mechanics of MNA insertion are complex, due in part to a 'bed of nails' effect, and difficult to elucidate experimentally. Therefore, comparisons between designs, functional assessment of production batches and ultimately the likelihood of clinical translation are challenging to predict. Here, we have develop the most sophisticated in silico model of MNA insertion into pre-tensioned human skin to predict the extent of MNA penetration and therefore the likelihood of successful therapeutic delivery. Researchers can customise this model to predict the penetration efficiency of any MNA design.

Microneedles in Drug Delivery: Progress and Challenges

In recent years, an innovative transdermal delivery technology has attracted great interest for its ability to distribute therapeutics and cosmeceuticals for several applications, including vaccines, drugs, and biomolecules for skin-related problems. The advantages of microneedle patch technology have been extensively evaluated in the latest literature; hence, the academic publications in this area are rising exponentially. Like all new technologies, the microneedle patch application has great potential but is not without limitations. In this review, we will discuss the possible limitations by highlighting the areas where a great deal of improvements are required. Emphasising these concerns early on should help scientists and technologists to address the matters in a timely fashion and to use their resources wisely.

Microneedle-based insulin transdermal delivery system: current status and translation challenges

Diabetes mellitus is a metabolic disease manifested by hyperglycemia. For patients with type 1 and advanced type 2 diabetes mellitus, insulin therapy is essential. Subcutaneous injection remains the most common administration method. Non-invasive insulin delivery technologies are pursued because of their benefits of decreasing patients' pain, anxiety, and stress. Transdermal delivery systems have gained extensive attention due to the ease of administration and absence of hepatic first-pass metabolism. Microneedle (MN) technology is one of the most promising tactics, which can effectively deliver insulin through skin stratum corneum in a minimally invasive and painless way. This article will review the research progress of MNs in insulin transdermal delivery, including hollow MNs, dissolving MNs, hydrogel MNs, and glucose-responsive MN patches, in which insulin dosage can be strictly controlled. The clinical studies about insulin delivery with MN devices have also been summarized and grouped based on the study phase. There are still several challenges to achieve successful translation of MNs-based insulin therapy. In this review, we also discussed these challenges including safety, efficacy, patient/prescriber acceptability, manufacturing and scale-up, and regulatory authority acceptability.

Continuous monitoring of diabetes with an integrated microneedle biosensing device through 3D printing

Diabetes is a prevalent chronic metabolic disease with multiple clinical manifestations and complications, and it is among the leading causes of death. Painless and continuous monitoring of interstitial glucose is highly desirable for diabetes management. Here we unprecedentedly show continuous monitoring of diabetes with an integrated microneedle biosensing device. The device was manufactured with a 3D printing process, a microfabrication process, an electroplating process, and an enzyme immobilization step. The device was inserted into the dermis layer of mouse skin and showed accurate sensing performance for monitoring subcutaneous glucose levels in normal or diabetic mice. The detection results were highly correlated with those obtained from a commercial blood glucose meter. We anticipate that the study could open exciting avenues for monitoring and managing diabetes, alongside fundamental studies of subcutaneous electronic devices.

Recent Advances in Microneedle-Based Sensors for Sampling, Diagnosis and Monitoring of Chronic Diseases

Chronic diseases (CDs) are noncommunicable illnesses with long-term symptoms accounting for ~70% of all deaths worldwide. For the diagnosis and prognosis of CDs, accurate biomarker detection is essential. Currently, the detection of CD-associated biomarkers is employed through complex platforms with certain limitations in their applicability and performance. There is hence unmet need to present innovative strategies that are applicable to the point-of-care (PoC) settings, and also, provide the precise detection of biomarkers. On the other hand, especially at PoC settings, microneedle (MN) technology, which comprises micron-size needles arranged on a miniature patch, has risen as a revolutionary approach in biosensing strategies, opening novel horizons to improve the existing PoC devices. Various MN-based platforms have been manufactured for distinctive purposes employing several techniques and materials. The development of MN-based biosensors for real-time monitoring of CD-associated biomarkers has garnered huge attention in recent years. Herein, we summarize basic concepts of MNs, including microfabrication techniques, design parameters, and their mechanism of action as a biosensing platform for CD diagnosis. Moreover, recent advances in the use of MNs for CD diagnosis are introduced and finally relevant clinical trials carried out using MNs as biosensing devices are highlighted. This review aims to address the potential use of MNs in CD diagnosis.

3D Printing-A "Touch-Button" Approach to Manufacture Microneedles for Transdermal Drug Delivery

Microneedles (MNs) represent the concept of attractive, minimally invasive puncture devices of micron-sized dimensions that penetrate the skin painlessly and thus facilitate the transdermal administration of a wide range of active substances. MNs have been manufactured by a variety of production technologies, from a range of materials, but most of these manufacturing methods are time-consuming and expensive for screening new designs and making any modifications. Additive manufacturing (AM) has become one of the most revolutionary tools in the pharmaceutical field, with its unique ability to manufacture personalized dosage forms and patient-specific medical devices such as MNs. This review aims to summarize various 3D printing technologies that can produce MNs from digital models in a single step, including a survey on their benefits and drawbacks. In addition, this paper highlights current research in the field of 3D printed MN-assisted transdermal drug delivery systems and analyzes parameters affecting the mechanical properties of 3D printed MNs. The current regulatory framework associated with 3D printed MNs as well as different methods for the analysis and evaluation of 3D printed MN properties are outlined.

3D printed hollow microneedles array using stereolithography for efficient transdermal delivery of rifampicin

A 3D printed assembly of hollow microneedles (HMNs) array, conjoined with a reservoir void, was designed and additively manufactured using stereolithography (SLA) technology utilizing a proprietary class-I resin. The HMNs array was utilized for transdermal delivery of high molecular weight antibiotics, i.e., rifampicin (M_w 822.94 g/mol), which suffers from gastric chemical instability, low bioavailability, and severe hepatotoxicity. HMNs morphology was designed with sub-apical holes present in a quarter of the needle tip to improve its mechanical strength and integrity of the HMNs array. The HMNs array was characterized by optical microscopy and electron microscopy to ascertain the print quality and uniformity across the array. The system was also subjected to mechanical characterization for failure and penetration analyses. The ex vivo permeation and consequent transport of rifampicin across porcine skin were systematically evaluated. Finally, in vivo examinations of rifampicin administration through the microneedle reservoir system in SD rats revealed efficient penetration and desired bioavailability.

Design and development of insulin microneedles for diabetes treatment

As a painless and minimally invasive method of self-administration, microneedle is very promising to replace subcutaneous injection of insulin for type I diabetes treatment. Since the introduction of microneedles, many scholars have paid attention to and studied this technology, which has made it developed rapidly. However, there is no product on the market or in clinical trials at present. The reason is that there are still many technical problems in microneedle drug delivery system, such as the perfect integration of stable, controllable, fast, long-lasting, safe, and other necessary conditions. Here, we review the achievements that researchers have made that contain one or more of the above factors, and put some ideas to solve the limitations of insulin delivery by microneedles for reference.

Hollow microneedles: A perspective in biomedical applications

Microneedles (MN) have the potential to become a highly progressive device for both drug delivery and monitoring purposes as they penetrate the skin and pierce the stratum corneum barrier, allowing the delivery of drugs in the viable skin layers and the extraction of body fluids. Despite the many years of research and the different types of MN developed, only hollow MN have reached the pharmaceutical market under the path of medical devices. Therefore, this review focuses on hollow MN, materials and methods for their fabrication as well as their application in drug delivery, vaccine delivery and monitoring purposes. Furthermore, novel approaches for the fabrication of hollow MN are included as well as prospects of microneedle-based products on the market.

Microneedle-mediated transdermal drug delivery for treating diverse skin diseases

Transdermal drug delivery is an attractive route for dermatological disease therapy because it can directly target the lesion site on the skin, reduce adverse reactions associated with systemic administration, and improve patient compliance. However, the stratum corneum, as the main skin barrier, severely limits transdermal drug penetration, with compromised bioavailability. Microneedles (MNs), which are leveraged to markedly improve the penetration of therapeutic agents by piercing the stratum corneum and creating hundreds of reversible microchannels in a minimally invasive manner, have been envisioned as a milestone for effective transdermal drug delivery, especially for superficial disease therapy. Here, the emergence of versatile MNs for the transdermal delivery of various drugs is reviewed, particularly focusing on the application of MNs for the treatment of diverse skin diseases, including superficial tumors, scars, psoriasis, herpes, acne, and alopecia. Additionally, the promises and challenges of the widespread translation of MN-mediated transdermal drug delivery in the dermatology field are summarized.

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.

High-resolution two-photon polymerization: the most versatile technique for the fabrication of microneedle arrays

Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.

Novel Drug Delivery Systems Fighting Glaucoma: Formulation Obstacles and Solutions

Glaucoma is considered to be one of the biggest health problems in the world. It is the main cause of preventable blindness due to its asymptomatic nature in the early stages on the one hand and patients' non-adherence on the other. There are several approaches in glaucoma treatment, whereby this has to be individually designed for each patient. The first-line treatment is medication therapy. However, taking into account numerous disadvantages of conventional ophthalmic dosage forms, intensive work has been carried out on the development of novel drug delivery systems for glaucoma. This review aims to provide an overview of formulation solutions and strategies in the development of in situ gel systems, nanosystems, ocular inserts, contact lenses, collagen corneal shields, ocular implants, microneedles, and iontophoretic devices. The results of studies confirming the effectiveness of the aforementioned drug delivery systems were also briefly presented.

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.

Microneedles: Characteristics, Materials, Production Methods and Commercial Development

Although transdermal drug delivery systems (DDS) offer numerous benefits for patients, including the avoidance of both gastric irritation and first-pass metabolism effect, as well as improved patient compliance, only a limited number of active pharmaceutical ingredients (APIs) can be delivered accordingly. Microneedles (MNs) represent one of the most promising concepts for effective transdermal drug delivery that penetrate the protective skin barrier in a minimally invasive and painless manner. The first MNs were produced in the 90s, and since then, this field has been continually evolving. Therefore, different manufacturing methods, not only for MNs but also MN molds, are introduced, which allows for the cost-effective production of MNs for drug and vaccine delivery and even diagnostic/monitoring purposes. The focus of this review is to give a brief overview of MN characteristics, material composition, as well as the production and commercial development of MN-based systems.

Progress and perspective of microneedle system for anti-cancer drug delivery

Transdermal drug delivery exhibited encouraging prospects, especially through superficial drug administration routes. However, only a few limited lipophilic drug molecules could cross the skin barrier, those are with low molecular weight and rational Log P value. Microneedles (MNs) can overcome these limitations to deliver numerous drugs into the dermal layer by piercing the outermost skin layer of the body. In the case of superficial cancer treatments, topical drug administration faces severely low transfer efficiency, and systemic treatments are always associated with side effects and premature drug degradation. MN-based systems have achieved excellent technical capabilities and been tested for pre-clinical chemotherapy, photothermal therapy, photodynamic therapy, and immunotherapy. In this review, we will focus on the features, progress, and opportunities of MNs in the anticancer drug delivery system. Then, we will discuss the strategies and advantages in these works and summarize challenges, perspectives, and translational potential for future applications.

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.