Directly Compressed Tablets: A Novel Drug-Containing Reservoir Combined with Hydrogel-Forming Microneedle Arrays for Transdermal Drug Delivery

Breaking boundaries: the advancements in transdermal delivery of antibiotics

Transdermal drug delivery systems (TDDS) for antibiotics have seen significant advances in recent years that aimed to improve the efficacy and safety of these drugs. TDDS offer many advantages over other conventional delivery systems such as non-invasiveness, controlled-release pattern, avoidance of first-pass metabolism. The objective of this review is to provide an overview on the recent advances in the TDDS of different groups of antibiotics including β-lactams, tetracyclines, macrolides, and lincosamides, utilized for their effective delivery through the skin and to explore the challenges associated with this field. The majority of antibiotics do not have favorable properties for passive transdermal delivery. Thus, novel strategies have been employed to improve the delivery of antibiotics through the skin, such as the use of nanotechnology (nanoparticles, solid-lipid nanoparticles, nanoemulsions, vesicular carriers, and liposomes) or the physical enhancement techniques like microneedles and ultrasound. In conclusion, the transdermal delivery systems could be a promising method for delivering antibiotics that have the potential to improve patient outcomes and enhance the efficacy of drugs. Further research and development are still needed to explore the potential of delivering more antibiotic drugs by using various transdermal drug delivery approaches.

Direct 3D printing of triple-responsive nanocomposite hydrogel microneedles for controllable drug delivery

Hydrogel microneedle patches have emerged as promising platforms for painless, minimally invasive, safe, and portable transdermal drug administration. However, the conventional mold-based fabrication processes and inherent single-functionality of such microneedles present significant hurdles to broader implementation. Herein, we have developed a novel approach utilizing a precursor solution of robust nanocomposite hydrogels to formulate photo-printable inks suitable for the direct 3D printing of high-precision, triple-responsive hydrogel microneedle patches through digital light processing (DLP) technology. The ink formulation comprises four functionally diverse monomers including 2-(dimethylamino)ethyl methacrylate, N-isopropylacrylamide, acrylic acid, and acrylamide, which were crosslinked by aluminum hydroxide nanoparticles (AH NPs) acting as both reinforcing agents and crosslinking centers. This results in the formation of a nanocomposite hydrogel characterized by exceptional mechanical strength, an essential attribute for the 3D printing of hydrogel microneeedle patches. Furthermore, this innovative 3D printing strategy facilitates facile customization of microneedle geometry and patch dimensions. As a proof-of-concept, we employed the fabricated hydrogel microneedles for transdermal delivery of bovine serum albumin (BSA). Importantly, these hydrogel microneedles displayed no cytotoxic effects and exhibited triple sensitivity to pH, temperature and glucose levels, thereby enabling more precise on-demand drug delivery. This study provides a universal method for the rapid fabrication of hydrogel microneedles with smart responsiveness for transdermal drug delivery applications.

The Synergistic Potential of Hydrogel Microneedles and Nanomaterials: Breaking Barriers in Transdermal Therapy

The stratum corneum, which acts as a strong barrier against external agents, presents a significant challenge to transdermal drug delivery. In this regard, microneedle (MN) patches, designed as modern systems for drug delivery via permeation through the skin with the ability to pass through the stratum corneum, are known to be convenient, painless, and effective. In fact, MN have shown significant breakthroughs in transdermal drug delivery, and among the various types, hydrogel MN (HMNs) have demonstrated desirable inherent properties. Despite advancements, issues such as limited loading capacity, uncontrolled drug release rates, and non-uniform therapeutic approaches persist. Conversely, nanomaterials (NMs) have shown significant promise in medical applications, however, their efficacy and applicability are constrained by challenges including poor stability, low bioavailability, limited payload capacity, and rapid clearance by the immune system. Incorporation of NMs within HMNs offers new prospects to address the challenges associated with HMNs and NMs. This combination can provide a promising field of research for improved and effective delivery of therapeutic agents and mitigate certain adverse effects, addressing current clinical concerns. The current review highlights the use of NMs in HMNs for various therapeutic and diagnostic applications.

Research Progress of Hydrogel Microneedles in Wound Management

Microneedles are a novel drug delivery system that offers advantages such as safety, painlessness, minimally invasive administration, simplicity of use, and controllable drug delivery. As a type of polymer microneedle with a three-dimensional network structure, hydrogel microneedles (HMNs) possess excellent biocompatibility and biodegradability and encapsulate various therapeutic drugs while maintaining drug activity, thus attracting significant attention. Recently, they have been widely employed to promote wound healing and have demonstrated favorable therapeutic effects. Although there are reviews about HMNs, few of them focus on wound management. Herein, we present a comprehensive overview of the design and preparation methods of HMNs, with a particular emphasis on their application status in wound healing, including acute wound healing, infected wound healing, diabetic wound healing, and scarless wound healing. Finally, we examine the advantages and limitations of HMNs in wound management and provide suggestions for future research directions.

Swellable Microneedles in Drug Delivery and Diagnostics

This manuscript explores the transformative potential of swellable microneedles (MNs) in drug delivery and diagnostics, addressing critical needs in medical treatment and monitoring. Innovations in hydrogel-integrated MN arrays facilitate controlled drug release, thereby expanding treatment options for chronic diseases and conditions that require precise dosage control. The review covers challenges, such as scalability, patient compliance, and manufacturing processes, as well as achievements in advanced manufacturing, biocompatibility, and versatile applications. Nonetheless, limitations in physiological responsiveness and long-term stability remain, necessitating further research in material innovation and integration with digital technologies. Future directions focus on expanding biomedical applications, material advancements, and regulatory considerations for widespread clinical adoption.

Ecofriendly Controlled-Release Insecticide Carrier: pH-/Temperature-Responsive Rosin-Derived Hydrogels for Avermectin Delivery against Mythimna separata (Walker)

The exploration of environmentally friendly, less toxic, sustained-release insecticide is increasing with the growing demand for food to meet the requirements of the expanding population. As a sustained-release carrier, the unique, environmentally friendly intelligent responsive hydrogel system is an important factor in improving the efficiency of insecticide utilization and accurate release. In this study, we developed a facile approach for incorporating the natural compound rosin (dehydroabietic acid, DA) and zinc ions (Zn2+) into a poly(N-isopropylacrylamide) (PNIPAM) hydrogel network to construct a controlled-release hydrogel carrier (DA-PNIPAM-Zn2+). Then, the model insecticide avermectin (AVM) was encapsulated in the carrier at a drug loading rate of 36.32% to form AVM@DA-PNIPAM-Zn2+. Surprisingly, the smart controlled carrier exhibited environmental responsiveness, strongly enhanced mechanical properties, self-healing ability, hydrophobicity, and photostability to ensure a balance between environmental friendliness and the precision of the drug release. The release experiments showed that the carboxyl and amide groups in the polymer chains alter the intermolecular forces within the hydrogel meshes and ingredient diffusion by changing temperatures (25 and 40 °C) and pH values (5.8, 7.4, and 8.5), leading to different release behaviors. The insecticidal activity of the AVM@DA-PNIPAM-Zn2+ against oriental armyworms was good, with an effective minimum toxicity toward aquatic animals. Therefore, AVM@DA-PNIPAM-Zn2+ is an effective drug delivery system against oriental armyworms. We anticipate that this ecofriendly, sustainable, smart-response carrier may broaden the utilization rosin and its possible applications in the agricultural sector.

Poly(acrylic acid)/Poly(vinyl alcohol) Microarray Patches for Continuous Transdermal Delivery of Levodopa and Carbidopa: In Vitro and In Vivo Studies

Levodopa (LD) has been the most efficacious medication and the gold standard therapy for Parkinson's disease (PD) for decades. However, its long-term administration is usually associated with motor complications, which are believed to be the result of the fluctuating pharmacokinetics of LD following oral administration. Duodopa® is the current option to offer a continuous delivery of LD and its decarboxylase inhibitor carbidopa (CD); however, its administration involves invasive surgical procedures, which could potentially lead to lifelong complications, such as infection. Recently, dissolving microarray patches (MAPs) have come to the fore as an alternative that can bypass the oral administration route in a minimally invasive way. This work explored the potential of using dissolving MAPs to deliver LD and CD across the skin. An acidic polymer poly(acrylic acid) (PAA) was used in the MAP fabrication to prevent the potential oxidation of LD at neutral pH. The drug contents of LD and CD in the formulated dissolving MAPs were 1.82 ± 0.24 and 0.47 ± 0.04 mg/patch, respectively. The in vivo pharmacokinetic study using female Sprague-Dawley® rats (Envigo RMS Holding Corp, Bicester, UK) demonstrated a simultaneous delivery of LD and CD and comparable AUC values between the dissolving MAPs and the oral LD/CD suspension. The relative bioavailability for the dissolving MAPs was calculated to be approximately 37.22%. Accordingly, this work highlights the use of dissolving MAPs as a minimally invasive approach which could potentially bypass the gastrointestinal pathway and deliver both drugs continuously without surgery.

Transdermal Delivery of Pramipexole Using Microneedle Technology for the Potential Treatment of Parkinson's Disease

Parkinson's disease (PD) is a debilitating neurodegenerative disease primarily impacting neurons responsible for dopamine production within the brain. Pramipexole (PRA) is a dopamine agonist that is currently available in tablet form. However, individuals with PD commonly encounter difficulties with swallowing and gastrointestinal motility, making oral formulations less preferable. Microneedle (MN) patches represent innovative transdermal drug delivery devices capable of enhancing skin permeability through the creation of microconduits on the surface of the skin. MNs effectively reduce the barrier function of skin and facilitate the permeation of drugs. The work described here focuses on the development of polymeric MN systems designed to enhance the transdermal delivery of PRA. PRA was formulated into both dissolving MNs (DMNs) and directly compressed tablets (DCTs) to be used in conjunction with hydrogel-forming MNs (HFMNs). In vivo investigations using a Sprague-Dawley rat model examined, for the first time, if it was beneficial to prolong the application of DMNs and HFMNs beyond 24 h. Half of the patches in the MN cohorts were left in place for 24 h, whereas the other half remained in place for 5 days. Throughout the entire 5 day study, PRA plasma levels were monitored for all cohorts. This study confirmed the successful delivery of PRA from DMNs (Cmax = 511.00 ± 277.24 ng/mL, Tmax = 4 h) and HFMNs (Cmax = 328.30 ± 98.04 ng/mL, Tmax = 24 h). Notably, both types of MNs achieved sustained PRA plasma levels over a 5 day period. In contrast, following oral administration, PRA remained detectable in plasma for only 48 h, achieving a Cmax of 159.32 ± 113.43 ng/mL at 2 h. The HFMN that remained in place for 5 days demonstrated the most promising performance among all investigated formulations. Although in the early stages of development, the findings reported here offer a hopeful alternative to orally administered PRA. The sustained plasma profile observed here has the potential to reduce the frequency of PRA administration, potentially enhancing patient compliance and ultimately improving their quality of life. This work provides substantial evidence advocating the development of polymeric MN-mediated drug delivery systems to include sustained plasma levels of hydrophilic pharmaceuticals.

Application of Biomaterials in the Development of Hydrogel-Forming Microneedles Integrated with a Cyclodextrin Drug Reservoir for Improved Pharmacokinetic Profiles of Telmisartan

Telmisartan (TEL) is a promising antihypertensive agent among other angiotensin receptor blockers. However, its oral application is limited by its poor water solubility. This study presents the successful utilization of biomaterial-based hydrogel-forming microneedles integrated with a direct compressed tablet reservoir (HFMN-DCT) for the transdermal delivery of telmisartan in the treatment of hypertension. The combination of PVP, PVA, and tartaric acid was used in the HFMN formulation. A range of cross-linking temperatures and times were employed to optimize the characteristics of the HFMN. The HFMN exhibited excellent swelling capacity, mechanical strength, and insertion properties. Additionally, the poorly soluble characteristic of TEL was improved by the inclusion complex formulation with β-cyclodextrin (βCD). Phase solubility analysis showed an Ap-type diagram, indicating a higher-order complex between TEL and βCD, with respect to βCD. A ratio of TEL:βCD of 1:4 mM demonstrates the highest solubility enhancement of TEL. The inclusion complex formation was confirmed by FTIR, XRD, DSC, and molecular docking studies. A significantly higher release of TEL (up to 20-fold) from the inclusion complex was observed in the in vitro release study. Subsequently, a DCT reservoir was developed using various concentrations of sodium starch glycolate. Essentially, both the HFMN and DCT reservoir exhibit hemocompatibility and did not induce any skin irritation. The optimized combination of the HFMN-DCT reservoir showed an ex vivo permeation profile of 83.275 ± 2.405%. Notably, the proposed system showed superior pharmacokinetic profiles in the in vivo investigation using male Wistar rats. Overall, this study highlights the potential of HFMN-DCT reservoir systems as a versatile platform for transdermal drug delivery applications.

Transdermal drug delivery using a porous microneedle device driven by a hydrogel electroosmotic pump

Integrating a hydrogel electroosmotic pump with a parylene C-coated porous microneedle (PMN) is developed for transdermal drug delivery applications. The hydrogel pump is fabricated by combining an anionic and a cationic hydrogel to generate enhanced electroosmosis flow (EOF) to drive the transportation of molecules via PMN.

Advances in biomedical systems based on microneedles: design, fabrication, and application

Wearable devices have become prevalent in biomedical studies due to their convenient portability and potential utility in biomarker monitoring for healthcare. Accessing interstitial fluid (ISF) across the skin barrier, microneedle (MN) is a promising minimally invasive wearable technology for transdermal sensing and drug delivery. MN has the potential to overcome the limitations of conventional transdermal drug administration, making it another prospective mode of drug delivery after oral and injectable. Subsequently, combining MN with multiple sensing approaches has led to its extensive application to detect biomarkers in ISF. In this context, employing MN platforms and control schemes to merge diagnostic and therapeutic capabilities into theranostic systems will facilitate on-demand therapy and point-of-care diagnostics, paving the way for future MN technologies. A comprehensive analysis of the growing advances of microneedles in biomedical systems is presented in this review to summarize the latest studies for academics in the field and to offer for reference the issues that need to be addressed in MN application for healthcare. Covering an array of novel studies, we discuss the following main topics: classification of microneedles in the biomedical field, considerations of MN design, current applications of microneedles in diagnosis and therapy, and the regulatory landscape and prospects of microneedles for biomedical applications. This review sheds light on the significance of microneedle-based innovations, presenting an analysis of their potential implications and contributions to the community of wearable healthcare technologies. The review provides a comprehensive understanding of the field's current state and potential, making it a valuable resource for academics and clinicians seeking to harness the full potential of MN applications.

Hydrogel-Based Microneedle as a Drug Delivery System

The skin is considered the largest and most accessible organ in the human body, and allows the use of noninvasive and efficient strategies for drug administration, such as the transdermal drug delivery system (TDDS). TDDSs are systems or patches, with the ability and purpose to deliver effective and therapeutic doses of drugs through the skin. Regarding the specific interaction between hydrogels (HG) and microneedles (MNs), we seek to find out how this combination would be applied in the context of drug delivery, and we detail some possible advantages of the methods used. Depending on the components belonging to the HG matrix, we can obtain some essential characteristics that make the combination of hydrogels-microneedles (HG-MNs) very advantageous, such as the response to external stimuli, among others. Based on multiple characteristics provided by HGMNs that are depicted in this work, it is possible to obtain unique properties that include controlled, sustained, and localized drug release, as well as the possibility of a synergistic association between the components of the formulation and the combination of more than one bioactive component. In conclusion, a system based on HG-MNs can offer many advantages in the biomedical field, bringing to light a new technological and safe system for improving the pharmacokinetics and pharmacodynamics of drugs and new treatment perspectives.

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.

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.

Advances and Prospects for Hydrogel-Forming Microneedles in Transdermal Drug Delivery

Transdermal drug delivery (TDD) is one of the key approaches for treating diseases, avoiding first-pass effects, reducing systemic adverse drug reactions and improving patient compliance. Microneedling, iontophoresis, electroporation, laser ablation and ultrasound facilitation are often used to improve the efficiency of TDD. Among them, microneedling is a relatively simple and efficient means of drug delivery. Microneedles usually consist of micron-sized needles (50-900 μm in length) in arrays that can successfully penetrate the stratum corneum and deliver drugs in a minimally invasive manner below the stratum corneum without touching the blood vessels and nerves in the dermis, improving patient compliance. Hydrogel-forming microneedles (HFMs) are safe and non-toxic, with no residual matrix material, high drug loading capacity, and controlled drug release, and they are suitable for long-term, multiple drug delivery. This work reviewed the characteristics of the skin structure and TDD, introduced TDD strategies based on HFMs, and summarized the characteristics of HFM TDD systems and the evaluation methods of HFMs as well as the application of HFM drug delivery systems in disease treatment. The HFM drug delivery system has a wide scope for development, but the translation to clinical application still has more challenges.

Rectal Bioavailability of Amoxicillin from Hollow-Type Suppositories: Effect of Chemical Form of Amoxicillin

Rectal drug administration could offer advantages in the delivery of medicines for children by avoiding swallowability issues, improving stability and enabling administration by caregivers. This study aimed to evaluate the rectal bioavailability of hollow-type suppositories (HTS) and understand the effect of two chemical forms of amoxicillin: amoxicillin sodium (AS) or amoxicillin trihydrate (AMT). HTS were prepared by incorporating a lipophilic core containing the antibiotic with a polyethylene glycol (PEG) shell. Formulations were characterised in vitro, and the absolute bioavailability was determined in a rabbit model, while drug-base interactions were evaluated using X-ray diffraction crystallography (XRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy. The in vitro amoxicillin release from AMT HTS was delayed, taking 27.3 ± 4.9 h to release 50% drug compared with 1.7 h for the AS HTS, likely due to solubility differences between AMT and AS. The presence of orthorhombic AMT and anhydrous AS crystals in respective HTS was confirmed via XRD and DSC. PEG shells were able to protect the drug chemical stability when stored at 25 °C/60% RH. Despite the difference in their in vitro release rates, a similar rectal bioavailability was found in both forms of amoxicillin (absolute bioavailability 68.2 ± 6.6% vs. 72.8 ± 32.2% for AMT HTS and AS HTS, respectively; p = 0.9682). Both HTS formulations showed little or no irritation to the rectal mucosa following a single dose.

A five-day treatment course of zanamivir for the flu with a single, self-administered, painless microneedle array patch: Revolutionizing delivery of poorly membrane-permeable therapeutics

Seasonal influenza virus infections cause a substantial number of deaths each year. While zanamivir (ZAN) is efficacious against oseltamivir-resistant influenza strains, the efficacy of the drug is limited by its route of administration, oral inhalation. Herein, we present the development of a hydrogel-forming microneedle array (MA) in combination with ZAN reservoirs for treating seasonal influenza. The MA was fabricated from Gantrez® S-97 crosslinked with PEG 10,000. Various reservoir formulations included ZAN hydrate, ZAN hydrochloric acid (HCl), CarraDres™, gelatin, trehalose, and/or alginate. In vitro permeation studies with a lyophilized reservoir consisting of ZAN HCl, gelatin, and trehalose resulted in rapid and high delivery of up to 33 mg of ZAN across the skin with delivery efficiency of up to ≈75% by 24 h. Pharmacokinetics studies in rats and pigs demonstrated that a single administration of a MA in combination with a CarraDres™ ZAN HCl reservoir offered a simple and minimally invasive delivery of ZAN into the systemic circulation. In pigs, efficacious plasma and lung steady-state levels of ∼120 ng/mL were reached within 2 h and sustained between 50 and 250 ng/mL over 5 days. MA-enabled delivery of ZAN could enable a larger number of patients to be reached during an influenza outbreak.

Hydrogel-forming microarray patches with solid dispersion reservoirs for transdermal long-acting microdepot delivery of a hydrophobic drug

Hydrogel-forming microarray patches (HF-MAPs) are used to circumvent the skin barrier and facilitate the noninvasive transdermal delivery of many hydrophilic substances. However, their use in the delivery of hydrophobic agents is a challenging task. This work demonstrates, for the first time, the successful transdermal long-acting delivery of the hydrophobic atorvastatin (ATR) via HF-MAPs using poly(ethylene)glycol (PEG)-based solid dispersion (SD) reservoirs. PEG-based SDs of ATR were able to completely dissolve within 90 s in vitro. Ex vivo results showed that 2.05 ± 0.23 mg of ATR/0.5 cm² patch was delivered to the receiver compartment of Franz cells after 24 h. The in vivo study, conducted using Sprague Dawley rats, proved the versatility of HF-MAPs in delivering and maintaining therapeutically-relevant concentrations (> 20 ng·mL^-1) of ATR over 14 days, following a single HF-MAP application for 24 h. The long-acting delivery of ATR suggests the successful formation of hydrophobic microdepots within the skin, allowing for the subsequent sustained delivery as they gradually dissolve over time, as shown in this work. When compared to the oral group, the use of the HF-MAP formulation improved the overall pharmacokinetics profile of ATR in plasma, where significantly higher AUC values resulting in ∼10-fold higher systemic exposure levels were obtained. This novel system offers a promising, minimally-invasive, long-acting alternative delivery system for ATR that is capable of enhancing patient compliance and therapeutic outcomes. It also proposes a unique promising platform for the long-acting transdermal delivery of other hydrophobic agents.

Hydrogel-forming microarray patch mediated transdermal delivery of tetracycline hydrochloride

Antibiotic resistance is one of the most serious health problems today and is expected to worsen in the coming decades. It has been suggested that antibiotic administration routes that bypass the human gut could potentially tackle this problem. In this work, an antibiotic hydrogel-forming microarray patch (HF-MAP) system, which can be used as an alternative antibiotic delivery technology, has been fabricated. Specifically, poly(vinyl alcohol)/poly(vinylpyrrolidone) (PVA/PVP) microarray showed excellent swelling properties with >600% swelling in PBS over 24 h. The tips on the HF-MAP were proven to be able to penetrate a skin model which is thicker than stratum corneum. The antibiotic (tetracycline hydrochloride) drug reservoir was mechanically robust and dissolved completely in an aqueous medium within a few minutes. In vivo animal studies using a Sprague Dawley rat model showed antibiotic administration using HF-MAP achieved a sustained release profile, in comparison with animals receiving oral gavage and intravenous (IV) injection, with a transdermal bioavailability of 19.1% and an oral bioavailability of 33.5%. The maximum drug plasma concentration for HF-MAP group reached 7.40 ± 4.74 μg/mL at 24 h, whereas the drug plasma concentration for both oral (5.86 ± 1.48 μg/mL) and IV (8.86 ± 4.19 μg/mL) groups peaked soon after drug administration and had decreased to below the limit of detection at 24 h. The results demonstrated that antibiotics can be delivered by HF-MAP in a sustained manner.

Polymer Gels: Classification and Recent Developments in Biomedical Applications

Polymer gels are a valuable class of polymeric materials that have recently attracted significant interest due to the exceptional properties such as versatility, soft-structure, flexibility and stimuli-responsive, biodegradability, and biocompatibility. Based on their properties, polymer gels can be used in a wide range of applications: food industry, agriculture, biomedical, and biosensors. The utilization of polymer gels in different medical and industrial applications requires a better understanding of the formation process, the factors which affect the gel's stability, and the structure-rheological properties relationship. The present review aims to give an overview of the polymer gels, the classification of polymer gels' materials to highlight their important features, and the recent development in biomedical applications. Several perspectives on future advancement of polymer hydrogel are offered.

Transdermal delivery of inflammatory factors regulated drugs for rheumatoid arthritis

Rheumatoid arthritis is a chronic autoimmune disease, with the features of recurrent chronic inflammation of synovial tissue, destruction of cartilage, and bone erosion, which further affects joints tissue, organs, and systems, and eventually leads to irreversible joint deformities and body dysfunction. Therapeutic drugs for rheumatoid arthritis mainly reduce inflammation through regulating inflammatory factors. Transdermal administration is gradually being applied to the treatment of rheumatoid arthritis, which can allow the drug to overcome the skin stratum corneum barrier, reduce gastrointestinal side effects, and avoid the first-pass effect, thus improving bioavailability and relieving inflammation. This paper reviewed the latest research progress of transdermal drug delivery in the treatment of rheumatoid arthritis, and discussed in detail the dosage forms such as gel (microemulsion gel, nanoemulsion gel, nanomicelle gel, sanaplastic nano-vesiclegel, ethosomal gel, transfersomal gel, nanoparticles gel), patch, drug microneedles, nanostructured lipid carrier, transfersomes, lyotropic liquid crystal, and drug loaded electrospinning nanofibers, which provide inspiration for the rich dosage forms of transdermal drug delivery systems for rheumatoid arthritis.

Amphotericin B- and Levofloxacin-Loaded Chitosan Films for Potential Use in Antimicrobial Wound Dressings: Analytical Method Development and Its Application

Levofloxacin (LVX) and amphotericin B (AMB) have been widely used to treat bacterial and fungal infections in the clinic. Herein, we report, for the first time, chitosan films loaded with AMB and LVX as wound dressings to combat antimicrobial infections. Additionally, we developed and validated a high-performance liquid chromatography (HPLC) method coupled with a UV detector to simultaneously quantify both AMB and LVX. The method is easy, precise, accurate and linear for both drugs at a concentration range of 0.7-5 µg/mL. The validated method was used to analyse the drug release, ex vivo deposition and permeation from the chitosan films. LVX was released completely from the chitosan film after a week, while approximately 60% of the AMB was released. Ex vivo deposition study revealed that, after 24-hour application, 20.96 ± 13.54 µg of LVX and approximately 0.35 ± 0.04 µg of AMB was deposited in porcine skin. Approximately 0.58 ± 0.16 µg of LVX permeated through the skin. AMB was undetectable in the receptor compartment due to its poor solubility and permeability. Furthermore, chitosan films loaded with AMB and LVX were found to be able to inhibit the growth of both Candida albicans and Staphylococcus aureus, indicating their potential for antimicrobial applications.

Metronidazole nanosuspension loaded dissolving microarray patches: An engineered composite pharmaceutical system for the treatment of skin and soft tissue infection

Bacteroides fragilis is one of the most common causative group of microorganisms that is associated with skin and soft tissue infections (SSTI). Metronidazole (MTZ) is the drug of choice used in the treatment of SSTI caused by the bacterium. However, owing to its physiochemical properties, MTZ have limited skin permeation, which render the drug unsuitable for the treatment of deep-rooted SSTIs. One strategy to overcome this limitation is to reformulate MTZ into nanosuspension which will then be loaded into dissolving microarray patches (MAPs) for the treatment of SSTIs caused by B. fragilis. Herein, we report for the first time on the preparation and optimisation of MAP loaded with MTZ nanosuspension (MTZ-NS). After screening a range of polymeric surfactants, we identified that Soluplus® resulted in the formation of MTZ-NS with the smallest particle size (115 nm) and a narrow PDI of 0.27. Next, the MTZ-NS was further optimised using a design of experiments (DoE) approach. The optimised MTZ-NS was then loaded into dissolving MAPs with varying MTZ-NS content. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cell proliferation assays along with LIVE/DEAD™ staining on the 3T3L1 cell line showed that the MTZ-NS loaded dissolving MAPs displayed minimal toxicity and acceptable biocompatibility. In vitro dermatokinetic studies showed that the MTZ-NS loaded MAPs were able to deliver the nitroimidazole antibiotic across all strata of the skin resulting in a delivery efficiency of 95 % after a 24-hour permeation study. Lastly, agar plating assay using bacterial cultures of B. fragilis demonstrated that MTZ-NS loaded MAP resulted in complete bacterial inhibition in the entire plate relative to the control group. Should this formulation be translated into clinical practice, this pharmaceutical approach may provide a minimally invasive strategy to treat SSTIs caused by B. fragilis.

Investigation and Optimization of Hydrogel Microneedles for Transdermal Delivery of Caffeine

Caffeine is therapeutically effective for treating apnea, cellulite formation, and pain management. It also exhibits neuroprotective and antioxidant activities in different models of Parkinson's disease and Alzheimer's disease. However, caffeine administration in a minimally invasive and sustainable manner through the transdermal route is challenging owing to its hydrophilic nature. Therefore, this study demonstrated a transdermal delivery approach for caffeine by utilizing hydrogel microneedle (MN) as a permeation enhancer. The influence of formulation parameters such as molecular weight (MW) of PMVE/MA (polymethyl vinyl ether/maleic anhydride) copolymer and sodium bicarbonate (NaHCO₃) concentration on the swelling kinetics and mechanical integrity of the hydrogel MNs was investigated. In addition, the effect of different MN application methods and needle densities of hydrogel MN on the skin insertion efficiency and penetration depth was also evaluated. The swelling degree at equilibrium percentage (% S_eq) recorded for hydrogels fabricated with Gantrez S-97 (MW = 1,500,000 Da) was significantly higher than formulation with Gantrez AN-139 (MW = 1,080,000 Da). Increasing the concentration of NaHCO₃ also significantly increased the % S_eq. Moreover, a 100% penetration was recorded for both the applicator and combination of applicator and thumb pressure compared with only 11% for thumb pressure alone. The average diameter of micropores created by the applicator method was 62.94 μm, which was significantly lower than the combination of both applicator and thumb pressure MN application (100.53 μm). Based on histological imaging, the penetration depth of hydrogel MN increased as the MN density per array decreased. The hydrogel MN with the optimized formulation and skin insertion parameters was tested for caffeine delivery in an in vitro Franz diffusion cell setup. Approximately 2.9 mg of caffeine was delivered within 24 h, and the drug release profile was best fitted to the Korsmeyer-Peppas model, displaying Super Case II kinetics. In conclusion, a combination of thumb and impact application methods and reduced needle density improved the skin penetration efficiency of hydrogel MNs. The results also show that hydrogel MNs fabricated from 3% w/w NaHCO₃ and high MW of copolymer exhibit optimum physical and swelling properties for enhanced transdermal delivery.

Feasibility of Enhancing Skin Permeability of Acyclovir through Sterile Topical Lyophilized Wafer on Self-Dissolving Microneedle-Treated Skin

Acyclovir is an antiviral drug that is frequently prescribed for the herpes virus. However, the drug requires frequent dosing due to limited bioavailability (10–26.7%). The rationale of the present study was to develop a self-dissolving microneedle system for local and systemic delivery of acyclovir using a topical lyophilized wafer on microneedle-treated skin to provide the drug at the site of infection. The microneedles prepared with hydroxypropyl methylcellulose (HPMC) (8% w/w) or HPMC (8% w/w)-polyvinyl pyrrolidone (PVP) (30% w/w) penetrated excised rat skin, showing sufficient mechanical strength and rapid polymer dissolution. The topical wafer was prepared with acyclovir (40% w/w; equivalent to 200 mg of drug), gelatin (10% w/w), mannitol (5% w/w), and sodium chloride (5% w/w). The uniform distribution of acyclovir within the wafer in an amorphous form was confirmed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). No polymer–drug interaction was evident in the lyophilized wafer as per Fourier transform infrared spectroscopy (FTIR) analysis. The wafer showed a sufficiently porous structure for rapid hydration as per scanning electron microscopy (SEM) analysis. During ex-vivo analysis, the skin was pre-treated with a self-dissolving microneedle array for 5 minutes, and the wafer was placed on this microporated-skin. Topical wafer provided ∼7–11 times higher skin concentration than the ID₉₉ reported with a lower lag-time. Based on in-vivo testing, ∼2.58 µg/ml of Cmax was achieved in rabbit plasma during 24 hours’ study. Our findings suggest that the self-dissolving microneedle-assisted topical wafer, proposed for the first time, would be efficacious against the infection residing in the skin layer and for systemic therapy.

The Role of 3D Printing Technology in Microengineering of Microneedles

Microneedles (MNs) are minimally invasive devices, which have gained extensive interest over the past decades in various fields including drug delivery, disease diagnosis, monitoring, and cosmetics. MN geometry and shape are key parameters that dictate performance and therapeutic efficacy, however, traditional fabrication methods, such as molding, may not be able to offer rapid design modifications. In this regard, the fabrication of MNs using 3D printing technology enables the rapid creation of complex MN prototypes with high accuracy and offers customizable MN devices with a desired shape and dimension. Moreover, 3D printing shows great potential in producing advanced transdermal drug delivery systems and medical devices by integrating MNs with a variety of technologies. This review aims to demonstrate the advantages of exploiting 3D printing technology as a new tool to microengineer MNs. Various 3D printing methods are introduced, and representative MNs manufactured by such approaches are highlighted in detail. The development of advanced MN devices is also included. Finally, clinical translation and future perspectives for the development of MNs using 3D printing are discussed.

Stimuli-Responsive Microneedles as a Transdermal Drug Delivery System: A Demand-Supply Strategy

Microneedles are one of the most prominent approaches capable of physically disrupting the stratum corneum without devastating the deeper tissues to deliver both small molecules and macromolecules into the viable epidermis/dermis for local/systemic effects. Over the past two decades, microneedles have caught the attention of many researchers because of their outstanding advantages over oral and parenteral drug delivery systems such as self-administration, pain-free, steady-plasma concentration maintenance, avoidance of first-pass hepatic biotransformation, and so on. So far, scientists have reported various types of microneedle patches to deliver the loaded therapeutics as soon as the microneedles are inserted into the skin, regardless of the demand for therapeutics to treat a specific condition. This way of drug delivery can lead to potential risks such as poor therapeutic efficacy or drug overdose. The stimuli-responsive microneedles are the most predominant tool to achieve the on-demand/need-based drug delivery, leading to safe and effective treatment. Various natural and synthetic polymers that can undergo significant transitions such as swelling, shrinking, dissolution, or disintegration play a pivotal role in the development of stimuli-responsive microneedles. The current Review provides brief information about the history, emergence, type, and working principles of microneedles. Furthermore, it selectively discusses various exogenous and endogenous stimuli-responsive microneedles along with their mechanism of action involved in treating different disease conditions. Collaterally, the emergence of "closed-loop" combinatorial stimuli-responsive microneedle patches for precise delivery of therapeutics is meticulously canvassed. Subsequently, it covers the patents of different stimuli-responsive microneedles and further highlights the existing challenges and future perspectives concerning clinical application and large-scale production.

Trilayer microneedle array assisted transdermal and intradermal delivery of dexamethasone

Dexamethasone is a synthesised glucocorticoid that is widely used in the treatment of various inflammatory skin conditions. Novel trilayer dissolving microneedle arrays were manufactured to assist dexamethasone delivery via the skin. Both transdermal delivery and intradermal delivery of dexamethasone can be achieved this way. Additionally, we proposed a novel strategy of co-formulating dexamethasone and its pro-drug dexamethasone sodium phosphate into the same dissolving microneedle array, with a view to achieving a fast onset of action and also sustained treatment. Here, a 3D-printing technique was employed, for the first time, to fabricate a baseplate for these microneedle arrays. The 3D-printed baseplates provided strong support to aid the insertion of the drug-encapsulated tips. A simple and rapid HPLC method was developed, and validated, to separate and quantify dexamethasone and dexamethasone sodium phosphate in the same sample. Ex-vivo studies found that these trilayer dissolving microneedle arrays could achieve a delivery efficiency of over 40% in intradermal delivery and over 50% in transdermal delivery. Trilayer microneedle-assisted delivery of this glucocorticoid provided a promising alternative to oral and parenteral routes of dexamethasone administration.

Rapidly dissolving microneedle patch of amphotericin B for intracorneal fungal infections

Chronic fungal infection of the cornea could lead to blindness if not treated properly. Topical amphotericin B (AMP-B) is considered the first treatment of choice for ocular fungal infection. However, factors related to its poor solubility and penetration through intact cornea lead to poor bioavailability. Microneedles (MNs) are emerging as a minimally invasive method to enhance ocular drug delivery. This study aims to investigate the potential use of biodegradable poly(vinylpyrrolidone) (PVP) and hyaluronic acid (HA)-based rapidly dissolving MNs for delivery of AMP-B to treat fungal infection. The data obtained illustrates PVP/HA MN arrays' reproducibility, good mechanical strength, and faster dissolution with 100% drug recovery. Multiphoton microscopic results revealed that MNs successfully penetrate the corneal tissue and enhance AMP-B permeation through corneal layers. Furthermore, PVP/HA MN arrays showed high solubility. Both PVP and HA successfully decreased AMP-B cytotoxicity when compared to free drug. More interestingly, the biocompatible MN formulations preserved the antifungal activity of AMP-B, as demonstrated by significant inhibition of fungal growth. Therefore, this study shows the feasibility of ocular delivery of the poorly soluble AMP-B using a fast-dissolving MN patch.

Nestorone nanosuspension-loaded dissolving microneedles array patch: A promising novel approach for "on-demand" hormonal female-controlled peritcoital contraception

"On demand" hormonal female-controlled pericoital contraception is one strategy which could be used to minimize the impact of unintended pregnancy. Nestorone (NES) is a potent contraceptive, with relatively few side effects in comparison with other contraceptives. NES presents an attractive option for "on demand" pericoital contraceptive. Unfortunately, the drug is inactive if taken orally, but it has high progestational activity and antiovulatory potency if administered parenterally. Current drug delivery systems, such as a transdermal hydrogel are not so satisfactory. Dissolving microneedles array (DMNs) are an attractive alternative, minimally-invasive, delivery system. In this study, we report, for the first time, development of tip-loaded NES-nanosuspension (NES-NS)-loaded bilayer DMNs to deliver NES intradermally for subsequent release. NES-NS was prepared and optimised, freeze-dried and then used to fabricate DMNs using a blend of two biocompatible polymers, namely poly(vinyl alcohol) and poly(vinyl pyrrolidone). Both NES-NS and the NES-NS-loaded DMNs were fully characterised and the performance of the DMNs was evaluated in vivo using Sprague Dawley rats. Results showed that the finalised NES-NS had particle size and PDI values of 666.06 ± 1.86 nm and 0.183 ± 0.01, respectively. The NES-NS-DMNs had relatively high tips-localised drug loading (approximately 2.26 ± 1.98 mg/array) and exhibited satisfactory mechanical and insertion properties. In Sprague Dawley rats, DMNs delivered NES into the skin, with the drug then appearing in blood and rapidly reaching its maximum concentration (C_max of 32.68 ± 14.06 ng/mL) within 1h post-DMNs application. Plasma levels above 3.4 ng/mL were maintained for 2 days. This suggests that DMNs are a promising drug delivery system that could be used to deliver NES as an "On demand" hormonal female-controlled pericoital contraceptive.

Nanoemulsion-based dissolving microneedle arrays for enhanced intradermal and transdermal delivery

The development of dissolving microneedles (DMN) is one of the advanced technologies in transdermal drug delivery systems, which precisely deliver the drugs through a rapid dissolution of polymers after insertion into the skin. In this study, we fabricated nanoemulsion-loaded dissolving microneedle (DMN) arrays for intradermal and transdermal drug delivery. For this task, model drug (amphotericin B, AmB)-loaded nanoemulsion (NE) were prepared by the probe-sonication method. AmB-loaded-NE was prepared using Capmul MCM C-8 EP/NF, Tween^® 80, poly(vinyl alcohol) (PVA-10 kDa), and poly (vinyl pyrrolidone) (PVP-360 kDa or K29/32) by using SpeedMixer™, followed by probe-sonication and evaluated for particle size and polydispersity index (PDI). Transmission electron microscopy (TEM) was also used to assess the particle size before and after DMN casting. AmB-NE embedded DMN arrays were found to be strong enough, revealed efficient skin insertion, and penetrated down to the fourth layer (depth ≈ 508 μm) of Parafilm M^® (validated skin model). Ex vivo skin deposition experiments in full-thickness neonatal porcine demonstrated that after 24 h, AmB-NE-DMN arrays were able to deposit 111.05 ± 48.4 µg/patch AmB into the skin. At the same time, transdermal porcine skin permeation studies showed significantly higher permeability of AmB (29.60 ± 8.23 μg/patch) from AmB-NE-DMN compared to MN-free AmB-NE patches (5.0 ± 6.15 μg/patch) over 24 h. Antifungal studies of optimized AmB-NE-DMN, AmB-loaded discs and drug-free DMN against Candida albicans, confirmed the synergistic activity of Campul-MCM C-8, used in the nanoemulsion formulation. This study establishes that nanoemulsion based dissolving microneedle may serve as an efficient system for intradermal as well as transdermal drug delivery.

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.

An Update on the Routes for the Delivery of Donepezil

Dementia is a significant public health problem in the 21st century. Alzheimer's disease (AD) is an essential factor in dementia. Currently, the drugs used for the treatment of AD are mainly acetylcholine inhibitors (AChEIs). As an AChEI, donepezil (DP) can improve patients' cognitive ability with low side effects and has been accepted by most patients and doctors. For AD patients, the dosage regimen is also crucial due to aging and diseases. Although there are DP oral tablets on the market, there are still many problems to be solved. At present, more and more research is conducted to optimize the route of administration of DP to improve the self-administration of patients. The research fields of DP administration include oral administration, injection administration, intranasal administration, and transdermal administration. This Review is to present the development of different DP administrations and evaluates the advantages and limitations of those works, hoping to optimize the DP dosage regimen for AD patients.

Antibiotic Therapy and the Gut Microbiome: Investigating the Effect of Delivery Route on Gut Pathogens

The contribution of the gut microbiome to human health has long been established, with normal gut microbiota conferring protection against invasive pathogens. Antibiotics can disrupt the microbial balance of the gut, resulting in disease and the development of antimicrobial resistance. The effect of antibiotic administration route on gut dysbiosis remains under-studied to date, with conflicting evidence on the differential effects of oral and parenteral delivery. We have profiled the rat gut microbiome following treatment with commonly prescribed antibiotics (amoxicillin and levofloxacin), via either oral or intravenous administration. Fecal pellets were collected over a 13-day period and bacterial populations were analyzed by 16S rRNA gene sequencing. Significant dysbiosis was observed in all treatment groups, regardless of administration route. More profound dysbiotic effects were observed following amoxicillin treatment than those with levofloxacin, with population richness and diversity significantly reduced, regardless of delivery route. The effect on specific taxonomic groups was assessed, revealing significant disruption following treatment with both antibiotics. Enrichment of a number of groups containing known gut pathogens was observed, in particular, with amoxicillin, such as the family Enterobacteriaceae. Depletion of other commensal groups was also observed. The degree of dysbiosis was significantly reduced toward the end of the sampling period, as bacterial populations began to return to pretreatment composition. Richness and diversity levels appeared to return to pretreatment levels more quickly in intravenous groups, suggesting convenient parenteral delivery systems may have a role to play in reducing longer term gut dysbiosis in the treatment of infection.

From the laboratory to the end-user: a primary packaging study for microneedle patches containing amoxicillin sodium

Abstract

As microneedle (MN) patches progress towards commercialisation, there is a need to address issues surrounding their translation from the laboratory to the end-user. One important aspect of MN patches moving forward is appropriate primary packaging. This research focuses on MN patches containing amoxicillin (AMX) sodium for the potential treatment of neonatal sepsis in hot and humid countries. A MN patch consists of a hydrogel-forming MN array and a drug-containing reservoir. Improper primary packaging in hot and humid countries may result in degradation of active pharmaceutical ingredients, with the use of substandard medicines a major health concern. The research presented here, for the first time, seeks to investigate the integrity of MN patches in different primary packaging when stored under accelerated storage conditions, according to international guidelines. At pre-defined intervals, the performance of the MN patch was investigated. Major causes of drug instability are moisture and temperature. To avoid unnecessary degradation, suitable primary packaging was sought. After 168 days, the percentage of AMX sodium recovered from drug-containing reservoirs packaged in Protect™ 470 foil was 103.51 ± 7.03%. However, packaged in poly(ester) foil, the AMX sodium content decreased significantly (p = 0.0286), which is likely due to the degradation of AMX sodium by the imbibed moisture. Therefore, convincing evidence was provided as to the importance of investigating the stability of MN patches in primary packaging intended for MN-mediated transdermal delivery so that they are ‘fit for purpose’ when it reaches the end-user. Future work will include qualitative studies to assess MN patch usability.

Graphical abstract