Drug delivery with dissolving microneedles: Skin puncture, its influencing factors and improvement strategies

Development and optimization of hydrogel-forming microneedles fabricated with 3d-printed molds for enhanced dermal diclofenac sodium delivery: a comprehensive in vitro, ex vivo, and in vivo study

With the developing manufacturing technologies, the use of 3D printers in microneedle production is becoming widespread. Hydrogel-forming microneedles (HFMs), a variant of microneedles, demonstrate distinctive features such as a high loading capacity and controlled drug release. In this study, the conical microneedle master molds with approximately 500 μm needle height and 250 μm base diameter were created using a Stereolithography (SLA) 3D printer and were utilized to fabricate composite HFMs containing diclofenac sodium. Using Box-Behnken Design, the effects of different polymers on swelling index and mechanical strength of the developed HFMs were evaluated. The optimum HFMs were selected according to experimental design results with the aim of the highest mechanical strength with varying swelling indexes, which was needed to use 20% Gantrez S97 and 0.1% (F22), 0.42% (F23), and 1% (F24) hyaluronic acid. The skin penetration and drug release properties of the optimum formulations were assessed. Ex vivo studies were conducted on formulations to determine drug penetration and accumulation. F24, which has the highest mechanical strength and optimized swelling index, achieved the highest drug accumulation in the skin tissue (17.70 ± 3.66%). All optimum HFMs were found to be non-cytotoxic by the MTT cell viability test (> 70% cell viability). In in vivo studies, the efficacy of the F24 was assessed for the treatment of xylene-induced ear edema by contrasting it to the conventional dosage form. It was revealed that HFMs might be an improved replacement for conventional dosage forms in terms of dermal diseases such as actinic keratosis.

Injectable and implantable hydrogels for localized delivery of drugs and nanomaterials for cancer chemotherapy: A review

Multiple chemotherapeutic strategies have been developed to tackle the complexity of cancer. Still, the outcome of chemotherapeutic regimens remains impaired by the drugs' weak solubility, unspecific biodistribution and poor tumor accumulation after systemic administration. Such constraints triggered the development of nanomaterials to encapsulate and deliver anticancer drugs. In fact, the loading of drugs into nanoparticles can overcome most of the solubility concerns. However, the ability of systemically administered drug-loaded nanomaterials to reach the tumor site has been vastly overestimated, limiting their clinical translation. The drugs' and drug-loaded nanomaterials' systemic administration issues have propelled the development of hydrogels capable of performing their direct/local delivery into the tumor site. The use of these macroscale systems to mediate a tumor-confined delivery of the drugs/drugs-loaded nanomaterials grants an improved therapeutic efficacy and, simultaneously, a reduction of the side effects. The manufacture of these hydrogels requires the careful selection and tailoring of specific polymers/materials as well as the choice of appropriate physical and/or chemical crosslinking interactions. Depending on their administration route and assembling process, these matrices can be classified as injectable in situ forming hydrogels, injectable shear-thinning/self-healing hydrogels, and implantable hydrogels, each type bringing a plethora of advantages for the intended biomedical application. This review provides the reader with an insight into the application of injectable and implantable hydrogels for performing the tumor-confined delivery of drugs and drug-loaded nanomaterials.

Microneedles: multifunctional devices for drug delivery, body fluid extraction, and bio-sensing

Microneedles represent a miniaturized mechanical structure with versatile applications, including transdermal drug delivery, vaccination, body-fluid extraction, and bio-sensing. Over the past two decades, microneedle-based devices have garnered considerable attention in the biomedicine field, exhibiting the potential for mitigating patient discomfort, enhancing treatment adherence, avoiding first-pass effects, and facilitating precise therapeutic interventions. As an application-oriented technology, the innovation of microneedles is generally carried out in response to a specific demand. Currently, three most common applications of microneedles are drug delivery, fluid extraction, and bio-sensing. This review focuses on the progress in the materials, fabrication techniques, and design of microneedles in recent years. On this basis, the progress and innovation of microneedles in the current research stage are introduced in terms of their three main 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.

Evolution of microneedle applicators for vaccination: the role of the latch applicator in optimizing dissolving microneedle-based immunization

INTRODUCTION

Dissolving microneedles (DMN) offer advantages in vaccine delivery, such as enhanced immunogenicity and simplified administration, by targeting immune-rich layers of the skin. However, these benefits require precise and consistent delivery, which poses practical challenges. To address this, specialized applicators are essential for ensuring the accurate deployment of DMNs, making this technology a viable alternative to traditional methods, particularly in low- and middle-income countries (LMICs), where healthcare infrastructure is limited.

AREAS COVERED

In this review, we examine the advancements in DMN-based vaccination and applicator design, focusing on their joint effort. These innovations have improved the precision and efficiency of DMN vaccine delivery. Complex and costly early-stage applicators have evolved into simpler and more cost-effective designs. We highlight these developments in this review, with the latch applicator as a key example of a feature that enhances vaccine delivery.

EXPERT OPINION

Although applicator development has advanced DMN-based vaccination toward practical use, challenges remain. Key areas for further optimization include user friendliness, cost, packaging volume, and wear time. Once optimized, DMN vaccination may become a highly effective and accessible tool for global immunization, supporting efforts to achieve worldwide vaccine equality.

Microneedle system for tissue engineering and regenerative medicines: a smart and efficient therapeutic approach

The global demand for an enhanced quality of life and extended lifespan has driven significant advancements in tissue engineering and regenerative medicine. These fields utilize a range of interdisciplinary theories and techniques to repair structurally impaired or damaged tissues and organs, as well as restore their normal functions. Nevertheless, the clinical efficacy of medications, materials, and potent cells used at the laboratory level is always constrained by technological limitations. A novel platform known as adaptable microneedles has been developed to address the abovementioned issues. These microneedles offer a solution for the localized distribution of various cargos while minimizing invasiveness. Microneedles provide favorable patient compliance in clinical settings due to their effective administration and ability to provide a painless and convenient process. In this review article, we summarized the most recent development of microneedles, and we started by classifying various microneedle systems, advantages, and fundamental properties. Subsequently, it provides a comprehensive overview of different types of microneedles, the material used to fabricate microneedles, the fundamental properties of ideal microneedles, and their applications in tissue engineering and regenerative medicine, primarily focusing on preserving and restoring impaired tissues and organs. The limitations and perspectives have been discussed by concluding their future therapeutic applications in tissue engineering and regenerative medicines.

Simulated skin model for in vitro evaluation of insertion performance of microneedles: design, development, and application verification

Microneedles, as a new efficient and safe transdermal drug delivery technology, has a wide range of applications in drug delivery, vaccination, medical cosmetology, and diagnostics. The degree of microneedles penetration into the skin determines the reliability of the delivery dose, but its evaluation is not yet well-established, which is one of the major constraints in the commercialization of microneedles. In this paper, a novel visual simulated skin model was developed with reference to the physical properties of real skin. The simulated skin model was well-designed and its prescription was optimized to make the thickness, hardness, elasticity, and other parameters close to those of real skin. It not only meets the need to assess the degree of insertion of microneedles but also provides a visual observation of the insertion state of microneedles.

Advances in skin gene therapy: utilizing innovative dressing scaffolds for wound healing, a comprehensive review

The skin, serving as the body's outermost layer, boasts a vast area and intricate structure, functioning as the primary barrier against external threats. Disruptions in the composition and functionality of the skin can lead to a diverse array of skin conditions, such as wounds, burns, and diabetic ulcers, along with inflammatory disorders, infections, and various types of skin cancer. These disorders not only exacerbate concerns regarding skin health and beauty but also have a significant impact on mental well-being. Due to the complexity of these disorders, conventional treatments often prove insufficient, necessitating the exploration of new therapeutic approaches. Researchers develop new therapies by deciphering these intricacies and gaining a thorough understanding of the protein networks and molecular processes in skin. A new window of opportunity has opened up for improving wound healing processes because of recent advancements in skin gene therapy. To enhance skin regeneration and healing, this extensive review investigates the use of novel dressing scaffolds in conjunction with gene therapy approaches. Scaffolds that do double duty as wound protectors and vectors for therapeutic gene delivery are being developed using innovative biomaterials. To improve cellular responses and speed healing, these state-of-the-art scaffolds allow for the targeted delivery and sustained release of genetic material. The most recent developments in gene therapy techniques include RNA interference, CRISPR-based gene editing, and the utilization of viral and non-viral vectors in conjunction with scaffolds, which were reviewed here to overcome skin disorders and wound complications. In the future, there will be rare chances to develop custom methods for skin health care thanks to the combination of modern technology and collaboration among disciplines.

Fabrication and mechanical modelling of dissolvable PVA/PVP composite microneedles with biocompatibility for efficient transdermal delivery of ibuprofen

Microneedles offer minimally invasive, user-friendly, and subcutaneously accessible transdermal drug delivery and have been widely investigated as an effective transdermal delivery system. Ibuprofen is a common anti-inflammatory drug to treat chronic inflammation. It is crucial to develop microneedle patches capable of efficiently delivering ibuprofen through the skin for the effective treatment of arthritis patients requiring repeated medication. In this study, the mechanical properties of a new type of polymer microneedle were studied by finite element analysis, and the experimental results showed that the microneedle could effectively deliver drugs through the skin. In addition, a high ibuprofen-loaded microneedle patch was successfully prepared by micromolding and subjected to evaluation of its infrared spectrum morphology and dissolve degree. The morphology of microneedles was characterized by scanning electron microscopy, and the mechanical properties were assessed using a built linear stretching system. In the in-vitro diffusion cell drug release test, the microneedle released 85.2 ± 1.52% (210 ± 3.7 μg) ibuprofen in the modified Franz diffusion within 4 h, exhibiting a higher drug release compared to other drug delivery methods. This study provides a portable, safe and efficient treatment approach for arthritis patients requiring daily repeated medication.

Coated Porous Microneedles for Effective Intradermal Immunization with Split Influenza Vaccine

In order to alleviate the pain associated with subcutaneous injections, microneedles (MNs) are gaining increasing attention as a novel transdermal drug delivery modality. Among them, porous microneedles (pMNs) are particularly suitable for the delivery of drugs and vaccines whose activity is sensitive to the microneedle preparation process. They can carry drugs actively to achieve an effective load and deliver drugs into the skin. In this study, the biocompatible cellulose acetate (CA) microporous MNs with a large pore size of 1.13 μm ± 0.45 and a high porosity of 74.8% ± 2.8% were prepared by using a safe nonsolvent-induced phase separation (NIPS) method. The MN patches prepared after adsorption of appropriate concentrations of split influenza vaccine fully met the dose loading requirements. A biocompatible carboxymethyl cellulose (CMC) solution was used in the pMN coating to strengthen their mechanical properties, with an average maximum stress of 32.89 N, and to act as a medium for the dispersion of an adjuvant in the coating layer. The influenza vaccine adsorbed in the micropore and the adjuvant dispersed in the coating were released intradermally to exert synergistic effects with different release patterns and rates. The coated pMNs induced an efficient immune response in Wistar rats with a hemagglutination inhibition (HI) titer of ≥1024, which was comparable to that of intramuscular injection. The research is organized around the goal of engineering exploration of innovative technologies, suggesting that pMNs have a tantalizing prospect for future applications. It opens up the possibility of eventually obtaining a simple, easy-to-use, and efficient application technology for the prevention of global epidemics like influenza.

Microneedle-mediated transdermal delivery of N-acetyl cysteine as a potential antidote for lewisite injury

Lewisite is a chemical warfare agent intended for use in World War and a potential threat to the civilian population due to presence in stockpiles or accidental exposure. Lewisite-mediated skin injury is characterized by acute erythema, pain, and blister formation. N-acetyl cysteine (NAC) is an FDA-approved drug for acetaminophen toxicity, identified as a potential antidote against lewisite. In the present study, we have explored the feasibility of rapid NAC delivery through transdermal route for potentially treating chemical warfare toxicity. NAC is a small, hydrophilic molecule with limited passive delivery through the skin. Using skin microporation with dissolving microneedles significantly enhanced the delivery of NAC into and across dermatomed human skin in our studies. Microporation followed by application of solution (poke-and-solution) resulted in the highest in vitro delivery (509.84 ± 155.04 µg/sq·cm) as compared to poke-and-gel approach (474.91 ± 70.09 µg/sq·cm) and drug-loaded microneedles (226.89 ± 33.41 µg/sq·cm). The lag time for NAC delivery through poke-and-solution approach (0.23 ± 0.04 h) was close to gel application (0.25 ± 0.02 h), with the highest for drug-loaded microneedles (1.27 ± 1.16 h). Thus, we successfully demonstrated the feasibility of rapid NAC delivery using various skin microporation approaches for potential treatment against lewisite-mediated skin toxicity.

Fast dissolving microneedle patch for pronounced systemic delivery of an antihyperlipidemic drug

Fast dissolving microneedles (F-dMN) are quite a novel approach delivering specific drug molecules directly into the bloodstream, bypassing the first-pass effect. The present study reported an F-dMN patch to enhance systemic delivery of simvastatin in a patient-friendly manner. The F-dMN patch was developed using polyvinyl pyrrolidone and polyvinyl alcohol and characterized using light microscopy, SEM, XRD, FTIR, mechanical strength, drug content (%), an ex-vivo penetration study, an ex-vivo drug release study, a skin irritation test, and a pharmacokinetics study. The optimized F-dMN patch exhibited excellent elongation of 35.17%, good tensile strength of 9.68  MPa, an appropriate moisture content of 5.65%, and good penetrability up to 560 µm. Moreover, it showed 93.4% of the drug content within the needles and 81.75% in-vitro release. Histopathological findings and a skin irritation study proved that the F-dMN patch was biocompatible and did not cause any sort of irritation on animal skin. Pharmacokinetic parameters of F-dMN patches were improved (Cmax 6.974 µg/ml, tmax 1 hr and AUC 19. 518 µg.h/ml) as compared to tablet Simva 20 mg solution (Cmax 2.485 µg/ml, tmax 1.4 hr and AUC 11.199 µg.h/ml), thus confirming bioavailability enhancement. Moreover, stability studies confirmed the stability of the developed F-dMN patch, as investigated by axial needle fracture force and drug content.

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.

Development of a Microfluidic Formatted Ultrasound-Controlled Monodisperse Lipid Vesicles' Hydrogel Dressing Combined with Ultrasound for Transdermal Drug Delivery System

Transdermal drug delivery system (TDDS) has attracted much attention in the pharmaceutical technology area. However, the current methods are difficult to ensure penetration efficiency, controllability, and safety in the dermis, so its widespread clinical use has been limited. This work proposes an ultrasound-controlled monodisperse lipid vesicles (U-CMLVs) hydrogel dressing, which combines with ultrasound to form TDDS. Using microfluidic technology, prepare size controllable U-CMLVs with high drug encapsulation efficiency and quantitative encapsulation of ultrasonic response materials, and even uniform mix them with hydrogel to prepare the required thickness of dressings. The high encapsulation efficiency can ensure sufficient dosage of the drugs and further realize the control of ultrasonic response through quantitative encapsulation of ultrasound-responsive materials. Using high frequency (5 MHz, 0.4 W cm-2 ) and low frequency (60 kHz, 1 W cm-2 ) ultrasound to control the movement and rupture of U-CMLVs, the contents not only penetrate the stratum corneum into the epidermis but also break through the bottleneck of penetration efficiency, and deep into the dermis. These findings provide the groundwork for deep, controllable, efficient, and safe drug delivery through TDDS and lay a foundation for further expanding its application.

Application of Medical Image Navigation Technology in Minimally Invasive Puncture Robot

Microneedle puncture is a standard minimally invasive treatment and surgical method, which is widely used in extracting blood, tissues, and their secretions for pathological examination, needle-puncture-directed drug therapy, local anaesthesia, microwave ablation needle therapy, radiotherapy, and other procedures. The use of robots for microneedle puncture has become a worldwide research hotspot, and medical imaging navigation technology plays an essential role in preoperative robotic puncture path planning, intraoperative assisted puncture, and surgical efficacy detection. This paper introduces medical imaging technology and minimally invasive puncture robots, reviews the current status of research on the application of medical imaging navigation technology in minimally invasive puncture robots, and points out its future development trends and challenges.

Xenon Difluoride Dry Etching for the Microfabrication of Solid Microneedles as a Potential Strategy in Transdermal Drug Delivery

Although hypodermic needles are a "gold standard" for transdermal drug delivery (TDD), microneedle (MN)-mediated TDD denotes an unconventional approach in which drug compounds are delivered via micron-size needles. Herein, an isotropic XeF₂ dry etching process is explored to fabricate silicon-based solid MNs. A photolithographic process, including mask writing, UV exposure, and dry etching with XeF₂ is employed, and the MN fabrication is successfully customized by modifying the CAD designs, photolithographic process, and etching conditions. This study enables fabrication of a very dense MNs (up to 1452 MNs cm^-2 ) with height varying between 80 and 300 µm. Geometrical features are also assessed using scanning electron microscopy (SEM) and 3D laser scanning microscope. Roughness of the MNs are improved from 0.71 to 0.35 µm after titanium and chromium coating. Mechanical failure test is conducted using dynamic mechanical analyzer to determine displacement and stress/strain values. The coated MNs are subjected to less displacement (≈15 µm) upon the applied force. COMSOL Multiphysics analysis indicates that MNs are safe to use in real-life applications with no fracture. This technique also enables the production of MNs with distinct shape and dimensions. The optimized process provides a wide range of solid MN types to be utilized for epidermis targeting.

Development and Characterization of PEGDA Microneedles for Localized Drug Delivery of Gemcitabine to Treat Inflammatory Breast Cancer

Inflammatory breast cancer (IBC) is one of the most belligerent types of breast cancer. While various modalities exist in managing/treating IBC, drug delivery using microneedles (MNs) is considered to be the most innovative method of localized delivery of anti-cancer agents. Localized drug delivery helps to treat IBC could limit their adverse reactions. MNs are nothing but small needle like structures that cause little or no pain at the site of administration for drug delivery via layers of the skin. The polyethylene glycol diacrylate (PEGDA) based MNs were fabricated by using three dimensional (3D) technology called Projection Micro-Stereo Lithography (PµSL). The fabricated microneedle patches (MNPs) were characterized and coated with a coating formulation comprising of gemcitabine and sodium carboxymethyl cellulose by a novel and inventive screen plate method. The drug coated MNPs were characterized by various instrumental methods of analysis and release profile studies were carried out using Franz diffusion cell. Coat-and-poke strategy was employed in administering the drug coated MNPs. Overall, the methods employed in the present study not only help in obtaining MNPs with accurate dimensions but also help in obtaining uniformly drug coated MNPs of gemcitabine for treatment of IBC. Most importantly, 100% drug release was achieved within the first one hour only.