Rapid microneedle fabrication by heating and photolithography

Dissolving microneedles: Drug delivery and disease treatment

Traditional transdermal drug delivery methods are often plagued by technical inefficiencies, limited absorption, and the potential for adverse reactions. In contrast, dissolving microneedles (DMNs) offer a novel approach to transdermal drug delivery by effectively merging the benefits of subcutaneous injection with those of conventional transdermal methods. These microneedles dissolve completely within the body, releasing the encapsulated antigen without leaving any sharp remnants. Furthermore, DMNs overcome the limitations of traditional transdermal patches, which are restricted to delivering only small molecule drugs. By facilitating the efficient transdermal absorption of large molecules, DMNs enable precise and painless disease treatment. With advantages such as effective delivery, safety, controllable administration, DMNs hold significant promise in the fields of disease treatment and drug delivery. This article explores the substrate materials, preparation techniques, characterization methods, and current applications of DMNs. We also discuss the current challenges and obstacles faced by DMNs. Finally, we outline potential future research directions for DMNs, aiming to provide a theoretical reference for researchers involved in their preparation and application.

Revolutionizing biosensing with wearable microneedle patches: innovations and applications

Wearable microneedle (MN) patches have emerged as a transformative platform for biosensing, offering a minimally invasive and user-friendly approach to real-time health monitoring and disease diagnosis. Primarily designed to access interstitial fluid (ISF) through shallow skin penetration, MNs enable precise and continuous sampling of biomarkers such as glucose, lactate, and electrolytes. Additionally, recent innovations have integrated MN arrays with microfluidic and porous structures to support sweat-based analysis, where MNs act as structural or functional components in hybrid wearable systems. This review explores the design, fabrication, and functional integration of MNs into wearable devices, highlighting advances in multi-analyte detection, wireless data transmission, and self-powered sensing. Challenges related to material biocompatibility, sensor stability, scalability, and user variability are addressed, alongside emerging opportunities in microfluidics, artificial intelligence, and soft materials. Overall, MN-based biosensing platforms are poised to redefine personalized healthcare by enabling dynamic, decentralized, and accessible health monitoring.

Beyond the Needle: Innovative Microneedle-Based Transdermal Vaccination

Vaccination represents a critical preventive strategy in the current global healthcare system, serving as an indispensable intervention against diverse pathogenic threats. Although conventional immunization relies predominantly on hypodermic needle-based administration, this method carries substantial limitations, including needle-associated fear, bloodborne pathogen transmission risks, occupational injuries among healthcare workers, waste management issues, and dependence on trained medical personnel. Microneedle technology has emerged as an innovative vaccine delivery system, offering convenient, effective, and minimally invasive administration. These microscale needle devices facilitate targeted antigen delivery to epidermal and dermal tissues, where abundant populations of antigen-presenting cells, specifically Langerhans and dermal dendritic cells, provide robust immunological responses. Multiple research groups have extensively investigated microneedle-based vaccination strategies. This transdermal delivery technique offers several advantages, notably circumventing cold-chain requirements and enabling self-administration. Numerous preclinical investigations and clinical trials have demonstrated the safety profile, immunogenicity, and patient acceptance of microneedle-mediated vaccine delivery across diverse immunization applications. This comprehensive review examines the fundamental aspects of microneedle-based immunization, including vaccination principles, transcutaneous immunization strategies, and microneedle-based transdermal delivery-including classifications, advantages, and barriers. Furthermore, this review addresses critical technical considerations, such as treatment efficacy, application methodologies, wear duration, dimensional optimization, manufacturing processes, regulatory frameworks, and sustainability considerations, followed by an analysis of the future perspective of this technology.

Therapeutic Potential of Microneedle Assisted Drug Delivery for Wound Healing: Current State of the Art, Challenges, and Future Perspective

Microneedles (MNs) appear as a transformative and minimally invasive platform for transdermal drug delivery, representing a highly promising strategy in wound healing therapeutics. This technology, entailing the fabrication of micron-scale needle arrays, enables the targeted and efficient delivery of bioactive agents into the epidermal and dermal layers without inducing significant pain or discomfort. The precise penetration of MNs facilitates localized and sustained drug release, which significantly enhances tissue regeneration and accelerates wound closure. Furthermore, MNs can be engineered to encapsulate essential bioactive compounds, including antimicrobial agents, growth factors, and stem cells, which are critical for modulating the wound healing cascade and mitigating infection risk. The biodegradable nature of these MNs obviates the need for device removal, rendering them particularly advantageous in the management of chronic wounds such as diabetic ulcers and pressure sores. The integration of nanotechnology within MNs further augments their drug-loading capacity, stability, and controlled-release kinetics, offering a sophisticated therapeutic modality. This cutting-edge approach has the potential to redefine wound care by optimizing therapeutic efficacy, reducing adverse effects, and enhancing patient adherence. As MN technology advances, its application in wound healing exemplifies a dynamic frontier within biomedical engineering and regenerative medicine.

Formulation, Characterization, and in vivo Immunogenicity of Heat-Stabilized Dissolvable Microneedles Containing a Novel VLP Vaccine

Since its introduction, vaccination has heavily improved health outcomes. However, implementing vaccination efforts can be challenging, particularly in low and middle-income countries with warmer climates. Microneedle technology has been developed for its simple and relatively painless applications of vaccines. However, no microneedle vaccine has yet been approved by the FDA. A few hurdles must be overcome, including the need to evaluate the safety and biocompatibility of the polymer used to fabricate these microneedles. Additionally, it is important to demonstrate reliable immune responses comparable to or better than those achieved through traditional administration routes. Scalability in manufacturing and the ability to maintain vaccine potency during storage and transportation are also critical factors. In this study, we developed vaccine-loaded dissolvable microneedles that showed preclinical immunogenicity after storage in extreme conditions. We developed our microneedles using the conventional micromolding technique with polyacrylic acid (PAA) polymer, incorporating a novel virus-like particle (VLP) vaccine targeting arboviruses. We performed characterization studies on these microneedles to assess needle sharpness, skin insertion force, and VLP integrity. We also investigated the thermostability of the vaccine after storing the microneedles at elevated temperatures for approximately 140 days. Finally, we evaluated the immunogenicity of this vaccine in mice, comparing transdermal (microneedle) with intramuscular (hypodermic needle) administration. We successfully fabricated and characterized VLP-loaded microneedles that could penetrate the skin and maintain vaccine integrity even after exposure to extreme storage conditions. These microneedles also elicited robust and long-lasting antibody responses similar to those achieved with intramuscular administration.

Advancements in Materials for 3D-Printed Microneedle Arrays: Enhancing Performance and Biocompatibility

The rapid advancement of 3D printing technology has revolutionized the fabrication of microneedle arrays (MNAs), which hold great promise in biomedical applications such as drug delivery, diagnostics, and therapeutic interventions. This review uniquely explores advanced materials used in the production of 3D-printed MNAs, including photopolymer resins, biocompatible materials, and composite resins, designed to improve mechanical properties, biocompatibility, and functional performance. Additionally, it introduces emerging trends such as 4D printing for programmable MNAs. By analyzing recent innovations, this review identifies critical challenges and proposes future directions to advance the field of 3D-printed MNAs. Unlike previous reviews, this paper emphasizes the integration of innovative materials with advanced 3D printing techniques to enhance both the performance and sustainability of MNAs.

3D bioprinted microneedles: merging drug delivery and scaffold science for tissue-specific applications

INTRODUCTION

Three-Dimensional (3D) microneedles have recently gained significant attention due to their versatility, biocompatibility, enhanced permeation, and predictable behavior. The incorporation of biological agents into these 3D constructs has advanced the traditional microneedle into an effective platform for wide-ranging applications.

AREAS COVERED

This review discusses the current state of microneedle fabrication as well as the developed 3D printed microneedles incorporating labile pharmaceutical agents and biological materials for potential biomedical applications. The mechanical and processing considerations for the preparation of microneedles and the barriers to effective 3D printing of microneedle constructs have additionally been reviewed along with their therapeutic applications and potential for tissue engineering and regenerative applications. Additionally, the regulatory considerations for microneedle approval have been discussed as well as the current clinical trial and patent landscapes.

EXPERT OPINION

The fields of tissue engineering and regenerative medicine are evolving at a significant pace with researchers constantly focused on incorporating advanced manufacturing techniques for the development of versatile, complex, and biologically specific platforms. 3D bioprinted microneedles, fabricated using conventional 3D printing techniques, have resultantly provided an alternative to 2D bioscaffolds through the incorporation of biological materials within 3D constructs while providing further mechanical stability, increased bioactive permeation and improved innervation into surrounding tissues. This advancement therefore potentially allows for a more effective biomimetic construct with improved tissue-specific cellular growth for the enhanced treatment of physiological conditions requiring tissue regeneration and replacement.

Remote-Controlled Sensing and Drug Delivery via 3D-Printed Hollow Microneedles

Remote health monitoring and treatment serve as critical drivers for advancing health equity, bridging geographical and socioeconomic disparities, ensuring equitable access to quality healthcare for those in underserved or remote regions. By democratizing healthcare, this approach offers timely interventions, continuous monitoring, and personalized care independent of one's location or socioeconomic status, thereby striving for an equitable distribution of health resources and outcomes. Meanwhile, microneedle arrays (MNAs), revolutionize painless and minimally invasive access to interstitial fluid for drug delivery and diagnostics. This paper introduces an integrated theranostic MNA system employing an array of colorimetric sensors to quantitatively measure -pH, glucose, and lactate, alongside a remotely-triggered system enabling on-demand drug delivery. Integration of an ultrasonic atomizer streamlines the drug delivery, facilitating rapid, pumpless, and point-of-care drug delivery, enhancing system portability while reducing complexities. An accompanying smartphone application interfaces the sensing and drug delivery components. Demonstrated capabilities include detecting pH (3 to 8), glucose (up to 16 mm), and lactate (up to 1.6 mm), showcasing on-demand drug delivery, and assessing delivery system performance via a scratch assay. This innovative approach confronts drug delivery challenges, particularly in managing chronic diseases requiring long-term treatment, while also offering avenues for non-invasive health monitoring through microneedle-based sensors.

Nanocomposite hydrogel microneedles: a theranostic toolbox for personalized medicine

Due to the severity and high prevalence of cancer, as well as its complex pathological condition, new strategies for cancer treatment and diagnostics are required. As such, it is important to design a toolbox that integrates multiple functions on a single smart platform. Theranostic hydrogels offer an innovative and personalized method to tackle cancer while also considering patient comfort, thereby facilitating future implementation and translation to the clinic. In terms of theranostic systems used in cancer therapy, nanoparticles are widely used as diagnostic and therapeutic tools. Nanoparticles can achieve systemic circulation, evade host defenses, and deliver drugs and signaling agents at the targeted site, to diagnose and treat the disease at a cellular and molecular level. In this context, hydrogel microneedles have a high potential for multifunctional operation in medical devices, while avoiding the complications associated with the systemic delivery of therapeutics. Compared with oral administration and subcutaneous injection, microneedles offer advantages such as better patient compliance, faster onset of action, and improved permeability and efficacy. In addition, they comprise highly biocompatible polymers with excellent degradability and tunable properties. Nanoparticles and microneedles thus offer the possibility to expand the theranostic potential through combined synergistic use of their respective features. We review herein recent advances concerning processing methods and material requirements within the realm of hydrogel microneedles as theranostic platforms, various approaches toward cancer therapy, and the incorporation of nanoparticles for added functionality.

Anti-Nociceptive Effect of Sufentanil Polymeric Dissolving Microneedle on Male Mice by Hot Plate Technique

Background

Despite the widespread use of opioids to manage severe pain, its systemic administration results in side effects. Among the subcutaneous and transdermal drug delivery systems developed to deal with adverse effects, microneedles have drawn attention due to their rapid action, high drug bioavailability, and improved permeability. Sufentanil (SUF) is an effective injectable opioid for treating severe pain. In this study, we investigated the analgesic effects of SUF using dissolvable microneedles.

Methods

SUF polymeric dissolvable microneedles were constructed through the mold casting method and characterized by SEM and FTIR analysis. Its mechanical strength was also investigated using a texture analyzer. Fluorescence microscopy was applied in vitro to measure the penetration depth of microneedle arrays. Irritation and microchannel closure time, drug release profile, and hemocompatibility test were conducted for the validation of microneedle efficiency. Hot plate test was also used to investigate the analgesic effect of microneedle in an animal model.

Results

Local administration of SUF via dissolving microneedles had an effective analgesic impact. One hour after administration, there was no significant difference between the subcutaneous and the microneedle groups, and the mechanical properties were within acceptable limits.

Conclusion

Microneedling is an effective strategy in immediate pain relief compared to the traditional methods.

Polymeric Microneedles for Health Care Monitoring: An Emerging Trend

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

Microneedles Based on a Biodegradable Polymer-Hyaluronic Acid

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

Development of stretchable microneedle arrays via single-step digital light-processing printing for delivery of rhodamine B into skin tissue

This paper introduces a novel approach for loading and releasing Rhodamine B (RhB) into the skin using minimally-invasive microneedle technology developed through digital light-processing (DLP) printing. Notably, this process involves the direct 3D fabrication of rigid microneedle arrays affixed to a flexible patch, marking a pioneering application of DLP printing in this context. The stretchable and durable design of the microneedle substrate enables it to adapt to dynamic movements associated with human activities. Moreover, the microneedle features a pore on each side of the pyramid needle, effectively optimizing its drug-loading capabilities. Results indicate that the microneedle patch can withstand up to 50 % strain without failure and successfully penetrates rat skin. In vitro drug release profiles, conducted through artificial and rat skin, were observed over a 70 h period. This study establishes the potential of a simple manufacturing process for the creation of pore-designed microneedle arrays with a stretchable substrate, showcasing their viability in transdermal drug delivery applications.

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.

Dissolving and Swelling Hydrogel-Based Microneedles: An Overview of Their Materials, Fabrication, Characterization Methods, and Challenges

Polymeric hydrogels are a complex class of materials with one common feature-the ability to form three-dimensional networks capable of imbibing large amounts of water or biological fluids without being dissolved, acting as self-sustained containers for various purposes, including pharmaceutical and biomedical applications. Transdermal pharmaceutical microneedles are a pain-free drug delivery system that continues on the path to widespread adoption-regulatory guidelines are on the horizon, and investments in the field continue to grow annually. Recently, hydrogels have generated interest in the field of transdermal microneedles due to their tunable properties, allowing them to be exploited as delivery systems and extraction tools. As hydrogel microneedles are a new emerging technology, their fabrication faces various challenges that must be resolved for them to redeem themselves as a viable pharmaceutical option. This article discusses hydrogel microneedles from a material perspective, regardless of their mechanism of action. It cites the recent advances in their formulation, presents relevant fabrication and characterization methods, and discusses manufacturing and regulatory challenges facing these emerging technologies before their approval.

The Effect of 3D Printing Tilt Angle on the Penetration of 3D-Printed Microneedle Arrays

Microneedle arrays (MNAs) are emerging devices that are mainly used for drug delivery and diagnostic applications through the skin. Different methods have been used to fabricate MNAs. Recently developed fabrication methods based on 3D printing have many advantages compared to conventional fabrication methods, such as faster fabrication in one step and the ability to fabricate complex structures with precise control over their geometry, form, size, and mechanical and biological properties. Despite the several advantages that 3D printing offers for the fabrication of microneedles, their poor penetration capability into the skin should be improved. MNAs need a sharp needle tip to penetrate the skin barrier layer, the stratum corneum (SC). This article presents a method to improve the penetration of 3D-printed microneedle arrays by investigating the effect of the printing angle on the penetration force of MNAs. The penetration force needed to puncture the skin for MNAs fabricated using a commercial digital light processing (DLP) printer, with different printing tilt angles (0-60°), was measured in this study. The results showed that the minimum puncture force was achieved using a 45° printing tilt angle. Using this angle, the puncture force was reduced by 38% compared to MNAs printed with a tilting angle of 0°. We also identified that a tip angle of 120° resulted in the smallest penetration force needed to puncture the skin. The outcomes of the research show that the presented method can significantly improve the penetration capability of 3D-printed MNAs into the skin.

Three Dimensional Printing and Its Applications Focusing on Microneedles for Drug Delivery

Microneedles (MNs) are considered to be a novel smart injection system that causes significantly low skin invasion upon puncturing, due to the micron-sized dimensions that pierce into the skin painlessly. This allows transdermal delivery of numerous therapeutic molecules, such as insulin and vaccines. The fabrication of MNs is carried out through conventional old methods such as molding, as well as through newer and more sophisticated technologies, such as three-dimensional (3D) printing, which is considered to be a superior, more accurate, and more time- and production-efficient method than conventional methods. Three-dimensional printing is becoming an innovative method that is used in education through building intricate models, as well as being employed in the synthesis of fabrics, medical devices, medical implants, and orthoses/prostheses. Moreover, it has revolutionary applications in the pharmaceutical, cosmeceutical, and medical fields. Having the capacity to design patient-tailored devices according to their dimensions, along with specified dosage forms, has allowed 3D printing to stand out in the medical field. The different techniques of 3D printing allow for the production of many types of needles with different materials, such as hollow MNs and solid MNs. This review covers the benefits and drawbacks of 3D printing, methods used in 3D printing, types of 3D-printed MNs, characterization of 3D-printed MNs, general applications of 3D printing, and transdermal delivery using 3D-printed MNs.

Microneedles: An Emerging Vaccine Delivery Tool and a Prospective Solution to the Challenges of SARS-CoV-2 Mass Vaccination

Vaccination is an effective measure to prevent infectious diseases. Protective immunity is induced when the immune system is exposed to a vaccine formulation with appropriate immunogenicity. However, traditional injection vaccination is always accompanied by fear and severe pain. As an emerging vaccine delivery tool, microneedles overcome the problems associated with routine needle vaccination, which can effectively deliver vaccines rich in antigen-presenting cells (APCs) to the epidermis and dermis painlessly, inducing a strong immune response. In addition, microneedles have the advantages of avoiding cold chain storage and have the flexibility of self-operation, which can solve the logistics and delivery obstacles of vaccines, covering the vaccination of the special population more easily and conveniently. Examples include people in rural areas with restricted vaccine storage facilities and medical professionals, elderly and disabled people with limited mobility, infants and young children afraid of pain. Currently, in the late stage of fighting against COVID-19, the main task is to increase the coverage of vaccines, especially for special populations. To address this challenge, microneedle-based vaccines have great potential to increase global vaccination rates and save many lives. This review describes the current progress of microneedles as a vaccine delivery system and its prospects in achieving mass vaccination against SARS-CoV-2.

Design and fabrication of r-hirudin loaded dissolving microneedle patch for minimally invasive and long-term treatment of thromboembolic disease

Cardiovascular disease is the leading cause of global mortality, with anticoagulant therapy being the main prevention and treatment strategy. Recombinant hirudin (r-hirudin) is a direct thrombin inhibitor that can potentially prevent thrombosis via subcutaneous (SC) and intravenous (IV) administration, but there is a risk of haemorrhage via SC and IV. Thus, microneedle (MN) provides painless and sanitary alternatives to syringes and oral administration. However, the current technological process for the micro mould is complicated and expensive. The micro mould obtained via three-dimensional (3D) printing is expected to save time and cost, as well as provide a diverse range of MNs. Therefore, we explored a method for MNs array model production based on 3D printing and translate it to micro mould that can be used for fabrication of dissolving MNs patch. The results show that r-hirudin-loaded and hyaluronic acid (HA)-based MNs can achieve transdermal drug delivery and exhibit significant potential in the prevention of thromboembolic disease without bleeding in animal models. These results indicate that based on 3D printing technology, MNs combined with r-hirudin are expected to achieve diverse customizable MNs and thus realize personalized transdermal anticoagulant delivery for minimally invasive and long-term treatment of thrombotic disease.

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.

Enhancement of Skin Delivery of Drugs Using Proposome Depends on Drug Lipophilicity

The study aims to investigate the propylene glycol-based liposomes named 'proposomes' in enhancing skin permeation of drugs with different physicochemical properties. Ibuprofen, tofacitinib citrate, rhodamine B, and lidocaine were loaded into proposomes. These drug formulations were analyzed for particle size, zeta potential, polydispersity index, entrapment efficiency, and in vitro skin permeation. The confocal laser scanning microscopy was performed on skin treated with calcein and rhodamine B laden proposomes. The transdermal delivery relative to physicochemical properties of drugs such as logP, melting point, molecular weight, solubility, etc., were analyzed. We tested the safety of the proposomes using reconstructed human skin tissue equivalents, which were fabricated in-house. We also used human cadaver skin samples as a control. The proposomes had an average diameter of 128 to 148 nm. The drug's entrapment efficiencies were in the range of 42.9-52.7%, translating into the significant enhancement of drug permeation through the skin. The enhancement ratio was 1.4 to 4.0, and linearly correlated to logP, molecular weight, and melting point. Confocal imaging also showed higher skin permeation of calcein and rhodamine B in proposome than in solution. The proposome was found safe for skin application. The enhancement of skin delivery of drugs through proposomes was dependent on the lipophilicity of the drug. The entrapment efficiency was positively correlated with logP of the drug, which led to high drug absorption.

Enhanced skin retention and permeation of a novel peptide via structural modification, chemical enhancement, and microneedles

Hyperpigmentation is a common skin condition with serious psychosocial consequences. Decapeptide-12, a novel peptide, has been found to be safer than hydroquinone in reducing melanin content, with efficacy up to more than 50% upon 16 weeks of twice-daily treatment. However, the peptide suffers from limited transcutaneous penetration due to its hydrophilicity and high molecular weight. Therefore, decapeptide-12 was modified by adding a palmitate chain in an attempt to overcome this limitation. Molecular docking results showed that the two peptides exhibited similar biological activity towards tyrosinase. We also tested the effect of chemical penetration enhancers and microneedles to deliver the two peptides into and through skin, using an in vitro human skin permeation method. It was shown that the palm-peptide achieved the best skin retention owing to the increased lipophilicity. In addition, skin permeation of the palm-peptides was enhanced by the chemical skin penetration enhancers, namely, oleic acid and menthol. Skin permeation of the native peptide was enhanced by the microneedle patch but not the chemical skin penetration enhancers. Cutaneous absorption of the palm-peptides was estimated to have achieved its therapeutic concentration within skin. The combinatory approach of using molecular modification, chemical penetration enhancement, and microneedle patch proves to be useful to enhanceskin permeation of the peptides.

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

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

Fabrication, evaluation and applications of dissolving microneedles

In recent years, transdermal preparations have emerged as one of the most promising modes of administration. In particular, dissolving microneedles have attracted extensive attention because of their painlessness, safety, high delivery efficiency and easily operation for patients. This article mainly reviews the preparation methods, the types of matrix polymer materials, the content of dissolving microneedles performance testing, and the applications of dissolving microneedles. It is expected to lay a solid knowledge foundation for the in-depth study of the dissolving microneedles.

3D-printed microneedles in biomedical applications

Conventional needle technologies can be advanced with emerging nano- and micro-fabrication methods to fabricate microneedles. Nano-/micro-fabricated microneedles seek to mitigate penetration pain and tissue damage, as well as providing accurately controlled robust channels for administrating bioagents and collecting body fluids. Here, design and 3D printing strategies of microneedles are discussed with emerging applications in biomedical devices and healthcare technologies. 3D printing offers customization, cost-efficiency, a rapid turnaround time between design iterations, and enhanced accessibility. Increasing the printing resolution, the accuracy of the features, and the accessibility of low-cost raw printing materials have empowered 3D printing to be utilized for the fabrication of microneedle platforms. The development of 3D-printed microneedles has enabled the evolution of pain-free controlled release drug delivery systems, devices for extracting fluids from the cutaneous tissue, biosignal acquisition, and point-of-care diagnostic devices in personalized medicine.

Microneedles: Characteristics, Materials, Production Methods and Commercial Development

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

Engineering Microneedles for Therapy and Diagnosis: A Survey

Microneedle (MN) technology is a rising star in the point-of-care (POC) field, which has gained increasing attention from scientists and clinics. MN-based POC devices show great potential for detecting various analytes of clinical interests and transdermal drug delivery in a minimally invasive manner owing to MNs' micro-size sharp tips and ease of use. This review aims to go through the recent achievements in MN-based devices by investigating the selection of materials, fabrication techniques, classification, and application, respectively. We further highlight critical aspects of MN platforms for transdermal biofluids extraction, diagnosis, and drug delivery assisted disease therapy. Moreover, multifunctional MNs for stimulus-responsive drug delivery systems were discussed, which show incredible potential for accurate and efficient disease treatment in dynamic environments for a long period of time. In addition, we also discuss the remaining challenges and emerging trend of MN-based POC devices from the bench to the bedside.