Safety Evaluation of Solid Polymer Microneedles in Human Volunteers at Different Application Sites

Dissolving microneedles: A transdermal drug delivery system for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder that impacts around 1% of the global population. Up to 20% of people become disabled within a year, which has a severely negative impact on their health and quality of life. RA has a complicated pathogenic mechanism, which initially affects small joints and progresses to larger ones over time. It can damage the skin, eyes, heart, kidney, and lung. Oral medications, intra-articular injections, and other treatments are being used; nevertheless, they have drawbacks, including low bioavailability, numerous adverse effects, and poor patient compliance. Dissolving microneedles (DMNs) are a safe and painless method for transdermal drug delivery, achieved through their ability to physically penetrate the epidermal barrier. They enable targeted drug delivery, significantly enhancing the bioavailability of medications and improving patient compliance. DMNs are particularly effective in delivering both lipophilic and high molecular weight biomolecules. The superior bioavailability of DMNs is demonstrated by the fact that low-dose DMN administration can achieve up to 25.8 times higher bioavailability compared to oral administration. This paper provides a comprehensive review of recent advancements in the use of DMNs for RA treatment, encompassing various materials (such as hyaluronic acid, chitosan, etc.), fabrication techniques (such as the two-step casting method, photopolymerization), and performance evaluations (including morphology, mechanical properties, skin penetration capability, solubility, and pharmacodynamics). Additionally, a thorough safety assessment has been conducted, revealing that DMNs cause minimal skin irritation and exhibit low cytotoxicity, ensuring their safety for clinical application. DMNs provide a highly effective and promising alternative to oral and injectable drug delivery systems, offering a novel therapeutic approach for RA patients that significantly improves treatment outcomes and enhances their quality of life.

Emerging Strategies for Local Delivery of Immune Checkpoint Inhibitors to Potentiate Cancer Immunotherapy: Current Status and Future Prospects

Cancer constitutes a significant threat to patients' lives worldwide. Immunotherapy, particularly immune checkpoint inhibitors (ICIs) that boost antitumor immunity by targeting immune checkpoint components, has emerged as a promising strategy for its treatment in recent years. However, the objective response rates of the ICIs are unsatisfactory. As the primary route, systemic administration of ICIs is often accompanied by immune-related adverse events. Local delivery of ICIs serves as a potential therapeutic strategy that can improve the efficacy while simultaneously reducing side effects through precise drug release at the tumor site. Initial validation of direct local application of ICIs for tumors in clinical trials has indicated reduced side effects and improved efficacy, while low bioavailability remains a challenge. Furthermore, research on various carriers, including nanoparticles, microneedles, hydrogels, combined platforms, and implantable devices for local release of ICIs has exhibited applying potential in treating murine tumors, among which combined platforms such as combined hydrogel system hold the highest promise due to their encompassment of the advantages of multiple carriers. These carriers, by incorporating ICIs and other therapeutics, could manage cancers more potently, which needs to be confirmed in clinical trials after the refinement of their biocompatibility. This review summarizes the latest research advancements regarding local administration of ICIs, with a particular focus on the carriers for local delivery as well as the combination therapies, thus providing novel insights and research guidance for scholars to enhance the efficacy of locally delivered ICIs on managing multiple cancers in the future.

Enhancing wound healing through innovative technologies: microneedle patches and iontophoresis

Introduction

Wound healing is a complex process involving multiple stages, including inflammation, proliferation, and remodeling. Effective wound management strategies are essential for accelerating healing and improving outcomes. The CELLADEEP patch, incorporating iontophoresis therapy and microneedle technology, was evaluated for its potential to enhance the wound healing process.

Methods

This study utilized a full-thickness skin defect model in Sprague-Dawley rats, researchers compared wound healing outcomes between rats treated with the CELLADEEP Patch and those left untreated. Various histological staining techniques were employed to examine and assess the wound healing process, such as H&E, MT and immunofluorescence staining. Furthermore, the anti-inflammatory and proliferative capabilities were further investigated using biochemical assays.

Results

Macroscopic and microscopic analyses revealed that the CELLADEEP patch significantly accelerated wound closure, reduced wound width, and increased epidermal thickness and collagen deposition compared to an untreated group. The CELLADEEP patch decreased nitric oxide and reactive oxygen species levels, as well as pro-inflammatory cytokines IL-6 and TNF-α, indicating effective modulation of the inflammatory response. Immunofluorescence staining showed reduced markers of macrophage activity (CD68, F4/80, MCP-1) in the patch group, suggesting a controlled inflammation process. Increased levels of vimentin, α-SMA, VEGF, collagen I, and TGF-β1 were observed, indicating enhanced fibroblast activity, angiogenesis, and extracellular matrix production.

Discussion

The CELLADEEP patch demonstrated potential in promoting effective wound healing by accelerating wound closure, modulating the inflammatory response, and enhancing tissue proliferation and remodeling. The CELLADEEP patch offers a promising non-invasive treatment option for improving wound healing outcomes.

Fabrication and evaluation of nanoemulsion based insulin loaded microneedles for transdermal drug delivery

Aim: Insulin therapy require self-administration of subcutaneous injection leading to painful and inconvenient drug therapy. The aim is to fabricate nanoemulsion (NE) based insulin loaded microneedles with improved bioavailability and patient compliance.Materials & methods: Different ratios of polyvinyl alcohol and polyvinylpyrrolidone as polymers were prepared through micro-molding technique for microneedles. Characterization of were performed using scanning electron microscope, differential scanning calorimetry, Fourier-transform infrared spectroscopy and circular dichroism. Mechanical strength, hygroscopicity and pain perception of these microneedles were also evaluated. In vitro release, permeation and in vivo PK/PD study of NE-based microneedles were conducted.Results: NE-based microneedles of insulin have improved bioavailability and quick response.Conclusion: Microneedles loaded with insulin can be effectively delivered insulin transdermally to treat diabetes with increased convenience and patient compliance.

Toward a solid microneedle patch for rapid and enhanced local analgesic action

Analgesic creams find widespread application as adjuncts for localized anesthesia prior to surgical procedures. Nevertheless, the onset of analgesic action is protracted due to the skin barrier's inherent characteristics, which necessitates prolonged intervals of patient and clinician waiting, consequently impinging upon patient compliance and clinician workflow efficiency. In this work, a biodegradable microneedles (MNs) patch was introduced to enhance the intradermal administration of lidocaine cream to achieve rapid analgesia through a minimally invasive and conveniently accessible modality. The polylactic acid (PLA) MNs were mass-produced using a simple hot-pressing method and served the purpose of creating microchannels across the skin's surface for rapid absorption of lidocaine cream. Optical and electron microscopes were applied to meticulously scrutinize the morphology of the fabricated MNs, and the comprehensive penetration tests involving dynamometer tests, evaluation on porcine cadaver skin, artificial film, optical coherence tomography (OCT), transepidermal water loss, and analysis on rats' skins, demonstrated the robust mechanical strength of PLA MNs for successful intradermal penetration. The behavioral pain sensitivity tests on living rats using Von Frey hair filaments revealed that the MN-assisted lidocaine treatment expeditiously accelerated the onset of action from 40 to 10 min and substantially enhanced the efficacy of localized anesthesia. Furthermore, different treatment protocols encompassing the sequence of drug application relative to MN treatment, MN dimensions, and the frequency of MN insertions exhibited noteworthy influence on the resultant local anesthesia efficacy. Together, these results demonstrated that the lidocaine cream followed by diverse PLA MN treatments would be a promising strategy for rapid clinical local anesthesia with wide-ranging applications.

Novel microneedle platforms for the treatment of wounds by drug delivery: A review

The management and treatment of wounds are complex and pose a substantial financial burden to the patient. However, the complex environment of wounds leads to inadequate drug absorption to achieve the desired therapeutic effect. As a novel technological platform, microneedles are widely used in drug delivery because of their multiple drug loading, multistage drug release, and multiple designs of topology. This study systematically summarizes and analyzes the manufacturing methods and limitations of different microneedles, as well as the latest research advances in pain management, drug delivery, and healing promotion, and presents the challenges and opportunities for clinical applications. On this basis, the development of microneedles in external wound repair and management is envisioned, and it is hoped that this study can provide guidelines for the design of microneedle systems in different application contexts, including the selection of materials, preparation methods, and structural design, to achieve better healing and regeneration results.

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.

Safety tests and clinical research on buccal and nasal microneedle swabs for genomic analysis

Conventional swabs have been used as a non-invasive method to obtain samples for DNA analysis from the buccal and the nasal mucosa. However, swabs may not always collect pure enough genetic material. In this study, buccal and nasal microneedle swab is developed to improve the accuracy and reliability of genomic analysis. A cytotoxicity test, a skin sensitivity test, and a skin irritation test are conducted with microneedle swabs. Polymer microneedle swabs meet the safety requirements for clinical research and commercial use. When buccal and nasal microneedle swabs are used, the amount of genetic material obtained is greater than that from commercially available swabs, and DNA purity is also high. The comparatively short microneedle swab (250 μm long) cause almost no pain to all 25 participants. All participants also report that the microneedle swabs are very easy to use. When genotypes are compared at five SNP loci from blood of a participant and from that person's buccal or nasal microneedle swab, the buccal and nasal microneedle swabs show 100% concordance for all five SNP genotypes. Microneedle swabs can be effectively used for genomic analysis and prevention through genomic analysis, so the utilization of microneedle swabs is expected to be high.

Functional insulin aspart/insulin degludec-based microneedles for promoting postprandial glycemic control

Insulin aspart (IAsp) and insulin degludec (IDeg), as the third generation of insulin, have a faster onset time or a more durable action period, which may simulate the secretion of insulin under physiological conditions. Microneedles (MNs) are transdermal delivery devices that may allow diabetic patients to easily deploy transdermal insulin therapy while considerably reducing injection pain. In this study, we investigated the combination of dissolving MNs with IAsp or IDeg therapy as an alternative to daily multiple insulin injections, aiming to improve glycemic control and patient compliance. Mechanical properties of the MNs, structural stability of insulin encapsulated in the MNs, and transdermal application characteristics were studied to assess the practicality of insulin-loaded MNs for diabetes therapy. In vivo experiments conducted on diabetic rats demonstrated that the IAsp- and IDeg-loaded MNs have comparable blood glucose control abilities to that of subcutaneous injections. In addition, the therapeutic properties of insulin-loaded MNs under diverse dietary conditions and application strategies were further investigated to provide new information to support future clinical trials. Taken together, the proposed MNs have the potential to improve balances between glycemic control, hypoglycemia risk, and convenience, providing patients with simpler regimens. STATEMENT OF SIGNIFICANCE: 1. The fabricated functional insulin-loaded dissolving microneedles closely matched the glucose rise that occurs in response to meals, demonstrating promising alternatives for multiple daily insulin injections. 2. The hypoglycemic properties of insulin microneedles were investigated under diverse dietary conditions and application strategies, yielding new information to support future clinical trials. 3. Molecular dynamics simulations were utilized to study the interactions between the insulin and microneedle matrix materials, providing a strategy for theoretically understanding drug stability as well as the release mechanism of drug-loaded microneedles.

Strategies to develop polymeric microneedles for controlled drug release

The remarkable appeal of microneedle controlled-release systems has captivated both the academic community and pharmaceutical industry due to their great potential for achieving spatiotemporally controlled release, coupled with their the minimally invasive nature and ease of application. Over the years, scientists have dedicated their efforts to advancing microneedle systems by manipulating the physicochemical properties of matrix materials, refining microneedle designs, and interfacing with external devices to provide tailored drug release profiles in a spatiotemporally controllable manner. Expanding upon our understanding of drug release mechanisms from polymeric microneedles, which include diffusion, swelling, degradation, triggering, and targeting, there is a growing focus on manipulating the location and rate of drug release through innovative microneedle designs. This burgeoning field of microneedle-based drug delivery systems offers further prospects for precise control over drug release. The design strategies of polymeric microneedle systems for temporally controlled and locally targeted release, as well as the delivery mechanisms by which drugs can be released from a microneedle system are critically reviewed in this work. Furthermore, this review also puts forward some perspectives on the potential and challenges involved in translating these microneedle-based delivery systems into the next generation therapies.

Advances in microneedle-based therapy for bone disorders

Bone-related disorders treatment is a serious public health concern, imposing a significant social and economic burden on patients and healthcare systems. Although conventional drug delivery systems have made advances in bone diseases prevention and management, the limited delivery efficiency and convoluted focal environment lead to inadequate drug absorption and lack of specificity to achieve the intended therapeutic impact. Microneedle-based therapy represents an extraordinarily safe and well-tolerable therapeutic approach for treating bone disorders, providing improved efficacy by breaking down the barriers and delivery of therapeutic components to the target sites with programable release profiles in a less invasive manner. Over the past decades, numerous significant achievements in the development of various types of drug-carried microneedles have been made to address the obstacles encountered in the bone-treating procedure, enabling the microneedle-based therapy to take an important step in practical applications. In this light, this review summarizes these remarkable researches in terms of microneedles types and drug delivery strategies, with the goal of demonstrating the benefits of exploiting microneedle-based therapy as a novel strategy for treating bone-related disorders. The remaining challenges and future perspectives are also discussed in the hope of inspiring more efficient and intelligent bone treatment strategies.

Progress in the preparation and evaluation of glucose-sensitive microneedle systems and their blood glucose regulation

Glucose-sensitive microneedle systems (GSMSs) as an intelligent strategy for treating diabetes can well solve the problems of puncture pain, hypoglycemia, skin damage, and complications caused by the subcutaneous injection of insulin. According to the various functions of each component, herein, therapeutic GSMSs are reviewed based on three parts (glucose-sensitive models, diabetes medications, and microneedle body). Moreover, the characteristics, benefits, and drawbacks of three types of typical glucose-sensitive models (phenylboronic acid based polymer, glucose oxidase, and concanavalin A) and their drug delivery models are reviewed. In particular, phenylboronic acid-based GSMSs can provide a long-acting drug dose and controlled release rate for the treatment of diabetes. Moreover, their painless, minimally invasive puncture also greatly improves patient compliance, treatment safety, and potential application prospects.

Research progress of physical transdermal enhancement techniques in tumor therapy

The advancement and popularity of transdermal drug delivery (TDD) based on the physical transdermal enhancement technique (PTET) has opened a new paradigm for local tumor treatment. The drug can be directly delivered to the tumor site through the skin, thus avoiding the toxic side effects caused by the first-pass effect and achieving high patient compliance. Further development of PTETs has provided many options for antitumor drugs and laid the foundation for future applications of wearable closed-loop targeting drug delivery systems. In this highlight, the different types of PTETs and related mechanisms, and applications of PTET-related tumor detection and therapy are highlighted. According to their type and characteristics, PTETs are categorized as follows: (1) iontophoresis, (2) electroporation, (3) ultrasound, (4) thermal ablation, and (5) microneedles. PTET-related applications in the local treatment of tumors are categorized as follows: (1) melanoma, (2) breast tumor, (3) squamous cell carcinoma, (4) cervical tumor, and (5) others. The challenges and future prospects of existing PTETs are also discussed. This highlight will provide guidance for the design of PTET-based wearable closed-loop targeting drug delivery systems and personalized therapy for tumors.

Subcutaneous Implantable Microneedle System for the Treatment of Alzheimer's Disease by Delivering Donepezil

To alleviate the dilemma of drug administration in Alzheimer's disease (AD) patients, it is of great significance to develop a new drug delivery system. In this study, a subcutaneously implanted microneedle (MN) device with a swellable gelatin methacryloyl (GelMA) needle body and a dissolvable polyvinyl alcohol (PVA) backing layer was designed. The backing layer quickly dissolved once the MN was introduced into the subcutaneous, and the hydrogel needles were implanted in the subcutaneous to enable prolonged drug release. Compared with oral administration, the MN system offers the benefits of a high administration rate, a fast onset of effect, and a longer duration of action. By detecting the concentration of acetylcholine (ACH) and Aβ 1-42, it was found that MN administration exhibited a stronger therapeutic effect. The biological safety of the MN system was also assessed, and no obvious signs of hemolysis, cytotoxicity, and inflammatory reaction were observed. Together, these findings suggested that the MN system is a convenient, efficient, and safe method of delivering donepezil hydrochloride (DPH) and may provide AD patients with a novel medicine administration option.

Improved pharmacodynamics of epidermal growth factor via microneedles-based self-powered transcutaneous electrical stimulation

Epidermal growth factor is an excellent drug for promoting wound healing; however, its conventional administration strategies are associated with pharmacodynamic challenges, such as low transdermal permeability, reduction, and receptor desensitization. Here, we develop a microneedle-based self-powered transcutaneous electrical stimulation system (mn-STESS) by integrating a sliding free-standing triboelectric nanogenerator with a microneedle patch to achieve improved epidermal growth factor pharmacodynamics. We show that the mn-STESS facilitates drug penetration and utilization by using microneedles to pierce the stratum corneum. More importantly, we find that it converts the mechanical energy of finger sliding into electricity and mediates transcutaneous electrical stimulation through microneedles. We demonstrate that the electrical stimulation applied by mn-STESS acts as an "adjuvant" that suppresses the reduction of epidermal growth factor by glutathione and upregulates its receptor expression in keratinocyte cells, successfully compensating for receptor desensitization. Collectively, this work highlights the promise of self-powered electrical adjuvants in improving drug pharmacodynamics, creating combinatorial therapeutic strategies for traditional drugs.

A novel method for fabrication of coated microneedles with homogeneous and controllable drug dosage for transdermal drug delivery

Over the years, scientists have been focused on the development of microneedle coating process to coat a broad range of therapeutic agents onto the surface of the solid microneedles for effective drug delivery. The precise dose control, content uniformity as well as large-scale production of coated microneedles are still the core issues that have been the interest of researchers in this topic. To this end, a repeatable method that involved a micro-molding process was demonstrated for mass fabrication of coated microneedles with homogeneous and controllable drug loading under mild conditions. In this system, the dissolvable drug carriers with precise dosage were first mounted onto the solid microneedles and then exposed to the high moisture condition to finally obtain the coated microneedle with uniform and precise drug loading. Using the microneedle molds with the volume of 4.71 nL, 8.24 nL, 10.47 nL, and 12.56 nL per cavity, the drug loadings were precisely controlled at 4.8 ng, 6.4 ng, 9.3 ng, and 13.5 ng per needle, with the standard deviation of 0.09, 0.01, 0.07, and 0.53%, respectively. Mechanical property tests showed that the coated microneedles are strong enough for reliable skin insertion, and with in vivo trials in diabetic mice, we further confirmed the similar hypoglycaemic effect of insulin-coated microneedles to subcutaneous injection. Taken together, the micro-molding-based fabrication process has practical merits in the mass production of coated microneedles with homogeneous and controllable drug loading, facilitating the clinical translation of the microneedle technique.

An update on biomaterials as microneedle matrixes for biomedical applications

Microneedles (MNs) have been developed for various applications such as drug delivery, cosmetics, diagnosis, and biosensing. To meet the requirements of MNs used in these areas, numerous materials have been used for the fabrication of MNs. However, MNs will be exposed to skin tissues after piercing the stratum corneum barrier. Thus, it is necessary to ensure that the matrix materials of MNs have the characteristics of low toxicity, good biocompatibility, biodegradability, and sufficient mechanical properties for clinical application. In this review, the matrix materials currently used for preparing MNs are summarized and reviewed in terms of these factors. In addition, MN products used on the market and their applications are summarized in the end. This work may provide some basic information to researchers in the selection of MN matrix materials and in developing new materials.

Microneedle-Based Glucose Sensor Platform: From Vitro to Wearable Point-of-Care Testing Systems

Significant advanced have recently been made in exploiting microneedle-based (MN-based) diabetes devices for minimally invasive wearable biosensors and for continuous glucose monitoring. Within this emerging class of skin-worn MN-based sensors, the ISF can be utilized as a rich biomarker source to diagnose diabetes. While initial work of MN devices focused on ISF extraction, the recent research trend has been oriented toward developing in vivo glucose sensors coupled with optical or electrochemical (EC) instrumentation. This outlook highlights the essential characteristics of the sensing mechanisms, rational design, sensing properties, and applications. Finally, we describe the opinions about the challenge and prospects of optical and EC MN-based device platforms for the fabrication of wearable biosensors and their application potential in the future.

Microneedle-based technology for cell therapy: current status and future directions

With the growing technological innovations in medical treatments, cell-based therapies hold great potential as efficient tools against various previously incurable diseases by restoring or altering the function of certain sets of cells. Along this line, an essential factor to determine the success of cell therapy is the choice of cell delivery strategy. In recent years, a novel trend is blooming in the application of microneedle systems, which are based on the miniaturization of multiple needles within a patch to the micrometer dimensions, aimed at the delivery of therapeutic cells to the target site with high efficiency and in a minimally invasive manner. This review aims to demonstrate the advantages of exploiting microneedle-based technology as a new tool for cell therapy. The advancements of microneedle-based strategies for cell delivery are summarized in terms of two categories: cell-free and cell-loaded microneedle systems. The majority of research on microneedle-based cell therapy has shown promising results for tissue regeneration, cancer immunotherapy, skin immune monitoring and targeted cell delivery. Finally, current challenges and future perspectives toward the development and application of microneedles for cell therapy are also discussed.

The Rise of Polymeric Microneedles: Recent Developments, Advances, Challenges, and Applications with Regard to Transdermal Drug Delivery

The current scenario of the quest for microneedles (MNs) with biodegradability and biocompatibility properties is a potential research area of interest. Microneedles are considered to be robust, can penetrate the skin's deep-seated layers, and are easy to manufacture, and their applications from the clinical perspective are still ongoing with standard escalation. This review paper focuses on some of the pivotal variants of polymeric microneedles which are specifically dissolvable and swell-based MNs. It further explores the drug dissolution kinetics and insertion behavior mechanisms with an emphasis on the need for mathematical modeling of MNs. This review further evaluates the multifarious fabrication methods, with an update on the advances in the fabrication of polymeric MNs, the choice of materials used for the fabrication, the challenges in polymeric MN fabrication, and the prospects of polymeric MNs with applications pertinent to healthcare, by exclusively focusing on the procurable literature over the last decade.

Recent Progress in Microneedles-Mediated Diagnosis, Therapy, and Theranostic Systems

Theranostic system combined diagnostic and therapeutic modalities is critical for the real-time monitoring of disease-related biomarkers and personalized therapy. Microneedles, as a multifunctional platform, are promising for transdermal diagnostics and drug delivery. They have shown attractive properties including painless skin penetration, easy self-administration, prominent therapeutic effects, and good biosafety. Herein, an overview of the microneedles-based diagnosis, therapies, and theranostic systems is given. Four microneedles-based detection methods are concluded based on the sensing mechanism: i) electrochemistry, ii) fluorometric, iii) colorimetric, and iv) Raman methods. Additionally, robust microneedles are suitable for implantable drug delivery. Microneedles-assisted transdermal drug delivery can be primarily classified as passive, active, and responsive drug release, based on the release mechanisms. Microneedles-assisted oral and implantable drug delivery mechanisms are also presented in this review. Furthermore, the key frontier developments in microneedles-mediated theranostic systems as the major selling points are emphasized in this review. These systems are classified into open-loop and closed-loop theranostic systems based on the indirectness and directness of feedback between the transdermal diagnosis and therapy, respectively. Finally, conclusions and future perspectives for next-generation microneedles-mediated theranostic systems are also discussed. Taken together, microneedle-based systems are promising as the new avenue for diagnosis, therapy, and disease-specific closed-loop theranostic applications.

Stability and Diffusion Properties of Insulin in Dissolvable Microneedles: A Multiscale Simulation Study

Microneedle (MN) technology has been proven to be promising to become an effective drug delivery route of insulin for diabetes treatment, with the advantages of high delivery efficiency, convenient management, and minimal risk of infection. However, efforts are still required to verify the insulin activity in MNs for further clinical application. Moreover, it is also essential to study the diffusion properties of insulin to understand the ability of various MN materials to control insulin release. Herein, we have combined all-atom molecular dynamics simulation and coarse-grained dissipative particle dynamics to systematically study insulin's structural stability and diffusion coefficient in polyvinyl alcohol and hyaluronic acid solutions. The all-atom simulation reveals the dissimilarities in the interaction mode between insulin and the two polymers. It also points out that the presence of the two polymers would not irreversibly impact the secondary structure of insulin, thereby ensuring regular insulin expression in vivo. Mesoscopic simulation results manifest that the diffusion coefficient of insulin in hyaluronic acid (HA) solution is greater than that of the polyvinyl alcohol (PVA) system. Meanwhile, through the study of insulin centroid trajectory, we have claimed two different diffusion mechanisms of insulin in polymer solution: The movement of insulin in the HA and water solution follows the Brownian motion rule. In comparison, the hopping effect of insulin has been observed in the PVA solution due to poor intermolecular affinity as well as lower polymer water solubility. By summarizing different diffusion mechanisms, this study can provide theoretical guidance for preparing insulin-loaded dissolvable MNs.

Mesoscopic Simulation for the Effect of Cross-Linking Reactions on the Drug Diffusion Properties in Microneedles

The drug diffusion issue in microneedles is the focus of its medical application. It will not only affect the distribution of drugs in the needle body but will also have an impact on the drug release performance of the microneedle. The utilization of cross-linked polymer materials to obtain the drug diffusion control has been experimentally verified as a feasible method. However, the mechanism research on the molecular level is still incomplete. In this study, the dissipative particle dynamics (DPD) simulation has been applied to study the effect of the cross-linking reaction on drug diffusion in hyaluronic acid microneedles. We have discovered that when the cross-linking degree reaches 90%, the diffusion coefficient of the drug is 6.45 times lower than that of the uncross-linked system. The main reason for the decline in drug diffusion ability is that the cross-linking reaction varies the conformation of the polymer. The amplification in the cross-linking degree makes the polymer coils more compact and approach each other, finally forming a continuously distributed cross-linked network, which reduces its degradation rate in the body. Simultaneously, these cross-linked networks can also hinder the interaction of soluble drugs with water, thereby preventing the premature release of drugs. The simulation results are consistent with the data collected in the previous microneedle experiment. This work will be an extension of DPD simulation in the application of biological materials.

Translation of Polymeric Microneedles for Treatment of Human Diseases: Recent Trends, Progress, and Challenges

The ongoing search for biodegradable and biocompatible microneedles (MNs) that are strong enough to penetrate skin barriers, easy to prepare, and can be translated for clinical use continues. As such, this review paper is focused upon discussing the key points (e.g., choice polymeric MNs) for the translation of MNs from laboratory to clinical practice. The review reveals that polymers are most appropriately used for dissolvable and swellable MNs due to their wide range of tunable properties and that natural polymers are an ideal material choice as they structurally mimic native cellular environments. It has also been concluded that natural and synthetic polymer combinations are useful as polymers usually lack mechanical strength, stability, or other desired properties for the fabrication and insertion of MNs. This review evaluates fabrication methods and materials choice, disease and health conditions, clinical challenges, and the future of MNs in public healthcare services, focusing on literature from the last decade.

Engineering biopharmaceutical formulations to improve diabetes management

Insulin was first isolated almost a century ago, yet commercial formulations of insulin and its analogs for hormone replacement therapy still fall short of appropriately mimicking endogenous glycemic control. Moreover, the controlled delivery of complementary hormones (such as amylin or glucagon) is complicated by instability of the pharmacologic agents and complexity of maintaining multiple infusions. In this review, we highlight the advantages and limitations of recent advances in drug formulation that improve protein stability and pharmacokinetics, prolong drug delivery, or enable alternative dosage forms for the management of diabetes. With controlled delivery, these formulations could improve closed-loop glycemic control.

Patchless administration of canine influenza vaccine on dog's ear using insertion-responsive microneedles (IRMN) without removal of hair and its in vivo efficacy evaluation

Microneedles provide the advantages of convenience and compliance by avoiding the pain and fear of needles that animals often experience. Insertion-responsive microneedles (IRMN) were used for administration to a hairy dog without removing the dog's hair. Canine H3N2 vaccine was administered with IRMN attached to the dog's ears ex vivo and the conventional microneedle system (MN) was administered for 15 min to compare puncture performance and delivery efficiency. The vaccine was also administered to compare antibody formation using IRMN with the use of intramuscular injection. The veterinarian observed the behavior of the dog during the course of the administration and compared the response to IRMN with that of intramuscular administration. The tips of IRMN were separated from the base and delivered into the hairy skin successfully. Puncture performance of IRMN were the same as that of coated microneedles (95%), but delivery efficiency of IRMN were 95% compared to less than 1% for coated microneedles. The H3N2 vaccine inoculated into the dog's ears showed the same antibody formation as the intramuscular injection. The dog appeared to be more comfortable with IRMN administration compared to syringe administration. IRMN are the first microneedle system to deliver a canine vaccine successfully into a hairy dog without removal of the dog's hair. The use of IRMN can provide both convenience and compliance for both the dog and the owner.