Fabrication and characterization of novel microneedles made of a polystyrene solution

Protocol to fabricate wearable stretchable microneedle-based sensors

Creating highly stretchable and robust electrodes while retaining conductivity and stability is challenging. Furthermore, combining these elastic parts with rigid ones brings its own problems due to the discrepancy in firmness between the flexible patches and rigid constructions. Here, we present a protocol to create a stable, conductive, and flexible microneedle sensor patch. We describe steps for using polystyrene-block-polyisoprene-block-polystyrene with silver nanowires, besides fabricating rigid microneedles and combining them together using a thickness-gradient strategy. For complete details on the use and execution of this protocol, please refer to Zheng et al. (2022).1.

Wearable Clinic: From Microneedle-Based Sensors to Next-Generation Healthcare Platforms

The rapid development of wearable biosensing calls for next-generation devices that allow continuous, real-time, and painless monitoring of health status along with responsive medical treatment. Microneedles have exhibited great potential for the direct access of dermal interstitial fluid (ISF) in a minimally invasive manner. Recent studies of microneedle-based devices have evolved from conventional off-line detection to multiplexed, wireless, and integrated sensing. In this review, the classification and fabrication techniques of microneedles are first introduced, and then the representative examples of microneedles for transdermal monitoring with different sensing modalities are summarized. State-of-the-art advances in therapeutic and closed-loop systems are presented to formulate guidelines for the development of next-generation microneedle-based healthcare platforms. The potential challenges and prospects are discussed to pave a new avenue toward pragmatic applications in the real world.

Microneedles: materials, fabrication, and biomedical applications

The microneedles have attracted great interests for a wide range of transdermal biomedical applications, such as biosensing and drug delivery, due to the advantages of being painless, semi-invasive, and sustainable. The ongoing challenges are the materials and fabrication methods of the microneedles in order to obtain a specific shape, configuration and function of the microneedles to achieve a target biomedical application. Here, this review would introduce the types of materials of the microneedles firstly. The hardness, Young's modulus, geometric structure, processability, biocompatibility and degradability of the microneedles are explored as well. Then, the fabrication methods for the solid and hollow microneedles in recent years are reviewed in detail, and the advantages and disadvantages of each process are analyzed and compared. Finally, the biomedical applications of the microneedles are reviewed, including biosensing, drug delivery, body fluid extraction, and nerve stimulation. It is expected that this work provides the fundamental knowledge for developing new microneedle devices, as well as the applications in a variety of biomedical fields.

Microneedle-mediated transdermal nanodelivery systems: a review

The greatest limitation in the development of transdermal drug delivery systems is that only a few drugs can permeate the skin due to the barrier function of the stratum corneum. Active and passive methods are generally available for improving the ability of drug transdermal delivery. However, nanoparticles, as a passive approach, exhibit capacity-constrained permeation enhancement. Thus, microneedle-mediated nanoparticles possess enormous potential and broad prospects. Microneedles promote the penetration of macromolecules by creating microchannels on the skin surface. In this review, the prevailing subknowledge on microneedles (mechanism, classification, and applications of microneedles combined with nanoparticles) is discussed to provide a guideline for readers and a basic reference for further in-depth studies of this novel drug delivery system.

Manufacturing Process of Polymeric Microneedle Sensors for Mass Production

In this work, we present a fabrication process for microneedle sensors made of polylactic acid (PLA), which can be utilized for the electrochemical detection of various biomarkers in interstitial fluid. Microneedles were fabricated by the thermal compression molding of PLA into a laser machined polytetrafluoroethylene (PTFE) mold. Sensor fabrication was completed by forming working, counter, and reference electrodes on each sensor surface by Au sputtering through a stencil mask, followed by laser dicing to separate individual sensors from the substrate. The devised series of processes was designed to be suitable for mass production, where multiple microneedle sensors can be produced at once on a 4-inch wafer. The operational stability of the fabricated sensors was confirmed by linear sweep voltammetry and cyclic voltammetry at the range of working potentials of various biochemical molecules in interstitial fluid.

Diagnostic and drug release systems based on microneedle arrays in breast cancer therapy

Microneedle arrays have recently received much attention as cancer detection and treatment platforms, because invasive injections and detection of the biopsy are not needed, and drug metabolism by the liver, as well as adverse effects of systemic drug administration, are diminished. Microneedles have been used for diagnosis, vaccination, and in targeted drug delivery of breast cancer. In this review, we summarize the recent progress in diagnosis and targeted drug delivery for breast cancer treatment, using microneedle arrays to deliver active molecules through the skin. The results not only suggest that health and well-being of patients are improved, but also that microneedle arrays can deliver anticancer compounds in a relatively noninvasive manner, based on body weight, breast tumor size, and circulation time of the drug. Moreover, microneedles could allow simultaneous loading of multiple drugs and enable controlled release, thus effectively optimizing or preventing drug-drug interactions. This review is designed to encourage the use of microneedles for diagnosis and treatment of breast cancer, by describing general properties of microneedles, materials used for construction, mechanism of action, and principal benefits. Ongoing challenges and future perspectives for the application of microneedle array systems in breast cancer detection and treatment are highlighted.

Marine polymeric microneedles for transdermal drug delivery

Transdermal drug delivery is considered one of the most attractive routes for administration of pharmaceutic and cosmetic active ingredients due to the numerous advantages, especially over oral and intravenous methodologies. However, some limitations still exist mainly regarding the need to improve the drugs permeation across the skin. For this, several strategies have been described, considering the application of chemical permeation enhancers, drugs' nanoformulations and physical methods. Of these, microneedles have been proposed in the last years as promising strategies to enhance transdermal drug delivery. In this review, different types of microneedles are described, and the most commonly used methods of fabrication systematized, as well as the materials typically used and their main therapeutical applications. A special attention is paid to polymeric microneedles, particularly those made from sustainable marine polysaccharides like chitosan, alginate and hyaluronic acid. The applications of marine based polymeric microneedle devices for transdermal drug delivery are examined in detail and the perspectives of translation from the clinical trials to the market demonstrated.

Iontophoresis-driven porous microneedle array patch for active transdermal drug delivery

A transdermal patch that combines microneedle array (MA) with iontophoresis can achieve synergistic and remarkable enhancement of drug delivery with precise electronic control. However, the development of an MA patch combined with iontophoresis that can enable in situ treatment, easy self-administration, and controllable delivery of liquid macromolecular drugs is still a challenge. Here, we presented an iontophoresis-driven porous MA patch (IDPMAP) for in situ, patient-friendly, and active delivery of charged macromolecular drugs. IDPMAP integrates porous MA with iontophoresis into a single transdermal patch, thus realizing the one-step drug administration strategy of "Penetration, Diffusion, and Iontophoresis." Moreover, a matching portable iontophoresis-driven device was developed for drug self-administration of IDPMAP. In vitro and in vivo studies showed that IDPMAP had approximately 99% skin penetration rate, negligible cytotoxicity, and good biocompatibility without skin irritation and hypersensitivity. In vivo transdermal delivery of insulin in type 1 diabetic rats demonstrated that IDPMAP could effectively deliver insulin nanovesicles and produce a robust hypoglycemic effect on the rats (maintain normal blood glucose for approximately 5.4 h), with more advanced controllability and efficiency than that achieved by pristine MA or iontophoresis. IDPMAP and its portable iontophoresis-driven device are user-friendly and thus show a promising potential for drug self-administration at home.

Safe Coated Microneedles with Reduced Puncture Occurrence after Administration

The goal of this study is the preparation of safer coated microneedles so that tips remaining after the initial use are less likely to be reinserted on a second use. Twelve groups of uncoated microneedles (u-MNs) were prepared from the combination of three different aspect ratios (height to base width) and four kinds of polymer (polyethylene (PE), polypropylene (PP), nylon and polylactic acid (PLA)). After coating the u-MNs with polyvinyl alcohol formulation to make coated MNs (c-MNs), the force displacement of the u-MNs and the c-MNs was measured. The aspect ratio was reduced from 2.2, 2.5 and 3.0 with u-MNs to 1.3, 1.4 and 1.6 with c-MNs, respectively, after the coating formulation was applied to the MNs. All PLA MNs had a puncture performance of more than 95%. However, the puncture performance of u-MNs made of PE and of PP with a 3.0 aspect ratio was only 8% and 53%, respectively, whereas the rates of c-MNs made of PE and of PP were 82% and 95%, respectively. In animal experiments with PP MNs with a 3.0 aspect ratio, the 59% rate of puncture performance with u-MNs increased to above 96% with c-MNs and fell to 13% for r-MNs. Safe c-MNs can overcome the disadvantages of standard c-MNs by reducing the probable contamination of remaining tips after use. Safe c-MNs have advantages over standard c-MNs in terms of humidity resistance, reasonable cost, sterilization process and short processing time through the separate process of u-MN preparation and simple dip-coating.

Transdermal Microneedles-A Materials Perspective

Transdermal drug delivery is an emerging field in the pharmaceutical remit compared with conventional methods (oral and parenteral). Microneedle (MN)-based devices have gained significant interest as a strategy to overcome the skin's formidable barrier: the stratum corneum. This approach provides a less invasive, more efficient, patient friendly method of drug delivery with the ability to incorporate various therapeutic agents including macromolecules (proteins and peptides), anti-cancer agents and other hydrophilic and hydrophobic compounds. This short review attempts to assess the various materials involved in the fabrication of MNs as well as incorporation of other excipients to improve drug delivery for novel medical devices. The focus will be on polymers, metals and other inorganic materials utilised for MN drug delivery, as well as their application, limitations and future work to be carried out.

Recent advances in microneedle composites for biomedical applications: Advanced drug delivery technologies

In the twenty-first century, microneedles based drug delivery is drawing attention worldwide in the research due to current signs of progress in the controlled release drug delivery through microneedles. The microneedles represent a promising technology to deliver therapeutic compounds into the skin for chronic complications like osteoporosis, diabetes, cancer and induction of immune responses from protein and DNA vaccines. However, the delivery of hydrophilic drugs and macromolecular agents are challenging. In this write up authors included the meticulous illustration of the chronological development of fabrication of microneedles with respect to an assortment of techniques, their modifications, clinical trials and regulatory perspectives period of 2000-2019. This review summarizes characterization, fabrications, biological applications and challenges. Additionally, relevant patents based on microneedle from USPTO) database are also highlighted.

Acid-Treated Water-Soluble Chitosan Suitable for Microneedle-Assisted Intracutaneous Drug Delivery

Chitosan has been widely used as a nature-derived polymeric biomaterial due to its high biocompatibility and abundance. However, poor solubility in aqueous solutions of neutral pH and multiple fabrication steps for the molding process limit its application to microneedle technology as a drug delivery carrier. Here, we present a facile method to prepare water-soluble chitosan and its application for sustained transdermal drug delivery. The water-soluble chitosan was prepared by acid hydrolysis using trifluoroacetic acid followed by dialysis in 0.1 M NaCl solutions. We successfully fabricated bullet-shaped microneedle (MN) arrays by the single molding process with neutral aqueous chitosan solutions (pH 6.0). The chitosan MN showed sufficient mechanical properties for skin insertion and, interestingly, exhibited slow dissolving behavior in wet conditions, possibly resulting from a physical crosslinking of chitosan chains. Chitosan MN patches loading rhodamine B, a model hydrophilic drug, showed prolonged release kinetics in the course of the dissolving process for more than 72 h and they were found to be biocompatible to use. Since the water-soluble chitosan can be used for MN fabrication in the mild conditions (neutral pH and 25 °C) required for the loading of bioactive agents such as proteins and achieve a prolonged release, this biocompatible chitosan MN would be suitable for sustained transdermal drug delivery of a diverse range of drugs.

A solid polymer microneedle patch pretreatment enhances the permeation of drug molecules into the skin

In this work, solid microneedles (MNs) for skin pretreatment were systematically studied including MN height, density, spacing, and so on.

Fabrication of biodegradable composite microneedles based on calcium sulfate and gelatin for transdermal delivery of insulin

To reduce the inconvenience and pain of subcutaneous needle injection, the calcium sulfate and gelatin biodegradable composite microneedle patches with high aspect-ratio microneedles (MNs) and a flexible substrate have been developed. The microneedles with an aspect-ratio approximate 6:1 exhibit excellent mechanical property which can achieve 0.4N for each needle. The cross-section views show the inside of microneedles that have abundant pores and channels which offer potential for different drug-release profiles. The preparation procedures, degradable property for the biodegradable composite microneedle patches are described in the paper. Insulin, the drug to control blood glucose levels in diabetic patients, has been embedded into the biodegradable composite MNs. The hypoglycemic effect for transdermal delivery of insulin is studied using diabetic Sprague-Dawley (SD) rats as models in vivo. After transdermal administration to the diabetic rats, the released insulin from biodegradable composite MNs exhibit an obvious and effective hypoglycemic effect for longer time compared with that of subcutaneous injection route. This work suggests that biodegradable composite MNs containing of insulin have a potential application in diabetes treatment via transdermal ingestion.