Investigation on fabrication process of dissolving microneedle arrays to improve effective needle drug distribution

Microneedle patch with pure drug tips for delivery of liraglutide: pharmacokinetics in rats and minipigs

Transdermal delivery of peptide drugs is almost impossible with conventional penetration enhancers because of epidermal barrier function. Microneedle (MN) patches can bypass the epidermal barrier and have been developed for trans- and intradermal delivery of peptide drugs and vaccines. However, dissolving MN patches are limited by low drug loading capacities due to their small size and admixture of drug and water-soluble excipients. Furthermore, few in vivo pharmacokinetic studies, especially in large animals such as pigs, have been performed to assess post-application systemic drug exposure. Here, we developed a dissolving MN patch with pure liraglutide at the needle tips. The MN patch could load up to 2.21 ± 0.14 mg of liraglutide in a patch size of 0.9 cm2, which was nearly two orders of magnitude higher than that obtained with conventional MN patches of the same size. Raman imaging confirmed that liraglutide was localized at the MN tips. The MN had sufficient mechanical strength to penetrate the epidermis and could deliver up to 0.93 ± 0.04 mg of liraglutide into skin with a dosing variability of less than 6.8%. The MN patch delivery enabled faster absorption of liraglutide than that provided by subcutaneous (S.C.) injection, and achieved relative bioavailability of 69.8% and 46.3% compared to S.C. injection in rats and minipigs, respectively. The MN patch also exhibited similar patterns of anti-hyperglycemic effect in diabetic rats and individual variability in pharmacokinetic parameters as S.C. injection. The liraglutide MN application was well tolerated; no skin irritation was observed in minipigs except for mild erythema occurring within 4 h after once daily administration for 7 days at the same site. Our preclinical study suggests that MN patch with pure drug needle tips might offer a safe and effective alternative to S.C. injection for administration of liraglutide.

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.

Dual engine-driven bionic microneedles for early intervention and prolonged treatment of Alzheimer's disease

The microneedle (MN) delivery system presents an attractive administration route for patients with Alzheimer's disease (AD). However, the passive drug delivery mode and low drug loading of MNs often result in unsatisfactory therapeutic efficiency. To address these dilemmas, we developed dual engine-drive bionic MNs for robust AD treatment. Specifically, free rivastigmine (RVT) and RVT particles were co-loaded within the MNs to construct the valve and chambers of the guava, respectively, which can serve as an active engine to promote drug permeation by generating capillary force. K2CO3 and citric acid were introduced as a pneumatic engine into the MNs to promote the permeation of free RVT into deeper skin layers for early intervention in AD. Further, the RVT particles served as a drug depot to provide continuous drug release for prolonged AD treatment. Compared with free RVT-loaded MNs, the dual engine-driven bionic MNs showed an increase in drug loading, cumulative transdermal permeability, and normalized bioavailability of approximately 40%, 22%, and 49%, respectively. Pharmacodynamic studies further confirmed that the dual engine-driven bionic MNs were most effective in restoring memory and recognition functions in mice with short-term memory dysfunction. Therefore, the dual engine-driven bionic MNs hold great promise for highly efficient AD treatment.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

HPMC/PVP K90 Dissolving Microneedles Fabricated from 3D-Printed Master Molds: Impact on Microneedle Morphology, Mechanical Strength, and Topical Dissolving Property

Three-dimensional (3D) printing can be used to fabricate custom microneedle (MN) patches instead of the conventional method. In this work, 3D-printed MN patches were utilized to fabricate a MN mold, and the mold was used to prepare dissolving MNs for topical lidocaine HCl (L) delivery through the skin. Topical creams usually take 1-2 h to induce an anesthetic effect, so the delivery of lidocaine HCl from dissolving MNs can allow for a therapeutic effect to be reached faster than with a topical cream. The dissolving-MN-patch-incorporated lidocaine HCl was constructed from hydroxypropyl methylcellulose (HPMC; H) and polyvinyl pyrrolidone (PVP K90; P) using centrifugation. Additionally, the morphology, mechanical property, skin insertion, dissolving behavior, drug-loading content, drug release of MNs and the chemical interactions among the compositions were also examined. H51P2-L, H501P2-L, and H901P2-L showed an acceptable needle appearance without bent tips or a broken structure, and they had a low % height change (<10%), including a high blue-dot percentage on the skin (>80%). These three formulations exhibited a drug-loading content approaching 100%. Importantly, the composition-dependent dissolving abilities of MNs were revealed. Containing the lowest amount of HPMC in its formulation, H901P2-L showed the fastest dissolving ability, which was related to the high amount of lidocaine HCl released through the skin. Moreover, the results of an FTIR analysis showed no chemical interactions among the two polymers and lidocaine HCl. As a result, HPMC/PVP K90 dissolving microneedles can be used to deliver lidocaine HCl through the skin, resulting in a faster onset of anesthetic action.

Overcoming challenges in dermal and transdermal delivery of herbal therapeutics with polymeric microneedles

Natural products are generally preferred medications owing to their low toxicity and irritancy potential. However, a good number of herbal therapeutics (HT) exhibit solubility, permeability and stability issues that eventually affect oral bioavailability. Transdermal administration has been successful in resolving some of these issues which has lead in commercialization of a few herbal transdermal products. Polymeric Microneedles (MNs) has emerged as a promising platform in transdermal delivery of HT that face problems in permeating the skin. Several biocompatible and biodegradable polymers used in the fabrication of MNs have been discussed. MNs have been exploited for cutaneous delivery of HT in management of skin ailments like skin cancer, acne, chronic wounds and hypertrophic scar. Considering the clinical need, MNs are explored for systemic delivery of potent HT for management of diverse disorders like asthma, disorders of central nervous system and nicotine replacement as it obviates first pass metabolism and elicits a quicker onset of therapeutic response. MNs of HT have found good number of aesthetic applications in topical delivery of HT to the skin. Interestingly, MNs have emerged as an attractive option as a minimally invasive diagnostic aid in sampling biomarkers from plants, skin and ocular interstitial fluid. The review updates the progress made by MN technology of HT for multiple therapeutic interventions along with the future challenges. An attempt is made to illustrate the challenging formulation strategies employed in the fabrication of polymeric MNs of HT. Efforts are on to extend the potential applications of polymeric MNs to HT for diverse therapeutic applications.

Anti-obesity and metabolic benefits of metformin: Comparison of different delivery routes

Obesity is a severe public health problem. Healthy lifestyle interventions are commonly recommended for fighting obesity. But they are hard to follow and have low efficacy. Pharmacotherapy and surgery are of high efficacy but are beset with side effects. Browning subcutaneous white adipose tissue (WAT) is a practical and efficient approach for combating obesity. Metformin, a commonly used FDA-approved antidiabetic drug, is potent to induce browning of WAT through phosphorylation and activation of AMP-activated protein kinase. However, oral administration of metformin has low oral bioavailability, fast renal clearance, and low target specificity that limit metformin's application in browning WAT. Local and transdermal delivery of metformin directly to subcutaneous WAT using injection or microneedle (MN) in combination with iontophoresis (INT) may solve these problems. In this paper, we administered metformin to C57BL/6J obese mice using the following three routes: transdermal delivery (MN and INT), local injection into inguinal WAT (IgWAT, a type of subcutaneous WAT in mice), and oral gavage. The anti-obesity and metabolic effects of metformin via these delivery routes were determined and compared. As compared to local IgWAT injection and oral gavage delivery, transdermal delivery of metformin using MN and INT resulted in 9% lower body weight and 7% decrease in body fat% accompanied by improved energy metabolism and decreased inflammation through browning IgWAT in obese C57BL/6J mice. Transdermal delivery of metformin using MN and INT is an effective approach in browning subcutaneous WAT for combating obesity and improving metabolic health.

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.

Fabrication of dissolving microneedles for transdermal delivery of protein and peptide drugs: polymer materials and solvent casting micromoulding method

Proteins and peptides are rapidly developing pharmaceutical products and are expected to continue growing in the future. However, due to their nature, their delivery is often limited to injection, with drawbacks such as pain and needle waste. To overcome these limitations, microneedles technology is developed to deliver protein and peptide drugs through the skin. One type of microneedles, known as dissolving microneedles, has been extensively studied for delivering various proteins and peptides, including ovalbumin, insulin, bovine serum albumin, polymyxin B, vancomycin, and bevacizumab. This article discusses polymer materials used for fabricating dissolving microneedles, which are poly(vinylpyrrolidone), hyaluronic acid, poly(vinyl alcohol), carboxymethylcellulose, GantrezTM, as well as other biopolymers like pullulan and ulvan. The paper is focused solely on solvent casting micromoulding method for fabricating dissolving microneedles containing proteins and peptides, which will be divided into one-step and two-step casting micromoulding. Additionally, future considerations in the market plan for dissolving microneedles are discussed in this article.

5-aminolevulinic acid-loaded dissolving microneedle array for photodynamic therapy of rheumatoid arthritis on rats

Photodynamic therapy (PDT) is a noninvasive technique that can be used to treat rheumatoid arthritis (RA) by irradiating photosensitizers with specific wavelengths of light to generate reactive oxygen species (ROS), thus leading to targeted cell necrosis. However, efficient delivery of photosensitizers with low side effects is a key issue. We developed a 5-aminolevulinic acid-loaded dissolving microneedle array (5-ALA@DMNA) that can locally and efficiently deliver photosensitizers for RA treatment by PDT. 5-ALA@DMNA was fabricated through a two-step molding process, which was characterized. The effects of 5-ALA-mediated PDT on RA fibroblast-like synoviocytes (RA-FLs) were investigated via in vitro experiments. Adjuvant arthritis rat models were established to evaluate the therapeutic effect of 5-ALA@DMNA-mediated PDT on RA. The results showed that 5-ALA@DMNA could penetrate the skin barrier and efficiently deliver photosensitizers. 5-ALA-mediated PDT can significantly inhibit the migration ability and selectively induce apoptosis of RA-FLs. Moreover, 5-ALA-mediated PDT had a significant therapeutic effect on rats with adjuvant arthritis, which may be related to the upregulation of interleukin (IL)- 4 and IL-10 and downregulation of TNF-α, IL-6, and IL-17. Thus, 5-ALA@DMNA-mediated PDT may be a potential therapy for RA.

Egg Microneedle for Transdermal Delivery of Active Liraglutide

Liraglutide, a human glucagon-like peptide-1 (GLP-1) analog, is promising for safely treating type 2 diabetes mellitus (T2DM), compared to insulin, by significantly reducing the risk of glucose-dependent hypoglycemia. Concerns related to injection prevent T2DM patients from taking liraglutide regularly, even though once-a-day subcutaneous (SC) injections. Dissolving microneedles (DMNs) are promising substitutes for SC injection and for improving patient convenience. However, there are two fundamental limitations: the low drug delivery due to incomplete insertion and loss of drug activity during DMN fabrication. Here, it is shown that an egg microneedle (EMN) designed with three functional layered structures can maintain the maximum activity of the loaded compound during DMN fabrication and deliver it completely into the skin, with the base layer allowing the complete delivery of liraglutide, and the shell layer maintaining the drug activity by mimicking the role of albumin in eggs. In a diabetic mouse model, liraglutide administration via EMN exhibited similar effect when compared to that of injection. Therefore, EMN-mediated liraglutide administration is a good potential option for replacing liraglutide injections in T2DM treatment.

Dissolving Microneedles Loaded with Gestodene: Fabrication and Characterization In Vitro and In Vivo

Background

Gestodene (GEST) is widely used in female contraception. It is currently being used as an oral contraceptive. However, unfortunately, oral contraceptives are often associated with several bothersome side effects and poor compliance. Therefore, a sustained delivery system for GEST to overcome these shortcomings is highly desirable.

Objectives

The present study successfully developed a kind of novel dissolving microneedles (DMNs) with a potential for sustained release and a minimally invasive intradermal treatment of GEST.

Methods

The dissolving microneedles containing GEST were fabricated using polyvinylpyrrolidone as the base material. The characteristics in vitro and pharmacokinetics in vivo of GEST-loaded DMNs were investigated.

Results

The results showed that the microneedle could pierce the porcine skin and release the drug at an average dose of 20µg/cm2 daily for seven days. The pharmacokinetic experiment of the microneedles indicated that the plasma level of GEST in rats increased with increasing drug dosage, and the plasma drug concentration-time curves were much flatter compared with subcutaneous injection and oral administration. In addition, no cutaneous irritation was observed.

Conclusions

GEST-loaded DMNs may be a promising intradermal sustained delivery system for contraceptive use.

Evaluation of design and insertion analysis of a conical shaped polymeric based microneedle for transdermal drug delivery applications

Transportation of drug through parental routes are conventionally followed through hypodermic injection methods, where hypodermic injections are administered into the human skin for drug release. However, there are some issues observed when these hypodermic needles are being used, there are instances where the needle is being inserted leaves some needle fractures in the skin. To cater to the issue scientific researchers are voraciously working on designing and developing polymeric type of microneedle structures for various medical diagnostic applications for glucose monitoring, drug delivery, and other applications. This article presents the structural design of a conicalshaped polymeric microneedle and the insertion force while being pierced into the skin. Simulations at different insertion angles on microneedle are analyzed by arriving with total needle displacements in the process of insertion. The von mises stress is also analyzed with applied force at different insertion angles resulted in incremental change in stress exerted by the microneedle. The resultant stress is below the yield stress which makes the microneedle pierce into the skin without breakage.

A wearable gamma radiation-responsive granulocyte colony-stimulating factor microneedle system protecting against ionizing radiation-induced injury

Exposure to a nuclear accident or a radiological attack may cause serious death events due to ionizing radiation-induced injury and acute radiation syndrome (ARS). Recombinant human granulocyte colony-stimulating factor (G-CSF) is now used for the treatment of ARS. However, the current injection formulation might not ensure treatment as early as possible after a nuclear accident, resulting in a decrease in therapeutic efficiency. In the present study, we have developed a G-CSF wearable system (GWS) consisting of a commercial microchip, a temperature sensor, a gamma-ray detection sensor, a flexible heater, and a G-CSF temperature-sensitive microneedle (GTSMN) patch. G-CSF-containing hyaluronic acid solutions were cast into the mold to obtain G-CSF microneedles (GMNs), which were coated with a temperature-sensitive layer of dodecanoic acid-cetylamine salt to obtain GTSMNs. The flexible heater was prepared by jet printing Ag nanoparticle inks. The GWS and its components are explored and optimized in the aspects of electronics, mechanics, heat transfer and drug diffusion. The γ radiation signal is sensitively monitored by the GWS. The wearable G-CSF system immediately releases G-CSF into the body in response to signal feedback and provides maximal protection against ionizing radiation-induced injury. Therefore, the GWS is a promising wearable system against emergent ionizing radiation injury. STATEMENT OF SIGNIFICANCE: Ionizing radiation-induced injury is always the very important public health problem all the global people care. Some medicines have been applied to protect the body from the injury. Unfortunately, sometimes the injuries accidently happen and the medicines cannot be administered in time, leading to serious acute radiation syndrome. Here, we design a wearable system loading G-CSF that has been approved by FDA to protect the body from ionizing radiation-induced injury. This system consists of a commercial microchip, a temperature sensor, a Gamma-ray detection sensor, a flexible heater, and a G-CSF temperature-sensitive microneedle patch. It can monitor γ radiation and immediately release G-CSF into the body to protect the body to the maximal extent. Therefore, the system is a promising wearable medical device against emergent ionizing radiation injury.

Dissolvable polymer microneedles for drug delivery and diagnostics

Dissolvable transdermal microneedles (μND) are promising micro-devices used to transport a wide selection of active compounds into the skin. To provide an effective therapeutic outcome, μNDs must pierce the human stratum corneum (~10 to 20 μm), without rupturing or bending during penetration, then release their cargo at the predetermined area and time. The ability of dissolvable μND arrays/patches to sufficiently pierce the skin is a crucial requirement, which depends on the material composition, μND geometry and fabrication techniques. This comprehensive review not only provides contemporary knowledge on the μND design approaches, but also the materials science facilitating these delivery systems and the opportunities these advanced materials can provide to enhance clinical outcomes.

Transdermal Delivery of Metformin Using Dissolving Microneedles and Iontophoresis Patches for Browning Subcutaneous Adipose Tissue

Obesity is a serious public health problem that is strongly associated with increased multiple comorbidities such as diabetes, cardiovascular disease, and some types of cancer. While current anti-obesity treatments have various issues, locally transforming energy-storing white adipose tissue (WAT) into energy-burning brown-like/beige adipose tissue, the so-called browning of WAT, has been suggested to enhance obesity treatment efficiency with minimized side effects. Metformin is a first-line antidiabetes drug and a potent activator of AMP-activated protein kinase. Emerging evidence has suggested that metformin might enhance energy expenditure via the browning of WAT and hence reduce body weight. Subcutaneous WAT is easier to access and has a stronger browning potential than other WAT depots. In this study, we used dissolvable poly (lactic-co-glycolic acid) microneedles (MN) to deliver metformin to the subcutaneous WAT in obese C57BL/6J mice with the assistance of iontophoresis (INT), and then investigated metformin-induced WAT browning and its subsequent thermogenesis effects. Compared with MN alone or INT alone, MN + INT had better anti-obesity activity, as indicated by decreasing body weight and fat gain, increased energy expenditure, decreased fat pad size, and improved energy metabolism through the browning of WAT. Browning subcutaneous WAT by delivering metformin and other browning agents using this MN + INT approach might combat obesity in an effective, easy, and safe regimen.

Tip-concentrated microneedle patch delivering everolimus for therapy of multiple sclerosis

Multiple sclerosis is a chronic progressive demyelinating disease of the central nervous system. At present, systemic drug therapy for multiple sclerosis has limited efficacy and serious side effects. Everolimus, as a new generation of mTOR inhibitors, can effectively alleviate the inflammatory reaction of the central nervous system and offers a promising choice for the treatment of multiple sclerosis. However, due to the low oral bioavailability and narrow response window of oral everolimus, a new delivery system is urgently needed to overcome the above problems. In this study, we constructed a tip-concentrated microneedle patch as a transdermal delivery system of everolimus for the treatment of multiple sclerosis. Here, the drug was concentrated in the needle tips by the rational design, making it delivered completely into the skin. The therapeutic effect of everolimus-loaded microneedles was evaluated using the experimental autoimmune encephalomyelitis (EAE) model and further verified with neurological function scores and the histopathological results of the spinal cord. These results indicated that the tip-concentrated microneedle patch provided an effective, safe and simple method for the transdermal delivery of everolimus, thus providing a new treatment for multiple sclerosis.

Non-dermal applications of microneedle drug delivery systems

Microneedles (MNs) are micron-scaled needles measuring 100 to 1000 μm that were initially explored for delivery of therapeutic agents across the skin. Considering the success in transcutaneous drug delivery, the application of microneedles has been extended to different tissues and organs. The review captures the application of microneedles to the oral mucosa, the eye, vagina, gastric mucosa, nail, scalp, and vascular tissues for delivery of vaccines, biologics, drugs, and diagnostic agents. The technology has created easy access to the poorly accessible segments of eye to facilitate delivery of monoclonal antibodies and therapeutic agents in management of neovascular disease. Microporation has been reported to drastically improve the drug delivery through the poorly permeable nail plate. Curved microneedles and spatially designed microneedle cuffs have been found to be capable of delivering stem cells and therapeutic macromolecules directly to the cardiac tissue and the vascular smooth muscle cells, respectively. Besides being minimally invasive and patient compliant, the technology has the potential to offer viable solutions to deliver drugs through impermeable barriers owing to the ability to penetrate several biological barriers. The technology has been successful to overcome the delivery hurdles and enable direct delivery of drug to the target sites, thus maximizing the efficacy thereby reducing the required dose. This review is an attempt to capture the non-dermatological applications of microneedles being explored and provides an insight on the future trends in the field of microneedle technology. Pictorial representation of different microneedle application.

Application of armodafinil-loaded microneedle patches against the negative influence induced by sleep deprivation

Cognition maintenance is essential for healthy and safe life if sleep deprivation happens. Armodafinil is a wake-promoting agent against sleep deprivation related disorders. However, only the tablet formulation is available, which may limit its potential in some circumstances. Here, we report the synthesis of a new formulation of armodafinil, microneedle patches, which can be conveniently used by any individual and removed in time if not wanted. To produce the needles of higher mechanical strength and higher drug loading, polyvinylpyrrolidone (PVP) K90 was used to fabricate armodafinil-loaded microneedles by applying the mold casting method after dissolving in methanol and drying. The higher mechanical strength was validated by COMSOL Multiphysics® software stimulation and universal mechanical testing machines. The obtained armodafinil microneedles can withstand a force of 70 N and penetrate the skin to a depth of 230 μm, and quickly released the drug within 1.5 h in vitro. The pharmacokinetic analysis showed that microneedle administration can maintain a more lasting and stable blood concentration as compared to oral administration. After the treatment of sleep deprived mice with microneedles, the in vivo pharmacodynamics study clearly demonstrated that armodafinil microneedles could eliminate the effects of sleep deprivation and improve the cognitive functions of sleep-deprived mice. A self-administered, high drug-loaded microneedle patch were prepared successfully, which appeared to be highly promising in preserving cognition by transdermal administration.

Efficient Drug Delivery into Skin Using a Biphasic Dissolvable Microneedle Patch with Water-Insoluble Backing

Dissolvable microneedle patches (MNPs) enable simplified delivery of therapeutics via the skin. However, most dissolvable MNPs do not deliver their full drug loading to the skin because only some of the drug is localized in the microneedles (MNs), and the rest remains adhered to the patch backing after removal from the skin. In this work, biphasic dissolvable MNPs are developed by mounting water-soluble MNs on a water-insoluble backing layer. These MNPs enable the drug to be contained in the MNs without migrating into the patch backing due to the inability of the drugs to partition into the hydrophobic backing materials during MNP fabrication. In addition, the insoluble backing is poorly wetted upon MN dissolution in the skin, which significantly reduces drug residue on the MNP backing surface after application. These effects enable a drug delivery efficiency of >90% from the MNPs into the skin 5 min after application. This study shows that the biphasic dissolvable MNPs can facilitate efficient drug delivery to the skin, which can improve the accuracy of drug dosing and reduce drug wastage.

Dissolving Polymer Microneedles for Transdermal Delivery of Insulin

It’s of great significance to develop insulin-loaded dissolving microneedles (MNs) which are fabricated with various methods and materials for transdermal delivery of insulin to effectively and efficiently treat diabetes. In this work, we present a kind of FITC-insulin tip-loaded dissolving MNs fabricated with the mixture of polyvinyl alcohol (PVA) and sucrose using homemade PDMS MNs mold under vacuum conditions. The uniform appearance of MN arrays contributes to controlling the drug dosage well as required. Sufficient mechanical strength for penetrating tough stratum corneum can be obtained by vacuum frozen-drying for at least 6 h after peeling MNs off the mold. About 90% of the FITC-insulin is localized in the conical MN tips and can be released into the skin within 2 min after insertion. The in vivo insulin absorption study and hypoglycemic effect in diabetic mice demonstrate that the proposed insulin-loaded MNs can efficiently deliver the insulin to the systemic circulation and exhibit a similar effect to hypodermic injection on hypoglycemic administration. Together these results suggested that the efficient MN fabrication process proposed in this work shows great potential for mass production and practical application of drug-loaded dissolving MNs in the future.

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.

Chemical imaging analysis of active pharmaceutical ingredient in dissolving microneedle arrays by Raman spectroscopy

The purpose of this study was to develop a quality evaluation method for dissolving microneedle arrays (DMNAs) and determine the spatial distribution pattern of drugs in DMNAs. Raman spectroscopy mapping was used to visualize the drug distribution in DMNAs and drug-loaded polymer films as a model. Powder X-ray diffraction (PXRD) and high-pressure liquid chromatography were also performed to characterize DMNAs. Drug-loaded polymer films and DMNAs were prepared by drying the aqueous solutions spread on the plates or casting. PXRD analysis suggested the crystallization of diclofenac sodium (DCF) in several forms depending on its amount in the sodium hyaluronate (HA)-based films. The Raman spectra of HA and DCF showed characteristic and non-overlapping peaks at 1376 and 1579 cm^-1 Raman shifts, respectively. The intensity of the characteristic peak of DCF in the DCF-loaded films increased linearly with the increasing drug content in the range of 4.8 to 16.7% (DCF, w/w). Raman imaging analysis revealed a homogenous dispersion of small DCF crystals in these films. Raman imaging indicates the distribution of DCF on the surface of the DMNA needle. This work highlights the benefit of using Raman spectroscopy mapping to reveal the spatial distribution of drugs in DMNAs.

Estriol dissolving microneedle patches for protection against ionizing radiation-induced injury

Estriol can be used to treat radiation-induced leukopenia by increasing peripheral blood leukocytes and therefore it plays an important role in radiation protection. However, only high-dose injectable suspensions are available when estriol is used to combat against ionizing radiation-induced injury. Intramuscular (i.m.) administration of estriol is very painful and inconvenient, and the lack of timely self-administered formulation greatly limits the wide application of estriol. This will facilitate quick response under emergent conditions in complementary with the available estriol formulations. Herein, we prepared estriol microneedle (MNs) patches for the convenient and efficient treatment of radiation-induced injury. A biocompatible polymer, polyvinylpyrrolidone K90, was dissolved in an estriol solution of methanol and cast into a mold to obtain conical-shaped MNs. N-vinyl pyrrolidone was poured on the base of the MNs and photocured to enhance the mechanical strength of estriol MNs (EMNs). EMNs were easily pierced 200 μm into the mouse skin. More importantly, the EMNs tips were dissolved very quickly within 5 min so that the drugs could permeate across skin. Mouse models of ionizing radiation-induced injury were established with 6.5 Gy radiation of ⁶⁰Co γ ray. Moreover, EMNs increased peripheral blood leukocytes in irradiated mice, protected the bone marrow hematopoietic system, and improved the survival rate of the irradiated mice to 80%. EMNs are a promising transdermal drug delivery system that allows for easy, rapid administration and protects the body from damage caused by ionizing radiation.

Recent advances in microneedles-mediated transdermal delivery of protein and peptide drugs

Proteins and peptides have become a significant therapeutic modality for various diseases because of their high potency and specificity. However, the inherent properties of these drugs, such as large molecular weight, poor stability, and conformational flexibility, make them difficult to be formulated and delivered. Injection is the primary route for clinical administration of protein and peptide drugs, which usually leads to poor patient's compliance. As a portable, minimally invasive device, microneedles (MNs) can overcome the skin barrier and generate reversible microchannels for effective macromolecule permeation. In this review, we highlighted the recent advances in MNs-mediated transdermal delivery of protein and peptide drugs. Emphasis was given to the latest development in representative MNs design and fabrication. We also summarize the current application status of MNs-mediated transdermal protein and peptide delivery, especially in the field of infectious disease, diabetes, cancer, and other disease therapy. Finally, the current status of clinical translation and a perspective on future development are also provided.

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.

Immune Checkpoint Inhibitor-Based Strategies for Synergistic Cancer Therapy

Immune checkpoint blockade therapy (ICBT) targeting checkpoints, such as, cytotoxic T-lymphocyte associated protein-4 (CTLA-4), programmed death-1 (PD-1), or programmed death-ligand 1 (PD-L1), can yield durable immune response in various types of cancers and has gained constantly increasing research interests in recent years. However, the efficacy of ICBT alone is limited by low response rate and immune-related side effects. Emerging preclinical and clinical studies reveal that chemotherapy, radiotherapy, phototherapy, or other immunotherapies can reprogramm immunologically "cold" tumor microenvironment into a "hot" one, thus synergizing with ICBT. In this review, the working principle and current development of various immune checkpoint inhibitors are summarized, while the interactive mechanism and recent progress of ICBT-based synergistic therapies with other immunotherapy, chemotherapy, phototherapy, and radiotherapy in fundamental and clinical studies in the past 5 years are depicted and highlighted. Moreover, the potential issues in current studies of ICBT-based synergistic therapies and future perspectives are also discussed.

Combination and efficiency: preparation of dissolving microneedles array loaded with two active ingredients and its anti-pigmentation effects on guinea pigs

Hyperpigmentation is a common skin disorder caused by excessive melanogenesis and uneven dispersion of melanin in the skin. To combine multiple active agents with an efficient transdermal drug delivery system is an effective strategy to combat UV induced skin pigmentation. In this work, Arbutin (Arb) and Vitamin C (Vc) mixed in 1:1 were found to have the greatest inhibition effects on melanogenesis and tyrosinase activity in B16 murine melanoma cells. And hyaluronic acid (HA) based dissolving microneedles array (DMNA) was employed to overcome the skin barriers for improved topical drug delivery, which exhibited the most desirable features, including morphology, mechanical properties, dissolving ability, and the highest drug loading. Furthermore, DMNA could greatly increase the stability of Vc during storage without adding any antioxidant which is an important issue for Vc administration. Pharmacodynamics study showed that DMNA loaded with Arb and Vc could synergistically suppress UVB-induced hyperpigmentation in guinea pig skin. This work provides a promising treatment strategy and solution for skin pigmentation and other skin problems.

Microneedles for painless transdermal immunotherapeutic applications

Immunotherapy has recently garnered plenty of attention to improve the clinical outcomes in the treatment of various diseases. However, owing to the dynamic nature of the immune system, this approach has often been challenged by concerns regarding the lack of adequate long-term responses in patients. The development of microneedles (MNs) has resulted in the improvement and expansion of immuno-reprogramming strategies due to the housing of high accumulation of dendritic cells, macrophages, lymphocytes, and mast cells in the dermis layer of the skin. In addition, MNs possess many outstanding properties, such as the ability for the painless traverse of the stratum corneum, minimal invasiveness, facile fabrication, excellent biocompatibility, convenient administration, and bypassing the first pass metabolism that allows direct translocation of therapeutics into the systematic circulation. These advantages make MNs excellent candidates for the delivery of immunological biomolecules to the dermal antigen-presenting cells in the skin with the aim of vaccinating or treating different diseases, such as cancer and autoimmune disorders, with minimal invasiveness and side effects. This review discusses the recent advances in engineered MNs and tackles limitations relevant to traditional immunotherapy of various hard-to-treat diseases.

Transdermal Delivery of Salmon Calcitonin Using a Dissolving Microneedle Array: Characterization, Stability, and In vivo Pharmacodynamics

Salmon calcitonin (sCT) is a polypeptide drug, possessing the ability to inhibit osteoclast-mediated bone resorption. Just like other bioactive macromolecules, sCT is generally administered to the patients by either injection for poor compliance or through nasal spray for low bioavailability, which limits its use as therapeutic drugs. In the present study, to overcome the limitations of the conventional routes, two new dissolving microneedle arrays (DMNAs) based on transdermal sCT delivery systems were developed, namely sCT-DMNA-1 (sCT/Dex/K90E) and sCT-DMNA-2 (sCT/Dex-Tre/K90E) with the same dimension, meeting the requirements of suitable mechanical properties. An accurate and reliable method was established to determine the needle drug loading proportion in sCT-DMNAs. The stability study exhibited that the addition of trehalose could improve the stability of sCT in DMNA under high temperature and humidity. Further, in vivo pharmacodynamic study revealed that DMNA patch could significantly enhanced relative bioavailability to approximately 70%, and the addition of trehalose was found to be beneficial for sCT transdermal delivery. Therefore, sCT-DMNA is expected to replace traditional dosage form, providing a secure, efficient, and low-pain therapeutic strategy for bone disorders.

Effective Dispensing Methods for Loading Drugs Only to the Tip of DNA Microneedles

Here, we propose a novel and simple method to efficiently capture the diffusion of fluorescein isothiocyanate (FITC)-dextran from a biocompatible substance and load the drug only to the tip of DNA microneedles. A dispensing and suction method was chosen to fabricate the designed microneedles with efficient amounts of FITC as the drug model. Importantly, the vacuum process, which could influence the capturing of FITC diffusion from the tip, was evaluated during the manufacturing process. In addition, the simulations were consistent with the experimental results and showed apparent diffusion. Moreover, dextrans of different molecular weights labeled with FITC were chosen to fabricate the tip of microneedles for demonstrating their applicability. Finally, a micro-jetting system with a micro-nozzle (diameter: 80 μm) was developed to achieve the accurate and rapid loading of small amounts of FITC using the anti-diffusion and micro-jetting methods. Our method not only uses a simple and fast manufacturing process, but also fabricates the tips of microneedles more efficiently with FITC compared with the existing methods. We believe that the proposed method is essential for the clinical applications of the microneedle drug delivery platform.

Current trends in polymer microneedle for transdermal drug delivery

Transdermal drug delivery using microneedles is increasingly gaining interest due to the issues associated with oral drug delivery routes. Gastrointestinal route exposes the drug to acid and enzymes present in the stomach, leading to denaturation of the compound and resulting in poor bioavailability. Microneedle transdermal drug delivery addresses the problems linked to oral delivery and to relieves the discomfort of patients associated with injections to increase patient compliance. Microneedles can be broadly classified into five types: solid microneedles, coated microneedles, dissolving microneedles, hollow microneedles, and hydrogel-forming microneedles. The materials used for the preparation of microneedles dictate the different applications and features present in the microneedle. Polymeric microneedle arrays present an improved method for transdermal administration of drugs as they penetrate the skin stratum corneum barrier with minimal invasiveness. The review summarizes the importance of polymeric microneedle and discussed some of the most important therapeutic drugs in research, mainly protein drugs, vaccines and small molecule drugs in regenerative medicine.

Non-invasive drug delivery technology: development and current status of transdermal drug delivery devices, techniques and biomedical applications

Pay-load deliveries across the skin barrier to the systemic circulation have been one of the most challenging delivery options. Necessitated requirements of the skin and facilitated skin layer cross-over delivery attempts have resulted in development of different non-invasive, non-oral methods, devices and systems which have been standardized, concurrently used and are in continuous upgrade and improvements. Iontophoresis, electroporation, sonophoresis, magnetophoresis, dermal patches, nanocarriers, needled and needle-less shots, and injectors are among some of the methods of transdermal delivery. The current review covers the current state of the art, merits and shortcomings of the systems, devices and transdermal delivery patches, including drugs' and other payloads' passage facilitation techniques, permeation and absorption feasibility studies, as well as physicochemical properties affecting the delivery through different transdermal modes along with examples of drugs, vaccines, genes and other payloads.

Development, Evaluation, and Pharmacokinetic Assessment of Polymeric Microarray Patches for Transdermal Delivery of Vancomycin Hydrochloride

Methicillin-resistant Staphylococcus aureus (MRSA) can cause harmful and potentially deadly infections. Vancomycin remains the first-line antibiotic treatment for MRSA-derived infections. Nevertheless, as a peptide drug, it is poorly absorbed when administered orally because of its high molecular weight and low permeability in the gastrointestinal tract and is therefore administered intravenously for the treatment of systemic diseases. In order to circumvent some of the many drawbacks associated with intravenous injection, other routes of drug delivery should be investigated. One of the strategies which has been employed to enhance transdermal drug delivery is based on microarray patches (MAPs). This work, for the first time, describes successful transdermal delivery of vancomycin hydrochloride (VCL) using dissolving MAPs (DMAPs) and hydrogel-forming MAPs (HFMAPs). VCL was formulated into DMAPs and reservoirs [film dosage forms, lyophilized wafers, and compressed tablets (CSTs)] using excipients such as poly(vinyl pyrrolidone), poly(vinyl alcohol), sodium hyaluronate, d-sorbitol, and glycerol. In this study, HFMAPs were manufactured using aqueous blends containing poly(methylvinyl ether-co-maleic acid) cross-linked by esterification with poly(ethylene glycol). The VCL-loaded CSTs (60% w/w VCL) were the most promising reservoirs to be integrated with HFMAPs based on the physicochemical evaluations performed. Both HFMAPs and DMAPs successfully delivered VCL in ex vivo studies with the percentage of drug that permeated across the neonatal porcine skin recorded at 46.39 ± 8.04 and 7.99 ± 0.98%, respectively. In in vivo studies, the area under the plasma concentration time curve from time zero to infinity (AUC_0-∞) values of 162.04 ± 61.84 and 61.01 ± 28.50 μg h/mL were achieved following the application of HFMAPs and DMAPs, respectively. In comparison, the AUC_0-∞ of HFMAPs was significantly greater than that of the oral administration control group, which showed an AUC_0-∞ of 30.50 ± 9.18 μg h/mL (p < 0.05). This work demonstrates that transdermal delivery of VCL is feasible using DMAPs and HFMAPs and could prove effective in the treatment of infectious diseases caused by MRSA, such as skin and soft tissue infections, lymphatic-related infections, and neonatal sepsis.

Amifostine-loaded armored dissolving microneedles for long-term prevention of ionizing radiation-induced injury

Amifostine is a cytoprotective agent against the hematopoietic damage induced by ionizing radiation, although the intravenous injection of amifostine is a unique administration method with strict dosing time limitation. Hence, the fields of application of amifostine are greatly limited. Here, we developed an amifostine-loaded armored microneedle (AAMN) with long-term prevention of hematopoietic injury induced by ionizing radiation. First, amifostine-loaded hyaluronic acid microneedles (AMNs) were fabricated, and the AMNs were then dipped in an N-vinyl-2-pyrrolidone (NVP) solution followed by ultraviolet (UV) photocuring to obtain AAMNs. AAMNs were nail-shaped with much higher mechanical strength compared to the conical shape and weak strength of AMNs, which was verified by their in silico simulation. In the in vitro release experiment, more than 55% of amifostine was released from AAMNs within 10 min, and 95% was released in 60 min. Drug skin permeation of AAMNs was also high, at twice that of AMNs. AAMNs provided long-term protection of the hematopoietic system from radiation within 3-7 h pre-radiation compared to the unique amifostine injection 0.5 h pre-radiation because topical application of AAMNs led to the long-term maintenance of the in vivo effective drug concentration. More importantly, AAMNs led to the survival of all irradiated mice due to intravenous amifostine. AAMNs are a promising transdermal delivery system of amifostine for long-term protection against ionizing radiation-induced injury. STATEMENT OF SIGNIFICANCE: An amifostine-loaded dissolving armored microneedle (AAMN) patch is developed for long-term prevention of ionizing radiation-induced injury. High drug loads in microneedles (MNs) with adequate mechanical strength is a challenge. We fabricated armors on the surface of high amifostine-loaded hyaluronic acid microneedles (AMNs) by dipping the tips of AMNs in N-vinyl-2-pyrrolidone (NVP) solutions and then subjecting them to UV irradiation, and high-strength armored AMNs (AAMNs) were obtained. AAMNs show deeper skin insertion and much higher drug permeation than AMNs. The controlled drug release from AAMNs in the mouse skins provides a long-term protection of radiation-induced injury with 3-7 h administration pre-radiation compared to the merely 0.5-h point of amifostine injection.

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.

Construction of a core-shell microneedle system to achieve targeted co-delivery of checkpoint inhibitors for melanoma immunotherapy

Synergistic anti-tumor effect of anti-PD-1/L1 antibody (aPD-1/aPD-L1) and 1-methyl-D,L-tryptophan (1-MT) in melanoma has been well demonstrated, while efficient topical delivery systems are still largely unexplored. Here, a highly drug-concentrated hybrid core-shell microneedle (CSMN) system for co-delivery of checkpoint inhibitors was developed. Based on the specific drug-matrix interaction, the system concentrated aPD-L1 in the tips of microneedles through electrostatic interactions, and increased the amount of 1-MT loaded in CSMN by preventing its premature crystallization using PVA, the material used to prepare CSMN core. The prepared CSMN exhibited high transdermal delivery efficiency and long topical retention time of aPD-L1 for 2 days. Drug-loaded CSMN achieved better anti-tumor efficacy than the intra-tumor injection group at the same dose, which was likely because the former recruited more T lymphocytes to the tumor site. These findings suggested that this CSMN system was a promising local delivery system of both aPD-L1 and 1-MT for melanoma immunotherapy, and its unique core-shell structure could be readily adapted as a modular platform for various diseases, where combination therapy of both biomacromolecular drugs and other small-molecular agents were required. STATEMENT OF SIGNIFICANCE: In the present study, a core-shell microneedle (CSMN) system was constructed to achieve targeted co-delivery of checkpoint inhibitors to melanoma, while preventing significant systemic exposure. To overcome the drawback of insufficient drug loading of microneedles and effectively encapsulate two drugs simultaneously, microneedles were divided into two independent functional areas, a charged shell and a hydrophilic core and encapsulated drugs based on respective drug-matrix interaction. The charged shell prepared by chitosan could concentrate aPD-L1 in the tips of microneedles through electrostatic interactions. The core prepared by PVA successfully increased the amount of 1-MT loaded in microneedles by preventing its premature crystallization. The prepared CSMN exhibited high transdermal delivery efficiency and better anti-tumor efficacy than intra-tumor injection at the same dose.

A novel scalable fabrication process for the production of dissolving microneedle arrays

Microneedle arrays have emerged as an alternative method for transdermal drug delivery. Although micromolding using a centrifugation method is widely used to prepare microneedles in laboratory, few researchers were focused on manufacturing processes capable of facile scale-up. A novel female mold was initially designed in this study, namely double-penetration female mold (DPFM) with the pinpoints covered by waterproof breather membrane which was beneficial to reduce the influence of gas resistance and solution viscosity. In addition, DPFM-based positive-pressure microperfusion technique (PPPT) was proposed for the scale-up fabrication of dissolving microneedle arrays (DMNA). In this method, polymer solution and base solution were poured into the DPFM by pressure difference, followed by drying and demolding. The results of optimal microscopy and SEM revealed that the obtained microneedles were uniformly distributed conical-shaped needles. The skin penetration test showed that DMNA prepared using PPPT were able to penetrate the rat skin with a high penetration rate. To realize the transition of microneedles fabrication from laboratory to industry, an automatic equipment was further designed in this study. Different from micromolding method using centrifugation, the equipment based on PPPT and DPFM has superiorities in the scale-up fabrication of microneedles in a highly effective, controllable, and scalable way.

Synergistic immunoreaction of acupuncture-like dissolving microneedles containing thymopentin at acupoints in immune-suppressed rats

Dissolving microneedles carried drug molecules can effectively penetrate the stratum corneum of skin to improve the transdermal drug delivery. The traditional Chinese medicine acupuncture is based on the needle stimulation at a specific location (acupoint) to generate and transmit biochemical and physiological signals which alter the pathophysiological state of patients. However, the pain associated with conventional acupuncture needles and the requirement of highly trained professionals limit the development of acupuncture in non-Asian countries. The purpose of this study is to investigate whether the dissolving microneedles can be utilized as a self-administered painless replacement for acupuncture and locally released drug molecules can achieve expected therapeutic outcomes. Immunosuppressive rats were treated with acupuncture at Zusanli (ST36) acupoint using microneedles containing thymopentin. The immune functions and psychological mood of the immunosuppressed animals were examined. The proliferation of splenocytes was examined by CCK-8 assay. CD4 and CD8 expression patterns in spleen cells were detected by flow cytometry. The current study showed that use of either microneedles containing thymopentin or conventional acupuncture both resulted in immune cell proliferation, which was confirmed by flow cytometry. Furthermore, either conventional acupuncture or microneedles were able to effectively mitigate the anxiety caused by immune-suppression when applied on the ST36.

Recent advances of controlled drug delivery using microfluidic platforms

Conventional systematically-administered drugs distribute evenly throughout the body, get degraded and excreted rapidly while crossing many biological barriers, leaving minimum amounts of the drugs at pathological sites. Controlled drug delivery aims to deliver drugs to the target sites at desired rates and time, thus enhancing the drug efficacy, pharmacokinetics, and bioavailability while maintaining minimal side effects. Due to a number of unique advantages of the recent microfluidic lab-on-a-chip technology, microfluidic lab-on-a-chip has provided unprecedented opportunities for controlled drug delivery. Drugs can be efficiently delivered to the target sites at desired rates in a well-controlled manner by microfluidic platforms via integration, implantation, localization, automation, and precise control of various microdevice parameters. These features accordingly make reproducible, on-demand, and tunable drug delivery become feasible. On-demand self-tuning dynamic drug delivery systems have shown great potential for personalized drug delivery. This review presents an overview of recent advances in controlled drug delivery using microfluidic platforms. The review first briefly introduces microfabrication techniques of microfluidic platforms, followed by detailed descriptions of numerous microfluidic drug delivery systems that have significantly advanced the field of controlled drug delivery. Those microfluidic systems can be separated into four major categories, namely drug carrier-free micro-reservoir-based drug delivery systems, highly integrated carrier-free microfluidic lab-on-a-chip systems, drug carrier-integrated microfluidic systems, and microneedles. Microneedles can be further categorized into five different types, i.e. solid, porous, hollow, coated, and biodegradable microneedles, for controlled transdermal drug delivery. At the end, we discuss current limitations and future prospects of microfluidic platforms for controlled drug delivery.