The role of microneedles for drug and vaccine delivery

Nanocarrier-Integrated Microneedles: Divulging the Potential of Novel Frontiers for Fostering the Management of Skin Ailments

The various kinds of nanocarriers (NCs) have been explored for the delivery of therapeutics designed for the management of skin manifestations. The NCs are considered as one of the promising approaches for the skin delivery of therapeutics attributable to sustained release and enhanced skin penetration. Despite the extensive applications of the NCs, the challenges in their delivery via skin barrier (majorly stratum corneum) have persisted. To overcome all the challenges associated with the delivery of NCs, the microneedle (MN) technology has emerged as a beacon of hope. Programmable drug release, being painless, and its minimally invasive nature make it an intriguing strategy to circumvent the multiple challenges associated with the various drug delivery systems. The integration of positive traits of NCs and MNs boosts therapeutic effectiveness by evading stratum corneum, facilitating the delivery of NCs through the skin and enhancing their targeted delivery. This review discusses the barrier function of skin, the importance of MNs, the types of MNs, and the superiority of NC-loaded MNs. We highlighted the applications of NC-integrated MNs for the management of various skin ailments, combinational drug delivery, active targeting, in vivo imaging, and as theranostics. The clinical trials, patent portfolio, and marketed products of drug/NC-integrated MNs are covered. Finally, regulatory hurdles toward benchtop-to-bedside translation, along with promising prospects needed to scale up NC-integrated MN technology, have been deliberated. The current review is anticipated to deliver thoughtful visions to researchers, clinicians, and formulation scientists for the successful development of the MN-technology-based product by carefully optimizing all the formulation variables.

Application of hydrogel microneedles in the oral cavity

Microneedles are a transdermal drug delivery system in which the needle punctures the epithelium to deliver the drug directly to deep tissues, thus avoiding the influence of the first-pass effect of the gastrointestinal tract and minimizing the likelihood of pain induction. Hydrogel microneedles are microneedles prepared from hydrogels that have good biocompatibility, controllable mechanical properties, and controllable drug release and can be modified to achieve environmental control of drug release in vivo. The large epithelial tissue in the oral cavity is an ideal site for drug delivery via microneedles. Hydrogel microneedles can overcome mucosal hindrances to delivering drugs to deep tissues; this prevents humidity and a highly dynamic environment in the oral cavity from influencing the efficacy of the drugs and enables them to obtain better therapeutic effects. This article analyzes the materials and advantages of common hydrogel microneedles and reviews the application of hydrogel microneedles in the oral cavity.

Microneedle-mediated nanomedicine to enhance therapeutic and diagnostic efficacy

Nanomedicine has been extensively explored for therapeutic and diagnostic applications in recent years, owing to its numerous advantages such as controlled release, targeted delivery, and efficient protection of encapsulated agents. Integration of microneedle technologies with nanomedicine has the potential to address current limitations in nanomedicine for drug delivery including relatively low therapeutic efficacy and poor patient compliance and enable theragnostic uses. In this Review, we first summarize representative types of nanomedicine and describe their broad applications. We then outline the current challenges faced by nanomedicine, with a focus on issues related to physical barriers, biological barriers, and patient compliance. Next, we provide an overview of microneedle systems, including their definition, manufacturing strategies, drug release mechanisms, and current advantages and challenges. We also discuss the use of microneedle-mediated nanomedicine systems for therapeutic and diagnostic applications. Finally, we provide a perspective on the current status and future prospects for microneedle-mediated nanomedicine for biomedical applications.

Recent progress of polymeric microneedle-assisted long-acting transdermal drug delivery

Microneedle (MN)-assisted drug delivery technology has gained increasing attention over the past two decades. Its advantages of self-management and being minimally invasive could allow this technology to be an alternative to hypodermic needles. MNs can penetrate the stratum corneum and deliver active ingredients to the body through the dermal tissue in a controlled and sustained release. Long-acting polymeric MNs can reduce administration frequency to improve patient compliance and therapeutic outcomes, especially in the management of chronic diseases. In addition, long-acting MNs could avoid gastrointestinal reactions and reduce side effects, which has potential value for clinical application. In this paper, advances in design strategies and applications of long-acting polymeric MNs are reviewed. We also discuss the challenges in scale manufacture and regulations of polymeric MN systems. These two aspects will accelerate the effective clinical translation of MN products.

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.

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.

Polymer Delivery Systems for Long-Acting Antiretroviral Drugs

The success of long-acting (LA) drug delivery systems (DDSs) is linked to their biocompatible polymers. These are used for extended therapeutic release. For treatment or prevention of human immune deficiency virus type one (HIV-1) infection, LA DDSs hold promise for improved regimen adherence and reduced toxicities. Current examples include Cabenuva, Apretude, and Sunlenca. Each is safe and effective. Alternative promising DDSs include implants, prodrugs, vaginal rings, and microarray patches. Each can further meet patients' needs. We posit that the physicochemical properties of the formulation chemical design can optimize drug release profiles. We posit that the strategic design of LA DDS polymers will further improve controlled drug release to simplify dosing schedules and improve regimen adherence.

Advanced Technologies of Drug Delivery to the Posterior Eye Segment Targeting Angiogenesis and Ocular Cancer

Retinoblastoma (RB), a childhood retinal cancer is caused due to RB1 gene mutation which affects the child below 5 years of age. Angiogenesis has been proven its role in RB metastasis due to the presence of vascular endothelial growth factor (VEGF) in RB cells. Therefore, exploring angiogenic pathway by inhibiting VEGF in treating RB would pave the way for future treatment. In preclinical studies, anti-VEGF molecule have shown their efficacy in treating RB. However, treatment requires recurrent intra-vitreal injections causing various side effects along with patient nonadherence. As a result, delivery of anti-VEGF agent to retina requires an ocular delivery system that can transport it in a non-invasive manner to achieve patient compliance. Moreover, development of these type of systems are challenging due to the complicated physiological barriers of eye. Adopting a non-invasive or minimally invasive approach for delivery of anti-VEGF agents would not only address the bioavailability issues but also improve patient adherence to therapy overcoming the side effects associated with invasive approach. The present review focuses on the eye cancer, angiogenesis and various novel ocular drug delivery systems that can facilitate inhibition of VEGF in the posterior eye segment by overcoming the eye barriers.

Advances of Smart Stimulus-Responsive Microneedles in Cancer Treatment

Microneedles (MNs) have emerged as a highly promising technology for delivering drugs via the skin. They provide several benefits, including high drug bioavailability, non-invasiveness, painlessness, and high safety. Traditional strategies for intravenous delivery of anti-tumor drugs have risks of systemic toxicity and easy development of drug resistance, while MN technology facilitates precise delivery and on-demand release of drugs in local tissues. In addition, by further combining with stimulus-responsive materials, the construction of smart stimulus-responsive MNs can be achieved, which can respond to specific physical/chemical stimuli from the internal or external environment, thereby further improving the accuracy of tumor treatment and reducing toxicity to surrounding tissues/cells. This review systematically summarizes the classification, materials, and reaction mechanisms of stimulus-responsive MNs, outlines the benefits and challenges of various types of MNs, and details their application and latest progress in cancer treatment. Finally, the development prospects of smart MNs in tumor treatment are also discussed, bringing inspiration for future precision treatment of tumors.

Microneedle-based cell delivery and cell sampling for biomedical applications

Cell-based therapeutics are novel therapeutic strategies that can potentially treat many presently incurable diseases through novel mechanisms of action. Cell therapies may benefit from the ease, safety, and efficacy of administering therapeutic cells. Despite considerable recent technological and biological advances, several barriers remain to the clinical translation and commercialization of cell-based therapies, including low patient compliance, personal handling inconvenience, poor biosafety, and limited biocompatibility. Microneedles (MNs) are emerging as a promising biomedical device option for improved cell delivery with little invasion, pain-free administration, and simplicity of disposal. MNs have shown considerable promise in treating a wide range of diseases and present the potential to improve cell-based therapies. In this review, we first summarized the latest advances in the various types of MNs developed for cell delivery and cell sampling. Emphasis was given to the design and fabrication of various types of MNs based on their structures and materials. Then we focus on the recent biomedical applications status of MNs-mediated cell delivery and sampling, including tissue repair (wound healing, heart repair, and endothelial repair), cancer treatment, diabetes therapy, cell sampling, and other applications. Finally, the current status of clinical application, potential perspectives, and the challenges for clinical translation are also highlighted.

Application of Nano-Delivery Systems in Lymph Nodes for Tumor Immunotherapy

Immunotherapy has become a promising research "hotspot" in cancer treatment. "Soldier" immune cells are not uniform throughout the body; they accumulate mostly in the immune organs such as the spleen and lymph nodes (LNs), etc. The unique structure of LNs provides the microenvironment suitable for the survival, activation, and proliferation of multiple types of immune cells. LNs play an important role in both the initiation of adaptive immunity and the generation of durable anti-tumor responses. Antigens taken up by antigen-presenting cells in peripheral tissues need to migrate with lymphatic fluid to LNs to activate the lymphocytes therein. Meanwhile, the accumulation and retaining of many immune functional compounds in LNs enhance their efficacy significantly. Therefore, LNs have become a key target for tumor immunotherapy. Unfortunately, the nonspecific distribution of the immune drugs in vivo greatly limits the activation and proliferation of immune cells, which leads to unsatisfactory anti-tumor effects. The efficient nano-delivery system to LNs is an effective strategy to maximize the efficacy of immune drugs. Nano-delivery systems have shown beneficial in improving biodistribution and enhancing accumulation in lymphoid tissues, exhibiting powerful and promising prospects for achieving effective delivery to LNs. Herein, the physiological structure and the delivery barriers of LNs were summarized and the factors affecting LNs accumulation were discussed thoroughly. Moreover, developments in nano-delivery systems were reviewed and the transformation prospects of LNs targeting nanocarriers were summarized and discussed.

Quantification methods comparing in vitro and in vivo percutaneous permeation by microneedles and passive diffusion

Microneedles (MNs) are needles with a tip diameter ranging from 10 to 100 um and a length ranging up to 1 mm. The first patent for drug delivery device for percutaneous administration filed by Alza corporation dates back to 1976 (Gerstel and Place, 1976), and in between 1989 and 2021 the filed patents for MNs are more than 4500 (Banks et al., 2010). These devices can potential overcome some drawbacks of traditional needles, such as the pain generated during insertion, requirement for trained personnel to manipulate syringes, and difficulty of performing injections in elderly and obese patients. MNs and MNs arrays are emerging as a convenient method to deliver compounds and extract blood without causing any pain. A promising application is the use of MNs as alternative solution to topical creams (TC) and transdermal patches (TP) for transdermal drug delivery. The external layer of human skin, the epidermis, offers a major barrier to transdermal drug delivery, thanks to the stratum corneum (SC). Exposed to the external environment, SC ultimately protects the human body from UV light radiation, heat, water loss, bacteria, fungi and viruses, and it is the barrier that controls diffusion rate for almost all compounds. TC and TP applications are limited by the skin permeability to lipophilic compounds and small molecules, and by the slow delivery rate of some compounds. MNs have been around for more than 35 year now, and it is a general opinion that MN increase delivery compared to passive diffusion, thanks to the feature of penetrating the SC and reaching the dermis. This review recollects the existing studies that compare MNs delivery of drugs with passive diffusion of the same drugs in alive organisms, giving an overview of what are the type of MNs, the chemical delivered and the methods employed to quantify drug delivery into skin and/or in the bloodstream. The final aim is to quantify the enhancement factor of MNs with respect to passive diffusion, and establish a possible standard on how tests can be performed in order to compare different data.

Dissolvable Self-Locking Microneedle Patches Integrated with Immunomodulators for Cancer Immunotherapy

Advancements in micro-resolution 3D printers have significantly facilitated the development of highly complex mass-producible drug delivery platforms. Conventionally, due to the limitations of micro-milling machineries, dissolvable microneedles (MNs) are mainly fabricated in cone-shaped geometry with limited drug delivery accuracy. Herein, to overcome the limitations of conventional MNs, a novel projection micro-stereolithography 3D printer-based self-locking MN for precise skin insertion, adhesion, and transcutaneous microdose drug delivery is presented. The geometry of self-locking MN consists of a sharp skin-penetrating tip, a wide skin interlocking body, and a narrow base with mechanical supports fabricated over a flexible hydrocolloid patch to improve the accuracy of skin penetration into irregular surfaces. Melanoma, a type of skin cancer, is selected as the model for the investigation of self-locking MNs due to its irregular and uneven surface. In vivo immunotherapy efficacy is evaluated by integrating SD-208, a novel transforming growth factor-β (TGF-β) inhibitor that suppresses the proliferation and metastasis of tumors, and anti-PD-L1 (aPD-L1 Ab), an immune checkpoint inhibitor that induces T cell-mediated tumor cell death, into self-locking MNs and comparing them with intratumoral injection. Evaluation of (aPD-L1 Ab)/SD-208 delivery effectiveness in B16F10 melanoma-bearing mice model confirms significantly improved dose efficacy of self-locking MNs compared with intratumoral injection.

Dissolvable microneedles for transdermal drug delivery showing skin pentation and modified drug release

Topical therapies for chronic skin diseases suffer from a low patient compliance due to the inconvenient treatment regimens of available products. Dissolvable microneedles (MN) with modified release offer an interesting possibility to increase the compliance by acting as a depot in the skin and thereby decreasing the dosing frequency. Furthermore, the bioavailability can be increased significantly by bypassing the barrier of the skin by the direct penetration of the MN into the skin. In this study the depot effect and skin penetration of an innovative dissolvable MN patch was assessed by insertion in ex vivo human skin and in vivo using minipigs. The MN patches are based on biodegradable polymers and the active pharmaceutical ingredients calcipotriol (Calci) and betamethasone-17-21-dipropionate (BDP) used to treat psoriasis. Using computed tomography (CT) and Coherent anti-Stokes Raman scattering (CARS) microscopy it was possible to visualize the skin penetration and follow the morphology of the MN as function of time in the skin. The depot effect was assessed by studying the modified in vitro release in an aqueous buffer and by comparing the drug release of a single application of a patch both ex vivo and in vivo to daily application of a marketed oleogel containing the same active pharmaceutical ingredients. The CT and CARS images showed efficient penetration of the MN patches into the upper dermis and a slow swelling process of the drug containing tip over a period of 8 days. Furthermore, CARS demonstrated that it can be used as a noninvasive technique with potential applicability in clinical settings. The in vitro release studies show a release of 54% over a time period of 30 days. The pharmacological relevance of MNs was confirmed in human skin explants and in vivo after single application and showed a similar response on calcipotriol and BDP mediated signaling events compared to daily application of the active oleogel. Altogether it was demonstrated that the MN can penetrate the skin and have the potential to provide a depot effect.

Randomized trial of microneedling combined with 2% minoxidil topical solution for the treatment of female pattern hair loss in a Chinese population

OBJECTIVE

To evaluate the efficacy and safety of 2% minoxidil combined with microneedling in the treatment of female pattern hair loss.

METHODS

Forty female patients with female pattern hair loss were randomly divided into two groups with 20 patients each. The control group was treated with 2% minoxidil. The combined treatment group was treated with weekly microneedling in addition to daily minoxidil. The treatment period of both groups was 24 weeks.

RESULTS

There were no significant differences in age or duration of disease between the two groups of patients. The effective rate in the combined treatment group was 85%, which was significantly higher than that of the control group (45%). The hair counts were also higher in the combined treatment group. All of the adverse reactions observed during the treatment period were mild. No severe adverse event was observed in either group.

CONCLUSION

Microneedling combined with minoxidil had better efficacy for female pattern hair loss during the treatment period and follow-up. Microneedling combined with minoxidil therapy was safe and effective.

Promotion of Hair Regrowth by Transdermal Dissolvable Microneedles Loaded with Rapamycin and Epigallocatechin Gallate Nanoparticles

Interest in transdermal delivery methods for stimulating hair regrowth has been increasing recently. The microneedle approach can break the barrier of the stratum corneum through puncture ability and improve drug delivery efficiency. Herein, we report a dissolvable microneedle device for the co-delivery of rapamycin and epigallocatechin gallate nanoparticles that can significantly promote hair regeneration. Compared with the mice without any treatment, our strategy can facilitate hair growth within 7 days. Higher hair shaft growth rate and hair follicle density with inconspicuous inflammation were exhibited in C57BL/6 mice, elucidating its potential for clinical application.

Recent advances in pain management based on nanoparticle technologies

BACKGROUND

Pain is a vital sense that indicates the risk of injury at a particular body part. Successful control of pain is the principal aspect in medical treatment. In recent years, the advances of nanotechnology in pain management have been remarkable. In this review, we focus on literature and published data that reveal various applications of nanotechnology in acute and chronic pain management.

METHODS

The presented content is based on information collected through pain management publications (227 articles up to April 2021) provided by Web of Science, PubMed, Scopus and Google Scholar services.

RESULTS

A comprehensive study of the articles revealed that nanotechnology-based drug delivery has provided acceptable results in pain control, limiting the side effects and increasing the efficacy of analgesic drugs. Besides the ability of nanotechnology to deliver drugs, sophisticated nanosystems have been designed to enhance imaging and diagnostics, which help in rapid diagnosis of diseases and have a significant impact on controlling pain. Furthermore, with the development of various tools, nanotechnology can accurately measure pain and use these measurements to display the efficiency of different interventions.

CONCLUSIONS

Nanotechnology has started a new era in the pain management and many promising results have been achieved in this regard. Nevertheless, there is still no substantial and adequate act of nanotechnology in this field. Therefore, efforts should be directed to broad investigations.

In-Plane Si Microneedles: Fabrication, Characterization, Modeling and Applications

Microneedles are getting more and more attention in research and commercialization since their advancement in the 1990s due to the advantages over traditional hypodermic needles such as minimum invasiveness, low material and fabrication cost, and precise needle geometry control, etc. The design and fabrication of microneedles depend on various factors such as the type of materials used, fabrication planes and techniques, needle structures, etc. In the past years, in-plane and out-of-plane microneedle technologies made by silicon (Si), polymer, metal, and other materials have been developed for numerous biomedical applications including drug delivery, sample collections, medical diagnostics, and bio-sensing. Among these microneedle technologies, in-plane Si microneedles excel by the inherent properties of Si such as mechanical strength, wear resistance, biocompatibility, and structural advantages of in-plane configuration such as a wide range of length, readiness of integration with other supporting components, and complementary metal-oxide-semiconductor (CMOS) compatible fabrication. This article aims to provide a review of in-plane Si microneedles with a focus on fabrication techniques, theoretical and numerical analysis, experimental characterization of structural and fluidic behaviors, major applications, potential challenges, and future prospects.

Long-acting microneedle patch loaded with adipose collagen fragment for preventing the skin photoaging in mice

Skin photoaging is one of the most serious public health problems in the 21st century that may lead to thin, saggy, and structurally weakened skin. Adipokine therapy toward skin photoaging is always associated with poor permeability, biologic stability and the short in vivo release duration. Our laboratory previously extracted an extracellular matrix component of adipose tissue by purely physical methods, namely "adipose collagen fragment (ACF)", which holds promise for preventing skin photoaging. However, the injection treatment of ACF requires repeated preparation processes and injection procedures, which may be time-consuming and painful. Therefore, we describe the fabrication and assessment of a detachable ACF-microneedle (ACF-MN) patch that creates minimally invasive dermal microtrauma upon application. And we evaluated the morphology characterization, mechanical properties and puncture performance in vitro. The delivery efficiency of ACF from the patches was estimated in vitro and vivo. Then, the therapeutic efficacy was identified through applying ACF-MN patches into the dermis of UVA-induced photoaging mice and the related detection of skin photoaging was estimated. Our results demonstrated that ACF-MN exhibited well skin puncture performance and could release ACF component slowly. Meanwhile, this microneedle device loaded with ACF exhibited the treatment efficiency on skin photoaging in a mouse model. Therefore, implantation of the microtrauma-mediated, long-acting ACF-MN system can be utilized as a potential candidate for preventing skin photoaging in the clinic.

Advances in the Novel Nanotechnology for the Targeted Tumor Therapy by the Transdermal Drug Delivery

Despite modern medicine advances greatly, cancer remains a serious challenge to world health for which effective methods of treatment have hardly been developed yet. However, throughout the recent years, the rapid-developing nanotechnology has provided a new outlook of cancer therapy by transdermal drug delivery. By disrupting the stratum corneum, drugs are delivered through the skin and navigated to the tumor site by drug delivery systems such as nanogels, microneedles, etc. The superiorities include the improvement of drug pharmacokinetics as well as reduced side effects. This paper reviews the reported novel development of transdermal drug delivery systems for targeted cancer therapy. Advanced techniques for penetrating the skin will be discussed as well.

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.

Silk fibroin double-layer microneedles for the encapsulation and controlled release of triptorelin

A double-layer silk fibroin microneedles (SF-MNs) was proposed for the transdermal delivery of triptorelin. Two-step pouring and centrifugation were employed to prepare SF-MNs. Triptorelin was wrapped in MNs in the form of microcrystals with a size of ∼1 μm. β-sheet nanocrystals (the secondary structure of silk fibroin) were adjusted in content by methanol-vapor treatment to manipulate the characteristics of SF-MNs prepared with two concentrations of silk fibroin. The mechanical strength of MNs was measured and analyzed in proportion to the β-sheet content. The triptorelin in MNs could be released sustainedly in phosphate-buffered saline for 168 h, and the release amount decreased with increasing β-sheet content. The Ritger-Peppas equation was employed to fit the release data. A linear decreasing relationship was observed between the diffusion coefficient and increased β-sheet content. After administration to rats, SF-MNs exhibited long-term testosterone inhibition and maintained castration levels for ≥7 d. Manipulable mechanical properties and release behavior combined with biocompatibility and biodegradability render SF-MNs as viable long-term transdermal delivery devices for triptorelin.

Dissolving microneedle rollers for rapid transdermal drug delivery

Dissolving microneedle patch (DMNP) is a minimally invasive and painless self-administration device. However, due to skin deformation, it is difficult to apply it on the large areas of skin or curved skin as the patch size increased for DMNP. Here, we propose a polyvinyl alcohol (PVA)-based dissolving microneedle roller (DMNR) device that can be used for delivering drugs rapidly on the large surface areas or curved skin and does not need to be attached on the skin all the time during drug delivery. The hypoglycemic effect of insulin-loaded DMNRs for transdermal delivery of insulin was studied on the type 1 diabetic rat models. It was found that the insulin-loaded DMNR has an immediate and effective hypoglycemic effect that the blood glucose level reduced below to 50% of original blood glucose at 1 h after DMNRs administrated.

Tutorial: using nanoneedles for intracellular delivery

Intracellular delivery of advanced therapeutics, including biologicals and supramolecular agents, is complex because of the natural biological barriers that have evolved to protect the cell. Efficient delivery of therapeutic nucleic acids, proteins, peptides and nanoparticles is crucial for clinical adoption of emerging technologies that can benefit disease treatment through gene and cell therapy. Nanoneedles are arrays of vertical high-aspect-ratio nanostructures that can precisely manipulate complex processes at the cell interface, enabling effective intracellular delivery. This emerging technology has already enabled the development of efficient and non-destructive routes for direct access to intracellular environments and delivery of cell-impermeant payloads. However, successful implementation of this technology requires knowledge of several scientific fields, making it complex to access and adopt by researchers who are not directly involved in developing nanoneedle platforms. This presents an obstacle to the widespread adoption of nanoneedle technologies for drug delivery. This tutorial aims to equip researchers with the knowledge required to develop a nanoinjection workflow. It discusses the selection of nanoneedle devices, approaches for cargo loading and strategies for interfacing to biological systems and summarises an array of bioassays that can be used to evaluate the efficacy of intracellular delivery.

Smart pills for gastrointestinal diagnostics and therapy

Ingestible smart pills have the potential to be a powerful clinical tool in the diagnosis and treatment of gastrointestinal disease. Though examples of this technology, such as capsule endoscopy, have been successfully translated from the lab into clinically used products, there are still numerous challenges that need to be overcome. This review gives an overview of the research being done in the area of ingestible smart pills and reports on the technical challenges in this field.

Preparation and evaluation of rapid disintegrating formulation from coated microneedle

Microneedles (MNs), one of the transdermal drug delivery systems, have received extensive interest as an alternative to parenteral or parenteral administrations. For the successful drug delivery of coated MNs, the coated drug or chemical of MNs should be dissolved by skin's interstitial fluid and completely released from the MNs. Thus, the rapid disintegration of the drug from MNs plays a crucial role in ideal drug delivery of MNs. In this study, we developed the rapid disintegration coating formulation to reduce the application time of MN. The rapid disintegration MN was developed using polymers (PVA or HPMC), glycerol, croscarmellose sodium, tween 80, and Brij, as thickener, plasticizer, disintegrating agent, and surfactants, respectively. HPMC MN showed the burst release and rapid disintegration. Moreover, the drug from HPMC MN was successfully delivered into porcine skin within 1 min. In toxicological evaluation, the HPMC MN did not alter the liver and kidney function. Besides, HPMC MN did not induce the acute inflammation and change of skin structure after the application on rat skin. Thus, the coating formulation in this study could be one of the options for the development of safe and rapid disintegration MN.

Pharmaceutical Perspective in Wearable Drug Delivery Systems

Humans have been dealing with health problems for millions of years. Normal health services need well-trained personnel and high-cost diagnostic tests, which forces patients to go to hospitals if medical treatment is required. To address this, prototype testing has been carried out into the wearable drug delivery health care perspectives. Researchers have devised a wide variety of formulations for the treatment of various diseases at home by performing real-time monitoring of different routes of drug administration such as ocular, transdermal, intraoral, intracochlear, and several more. A comprehensive review of the different types of wearable drug delivery systems with respect to their manufacturing, mechanism of action and specifications has been done. In the pharmaceutical context, these devices are technologically well-equipped interfaces for diverse physicochemical signals. Above mentioned information with a broader perspective has also been discussed in this article. Several wearable drug delivery systems have been introduced in the market in recent years. But a lot of testing needs to be conducted to address the numerous obstacles before the wearable devices are successfully launched in the market.

Chitosan-based microneedles as a potential platform for drug delivery through the skin: Trends and regulatory aspects

Microneedles (MNs) fabrication using chitosan has gained significant interest due to its ability of film-forming, biodegradability, and biocompatibility, making it suitable for topical and transdermal drug delivery. The presence of amine and hydroxyl functional groups on chitosan permits the modification with tunable properties and functionalities. In this regard, chitosan is the preferred material for fabrication of MNs because it does not produce an immune response in the body and can be tailored as per required strength and functionalities. Therefore, many researchers have attempted to use chitosan as a drug delivery vehicle for hydrophilic drugs, peptides, and hormones. In 2020, the FDA has issued "Regulatory Considerations for Microneedling Products". This official guidance is a sign for future opportunities in the development of MNs. The present review focuses on properties, and modifications of chitosan used in the fabrication of MNs. The therapeutic and diagnostic applications of different types of chitosan-based MNs have been discussed. Further, the regulatory aspects of MN-based devices, and patents related to chitosan-based MNs are discussed.

Microarray patches: Breaking down the barriers to contraceptive care and HIV prevention for women across the globe

Despite the existence of a variety of contraceptive products for women, as well as decades of research into the prevention and treatment of human immunodeficiency virus (HIV), there is still a globally unmet need for easily accessible, acceptable, and affordable products to protect women's sexual and reproductive health. Microarray patches (MAPs) are a novel platform being developed for the delivery of hormonal contraception and antiretroviral drugs. MAPs provide enhanced drug delivery to the systemic circulation via the transdermal route when compared to transdermal patches, oral and injectable formulations. These minimally invasive patches can be self-administered by the user, reducing the burden on health care personnel. Since MAPs represent needle-free drug delivery, no sharps waste is generated after application, thereby eliminating possible MAP reuse and risk of needle-stick injuries. This review discusses the administration of contraceptive and antiretroviral drugs using MAPs, their acceptability by end-users, and the future perspective of the field.

Etravirine-loaded dissolving microneedle arrays for long-acting delivery

A key challenge of HIV treatment with multiple antiretroviral drugs is patient adherence. Thus, there is an urgent need for long-acting depot systems for delivering drugs over an extended duration. Although the parenteral route is preferred for depot systems, it is associated with obvious drawbacks, such as painful injections, potentially-contaminated sharps waste, and the necessity of trained healthcare personnel for administration. Amongst a small number of alternatives in development microneedles are versatile delivery systems enabling systemic drug delivery and potentially improving patient adherence due to their capacity for self-administration. We have developed dissolving microneedle (DMNs) embedded with etravirine nanosuspension (ETR NS) as a long-acting HIV therapy to improve patient adherence. The ETR NS prepared by sonoprecipitation yielded particle sizes of 764 ± 96.2 nm, polydispersity indices of of 0.23 ± 0.02, and zeta potentials of -19.75 ± 0.55 mV. The DMNs loaded with ETR NS demonstrated 12.84 ± 1.33% ETR deposition in ex-vivo neonatal porcine skin after 6 h application. In in vivo rat pharmacokinetic studies, the Cmax exhibited by DMNs loaded with ETR powder and ETR NS were 158 ± 10 ng/mL and 177 ± 30 ng/mL, respectively. DMN groups revealed a higher t_1/2, Tmax, and mean residence time compared to intravenous ETR solutions, suggesting the long-acting potential of etravirine delivered intradermally using DMNs.

Clustering and Erratic Movement Patterns of Syringe-Injected versus Mosquito-Inoculated Malaria Sporozoites Underlie Decreased Infectivity

Malaria vaccine candidates based on live, attenuated sporozoites have led to high levels of protection. However, their efficacy critically depends on the sporozoites' ability to reach and infect the host liver. Administration via mosquito inoculation is by far the most potent method for inducing immunity but highly impractical. Here, we observed that intradermal syringe-injected Plasmodium berghei sporozoites (^syrSPZ) were 3-fold less efficient in migrating to and infecting mouse liver than mosquito-inoculated sporozoites (^msqSPZ). This was related to a clustered dermal distribution (2-fold-decreased median distance between ^syrSPZ and ^msqSPZ) and, more importantly, a 1.4-fold (significantly)-slower and more erratic movement pattern. These erratic movement patterns were likely caused by alteration of dermal tissue morphology (>15-μm intercellular gaps) due to injection of fluid and may critically decrease sporozoite infectivity. These results suggest that novel microvolume-based administration technologies hold promise for replicating the success of mosquito-inoculated live, attenuated sporozoite vaccines.IMPORTANCE Malaria still causes a major burden on global health and the economy. The efficacy of live, attenuated malaria sporozoites as vaccine candidates critically depends on their ability to migrate to and infect the host liver. This work sheds light on the effect of different administration routes on sporozoite migration. We show that the delivery of sporozoites via mosquito inoculation is more efficient than syringe injection; however, this route of administration is highly impractical for vaccine purposes. Using confocal microscopy and automated imaging software, we demonstrate that syringe-injected sporozoites do cluster, move more slowly, and display more erratic movement due to alterations in tissue morphology. These findings indicate that microneedle-based engineering solutions hold promise for replicating the success of mosquito-inoculated live, attenuated sporozoite vaccines.

Microarray patches enable the development of skin-targeted vaccines against COVID-19

The COVID-19 pandemic is a serious threat to global health and the global economy. The ongoing race to develop a safe and efficacious vaccine to prevent infection by SARS-CoV-2, the causative agent for COVID-19, highlights the importance of vaccination to combat infectious pathogens. The highly accessible cutaneous microenvironment is an ideal target for vaccination since the skin harbors a high density of antigen-presenting cells and immune accessory cells with broad innate immune functions. Microarray patches (MAPs) are an attractive intracutaneous biocargo delivery system that enables safe, reproducible, and controlled administration of vaccine components (antigens, with or without adjuvants) to defined skin microenvironments. This review describes the structure of the SARS-CoV-2 virus and relevant antigenic targets for vaccination, summarizes key concepts of skin immunobiology in the context of prophylactic immunization, and presents an overview of MAP-mediated cutaneous vaccine delivery. Concluding remarks on MAP-based skin immunization are provided to contribute to the rational development of safe and effective MAP-delivered vaccines against emerging infectious diseases, including COVID-19.

Dissolvable Microneedle Patches to Enable Increased Access to Vaccines against SARS-CoV-2 and Future Pandemic Outbreaks

Vaccines are an essential component of pandemic preparedness but can be limited due to challenges in production and logistical implementation. While vaccine candidates were rapidly developed against severe acute respiratory syndrome coronavirus 2 (SARS-COV-2), immunization campaigns remain an obstacle to achieving herd immunity. Dissolvable microneedle patches are advantageous for many possible reasons: improved immunogenicity; dose-sparing effects; expected low manufacturing cost; elimination of sharps; reduction of vaccine wastage; no need for reconstitution; simplified supply chain, with reduction of cold chain supply through increased thermostability; ease of use, reducing the need for healthcare providers; and greater acceptability compared to traditional hypodermic injections. When applied to coronavirus disease 2019 (COVID-19) and future pandemic outbreaks, microneedle patches have great potential to improve vaccination globally and save many lives.

STAR particles in context: a novel contender in the search for optimized drug-delivery systems

Targeted delivery, maximized bioavailability, minimal invasiveness, minimal side effects and cost-effectiveness are all markers of a successful drug delivery method. Although topical therapy, where diseased skin is targeted, remains a method of limited use, transdermal drug delivery systems seek to utilize skin as a vehicle for deeper systemic effects. Recently, Tadros et al. outlined an innovation to maximize the potential of topical delivery as a minimally invasive, user-friendly and safe medium. STAR particles seek to improve transdermal delivery by creating micropores in the stratum corneum. Several investigations have been conducted with promising results, including in vitro and in vivo animal and human studies. Despite a number of limitations and further considerations, the potential implications of STAR particles in the clinical disease setting are monumental.

Development of syringes and vials for delivery of biologics: current challenges and innovative solutions

INTRODUCTION

Several new biopharmaceutical dosage forms have developed over time, such as lyophilized vial, liquid vial, and liquid prefilled syringe formulations. This review summarizes major pharmaceutical dosage forms and their advantages, disadvantages, and countermeasures against the shortcomings of each formulation. The appropriate combination of active pharmaceutical ingredients, excipients, and containers should be selected for the safe and less burdensome administration to the patients. Finally, we note certain opinions on the future development of not only therapeutic proteins but also gene therapeutics.

AREAS COVERED

This review is to discuss the challenges of the development of dosage forms to improve pharmaceutical stability and how they can be overcome.

EXPERT OPINION

Silicone oil-free syringes are highly preferable for minimizing subvisible particles in the drug. It can be proposed that materials with less protein adsorption property are preferable for the suppression of protein aggregation. It is required to minimize adverse effects of biopharmaceuticals through proper quality control of the drug in a container, based on the understating of physicochemical stability of the protein in solution, the physicochemical properties of the container, and their combinations.

Characterization of microneedles and microchannels for enhanced transdermal drug delivery

Microneedle (MN)-based technologies are currently one of the most innovative approaches that are being extensively investigated for transdermal delivery of low molecular weight drugs, biotherapeutic agents and vaccines. Extensive research reports, describing the fabrication and applications of different types of MNs, can be readily found in the literature. Effective characterization tools to evaluate the quality and performance of the MNs as well as for determination of the dimensional and kinetic properties of the microchannels created in the skin, are an essential and critical part of MN-based research. This review paper provides a comprehensive account of all such tools and techniques.

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.

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.

Progress and perspective of microneedle system for anti-cancer drug delivery

Transdermal drug delivery exhibited encouraging prospects, especially through superficial drug administration routes. However, only a few limited lipophilic drug molecules could cross the skin barrier, those are with low molecular weight and rational Log P value. Microneedles (MNs) can overcome these limitations to deliver numerous drugs into the dermal layer by piercing the outermost skin layer of the body. In the case of superficial cancer treatments, topical drug administration faces severely low transfer efficiency, and systemic treatments are always associated with side effects and premature drug degradation. MN-based systems have achieved excellent technical capabilities and been tested for pre-clinical chemotherapy, photothermal therapy, photodynamic therapy, and immunotherapy. In this review, we will focus on the features, progress, and opportunities of MNs in the anticancer drug delivery system. Then, we will discuss the strategies and advantages in these works and summarize challenges, perspectives, and translational potential for future applications.

Characterization of Hepatitis B Surface Antigen Loaded Polylactic Acid-Based Microneedle and Its Dermal Safety Profile

A surge of interest in microneedle (MN) vaccines as a novel vaccination system has emerged. Before the clinical application of MN vaccine, an assessment of potential biological risks to skin and quality control of MN must be performed. Therefore, the present study aims to evaluate the physicochemical properties of MN and to evaluate the histological changes and inflammatory cell infiltrations after the application of MN with hepatitis B surface antigen (HBsAg). During in vitro and in vivo release testing, HBsAg MN released over 70% of HBsAg at 30 min. During the pyrogen test of HBsAg MN in rabbit, no rabbit showed an individual rise in temperature of 0.5 °C or more. MN with HBsAg produced the moderate immunization in mice. MN application did not alter the thickness of dermal and epidermal layers in mice. In addition, the topical applications of MN and MN for hepatitis B vaccine did not acutely induce the inflammation, allergic reaction, dermal toxicity and skin irritation. Thus, the MN system for the delivery of HBsAg could be the promising technology in the hepatitis B vaccination.

Microneedle-mediated gene delivery for the treatment of ischemic myocardial disease

Cardiovascular disorders are still the primary cause of mortality worldwide. Although intramyocardial injection can effectively deliver agents to the myocardium, this approach is limited because of its restriction to needle-mediated injection and the minor retention of agents in the myocardium. Here, we engineered phase-transition microneedles (MNs) coated with adeno-associated virus (AAV) and achieved homogeneous distribution of AAV delivery. Bioluminescence imaging revealed the successful delivery and transfection of AAV-luciferase. AAV-green fluorescent protein-transfected cardiomyocytes were homogeneously distributed on postoperative day 28. AAV-vascular endothelial growth factor (VEGF)-loaded MNs improved heart function by enhancing VEGF expression, promoting functional angiogenesis, and activating the Akt signaling pathway. The results indicated the superiority of MNs over direct muscle injection. Consequently, MNs might emerge as a promising tool with great versatility for delivering various agents to treat ischemic myocardial disease.

Gut Check Time: Antibiotic Delivery Strategies to Reduce Antimicrobial Resistance

Antimicrobial resistance (AMR) has developed into a huge threat to global health, and reducing it is an urgent priority for public health authorities. The importance of a healthy and balanced gut microbiome has been identified as a key protective factor against AMR development, but this can be significantly affected by antibiotic therapy, resulting in dysbiosis and reduction of taxonomic richness. The way in which antibiotics are administered could form an important part of future antimicrobial stewardship strategies, where drug delivery is ideally placed to play a key role in the fight against AMR. This review focuses on drug delivery strategies for antibiotic administration, including avoidance of the gut microbiome and targeted delivery approaches, which may reduce AMR.

Topical and Transdermal Drug Delivery: From Simple Potions to Smart Technologies

This overview on skin delivery considers the evolution of the principles of percutaneous ab-sorption and skin products from ancient times to today. Over the ages, it has been recognised that products may be applied to the skin for either local or systemic effects. As our understanding of the anatomy and physiology of the skin has improved, this has facilitated the development of technologies to effectively and quantitatively deliver solutes across this barrier to specific target sites in the skin and beyond. We focus on these technologies and their role in skin delivery today and in the future.

Design and Development of Liquid Drug Reservoirs for Microneedle Delivery of Poorly Soluble Drug Molecules

The poor aqueous solubility of existing and emerging drugs is a major issue faced by the pharmaceutical industry. Water-miscible organic solvents, termed co-solvents, can be used to enhance the solubility of poorly soluble substances. Typically, drugs with poor aqueous solubility and Log P > 3 are not amenable to delivery across the skin. This study investigated the use of co-solvents as reservoirs to be used in combination with hydrogel-forming microneedles to enhance the transdermal delivery of hydrophobic compounds, namely Nile red, olanzapine and atorvastatin. A custom-made Franz cell apparatus was fabricated to test the suitability of a liquid drug reservoir in combination with polymeric microneedles. A co-solvency approach to reservoir formulation proved effective, with 83.30% ± 9.38% of Nile red dye, dissolved in 1 mL poly(ethylene glycol) (PEG 400), permeating neonatal porcine skin over 24 h. PEG 400 and propylene glycol were found to be suitable reservoir media for olanzapine and atorvastatin, with approximately 50% of each drug delivered after 24 h. This work provides crucial proof-of-concept evidence that the manipulation of microneedle reservoir properties is an effective method to facilitate microneedle-mediated delivery of hydrophobic compounds.