Cross-Linking-Density-Changeable Microneedle Patch Prepared from a Glucose-Responsive Hydrogel for Insulin Delivery

Biodegradable polymeric insulin microneedles - a design and materials perspective review

Microneedle (MN) delivery devices are more accepted by people than regular traditional needle injections (e.g. vaccination) due to their simplicity and adaptability. Thus, patients of chronic diseases like diabetes look for alternative pain-free treatment regimens circumventing regular subcutaneous injections. Insulin microneedles (INS-MNs) are a thoughtfully researched topic (1) to overcome needle phobia in patients, (2) for controlled delivery of the peptide, (3) decreasing the frequency of drug administration, (4) to ease the drug administration procedure, and (5) thus increasing patient adherence to the treatment dosage regimes. MNs physically disrupt the hard outer skin layer to create minuscule pores for insulin (INS) to pass through the dermal capillaries into the systemic circulation. Biodegradable polymeric MNs are of greater significance for INS and vaccine delivery than silicon, metal, glass, or non-biodegradable polymeric MNs due to their ease of fabrication, mass production, cost-effectiveness, and bioerodability. In recent years, INS-MNs have been researched to deliver INS through the transdermal implants, buccal mucosa, stomach wall, intestinal mucosal layers, and colonic mucosa apart from the usual transdermal delivery. This review focuses on the design characteristics and the applications of biodegradable/dissolvable polymeric INS-MNs in transdermal, intra-oral, gastrointestinal (GI), and implantable delivery. The prospective approaches to formulate safe, controlled-release INS-MNs were highlighted. Biodegradable/dissolvable polymers, their significance, their impact on MN morphology, and INS release characteristics were outlined. The developments in biodegradable polymeric INS-MN technology were briefly discussed. Bio-erodible polymer selection, MN fabrication and evaluation factors, and other design aspects were elaborated.

Promising strategies for smart insulin delivery system: Glucose-sensitive microneedle

The diabetes treatment landscape is rapidly evolving towards intelligent and precise therapeutic interventions. Among these advancements, glucose-sensitive microneedle patches (GSMPs), which can automatically adjust the transdermal release rate of insulin based on glucose concentrations, are emerging as a promising strategy. In this work, a new classification method has been proposed for GSMPs, categorizing them into integrated, all-in-one, and core-shell structures. The working mechanism and performance of GSMPs are thoroughly analyzed to compare the advantages and disadvantages of these three forms. The correlation between glucose-sensitive performance and normal blood glucose maintenance time (NGT) is further explored. Our findings indicate that all-in-one GSMPs demonstrate a positive correlation between in vitro glucose-sensitive controlled-release performance and NGT, unlike assembled GSMPs, where the performance is influenced by the matrix material and crosslinking factors. Simultaneously, challenges in clinical translation and future development trends are discussed from a patient's perspective. In summary, the new classification method, in-depth explanation of mechanisms, and analysis of challenges in this work contribute to a better understanding of the field of GSMPs and provide guidance for the development of more advanced and efficient GSMPs.

Swellable Microneedles in Drug Delivery and Diagnostics

This manuscript explores the transformative potential of swellable microneedles (MNs) in drug delivery and diagnostics, addressing critical needs in medical treatment and monitoring. Innovations in hydrogel-integrated MN arrays facilitate controlled drug release, thereby expanding treatment options for chronic diseases and conditions that require precise dosage control. The review covers challenges, such as scalability, patient compliance, and manufacturing processes, as well as achievements in advanced manufacturing, biocompatibility, and versatile applications. Nonetheless, limitations in physiological responsiveness and long-term stability remain, necessitating further research in material innovation and integration with digital technologies. Future directions focus on expanding biomedical applications, material advancements, and regulatory considerations for widespread clinical adoption.

Dually crosslinked degradable polyionic micelles for sustained glucose-responsive insulin release

Glucose -sensitive delivery systems hold great promise as a therapeutic approach for high-incidence diabetes owing to their ability to release insulin whenever elevated glycemia is detected. However, they are unstable in a hyperglycemic environment, which leads to short-term sustained insulin release. Herein, we designed dually crosslinked insulin polyionic micelles (DCM@insulin) based on triblock polymers of o-glycol and phenylboronic acid-functionalized poly(ethylene glycol)-poly(dimethylamino carbonate)-poly(dimethylamino-trimethylene carbonate) (mPEG-P(AC-co-MPD)-PDMAC and mPEG-P(AC-co-MAPBA)-PDMATC, respectively) for sustained glucose-responsive insulin release. DCM@insulin with a phenylboronic acid ester structure (first crosslinking structure) enhanced glycemic responsiveness by regulating insulin release in a hyperglycemic environment. Additionally, the UV-crosslinking structure (second crosslinking structure) formed by the residual double bonds in AC units endowed DCM@insulin with the ability to effectively protect the loaded insulin against protease degradation and avoid burst release under multiple insulin release. The in vivo findings demonstrated that DCM@insulin effectively maintained glycemic levels (BGLs) within the normal range for 6 h in comparison to single-crosslinked micelles (SCM@insulin). Therefore, the glucose-responsive and dually crosslinked polyionic micelle system exhibits potential as a viable option for the treatment of diabetes.

Latest advances in glucose-responsive microneedle-based systems for transdermal insulin delivery

The development of a self-regulated minimally invasive system for insulin delivery can be considered as the holy grail in the field of diabetes mellitus. A delivery system capable of releasing insulin in response to blood glucose levels would significantly improve the quality of life of diabetic patients, eliminating the need for frequent finger-prick tests and providing better glycaemic control with lower risk of hypoglycaemia. In this context, the latest advances in glucose-responsive microneedle-based transdermal insulin delivery are here compiled with a thorough analysis of the delivery mechanisms and challenges lying ahead in their clinical translation. Two main groups of microneedle-based systems have been developed so far: glucose oxidase-containing and phenylboronic acid-containing systems. Both strategies in combination have also been tested and two other novel strategies are under development, namely electronic closed-loop and glucose transporter-based systems. Results from preclinical studies conducted using these different types of glucose-triggered release systems are comprehensively discussed. Altogether, this analysis from both a mechanistic and translational perspective will provide rationale and/or guidance for future trends in the research hotspot of glucose-responsive microneedle-based insulin delivery systems.

Innovative freeze-drying technique in the fabrication of dissolving microneedle patch: Enhancing transdermal drug delivery efficiency

Microneedle patch (MNP) has become a hot research topic in the field of transdermal drug delivery due to its ability to overcome the stratum corneum barrier. Among the various types of microneedles, dissolving microneedles represent one of the most promising transdermal delivery methods. However, the most used method for preparing dissolving microneedles, namely microfabrication, suffers from issues such as long drying time, susceptibility to humidity, and large batch-to-batch variability, which limit the development of dissolving microneedles. In this study, we report for the first time a method for preparing dissolving microneedles using freeze-drying technology. We screened substrates suitable for freeze-dried microneedle patch (FD-MNP) and used coating technology to enhance the mechanical strength of FD-MNP, allowing them to meet the requirements for skin penetration. We successfully prepared FD-MNP using hyaluronic acid as the substrate and insulin as the model drug. Scanning electron microscopy revealed that the microneedles had a porous structure. After coating, the mechanical strength of the microneedles was 0.61 N/Needle, and skin penetration rate was 97%, with a penetration depth of 215 μm. The tips of the FD-MNP dissolved completely within approximately 60 s after skin penetration, which is much faster than conventional MNP (180 s). In vitro transdermal experiments showed that the FD-MNP shortened the lag time for transdermal delivery of rhodamine 123 and insulin compared to conventional MNP, indicating a faster transdermal delivery rate. Pharmacological experiments showed that the FD-MNP lowered mouse blood glucose levels more effectively than conventional MNP, with a relative pharmacological availability of 96.59 ± 2.84%, higher than that of conventional MNP (84.34 ± 3.87%), P = 0.0095. After storage under 40℃ for two months, the insulin content within the FD-MNP remained high at 95.27 ± 4.46%, which was much higher than that of conventional MNP (58.73 ± 3.71%), P < 0.0001. In conclusion, freeze-drying technology is a highly valuable method for preparing dissolving microneedles with potential applications in transdermal drug delivery.

Electrostatic-Interaction-Aided Microneedle Patch for Enhanced Glucose-Responsive Insulin Delivery and Three-Meal-Per-Day Blood-Glucose Regulation

The phenylborate-ester-cross-linked hydrogel microneedle patch (MNP) was promising in the diabetic field for the glucose-responsive insulin-delivering property and simple fabrication process. However, the unfit design of the charging microneedle network limited the improvement of blood-glucose regulating performances. In this work, insulin-loaded phenylborate-ester-cross-linked MNPs, with the polyzwitterion property, were constructed based on the modified ε-polylysine and poly(vinyl alcohol). The relationship between the charging nature of the MNP network and insulin release was verified by regulating the content of postprotonated positively charged amino groups. The elaborately designed MNP possessed improved glucose-responsive insulin-delivering performance. The in vivo study revealed the satisfactory results on blood-glucose regulation by the optimized MNP under the mimic three-meal-per-day mode. Moreover, the insulin bioactivity in the MNP could be maintained for 2 weeks under 25 °C. In summary, this work developed an effective strategy to improve the glucose-responsive phenylborate-ester-cross-linked MNP and enhance its potential for clinical transformation.

Smart Responsive Microneedles for Controlled Drug Delivery

As an emerging technology, microneedles offer advantages such as painless administration, good biocompatibility, and ease of self-administration, so as to effectively treat various diseases, such as diabetes, wound repair, tumor treatment and so on. How to regulate the release behavior of loaded drugs in polymer microneedles is the core element of transdermal drug delivery. As an emerging on-demand drug-delivery technology, intelligent responsive microneedles can achieve local accurate release of drugs according to external stimuli or internal physiological environment changes. This review focuses on the research efforts in smart responsive polymer microneedles at home and abroad in recent years. It summarizes the response mechanisms based on various stimuli and their respective application scenarios. Utilizing innovative, responsive microneedle systems offers a convenient and precise targeted drug delivery method, holding significant research implications in transdermal drug administration. Safety and efficacy will remain the key areas of continuous efforts for research scholars in the future.

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

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

"Smart" Matrix Microneedle Patch Made of Self-Crosslinkable and Multifunctional Polymers for Delivering Insulin On-Demand

A transdermal patch that delivers insulin at high glucose concentrations can offer tremendous advantages to ease the concern of safety and improve the quality of life for people with diabetes. Herein, a novel self-crosslinkable and glucose-responsive polymer-based microneedle patch (MN) is designed to deliver insulin at hyperglycemia. The microneedle patch is made of hyaluronic acid polymers functionalized with dopamine and 4-amino-3-fluorophenylboronic acid (AFBA) that can be quickly crosslinked upon mixing of the polymer solutions in the absence of any chemicalcrosslinking agents or organic solvents. The catechol groups in the dopamine (DA) units form covalent crosslinkages among themselves by auto-oxidation and dynamic crosslink with phenylboronic acid (PBA) via complexation. The reversible crosslinkages between catechol and boronate decrease with increasing glucose concentration leading to higher swelling and faster insulin release at hyperglycemia as compared to euglycemia. Such superior glucose-responsive properties are demonstrated by in vitro analyses and in vivo efficacy studies. The hydrogel polymers also preserve native structure and bioactivity of insulin, attributable to the interaction of hyaluronic acid (HA) with insulin molecules, as revealed by experiments and molecular dynamics simulations. The simplicity in the design and fabrication process, and glucose-responsiveness in insulin delivery impart the matrix microneedle (mMN) patch great potential for clinical translation.

Advances in Intelligent Stimuli-Responsive Microneedle for Biomedical Applications

Microneedles (MNs) are a new type of drug delivery method that can be regarded as an alternative to traditional transdermal drug delivery systems. Recently, MNs have attracted widespread attention for their advantages of effectiveness, safety, and painlessness. However, the functionality of traditional MNs is too monotonous and limits their application. To improve the efficiency of disease treatment and diagnosis by combining the advantages of MNs, the concept of intelligent stimulus-responsive MNs is proposed. Intelligent stimuli-responsive MNs can exhibit unique biomedical functions according to the internal and external environment changes. This review discusses the classification and principles of intelligent stimuli-responsive MNs, such as magnet, temperature, light, electricity, reactive oxygen species, pH, glucose, and protein. This review also highlights examples of intelligent stimuli-responsive MNs for biomedical applications, such as on-demand drug delivery, tissue repair, bioimaging, detection and monitoring, and photothermal therapy. These intelligent stimuli-responsive MNs offer the advantages of high biocompatibility, targeted therapy, selective detection, and precision treatment. Finally, the prospects and challenges for the application of intelligent stimuli-responsive MNs are discussed.

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.

Molecular Docking-Guided Design on Glucose-Responsive Nanoparticles for Microneedle Fabrication and "Three-Meal-per-Day" Blood-Glucose Regulation

It was greatly significant, but difficult, to develop stimulus-responsive polymeric nanoparticles with efficient protein-loading and protein-delivering properties. Crucial obstacles were the ambiguous protein/nanoparticle-interacting mechanisms and the corresponding inefficient trial-and-error strategies, which brought large quantities of experiments in design and optimization. In this work, a molecular docking-guided universal "segment-functional group-polymer" process was proposed to simplify the previous laborious experimental step. The insulin-delivering glucose-responsive polymeric nanoparticles for diabetic treatments were taken as the examples. The molecular docking study obtained insights from the insulin/segment interactions. It was then experimentally confirmed in six functional groups for insulin-loading performances of their corresponding polymers. The optimization formulation was further proved effective in blood-glucose stabilization on the diabetic rats under the "three-meal-per-day" mode. It was believed that the molecular docking-guided designing process was promising in the protein-delivering field.

Research progress of advanced microneedle drug delivery system and its application in biomedicine

Transdermal drug delivery is an effective way of drug delivery in addition to oral and intravenous administration. Among them, microneedle administration is a new type of subcutaneous drug delivery, which forms micron-level pores on the surface of the skin, making the drug enter the dermis through the cuticular layer of the skin in the least invasive way. This mode of drug delivery not only increases the permeation efficiency of transdermal drug delivery but also improves the bioavailability of drug delivery. At present, there are many kinds of research on microneedles, such as solid microneedles, hollow microneedles, soluble polymer microneedles, etc. However, some new microneedle drug delivery systems have been gradually developed and applied with the development of microneedle drug delivery technology, for meeting the more complex pathological environment. In this review, we focus on the principle, structure, and function of some new types of microneedles, such as stimulus-response microneedles, iontophoresis microneedles, and bionic microneedles. We summarize the effects of materials, geometry, and size on the properties of microneedles as well as their applications and potential developments in the field of biomedicine. We hope that this review can provide new ideas and help with the development of new microneedle drug delivery systems.

Microneedles with Two-Stage Glucose-Sensitive Controlled Release for Long-Term Insulin Delivery

Diabetes patients cannot complete effective blood glucose regulation due to their impaired pancreatic function. At present, subcutaneous insulin injection is the only treatment for patients with type 1 and severe type 2 diabetes. However, long-term subcutaneous injection will cause patients with intense physical pain and lasting psychological burden. In addition, subcutaneous injection will lead to hypoglycemia risk to a large extent because of the uncontrollable release of insulin. In this work, we developed a glucose-sensitive microneedle patch based on phenylboronic acid (PBA)-modified chitosan (CS) particles and poly(vinyl alcohol) (PVA)/poly(vinylpyrrolidone) (PVP) hydrogel for the efficient delivery of insulin. Meanwhile, through the double glucose-sensitive response process of CS-PBA particle and external hydrogel, the sudden release of insulin was well restrained, and a more persistent blood glucose control was achieved. Finally, the painless, minimally invasive, and efficient treatment effect of the glucose-sensitive microneedle patch indicated its great advantages as a new generation of injection therapy.

Current state of knowledge on intelligent-response biological and other macromolecular hydrogels in biomedical engineering: A review

Because intelligent hydrogels have good biocompatibility, a rapid response, and good degradability as well as a stimulus response mode that is rich, hydrophilic, and similar to the softness and elasticity of living tissue, they have received widespread attention and are widely used in biomedical engineering. In this article, we conduct a systematic review of the use of smart hydrogels in biomedical engineering. First, we introduce the properties and applications of hydrogels and compare the similarities and differences between traditional hydrogels and smart hydrogels. Secondly, we summarize the intelligent hydrogel types, the mechanisms of action used by different hydrogels, and the materials for preparing different types of hydrogels, such as the materials for the preparation of temperature-responsive hydrogels, which mainly include gelatin, carrageenan, agarose, amylose, etc.; summarize the morphologies of different hydrogels, such as films, fibers and microspheres; and summarize the application of smart hydrogels in biomedical engineering, such as for the delivery of proteins, antibiotics, deoxyribonucleic acid, etc. Finally, we summarize the shortcomings of current research and present future prospects for smart hydrogels. The purpose of this paper is to provide researchers engaged in related fields with a systematic review of the application of intelligent hydrogels in biomedical engineering. We hope that they will get some inspiration from this work to provide new directions for the development of related fields.

Progress in Intradermal and Transdermal Gene Therapy with Microneedles

Gene therapy is one of the most widely studied treatments and has the potential to treat a variety of intractable diseases. The skin's limited permeability, as the body's initial protective barrier, drastically inhibits the delivery effect of gene medicine. Given the potential adverse effects and physicochemical features of the medications, improving generic drug penetration into the skin barrier and achieving an effective level of target tissues remains a challenge. Microneedles have made tremendous improvements in aided gene transfer and medication delivery as a unique method. Microneedles offer the advantage of being minimally invasive and painless, as well as the ability to distribute gene medicines straight through the stratum corneum. Microneedles have been used to penetrate skin tissue with various nucleic acids and medicines in recent years, allowing for a wide range of applications in the treatment of skin ailments. This review focuses on skin-related disorders and immunity, and it primarily discusses the progress of microneedle transdermal gene therapy in recent years. It also complements the current major vectors and related microneedle gene therapy applications.

Multitasking smart hydrogels based on the combination of alginate and poly(3,4-ethylenedioxythiophene) properties: A review

Poly(3,4-ethylenedioxythiophene) (PEDOT), a very stable and biocompatible conducting polymer, and alginate (Alg), a natural water-soluble polysaccharide mainly found in the cell wall of various species of brown algae, exhibit very different but at the same complementary properties. In the last few years, the remarkable capacity of Alg to form hydrogels and the electro-responsive properties of PEDOT have been combined to form not only layered composites (PEDOT-Alg) but also interpenetrated multi-responsive PEDOT/Alg hydrogels. These materials have been found to display outstanding properties, such as electrical conductivity, piezoelectricity, biocompatibility, self-healing and re-usability properties, pH and thermoelectric responsiveness, among others. Consequently, a wide number of applications are being proposed for PEDOT-Alg composites and, especially, PEDOT/Alg hydrogels, which should be considered as a new kind of hybrid material because of the very different chemical nature of the two polymeric components. This review summarizes the applications of PEDOT-Alg and PEDOT/Alg in tissue interfaces and regeneration, drug delivery, sensors, microfluidics, energy storage and evaporators for desalination. Special attention has been given to the discussion of multi-tasking applications, while the new challenges to be tackled based on aspects not yet considered in either of the two polymers have also been highlighted.

Recent advances in polymer microneedles for drug transdermal delivery: Design strategies and applications

In recent years, the transdermal drug delivery based on microneedles (MNs) technology has received extensive attention, which offers a safer and painless alternative to hypodermic needle injection. They can pierce the stratum corneum and deliver drugs to the epidermis and dermis-structures of skin, showing prominent properties such as minimally invasive, bypassing first-pass metabolism, and self-administered. A range of materials have been used to fabricate MNs, such as silicon, metal, glass, and polymers. Among them, polymer MNs have gained increasing attention from pharmaceutical and cosmetic companies as one of the promising drug delivery methods. Microneedle products have recently become available on the market, and some of them are under evaluation for efficacy and safety. This paper focuses on current state of polymer MNs in the drug transdermal delivery. The materials and methods for the fabrication of polymer MNs and their drug administration are described. The recent progresses of polymer MNs for treatment of cancer, vaccine delivery, blood glucose regulation, androgenetic alopecia, obesity, tissue healing, myocardial infarction and gout are reviewed. The challenges of MNs technology are summarized and the future development trend of MNs is also prospected. This article is protected by copyright. All rights reserved.

Stimuli-Responsive Microneedles as a Transdermal Drug Delivery System: A Demand-Supply Strategy

Microneedles are one of the most prominent approaches capable of physically disrupting the stratum corneum without devastating the deeper tissues to deliver both small molecules and macromolecules into the viable epidermis/dermis for local/systemic effects. Over the past two decades, microneedles have caught the attention of many researchers because of their outstanding advantages over oral and parenteral drug delivery systems such as self-administration, pain-free, steady-plasma concentration maintenance, avoidance of first-pass hepatic biotransformation, and so on. So far, scientists have reported various types of microneedle patches to deliver the loaded therapeutics as soon as the microneedles are inserted into the skin, regardless of the demand for therapeutics to treat a specific condition. This way of drug delivery can lead to potential risks such as poor therapeutic efficacy or drug overdose. The stimuli-responsive microneedles are the most predominant tool to achieve the on-demand/need-based drug delivery, leading to safe and effective treatment. Various natural and synthetic polymers that can undergo significant transitions such as swelling, shrinking, dissolution, or disintegration play a pivotal role in the development of stimuli-responsive microneedles. The current Review provides brief information about the history, emergence, type, and working principles of microneedles. Furthermore, it selectively discusses various exogenous and endogenous stimuli-responsive microneedles along with their mechanism of action involved in treating different disease conditions. Collaterally, the emergence of "closed-loop" combinatorial stimuli-responsive microneedle patches for precise delivery of therapeutics is meticulously canvassed. Subsequently, it covers the patents of different stimuli-responsive microneedles and further highlights the existing challenges and future perspectives concerning clinical application and large-scale production.