The Role of 3D Printing Technology in Microengineering of Microneedles

Biodegradable polymeric insulin microneedles - a design and materials perspective review

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

Dissolving microneedles for transdermal drug delivery in cancer immunotherapy

Immunotherapy is an important approach in cancer treatment. Transdermal administration is emerging as a promising method for delivering immunotherapeutics. Dissolving microneedles are made mainly of soluble or biodegradable polymers and have garnered widespread attention due to their painlessness, safety, convenience, excellent drug loading capacity, and easy availability of various materials, making them an ideal transdermal delivery system. This review comprehensively summarized the preparation methods, materials, and applications of dissolving microneedles in cancer vaccines, immune checkpoint inhibitors, and adoptive cell therapy. Additionally, the challenges and perspectives associated with their future clinical translation are discussed.

Swellable Microneedles in Drug Delivery and Diagnostics

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

Calcipotriol Nanosuspension-Loaded Trilayer Dissolving Microneedle Patches for the Treatment of Psoriasis: In Vitro Delivery and In Vivo Antipsoriatic Activity Studies

Psoriasis, affecting 2-3% of the global population, is a chronic inflammatory skin condition without a definitive cure. Current treatments focus on managing symptoms. Recognizing the need for innovative drug delivery methods to enhance patient adherence, this study explores a new approach using calcipotriol monohydrate (CPM), a primary topical treatment for psoriasis. Despite its effectiveness, CPM's therapeutic potential is often limited by factors like the greasiness of topical applications, poor skin permeability, low skin retention, and lack of controlled delivery. To overcome these challenges, the study introduces CPM in the form of nanosuspensions (NSs), characterized by an average particle size of 211 ± 2 nm. These CPM NSs are then incorporated into a trilayer dissolving microneedle patch (MAP) made from poly(vinylpyrrolidone) and w poly(vinyl alcohol) as needle arrays and prefrom 3D printed polylactic acid backing layer. This MAP features rapidly dissolving tips and exhibits good mechanical properties and insertion capability with delivery efficiency compared to the conventional Daivonex ointment. The effectiveness of this novel MAP was tested on Sprague-Dawley rats with imiquimod-induced psoriasis, demonstrating efficacy comparable to the marketed ointment. This innovative trilayer dissolving MAP represents a promising new local delivery system for calcipotriol, potentially revolutionizing psoriasis treatment by enhancing drug delivery and patient compliance.

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.

Inflammatory macrophage reprogramming strategy of fucoidan microneedles-mediated ROS-responsive polymers for rheumatoid arthritis

During the pathogenesis of rheumatoid arthritis, inflammatory cells usually infiltrate synovial tissues, notably, M1-type macrophages, whose redox imbalance leads to the degradation of joint structures and deterioration of function. Natural active products play a vital role in immune modulation and antioxidants. In this study, we constructed a ROS-responsive nanoparticle called FTL@SIN, which consists of fucoidan (Fuc) and luteolin (Lut) connected by a ROS-responsive bond, Thioketal (TK), and encapsulated with an anti-rheumatic drug, Sinomenine (SIN), for synergistic anti-inflammatory effects. The FTL@SIN is then dispersed in high molecular weight Fuc-fabricated dissolvable microneedles (FTL@SIN MNs) for local administration. Therapy of FTL@SIN MNs afforded a significant decrease in macrophage inflammation while decreasing key pro-inflammatory cytokines and repolarizing M1 type to M2 type, thereby ameliorating synovial inflammation, and promoting cartilage repair. Additionally, our investigations have revealed that Fucoidan (Fuc) demonstrates synergistic effects, exhibiting superior mechanical strength and enhanced physical stability when compared to microneedles formulated solely with hyaluronic acid. This study combines nanomedicine with traditional Chinese medicine, a novel drug delivery strategy that presents a promising avenue for therapeutic intervention in rheumatoid arthritis.

Advancements in microneedle fabrication techniques: artificial intelligence assisted 3D-printing technology

Microneedles (MNs) are micron-scale needles that are a painless alternative to injections for delivering drugs through the skin. MNs find applications as biosensing devices and could serve as real-time diagnosis tools. There have been numerous fabrication techniques employed for producing quality MN-based systems, prominent among them is the three-dimensional (3D) printing. 3D printing enables the production of quality MNs of tuneable characteristics using a variety of materials. Further, the possible integration of artificial intelligence (AI) tools such as machine learning (ML) and deep learning (DL) with 3D printing makes it an indispensable tool for fabricating microneedles. Provided that these AI tools can be trained and act with minimal human intervention to control the quality of products produced, there is also a possibility of mass production of MNs using these tools in the future. This work reviews the specific role of AI in the 3D printing of MN-based devices discussing the use of AI in predicting drug release patterns, its role as a quality control tool, and in predicting the biomarker levels. Additionally, the autonomous 3D printing of microneedles using an integrated system of the internet of things (IoT) and machine learning (ML) is discussed in brief. Different categories of machine learning including supervised learning, semi-supervised learning, unsupervised learning, and reinforced learning have been discussed in brief. Lastly, a brief section is dedicated to the biosensing applications of MN-based devices.

Nanozyme-Incorporated Microneedles for the Treatment of Chronic Wounds

Acute wounds are converted to chronic wounds due to advanced age and diabetic complications. Nanozymes catalyze ROS production to kill bacteria without causing drug resistance, while microneedles (MNs) can break through the skin barrier to deliver drugs effectively. Nanozymes can be intergrateded into MNs delivery systems to improve painless drug delivery. It can also reduce the effective dose of drug sterilization while increasing delivery efficiency and effectively killing wounded bacteria while preventing drug resistance. This paper describes various types of metal nanozymes from previous studies and compares their mutual enhancement with nanozymes. The pooled results show that the MNs, through material innovation, are able to both penetrate the scab and deliver nanozymes and exert additional anti-inflammatory and bactericidal effects. The catalytic effect of some of the nanozymes can also accelerate the lysis of the MNs or create a cascade reaction against inflammation and infection. However, the issue of increased toxicity associated with skin penetration and clinical translation remains a challenge. This study reviews the latest published results and corresponding challenges associated with the use of MNs combined with nanozymes for the treatment of wounds, providing further information for future research.

Microneedles Based on a Biodegradable Polymer-Hyaluronic Acid

Transdermal transport can be challenging due to the difficulty in diffusing active substances through the outermost layer of the epidermis, as the primary function of the skin is to protect against the entry of exogenous compounds into the body. In addition, penetration of the epidermis for substances hydrophilic in nature and particles larger than 500 Da is highly limited due to the physiological properties and non-polar nature of its outermost layer, namely the stratum corneum. A solution to this problem can be the use of microneedles, which "bypass" the problematic epidermal layer by dispensing the active substance directly into the deeper layers of the skin. Microneedles can be obtained with various materials and come in different types. Of special interest are carriers based on biodegradable and biocompatible polymers, such as polysaccharides. Therefore, this paper reviews the latest literature on methods to obtain hyaluronic acid-based microneedles. It focuses on the current advancements in this field and consequently provides an opportunity to guide future research in this area.

Improved pharmacokinetic and lymphatic uptake of Rose Bengal after transfersome intradermal deposition using hollow microneedles

The lymphatic system is active in several processes that regulate human diseases, among which cancer progression stands out. Thus, various drug delivery systems have been investigated to promote lymphatic drug targeting for cancer therapy; mainly, nanosized particles in the 10-150 nm range quickly achieve lymphatic vessels after an interstitial administration. Herein, a strategy to boost the lymphotropic delivery of Rose Bengal (RB), a hydrosoluble chemotherapeutic, is proposed, and it is based on the loading into Transfersomes (RBTF) and their intradermal deposition in vivo by microneedles. RBTF of 96.27 ± 13.96 nm (PDI = 0.29 ± 0.02) were prepared by a green reverse-phase evaporation technique, and they showed an RB encapsulation efficiency of 98.54 ± 0.09%. In vitro, RBTF remained physically stable under physiological conditions and avoided the release of RB. In vivo, intravenous injection of RBTF prolonged RB half-life of 50 min in healthy rats compared to RB intravenous injection; the RB half-life in rat body was further increased after intradermal injection reaching 24 h, regardless of the formulation used. Regarding lymphatic targeting, RBTF administered intravenously provided an RB accumulation in the lymph nodes of 12.3 ± 0.14 ng/mL after 2 h, whereas no RB accumulation was observed after RB intravenous injection. Intradermally administered RBTF resulted in the highest RB amount detected in lymph nodes after 2 h from the injection (84.2 ± 25.10 ng/mL), which was even visible to the naked eye based on the pink colouration of the drug. In the case of intradermally administered RB, RB in lymph node was detected only at 24 h (13.3 ± 1.41 ng/mL). In conclusion, RBTF proved an efficient carrier for RB delivery, enhancing its pharmacokinetics and promoting lymph-targeted delivery. Thus, RBTF represents a promising nanomedicine product for potentially facing the medical need for novel strategies for cancer therapy.

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.

Microneedle-mediated nanomedicine to enhance therapeutic and diagnostic efficacy

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

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.

Recent advances in hydrogel microneedle-based biofluid extraction and detection in food and agriculture

Microneedle (MN) technology has been extensively studied for its advantages of minimal invasiveness and user-friendliness. Notably, hydrogel microneedles (HMNs) have garnered considerable attention for biofluid extraction due to its high swelling properties and biocompatibility. This review provides a comprehensive overview of definition, materials, and fabrication methods associated with HMNs. The extraction mechanisms and optimization strategies for enhancing extraction efficiency are summarized. Moreover, particular emphasis is placed on HMN-based biofluid extraction and detection in the domains of food and agriculture, encompassing the detection of small molecules, nucleic acids, and other relevant analytes. Finally, current challenges and possible solutions associated with HMN-based biofluid extraction are discussed.

Coated Microneedle System for Delivery of Clotrimazole in Deep-Skin Mycoses

Mycoses of the skin are infectious diseases caused by fungal microorganisms that are generally treated with topical agents. However, such therapy is often ineffective and has to be supported by oral use of active substances, which, in turn, can cause many side effects. A good alternative for the treatment of deep-skin mycoses seems to be microneedles (MNs). The aim of this research was to fabricate and evaluate the properties of innovative MNs coated with a hydrogel as potential carriers for clotrimazole (CLO) in the treatment of deep fungal skin infections. A 3D printing technique using a photo-curable resin was employed to produce MNs, which were coated with hydrogels using a dip-coating method. Hydrogels were prepared with carbopol EZ-3 Polymer (Lubrizol) in addition to glycerol and triisopropanolamine. Clotrimazole was introduced into the gel as the solution in ethanol or was suspended. In the first step of the investigation, a texture analysis of hydrogels was prepared with a texture analyzer, and the drug release studies were conducted with the use of automatic Franz diffusion cells. Next, the release profiles of CLO for coated MNs were checked. The last part of the investigation was the evaluation of the antifungal activity of the prepared systems, and the inhibition of the growth of Candida albicans was checked with the diffusion and suspended-plate methods. The texture profile analysis (TPA) for the tested hydrogels showed that the addition of ethanol significantly affects the following studied parameters: hardness, adhesiveness and gumminess, causing a decrease in their values. On the other hand, for the gels with suspended CLO, better spreadability was seen compared to gels with dissolved CLO. The presence of the active substance did not significantly affect the values of the tested parameters. In the dissolution study, the results showed that higher amounts of CLO were released for MNs coated with a hydrogel containing dissolved CLO. Also, microbiological tests proved its efficacy against fungal cultures. Qualitative tests carried out using the diffusion method showed that circular zones of inhibition of fungal growth on the plate were obtained, confirming the hypothesis of effectiveness. The suspension-plate technique confirmed the inhibitory effect of applied CLO on the growth of Candida albicans. From the analysis of the data, the MNs coated with CLO dissolved in hydrogel showed better antifungal activity. All received results seem to be helpful in developing further studies for MNs as carriers of antifungal substances.

Multi-material 3D printed eutectogel microneedle patches integrated with fast customization and tunable drug delivery

Microneedle patches are emerging multifunctional platforms for transdermal diagnostics and drug delivery. However, it still remains challenging to develop smart microneedles integrated with customization, sensing, detection and drug delivery by 3D printing strategy. Here, we present an innovative but facile strategy to rationally design and fabricate multifunctional eutectogel microneedle (EMN) patches via multi-material 3D printing. Polymerizable deep eutectic solvents (PDES) were selected as printing inks for rapid one-step fabrication of 3D printing functional EMN patches due to fast photopolymerization rate and ultrahigh drug solubility. Moreover, stretchable EMN patches incorporating rigid needles and flexible backing layers were easily realized by changing PDES compositions of multi-material 3D printing. Meanwhile, we developed multifunctional smart multi-material EMN patches capable of performing wireless monitoring of body movements, painless colorimetric glucose detection, and controlled transdermal drug delivery. Thus, such multi-material EMN system could provide an effective platform for the painless diagnosis, detection, and therapy of a variety of diseases.

Novel Drug Delivery Systems for the Management of Fungal Keratitis

Fungal keratitis (FK) is a dangerous corneal infection that is common in tropical and subtropical areas. Its incidence is extremely high, and ocular trauma and contact lenses can lead to FK, but its common treatment such as using topical antifungal eye drop instillation is often less effective because of several drawbacks of the drugs typically used, including limited ocular penetration, high frequency of dosing, poor biocompatibility, and the potential for severe drug reactions. Therefore, the development of novel drug delivery devices for the treatment of FK is urgent. The urgent need for novel drug delivery devices to treat FK has led to the development of several techniques, including nanoparticles (NPs), in situ forming hydrogels, contact lenses, and microneedles (MNs). However, it is important to note that the main mechanisms differ between these techniques. NPs can transport large amounts of drugs and be taken up by cells owing to their large surface area and small size. In situ forming hydrogels can significantly extend the residence time of drugs because of their strong adhesive properties. Contact lenses, with their comfortable shape and drug-carrying capacity, can also act as drug delivery devices. MNs can create channels in the cornea, bypassing its barrier and enhancing drug bioavailability. This article will go over novel medication delivery techniques for treating FK and make a conclusion about their advantages and limitations in anticipation to serve the best option for the individual therapy of FK.

3D Printed Ion-Responsive Personalized Transdermal Patch

Microneedle patches are easy-to-use medical devices for transdermal administration. However, the insufficient insertion of microneedles due to the gap between planar patches and contoured skin affects drug delivery. Herein, we formulate a prepolymer for high-fidelity three-dimensional (3D) printed personalized transdermal patches. With the excellent photoinitiation ability of 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (Tz), a high-fidelity and precise microneedle patch is successfully fabricated. Upon irradiation of the white illuminator, the doped gold nanoparticles (AuNPs) in the patch release heat and promisingly induce sweat production. With the introduction of Na+, the dominant component of sweat, the curvature of the produced transdermal patch is observed due to the ion-induced network rearrangement. The alkanethiol-stabilized AuNP with an end group of a carboxyl group causes controlled drug release behavior. Furthermore, the irradiation-induced photothermal heating of AuNP can facilitate the sustainability of drug release thanks to the substantially increased particle size of AuNP. These findings demonstrate that the developed prepolymer is a promising candidate for the production of transdermal patches fitting the curvature of the body surface.

Formulating biopharmaceuticals using three-dimensional printing

Additive manufacturing, commonly referred to as three-dimensional (3D) printing, has the potential to initiate a paradigm shift in the field of medicine and drug delivery. Ever since the advent of the first-ever United States Food and Drug Administration (US FDA)-approved 3D printed tablet, there has been an increased interest in the application of this technology in drug delivery and biomedical applications. 3D printing brings us one step closer to personalized medicine, hence rendering the "one size fits all" concept in drug dosing obsolete. In this review article, we focus on the recent developments in the field of modified drug delivery systems in which various types of additive manufacturing technologies are applied.

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.

Design and fabrication of customizable microneedles enabled by 3D printing for biomedical applications

Microneedles (MNs) is an emerging technology that employs needles ranging from 10 to 1000 μm in height, as a minimally invasive technique for various procedures such as therapeutics, disease monitoring and diagnostics. The commonly used method of fabrication, micromolding, has the advantage of scalability, however, micromolding is unable to achieve rapid customizability in dimensions, geometries and architectures, which are the pivotal factors determining the functionality and efficacy of the MNs. 3D printing offers a promising alternative by enabling MN fabrication with high dimensional accuracy required for precise applications, leading to improved performance. Furthermore, enabled by its customizability and one-step process, there is propitious potential for growth for 3D-printed MNs especially in the field of personalized and on-demand medical devices. This review provides an overview of considerations for the key parameters in designing MNs, an introduction on the various 3D-printing techniques for fabricating this new generation of MNs, as well as highlighting the advancements in biomedical applications facilitated by 3D-printed MNs. Lastly, we offer some insights into the future prospects of 3D-printed MNs, specifically its progress towards translation and entry into market.

MAP-box: a novel, low-cost and easy-to-fabricate 3D-printed box for the storage and transportation of dissolving microneedle array patches

Research on the use of microarray patches (MAPs) has progressed at an unprecedented rate over the years, leading to the development of many novel drug delivery systems. As the technology approaches patients, there are several key aspects that ought to be addressed in order to facilitate the smooth translation of MAPs from bench to bedside. One integral factor includes the choice of devices and packaging for the storage of MAPs. In the current work, a slide-and-seal box, MAP-box, was developed for the storage of dissolving MAPs, using fused-deposition modelling. The device has been designed to act as a pill-box for MAPs not only to provide protection for MAPs from the environment, but also to improve patient's adherence to treatment. The overall design of the MAP-box was simple, yet offers the capability of sealing and protecting dissolving MAPs up to 30 days. Donepezil HCl was formulated into a dissolvable MAP, which was used to treat dementia related to Alzheimer's disease. This compound was used as a model formulation to evaluate the utility of the 3D printed MAP-box when placed under three storage conditions: 5 °C and ambient humidity, 25 °C and 65% relative humidity and 40 °C and 75% relative humidity. It was shown that the slide-and-seal box was able to confer protection to MAPs for up to 30 days under accelerated stability study conditions as the drug loading, mechanical properties and insertion properties of MAPs remained unaffected when compared to the unpackaged MAPs stored under these same parameters. These preliminary data provide evidence that the MAP-box prototype may be of great utility for the storage of single or multiple MAPs. Nevertheless, future work will be needed to evaluate their patient usability and its application to different types of MAP systems to fully validate the overall robustness of the prototype.

Projection Micro-Stereolithography to Manufacture a Biocompatible Micro-Optofluidic Device for Cell Concentration Monitoring

In this work, a 3D printed biocompatible micro-optofluidic (MoF) device for two-phase flow monitoring is presented. Both an air-water bi-phase flow and a two-phase mixture composed of micrometric cells suspended on a liquid solution were successfully controlled and monitored through its use. To manufacture the MoF device, a highly innovative microprecision 3D printing technique was used named Projection Microstereolithography (PμSL) in combination with the use of a novel 3D printable photocurable resin suitable for biological and biomedical applications. The concentration monitoring of biological fluids relies on the absorption phenomenon. More precisely, the nature of the transmission of the light strictly depends on the cell concentration: the higher the cell concentration, the lower the optical acquired signal. To achieve this, the microfluidic T-junction device was designed with two micrometric slots for the optical fibers' insertion, needed to acquire the light signal. In fact, both the micro-optical and the microfluidic components were integrated within the developed device. To assess the suitability of the selected biocompatible transparent resin for optical detection relying on the selected working principle (absorption phenomenon), a comparison between a two-phase flow process detected inside a previously fully characterized micro-optofluidic device made of a nonbiocompatible high-performance resin (HTL resin) and the same made of the biocompatible one (BIO resin) was carried out. In this way, it was possible to highlight the main differences between the two different resin grades, which were further justified with proper chemical analysis of the used resins and their hydrophilic/hydrophobic nature via static water contact angle measurements. A wide experimental campaign was performed for the biocompatible device manufactured through the PμSL technique in different operative conditions, i.e., different concentrations of eukaryotic yeast cells of Saccharomyces cerevisiae (with a diameter of 5 μm) suspended on a PBS (phosphate-buffered saline) solution. The performed analyses revealed that the selected photocurable transparent biocompatible resin for the manufactured device can be used for cell concentration monitoring by using ad hoc 3D printed micro-optofluidic devices. In fact, by means of an optical detection system and using the optimized operating conditions, i.e., the optimal values of the flow rate FR=0.1 mL/min and laser input power P∈{1,3} mW, we were able to discriminate between biological fluids with different concentrations of suspended cells with a robust working ability R2=0.9874 and Radj2=0.9811.

Empowering Precision Medicine: The Impact of 3D Printing on Personalized Therapeutic

This review explores recent advancements and applications of 3D printing in healthcare, with a focus on personalized medicine, tissue engineering, and medical device production. It also assesses economic, environmental, and ethical considerations. In our review of the literature, we employed a comprehensive search strategy, utilizing well-known databases like PubMed and Google Scholar. Our chosen keywords encompassed essential topics, including 3D printing, personalized medicine, nanotechnology, and related areas. We first screened article titles and abstracts and then conducted a detailed examination of selected articles without imposing any date limitations. The articles selected for inclusion, comprising research studies, clinical investigations, and expert opinions, underwent a meticulous quality assessment. This methodology ensured the incorporation of high-quality sources, contributing to a robust exploration of the role of 3D printing in the realm of healthcare. The review highlights 3D printing's potential in healthcare, including customized drug delivery systems, patient-specific implants, prosthetics, and biofabrication of organs. These innovations have significantly improved patient outcomes. Integration of nanotechnology has enhanced drug delivery precision and biocompatibility. 3D printing also demonstrates cost-effectiveness and sustainability through optimized material usage and recycling. The healthcare sector has witnessed remarkable progress through 3D printing, promoting a patient-centric approach. From personalized implants to radiation shielding and drug delivery systems, 3D printing offers tailored solutions. Its transformative applications, coupled with economic viability and sustainability, have the potential to revolutionize healthcare. Addressing material biocompatibility, standardization, and ethical concerns is essential for responsible adoption.

Multifunctional Microneedle Patches via Direct Ink Drawing of Nanocomposite Inks for Personalized Transdermal Drug Delivery

Additive manufacturing, commonly known as 3D printing, allows decentralized drug fabrication of orally administered tablets. Microneedles are comparatively favorable for self-administered transdermal drug delivery with improved absorption and bioavailability. Due to the cross-scale geometric characteristics, 3D-printed microneedles face a significant trade-off between the feature resolution and production speed in conventional layer-wise deposition sequences. In this study, we introduce an economical and scalable direct ink drawing strategy to create drug-loaded microneedles. A freestanding microneedle is efficiently generated upon each pneumatic extrusion and controlled drawing process. Sharp tips of ∼5 μm are formed with submillimeter nozzles, representing 2 orders of magnitude improved resolution. As the key enabler of this fabrication strategy, the yield-stress fluid inks are formulated by simply filling silica nanoparticles into regular polymer solutions. The approach is compatible with various microneedles based on dissolvable, biodegradable, and nondegradable polymers. Various matrices are readily adopted to adjust the release behaviors of the drug-loaded microneedles. Successful fabrication of multifunctional patches with heterogeneously integrated microneedles allows the treatment of melanoma via synergistic photothermal therapy and combination chemotherapy. The personalized patches are designed for cancer severity to achieve high therapeutic efficacy with minimal side effects. The direct ink drawing reported here provides a facile and low-cost fabrication strategy for multifunctional microneedle patches for self-administering transdermal drug delivery.

Dissolving and Swelling Hydrogel-Based Microneedles: An Overview of Their Materials, Fabrication, Characterization Methods, and Challenges

Polymeric hydrogels are a complex class of materials with one common feature-the ability to form three-dimensional networks capable of imbibing large amounts of water or biological fluids without being dissolved, acting as self-sustained containers for various purposes, including pharmaceutical and biomedical applications. Transdermal pharmaceutical microneedles are a pain-free drug delivery system that continues on the path to widespread adoption-regulatory guidelines are on the horizon, and investments in the field continue to grow annually. Recently, hydrogels have generated interest in the field of transdermal microneedles due to their tunable properties, allowing them to be exploited as delivery systems and extraction tools. As hydrogel microneedles are a new emerging technology, their fabrication faces various challenges that must be resolved for them to redeem themselves as a viable pharmaceutical option. This article discusses hydrogel microneedles from a material perspective, regardless of their mechanism of action. It cites the recent advances in their formulation, presents relevant fabrication and characterization methods, and discusses manufacturing and regulatory challenges facing these emerging technologies before their approval.

Conceptual Design and Numerical Validation of a Carbon-Based Ink Injector

This paper shows the design of an injector, using carbon nanotubes as inkjet material, implemented in a 3D printer. According to the available literature, few injectors are capable of depositing material. Due to the lack of information, the central part of this research is to develop a suitable device for ink injection that is capable of applying the Fused Deposition Modeling (FDM) method to print nanomaterial ink. The injector was designed using a CAD program based on an open-source desktop 3D printer, which allows it to be modified according to the needs of the injector. This prototype was manufactured in aluminum alloy 7075T6. Computational fluid dynamics (CFD) were carried out to analyze the behavior of the fluid when it passes through the injector, obtaining parameters such as pressure, velocity, and vorticity. An experimental matrix of the injector operation was carried out to achieve an adequate printing speed. The results show that the optimum speed was 250 ms, considering that a temperature of 100 °C is needed in the heated bed to dry the ink so that it does not undergo expansion.

Modern microelectronics and microfluidics on microneedles

Possessing the attractive advantages of moderate invasiveness and high compliance, there is no doubt that microneedles (MNs) have been a gradually rising star in the field of medicine. Recent evidence implies that microelectronics technology based on microcircuits, microelectrodes and other microelectronic elements combined with MNs can realize mild electrical stimulation, drug release and various types of electrical sensing detection. In addition, the combination of microfluidics technology and MNs makes it possible to transport fluid drugs and access a small quantity of body fluids which have shown significant untapped potential for a wide range of diagnostics. Of particular note is that combining both technologies and MNs is more difficult, but is promising to build a modern healthcare platform with more comprehensive functions. This review introduces the properties of MNs that can form integrated systems with microelectronics and microfluidics, and summarizes these systems and their applications. Furthermore, the future challenges and perspectives of the integrated systems are conclusively proposed.

Supramolecular chemistry enables vat photopolymerization 3D printing of novel water-soluble tablets

Vat photopolymerization has garnered interest from pharmaceutical researchers for the fabrication of personalised medicines, especially for drugs that require high precision dosing or are heat labile. However, the 3D printed structures created thus far have been insoluble, limiting printable dosage forms to sustained-release systems or drug-eluting medical devices which do not require dissolution of the printed matrix. Resins that produce water-soluble structures will enable more versatile drug release profiles and expand potential applications. To achieve this, instead of employing cross-linking chemistry to fabricate matrices, supramolecular chemistry may be used to impart dynamic interaction between polymer chains. In this study, water-soluble drug-loaded printlets (3D printed tablets) are fabricated via digital light processing (DLP) 3DP for the first time. Six formulations with varying ratios of an electrolyte acrylate monomer, [2-(acryloyloxy)ethyl]trimethylammonium chloride (TMAEA), and a co-monomer, 1-vinyl-2-pyrrolidone (NVP), were prepared to produce paracetamol-loaded printlets. 1H NMR spectroscopy analysis confirmed the integration of TMAEA and NVP in the polymer, and residual TMAEA monomers were found to be present only in trace amounts (0.71 - 1.37 %w/w). The apparent molecular mass of the photopolymerised polymer was found to exceed 300,000 Da with hydrodynamic radii of 15 - 20 nm, estimated based on 1H DOSY NMR measurements The loaded paracetamol was completely released from the printlets between 45 minutes to 5 hours. In vivo single-dose acute toxicity studies in rats suggest that the printlets did not cause any tissue damage. The findings reported in this study represent a significant step towards the adoption of vat photopolymerization-based 3DP to produce personalised medicines.

Industrial perspectives for personalized microneedles

Microneedles and, subsequently, microneedle arrays are emerging miniaturized medical devices for painless transdermal drug delivery. New and improved additive manufacturing methods enable novel microneedle designs to be realized for preclinical and clinical trial assessments. However, current literature reviews suggest that industrial manufacturers and researchers have focused their efforts on one-size-fits-all designs for transdermal drug delivery, regardless of patient demographic and injection site. In this perspective article, we briefly review current microneedle designs, microfabrication methods, and industrialization strategies. We also provide an outlook where microneedles may become personalized according to a patient's demographic in order to increase drug delivery efficiency and reduce healing times for patient-centric care.

Fabrication of Antibacterial Sponge Microneedles for Sampling Skin Interstitial Fluid

Microneedles (MNs) have recently garnered extensive interest concerning direct interstitial fluid (ISF) extraction or their integration into medical devices for continuous biomarker monitoring, owing to their advantages of painlessness, minimal invasiveness, and ease of use. However, micropores created by MN insertion may provide pathways for bacterial infiltration into the skin, causing local or systemic infection, especially with long-term in situ monitoring. To address this, we developed a novel antibacterial sponge MNs (SMNs@PDA-AgNPs) by depositing silver nanoparticles (AgNPs) on polydopamine (PDA)-coated SMNs. The physicochemical properties of SMNs@PDA-AgNPs were characterized regarding morphology, composition, mechanical strength, and liquid absorption capacity. The antibacterial effects were evaluated and optimized through agar diffusion assays in vitro. Wound healing and bacterial inhibition were further examined in vivo during MN application. Finally, the ISF sampling ability and biosafety of SMNs@PDA-AgNPs were assessed in vivo. The results demonstrate that antibacterial SMNs enable direct ISF extraction while preventing infection risks. SMNs@PDA-AgNPs could potentially be used for direct sampling or combined with medical devices for real-time diagnosis and management of chronic diseases.

Microneedle-Integrated Sensors for Extraction of Skin Interstitial Fluid and Metabolic Analysis

Skin interstitial fluid (ISF) has emerged as a fungible biofluid sample for blood serum and plasma for disease diagnosis and therapy. The sampling of skin ISF is highly desirable considering its easy accessibility, no damage to blood vessels, and reduced risk of infection. Particularly, skin ISF can be sampled using microneedle (MN)-based platforms in the skin tissues, which exhibit multiple advantages including minimal invasion of the skin tissues, less pain, ease of carrying, capacity for continuous monitoring, etc. In this review, we focus on the current development of microneedle-integrated transdermal sensors for collecting ISF and detecting specific disease biomarkers. Firstly, we discussed and classified microneedles according to their structural design, including solid MNs, hollow MNs, porous MNs, and coated MNs. Subsequently, we elaborate on the construction of MN-integrated sensors for metabolic analysis with highlights on the electrochemical, fluorescent, chemical chromogenic, immunodiagnostic, and molecular diagnostic MN-integrated sensors. Finally, we discuss the current challenges and future direction for developing MN-based platforms for ISF extraction and sensing applications.

Microneedle technology for potential SARS-CoV-2 vaccine delivery

INTRODUCTION

Microneedle fabrication was conceptualised in the 1970s as devices for painless transdermal drug delivery. The last two decades have seen considerable research and financial investment in this area with SARS-CoV-2 and other vaccines catalysing their application to in vivo intradermal vaccine delivery. Microneedle arrays have been fabricated in different shapes, geometries, formats, and out of different materials.

AREAS COVERED

The recent pandemic has offered microneedle platforms the opportunity to be employed as a vehicle for SARS-CoV-2 vaccine administration. The various modes of vaccination delivery and the potential of microneedle arrays-based vaccines will be presented, with a specific focus placed on recent SARS-CoV-2 research. The advantages of microneedle-based vaccine administration, in addition to the major hurdles to their en masse implementation, will be examined.

EXPERT OPINION

Considering the widely acknowledged disadvantages of current vaccine delivery, such as anxiety, pain, and the requirement for professional administration, a large shift in this research sphere is imminent. The SARS-CoV-2 pandemic has catalysed the development of alternate vaccination platforms, working to avoid the requirement for mass vaccination centres. As microneedle vaccine patches are transitioning through clinical study phases, research will be required to ready this technology for a more mass production environment.

3D-printed morphology-customized microneedles: understanding the correlation between their morphologies and the received qualities

Despite remarkable progress in the last decade in transdermal microneedle drug delivery systems, great difficulties in precisely manufacturing microneedles with sophisticated microstructures still strongly retard their practical applications. Herein we propose morphology-customized microneedles (spiral, conical, cylindroid, ring-like, arrow-like and tree-like) fabricated by stereolithography (SLA) based 3D-printing technique, and in-depth investigate the correlation between the customized morphologies and the received qualities of the corresponding microneedles such as the mechanical properties and skin penetration behavior, drug loading capacity and the drug release profiles. Results indicated that 3D-printed morphology-customized microneedles not only enhanced the mechanical strength but also improved both drug loading capacity and drug release behavior, which resulted from their highly controllable and 3D-printable morphologies (surface area and volume). And the in vivo study demonstrated that the 3D-printed morphology-customized microneedles successfully promoted the transdermal delivery of the loaded drug (verapamil hydrochloride) with an enhanced therapeutic efficacy for the treatment of hypertrophic scar.

Hopping Light Vat Photopolymerization for Multiscale Fabrication

3D objects with features spanning from microscale to macroscale have various applications. However, the fabrication of such objects presents challenges to additive manufacturing (AM) due to the tradeoffs among manufacturable feature resolution, maximum build area, and printing speed. This paper presents a projection-based AM process called hopping light vat photopolymerization (HL-VPP) to address this critical barrier. The key idea of HL-VPP is to synchronize linear scanning projection with a galvo mirror's rotation. The projector moves continuously at a constant speed while periodically rotating a one-axis galvo mirror to compensate for the projector's linear movement so synchronized hopping motion can be achieved. By this means, HL-VPP can simultaneously achieve large-area (over 200 mm), fast-speed (scanning speed of 13.5 mm s^-1 ), and high-resolution (10 µm pixel size) fabrication. The distinguishing characteristic of HL-VPP is that it allows for hundreds of times lower refresh rates without motion blur. Thus, HL-VPP decouples the fabrication efficiency limit imposed by the refresh rate and will enable super-fast curing in the future. This work will significantly advance VPP's use in applications that require macroscale part size with microscale features. The process has been verified by fabricating multiple multiscale objects, including microgrids and biomimetic structures.

Microneedle-based interstitial fluid extraction for drug analysis: Advances, challenges, and prospects

Similar to blood, interstitial fluid (ISF) contains exogenous drugs and biomarkers and may therefore substitute blood in drug analysis. However, current ISF extraction techniques require bulky instruments and are both time-consuming and complicated, which has inspired the development of viable alternatives such as those relying on skin or tissue puncturing with microneedles. Currently, microneedles are widely employed for transdermal drug delivery and have been successfully used for ISF extraction by different mechanisms to facilitate subsequent analysis. The integration of microneedles with sensors enables in situ ISF analysis and specific compound monitoring, while the integration of monitoring and delivery functions in wearable devices allows real-time dose modification. Herein, we review the progress in drug analysis based on microneedle-assisted ISF extraction and discuss the related future opportunities and challenges.

3D printing of microneedle arrays for hair regeneration in a controllable region

Hair loss is a common skin disease that causes intense emotional suffering. Hair regeneration in a personalized area is highly desirable for patients with different balding conditions. However, the existing pharmaceutical treatments have difficulty precisely regenerating hair in a desired area. Here, we show a method to precisely control the hair regeneration using customized microneedle arrays (MNAs). The MNA with a customized shape is fast fabricated by a static optical projection lithography process in seconds, which is a 3D printing technology developed by our group. In the mouse model, MNA treatment could induce hair regrowth in a defined area corresponding to the customized shape of MNA. And the regenerated hair promoted by MNAs had improved quality. Cellular and molecular analysis indicated that MNA treatment could recruit macrophages in situ and then initiate the proliferation of hair follicle stem cells, thereby improving hair regeneration. Meanwhile, the activation of the Wnt/β-catenin signaling pathway was observed in hair follicles. The expressions of Hgf, Igf 1 and Tnf-α were also upregulated in the treated skin, which may also be beneficial for the MNA-induced hair regeneration. This study provides a strategy to precisely control hair regeneration using customized microneedle arrays by recruiting macrophages in situ, which holds the promise for the personalized treatment of hair loss.

Additive manufacturing technologies with emphasis on stereolithography 3D printing in pharmaceutical and medical applications: A review

Three-dimensional (3D) printing or Additive Manufacturing (AM) technology is an innovative tool with great potential and diverse applications in various fields. As 3D printing has been burgeoning in recent times, a tremendous transformation can be envisaged in medical care, especially the manufacturing procedures leading to personalized medicine. Stereolithography (SLA), a vat-photopolymerization technique, that uses a laser beam, is known for its ability to fabricate complex 3D structures ranging from micron-size needles to life-size organs, because of its high resolution, precision, accuracy, and speed. This review presents a glimpse of varied 3D printing techniques, mainly expounding SLA in terms of the materials used, the orientation of printing, and the working mechanisms. The previous works that focused on developing pharmaceutical dosage forms, drug-eluting devices, and tissue scaffolds are presented in this paper, followed by the challenges associated with SLA from an industrial and regulatory perspective. Due to its excellent advantages, this technology could transform the conventional "one dose fits all" concept to bring digitalized patient-centric medication into reality.

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.

Recent developments in antibacterial or antibiofilm compound coating for biliary stents

Cholestasis of the indwelling biliary stents usually leads to stone recurrence after endoscopic retrograde cholangio pancreatoraphy (ERCP). Biliary stents, including metallic and none-degradable plastic stents are widely used in clinical settings due to their many excellent properties. However, conventional biliary stents still suffer from poor antibacterial activity and anti-bile-adhesion, which lead to injured, local fibroblasts proliferating. Currently, various coatings for biliary stents have been prepared to meet the clinical demands. In this review, we start by summarizing and discussing classifications of biliary stents and antibacterial/antibiofilm mechanism. Then, the latest advances about developing antibacterial and antibiofilm coatings for improving the properties of biliary stents are reviewed and discussed in detail. Lastly, we list several possible directions for future development of biliary stents coatings and biliary stent, such as anti-bile-adhesion coating, multifunctional coating, drug-eluting biodegradable biliary stents and 3D printed biliary stents.

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.