Microneedles: Characteristics, Materials, Production Methods and Commercial Development

Droplet-based microfluidics for drug delivery applications

The microfluidic method primainly utilizes two incompatible liquids as continuous phase and dispersed phase respectively. It controls the formation of droplets by managing the microchannel structure and the flow rate ratio of the two phases. Droplet-based microfluidics is a rapidly expanding interdisciplinary research field encompassing physics, biochemistry, and Microsystems engineering. Droplet microfluidics offer a diverse and practical toolset that enables chemical and biological experiments to be conducted at high speeds and with greater efficiency compared to traditional instruments. The applications of droplet-based microfluidics are vast, including areas such as drug delivery, owing to its compatibility with numerous chemical and biological reagents and its ability to carry out various operations. This technology has been extensively researched due to its promising features. In this review, we delve into the materials used in droplet generation-based microfluidic devices, manufacturing techniques, methods for droplet generation in channels, and, finally, we summarize the applications of droplet generation-based microfluidics in drug delivery vectors, encompassing nanoparticles, microspheres, microcapsules, and hydrogel particles. We also discuss the challenges and future prospects of this technology across a wide array of applications.

Advances in microneedle technology for biomedical detection

Microneedles have recently emerged as a groundbreaking technology in the field of biomedical detection. Notable for their small size and ability to penetrate the superficial layers of the skin, microneedles provide an innovative platform for localized and real-time detection. This review explores the integration of various detection methods with microneedle technology, focusing particularly on its applications in biomedical contexts. First, the common detection methods, such as colorimetric, electrochemical, spectrometric, and fluorescence methods, combined with microneedle technology, are summarized. Then we showcase exemplary uses of microneedle technology in biomedical detection, including the monitoring of blood glucose levels, evaluating infection statuses in skin wounds, facilitating point-of-care testing, and identifying biomarkers in the interstitial fluid of the skin. Microneedle-based detection, with its painless, minimally invasive, and biocompatible approach, holds significant promise for enhancing biological assays. Finally, the review concludes by assessing the future potential and challenges of microneedle detection technology, underscoring its transformative capacity to advance personalized medicine and revolutionize healthcare practices.

Nanoformulation-assisted microneedle transdermal drug delivery system: An innovative platform enhancing rheumatoid arthritis treatment

A transdermal delivery system offers high bioavailability and favorable patient adherence, constituting an optimal approach for localized administration in rheumatoid arthritis (RA) treatment. However, the stratum corneum (SC) impedes the delivery efficiency of conventional transdermal drug delivery systems. Microneedles (MNs) can temporarily create micropores within the SC, enabling drug distribution via bypassing this barrier and enhancing transdermal delivery effectiveness. Notably, MNs provide a painless method of drug delivery through the skin and may directly modulate inflammation in immune cells by delivering drugs via the lymphatic system during transdermal administration. However, the MN delivery system is not suitable for drugs with low water solubility and stability. Additionally, major concerns exist regarding the safety of using MN delivery for highly cytotoxic drugs, given that it could result in high local drug concentration at the delivery site. While MNs exhibit some degree of targeted delivery to the immune and inflammatory environment, their targeting efficiency remains suboptimal. Nanoformulations have the potential to significantly address the limitations of MNs in RA treatment by improving drug targeting, solubility, stability, and biocompatibility. Therefore, this review provides a concise overview of the advantages, disadvantages, and mechanisms of different types of MNs for RA treatment. It specifically focuses on the application and advantages of combining nanoformulation with MNs for RA treatment and summarizes the current trends in the development of nanoformulations combined with MNs in the field of RA treatment, offering theoretical support for future advancements and clinical applications.

Dissolving Microneedles Patch: A Promising Approach for Advancing Transdermal Delivery of Antischizophrenic Drug

OBJECTIVE

Microneedles (MNs) are minimally invasive transdermal drug delivery systems capable of penetrating the stratum corneum to overcome the barrier properties. The primary objective of this research was to prepare dissolving microneedle patches (DMNP) loaded with quetiapine (QTP).

METHODS

DMNP were fabricated employing the solvent casting technique, utilizing various polymer feed ratios including polyvinyl alcohol (PVA), polyvinylpyrrolidone K30 (PVP-K30), and polylactide-co-glycolide (PLGA) polymers. The loaded DMNP with QTP underwent a comprehensive characterization process encompassing assessments for compatibility, thickness, insertion potential, morphology, thermal behavior, X-ray diffraction, ex-vivo permeation, skin irritation, and histopathological changes.

RESULTS

FTIR studies confirmed the compatibility of QTP with the microneedle patch composites. The thickness of the drug-loaded DMNP ranged from 0.67 mm to 0.97 mm. These microneedles exhibited an impressive penetration depth of 480 μm, with over 80% of the needles maintaining their original shape after piercing Parafilm-M. SEM analysis of the optimized DMNP-2 revealed the formation of sharp-tipped and uniformly surfaced needles, measuring 570 μm in length. Remarkably, the microneedles did not elicit any signs of irritation upon application of the prepared DMNP. The DMNP-2 showcased an impressive cumulative ex-vivo permeation of QTP, reaching 17.82 µg/cm2/hr. Additionally, histopathological assessment of vital organs in rabbits attested to the safety profile of the formulated microneedle patches.

CONCLUSIONS

In conclusion, the developed microneedle patch represents a promising strategy for enhancing the transdermal delivery of QTP. This innovative approach has the potential to increase patient compliance, offering a more efficient and patient-friendly method of administering QTP.

Advances in Polysaccharide-Based Microneedle Systems for the Treatment of Ocular Diseases

The eye, a complex organ isolated from the systemic circulation, presents significant drug delivery challenges owing to its protective mechanisms, such as the blood-retinal barrier and corneal impermeability. Conventional drug administration methods often fail to sustain therapeutic levels and may compromise patient safety and compliance. Polysaccharide-based microneedles (PSMNs) have emerged as a transformative solution for ophthalmic drug delivery. However, a comprehensive review of PSMNs in ophthalmology has not been published to date. In this review, we critically examine the synergy between polysaccharide chemistry and microneedle technology for enhancing ocular drug delivery. We provide a thorough analysis of PSMNs, summarizing the design principles, fabrication processes, and challenges addressed during fabrication, including improving patient comfort and compliance. We also describe recent advances and the performance of various PSMNs in both research and clinical scenarios. Finally, we review the current regulatory frameworks and market barriers that are relevant to the clinical and commercial advancement of PSMNs and provide a final perspective on this research area.

Potential of biosurfactant as green pharmaceutical excipients for coating of microneedles: A mini review

Microneedles, a novel transdermal delivery system, were designed to improve drug delivery and address the challenges typically encountered with traditional injection practices. Discovering new and safe excipients for microneedle coating to replace existing chemical surfactants is advantageous to minimize their side effect on viable tissues. However, some side effects have also been observed for this application. The vast majority of studies suggest that using synthetic surfactants in microneedle formulations may result in skin irritation among other adverse effects. Hence, increasing knowledge about these components and their potential impacts on skin paves the way for finding preventive strategies to improve their application safety and potential efficacy. Biosurfactants, which are naturally produced surface active microbial products, are proposed as an alternative to synthetic surfactants with reduced side effects. The current review sheds light on potential and regulatory aspects of biosurfactants as safe excipients in the coating of microneedles.

Recent Update on Nanocarrier(s) as the Targeted Therapy for Breast Cancer

Despite ongoing advances in cancer therapy, the results for the treatment of breast cancer are not satisfactory. The advent of nanotechnology promises to be an essential tool to improve drug delivery effectiveness in cancer therapy. Nanotechnology provides an opportunity to enhance the treatment modality by preventing degradation, improving tumour targeting, and controlling drug release. Recent advances have revealed several strategies to prevent cancer metastasis using nano-drug delivery systems (NDDS). These strategies include the design of appropriate nanocarriers loaded with anti-cancer drugs that target the optimization of physicochemical properties, modulate the tumour microenvironment, and target biomimetic techniques. Nanocarriers have emerged as a preferential approach in the chemotropic treatment for breast cancer due to their pivotal role in safeguarding the therapeutic agents against degradation. They facilitate efficient drug concentration in targeted cells, surmount the resistance of drugs, and possess a small size. Nevertheless, these nanocarrier(s) have some limitations, such as less permeability across the barrier and low bioavailability of loaded drugs. To overcome these challenges, integrating external stimuli has been employed, encompassing infrared light, thermal stimulation, microwaves, and X-rays. Among these stimuli, ultrasound-triggered nanocarriers have gained significant attention due to their cost-effectiveness, non-invasive nature, specificity, ability to penetrate tissues, and capacity to deliver elevated drug concentrations to intended targets. This article comprehensively reviews recent advancements in different nanocarriers for breast cancer chemotherapy. It also delves into the associated hurdles and offers valuable insights into the prospective directions for this innovative field.

Additive manufacturing of microneedles for sensing and drug delivery

INTRODUCTION

Microneedles (MNs) are miniaturized, painless, and minimally invasive platforms that have attracted significant attention over recent decades across multiple fields, such as drug delivery, disease monitoring, disease diagnosis, and cosmetics. Several manufacturing methods have been employed to create MNs; however, these approaches come with drawbacks related to complicated, costly, and time-consuming fabrication processes. In this context, employing additive manufacturing (AM) technology for MN fabrication allows for the quick production of intricate MN prototypes with exceptional precision, providing the flexibility to customize MNs according to the desired shape and dimensions. Furthermore, AM demonstrates significant promise in the fabrication of sophisticated transdermal drug delivery systems and medical devices through the integration of MNs with various technologies.

AREAS COVERED

This review offers an extensive overview of various AM technologies with great potential for the fabrication of MNs. Different types of MNs and the materials utilized in their fabrication are also discussed. Recent applications of 3D-printed MNs in the fields of transdermal drug delivery and biosensing are highlighted.

EXPERT OPINION

This review also mentions the critical obstacles, including drug loading, biocompatibility, and regulatory requirements, which must be resolved to enable the mass-scale adoption of AM methods for MN production, and future trends.

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.

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.

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.

Microneedle-mediated nanomedicine to enhance therapeutic and diagnostic efficacy

Nanomedicine has been extensively explored for therapeutic and diagnostic applications in recent years, owing to its numerous advantages such as controlled release, targeted delivery, and efficient protection of encapsulated agents. Integration of microneedle technologies with nanomedicine has the potential to address current limitations in nanomedicine for drug delivery including relatively low therapeutic efficacy and poor patient compliance and enable theragnostic uses. In this Review, we first summarize representative types of nanomedicine and describe their broad applications. We then outline the current challenges faced by nanomedicine, with a focus on issues related to physical barriers, biological barriers, and patient compliance. Next, we provide an overview of microneedle systems, including their definition, manufacturing strategies, drug release mechanisms, and current advantages and challenges. We also discuss the use of microneedle-mediated nanomedicine systems for therapeutic and diagnostic applications. Finally, we provide a perspective on the current status and future prospects for microneedle-mediated nanomedicine for biomedical applications.

Contemporary strategies and approaches for characterizing composition and enhancing biofilm penetration targeting bacterial extracellular polymeric substances

Extracellular polymeric substances (EPS) constitutes crucial elements within bacterial biofilms, facilitating accelerated antimicrobial resistance and conferring defense against the host's immune cells. Developing precise and effective antibiofilm approaches and strategies, tailored to the specific characteristics of EPS composition, can offer valuable insights for the creation of novel antimicrobial drugs. This, in turn, holds the potential to mitigate the alarming issue of bacterial drug resistance. Current analysis of EPS compositions relies heavily on colorimetric approaches with a significant bias, which is likely due to the selection of a standard compound and the cross-interference of various EPS compounds. Considering the pivotal role of EPS in biofilm functionality, it is imperative for EPS research to delve deeper into the analysis of intricate compositions, moving beyond the current focus on polymeric materials. This necessitates a shift from heavy reliance on colorimetric analytic methods to more comprehensive and nuanced analytical approaches. In this study, we have provided a comprehensive summary of existing analytical methods utilized in the characterization of EPS compositions. Additionally, novel strategies aimed at targeting EPS to enhance biofilm penetration were explored, with a specific focus on highlighting the limitations associated with colorimetric methods. Furthermore, we have outlined the challenges faced in identifying additional components of EPS and propose a prospective research plan to address these challenges. This review has the potential to guide future researchers in the search for novel compounds capable of suppressing EPS, thereby inhibiting biofilm formation. This insight opens up a new avenue for exploration within this research domain.

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.

Potential strategy of microneedle-based transdermal drug delivery system for effective management of skin-related immune disorders

Skin-related immune disorders are a category of diseases that lead to the dysregulation of the body's immune response due to imbalanced immune regulation. These disorders exhibit diverse clinical manifestations and complicated pathogenesis. The long-term use of corticosteroids, anti-inflammatory drugs, and immunosuppressants as traditional treatment methods for skin-related immune disorders frequently leads to adverse reactions in patients. In addition, the effect of external preparations is not ideal in some cases due to the compacted barrier function of the stratum corneum (SC). Microneedles (MNs) are novel transdermal drug delivery systems that have theapparent advantages ofpenetrating the skin barrier, such as long-term and controlled drug delivery, less systemic exposure, and painless and minimally invasive targeted delivery. These advantages make it a good candidate formulation for the treatment of skin-related immune disorders and a hotspot for research in this field. This paper updates the classification, preparation, evaluation strategies, materials, and related applications of five types of MNs. Specific information, including the mechanical properties, dimensions, stability, and in vitro and in vivo evaluations of MNs in the treatment of skin-related immune disorders, is also discussed. This review provides an overview of the advances and applications of MNs in the effective treatment of skin-related immune disorders and their emerging trends.

Tissue Nanotransfection Silicon Chip and Related Electroporation-Based Technologies for In Vivo Tissue Reprogramming

Tissue nanotransfection (TNT), a cutting-edge technique of in vivo gene therapy, has gained substantial attention in various applications ranging from in vivo tissue reprogramming in regenerative medicine, and wound healing to cancer treatment. This technique harnesses the advancements in the semiconductor processes, facilitating the integration of conventional transdermal gene delivery methods-nanoelectroporation and microneedle technologies. TNT silicon chips have demonstrated considerable promise in reprogramming fibroblast cells of skin in vivo into vascular or neural cells in preclinical studies to assist in the recovery of injured limbs and damaged brain tissue. More recently, the application of TNT chips has been extended to the area of exosomes, which are vital for intracellular communication to track their functionality during the wound healing process. In this review, we provide an in-depth examination of the design, fabrication, and applications of TNT silicon chips, alongside a critical analysis of the electroporation-based gene transfer mechanisms. Additionally, the review discussed the existing limitations and challenges in the current technique, which may project future trajectories in the landscape of gene therapy. Through this exploration, the review aims to shed light on the prospects of TNT in the broader context of gene therapy and tissue regeneration.

Tunable theranostics: innovative strategies in combating oral cancer

Objective

This study aims to assess and compare the potential of advanced nano/micro delivery systems, including quantum dots, carbon nanotubes, magnetic nanoparticles, dendrimers, and microneedles, as theranostic platforms for oral cancer. Furthermore, we seek to evaluate their respective advantages and disadvantages over the past decade.

Materials and Methods

A comprehensive literature search was performed using Google Scholar and PubMed, with a focus on articles published between 2013 and 2023. Search queries included the specific advanced delivery system as the primary term, followed by oral cancer as the secondary term (e.g., "quantum dots AND oral cancer," etc.).

Results

The advanced delivery platforms exhibited notable diagnostic and therapeutic advantages when compared to conventional techniques or control groups. These benefits encompassed improved tumor detection and visualization, enhanced precision in targeting tumors with reduced harm to neighboring tissues, and improved drug solubility and distribution, leading to enhanced drug absorption and tumor uptake.

Conclusion

The findings suggest that advanced nano/micro delivery platforms hold promise for addressing numerous challenges associated with chemotherapy. By enabling precise targeting of cancerous cells, these platforms have the potential to mitigate adverse effects on surrounding healthy tissues, thus encouraging the development of innovative diagnostic and therapeutic strategies for oral cancer.

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.

AgNPs-Modified Polylactic Acid Microneedles: Preparation and In Vivo/In Vitro Antimicrobial Studies

OBJECTIVE

To prepare polylactic acid microneedles (PLAMNs) with sustained antibacterial effect to avoid skin infection caused by traditional MNs-based biosensors.

METHODS

Silver nanoparticles (AgNPs) were synthesized using an in-situ reduction process with polydopamine (PDA). PLAMNs were fabricated using the hot-melt method. A series of pressure tests and puncture experiments were conducted to confirm the physicochemical properties of PLAMNs. Then AgNPs were modified on the surface of PLAMNs through in-situ reduction of PDA, resulting in the formation of PLAMNs@PDA-AgNPs. The in vitro antibacterial efficacy of PLAMNs@PDA-AgNPs was evaluated using agar diffusion assays and bacterial liquid co-culture approach. Wound healing and simulated long-term application were performed to assess the in vivo antibacterial effectiveness of PLAMNs@PDA-AgNPs.

RESULTS

The MNs array comprised 169 tiny needle tips in pyramidal rows. Strength and puncture tests confirmed a 100% puncture success rate for PLAMNs on isolated rat skin and tin foil. SEM analysis revealed the integrity of PLAMNs@PDA-AgNPs with the formation of new surface substances. EDS analysis indicated the presence of silver elements on the surface of PLAMNs@PDA-AgNPs, with a content of 14.44%. Transepidermal water loss (TEWL) testing demonstrated the rapid healing of micro-pores created by PLAMNs@PDA-AgNPs, indicating their safety. Both in vitro and in vivo tests confirmed antibacterial efficacy of PLAMNs@PDA-AgNPs.

CONCLUSIONS

In conclusion, the sustained antibacterial activity exhibited by PLAMNs@PDA-AgNPs offers a promising solution for addressing skin infections associated with MN applications, especially when compared to traditional MN-based biosensors. This advancement offers significant potential for the field of MN technology.

Advances in Formulations of Microneedle System for Rheumatoid Arthritis Treatment

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic joint inflammation, eventually leading to severe disability and premature death. At present, the treatment of RA is mainly to reduce inflammation, swelling, and pain. Commonly used drugs are non-steroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, and disease-modifying anti-rheumatic drugs (DMARDs). These drugs lack specificity and require long-term, high-dose administration, which can cause serious adverse effects. In addition, the oral, intravenous, and intra-articular injections will reduce patient compliance, resulting in high cost and low bioavailability. Due to these limitations, microneedles (MNs) have emerged as a new strategy to efficiently localize the drugs in inflamed joints for the treatment of RA. MNs can overcome the cuticle barrier of the skin without stimulating nerves and blood vessels. Which can increase patient compliance, improve bioavailability, and avoid systemic circulation. This review summarizes and evaluates the application of MNs in RA, especially dissolving MNs (DMNs). We encourage the use of MNs to treat RA, by describing the general properties of MNs, materials, preparation technology, drug release mechanism, and advantages. Furthermore, we discussed the biological safety, development prospects, and future challenges of MNs, hoping to provide a new strategy for the treatment of RA.

Implantable Nerve Conduit Made of a Self-Powered Microneedle Patch for Sciatic Nerve Repair

Peripheral nerve defects, particularly those of a larger size, pose a significant challenge in clinical practice due to their limited regenerative capacity. To tackle this challenge, an advanced self-powered enzyme-linked microneedle (MN) nerve conduit is designed and fabricated. This innovative conduit is composed of anodic and cathodic MN arrays, which contain glucose oxidase (GOx) and horseradish peroxidase (HRP) encapsulated in ZIF-8 nanoparticles, respectively. Through an enzymatic cascade reaction, this MN nerve conduit generates microcurrents that stimulate the regeneration of muscles, blood vessels, and nerve fibers innervated by the sciatic nerve, eventually accelerating the repair of sciatic nerve injury. It is clear that this self-powered MN nerve conduit will revolutionize traditional treatment methods for sciatic nerve injury and find widespread application in the field of nerve tissue repair.

Transdermal drug delivery via microneedles for musculoskeletal systems

As the population is ageing and lifestyle is changing, the prevalence of musculoskeletal (MSK) disorders is gradually increasing with each passing year, posing a serious threat to the health and quality of the public, especially the elderly. However, currently prevalent treatments for MSK disorders, mainly administered orally and by injection, are not targeted to the specific lesion, resulting in low efficacy along with a series of local and systemic adverse effects. Microneedle (MN) patches loaded with micron-sized needle array, combining the advantages of oral administration and local injection, have become a potentially novel strategy for the administration and treatment of MSK diseases. In this review, we briefly introduce the basics of MNs and focus on the main characteristics of the MSK systems and various types of MN-based transdermal drug delivery (TDD) systems. We emphasize the progress and broad applications of MN-based transdermal drug delivery (TDD) for MSK systems, including osteoporosis, nutritional rickets and some other typical types of arthritis and muscular damage, and in closing summarize the future prospects and challenges of MNs application.

Poly(2-Hydroxyethyl Methacrylate) Hydrogel-Based Microneedles for Metformin Release

The release of metformin, a drug used in the treatment of cancer and diabetes, from poly(2-hydroxyethyl methacrylate), pHEMA, hydrogel-based microneedle patches is demonstrated in vitro. Tuning the composition of the pHEMA hydrogels enables preparation of robust microneedle patches with mechanical properties such that they would penetrate skin (insertion force of a single microneedle to be ≈40 N). Swelling experiments conducted at 20, 35, and 60 °C show temperature-dependent degrees of swelling and diffusion kinetics. Drug release from the pHEMA hydrogel-based microneedles is fitted to various models (e.g., zero order, first order, second order). Such pHEMA microneedles have potential application for transdermal delivery of metformin for the treatment of aging, cancer, diabetes, etc.

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

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

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

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

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.

Rapidly Dissolving Microneedles for the Delivery of Steroid-Loaded Nanoparticles Intended for the Treatment of Inflammatory Skin Diseases

Drug delivery through the skin has immense advantages compared to other routes of administration and offers an optimal way to treat inflammatory skin diseases, where corticosteroids are the cornerstone of topical therapy. Still, their therapeutic efficiency is limited due to inadequate skin permeability, potential side effects, and reduced patient compliance. To overcome these drawbacks, we propose a drug delivery system consisting of dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) incorporated in sodium alginate (SA) microneedles (MNs) as a minimally invasive dosage form for controlled drug release. Drug-loaded PLGA NPs were prepared by a nanoprecipitation method with a high encapsulation yield. They exhibited a controlled release pattern over 120 h. A modified vacuum-deposition micromolding method was used to load the obtained DEX-NPs into the tips of dissolving MNs. The NP-MNs showed improved insertion capabilities into the skin-simulant parafilm model and enhanced mechanical strength when tested against different static forces compared to their counterparts (SA-MNs). The results of an MN dissolution study following application to ex vivo chicken skin and agarose gel indicate that the NP-loaded segments of MNs dissolve within 15 s, in which the NPs are released into the skin. Taken together, the incorporation of DEX-NPs into SA-MNs could be a promising approach to bypass the limitations of conventional topical treatment of skin diseases, allowing for self-administration, increased patient compliance, and controlled drug release.

Modeling of Microneedle Arrays in Transdermal Drug Delivery Applications

The use of computational tools for the development of technologies in fields such as medicine and engineering has facilitated the process of designing new components and devices for these areas. In this work, two proposals focused on a hollow microneedle array (MNA) for the administration of an analgesic drug are shown and evaluated by means of a computational fluid dynamics (CFD) simulation distributed in three stages. In the first stage, the behavior of lidocaine through the MNA was evaluated as a workflow. Then, the possible entry of the drug into the organism, which was established as a porous aqueous medium, was modeled. Finally, a joint simulation was performed to understand the general behavior in the interaction between the outflow of an MNA and the body to which lidocaine is administered. The input parameters to the simulation were set at a velocity of 0.05 m∙s^-1, at a pressure of 2000 Pa, the dominant behavior was defined as laminar flow, and a resistive pressure at the inlet of 400 Pa. Our results indicate that the vertical flow exhibits a better fluid distribution across the MNAs and favorable infiltration behavior, representing better delivery of the analgesic to the skin capillaries.

Transdermal delivery of colchicine using dissolvable microneedle arrays for the treatment of acute gout in a rat model

Colchicine (Col) is used to prevent and treat acute gout flare; however, its therapeutic use is strictly limited owing to severe gastrointestinal side effects after oral administration. Therefore, we developed a dissolvable Col-loaded microneedle (MN) with hyaluronic acid to deliver Col via the transdermal route. We studied the preparation, mechanical properties, skin insertion, skin irritation, drug content, and transdermal release of the Col-loaded MN. The pharmacokinetics of Col after Col-loaded MN application were compared with those of Col solution gavage over 24 h. Knee joint edema evaluation and the hindfoot mechanical threshold test were conducted to determine the pharmacodynamic profile. The dissolvable Col-loaded MN possessed sufficient mechanical strength to penetrate the skin and release the loaded drug. No skin irritation was observed for 3 days after application. We found that 3.36-fold more Col contained in MNs was delivered through the skin compared with that in gel in vitro, and moderate relative bioavailability in vivo. The Col-loaded MN significantly relieved swollen knee joints and mechanical hypernociception in an acute gout model in rats. The dissolvable Col-loaded MN array reduced inflammation and pain via topical administration when acute gout occurred. Reducing the gastrointestinal side effects of Col-loaded MNs is expected to optimize the therapeutic effects of Col and improve patient compliance.

Polymeric Biomaterials for Topical Drug Delivery in the Oral Cavity: Advances on Devices and Manufacturing Technologies

There are several routes of drug administration, and each one has advantages and limitations. In the case of the topical application in the oral cavity, comprising the buccal, sublingual, palatal, and gingival regions, the advantage is that it is painless, non-invasive, allows easy application of the formulation, and it is capable of avoiding the need of drug swallowing by the patient, a matter of relevance for children and the elderly. Another advantage is the high permeability of the oral mucosa, which may deliver very high amounts of medication rapidly to the bloodstream without significant damage to the stomach. This route also allows the local treatment of lesions that affect the oral cavity, as an alternative to systemic approaches involving injection-based methods and oral medications that require drug swallowing. Thus, this drug delivery route has been arousing great interest in the pharmaceutical industry. This review aims to condense information on the types of biomaterials and polymers used for this functionality, as well as on production methods and market perspectives of this topical drug delivery route.

Improved Topical Drug Delivery: Role of Permeation Enhancers and Advanced Approaches

The delivery of drugs via transdermal routes is an attractive approach due to ease of administration, bypassing of the first-pass metabolism, and the large skin surface area. However, a major drawback is an inability to surmount the skin's stratum corneum (SC) layer. Therefore, techniques reversibly modifying the stratum corneum have been a classical approach. Surmounting the significant barrier properties of the skin in a well-organised, momentary, and harmless approach is still challenging. Chemical permeation enhancers (CPEs) with higher activity are associated with certain side effects restricting their advancement in transdermal drug delivery. Furthermore, complexity in the interaction of CPEs with the skin has led to difficulty in elucidating the mechanism of action. Nevertheless, CPEs-aided transdermal drug delivery will accomplish its full potential due to advancements in analytical techniques, synthetic chemistry, and combinatorial studies. This review focused on techniques such as drug-vehicle interaction, vesicles and their analogues, and novel CPEs such as lipid synthesis inhibitors (LSIs), cell-penetrating peptides (CPPs), and ionic liquids (ILs). In addition, different types of microneedles, including 3D-printed microneedles, have been focused on in this review.

3D-Printed Microarray Patches for Transdermal Applications

The intradermal (ID) space has been actively explored as a means for drug delivery and diagnostics that is minimally invasive. Microneedles or microneedle patches or microarray patches (MAPs) are comprised of a series of micrometer-sized projections that can painlessly puncture the skin and access the epidermal/dermal layer. MAPs have failed to reach their full potential because many of these platforms rely on dated lithographic manufacturing processes or molding processes that are not easily scalable and hinder innovative designs of MAP geometries that can be achieved. The DeSimone Laboratory has recently developed a high-resolution continuous liquid interface production (CLIP) 3D printing technology. This 3D printer uses light and oxygen to enable a continuous, noncontact polymerization dead zone at the build surface, allowing for rapid production of MAPs with precise and tunable geometries. Using this tool, we are now able to produce new classes of lattice MAPs (L-MAPs) and dynamic MAPs (D-MAPs) that can deliver both solid state and liquid cargos and are also capable of sampling interstitial fluid. Herein, we will explore how additive manufacturing can revolutionize MAP development and open new doors for minimally invasive drug delivery and diagnostic platforms.

Microneedle-based ocular drug delivery systems - recent advances and challenges

Eye diseases and injuries constitute a significant clinical problem worldwide. Safe and effective delivery of drugs to the eye is challenging mostly due to the presence of ocular barriers and clearance mechanisms. In everyday practice, the traditional eye drops, gels and ointments are most often used. Unfortunately, they are usually not well tolerated by patients due to the need for frequent use as well as the discomfort during application. Therefore, novel drug delivery systems with improved biopharmaceutical properties are a subject of ongoing scientific investigations. Due to the developments in microtechnology, in recent years, there has been a remarkable advance in the development of microneedle-based systems as an alternative, non-invasive form for administering drugs to the eye. This review summarizes the latest achievements in the field of obtaining microneedle ocular patches. In the manuscript, the most important manufacturing technologies, microneedle classification, and the research studies related to ophthalmic application of microneedles are presented. Finally, the most important advantages and drawbacks, as well as potential challenges related to the unique anatomy and physiology of the eye are summarized and discussed.

Transdermal Maltose-Based Microneedle Patch as Adjunct to Enhance Topical Anesthetic before Intravenous Cannulation of Pediatric Thalassemic Patients Receiving Blood Transfusion: A Randomized Controlled Trial Protocol

Intravenous cannulation is experientially traumatic to children. To minimize this, EMLA^® is applied on the would-be-cannulated area before IV cannula insertion. However, the time to achieve its maximum efficacy may be affected due to incomplete cutaneous absorption and the duration of application. The latter may be a limiting factor in a busy healthcare facility. The usage of dissolvable maltose microneedles may circumvent this problem by introducing micropores that will facilitate EMLA^® absorption. A randomized phase II cross-over trial will be conducted to compare the Visual Analogue Scale (VAS) pain scores and skin conductance algesimeter index between 4 different interventions (1 fingertip unit (FTU) of EMLA^® with microneedle patch for 30 min before cannulation; 0.5 FTU of EMLA^® with microneedle patch for 30 min; 1 FTU of EMLA^® with microneedle for 15 min; 1 FTU of EMLA^® with sham patch for 30 min). A total of 26 pediatric patients with thalassemia aged between 6 and 18 years old and requiring blood transfusion will be recruited in this trial. During the visits, the VAS scores and skin conductance algesimeter index at venous cannulation will be obtained using the VAS rulers and PainMonitor™ machine, respectively. The trial will commence in August 2021 and is anticipated to end by August 2022.

Design and Prototype Fabrication of a Cost-Effective Microneedle Drug Delivery Apparatus Using Fused Filament Fabrication, Liquid Crystal Display and Semi-Solid Extrusion 3D Printing Technologies

The current study describes the design of a cost-effective drug delivery apparatus that can be manufactured, assembled, and utilized as easily and quickly as possible, minimizing the time and expense of the supply chain. This apparatus could become a realistic alternative method of providing a vaccine or drug in harsh circumstances, including humanitarian disasters or a lack of medical and nursing staff, conditions that are frequently observed in developing countries. Simultaneously, with the use of microneedles (MNs), the apparatus can benefit from the numerous advantages offered by them during administration. The hollow microneedles in particular are internally perforated and are capable of delivering the active substance to the skin. The apparatus was designed with appropriate details in computer aided design software, and various 3D printing technologies were utilized in order to fabricate the prototype. The parts that required minimum accuracy, such as the main body of the apparatus, were fabricated with fused filament fabrication. The internal parts and the hollow microneedles were fabricated with liquid crystal display, and the substance for the drug loading carrier, which was an alginate gel cylinder, was fabricated with semi-solid extrusion 3D printing.

Advances in biomaterials for the treatment of retinoblastoma

Retinoblastoma is the most common primary intraocular malignancy in children. Although traditional chemotherapy has shown some success in retinoblastoma management, there are several shortcomings to this approach, including inadequate pharmacokinetic parameters, multidrug resistance, low therapeutic efficiency, nonspecific targeting, and the need for adjuvant therapy, among others. The revolutionary developments in biomaterials for drug delivery have enabled breakthroughs in cancer management. Today, biomaterials are playing a crucial role in developing more efficacious retinoblastoma treatments. The key goal in the evolution of drug delivery biomaterials for retinoblastoma therapy is to resolve delivery-associated obstacles and lower nonlocal exposure while ameliorating certain adverse effects. In this review, we will first delve into the historical perspective of retinoblastoma with a focus on the classical treatments currently used in clinics to enhance patients' quality of life and survival rate. As we move along, we will discuss biomaterials for drug delivery applications. Various aspects of biomaterials for drug delivery will be dissected, including their features and recent advances. In accordance with the current advances in biomaterials, we will deliver a synopsis on the novel chemotherapeutic drug delivery strategies and evaluate these approaches to gain new insights into retinoblastoma treatment.

Polymer nanotherapeutics: A versatile platform for effective rheumatoid arthritis therapy

Rheumatoid arthritis is an aggressive and severely debilitating disorder that is characterized by joint pain and cartilage damage. It restricts mobility in patients, leaving them unable to carry out simple tasks. RA presents itself with severe lasting pain, swelling and stiffness in the joints and may cause permanent disability in patients. Treatment regimens currently employed for rheumatoid arthritis revolve around keeping clinical symptoms like joint pain, inflammation, swelling and stiffness at bay. The current therapeutic interventions in rheumatoid arthritis involve the use of non-steroidal anti-inflammatory drugs, glucocorticoids, disease-modifying anti-rheumatic drugs and newer biological drugs that are engineered for inhibiting the expression of pro-inflammatory mediators. These conventional drugs are plagued with severe adverse effects because of their higher systemic distribution, lack of specificity and higher doses. Oral, intra-articular, and intravenous routes are routinely used for drug delivery which is associated with decreased patient compliance, high cost, poor bioavailability and rapid systemic clearance. All these drawbacks have enticed researchers to create novel strategies for drug delivery, the main approach being nanocarrier-based systems. In this article, we aim to consolidate the remarkable contributions of polymeric carrier systems including microneedle technology and smart trigger-responsive polymeric carriers in the management of rheumatoid arthritis along with its detailed pathophysiology. This review also briefly describes the safety and regulatory aspects of polymer therapeutics.

Recent Advancements in Microneedle Technology for Multifaceted Biomedical Applications

Microneedle (MNs) technology is a recent advancement in biomedical science across the globe. The current limitations of drug delivery, like poor absorption, low bioavailability, inadequate skin permeation, and poor biodistribution, can be overcome by MN-based drug delivery. Nanotechnology made significant changes in fabrication techniques for microneedles (MNs) and design shifted from conventional to novel, using various types of natural and synthetic materials and their combinations. Nowadays, MNs technology has gained popularity worldwide in biomedical research and drug delivery technology due to its multifaceted and broad-spectrum applications. This review broadly discusses MN's types, fabrication methods, composition, characterization, applications, recent advancements, and global intellectual scenarios.

Potential of Microneedle Systems for COVID-19 Vaccination: Current Trends and Challenges

To prevent the coronavirus disease 2019 (COVID-19) pandemic and aid restoration to prepandemic normality, global mass vaccination is urgently needed. Inducing herd immunity through mass vaccination has proven to be a highly effective strategy for preventing the spread of many infectious diseases, which protects the most vulnerable population groups that are unable to develop immunity, such as people with immunodeficiencies or weakened immune systems due to underlying medical or debilitating conditions. In achieving global outreach, the maintenance of the vaccine potency, transportation, and needle waste generation become major issues. Moreover, needle phobia and vaccine hesitancy act as hurdles to successful mass vaccination. The use of dissolvable microneedles for COVID-19 vaccination could act as a major paradigm shift in attaining the desired goal to vaccinate billions in the shortest time possible. In addressing these points, we discuss the potential of the use of dissolvable microneedles for COVID-19 vaccination based on the current literature.

Microneedle-Based Vaccine Delivery: Review of an Emerging Technology

Vaccination has produced a great improvement to the global health by decreasing/eradicating many infectious diseases responsible for significant morbidity and mortality. Thanks to vaccines, many infections affecting childhood have been greatly decreased or even eradicated (smallpox, measles, and polio). That is why great efforts are made to achieve mass vaccination against COVID-19. However, developed vaccines face many challenges with regard to their safety and stability. Moreover, needle phobia could prevent a significant proportion of the population from receiving vaccines. In this context, microneedles (MNs) could potentially present a solution to address these challenges. MNs represent single dose administration systems that do not need reconstitution or cold-chain storage. Being self-administered, pain-free, and capable of producing superior immunogenicity makes them a more attractive alternative. This review explores microneedles’ types, safety, and efficacy in vaccine delivery. Preclinical and clinical studies for microneedle-based vaccines are discussed and patent examples are included.

Emerging trends in microneedle-based drug delivery strategies for the treatment of rheumatoid arthritis

INTRODUCTION

The current drug therapies for treating Rheumatoid Arthritis (RA) include NSAIDs, DMARDs, or biological products designed to mitigate the symptoms of the disease. These therapies with conventional delivery systems possess limitations such as lack of selectivity and adverse effects in the extra-articular tissues. Microneedles-based transdermal drug delivery gained huge attention that can overcome the limitations associated with conventional preparations.

AREAS COVERED

This review aims to provide detailed information on types of Microneedles (MNs) and their usage in drug delivery for the management of Rheumatoid Arthritis. In addition, it also provides evidence for the effective use of MNs in RA treatment. Various types of MNs, their regulatory status, clinical trials and patents are also compiled in this review.

EXPERT OPINION

Microneedles are small patch-like structures consisting of needles in micron range arranged in array-like structure, used to manage drugs designed to be given via transdermal route. Microneedles provide painless delivery, fast onset of action, bypass the first-pass metabolism and be easily self-administered. In the case of RA treatment, which requires a long-term application of drugs, MNs is a new and emerging way to ease the symptoms of RA.

Mapping the Mechanical and Immunological Profiles of Polymeric Microneedles to Enable Vaccine and Immunotherapy Applications

Biomaterials hold great promise for vaccines and immunotherapy. One emerging biomaterials technology is microneedle (MNs) delivery. MNs are arrays of micrometer-sized needles that are painless and efficiently deliver cargo to the specialized immunological niche of the skin. MNs typically do not require cold storage and eliminate medical sharps. Nearly all materials exhibit intrinsic properties that can bias immune responses toward either pro-immune or inhibitory effects. Thus, because MNs are fabricated from degradable polymers to enable cargo loading and release, understanding the immunological profiles of these matrices is essential to enable new MN vaccines and immunotherapies. Additionally, understanding the mechanical properties is important because MNs must penetrate the skin and conform to a variety of skin or tissue geometries. Here we fabricated MNs from important polymer classes – including extracellular matrix biopolymers, naturally-derived polymers, and synthetic polymers – with both high- and low-molecular-weights (MW). We then characterized the mechanical properties and intrinsic immunological properties of these designs. The library of polymer MNs exhibited diverse mechanical properties, while causing only modest changes in innate signaling and antigen-specific T cell proliferation. These data help inform the selection of MN substrates based on the mechanical and immunological requirements needed for a specific vaccine or immunotherapy application.