Optimization of Printing Parameters for Digital Light Processing 3D Printing of Hollow Microneedle Arrays

Direct 3D printing of triple-responsive nanocomposite hydrogel microneedles for controllable drug delivery

Hydrogel microneedle patches have emerged as promising platforms for painless, minimally invasive, safe, and portable transdermal drug administration. However, the conventional mold-based fabrication processes and inherent single-functionality of such microneedles present significant hurdles to broader implementation. Herein, we have developed a novel approach utilizing a precursor solution of robust nanocomposite hydrogels to formulate photo-printable inks suitable for the direct 3D printing of high-precision, triple-responsive hydrogel microneedle patches through digital light processing (DLP) technology. The ink formulation comprises four functionally diverse monomers including 2-(dimethylamino)ethyl methacrylate, N-isopropylacrylamide, acrylic acid, and acrylamide, which were crosslinked by aluminum hydroxide nanoparticles (AH NPs) acting as both reinforcing agents and crosslinking centers. This results in the formation of a nanocomposite hydrogel characterized by exceptional mechanical strength, an essential attribute for the 3D printing of hydrogel microneeedle patches. Furthermore, this innovative 3D printing strategy facilitates facile customization of microneedle geometry and patch dimensions. As a proof-of-concept, we employed the fabricated hydrogel microneedles for transdermal delivery of bovine serum albumin (BSA). Importantly, these hydrogel microneedles displayed no cytotoxic effects and exhibited triple sensitivity to pH, temperature and glucose levels, thereby enabling more precise on-demand drug delivery. This study provides a universal method for the rapid fabrication of hydrogel microneedles with smart responsiveness for transdermal drug delivery applications.

Digital light processing (DLP) 3D printing of polymer networks comprising virus-like particles

In this work, we introduce a 3D-printable virus-like particle (VLP)-enhanced cross-linked biopolymer system. VLPs displaying surface-available acrylate groups were prepared through aza-Michael addition to serve as resins. The VLP resins were then photopolymerized into a poly(ethylene glycol) diacrylate (PEGDA) network following DLP 3D printing. This approach represents a convergence of disciplines, where the synergistic interaction between virology and additive manufacturing unlocks new frontiers in biotechnology.

Fabrication of Hybrid Coated Microneedles with Donepezil Utilizing Digital Light Processing and Semisolid Extrusion Printing for the Management of Alzheimer's Disease

Microneedle (MN) patches are gaining increasing attention as a cost-effective technology for delivering drugs directly into the skin. In the present study, two different 3D printing processes were utilized to produce coated MNs, namely, digital light processing (DLP) and semisolid extrusion (SSE). Donepezil (DN), a cholinesterase inhibitor administered for the treatment of Alzheimer's disease, was incorporated into the coating material. Physiochemical characterization of the coated MNs confirmed the successful incorporation of donepezil as well as the stability and suitability of the materials for transdermal delivery. Optical microscopy and SEM studies validated the uniform weight distribution and precise dimensions of the MN arrays, while mechanical testing ensured the MNs' robustness, ensuring efficient skin penetration. In vitro studies were conducted to evaluate the produced transdermal patches, indicating their potential use in clinical treatment. Permeation studies revealed a significant increase in DN permeation compared to plain coating material, affirming the effectiveness of the MNs in enhancing transdermal drug delivery. Confocal laser scanning microscopy (CLSM) elucidated the distribution of the API, within skin layers, demonstrating sustained drug release and transcellular transport pathways. Finally, cell studies were also conducted on NIH3T3 fibroblasts to evaluate the biocompatibility and safety of the printed objects for transdermal applications.

Vat-based photopolymerization 3D printing: From materials to topical and transdermal applications

Three-dimensional (3D) printing is an innovative manufacturing method with the potential to revolutionize topical and transdermal dosage forms. Nowadays, it is established that Vat-based photopolymerization (VP) 3D printing technologies offer superior printing efficiency and versatility compared to other 3D printing technologies available on the market. However, there are some limitations that impair their full application in pharmaceutical contexts, such as the lack of a range of biocompatible materials for topical and transdermal applications. This review article explores all types of VP-based 3D printing and discusses the relevance of implementing this kind of technology. We start with a detailed description of the printing process, focusing on the commercial materials available and lab-made resins proposed by different authors. We also review recent studies in this field, which mainly focus on the fabrication of transdermal devices based on microneedle arrays. In the future, it is expected that the manufacturers of 3D printers invest in modifications to the printing apparatus to allow the simultaneous printing of different resins and/or compound types, which will open frontiers to the personalization of treatment approaches.

Hollow microneedles for ocular drug delivery

Microneedles (MNs) are micron-sized needles, typically <2 mm in length, arranged either as an array or as single needle. These MNs offer a minimally invasive approach to ocular drug delivery due to their micron size (reducing tissue damage compared to that of hypodermic needles) and overcoming significant barriers in drug administration. While various types of MNs have been extensively researched, significant progress has been made in the use of hollow MNs (HMNs) for ocular drug delivery, specifically through suprachoroidal injections. The suprachoroidal space, situated between the sclera and choroid, has been targeted using optical coherence tomography-guided injections of HMNs for the treatment of uveitis. Unlike other MNs, HMNs can deliver larger volumes of formulations to the eye. This review primarily focuses on the use of HMNs in ocular drug delivery and explores their ocular anatomy and the distribution of formulations following potential HMN administration routes. Additionally, this review focuses on the influence of formulation characteristics (e.g., solution viscosity, particle size), HMN properties (e.g., bore or lumen diameter, MN length), and routes of administration (e.g., periocular transscleral, suprachoroidal, intravitreal) on the ocular distribution of drugs. Overall, this paper highlights the distinctive properties of HMNs, which make them a promising technology for improving drug delivery efficiency, precision, and patient outcomes in the treatment of ocular diseases.

3D printing redefines microneedle fabrication for transdermal drug delivery

Microneedles (MNs) have emerged as an innovative, virtually painless technique for intradermal drug delivery. However, the complex and costly fabrication process has limited their widespread accessibility, especially for individuals requiring frequent drug administration. This study introduces a groundbreaking and cost-effective method for producing MNs utilizing fused deposition modeling (FDM) 3D printing technology to enhance transdermal drug delivery. The proposed fabrication process involves the elongation of molten polylactic acid (PLA) filaments to create meticulously designed conoid and neiloid MNs with smooth surfaces. This study underscores the critical role of printing parameters, particularly extrusion length and printing speed, in determining the shape of the MNs. Notably, the conoid-shaped MNs exhibit exceptional skin-penetrating capabilities. In order to evaluate their effectiveness, the MNs were tested on a polydimethylsiloxane (PDMS) skin model for skin penetration. The results highlight the high potential of 3D-printed MNs for transdermal drug administration. This novel approach capitalizes on the benefits of 3D printing technology to fabricate MNs that hold the promise of transforming painless drug administration for a variety of medical applications.

Porous Microneedles Through Direct Ink Drawing with Nanocomposite Inks for Transdermal Collection of Interstitial Fluid

Interstitial fluid (ISF) is an attractive alternative to regular blood sampling for health checks and disease diagnosis. Porous microneedles (MNs) are well suited for collecting ISF in a minimally invasive manner. However, traditional methods of molding MNs from microfabricated templates involve prohibitive fabrication costs and fixed designs. To overcome these limitations, this study presents a facile and economical additive manufacturing approach to create porous MNs. Compared to traditional layerwise build sequences, direct ink drawing with nanocomposite inks can define sharp MNs with tailored shapes and achieve vastly improved fabrication efficiency. The key to this fabrication strategy is the yield-stress fluid ink that is easily formulated by dispersing silica nanoparticles into the cellulose acetate polymer solution. As-printed MNs are solidified into interconnected porous microstructure inside a coagulation bath of deionized water. The resulting MNs exhibit high mechanical strength and high porosity. This approach also allows porous MNs to be easily integrated on various substrates. In particular, MNs on filter paper substrates are highly flexible to rapidly collect ISF on non-flat skin sites. The extracted ISF is used for quantitative analysis of biomarkers, including glucose, = calcium ions, and calcium ions. Overall, the developments allow facile fabrication of porous MNs for transdermal diagnosis and therapy.

Pharmaceutical applications and requirements of resins for printing by digital light processing (DLP)

The digital light processing (DLP) printer has proven to be effective in biomedical and pharmaceutical applications, as its printing method does not induce shear and a strong temperature on the resin. In addition, the DLP printer has good resolution and print quality, which makes it possible to print complex structures with a customized shape, being used for various purposes ranging from jewelry application to biomedical and pharmaceutical areas. The big disadvantage of DLP is the lack of a biocompatible and non-toxic resin on the market. To overcome this limitation, an ideal resin for biomedical and pharmaceutical use is needed. The resin must have appropriate properties, so that the desired format is printed when with a determined wavelength is applied. Thus, the aim of this work is to bring the basic characteristics of the resins used by this printing method and the minimum requirements to start printing by DLP for pharmaceutical and biomedical applications. The DLP method has proven to be effective in obtaining pharmaceutical devices such as drug delivery systems. Furthermore, this technology allows the printing of devices of ideal size, shape and dosage, providing the patient with personalized treatment.

Unravelling the role of microneedles in drug delivery: Principle, perspectives, and practices

In recent year, the research of transdermal drug delivery systems has got substantial attention towards the development of microneedles (MNs). This shift has occurred due to multifaceted advantages of MNs as they can be utilized to deliver the drug deeper to the skin with minimal invasion, offer successful delivery of drugs and biomolecules that are susceptible to degradation in gastrointestinal tract (GIT), act as biosensors, and help in monitoring the level of biomarkers in the body. These can be fabricated into different types based on their applications as well as material for fabrication. Some of their types include solid MNs, hollow MNs, coated MNs, hydrogel forming MNs, and dissolving MNs. These MNs deliver the therapeutics via microchannels deeper into the skin. The coated and hollow MNs have been found successful. However, they suffer from poor drug loading and blocking of pores. In contrast, dissolving MNs offer high drug loading. These MNs have also been utilized to deliver vaccines and biologicals. They have also been used in cosmetics. The current review covers the different types of MNs, materials used in their fabrication, properties of MNs, and various case studies related to their role in delivering therapeutics, monitoring level of biomarkers/hormones in body such as insulin. Various patents and clinical trials related to MNs are also covered. Covered are the major bottlenecks associated with their clinical translation and potential future perspectives.

A 3D-printed hollow microneedle-based electrochemical sensing device for in situ plant health monitoring

Plant health monitoring is devised as a new concept to elucidate in situ physiological processes. The need for increased food production to nourish the growing global population is inconsistent with the dramatic impact of climate change, which hinders crop health and exacerbates plant stress. In this context, wearable sensors play a crucial role in assessing plant stress. Herein, we present a low-cost 3D-printed hollow microneedle array (HMA) patch as a sampling device coupled with biosensors based on screen-printing technology, leading to affordable analysis of biomarkers in the plant fluid of a leaf. First, a refinement of the 3D-printing method showed a tip diameter of 25.9 ± 3.7 μm with a side hole diameter on the microneedle of 228.2 ± 18.6 μm using an affordable 3D printer (<500 EUR). Notably, the HMA patch withstanded the forces exerted by thumb pressing (i.e. 20-40 N). Subsequently, the holes of the HMA enabled the fluid extraction tested in vitro and in vivo in plant leaves (i.e. 13.5 ± 1.1 μL). A paper-based sampling strategy adapted to the HMA allowed the collection of plant fluid. Finally, integrating the sampling device onto biosensors facilitated the in situ electrochemical analysis of plant health biomarkers (i.e. H2O2, glucose, and pH) and the electrochemical profiling of plants in five plant species. Overall, this electrochemical platform advances precise and versatile sensors for plant health monitoring. The wearable device can potentially improve precision farming practices, addressing the critical need for sustainable and resilient agriculture in changing environmental conditions.

3D printing processes in precise drug delivery for personalized medicine

With the advent of personalized medicine, the drug delivery system will be changed significantly. The development of personalized medicine needs the support of many technologies, among which three-dimensional printing (3DP) technology is a novel formulation-preparing process that creates 3D objects by depositing printing materials layer-by-layer based on the computer-aided design method. Compared with traditional pharmaceutical processes, 3DP produces complex drug combinations, personalized dosage, and flexible shape and structure of dosage forms (DFs) on demand. In the future, personalized 3DP drugs may supplement and even replace their traditional counterpart. We systematically introduce the applications of 3DP technologies in the pharmaceutical industry and summarize the virtues and shortcomings of each technique. The release behaviors and control mechanisms of the pharmaceutical DFs with desired structures are also analyzed. Finally, the benefits, challenges, and prospects of 3DP technology to the pharmaceutical industry are discussed.

Imiquimod nanocrystal-loaded dissolving microneedles prepared by DLP printing

The utilization of 3D printing- digital light processing (DLP) technique, for the direct fabrication of microneedles encounters the problem of drug solubility in printing resin, especially if it is predominantly composed of water. The possible solution how to ensure ideal belonging of drug and water-based printing resin is its pre-formulation in nanosuspension such as nanocrystals. This study investigates the feasibility of this approach on a resin containing nanocrystals of imiquimod (IMQ), an active used in (pre)cancerous skin conditions, well known for its problematic solubility and bioavailability. The resin blend of polyethylene glycol diacrylate and N-vinylpyrrolidone, and lithium phenyl-2,4,6-trimethylbenzoylphosphinate as a photoinitiator, was used, mixed with IMQ nanocrystals in water. The final microneedle-patches had 36 cylindrical microneedles arranged in a square grid, measuring approximately 600 μm in height and 500 μm in diameter. They contained 5wt% IMQ, which is equivalent to a commercially available cream. The homogeneity of IMQ distribution in the matrix was higher for nanocrystals compared to usual crystalline form. The release of IMQ from the patches was determined ex vivo in natural skin and revealed a 48% increase in efficacy for nanocrystal formulations compared to the crystalline form of IMQ.

3D Printing of Biodegradable Polymeric Microneedles for Transdermal Drug Delivery Applications

Microneedle (MN) technology is an optimal choice for the delivery of drugs via the transdermal route, with a minimally invasive procedure. MN applications are varied from drug delivery, cosmetics, tissue engineering, vaccine delivery, and disease diagnostics. The MN is a biomedical device that offers many advantages including but not limited to a painless experience, being time-effective, and real-time sensing. This research implements additive manufacturing (AM) technology to fabricate MN arrays for advanced therapeutic applications. Stereolithography (SLA) was used to fabricate six MN designs with three aspect ratios. The MN array included conical-shaped 100 needles (10 × 10 needle) in each array. The microneedles were characterized using optical and scanning electron microscopy to evaluate the dimensional accuracy. Further, mechanical and insertion tests were performed to analyze the mechanical strength and skin penetration capabilities of the polymeric MN. MNs with higher aspect ratios had higher deformation characteristics suitable for penetration to deeper levels beyond the stratum corneum. MNs with both 0.3 mm and 0.4 mm base diameters displayed consistent force-displacement behavior during a skin-equivalent penetration test. This research establishes guidelines for fabricating polymeric MN for high-accuracy and low-cost 3D printing.

Urethane dimethacrylate-based photopolymerizable resins for stereolithography 3D printing: A physicochemical characterisation and biocompatibility evaluation

Vat photopolymerisation (VP) three-dimensional printing (3DP) has attracted great attention in many different fields, such as electronics, pharmaceuticals, biomedical devices and tissue engineering. Due to the low availability of biocompatible photocurable resins, its application in the healthcare sector is still limited. In this work, we formulate photocurable resins based on urethane dimethacrylate (UDMA) combined with three different difunctional methacrylic diluents named ethylene glycol dimethacrylate (EGDMA), di(ethylene glycol) dimethacrylate (DEGDMA) or tri(ethylene glycol) dimethacrylate (TEGDMA). The resins were tested for viscosity, thermal behaviour and printability. After printing, the 3D printed specimens were measured with a digital calliper in order to investigate their accuracy to the digital model and tested with FT-IR, TGA and DSC. Their mechanical properties, contact angle, water sorption and biocompatibility were also evaluated. The photopolymerizable formulations investigated in this work achieved promising properties so as to be suitable for tissue engineering and other biomedical applications.

Flavonoid and Chalcone Scaffolds as Inhibitors of BACE1: Recent Updates

Flavonoids and chalcones are two major classes of chemical moieties that have a vast background of pharmacological activities. Chalcone is a subclass of flavonoids whose therapeutic potential has been implicated due to an array of bioactivities. A lot of research works have shown interest in investigating the neuroprotective effect of these molecules, and have revealed them to be much more potent molecules that can be used to treat neurodegenerative disorders. Beta-site APP cleaving enzyme (BACE1), which is majorly found in the brain, is one of the reasons behind the development of Alzheimer's disease (AD). Flavonoids and chalcones have proven clinical data that they inhibit the production of Aβ plaques that are involved in the progression of AD. In this article, we have provided a detailed chronological review of the research work on the BACE1 inhibiting potency of both flavonoids and chalcones. Almost all the flavonoids and chalcones mentioned in this article have shown very good in vitro and in vivo BACE1 inhibiting activity. The docking studies and the structural importance of some BACE1-inhibiting flavonoids, as well as chalcones, are also mentioned here.

Evolution of Transdermal Drug Delivery Devices and Novel Microneedle Technologies: A Historical Perspective and Review

The history of transdermal drug delivery is as old as humankind. Transdermal drug delivery has undergone three generations of development; the third generation has involved the use of medical devices and instruments. This review provides a historical perspective on the primary approaches employed in the three generations of transdermal drug delivery. In addition, we explore some of the recently developed transdermal techniques that are deemed promising in the field of drug delivery. We discuss how advances in these techniques have led to the development of devices for the delivery of a therapeutically effective amount of drug across human skin and highlight the limitations of the first- and second-generation drug delivery tools. As such, a review of the performance of these techniques and the toxicity of the devices used in transdermal drug delivery are considered. In the last section of the review, a discussion of the fabrication and operation of different types of microneedles is presented. The applications of microneedles in the sensing and delivery of various therapeutic agents are described in detail. Furthermore, an overview of the efficacy of microneedles as emerging tools for the controlled release of drugs is presented.

Customized flexible hollow microneedles for psoriasis treatment with reduced-dose drug

Microneedles, especially hollow microneedles (HMNs), play an important role in drug delivery, but most of the current HMNs are manufactured based on silicon microfabrication (lithography, etching, etc.), which are slightly conservative due to the lack of low-cost, batch-scale and customized preparation approach, especially for the HMNs with flexible substrate. For the first time, we propose the use of a high-precision 3D printed master mold followed by a dual-molding process for the preparation of HMNs with different shapes, heights, and inner and outer diameters to satisfy different drug delivery needs. The 3D printed master mold and negative mold can be reused, thereby significantly reducing the cost. HMNs are based on biocompatible materials, such as heat-curing polymers or light-curing resins. The thickness and rigidity/flexibility characteristics of the substrate can be customized for different applications. The drug delivery efficiency of the fabricated HMNs was verified by the in situ treatment of psoriasis on the backs of mice, which required only a 0.1-fold oral dose to achieve similar efficacy, and the associated side effects and drug toxicity were reduced. Thus, this dual-molding process can reinvigorate HMNs development.

Transdermal on-demand drug delivery based on an iontophoretic hollow microneedle array system

Transdermal drug delivery has emerged as an alternative administration route for therapeutic drugs, overcoming current issues in oral and parenteral administration. However, this technology is hindered by the low permeability of the stratum corneum of the skin. In this work, we develop a synergic combination of two enhancing technologies to contribute to an improved and on-demand drug delivery through an iontophoretic system coupled with hollow microneedles (HMNs). For the first time, a polymeric HMN array coupled with integrated iontophoresis for the delivery of charged molecules and macromolecules (e.g. proteins) is devised. To prove the concept, methylene blue, fluorescein sodium, lidocaine hydrochloride, and bovine serum albumin-fluorescein isothiocyanate conjugate (BSA-FITC) were first tested in an in vitro setup using 1.5% agarose gel model. Subsequently, the ex vivo drug permeation study using a Franz diffusion cell was conducted, exhibiting a 61-fold, 43-fold, 54-fold, and 17-fold increment of the permeation of methylene blue, fluorescein sodium, lidocaine hydrochloride, and BSA-FITC, respectively, during the application of 1 mA cm^-2 current for 6 h. Moreover, the total amount of drug delivered (i.e. in the skin and receptor compartment) was analysed to untangle the different delivery profiles according to the types of molecule. Finally, the integration of the anode and cathode into an iontophoretic hollow microneedle array system (IHMAS) offers the full miniaturisation of the concept. Overall, the IHMAS device provides a versatile wearable technology for transdermal on-demand drug delivery that can improve the administration of personalised doses, and potentially enhance precision medicine.

3D Printed Hollow Microneedles for Treating Skin Wrinkles Using Different Anti-Wrinkle Agents: A Possible Futuristic Approach

Skin wrinkles are an inevitable phenomenon that is brought about by aging due to the degradation of scleroprotein fibers and significant collagen reduction, which is the fundamental basis of anti-wrinkle technology in use today. Conventional treatments such as lasering and Botulinum toxin have some drawbacks including allergic skin reactions, cumbersome treatment procedures, and inefficient penetration of the anti-wrinkle products into the skin due to the high resistance of stratum corneum. Bearing this in mind, the cosmetic industry has exploited the patient-compliant technology of microneedles (MNs) to treat skin wrinkles, developing several products based on solid and dissolvable MNs incorporated with antiwrinkle formulations. However, drug administration via these MNs is limited by the high molecular weight of the drugs. Hollow MNs (HMNs) can deliver a wider array of active agents, but that is a relatively unexplored area in the context of antiwrinkle technology. To address this gap, we discuss the possibility of bioinspired 3D printed HMNs in treating skin wrinkles in this paper. We compare the previous and current anti-wrinkling treatment options, as well as the techniques and challenges involved with its manufacture and commercialization.

3D Printing of CNT- and YSZ-Added Dental Resin-Based Composites by Digital Light Processing and Their Mechanical Properties

This study demonstrates the successful 3D printing of dental resin-based composites (DRCs) containing ceramic particles using the digital light processing (DLP) technique. The mechanical properties and oral rinsing stability of the printed composites were evaluated. DRCs have been extensively studied for restorative and prosthetic dentistry due to their clinical performance and aesthetic quality. They are often subjected to periodic environmental stress, and thus can easily undergo undesirable premature failure. Here, we investigated the effects of two different high-strength and biocompatible ceramic additives, carbon nanotube (CNT) and yttria-stabilized zirconia (YSZ), on the mechanical properties and oral rinsing stabilities of DRCs. Dental resin matrices containing different wt.% of CNT or YSZ were printed using the DLP technique after analyzing the rheological behavior of slurries. Mechanical properties such as Rockwell hardness and flexural strength, as well as the oral rinsing stability of the 3D-printed composites, were systematically investigated. The results indicated that a DRC with 0.5 wt.% YSZ exhibits the highest hardness of 19.8 ± 0.6 HRB and a flexural strength flexural strength of 50.6 ± 6 MPa, as well as reasonable oral rinsing steadiness. This study provides a fundamental perspective for designing advanced dental materials containing biocompatible ceramic particles.

The manufacturing of 3D-printed microfluidic chips to analyse the effect upon particle size during the synthesis of lipid nanoparticles

OBJECTIVES

The process of 3D printing to produce microfluidic chips is becoming commonplace, due to its quality, versatility and newfound availability. In this study, a UV liquid crystal display (LCD) printer has been implemented to produce a progression of microfluidic chips for the purpose of liposomal synthesis. The emphasis of this research is to test the limitations of UV LCD printing in terms of resolution and print speed optimisation for the production of microfluidic chips.

KEY FINDINGS

By varying individual channel parameters such as channel length and internal geometries, the essential channel properties for optimal liposomal formulation are being investigated to act as a basis for future experimentation including the encapsulation of active pharmaceutical ingredients. Using the uniquely designed chips, liposomes of ≈120 nm, with polydispersity index values of ≤0.12 are able to be reproducibly synthesised.

CONCLUSIONS

The influence of total flow rates and lipid choice is investigated in depth, to provide further clarification on how a microfluidic setup should be optimised. In-depth explanations of the importance of each channel parameter are also explained throughout, with reference to their importance for the properties of a successful liposome.

Microneedle system for tissue engineering and regenerative medicine

Global increasing demand for high life quality and length facilitates the development of tissue engineering and regenerative medicine, which apply multidisciplinary theories and techniques to achieve the structural reconstruction and functional recovery of disordered or damaged tissues and organs. However, the clinical performances of adopted drugs, materials, and powerful cells in the laboratory are inescapably limited by the currently available technologies. To tackle the problems, versatile microneedles are developed as the new platform for local delivery of diverse cargos with minimal invasion. The efficient delivery, as well as painless and convenient procedure endow microneedles with good patient compliance in clinic. In this review, we first categorize different microneedle systems and delivery models, and then summarize their applications in tissue engineering and regenerative medicine mainly involving maintenance and rehabilitation of damaged tissues and organs. In the end, we discuss the advantages, challenges, and prospects of microneedles in depth for future clinical translations.

Combining 3D Printing and Microfluidic Techniques: A Powerful Synergy for Nanomedicine

Nanomedicine has grown tremendously in recent years as a responsive strategy to find novel therapies for treating challenging pathological conditions. As a result, there is an urgent need to develop novel formulations capable of providing adequate therapeutic treatment while overcoming the limitations of traditional protocols. Lately, microfluidic technology (MF) and additive manufacturing (AM) have both acquired popularity, bringing numerous benefits to a wide range of life science applications. There have been numerous benefits and drawbacks of MF and AM as distinct techniques, with case studies showing how the careful optimization of operational parameters enables them to overcome existing limitations. Therefore, the focus of this review was to highlight the potential of the synergy between MF and AM, emphasizing the significant benefits that this collaboration could entail. The combination of the techniques ensures the full customization of MF-based systems while remaining cost-effective and less time-consuming compared to classical approaches. Furthermore, MF and AM enable highly sustainable procedures suitable for industrial scale-out, leading to one of the most promising innovations of the near future.

A Review of 3D-Printing of Microneedles

Microneedles are micron-sized devices that are used for the transdermal administration of a wide range of active pharmaceutics substances with minimally invasive pain. In the past decade, various additive manufacturing technologies have been used for the fabrication of microneedles; however, they have limitations due to material compatibility and bioavailability and are time-consuming and expensive processes. Additive manufacturing (AM), which is popularly known as 3D-printing, is an innovative technology that builds three-dimensional solid objects (3D). This article provides a comprehensive review of the different 3D-printing technologies that have the potential to revolutionize the manufacturing of microneedles. The application of 3D-printed microneedles in various fields, such as drug delivery, vaccine delivery, cosmetics, therapy, tissue engineering, and diagnostics, are presented. This review also enumerates the challenges that are posed by the 3D-printing technologies, including the manufacturing cost, which limits its viability for large-scale production, the compatibility of the microneedle-based materials with human cells, and concerns around the efficient administration of large dosages of loaded microneedles. Furthermore, the optimization of microneedle design parameters and features for the best printing outcomes is of paramount interest. The Food and Drug Administration (FDA) regulatory guidelines relating to the safe use of microneedle devices are outlined. Finally, this review delineates the implementation of futuristic technologies, such as artificial intelligence algorithms, for 3D-printed microneedles and 4D-printing capabilities.

3D-printed microneedle arrays for drug delivery

Microneedle arrays provide an efficient tool for transdermal drug delivery in a minimally invasive and painless manner, showing great potential applications in medicine. However, it remains challenging to fabricate the desired microneedle arrays, because of their micron-scale size and fine structure. Novel manufacturing technologies are very wanted for the development of microneedle arrays, which would solidly advance the clinical translation of microneedle arrays. 3D printing technology is a powerful manufacturing technology with superiority in fabricating personalized and complex structures. Currently, 3D printing technology has been employed to fabricate microneedle arrays, which could push more microneedle arrays into clinic and inspire the development of future microneedle arrays. This work reviews the art of 3D printing microneedle arrays, the benefits of fabricating microneedle arrays with 3D printing, and the considerations for clinical translation of 3D-printed microneedle arrays. This work provides an overview of the current 3D-printed microneedle arrays in drug delivery.

Emerging technologies for combating pandemics

INTRODUCTION

Covid-19, alongside previous pandemics, has highlighted the need for the continued development of technologies that are at our disposal. Emerging technologies are those that show true promise in achieving such a goal and have begun to form sturdy independent research areas. Technological advances in healthcare must continually develop to ensure that the world is prepared for any future diseases that may ensue. As such, a strategic review into 39 manuscripts since 2019 has been conducted to determine the prominence of emerging technologies since the beginning of the Covid-19 pandemic.

AREAS COVERED

Relating to their use in a pandemic state, additive manufacturing (AM), biofabrication, microfluidics, biomedical microelectromechanical systems (BioMEMS), and artificial intelligence (AI) are described. Applications over the past 2-3 years, as well as future developments, are considered throughout.

EXPERT OPINION

All the technologies mentioned in this review are sure to develop further, having shown their importance and value during the covid-19 pandemic. As research continues within the area, their efficacy will increase to the point where it likely will become gold standard for pandemic control. Combining certain technologies mentioned has also proved to have had great success in improving the final results obtained.

Fast Customization of Hollow Microneedle Patches for Insulin Delivery

Hollow microneedle patches (HMNPs) have great promise for efficient and precise transdermal drug delivery in a painless manner. Currently, the clinical application of HMNPs is restricted by its complex manufacturing processes. Here, we use a new three-dimensional (3D) printing technology, static optical projection lithography (SOPL), for the fast fabrication of HMNPs. In this technology, a light beam is modulated into a customized pattern by a digital micromirror device (DMD) and projected to induce the spatial polymerization of monomer solutions which is controlled by the distribution of the light intensity in the monomer solutions. After an annulus picture is inputted into the DMD via the computer, the microneedles with hollow-cone structure can be precisely printed in seconds. By designing the printing pictures, the personalized HMNPs can be fast customized, which can afford the scale-up preparation of personalized HMNPs. Meanwhile, the obtained hollow microneedles (HMNs) have smooth surface without layer-by-layer structure in the commonly 3D-printed products. After being equipped with a micro-syringe, the HMNPs can efficiently deliver insulin into the skin by injection, resulting in effective control of the blood glucose level in diabetic mice. This work demonstrates a SOPL-based 3D printing technology for fast customization of HMNPs with promising medical applications.