Microneedle-based drug and vaccine delivery via nanoporous microneedle arrays

Recent progress of microneedles in transdermal immunotherapy: A review

Since human skin is an immune organ, a large number of immune cells are distributed in the epidermis and the dermis of the skin. Transdermal immunotherapy shows great therapeutic advantages in innate immunotherapy and adaptive immunotherapy. To solve the problem that macromolecules are difficult to penetrate into the skin, the microneedle technology can directly break through the skin barrier using micron-sized needles in a non-invasive and painless way for transdermal drug delivery. Therefore, it is considered to be an effective technology to increase drug transdermal absorption. In this review, the types of preparation, the combinations with different techniques and the mechanisms of microneedles in transdermal immunotherapy were summarized. Compared with traditional immunotherapy like intramuscular injection and subcutaneous injection, the microneedle has many advantages in transdermal immunotherapy, such as reducing patient pain, enhancing vaccine stability, and inducing stronger immune responses. Although there are still some limitations to be solved, the application of microneedle technology in transdermal immunotherapy is undoubtedly a promising means of drug delivery.

Soft and Flexible Bioelectronic Micro-Systems for Electronically Controlled Drug Delivery

The concept of targeted and controlled drug delivery, which directs treatment to precise anatomical sites, offers benefits such as fewer side effects, reduced toxicity, optimized dosages, and quicker responses. However, challenges remain to engineer dependable systems and materials that can modulate host tissue interactions and overcome biological barriers. To stay aligned with advancements in healthcare and precision medicine, novel approaches and materials are imperative to improve effectiveness, biocompatibility, and tissue compliance. Electronically controlled drug delivery (ECDD) has recently emerged as a promising approach to calibrated drug delivery with spatial and temporal precision. This article covers recent breakthroughs in soft, flexible, and adaptable bioelectronic micro-systems designed for ECDD. It overviews the most widely reported operational modes, materials engineering strategies, electronic interfaces, and characterization techniques associated with ECDD systems. Further, it delves into the pivotal applications of ECDD in wearable, ingestible, and implantable medical devices. Finally, the discourse extends to future prospects and challenges for ECDD.

Microneedles: A minimally invasive delivery system for ocular treatment

This review article delves into the extensive use of microneedles in ocular therapy, emphasizing their efficacy in delivering drug substances to the posterior region of the eye. The conventional methods of drug delivery, while widely employed, are marred by inherent drawbacks such as neovascularization, abrasion, and infiltration. To address these limitations, the review explores various approaches to microneedle fabrication, shedding light on the diverse materials employed in the process. Furthermore, the article meticulously examines the delivered drug substances using distinct microneedle approaches and their applications in ocular therapy. By critically evaluating the drawbacks associated with conventional ophthalmic drug delivery, the review seeks to pave the way for a paradigm shift. It advocates for a novel approach centered around minimally invasive microneedles, presenting them as a promising solution to overcome the limitations of current drug delivery methods. The comprehensive discussion within this article not only offers insights into the fabrication techniques and materials used for microneedles but also provides a nuanced understanding of the applications and advantages associated with this innovative approach. As the exploration of microneedle technology continues to evolve, this review serves as a valuable resource for researchers, clinicians, and pharmaceutical professionals seeking to enhance ocular therapy by embracing the potential of minimally invasive microneedles.

Microfluidic Mechanoporation: Current Progress and Applications in Stem Cells

Intracellular delivery, the process of transporting substances into cells, is crucial for various applications, such as drug delivery, gene therapy, cell imaging, and regenerative medicine. Among the different approaches of intracellular delivery, mechanoporation stands out by utilizing mechanical forces to create temporary pores on cell membranes, enabling the entry of substances into cells. This method is promising due to its minimal contamination and is especially vital for stem cells intended for clinical therapy. In this review, we explore various mechanoporation technologies, including microinjection, micro-nano needle arrays, cell squeezing through physical confinement, and cell squeezing using hydrodynamic forces. Additionally, we highlight recent research efforts utilizing mechanoporation for stem cell studies. Furthermore, we discuss the integration of mechanoporation techniques into microfluidic platforms for high-throughput intracellular delivery with enhanced transfection efficiency. This advancement holds potential in addressing the challenge of low transfection efficiency, benefiting both basic research and clinical applications of stem cells. Ultimately, the combination of microfluidics and mechanoporation presents new opportunities for creating comprehensive systems for stem cell processing.

State-of-the-art drug delivery system to target the lymphatics

PRIMARY OBJECTIVE

The primary objective of the review is to assess the potential of lymphatic-targeted drug delivery systems, with a particular emphasis on their role in tumour therapy and vaccination efficacy.

REASON FOR LYMPHATIC TARGETING

The lymphatic system's crucial functions in maintaining bodily equilibrium, regulating metabolism, and orchestrating immune responses make it an ideal target for drug delivery. Lymph nodes, being primary sites for tumour metastasis, underscore the importance of targeting the lymphatic system for effective treatment.

OUTCOME

Nanotechnologies and innovative biomaterials have facilitated the development of lymphatic-targeted drug carriers, leveraging endogenous macromolecules to enhance drug delivery efficiency. Various systems such as liposomes, micelles, inorganic nanomaterials, hydrogels, and nano-capsules demonstrate significant potential for delivering drugs to the lymphatic system.

CONCLUSION

Understanding the physiological functions of the lymphatic system and its involvement in diseases underscores the promise of targeted drug delivery in improving treatment outcomes. The strategic targeting of the lymphatic system presents opportunities to enhance patient prognosis and advance therapeutic interventions across various medical contexts, indicating the importance of ongoing research and development in this area.

Coated Porous Microneedles for Effective Intradermal Immunization with Split Influenza Vaccine

In order to alleviate the pain associated with subcutaneous injections, microneedles (MNs) are gaining increasing attention as a novel transdermal drug delivery modality. Among them, porous microneedles (pMNs) are particularly suitable for the delivery of drugs and vaccines whose activity is sensitive to the microneedle preparation process. They can carry drugs actively to achieve an effective load and deliver drugs into the skin. In this study, the biocompatible cellulose acetate (CA) microporous MNs with a large pore size of 1.13 μm ± 0.45 and a high porosity of 74.8% ± 2.8% were prepared by using a safe nonsolvent-induced phase separation (NIPS) method. The MN patches prepared after adsorption of appropriate concentrations of split influenza vaccine fully met the dose loading requirements. A biocompatible carboxymethyl cellulose (CMC) solution was used in the pMN coating to strengthen their mechanical properties, with an average maximum stress of 32.89 N, and to act as a medium for the dispersion of an adjuvant in the coating layer. The influenza vaccine adsorbed in the micropore and the adjuvant dispersed in the coating were released intradermally to exert synergistic effects with different release patterns and rates. The coated pMNs induced an efficient immune response in Wistar rats with a hemagglutination inhibition (HI) titer of ≥1024, which was comparable to that of intramuscular injection. The research is organized around the goal of engineering exploration of innovative technologies, suggesting that pMNs have a tantalizing prospect for future applications. It opens up the possibility of eventually obtaining a simple, easy-to-use, and efficient application technology for the prevention of global epidemics like influenza.

Establishing immunogenicity and safety of needle-free intradermal delivery by nanoporous ceramic skin patch of mRNA SARS-CoV-2 vaccine as a revaccination strategy in healthy volunteers

INTRODUCTION

Nanoporous microneedle arrays (npMNA) are being developed as skin patches for vaccine delivery. As alternative for needle-based immunisation, they may potentially result in higher vaccine acceptance, which is important for future mass vaccination campaigns to control outbreaks, such as COVID-19, and for public vaccination in general. In this study we investigated the safety and immunogenicity of needle-free intradermal delivery of a fractional third or fourth dose of mRNA-1273 vaccine by npMNA.

METHODS

This study was an open-label, randomised-controlled, proof-of-concept study. Healthy adults were eligible if they had received a primary immunisation series against SARS-CoV-2 with two doses of mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech) mRNA vaccine. A history of a COVID-19 infection or booster vaccination with mRNA-1273 or BNT162b2 was allowed if it occurred at least three months before inclusion. Participants were randomised in a 1:1 ratio to receive 20 µg mRNA-1273 vaccine, either through npMNA patch applied on the skin (ID-patch group), or through intramuscular (IM) injection (IM-control group). Primary outcomes were reactogenicity up to two weeks after vaccination, and fold-increase of SARS-CoV-2 spike S1-specific IgG antibodies 14 days post-vaccination.

RESULTS

In April 2022, 20 participants were enroled. The geometric mean concentration (GMC) did not increase in the ID-patch group after vaccination, in contrast to the IM-control group (GMC was 1,006 BAU/mL (95% CI 599-1,689), 3,855 (2,800-5,306), and 3,513 (2,554-4,833) at day 1, 15 and 29, respectively). In addition, SARS-CoV-2-specific T cell responses were lower after ID vaccination through npMNA.

CONCLUSION

Needle-free delivery of 20 µg mRNA-1273 vaccine by npMNA failed to induce antibody and T cell responses. As this is a potentially very useful vaccination method, it is important to determine which adjustments are needed to make this npMNA successful. CLINICAL TRIAL REGISTRY (ON CLINICALTRIAL.GOV): NCT05315362.

Porous Microneedles for Therapy and Diagnosis: Fabrication and Challenges

The use of microneedles (MNs), an innovative transdermal technology, enables efficient, convenient, painless, and controlled-release drug delivery. Porous microneedles (pMNs), special MNs with abundant interconnected pores that can produce capillary action, are gaining increasing attention as a novel MNs technology. pMNs can actively adsorb bioactive ingredients from solutions of drugs or vaccines for in vivo delivery or from interstitial skin fluids (ISFs) for wearable and point-of-care testing (POCT) products. Different pore sizes and porosities of pMNs can be achieved with different materials and preparation processes, which makes the application of pMNs adaptable to multiple scenarios. In addition, easier and faster detection will be accomplished by the smart combination of pMNs with other detection technologies. This paper aims to summarize the recent research progress of pMNs, focusing on the influence of various materials and their corresponding preparation methods on its structure and function display, discussing the key issues and looking forward to the future development.

Metallic Microneedles for Transdermal Drug Delivery: Applications, Fabrication Techniques and the Effect of Geometrical Characteristics

Current procedures for transdermal drug delivery (TDD) have associated limitations including poor administration of nucleic acid, small or large drug molecules, pain and stress for needle phobic people. A painless micro-sized device capable of delivering drugs easily and efficiently, eliminating the disadvantages of traditional systems, has yet to be developed. While polymeric-based microneedle (MN) arrays have been used successfully and clinically as TDD systems, these devices lack mechanical integrity, piercing capacity and the ability to achieve tailored drug release into the systemic circulation. Recent advances in micro/nano fabrication techniques using Additive Manufacturing (AM), also known as 3D printing, have enabled the fabrication of metallic MN arrays, which offer the potential to overcome the limitations of existing systems. This review summarizes the different types of MNs used in TDD and their mode of drug delivery. The application of MNs in the treatment of a range of diseases including diabetes and cancer is discussed. The potential role of solid metallic MNs in TDD, the various techniques used for their fabrication, and the influence of their geometrical characteristics (e.g., shape, size, base diameter, thickness, and tip sharpness) on effective TDD are explored. Finally, the potential and the future directions relating to the optimization of metallic MN arrays for TDD are highlighted.

Transdermal Insulin Delivery and Microneedles-based Minimally Invasive Delivery Systems

Diabetes has become a serious threat to human health, causing death and pain to numerous patients. Transdermal insulin delivery is a substitute for traditional insulin injection to avoid pain from the injection. Transdermal methods include non-invasive and invasive methods. As the non-invasive methods could hardly get through the stratum corneum, minimally invasive devices, especially microneedles, could enhance the transappendageal route in transcutaneous insulin delivery, and could act as connectors between the tissue and outer environment or devices. Microneedle patches have been in quick development in recent years and with different types, materials and functions. In those patches, the smart microneedle patch could perform as a sensor and reactor responding to glucose to regulate the blood level. In the smart microneedles field, the phenylboronic acid system and the glucose oxidase system have been successfully applied on the microneedle platform. Insulin transdermal delivery strategy, microneedles technology and smart microneedles' development would be discussed in this review.

Closed-Loop Diabetes Minipatch Based on a Biosensor and an Electroosmotic Pump on Hollow Biodegradable Microneedles

Developing a miniaturized, low-cost, and smart closed-loop system for diabetes could significantly improve life quality and benefit millions of people. Conventional closed-loop devices are large in size and exorbitant. Here, we unprecedentedly demonstrate an electrically controlled flexible closed-loop patch for continuous diabetes management by integrating hollow biodegradable microneedles with a biosensing device and an electroosmotic pump. The hollow microneedles were fabricated using a combination of soft lithography and micromachining. The outer layer of the microneedles was functionalized to serve as a biosensing device for the in situ sensitive and accurate monitoring of interstitial glucose. The inner layer of the microneedles was integrated with a flexible electroosmotic pump to deliver insulin, and the delivery rate was electrically controlled by the glucose level from the biosensing device. The closed-loop system successfully stabilized the blood glucose levels of diabetic rats in a normal and safe range. The system is painless, miniaturized, cost-effective, and flexible. It is anticipated that it could open up exciting new avenues for fundamental studies of new closed-loop devices as well as practical applications for diabetes management.

Antibiofilm Efficacy of the Pseudomonas aeruginosa Pbunavirus vB_PaeM-SMS29 Loaded onto Dissolving Polyvinyl Alcohol Microneedles

Resistant bacteria prevail in most chronic skin wounds and other biofilm-related topical skin infections. Bacteriophages (phages) have proven their antimicrobial effectiveness for treating different antibiotic-resistant and multidrug-resistant bacterial infections, but not all phages are effective against biofilms. Phages possessing depolymerases can reach different biofilm layers; however, those that do not have depolymerase activity struggle to penetrate and navigate in the intricate 3D biofilm structure and mainly infect bacteria lodged in the outer biofilm layers. To address this, Pseudomonas aeruginosa phage vB_PaeM-SMS29, a phage with poor antibiofilm properties, was incorporated into polyvinyl alcohol (PVA, Mowiol 4:88) supplemented with 0.1% (v/v) of glycerol, and cast onto two different microneedle arrays varying in geometry. The dissolving microneedles were thoroughly characterized by microscopy, force-displacement, swelling, phage release and stability. Furthermore, 48 h-old biofilms were formed using the colony biofilm procedure (absence of broth), and the antibiofilm efficacy of the phage-loaded microneedles was evaluated by viable cell counts and microscopy and compared to free phages. The phages in microneedles were fairly stable for six months when stored at 4 °C, with minor decreases in phage titers observed. The geometry of the microneedles influenced the penetration and force-displacement characteristics but not the antimicrobial efficacy against biofilms. The two PVA microneedles loaded with phages reduced P. aeruginosa PAO1 biofilms by 2.44 to 2.76 log₁₀ CFU·cm^-2 at 24 h. These values are significantly higher than the result obtained after the treatment with the free phage (1.09 log₁₀ CFU·cm^-2). Overall, this study shows that the distribution of phages caused by the mechanical disruption of biofilms using dissolving microneedles can be an effective delivery method against topical biofilm-related skin infections.

Hard polymeric porous microneedles on stretchable substrate for transdermal drug delivery

Microneedles offer a convenient transdermal delivery route with potential for long term sustained release of drugs. However current microneedle technologies may not have the mechanical properties for reliable and stable penetration (e.g. hydrogel microneedles). Moreover, it is also challenging to realize microneedle arrays with large size and high flexibility. There is also an inherent upper limit to the amount and kind of drugs that can be loaded in the microneedles. In this paper, we present a new class of polymeric porous microneedles made from biocompatible and photo-curable resin that address these challenges. The microneedles are unique in their ability to load solid drug formulation in concentrated form. We demonstrate the loading and release of solid formulation of anesthetic and non-steroidal anti-inflammatory drugs, namely Lidocaine and Ibuprofen. Paper also demonstrates realization of large area (6 × 20 cm²) flexible and stretchable microneedle patches capable of drug delivery on any body part. Penetration studies were performed in an ex vivo porcine model supplemented through rigorous compression tests to ensure the robustness and rigidity of the microneedles. Detailed release profiles of the microneedle patches were shown in an in vitro skin model. Results show promise for large area transdermal delivery of solid drug formulations using these porous microneedles.

Recent advances in porous microneedles: materials, fabrication, and transdermal applications

In the past two decades, microneedles (MNs), as a painless and simple drug delivery system, have received increasing attention for various biomedical applications such as transdermal drug delivery, interstitial fluid (ISF) extraction, and biosensing. Among the various types of MNs, porous MNs have been recently researched owing to their distinctive and unique characteristics, where porous structures inside MNs with continuous nano- or micro-sized pores can transport drugs or biofluids by capillary action. In addition, a wide range of materials, including non-polymers and polymers, were researched and used to form the porous structures of porous MNs. Adjustable porosity by different fabrication methods enables the achievement of sufficient mechanical strength by optimising fluid flows inside MNs. Moreover, biocompatible porous MNs integrated with biosensors can offer portable detection and rapid measurement of biomarkers in a minimally invasive manner. This review focuses on several aspects of current porous MN technology, including material selection, fabrication processes, biomedical applications, primarily covering transdermal drug delivery, ISF extraction, and biosensing, along with future prospects as well as challenges.

Microfluidic mechanoporation for cellular delivery and analysis

Highly efficient intracellular delivery strategies are essential for developing therapeutic, diagnostic, biological, and various biomedical applications. The recent advancement of micro/nanotechnology has focused numerous researches towards developing microfluidic device-based strategies due to the associated high throughput delivery, cost-effectiveness, robustness, and biocompatible nature. The delivery strategies can be carrier-mediated or membrane disruption-based, where membrane disruption methods find popularity due to reduced toxicity, enhanced delivery efficiency, and cell viability. Among all of the membrane disruption techniques, the mechanoporation strategies are advantageous because of no external energy source required for membrane deformation, thereby achieving high delivery efficiencies and increased cell viability into different cell types with negligible toxicity. The past two decades have consequently seen a tremendous boost in mechanoporation-based research for intracellular delivery and cellular analysis. This article provides a brief review of the most recent developments on microfluidic-based mechanoporation strategies such as microinjection, nanoneedle arrays, cell-squeezing, and hydroporation techniques with their working principle, device fabrication, cellular delivery, and analysis. Moreover, a brief discussion of the different mechanoporation strategies integrated with other delivery methods has also been provided. Finally, the advantages, limitations, and future prospects of this technique are discussed compared to other intracellular delivery techniques.

Structural analysis and simulation of solid microneedle array for vaccine delivery applications

This paper promotes a basic, quick, stature adaptable, and direct approach to selecting exceptionally suitable materials in polyethylene glycol diacrylate (PEGDA) and silicon for microneedle fabrication. Researchers and scientists are facing challenges in readily selecting biocompatible materials for microneedle fabrication. Solid porous silicon and PEGDA microneedles are particularly biocompatible and desirable for vaccine delivery by the transdermal vaccine delivery method if microneedle arrays are fabricated successfully using lithography techniques as they belong to enhanced patient concurrence and well-being. Moreover, silicon and PEGDA microneedles are the ultimate for conveying coronavirus vaccines. In this work, we applied the ANSYS workbench tool to investigate the properties of triangular pyramidal-shaped solid silicon and PEGDA microneedle array to perform structural analysis on microneedle for estimating the capability of an array of needles to enter and convey vaccines along with the skin. These outcomes demonstrated that microneedles of porous silicon are better than polymers such as PEGDA as far as mechanical strength and capacity to convey drugs. Buckling was anticipated as the fundamental method to estimate the failure of microneedles and finally, by analysis, it was clear that buckling does not impact the potential of the silicon microneedle needle array. Silicon and PEGDA microneedles are penetrated against human skin surfaces in explicit dynamics by utilizing the ANSYS tool to select the best material. Along these lines, the current strategy can work with silicon and PEGDA microneedles for useful applications. The von Mises stresses generated by applying loads on silicon and PEGDA arrays were greater than the skin resistance of 3.18 MPa and suitable for skin insertion. Silicon microneedles are sustained due to buckling but PEGDA needles fail if the loading is more than 0.1 N. Vaccination can be provided to humans if needle arrays are fabricated based on this approach and design analysis and considering parameters.

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.

Wearable patch delivery system for artificial pancreas health diagnostic-therapeutic application: A review

The advanced stimuli-responsive approaches for on-demand drug delivery systems have received tremendous attention as they have great potential to be integrated with sensing and multi-functional electronics on a flexible and stretchable single platform (all-in-one concept) in order to develop skin-integration with close-loop sensation for personalized diagnostic and therapeutic application. The wearable patch pumps have evolved from reservoir-based to matrix patch and drug-in-adhesive (single-layer or multi-layer) type. In this review, we presented the basic requirements of an artificial pancreas, surveyed the design and technologies used in commercial patch pumps available on the market and provided general information about the latest wearable patch pump. We summarized the various advanced delivery strategies with their mechanisms that have been developed to date and representative examples. Mechanical, electrical, light, thermal, acoustic and glucose-responsive approaches on patch form have been successfully utilized in the controllable transdermal drug delivery manner. We highlighted key challenges associated with wearable transdermal delivery systems, their research direction and future development trends.

Polymer microneedles with interconnected porous structures via a phase inversion route for transdermal medical applications

Porous polymer microneedles (MNs) have great potential in transdermal medical applications due to their three-dimensional (3D) porous structures and high porosity. However, existing approaches for the fabrication of such porous polymer MNs are complicated and only applicable to limited types of polymers. Here, we describe a facile yet effective phase inversion route to prepare polymer MNs with highly porous and interconnected pore structures. The fabrication process is simple and mild without involving high temperatures or irradiation, and can be applied to a broad spectrum of commonly used polymers (e.g., cellulose acetate (CA), polysulfone (PSF), polyethersulfone (PES), polylactic acid (PLA), etc.). Thanks to the capillary effect and large cavity given by highly porous and interconnected structures, the resulting porous polymer MNs show the capability of rapidly extracting dermal interstitial fluid (ISF) and efficiently loading/releasing drug compounds. As a proof of concept, we demonstrate the use of these porous CA MNs in the highly efficient extraction of ISF for glucose level detection and administration of insulin for hyperglycemia. Given the recent trend of painless techniques in diagnosis and treatment, the current study provides a new opportunity for the fabrication of MN-based devices for transdermal ISF extraction and drug delivery.

Engineering Microneedle Patches for Improved Penetration: Analysis, Skin Models and Factors Affecting Needle Insertion

Transdermal microneedle (MN) patches are a promising tool used to transport a wide variety of active compounds into the skin. To serve as a substitute for common hypodermic needles, MNs must pierce the human stratum corneum (~ 10 to 20 µm), without rupturing or bending during penetration. This ensures that the cargo is released at the predetermined place and time. Therefore, the ability of MN patches to sufficiently pierce the skin is a crucial requirement. In the current review, the pain signal and its management during application of MNs and typical hypodermic needles are presented and compared. This is followed by a discussion on mechanical analysis and skin models used for insertion tests before application to clinical practice. Factors that affect insertion (e.g., geometry, material composition and cross-linking of MNs), along with recent advancements in developed strategies (e.g., insertion responsive patches and 3D printed biomimetic MNs using two-photon lithography) to improve the skin penetration are highlighted to provide a backdrop for future research.

Transdermal electroosmotic flow generated by a porous microneedle array patch

A microneedle array is an attractive option for a minimally invasive means to break through the skin barrier for efficient transdermal drug delivery. Here, we report the applications of solid polymer-based ion-conductive porous microneedles (PMN) containing interconnected micropores for improving iontophoresis, which is a technique of enhancing transdermal molecular transport by a direct current through the skin. The PMN modified with a charged hydrogel brings three innovative advantages in iontophoresis at once: (1) lowering the transdermal resistance by low-invasive puncture of the highly resistive stratum corneum, (2) transporting of larger molecules through the interconnected micropores, and (3) generating electroosmotic flow (EOF). In particular, the PMN-generated EOF greatly enhances the transdermal molecular penetration or extraction, similarly to the flow induced by external pressure. The enhanced efficiencies of the EOF-assisted delivery of a model drug (dextran) and of the extraction of glucose are demonstrated using a pig skin sample. Furthermore, the powering of the PMN-based transdermal EOF system by a built-in enzymatic biobattery (fructose / O₂ battery) is also demonstrated as a possible totally organic iontophoresis patch.

Hydrophilic and anti-adhesive modification of porous polymer microneedles for rapid dermal interstitial fluid extraction

Porous polymer microneedles (MNs) with interconnected structures demonstrate great potential in dermal interstitial fluid (ISF) extraction. However, the fluid extraction rate and the recovery of the extracted ISF by the porous MNs are limited by the poor hydrophilicity and the adhesion of porous MNs. Herein, we present a facile and mild polydopamine (PDA) and poly(ethylene glycol) (PEG) coating strategy for hydrophilic and anti-adhesive modification of porous polymer MNs from a phase inversion method. As a proof-of-concept, taking polysulfone (PSF) as an example, PDA and PEG-coated MNs (PSF@PDA@PEG) are fabricated through the self-polymerization of dopamine and PEG anchoring. Thanks to the hydrophilicity and anti-adhesion of PEG, the resulting PSF@PDA@PEG MNs demonstrate improved hydrophilicity, fast fluid extraction speed, and low target molecular adhesion. Besides, this method can be extended to hydrophobic polymers generally used in medical fields, including polylactic acid (PLA), polyvinylidene fluoride (PVDF), etc. This investigation provides a new road for MN-based off-line analysis in point-of-care testing (POCT).

Trends of microneedle technology in the scientific literature, patents, clinical trials and internet activity

The powerful and intriguing idea that drives the emerging technology of microneedles-shrinking the standard needle to a micron scale-has fostered an entire field of microneedle study and subsequent exponential growth in research and product development. Originally enabled by microfabrication tools derived from the microelectronic industry, microneedles are now produced through a number of methods in a variety of forms including solid, coated, dissolvable, and hollow microneedles. They are used to deliver a broad spectrum of molecules, including small molecules, biomolecules, and vaccines, as well as various forms of energy into the skin, eye, and other tissues. Microneedles are also being exploited for use in diagnostics, as well as additional medical, cosmetic, and other applications. This review elucidates the relative roles of different aspects of microneedle technology development, as shown through scientific papers, patents, clinical studies, and internet/social media activity. Considering >1000 papers, 750 patents, and almost 80 clinical trials, we analyze different attributes of microneedles such as usage of microneedles, types of microneedles, testing environment, types of patent claims, and phases of clinical trials, as well as which institutions and people in academia and industry from different locations and in different journals are publishing, patenting, and otherwise studying the potential of microneedles. We conclude that there is robust and growing activity in the field of microneedles; the technology is rapidly developing and being used for novel applications to benefit human health and well-being.

Flexible and porous microneedles of PDMS for continuous glucose monitoring

Microneedle (MN) is a key technology of the biomedical engineering field due to its capability of accessing the biological information in a minimally invasive manner. One of the huge demands for next-generation healthcare monitoring is continuous monitoring, especially of blood glucose concentration. For this, MN should be kept inserted into the human skin for a certain period of time, enduring stresses induced by daily human motion and at the same time measuring biomarkers in ISF. However, conventional MNs for biosensing are not suitable for a long term insertion due to the rigid structure and biological risks of MN breakage. In this study, a novel MN structure is proposed and investigated by combining flexible "sponge-like" porous PDMS matrix and coating by biodissolving hyaluronic acid (HA). The fabricated porous MNs coated with HA show ideal mechanical characteristics, by which the MNs are rigid enough to penetrate the skin and become flexible after insertion into the skin. It is also shown that the MN array successfully extracts ISF in vitro and in vivo not by capillary action but by repeated compressions. The results show the applicability of the flexible MNs to continuous blood glucose monitoring.

Agricultural nanodiagnostics for plant diseases: recent advances and challenges

Crop diseases caused by pathogenic microorganisms pose severe threats to the global food supply. Effective diagnostic tools for timely determination of plant diseases become essential to the assurance of agricultural sustainability and global food security. Nucleic acid- and antibody-based molecular assays are gold-standard methodologies for the diagnosis of plant diseases, but the analyzing procedures are complex and laborious. The prominent physical or chemical properties of nanomaterials have enabled their use as innovative and high-performance diagnostic tools for numerous plant pathogens and other important disease biomarkers. Engineered nanomaterials have been incorporated into traditional laboratory molecular assays or sequencing technologies that offer notable enhancement in sensitivity and selectivity. Meanwhile, nanostructure-supported noninvasive detection tools combined with portable imaging devices (e.g., smartphones) have paved the way for fast and on-site diagnosis of plant diseases and long-term monitoring of plant health conditions, especially in resource-poor settings.

Microneedle-Based Delivery: An Overview of Current Applications and Trends

Microneedle arrays (MNA) are considered as one of the most promising resources to achieve systemic effects by transdermal delivery of drugs. They are designed as a minimally invasive, painless system which can bypass the stratum corneum, overcoming the potential drawbacks of subcutaneous injections and other transdermal delivery systems such as chemical enhancers, nano and microparticles, or physical treatments. As a trendy field in pharmaceutical and biomedical research, its applications are constantly evolving, even though they are based on very well-established techniques. The number of molecules administered by MNA are also increasing, with insulin and vaccines administration being the most investigated. Furthermore, MNA are being used to deliver cells and applied in other organs and tissues like the eyes and buccal mucosae. This review intends to offer a general overview of the current state of MNA research, focusing on the strategies, applications, and types of molecules delivered recently by these systems. In addition, some information about the materials and manufacturing processes is presented and safety data is discussed.

Nanoporous microneedle arrays seamlessly connected to a drug reservoir for tunable transdermal delivery of memantine

Conventional transdermal drug patches have been on the market since 1997 but their applicability for drug delivery is limited: currently only nearly two dozen of molecules have been approved by the regulatory authorities for transdermal administration and have reached the market. The possibilities for drug delivery via the skin can be improved and expanded by using microneedle patch technologies. However, most microneedle patches focus on the delivery of low amounts of drugs that are generally very potent due to the small dimensions of the microneedle systems. In this study nanoporous microneedle arrays (npMNAs) were combined with a liquid drug reservoir. The parameters that influence the diffusion of memantine from the drug reservoir through the npMNAs in an acceptor solution were investigated. Based on these results a model was developed to predict the diffusion of low-molecular-weight drugs as a function of npMNA properties (i.e., backplate thickness and surface area) and reservoir properties (i.e., volume and drug concentration). This generated an in silico model to predict the release of low-molecular-weight drug from a drug reservoir through a microneedle array into receptor solution, showed a good correlation with the delivery of memantine in a preclinical minipig study. The drug release rates by the npMNAs can be tuned and allow for both zero and first order release kinetics. Summarizing, this work shows that the npMNA technology is a versatile drug delivery system. The npMNAs can be combined with a (seamlessly connected) external drug reservoir and this integrated drug delivery system can be used to deliver at least 9 mg of memantine over 72 h in a preclinical minipig study.

Fabrication of Tip-Hollow and Tip-Dissolvable Microneedle Arrays for Transdermal Drug Delivery

We developed a modified micromolding method for the mass production of a novel tip-hollow microneedle array (MA). The tip-hollow MA was fabricated by tuning of the vacuum degree at -80 kPa for 60 s during the micromolding process. Subsequently, a tip-dissolvable MA encapsulated with drugs in the microcraters was fabricated from tip-hollow MA using repeated dipping and the freeze-drying process. Both the tip-hollow and tip-dissolvable MAs could easily penetrate in the rabbit skin without breakage, while the tip-hollow MA can just create a shallow loop hole in the skin. The drug-loaded tip-dissolvable MA can rapidly dissolve, releasing and diffusing the drug in the skin. The tip-dissolvable MA exhibited the best drug permeation ability in that the corresponding flux through the punctured skin using tip-dissolvable MA loaded with Rhodamine B is about 1.7- and 5.8-fold of that through the punctured skin using solid MA and the intact skin, respectively. The tip-dissolvable MA loaded with 5 IU insulin was fabricated to in vivo treat the type 1 diabetic SD rats. The tip-dissolvable MA had a good hypoglycemic effect and exhibited longer normoglycemic period in comparison with subcutaneous injection (5 IU). Therefore, our tip-dissolve MA is a promising medical device for transdermal drug delivery.

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.

3D Printed Multi-Functional Hydrogel Microneedles Based on High-Precision Digital Light Processing

Traditional injection and extraction devices often appear painful and cumbersome for patients. In recent years, polymer microneedles (MNs) have become a novel tool in the field of clinical medicine and health. However, the cost of building MNs into any shapes still remains a challenge. In this paper, we proposed hydrogel microneedles fabricated by high-precision digital light processing (H-P DLP) 3D printing system. Benefits from the sharp protuberance and micro-porous of the hydrogel microneedle, the microneedle performed multifunctional tasks such as drug delivery and detection with minimally invasion. Critical parameters for the fabrication process were analyzed, and the mechanical properties of MNs were measured to find a balance between precision and stiffness. Results shows that the stiffness and precision were significantly influenced by exposure time of each layer, and optimized printing parameters provided a balance between precision and stiffness. Bio-compatible MNs based on our H-P DLP system was able to execute drug injection and drug detection in our experiments. This work provided a low-cost and fast method to build MNs with 3D building, qualified the mechanical performance, drug injection, drug detection ability of MNs, and may be helpful for the potential clinical application.

Rapidly Fabricated Microneedle Arrays Using Magnetorheological Drawing Lithography for Transdermal Drug Delivery

Microneedle arrays (MAs) are among the most promising transdermal drug delivery systems in the last decades due to its minimally invasive nature, convenient operation, and first-pass-metabolism avoidance. However, most MA fabrication methods are difficult to operate, need multiple steps, or require expensive equipment. A novel magnetorheological drawing lithography approach was proposed to rapidly fabricate a flexible microneedle array (FMA) for transdermal drug delivery. A 3D structural liquid MA was drawn in one step from the droplets of curable magnetorheological fluid and maintained its shape under an external magnetic field. The liquid MA was subsequently solidified and sputter-coated with the Ti/Au film to fabricate FMA. FMA morphology, mechanical properties, and transdermal drug delivery performance in vitro were experimentally investigated. FMA consisted of a 5 × 5 cone-shaped microneedle array on a PET flexible substrate. FMA exhibited good strength and excellent penetration performance. It could easily penetrate into skin without breakage, creating microchannels for the promotion of skin permeability. Drugs could be well permeated and diffused in the skin along the microchannels created by FMA. Finally, a dissolvable microneedle array (DMA) was also fabricated by a micromolding technique using FMA as a master template. The DMA exhibited good dissolvable and permeable performance in the agarose block.

Fabrication of gradient porous microneedle array by modified hot embossing for transdermal drug delivery

A gradient porous microneedle array (GPMA) is developed for transdermal drug delivery. A modified hot embossing approach is proposed to fabricate the GPMA from poly (lactic-co-glycolic acid) powders within a cavity array mold under the coupling combination of gradient thermal and pressure multi-fields. The porosity of the microneedles is a gradient, and the pores are mainly distributed in the tip region. The liquid drug formulation can directly be loaded in the pores of the microneedle tips by dipping. GPMA could penetrate into the rabbit skin without breakage and the penetration force per microneedle is approximately 22 mN. The GPMA can diffuse a dry model drug, namely Rhodamine B, in vitro in the rabbit skin dermis. The GPMA can also effectively deliver an insulin solution in vivo in diabetes rats, lowering the blood glucose levels. Above all, as a dry or liquid drug carrier and a minimally invasive injector, the GPMA offers an effective alternative for transdermal drug delivery.

Universal Applicator for Digitally-Controlled Pressing Force and Impact Velocity Insertion of Microneedles into Skin

Microneedle technologies have been developed for dermal drug and vaccine delivery, including hollow-, solid-, coated-, and dissolving microneedles. Microneedles have been made in many different geometries and of many different materials, all of which may influence their skin-penetrating ability. To ensure reproducible and effective drug and vaccine delivery via microneedles, the optimal insertion parameters should be known. Therefore, a digitally-controlled microneedle applicator was developed to insert microneedles into the skin via impact insertion (velocity) or via pressing force insertion. Six microneedle arrays with different geometries and/or materials were applied onto ex vivo human skin with varying velocities or pressing forces. Penetration efficiency and delivered antigen dose into the skin after application of microneedles were determined. In general, microneedles pierced the skin more efficiently when applied by impact application as compared to application via pressing force. However, the angle of application of the applicator on the skin can affect the velocity of the impact, influencing the penetration efficiency of microneedles. Regarding the antigen delivery into the skin, the delivered dose was increasing by increasing the velocity or pressure, and thus, increasing the penetration efficiency. These data demonstrate that an applicator is an important tool to determine optimal application conditions with ex vivo human skin.

Touch-actuated microneedle array patch for closed-loop transdermal drug delivery

To date, only approximately 20 drugs synthesized with small molecules have been approved by the FDA for use in traditional transdermal patches (TTP) owing to the extremely low permeation rate of the skin barrier for macromolecular drugs. A novel touch-actuated microneedle array patch (TMAP) was developed for transdermal delivery of liquid macromolecular drugs. TMAP is a combination of a typical TTP and a solid microneedle array (MA). High doses of liquid drug formulations, especially heat-sensitive compounds can be easily filled and stored in the drug reservoir of TMAPs. TMAP can easily penetrate the skin and automatically retract from it to create microchannels through the stratum corneum (SC) layer using touch-actuated 'press and release' actions for passive permeation of liquid drugs. Comparison of subcutaneous injection, TTP, solid MA, and dissolvable MA, indicated that insulin-loaded TMAP exhibited the best hypoglycemic effect on type 1 diabetic rats. A 'closed-loop' permeation control was also provided for on-demand insulin delivery based on feedback of blood glucose levels (BGLs). Twenty IU-insulin-loaded TMAP maintained the type 1 diabetic rats in a normoglycemic state for approximately 11.63 h, the longest therapeutic duration among all previously reported results on microneedle-based transdermal patches. TMAP possesses excellent transdermal drug delivery capabilities.

Functionalized microneedles for continuous glucose monitoring

Microneedles (MNs) have been established as promising medical devices as they are minimally invasive, cause less pain, and can be utilized for self-administration of drugs by patients. There has been rapid development in MNs for transdermal monitoring and diagnostic systems, following the active research on fabrication methods and applications for drug delivery. In this paper, recent investigations on bio-sensing using MNs are reviewed in terms of the applicability to continuous glucose monitoring system (CGMS), which is one of the main research focuses of medical engineering technologies. The trend of the functionalized MNs can be categorized as follows: (i) as a sensing probe, and (ii) as a biological fluid collector. MNs as in vivo sensors are mainly integrated or coated with conductive materials to have the function as electrodes. MNs as fluid collectors are given a certain geometrical design, such as a hollow and porous structure aided by a capillary action or negative pressure, to extract the interstitial fluids or blood for ex vivo analysis. For realization of CGMS with MNs, a long-term accurate measurement by the MN-based sensing probe or a fluidic connection between the MN-based fluid collector and the existing microfluidic measurement systems should be investigated.

Metallic microneedles with interconnected porosity: A scalable platform for biosensing and drug delivery

Metallic-based microneedles (MNs) offer a robust platform for minimally invasive drug delivery and biosensing applications due to their mechanical strength and proven tissue and drug compatibility. However, current designs suffer from limited functional surface area or challenges in manufacturing scalability. Here, porous 316L stainless steel MN patches are proposed. Fabricated through a scalable manufacturing process, they are suitable for storage and delivery of drugs and rapid absorption of fluids for biosensing. Fabrication of these MNs involves hot embossing a patch of stainless steel-based feedstock, sintering at 1100 °C and subsequent electropolishing. Optimisation of this manufacturing process yields devices that maintain mechanical integrity yet possess high surface area and associated porosity (36%) to maximise loading capacity. Similarly, a small pore size has been targeted (average diameter 2.22 μm, with 90% between 1.56 μm and 2.93 μm) to maximise capillarity and loading efficiency. This porous network has a theoretical wicking rate of 4.7 μl/s and can wick-up 27 ± 5 μl of fluid through capillary action which allows for absorption of pharmaceuticals for delivery. When inserted into a metabolite-loaded skin model, the MNs absorbed and recovered 17 ± 3 μl of the metabolite solution. The drug delivery performance of the porous metallic MNs (22.4 ± 4.9 µg/cm²) was found to be threefold higher than that of topical administration (7.1 ± 4.3 µg/cm²). The porous metallic MN patches have been shown to insert into porcine skin under a 19 N load. These results indicate the potential of design-for-manufacturing porous stainless steel MNs in biosensing and drug delivery applications. STATEMENT OF SIGNIFICANCE: Microneedles are micro-scale sharp protrusions used to bypass the stratum corneum, the skin's outer protective layer, and painlessly access dermal layers suitable for drug delivery and biosensing. Despite a depth of research in the area we have not yet seen large-scale clinical adoption of microneedle devices. Here we describe a device designed to address the potential barriers to adoption seen by other microneedles devices. We have developed a scalable, cost effective process to produce medical grade stainless steel microneedle patches which passively absorb and store drugs or interstitial fluid though a porous network and capillary action. This device, with low manufacturing and regulatory burdens may help the large-scale adoption of microneedles.

Preparation, properties and challenges of the microneedles-based insulin delivery system

Microneedle technology relates to pharmacy, polymer chemistry and micromachining. Microneedle can effectively deliver insulin into systemic circulation across the skin. This process does not affect the activity of insulin. Compared to subcutaneous injection, microneedles cause less pain for their special structure. This review thoroughly discusses the preparation technologies of the microneedles-based insulin delivery system including solid, hollow, dissolving, phase transition, glucose-responsive microneedle patches. In the meantime, the properties, challenges and clinical/commercial status of the microneedles-based insulin delivery system are also discussed in this review.

Tailoring Porous Silicon for Biomedical Applications: From Drug Delivery to Cancer Immunotherapy

In the past two decades, porous silicon (PSi) has attracted increasing attention for its potential biomedical applications. With its controllable geometry, tunable nanoporous structure, large pore volume/high specific surface area, and versatile surface chemistry, PSi shows significant advantages over conventional drug carriers. Here, an overview of recent progress in the use of PSi in drug delivery and cancer immunotherapy is presented. First, an overview of the fabrication of PSi with various geometric structures is provided, with particular focus on how the unique geometry of PSi facilitates its biomedical applications, especially for drug delivery. Second, surface chemistry and modification of PSi are discussed in relation to the strengthening of its performance in drug delivery and bioimaging. Emerging technologies for engineering PSi-based composites are then summarized. Emerging PSi advances in the context of cancer immunotherapy are also highlighted. Overall, very promising research results encourage further exploration of PSi for biomedical applications, particularly in drug delivery and cancer immunotherapy, and future translation of PSi into clinical applications.

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.

3D printing applications for transdermal drug delivery

The role of two and three-dimensional printing as a fabrication technology for sophisticated transdermal drug delivery systems is explored in literature. 3D printing encompasses a family of distinct technologies that employ a virtual model to produce a physical object through numerically controlled apparatuses. The applicability of several printing technologies has been researched for the direct or indirect printing of microneedle arrays or for the modification of their surface through drug-containing coatings. The findings of the respective studies are presented. The range of printable materials that are currently used or potentially can be employed for 3D printing of transdermal drug delivery (TDD) systems is also reviewed. Moreover, the expected impact and challenges of the adoption of 3D printing as a manufacturing technique for transdermal drug delivery systems, are assessed. Finally, this paper outlines the current regulatory framework associated with 3D printed transdermal drug delivery systems.