Microneedle array systems for long-acting drug delivery

Implantable trilayer microneedle transdermal delivery system to enhance bioavailability and brain delivery of rivastigmine for Alzheimer treatment: A proof-of-concept study

Alzheimer's disease (ALZ) is a neurological disorder characterized by cognitive decline. Rivastigmine (RV), an acetylcholinesterase inhibitor, is commonly used to treat ALZ. Unfortunately, RV is availablein capsule form, which is associated with low drug bioavailability, and in patch form, which can lead to skin irritation upon repeated use. This study successfully fabricated a trilayer dissolving microneedle (TDMN) containing RV with adequate mechanical strength by using the molding method. In vitro release and ex vivo permeation showed that the release and permeation of RV were significantly sustained compared to control without PCL. The release and permeation percentages were 91.34 ± 11.39 % and 13.76 ± 1.49 μg/cm2, respectively. In addition, the concentration of RV in plasma and brain after 168 h was measured to be 0.44 ± 0.09 µg/mL and 1.23 ± 0.26 µg/g, respectively, which reached the minimum concentration to inhibit AcHE and BuChe. Pharmacokinetic testing revealed higher AUC values after administration of TDMN, indicating better bioavailability and RV concentrations in the brain were twice as high as those achieved with oral administration. This study suggests TDMN may enhance the bioavailability and brain delivery of RV.

Separable nanocomposite hydrogel microneedles for intradermal and sustained delivery of antigens to enhance adaptive immune responses

Vaccines play a critical role in combating infectious diseases and cancers, yet improving their efficacy remains challenging. Here, we introduce a separable nanocomposite hydrogel microneedle (NHMN) patch designed for intradermal and sustained delivery of ovalbumin (OVA), a model antigen, to enhance adaptive immune responses. The NHMN patch consists of an array of OVA-loaded microneedles made from photo-cross-linked methacrylated hyaluronic acid and laponite (LAP), supported by a hyaluronic acid backing. The incorporation of LAP not only enhances the mechanical strength of the pure hydrogel microneedles but also significantly prolongs OVA release. Furthermore, in vitro cell experiments demonstrate that NHMNs effectively activate dendritic cells without compromising cell viability. Upon skin penetration, NHMNs detach from the backing as the hyaluronic acid rapidly dissolves upon contact with the skin interstitial fluid, thereby acting as antigen reservoirs to release antigens to abundant skin dendritic cells. NHMNs containing 0.5% w/v LAP achieved a 15-day OVA release in vivo. Immunization studies demonstrate that the intradermal and sustained release of OVA via NHMNs elicited stronger and longer-lasting adaptive immune responses compared to conventional bolus injection. Given its easy to use, painless and minimally invasive features, the NHMN patch shows promise in improving vaccination accessibility and efficacy against a range of diseases. STATEMENT OF SIGNIFICANCE: The study introduces a separable nanocomposite hydrogel microneedle (NHMN) patch. This patch consists of an array of ovalbumin (OVA, a model antigen)-loaded microneedles made from photo-cross-linked methacrylated hyaluronic acid and laponite, with a hyaluronic acid backing, designed for intradermal and sustained delivery of antigens. This patch addresses several key challenges in traditional vaccination methods, including poor antigen uptake and presentation, and rapid systematic clearance. The incorporation of laponite enhances mechanical strength of microneedles, promotes dendritic cell activation, and significantly slows down antigen release. NHMN-based vaccination elicits stronger and longer-lasting adaptive immune responses compared to conventional bolus injection. This NHMN patch holds great potential for improving the efficacy, accessibility, and patient comfort of vaccinations against a range of diseases.

Dissolving microarray patches for transdermal delivery of risperidone for schizophrenia management

Schizophrenia is a psychiatric disorder that results from abnormal levels of neurotransmitters in the brain. Risperidone (RIS) is a common drug prescribed for the treatment of schizophrenia. RIS is a hydrophobic drug that is typically administered orally or intramuscularly. Transdermal drug delivery (TDD) could potentially improve the delivery of RIS. This study focused on the development of RIS nanocrystals (NCs), for the first time, which were incorporated into dissolving microneedle array patches (DMAPs) to facilitate the drug delivery of RIS. RIS NCs were formulated via wet-media milling technique using poly(vinylalcohol) (PVA) as a stabiliser. NCs with particle size of 300 nm were produced and showed an enhanced release profile up to 80 % over 28 days. Ex vivo results showed that 1.16 ± 0.04 mg of RIS was delivered to both the receiver compartment and full-thickness skin from NCs loaded DMAPs compared to 0.75 ± 0.07 mg from bulk RIS DMAPs. In an in vivo study conducted using female Sprague Dawley rats, both RIS and its active metabolite 9-hydroxyrisperidone (9-OH-RIS) were detected in plasma samples for 5 days. In comparison with the oral group, DMAPs improved the overall pharmacokinetic profile in plasma with a ∼ 15 folds higher area under the curve (AUC) value. This work has represented the novel delivery of the antipsychotic drug, RIS, through microneedles. It also offers substantial evidence to support the broader application of MAPs for the transdermal delivery of poorly water-soluble drugs.

Block copolymer micelles as ocular drug delivery systems

Block copolymer micelles, formed by the self-assembly of amphiphilic polymers, address formulation challenges, such as poor drug solubility and permeability. These micelles offer advantages including a smaller size, easier preparation, sterilization, and superior solubilization, compared with other nanocarriers. Preclinical studies have shown promising results, advancing them toward clinical trials. Their mucoadhesive properties enhance and prolong contact with the ocular surface, and their small size allows deeper penetration through tissues, such as the cornea. Additionally, copolymeric micelles improve the solubility and stability of hydrophobic drugs, sustain drug release, and allow for surface modifications to enhance biocompatibility. Despite these benefits, long-term stability remains a challenge. In this review, we highlight the preclinical performance, structural frameworks, preparation techniques, physicochemical properties, current developments, and prospects of block copolymer micelles as ocular drug delivery systems.

Validation of UV-Vis spectrophotometric and colorimetric methods to quantify methotrexate in plasma and rat skin tissue: Application to in vitro release, ex vivo and in vivo studies from dissolving microarray patch loaded pH-sensitive nanoparticle

This research transformed MTX into smart nanoparticles that respond to the acidic conditions present in inflammation. These nanoparticles were then incorporated into a patch that dissolves over time, aiding their penetration. A method using UV-Vis spectrophotometry was validated to support the development of this new delivery system. This method was used to measure the quantity of MTX in the prepared patches in various scenarios: in laboratory solutions with pH 7.4 and pH 5.0, in skin tissue, and plasma. This validation was conducted in laboratory studies, tissue samples, and live subjects, adhering to established guidelines. The resulting calibration curve displayed a linear relationship (correlation coefficient 0.999) across these scenarios. The lowest quantity of MTX that could be accurately detected was 0.6 µg/mL in pH 7.4 solutions, 1.46 µg/mL in pH 5.0 solutions, 1.11 µg/mL in skin tissue, and 1.48 µg/mL in plasma. This validated method exhibited precision and accuracy and was not influenced by dilution effects. The method was effectively used to measure MTX levels in the developed patch in controlled lab settings and biological systems (in vitro, ex vivo, and in vivo). This showed consistent drug content in the patches, controlled release patterns over 24 h, and pharmacokinetic profiles spanning 48 h. However, additional analytical approaches were necessary for quantifying MTX in studies focused on the drug's effects on the body's functions.

Toward a solid microneedle patch for rapid and enhanced local analgesic action

Analgesic creams find widespread application as adjuncts for localized anesthesia prior to surgical procedures. Nevertheless, the onset of analgesic action is protracted due to the skin barrier's inherent characteristics, which necessitates prolonged intervals of patient and clinician waiting, consequently impinging upon patient compliance and clinician workflow efficiency. In this work, a biodegradable microneedles (MNs) patch was introduced to enhance the intradermal administration of lidocaine cream to achieve rapid analgesia through a minimally invasive and conveniently accessible modality. The polylactic acid (PLA) MNs were mass-produced using a simple hot-pressing method and served the purpose of creating microchannels across the skin's surface for rapid absorption of lidocaine cream. Optical and electron microscopes were applied to meticulously scrutinize the morphology of the fabricated MNs, and the comprehensive penetration tests involving dynamometer tests, evaluation on porcine cadaver skin, artificial film, optical coherence tomography (OCT), transepidermal water loss, and analysis on rats' skins, demonstrated the robust mechanical strength of PLA MNs for successful intradermal penetration. The behavioral pain sensitivity tests on living rats using Von Frey hair filaments revealed that the MN-assisted lidocaine treatment expeditiously accelerated the onset of action from 40 to 10 min and substantially enhanced the efficacy of localized anesthesia. Furthermore, different treatment protocols encompassing the sequence of drug application relative to MN treatment, MN dimensions, and the frequency of MN insertions exhibited noteworthy influence on the resultant local anesthesia efficacy. Together, these results demonstrated that the lidocaine cream followed by diverse PLA MN treatments would be a promising strategy for rapid clinical local anesthesia with wide-ranging applications.

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.

Design of a Novel Delivery Efficiency Feedback System for Biphasic Dissolving Microarray Patches Based on Poly(Lactic Acid) and Moisture-Indicating Silica

Dissolving microarray patches (DMAPs) represent an innovative approach to minimally invasive transdermal drug delivery, demonstrating efficacy in delivering both small and large therapeutic molecules. However, concerns raised in end-user surveys have hindered their commercialization efforts. One prevalent issue highlighted in these surveys is the lack of clear indicators for successful patch insertion and removal time. To address this challenge, a color-change-based feedback system is devised, which confirms the insertion and dissolution of DMAPs, aiming to mitigate the aforementioned problems. The approach combines hydrophilic needles containing model drugs (fluorescein sodium and fluorescein isothiocyanate (FITC)-dextran) with a hydrophobic poly(lactic acid) baseplate infused with moisture-sensitive silica gel particles. The successful insertion and subsequent complete dissolution of the needle shaft are indicated by the progressive color change of crystal violet encapsulated in the silica. Notably, distinct color alterations on the baseplate, observed 30 min and 1 h after insertion for FITC-dextran and fluorescein sodium DMAPs respectively, signal the full dissolution of the needles, confirming the complete cargo delivery and enabling timely patch removal. This innovative feedback system offers a practical solution for addressing end-user concerns and may significantly contribute to the successful commercialization of DMAPs by providing a visualized drug delivery method.

Hollow microneedles for ocular drug delivery

Microneedles (MNs) are micron-sized needles, typically <2 mm in length, arranged either as an array or as single needle. These MNs offer a minimally invasive approach to ocular drug delivery due to their micron size (reducing tissue damage compared to that of hypodermic needles) and overcoming significant barriers in drug administration. While various types of MNs have been extensively researched, significant progress has been made in the use of hollow MNs (HMNs) for ocular drug delivery, specifically through suprachoroidal injections. The suprachoroidal space, situated between the sclera and choroid, has been targeted using optical coherence tomography-guided injections of HMNs for the treatment of uveitis. Unlike other MNs, HMNs can deliver larger volumes of formulations to the eye. This review primarily focuses on the use of HMNs in ocular drug delivery and explores their ocular anatomy and the distribution of formulations following potential HMN administration routes. Additionally, this review focuses on the influence of formulation characteristics (e.g., solution viscosity, particle size), HMN properties (e.g., bore or lumen diameter, MN length), and routes of administration (e.g., periocular transscleral, suprachoroidal, intravitreal) on the ocular distribution of drugs. Overall, this paper highlights the distinctive properties of HMNs, which make them a promising technology for improving drug delivery efficiency, precision, and patient outcomes in the treatment of ocular diseases.

Transdermal delivery of resveratrol loaded solid lipid nanoparticle as a microneedle patch: a novel approach for the treatment of Parkinson's disease

Parkinson's disease (PD), affecting millions of people worldwide and expected to impact 10 million by 2030, manifests a spectrum of motor and non-motor symptoms linked to the decline of dopaminergic neurons. Current therapies manage PD symptoms but lack efficacy in slowing disease progression, emphasizing the urgency for more effective treatments. Resveratrol (RSV), recognized for its neuroprotective and antioxidative properties, encounters challenges in clinical use for PD due to limited bioavailability. Researchers have investigated lipid-based nanoformulations, specifically solid lipid nanoparticles (SLNs), to enhance RSV stability. Oral drug delivery via SLNs faces obstacles, prompting exploration into transdermal delivery using SLNs integrated with microneedles (MNs) for improved patient compliance. In this study, an RSV-loaded SLNs (RSV -SLNs) incorporated into the MN patch was developed for transdermal RSV delivery to improve its stability and patient compliance. Characterization studies demonstrated favorable physical properties of SLNs with a sustained drug release profile of 78.36 ± 0.74%. The developed MNs exhibited mechanical robustness and skin penetration capabilities. Ex vivo permeation studies displayed substantial drug permeation of 68.39 ± 1.4% through the skin. In an in vivo pharmacokinetic study, the RSV-SLNs delivered through MNs exhibited a significant increase in Cmax, Tmax, and AUC0 - t values, alongside a reduced elimination rate in blood plasma in contrast to the administration of pure RSV via MNs. Moreover, an in vivo study showcased enhanced behavioral functioning and increased brain antioxidant levels in the treated animals. In-vivo skin irritation study revealed no signs of irritation till 24 h which permits long-term MNs application. Histopathological analysis showed notable changes in the brain regions of the rat, specifically the striatum and substantia nigra, after the completion of the treatment. Based on these findings, the development of an RSV-SLN loaded MNs (RSVSNLMP) patch presents a novel approach, with the potential to enhance the drug's efficiency, patient compliance, and therapeutic outcomes for PD, offering a promising avenue for advanced PD therapy.

Recent advances in transdermal insulin delivery technology: A review

Transdermal drug delivery refers to the administration of drugs through the skin, after which the drugs can directly act on or circulate through the body to the target organs or cells and avoid the first-pass metabolism in the liver and kidneys experienced by oral drugs, reducing the risk of drug poisoning. From the initial singular approach to transdermal drug delivery, there has been a shift toward combining multiple methods to enhance drug permeation efficiency and address the limitations of individual approaches. Technological advancements have also improved the accuracy of drug delivery. Optimizing insulin itself also enables its long-term release via needle-free injectors. In this review, the diverse transdermal delivery methods employed in insulin therapy and their respective advantages and limitations are discussed. By considering factors such as the principles of transdermal penetration, drug delivery efficiency, research progress, synergistic innovations among different methods, patient compliance, skin damage, and posttreatment skin recovery, a comprehensive evaluation is presented, along with prospects for potential novel combinatorial approaches. Furthermore, as insulin is a macromolecular drug, insights gained from its transdermal delivery may also serve as a valuable reference for the use of other macromolecular drugs for treatment.

Optimization of stereolithography 3D printing of microneedle micro-molds for ocular drug delivery

Microneedles (MN) have emerged as an innovative technology for drug delivery, offering a minimally invasive approach to administer therapeutic agents. Recent applications have included ocular drug delivery, requiring the manufacture of sub-millimeter needle arrays in a reproducible and reliable manner. The development of 3D printing technologies has facilitated the fabrication of MN via mold production, although there is a paucity of information available regarding how the printing parameters may influence crucial issues such as sharpness and penetration efficacy. In this study, we have developed and optimized a 3D-printed MN micro-mold using stereolithography (SLA) 3D printing to prepare a dissolving ocular MN patch. The effects of a range of parameters including aspect ratio, layer thickness, length, mold shape and printing orientation have been examined with regard to both architecture and printing accuracy of the MN micro-mold, while the effects of printing angle on needle fidelity was also examined for a range of basic shapes (conical, pyramidal and triangular pyramidal). Mechanical strength and in vitro penetration of the polymeric (PVP/PVA) MN patch produced from reverse molds fabricated using MN with a range of shapes and height, and aspect ratios were assessed, followed by ex vivo studies of penetration into excised scleral and corneal tissues. The optimization process identified the parameters required to produce MN with the sharpest tips and highest dimensional fidelity, while the ex vivo studies indicated that these optimized systems would penetrate the ocular tissue with minimal applied pressure, thereby allowing ease of patient self-administration.

Calcipotriol Nanosuspension-Loaded Trilayer Dissolving Microneedle Patches for the Treatment of Psoriasis: In Vitro Delivery and In Vivo Antipsoriatic Activity Studies

Psoriasis, affecting 2-3% of the global population, is a chronic inflammatory skin condition without a definitive cure. Current treatments focus on managing symptoms. Recognizing the need for innovative drug delivery methods to enhance patient adherence, this study explores a new approach using calcipotriol monohydrate (CPM), a primary topical treatment for psoriasis. Despite its effectiveness, CPM's therapeutic potential is often limited by factors like the greasiness of topical applications, poor skin permeability, low skin retention, and lack of controlled delivery. To overcome these challenges, the study introduces CPM in the form of nanosuspensions (NSs), characterized by an average particle size of 211 ± 2 nm. These CPM NSs are then incorporated into a trilayer dissolving microneedle patch (MAP) made from poly(vinylpyrrolidone) and w poly(vinyl alcohol) as needle arrays and prefrom 3D printed polylactic acid backing layer. This MAP features rapidly dissolving tips and exhibits good mechanical properties and insertion capability with delivery efficiency compared to the conventional Daivonex ointment. The effectiveness of this novel MAP was tested on Sprague-Dawley rats with imiquimod-induced psoriasis, demonstrating efficacy comparable to the marketed ointment. This innovative trilayer dissolving MAP represents a promising new local delivery system for calcipotriol, potentially revolutionizing psoriasis treatment by enhancing drug delivery and patient compliance.

Lubricating Microneedles System with Multistage Sustained Drug Delivery for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a typical joint degenerative disease that is prevalent worldwide and significantly affects the normal activities of patients. Traditional treatments using diclofenac (DCF) as an anti-inflammatory drug by oral administration and transdermal delivery have many inherent deficiencies. In this study, a lubricating microneedles (MNs) system for the treatment of osteoarthritis with multistage sustained drug delivery and great reduction in skin damage during MNs penetration is developed. The bilayer dissolvable MNs system, namely HA-DCF@PDMPC, is prepared by designating the composite material of hyaluronic acid (HA) and covalently conjugated drug compound (HA-DCF) as the MNs tips and then modifying the surface of MNs tips with a self-adhesive lubricating copolymer (PDMPC). The MNs system is designed to achieve sustained drug release of DCF via ester bond hydrolysis, physical diffusion from MNs tips, and breakthrough of lubrication coating. Additionally, skin damage is reduced due to the presence of the lubrication coating on the superficial surface. Therefore, the lubricating MNs with multistage sustained drug delivery show good compliance as a transdermal patch for OA treatment, which is validated from anti-inflammatory cell tests and therapeutic animal experiments, down-regulating the expression levels of pro-inflammatory factors and alleviating articular cartilage destruction.

Unravelling the role of microneedles in drug delivery: Principle, perspectives, and practices

In recent year, the research of transdermal drug delivery systems has got substantial attention towards the development of microneedles (MNs). This shift has occurred due to multifaceted advantages of MNs as they can be utilized to deliver the drug deeper to the skin with minimal invasion, offer successful delivery of drugs and biomolecules that are susceptible to degradation in gastrointestinal tract (GIT), act as biosensors, and help in monitoring the level of biomarkers in the body. These can be fabricated into different types based on their applications as well as material for fabrication. Some of their types include solid MNs, hollow MNs, coated MNs, hydrogel forming MNs, and dissolving MNs. These MNs deliver the therapeutics via microchannels deeper into the skin. The coated and hollow MNs have been found successful. However, they suffer from poor drug loading and blocking of pores. In contrast, dissolving MNs offer high drug loading. These MNs have also been utilized to deliver vaccines and biologicals. They have also been used in cosmetics. The current review covers the different types of MNs, materials used in their fabrication, properties of MNs, and various case studies related to their role in delivering therapeutics, monitoring level of biomarkers/hormones in body such as insulin. Various patents and clinical trials related to MNs are also covered. Covered are the major bottlenecks associated with their clinical translation and potential future perspectives.

Spatiotemporal fate of nanocarriers-embedded dissolving microneedles: the impact of needle dissolving rate

OBJECTIVE

Dissolving microneedles (DMNs) have shown great potential for transdermal drug delivery due to their excellent skin-penetrating ability and combination with nanocarriers (NCs) can realize targeted drug delivery. The objective of this study was to investigate the impact of microneedle dissolving rate on the in vivo fate of NC-loaded DMNs, which would facilitate the clinical translation of such systems.

METHODS

Solid lipid nanoparticles (SLNs) were selected as the model NC for loading in DMNs, which were labeled by P4 probes with aggregation-quenching properties. Sodium hyaluronate acid (HA) and chitosan (CS), with different aqueous dissolving rates, were chosen as model tip materials. The effects of needle dissolving rate on the in vivo fate of NC-loaded DMNs was investigated by tracking the distribution of fluorescence signals after transdermal exposure.

RESULTS

P4 SLNs achieved a deeper diffusion depth of 180 μm in DMN-HA with a faster dissolution rate, while the diffusion depth in DMN-CS with a slower dissolution rate was lower (140 μm). The in vivo experiments demonstrated that P4 SLNs had a T1/2 value of 12.14 h in DMN-HA, whilst a longer retention time was found in DMN-CS, with a T1/2 of 13.12 h.

CONCLUSIONS

This study confirmed that the in vivo diffusion rate of NC-loaded DMNs was determined by the dissolving rate of DMNs materials and provided valuable guidance for the design and development of NC-loaded DMNs in the future.

Nanozyme-Incorporated Microneedles for the Treatment of Chronic Wounds

Acute wounds are converted to chronic wounds due to advanced age and diabetic complications. Nanozymes catalyze ROS production to kill bacteria without causing drug resistance, while microneedles (MNs) can break through the skin barrier to deliver drugs effectively. Nanozymes can be intergrateded into MNs delivery systems to improve painless drug delivery. It can also reduce the effective dose of drug sterilization while increasing delivery efficiency and effectively killing wounded bacteria while preventing drug resistance. This paper describes various types of metal nanozymes from previous studies and compares their mutual enhancement with nanozymes. The pooled results show that the MNs, through material innovation, are able to both penetrate the scab and deliver nanozymes and exert additional anti-inflammatory and bactericidal effects. The catalytic effect of some of the nanozymes can also accelerate the lysis of the MNs or create a cascade reaction against inflammation and infection. However, the issue of increased toxicity associated with skin penetration and clinical translation remains a challenge. This study reviews the latest published results and corresponding challenges associated with the use of MNs combined with nanozymes for the treatment of wounds, providing further information for future research.

Polymeric Microneedles for Health Care Monitoring: An Emerging Trend

Bioanalyte collection by blood draw is a painful process, prone to needle phobia and injuries. Microneedles can be engineered to penetrate the epidermal skin barrier and collect analytes from the interstitial fluid, arising as a safe, painless, and effective alternative to hypodermic needles. Although there are plenty of reviews on the various types of microneedles and their use as drug delivery systems, there is a lack of systematization on the application of polymeric microneedles for diagnosis. In this review, we focus on the current state of the art of this field, while providing information on safety, preclinical and clinical trials, and market distribution, to outline what we believe will be the future of health monitoring.

Microneedles Based on a Biodegradable Polymer-Hyaluronic Acid

Transdermal transport can be challenging due to the difficulty in diffusing active substances through the outermost layer of the epidermis, as the primary function of the skin is to protect against the entry of exogenous compounds into the body. In addition, penetration of the epidermis for substances hydrophilic in nature and particles larger than 500 Da is highly limited due to the physiological properties and non-polar nature of its outermost layer, namely the stratum corneum. A solution to this problem can be the use of microneedles, which "bypass" the problematic epidermal layer by dispensing the active substance directly into the deeper layers of the skin. Microneedles can be obtained with various materials and come in different types. Of special interest are carriers based on biodegradable and biocompatible polymers, such as polysaccharides. Therefore, this paper reviews the latest literature on methods to obtain hyaluronic acid-based microneedles. It focuses on the current advancements in this field and consequently provides an opportunity to guide future research in this area.

Fabrication of Multiple-Channel Electrochemical Microneedle Electrode Array via Separated Functionalization and Assembly Method

Real-time monitoring of physiological indicators inside the body is pivotal for contemporary diagnostics and treatments. Implantable electrodes can not only track specific biomarkers but also facilitate therapeutic interventions. By modifying biometric components, implantable electrodes enable in situ metabolite detection in living tissues, notably beneficial in invasive glucose monitoring, which effectively alleviates the self-blood-glucose-managing burden for patients. However, the development of implantable electrochemical electrodes, especially multi-channel sensing devices, still faces challenges: (1) The complexity of direct preparation hinders functionalized or multi-parameter sensing on a small scale. (2) The fine structure of individual electrodes results in low spatial resolution for sensor functionalization. (3) There is limited conductivity due to simple device structures and weakly conductive electrode materials (such as silicon or polymers). To address these challenges, we developed multiple-channel electrochemical microneedle electrode arrays (MCEMEAs) via a separated functionalization and assembly process. Two-dimensional microneedle (2dMN)-based and one-dimensional microneedle (1dMN)-based electrodes were prepared by laser patterning, which were then modified as sensing electrodes by electrochemical deposition and glucose oxidase decoration to achieve separated functionalization and reduce mutual interference. The electrodes were then assembled into 2dMN- and 1dMN-based multi-channel electrochemical arrays (MCEAs), respectively, to avoid damaging functionalized coatings. In vitro and in vivo results demonstrated that the as-prepared MCEAs exhibit excellent transdermal capability, detection sensitivity, selectivity, and reproducibility, which was capable of real-time, in situ glucose concentration monitoring.

Nanocarrier-Integrated Microneedles: Divulging the Potential of Novel Frontiers for Fostering the Management of Skin Ailments

The various kinds of nanocarriers (NCs) have been explored for the delivery of therapeutics designed for the management of skin manifestations. The NCs are considered as one of the promising approaches for the skin delivery of therapeutics attributable to sustained release and enhanced skin penetration. Despite the extensive applications of the NCs, the challenges in their delivery via skin barrier (majorly stratum corneum) have persisted. To overcome all the challenges associated with the delivery of NCs, the microneedle (MN) technology has emerged as a beacon of hope. Programmable drug release, being painless, and its minimally invasive nature make it an intriguing strategy to circumvent the multiple challenges associated with the various drug delivery systems. The integration of positive traits of NCs and MNs boosts therapeutic effectiveness by evading stratum corneum, facilitating the delivery of NCs through the skin and enhancing their targeted delivery. This review discusses the barrier function of skin, the importance of MNs, the types of MNs, and the superiority of NC-loaded MNs. We highlighted the applications of NC-integrated MNs for the management of various skin ailments, combinational drug delivery, active targeting, in vivo imaging, and as theranostics. The clinical trials, patent portfolio, and marketed products of drug/NC-integrated MNs are covered. Finally, regulatory hurdles toward benchtop-to-bedside translation, along with promising prospects needed to scale up NC-integrated MN technology, have been deliberated. The current review is anticipated to deliver thoughtful visions to researchers, clinicians, and formulation scientists for the successful development of the MN-technology-based product by carefully optimizing all the formulation variables.

Long-Acting Strategies for Antibody Drugs: Structural Modification, Controlling Release, and Changing the Administration Route

Because of their high specificity, high affinity, and targeting, antibody drugs have been widely used in the treatment of many diseases and have become the most favored new drugs for research in the world. However, some antibody drugs (such as small-molecule antibody fragments) have a short half-life and need to be administered frequently, and are often associated with injection-site reactions and local toxicities during use. Increasing attention has been paid to the development of antibody drugs that are long-acting and have fewer side effects. This paper reviews existing strategies to achieve long-acting antibody drugs, including modification of the drug structure, the application of drug delivery systems, and changing their administration route. Among these, microspheres have been studied extensively regarding their excellent tolerance at the injection site, controllable loading and release of drugs, and good material safety. Subcutaneous injection is favored by most patients because it can be quickly self-administered. Subcutaneous injection of microspheres is expected to become the focus of developing long-lasting antibody drug strategies in the near future.

Minoxidil Nanosuspension-Loaded Dissolved Microneedles for Hair Regrowth

Minoxidil (MIN) is used topically to treat alopecia. However, its low absorption limits its use, warranting a new strategy to enhance its delivery into skin layers. The objective of this study was to evaluate the dermal delivery of MIN by utilizing dissolved microneedles (MNs) loaded with MIN nanosuspension (MIN-NS) for hair regrowth. MIN-NS was prepared by the solvent-antisolvent precipitation technique. The particle size of MIN-NS was 226.7 ± 9.3 nm with a polydispersity index of 0.29 ± 0.17 and a zeta potential of -29.97 ± 1.23 mV. An optimized formulation of MIN-NS was selected, freeze-dried, and loaded into MNs fabricated with sodium carboxymethyl cellulose (Na CMC) polymeric solutions (MIN-NS-loaded MNs). MNs were evaluated for morphology, dissolution rate, skin insertion, drug content, mechanical properties, ex vivo permeation, in vivo, and stability studies. MNs, prepared with 14% Na CMC, were able to withstand a compression force of 32 N for 30 s, penetrate Parafilm M® sheet at a depth of 374-504 µm, and dissolve completely in the skin within 30 min with MIN %recovery of 95.1 ± 6.5%. The release of MIN from MIN-NS-loaded MNs was controlled for 24 h. MIN-NS-loaded MNs were able to maintain their mechanical properties and chemical stability for 4 weeks, when kept at different storage conditions. The in vivo study of the freeze-dried MIN-NS and MIN-NS-loaded MNs proved hair regrowth on rat skin after 11 and 7 days, respectively. These results showed that MIN-NS-loaded MNs could potentially improve the dermal delivery of MIN through the skin to treat alopecia.

Novel Drug Delivery Systems for the Management of Fungal Keratitis

Fungal keratitis (FK) is a dangerous corneal infection that is common in tropical and subtropical areas. Its incidence is extremely high, and ocular trauma and contact lenses can lead to FK, but its common treatment such as using topical antifungal eye drop instillation is often less effective because of several drawbacks of the drugs typically used, including limited ocular penetration, high frequency of dosing, poor biocompatibility, and the potential for severe drug reactions. Therefore, the development of novel drug delivery devices for the treatment of FK is urgent. The urgent need for novel drug delivery devices to treat FK has led to the development of several techniques, including nanoparticles (NPs), in situ forming hydrogels, contact lenses, and microneedles (MNs). However, it is important to note that the main mechanisms differ between these techniques. NPs can transport large amounts of drugs and be taken up by cells owing to their large surface area and small size. In situ forming hydrogels can significantly extend the residence time of drugs because of their strong adhesive properties. Contact lenses, with their comfortable shape and drug-carrying capacity, can also act as drug delivery devices. MNs can create channels in the cornea, bypassing its barrier and enhancing drug bioavailability. This article will go over novel medication delivery techniques for treating FK and make a conclusion about their advantages and limitations in anticipation to serve the best option for the individual therapy of FK.

Self-Healing Porous Microneedles Fabricated Via Cryogenic Micromoulding and Phase Separation for Efficient Loading and Sustained Delivery of Diverse Therapeutics

Sustained-release drug delivery formulations are preferable for treating various diseases as they enhance and prolong efficacy, minimize adverse effects, and avoid frequent dosing. However, these formulations are associated with poor patient compliance, require trained personnel for administration, and involve harsh manufacturing conditions that compromise drug stability. Here, a self-healing biodegradable porous microneedle (PMN) patch is reported for sustained drug delivery. The PMN patch is fabricated by a cryogenic micromoulding followed by phase separation, leading to formation of interconnected pores on the surface and internals of MNs. The pores with self-healing feature enable the PMNs to load hydrophilic drugs with different molecular weights in a mild and efficient manner. The healed PMNs can easily penetrate into the skin under press and detach from the supporting substrate under shear, thereby acting as implantable drug reservoirs for achieving sustained release of drugs for at least 40 days. One-time administration of desired therapeutics using the sustained-release healed PMNs resulted in stronger and longer-lasting efficacy in mitigating psoriasis and eliciting immunity compared to conventional methods with multiple administrations. The self-healing PMN patch for self-administrated and long-acting drug delivery can eventually improve medication adherence in prophylactic and therapeutic protocols that typically require frequent dosages.

Self-Heating Multistage Microneedle Patch for Topical Therapy of Skin Cancer

Topical therapy is a favored route for treating skin cancers, but remain many challenges, such as low delivery efficiency, limited tumor tissue penetration, and unsatisfactory blood circulation. Here, a self-heating microneedle (MN) patch with multilevel structures, including a dissolvable base for rapid drug release, a degradable tip for sustained drug release, and a self-heating substrate is described. The thermally enhanced drug release performance is validated through both in vitro and in vivo experiments. High tumor therapeutic efficacy can be achieved due to the rapid release of 5-fluorouracil, while the sustained release of thymoquinone endows the MN patch with long-term tumor inhibition ability. It is further demonstrated the feasibility of such an MN patch for in vivo topical therapy of cutaneous squamous cell carcinoma with high efficacy, low side effects, and long-term inhibition of recurrence. This self-heating MN patch holds great promise for potential clinical applications, especially for the treatment of skin cancers.

Polymeric microneedles for the eye: An overview of advances and ocular applications for minimally invasive drug delivery

Ocular drug delivery is challenging due to the presence of tissue barriers and clearance mechanisms. Most widely used topical formulations need frequent application because of poor permeability, short retention, and low bioavailability. Invasive intraocular injections and implants that deliver drugs at the target site are associated with infections, inflammation, and even vision loss post-use. These gaps can be addressed by a delivery platform that can efficiently deliver drug with minimal tissue damage. Microneedles were introduced as a delivery platform for overcoming dermal barriers with minimal tissue damage. After the successful clinical transition of microneedles in the transdermal drug delivery, they are now being extensively studied for ocular applications. The attributes of minimally invasive application and the capability to deliver a wide range of therapeutics make microneedles an attractive candidate for ocular drug delivery. The current manuscript provides a detailed overview of the recent advancements in the field of microneedles for ocular use. This paper reviews research focusing on polymeric microneedles and their pharmaceutical and biopharmaceutical properties. A brief discussion about their clinical translation and regulatory concerns is also covered. The multitude of research articles supports the fact that microneedles are a potential, minimally invasive drug delivery platform for ophthalmic use.

Development of pH-Sensitive Nanoparticle Incorporated into Dissolving Microarray Patch for Selective Delivery of Methotrexate

PURPOSE

Rheumatoid arthritis (RA) is a systemic autoimmune disease that attacks human joints. Methotrexate (MTX), as one the most effective medications to treat RA, has limitations when administered either orally or by injection. To overcome this limitation, we formulated MTX through a smart nanoparticle (SNP) combined with dissolving microarray patch (DMAP) to achieve selective-targeted delivery of RA.

METHODS

SNP was made using the combination of polyethylene glycol (PEG) and polycaprolactone (PCL) polymers, while DMAP was made using the combination of hyaluronic acid and polyvinylpyrrolidone K-30. SNP-DMAP was then evaluated for its mechanical and chemical characteristics, ex vivo permeation test, in vivo pharmacokinetic study, hemolysis, and hen's egg test-chorioallantoic membrane (HET-CAM) test.

RESULT

The results showed that the characteristics of the SNP-DMAP-MTX formulas meet the requirements for transdermal delivery, with the particle size of 189.09 ±12.30 nm and absorption efficiency of 65.40 ± 5.0%. The hemolysis and HET-CAM testing indicate that this formula was non-toxic and non-irritating. Ex vivo permeation shows a concentration of 51.50 ± 3.20 µg/mL of SNP-DMAP-MTX in PBS pH 5.0. The pharmacokinetic profile of SNP-DMAP-MTX showed selectivity and sustained release compared with oral and DMAP-MTX with values of t1/2 (4.88 ± 0 h), Tmax (8 ± 0 h), Cmax (0.50 ± 0.04 μg/mL), AUC (3.15 ± 0.54 μg/mL.h), and mean residence time (MRT) (9.13 ± 0 h).

CONCLUSION

The developed SNP-DMAP-MTX has been proven to deliver MTX transdermal and selectively at the RA site, potentially avoiding conventional MTX side effects and enhancing the effectiveness of RA therapy.

Recent progress of polymeric microneedle-assisted long-acting transdermal drug delivery

Microneedle (MN)-assisted drug delivery technology has gained increasing attention over the past two decades. Its advantages of self-management and being minimally invasive could allow this technology to be an alternative to hypodermic needles. MNs can penetrate the stratum corneum and deliver active ingredients to the body through the dermal tissue in a controlled and sustained release. Long-acting polymeric MNs can reduce administration frequency to improve patient compliance and therapeutic outcomes, especially in the management of chronic diseases. In addition, long-acting MNs could avoid gastrointestinal reactions and reduce side effects, which has potential value for clinical application. In this paper, advances in design strategies and applications of long-acting polymeric MNs are reviewed. We also discuss the challenges in scale manufacture and regulations of polymeric MN systems. These two aspects will accelerate the effective clinical translation of MN products.

Incorporating surfactants into PCL microneedles for sustained release of a hydrophilic model drug

Polymeric microneedles (MNs) are widely used for sustained drug release due to their distinct advantages over other types of MNs. Poly-ε-caprolactone (PCL) stands out as a biodegradable and biocompatible hydrophobic polymer commonly employed in drug delivery applications. This study explores the impact of surfactants on the encapsulation and release rate of a model hydrophilic drug, minoxidil (MXD), from PCL MNs. Three nonionic surfactants, Tween 80, Span 60, and polyethylene glycol (PEG), were integrated into PCL MNs at varying concentrations. Compared to the other types of surfactants, PEG-containing PCL MNs exhibit enhanced insertion capabilities into a skin-simulant parafilm model and increased mechanical strength, suggesting facile penetration into the stratum corneum. Furthermore, MXD-PEG MNs show the highest encapsulation efficiency and are further characterized using FTIR, DSC and XRD. Their mechanical strength against different static forces was measured. The MNs exhibit a sustained release pattern over 20 days. Eventually, MXD-PEG MNs were subjected to penetration testing using chicken skin and required minimal insertion forces with no observed MN failure during experimentation even after compression with the maximum force applied (32 N per patch). Taken together, the present work demonstrates the feasibility of incorporating nonionic surfactants like PEG into the tips of hydrophobic PCL MNs for sustained delivery of a model hydrophilic drug. This formulation strategy can be used to improve patient compliance by allowing self-administration and achieving prolonged drug release.

Advancements in transdermal drug delivery: A comprehensive review of physical penetration enhancement techniques

Transdermal drug administration has grown in popularity in the pharmaceutical research community due to its potential to improve drug bioavailability, compliance among patients, and therapeutic effectiveness. To overcome the substantial barrier posed by the stratum corneum (SC) and promote drug absorption within the skin, various physical penetration augmentation approaches have been devised. This review article delves into popular physical penetration augmentation techniques, which include sonophoresis, iontophoresis, magnetophoresis, thermophoresis, needle-free injection, and microneedles (MNs) Sonophoresis is a technique that uses low-frequency ultrasonic waves to break the skin's barrier characteristics, therefore improving drug transport and distribution. In contrast, iontophoresis uses an applied electric current to push charged molecules of drugs inside the skin, effectively enhancing medication absorption. Magnetophoresis uses magnetic fields to drive drug carriers into the dermis, a technology that has shown promise in aiding targeted medication delivery. Thermophoresis is the regulated heating of the skin in order to improve drug absorption, particularly with thermally sensitive drug carriers. Needle-free injection technologies, such as jet injectors (JIs) and microprojection arrays, offer another option by producing temporary small pore sizes in the skin, facilitating painless and effective drug delivery. MNs are a painless, minimally invasive method, easy to self-administration, as well as high drug bioavailability. This study focuses on the underlying processes, current breakthroughs, and limitations connected with all of these approaches, with an emphasis on their applicability in diverse therapeutic areas. Finally, a thorough knowledge of these physical enhancement approaches and their incorporation into pharmaceutical research has the potential to revolutionize drug delivery, providing more efficient and secure treatment choices for a wide range of health-related diseases.

Protein-based microneedles for biomedical applications: A systematic review

Microneedles are minimally-invasive devices with the unique capability of bypassing physiological barriers. Hence, they are widely used for different applications from drug/vaccine delivery to diagnosis and cosmetic fields. Recently, natural biopolymers (particularly carbohydrates and proteins) have garnered attention as safe and biocompatible materials with tailorable features for microneedle construction. Several review articles have dealt with carbohydrate-based microneedles. This review aims to highlight the less-noticed role of proteins through a systematic search strategy based on the PRISMA guideline from international databases of PubMed, Science Direct, Scopus, and Google Scholar. Original English articles with the keyword "microneedle(s)" in their titles along with at least one of the keywords "biopolymers, silk, gelatin, collagen, zein, keratin, fish-scale, mussel, and suckerin" were collected and those in which the proteins undertook a structural role were screened. Then, we focused on the structures and applications of protein-based microneedles. Also, the unique features of some protein biopolymers that make them ideal for microneedle construction (e.g., excellent mechanical strength, self-adhesion, and self-assembly), as well as the challenges associated with them were reviewed. Altogether, the proteins identified so far seem not only promising for the fabrication of "better" microneedles in the future but also inspiring for designing biomimetic structural biopolymers with ideal characteristics.

The Necessity to Investigate In Vivo Fate of Nanoparticle-Loaded Dissolving Microneedles

Transdermal drug delivery systems are rapidly gaining prominence and have found widespread application in the treatment of numerous diseases. However, they encounter the challenge of a low transdermal absorption rate. Microneedles can overcome the stratum corneum barrier to enhance the transdermal absorption rate. Among various types of microneedles, nanoparticle-loaded dissolving microneedles (DMNs) present a unique combination of advantages, leveraging the strengths of DMNs (high payload, good mechanical properties, and easy fabrication) and nanocarriers (satisfactory solubilization capacity and a controlled release profile). Consequently, they hold considerable clinical application potential in the precision medicine era. Despite this promise, no nanoparticle-loaded DMN products have been approved thus far. The lack of understanding regarding their in vivo fate represents a critical bottleneck impeding the clinical translation of relevant products. This review aims to elucidate the current research status of the in vivo fate of nanoparticle-loaded DMNs and elaborate the necessity to investigate the in vivo fate of nanoparticle-loaded DMNs from diverse aspects. Furthermore, it offers insights into potential entry points for research into the in vivo fate of nanoparticle-loaded DMNs, aiming to foster further advancements in this field.

Is roller milling - the low energy wet bead media milling - a reproducible and robust milling method for formulation investigation of aqueous suspensions?

Long-acting injectables have shown to offer a prolonged release of a drug compound up to several months, providing the opportunity to increase patient compliance for treatment of long-term and chronic conditions. Different formulation technologies have already been utilized for long-acting injectables, and especially aqueous suspensions with crystalline drug particles in the sub-micron range have sparked an interest for future development of long-acting injectables. Wet bead milling is a common top-down process used to prepare nano- and microsuspensions of crystalline drug particles with the addition of surfactants in the dispersion medium, which are working as stabilizers to prevent agglomeration or crystal growth that ultimately may influence the physical stability of nano- and microsuspensions. To examine the reproducibility of the suspensions manufactured and the behavior of their physical stability, i.e., changes in particle sizes over time, low-energy roller mill was utilized for the manufacturing of nano- and microsuspensions in the present study. Investigated formulation parameters was stabilizer type and concentration and milling parameters varied in bead size and duration of milling. The obtained results demonstrated that the physical stability of suspensions containing the two model compounds, cinnarizine and indomethacin, was highly affected by the constitution of surfactant and processing. Various size classes were obtained and accompanied by high variations between the individual samples that indicated uneven and unpredictable milling by the low-energy roller mill, limiting the possibility to prepare reproducible and physical stable suspensions. Short-term stability studies revealed clear tendencies towards reversed Ostwald ripening of suspensions stabilized with poloxamer 188 that contained cinnarizine as the drug compound, and to a smaller extent suspensions containing indomethacin. Furthermore, X-ray Powder Diffraction confirmed no alteration of the drug compounds crystal structure after roller milling for multiple days.

Fabrication of controlled-release silver nanoparticle polylactic acid microneedles with long-lasting antibacterial activity using a micro-molding solvent-casting technique

Most topical drug delivery techniques do not provide therapeutic concentrations for treatment of surgical site and other local infections and, therefore, require some kind of enhancement, such as physical methods like microneedles, the subject of the present investigation. Here, controlled-release long-lasting antibacterial polylactic acid (PLA) microneedles containing 1, 3, and 5% silver nanoparticles (AgNP) were prepared using micro-molding solvent-casting technique. Microneedles were characterized using optical microscopy, SEM, FTIR, XRD, and DSC. Also, mechanical strength, barrier disruption ability, insertion depth, in-vitro release kinetics, antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa, and silver permeation through rat skin were studied. Microneedles showed good mechanical strength with no signs of failure at an optimum PLA concentration of 25% (w/v). FTIR revealed no chemical interaction between ingredients, and XRD confirmed presence of AgNP in microneedles. Microneedles penetrated the skin model at depth of up to 1143 μm resulting 5-7 times increase in transepidermal water loss (TEWL). Release studies showed 2.2, 6.8, and 8.1 µg silver release from the whole body (obeying Higuchi's release model) and 0.33, 0.45, and 0.78 µg from the needles alone (obeying Fickian-cylindrical type release) for 1, 3, and 5% AgNP microneedles, respectively. Also, prolonged antibacterial activity (for 34 days) was observed. Skin studies over 72 h indicated that besides needles, silver is also released from the baseplate which had a marginal share in total silver permeation through the skin. In conclusion, a straightforward solvent-casting technique can be used to successfully prepare strong AgNP-containing PLA microneedles capable of long-lasting antibacterial activity.

Polymer Delivery Systems for Long-Acting Antiretroviral Drugs

The success of long-acting (LA) drug delivery systems (DDSs) is linked to their biocompatible polymers. These are used for extended therapeutic release. For treatment or prevention of human immune deficiency virus type one (HIV-1) infection, LA DDSs hold promise for improved regimen adherence and reduced toxicities. Current examples include Cabenuva, Apretude, and Sunlenca. Each is safe and effective. Alternative promising DDSs include implants, prodrugs, vaginal rings, and microarray patches. Each can further meet patients' needs. We posit that the physicochemical properties of the formulation chemical design can optimize drug release profiles. We posit that the strategic design of LA DDS polymers will further improve controlled drug release to simplify dosing schedules and improve regimen adherence.

Microneedles: A Versatile Drug Delivery Carrier for Phytobioactive Compounds as a Therapeutic Modulator for Targeting Mitochondrial Dysfunction in the Management of Neurodegenerative Diseases

Neurodegenerative disease (ND) is the fourth leading cause of death worldwide, with limited symptomatic therapies. Mitochondrial dysfunction is a major risk factor in the progression of ND, and it-increases the generation of reactive oxygen species (ROS). Overexposure to these ROS induces apoptotic changes leading to neuronal cell death. Many studies have shown the prominent effect of phytobioactive compounds in managing mitochondrial dysfunctions associated with ND, mainly due to their antioxidant properties. The drug delivery to the brain is limited due to the presence of the blood-brain barrier (BBB), but effective drug concentration needs to reach the brain for the therapeutic action. Therefore, developing safe and effective strategies to enhance drug entry in the brain is required to establish ND's treatment. The microneedle-based drug delivery system is one of the effective non-invasive techniques for drug delivery through the transdermal route. Microneedles are micronsized drug delivery needles that are self-administrable. It can penetrate through the stratum corneum skin layer without hitting pain receptors, allowing the phytobioactive compounds to be released directly into systemic circulation in a controlled manner. With all of the principles mentioned above, this review discusses microneedles as a versatile drug delivery carrier for the phytoactive compounds as a therapeutic potentiating agent for targeting mitochondrial dysfunction for the management of ND.

Fabrication of dissolving microneedles for transdermal delivery of protein and peptide drugs: polymer materials and solvent casting micromoulding method

Proteins and peptides are rapidly developing pharmaceutical products and are expected to continue growing in the future. However, due to their nature, their delivery is often limited to injection, with drawbacks such as pain and needle waste. To overcome these limitations, microneedles technology is developed to deliver protein and peptide drugs through the skin. One type of microneedles, known as dissolving microneedles, has been extensively studied for delivering various proteins and peptides, including ovalbumin, insulin, bovine serum albumin, polymyxin B, vancomycin, and bevacizumab. This article discusses polymer materials used for fabricating dissolving microneedles, which are poly(vinylpyrrolidone), hyaluronic acid, poly(vinyl alcohol), carboxymethylcellulose, GantrezTM, as well as other biopolymers like pullulan and ulvan. The paper is focused solely on solvent casting micromoulding method for fabricating dissolving microneedles containing proteins and peptides, which will be divided into one-step and two-step casting micromoulding. Additionally, future considerations in the market plan for dissolving microneedles are discussed in this article.

Physiologically Based Pharmacokinetic Modelling of Cabotegravir Microarray Patches in Rats and Humans

Microarray patches (MAPs) are currently under investigation as a self-administered, pain-free alternative used to achieve long-acting (LA) drug delivery. Cabotegravir is a potent antiretroviral that has demonstrated superior results over current pre-exposure prophylaxis (PrEP) regimens. This study aimed to apply physiologically based pharmacokinetic (PBPK) modelling to describe the pharmacokinetics of the dissolving bilayer MAP platform and predict the optimal dosing strategies for a once-weekly cabotegravir MAP. A mathematical description of a MAP was implemented into a PBPK model, and empirical models were utilised for parameter estimation. The intradermal PBPK model was verified against previously published in vivo rat data for intramuscular (IM) and MAP administration, and in vivo human data for the IM administration of LA cabotegravir. The verified model was utilised for the prediction of 300 mg, 150 mg and 75 mg once-weekly MAP administration in humans. Cabotegravir plasma concentrations >4 × protein-adjusted 90% inhibitory concentration (PA-IC90) (0.664 µg/mL) and >8 × PA-IC90 (1.33 µg/mL) were set as targets. The 75 mg, 150 mg and 300 mg once-weekly cabotegravir MAP regimens were predicted to sustain plasma concentrations >4 × PA-IC90, while the 300 mg and 150 mg regimens achieved plasma concentrations >8 × PA-IC90. These data demonstrate the potential for a once-weekly cabotegravir MAP using practical patch sizes for humans and inform the further development of cabotegravir MAPs for HIV PrEP.

Tip loaded cyclodextrin-carvedilol complexes microarray patches

Carvedilol, a β-blocker prescribed for chronic heart failure, suffers from poor bioavailability and rapid first pass metabolism when administered orally. Herein, we present the development of tip microarray patches (MAPs) composed of ternary cyclodextrin (CD) complexes of carvedilol for transdermal delivery. The ternary complex with hydroxypropyl γ-cyclodextrin (HPγCD) and poly(vinyl pyrrolidone) (PVP) reduced the crystallinity of carvedilol, as evidenced by DSC, XRD, NMR, and SEM analysis. MAPs were fabricated using a two-step process with the ternary complex as the needle layer. The resulting MAPs were capable of breaching ex vivo neonatal porcine skin to a depth ≈600 μm with minimal impact to needle height. Upon insertion, the needle dissolved within 2 h, leading to the transdermal delivery of carvedilol. The MAPs displayed minimal toxicity and acceptable biocompatibility in cell assays. In rats, MAPs achieved significantly higher AUC levels of carvedilol than oral administration, with a delayed Tmax and sustained plasma levels over several days. These findings suggest that the carvedilol-loaded dissolving MAPs have the potential to revolutionise the treatment of chronic heart failure.

Wet bead milling by dual centrifugation - An approach to obtain reproducible and differentiable suspensions

Aqueous nano- and microsuspensions containing poorly water-soluble, crystalline drug particles have in the recent years sparked an interest for the preparation of long-acting injectables (LAIs), which increase patient compliance for patients treated for long-term or chronic conditions. Nano- and microsuspensions are often prepared by top-down methods, such as wet bead milling, with the addition of stabilizers in the dispersion media, such as surfactants, which influence the particle sizes and physical stability of the suspension. To improve the efficacy of formulation screening for nano- and microsuspensions, dual centrifugation was utilized in this study whereby 40 samples could be manufactured simultaneously to support the formulation definition. Hence, the type and concentration of stabilizer as well as bead size and milling speed was investigated throughout the presented study, but also the ability of the method to produce consistent data was investigated. The obtained results demonstrated that the particle profile obtained after milling was very consistent from run to run and so was the observed stability data, i.e., running n = 1 experiment per combination could clearly be justified as a predictable approach for the formulation screening. The data also showed that the stabilizer, as well as its concentration highly influenced the physical stability of suspensions containing both the two investigated model compounds, i.e., both cinnarizine and indomethacin, where the biggest increase in particle sizes was observed within the first week. For short-term studies, polysorbate 20 was found to be a suitable stabilizer for suspensions of cinnarizine, whereas sodium dodecyl sulphate was more suitable for indomethacin suspensions immediately after the milling even with 1% (w/v) stabilizer solution, but not sufficient for short-term stability due to an insufficient stabilizer concentration. Smaller particles sizes could be achieved by milling the suspensions with the smallest bead sizes and at the highest speed of 1500 rpm without disrupting the crystal structure of the active pharmaceutical ingredient (API), which was confirmed by X-ray Powder Diffraction.

Applications and recent advances in transdermal drug delivery systems for the treatment of rheumatoid arthritis

Rheumatoid arthritis is a chronic, systemic autoimmune disease predominantly based on joint lesions with an extremely high disability and deformity rate. Several drugs have been used for the treatment of rheumatoid arthritis, but their use is limited by suboptimal bioavailability, serious adverse effects, and nonnegligible first-pass effects. In contrast, transdermal drug delivery systems (TDDSs) can avoid these drawbacks and improve patient compliance, making them a promising option for the treatment of rheumatoid arthritis (RA). Of course, TDDSs also face unique challenges, as the physiological barrier of the skin makes drug delivery somewhat limited. To overcome this barrier and maximize drug delivery efficiency, TDDSs have evolved in terms of the principle of transdermal facilitation and transdermal facilitation technology, and different generations of TDDSs have been derived, which have significantly improved transdermal efficiency and even achieved individualized controlled drug delivery. In this review, we summarize the different generations of transdermal drug delivery systems, the corresponding transdermal strategies, and their applications in the treatment of RA.

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 for advanced ocular drug delivery

In the field of ocular drug delivery, topical delivery remains the most common treatment option for managing anterior segment diseases, whileintraocular injectionsare the current gold standard treatment option for treating posterior segment diseases. Nonetheless, topical eye drops are associated with low bioavailability (<5%), and theintravitreal administration procedure is highly invasive, yielding poor patient acceptability. In both cases, frequent administration is currently required. As a result, there is a clear unmet need for sustained drug delivery to the eye, particularly in a manner that can be localised. Microneedles, which are patches containing an array of micron-scale needles (<1 mm), have the potential to meet this need. These platforms can enable localised drug delivery to the eye while enhancing penetration of drug molecules through key ocular barriers, thereby improving overall therapeutic outcomes. Moreover, the minimally invasive manner in which microneedles are applied could provide significant advantages over traditional intravitreal injections regarding patient acceptability. Considering the benefitsofthis novel ocular delivery system, this review provides an in-depth overviewofthe microneedle systems for ocular drug delivery, including the types of microneedles used and therapeutics delivered. Notably, we outline and discuss the current challenges associated with the clinical translation of these platforms and offer opinions on factors which should be considered to improve such transition from lab to clinic.

Microneedle array patches for sustained delivery of fluphenazine: A micron scale approach for the management of schizophrenia

Schizophrenia is a severe chronic mental illness characterised by impaired emotional and cognitive functioning. To treat this condition, antipsychotics are available in limited dosage forms, mainly oral and injectable formulations. Although injectable antipsychotics were designed to enhance adherence, they are invasive, painful and require a healthcare professional to be administered. To overcome such administration issues, extensive research has been focused on developing transdermal antipsychotic formulations. In this work, three microneedle (MN) systems were developed to deliver fluphenazine (FLU) systemically. A decanoic prodrug of FLU called fluphenazine decanoate (FLUD) was used in two of the MN formulations due to its high lipophilicity. FLU-D was loaded into dissolving MNs and nanoemulsion (NE)-loaded MNs. The parent drug FLU was loaded into poly(lactic-co-glycolic acid) (PLGA)-tipped MNs. All MN systems were characterised and evaluated in vitro and in vivo. The in vivo evaluation of the three developed MN systems showed their ability to deliver FLU into the systemic circulation, as the Cmax of FLU-D dissolving MNs was 36.11 ± 12.37 ng/ml. However, the Cmax of FLU-D NE loaded dissolving MNs was 12.92 ± 6.3 ng/ml and for FLU-PLGA tipped MNs was 21.57 ± 2.45 ng/ml. Compared to an intramuscular (IM) injection of FLU-D in sesame oil, the relative bioavailabilities were 26.96 %, 21.73 % and 42.45 % for FLU-D dissolving MNs, FLU-D NE dissolving MNs and FLU-PLGA tipped MNs, respectively. FLU plasma levels were maintained above the minimum human therapeutic limits for a week. Consequently, these various MN formulations are considered to be a viable options for the transdermal delivery of fluphenazine and its prodrug. The three MN systems developed offer patients a user-friendly, painless, and convenient long-acting delivery method for FLU. Reducing dosing frequency and using less invasive drug administration methods can enhance adherence and foster positive therapeutic outcomes. This study demonstrates the capability and adaptability of MNs technology to transport hydrophobic molecules from the skin to the systemic circulation.

Applications of Degradable Hydrogels in Novel Approaches to Disease Treatment and New Modes of Drug Delivery

Hydrogels are particularly suitable materials for loading drug delivery agents; their high water content provides a biocompatible environment for most biomolecules, and their cross-linked nature protects the loaded agents from damage. During delivery, the delivered substance usually needs to be released gradually over time, which can be achieved by degradable cross-linked chains. In recent years, biodegradable hydrogels have become a promising technology in new methods of disease treatment and drug delivery methods due to their many advantageous properties. This review briefly discusses the degradation mechanisms of different types of biodegradable hydrogel systems and introduces the specific applications of degradable hydrogels in several new methods of disease treatment and drug delivery methods.

Drug Delivery and Therapy Strategies for Osteoporosis Intervention

With the advent of the aging society, osteoporosis (OP) risk increases yearly. Currently, the clinical usage of anti-OP drugs is challenged by recurrent side effects and poor patient compliance, regardless of oral, intravenous, or subcutaneous administration. Properly using a drug delivery system or formulation strategy can achieve targeted drug delivery to the bone, diminish side effects, improve bioavailability, and prolong the in vivo residence time, thus effectively curing osteoporosis. This review expounds on the pathogenesis of OP and the clinical medicaments used for OP intervention, proposes the design approach for anti-OP drug delivery, emphatically discusses emerging novel anti-OP drug delivery systems, and enumerates anti-OP preparations under clinical investigation. Our findings may contribute to engineering anti-OP drug delivery and OP-targeting therapy.

Microneedle-Mediated Transcutaneous Immunization: Potential in Nucleic Acid Vaccination

Efforts aimed at exploring economical and efficient vaccination have taken center stage to combat frequent epidemics worldwide. Various vaccines have been developed for infectious diseases, among which nucleic acid vaccines have attracted much attention from researchers due to their design flexibility and wide application. However, the lack of an efficient delivery system considerably limits the clinical translation of nucleic acid vaccines. As mass vaccinations via syringes are limited by low patient compliance and high costs, microneedles (MNs), which can achieve painless, cost-effective, and efficient drug delivery, can provide an ideal vaccination strategy. The MNs can break through the stratum corneum barrier in the skin and deliver vaccines to the immune cell-rich epidermis and dermis. In addition, the feasibility of MN-mediated vaccination is demonstrated in both preclinical and clinical studies and has tremendous potential for the delivery of nucleic acid vaccines. In this work, the current status of research on MN vaccines is reviewed. Moreover, the improvements of MN-mediated nucleic acid vaccination are summarized and the challenges of its clinical translation in the future are discussed.

Polymeric in situ forming depots for long-acting drug delivery systems

Polymeric in situ forming depots have emerged as highly promising drug delivery systems for long-acting applications. Their effectiveness is attributed to essential characteristics such as biocompatibility, biodegradability, and the ability to form a stable gel or solid upon injection. Moreover, they provide added versatility by complementing existing polymeric drug delivery systems like micro- and nanoparticles. The formulation's low viscosity facilitates manufacturing unit operations and enhances delivery efficiency, as it can be easily administered via hypodermic needles. The release mechanism of drugs from these systems can be predetermined using various functional polymers. To enable unique depot design, numerous strategies involving physiological and chemical stimuli have been explored. Important assessment criteria for in situ forming depots include biocompatibility, gel strength and syringeability, texture, biodegradation, release profile, and sterility. This review focuses on the fabrication approaches, key evaluation parameters, and pharmaceutical applications of in situ forming depots, considering perspectives from academia and industry. Additionally, insights about the future prospects of this technology are discussed.