Biodegradable polymer microneedles: fabrication, mechanics and transdermal drug delivery

Motion artifact-controlled micro-brain sensors between hair follicles for persistent augmented reality brain-computer interfaces

Modern brain-computer interfaces (BCI), utilizing electroencephalograms for bidirectional human-machine communication, face significant limitations from movement-vulnerable rigid sensors, inconsistent skin-electrode impedance, and bulky electronics, diminishing the system's continuous use and portability. Here, we introduce motion artifact-controlled micro-brain sensors between hair strands, enabling ultralow impedance density on skin contact for long-term usable, persistent BCI with augmented reality (AR). An array of low-profile microstructured electrodes with a highly conductive polymer is seamlessly inserted into the space between hair follicles, offering high-fidelity neural signal capture for up to 12 h while maintaining the lowest contact impedance density (0.03 kΩ·cm-2) among reported articles. Implemented wireless BCI, detecting steady-state visually evoked potentials, offers 96.4% accuracy in signal classification with a train-free algorithm even during the subject's excessive motions, including standing, walking, and running. A demonstration captures this system's capability, showing AR-based video calling with hands-free controls using brain signals, transforming digital communication. Collectively, this research highlights the pivotal role of integrated sensors and flexible electronics technology in advancing BCI's applications for interactive digital environments.

Recent advances in iontophoresis-assisted microneedle devices for transdermal biosensing and drug delivery

Integrating advanced manufacturing techniques and nanotechnology with cutting-edge materials has driven significant progress in global healthcare. Microneedles, recognized for their minimally invasive approach to transdermal sensing and drug delivery, achieve enhanced functionality when combined with iontophoresis. Iontophoresis-assisted microneedles have emerged as an innovative solution, enabling real-time biosensing and precise drug delivery within closed-loop systems. These integrated platforms represent a major advancement in personalized medicine, allowing dynamic therapeutic adjustments based on continuous feedback. This review highlights the latest developments in iontophoresis-assisted microneedles for transdermal biosensing, drug delivery, and closed-loop applications. It delves into the mechanisms of iontophoresis, assesses its advantages and limitations, and explores future directions for these transformative technologies.

Additional Use of Hyaluronic Acid-Based Dissolving Microneedle Patches to Treat Psoriatic Plaques: A Randomized Controlled Trial

BACKGROUND

Despite advances in systemic targeted therapies, topical agents remain the primary treatment for localized psoriasis. However, their therapeutic effects are often delayed and unsatisfactory. The dissolving microneedle (DMN) patch, a novel transdermal drug delivery system, enhances the absorption of topical agents through micro-channels.

OBJECTIVE

To evaluate the efficacy of DMN patches in enhancing drug delivery and improving clinical outcomes in psoriatic plaques.

METHODS

A prospective, randomized, split-body study was conducted to verify the efficacy of additional use of DMN patches after topical agent application in psoriasis treatment. Patients with mild psoriasis were enrolled and 6 paired lesions per patient were randomized into 3 groups: ointment-only, ointment-with-no needle patch, and ointment-with-DMN patch. Lesions were treated with a topical agent (betamethasone and calcipotriol) once daily for 2 weeks. Modified psoriasis area and severity index (mPASI) scores were measured weekly. In vitro and ex vivo experiments were performed to confirm micro-channel formation, microneedle dissolution, and drug penetration enhancement.

RESULTS

A total of 132 paired lesions from 22 patients were analyzed. The ointment-with-DMN patch group showed significantly improved mPASI scores (80.4%±20.5%; 5.42→1.06) compared to the ointment-with-no needle patch (64.6%±33.0%; 4.94→1.68) (p<0.05) and ointment-only groups (55.5%±31.4%; 5.00→2.15) (p<0.001). In vitro studies demonstrated 2.1-fold enhanced drug delivery with DMN patches, while ex vivo histological analysis confirmed micro-channel formation. No adverse events, including infection or psoriasis exacerbation, were observed.

CONCLUSION

The DMN patch is an effective adjunctive tool that enhances transdermal drug delivery and improves therapeutic outcomes in psoriatic plaques, particularly those refractory to topical agents.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02955576.

Insights into preclinical evaluation of dissolvable microarray patches

Drug-loaded dissolvable microarray patches (MAP) have gained significant attention due to their patient-friendly, economical, and environmentally beneficial attributes. Despite extensive research and advancements, only a limited number of MAP have progressed to clinical trials. While existing literature predominantly covers the initial stages of MAP development (e.g., manufacturing techniques, materials, design), there remains a notable gap in examining an experimental design during preclinical evaluation phase undertaken to inform progression to clinical studies. To address this gap, we present a comprehensive review of the experimental factors influencing MAP performance in preclinical research. Our in-depth analysis of the skin environment and its implications to in vitro MAP performance revealed that skin insertion methodology, media used for release and permeation testing, skin models for permeation studies, and skin metabolism are key factors that need to be considered. We critically assess current research trends and propose potential optimisations to enhance efficacy and biorelevance of in vitro methods for MAP. Additionally, we review factors influencing in vivo and in silico performance, underscoring the promising potential of in silico approaches. This article aims to provide insights that will facilitate the development and standardisation of reliable methodologies in preclinical studies of drug-loaded MAP, ultimately advancing their clinical translation.

Hydrogel-based microneedles for the delivery of catalase protein

Transdermal microneedles (MNs) have emerged as a powerful new technique for medicine and drug delivery. MNs are highly bioavailable, biocompatible, and non-invasive drug delivery systems. Catalase is one of the antioxidant enzymes that decomposes hydrogen peroxide to overcome oxidative damage. Enzymatic proteins such as catalase have a great therapeutic potential; however, their application in vivo is limited until now. For example, when they are administered orally, therapeutic proteins are easily degraded by proteases such as pepsin. In general, MNs can create micron-size channels, overcome the stratum corneum barrier, and deliver therapeutic proteins efficiently. Here, we designed hydrogel-based MNs to deliver catalase protein efficiently. For the fabrication of hydrogel-based MNs, the first step was to produce a MN master mold by using a 3D printer. The second step was to generate a polydimethylsiloxane (PDMS) mold by the reverse micro-molding technique. Next, a hydrogel solution with polyvinyl alcohol (PVA) and chitosan was optimized to produce casted hydrogel MN embraced with good mechanical properties. Among the ratio of PVA to chitosan used in the MN fabrication, the 2:1 ratio (w/w) of PVA:chitosan was the optimized composition for attaining ideal morphology and mechanical strength. Catalase was subsequently loaded onto the hydrogel MNs, and it was successfully delivered into the pig ear through passive diffusion. A longer residence time until 1 h improved the delivery of catalase that kept enzymatic activity after the delivery. Protein delivery using MNs was also strongly enhanced by external stimulations such as ethanol or ultrasound, which was known to disrupt the stratum corneum. The global market for MNs as a drug delivery system is ready to expand, and numerous applications of hydrogel-based MNs are anticipated to deliver therapeutic proteins.

Optimising distribution of hollow microneedle in arrays for transdermal drug delivery considering effects of tissue compression on drug permeability

Hollow microneedles (HMNs) are advanced transdermal drug delivery (TDD) devices that can create micro-perforations in the skin, enabling high molecular weight drugs to bypass the resistance of the skin's top layer, the stratum corneum. These MNs have been shown to enhance drug permeability K in skin with minimal or no discomfort. It is recognised that the variability and interplay of different MN parameters, including the MN distribution within an array, can significantly influence the HMN-based TDD rate. However, optimising these parameters can achieve consistent MN performance. In recognising this, our paper aims to develop a theoretical framework for optimising the HMN distribution in the arrays. The methodology involves formulating an optimisation function g based on different geometrical and physical properties of the MN and skin and associating this with the skin permeability (K) of drugs delivered via the HMNs. The methodology has been established to quantitatively assess the impact of MN design parameters on drug diffusion through the skin, including the effects of compressive strain caused by HMN insertion. The studyshows that an elevated value of g is associated with increased drug K in the skin. The results from the established framework have enabled us to determine the optimal design for various HMN configurations. The data generated from this optimisation technique is subsequently utilised to estimate the skin K of several high molecular weight drugs delivered through an HMN system.

Transdermal microneedle patch for antioxidants release

Polymer based microneedle transdermal drug delivery system fits the criterion for an efficient patient compliant drug delivery system of the future. Smart and controlled microneedle drug delivery systems remain an emerging research area. One of the objectives of this study was to design an accessible approach of molding microneedles using a beeswax mold. The second objective was to evaluate a polymer-based microneedle drug release transdermal platform fabricated via layer by layer (LbL) assembly of conductive polydimethylsiloxane integrated with carbon nanotubes, cellulose nanocrystal and polyaniline (PDMS@CNT/CNC@PANI). The electrically conductive PDMS@CNT/CNC@PANI microneedle patch provides a platform for drug loading, stabilization and transdermal controlled drug release. The drug loaded PDMS@CNT/CNC@PANI microneedle patch was evaluated for diffusion and voltage mediated transdermal delivery of thymol blue and rutin as model compounds. Chicken skin was used as an analogue of human skin. Both electrochemical and passive release from the rutin loaded PDMS@CNC/CNT microneedle patch resulted in ~ 66%. On the other hand, the PDMS@CNC/CNT@PANI patch loaded with rutin resulted in 66-84% release. The results show the novel microneedle patches could effectively release rutin in a controlled manner, and as such showed promise for potential use in clinical drug release applications.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43939-025-00240-8.

Development and comparative analysis of clobetasol-loaded microneedle patches versus clobetasol propionate ointment in experimental induced-psoriasis model

The utilization of dissolvable microneedles (MNs) is a promising and cutting-edge approach to drug delivery for the treatment of psoriasis, an autoimmune skin disorder characterized by the appearance of red, scaly patches on the skin. This study presents the development of a dissolving MN patch made of polyvinylpyrrolidone for the purpose of delivering Clobetasol 17-Propionate through the skin. The MN patches were evaluated for their physical characteristics, including morphology, solubility, strength, and ability to penetrate the skin. This evaluation was conducted on both unloaded and drug-loaded MN patches to determine their suitability for future applications. The manufacturing of 484 pyramidal-shaped tips, each measuring roughly 400 µm in height, was demonstrated by microscopy photographs. Compression tests revealed that the MN patch could endure a force greater than 1 N/needle while displacing around 300 µm, confirming the needle's ability to penetrate the stratum corneum. Following H&E staining, the penetration depth in mice skin was determined to be around 200 µm. The MN tips exhibited rapid drug release within a 10-minute timeframe, while the MN patch dissolved in the mice skin in roughly 20 min. An animal model was utilized to examine the effects of the produced patches on the treatment of psoriasis. Psoriasis was artificially induced in three groups of mice using imiquimod cream, applied for eight consecutive days to evaluate the inhibitory effect of clobetasol on exacerbating the disease. This assessment was accomplished using two methods: applying clobetasol ointment and using CP-loaded MNs. This innovative drug delivery system demonstrated encouraging results in terms of quick and effective administration, highlighting the potential of dissolvable MNs for psoriasis treatment.

Mechanical finite element analysis of needle tip shape to develop insertable polymer-based microneedle without plastic deformation

Bioabsorbable polymer microneedles are highly attractive as modernized medical devices for efficient yet safe transdermal drug delivery and biofluid biopsy. In this study, the elastoplastic deformation of polymer microneedles, having a high aspect ratio (over 5-10), is investigated using poly(lactic) acid polymer approved by the United States Food and Drug Administration to be generally considered safe. Microneedle geometries are comprehensively analyzed for tip geometries comprising the tip diameter (ϕt) and tip taper length (lt) of 100 designs. Elastoplastic analysis is conducted using the finite element method to determine the typical geometries of the polymer microneedles to avoid elastoplastic deformation accompanied by fatal fracture based on the mechanical properties of the polymer materials. The design principles of microneedle geometries based on polymer material properties are important guidelines for developing polymer microneedles, overcoming their mechanical weakness, and ensuring excellent functions.

Microneedle electrodes: materials, fabrication methods, and electrophysiological signal monitoring-narrative review

Flexible, microneedle-based electrodes offer an innovative solution for high-quality physiological signal monitoring, reducing the need for complex algorithms and hardware, thus streamlining health assessments, and enabling earlier disease detection. These electrodes are particularly promising for improving patient outcomes by providing more accurate, reliable, and long-term electrophysiological data, but their clinical adoption is hindered by the limited availability of large-scale population testing. This review examines the key advantages of flexible microneedle electrodes, including their ability to conform to the skin, enhance skin-electrode contact, reduce discomfort, and deliver superior signal fidelity. The mechanical and electrical properties of these electrodes are thoroughly explored, focusing on critical aspects like fracture force, skin penetration efficiency, and impedance measurements. Their applications in capturing electrophysiological signals such as ECG, EMG, and EEG are also highlighted, demonstrating their potential in clinical scenarios. Finally, the review outlines future research directions, emphasizing the importance of further studies to enhance the clinical and consumer use of flexible microneedle electrodes in medical diagnostics.

Enhancement of Transdermal Drug Delivery: Integrating Microneedles with Biodegradable Microparticles

This investigation aimed to enhance transdermal methotrexate delivery through human skin by employing Dr. Pen microneedles and poly(d,l-lactide-co-glycolide) acid microparticles formulated from eight polymer grades (Expansorb DLG 95-4A, DLG 75-5A, DLG 50-2A, DLG 50-5A, DLG 50-8A, DLG 50-6P, DLG 50-7P, and DLL 10-15A). A comprehensive characterization of the microparticles was performed, encompassing various parameters such as size, charge, morphology, microencapsulation efficiency, yield, release kinetics, and chemical composition. The efficacy of microneedles in disrupting skin integrity was demonstrated by scanning electron microscopy, dye binding, histological examination, confocal laser microscopy, and pore size analysis. Microneedle-mediated skin microporation led to a substantial reduction in skin electrical resistance and a concomitant increase in transepidermal water loss. In vitro permeation experiments using human skin delivered microparticles into microporated skin and demonstrated a considerable difference in methotrexate delivery among the polymer groups. Microneedle treatment significantly amplified cumulative drug delivery, steady-state flux, diffusion coefficient, permeability coefficient, and drug concentration within skin layers while concurrently diminishing lag time (p < 0.05). Furthermore, a robust correlation was established between microparticle properties (cumulative release, release rate, encapsulation efficiency) and drug deposition in the skin. In conclusion, the synergistic combination of Dr. Pen microneedles and PLGA microparticles facilitated enhanced and regulated transdermal methotrexate delivery.

Liposome-loaded dissolvable microneedle patches for more efficient intradermal antigen delivery of Hepatitis B vaccine

The aim of this study was to improve the efficacy of Hepatitis B surface antigen (HBsAg) vaccination via liposome-loaded dissolvable microneedle (Lipo-dMN) patches. HBsAg liposomes were prepared using the thin-film hydration method and subsequently incorporated into dissolvable microneedle patches via a pre-vacuum approach. Liposomes, dissolvable microneedle patches (dMN), and Lipo-dMN were characterized for encapsulation efficiency, mechanical properties, morphology, skin insertion, in vitro release, cellular uptake, and in vivo vaccination studies. The HBsAg was encapsulated into liposomes with encapsulation efficiencies around 50 %, particle size around 160 nm, and zeta potential around -20 mV. HBsAg can maintain its activity during the preparation of dMN and Lipo-dMN. The intact pyramid microneedle has a sharp end and strong mechanical properties that allow easy insertion into the ex vivo pig skin. The dMN and Lipo-dMN, with a mechanical property of 1.6 N, readily penetrate the epidermis and release the HBsAg and HBsAg liposome to modulate the immune response. A comprehensive comparison of HBsAg subcutaneous injection and intradermal delivery of HBsAg and HBsAg liposome by dMN revealed different levels of anti-HBsAg IgG antibody. Inoculation with dMN and Lipo-dMN resulted in significantly higher levels of anti-HBsAg IgG antibodies (p < 0.01) compared to subcutaneous injection of HBsAg. In addition, we found that IgG levels increased significantly (P < 0.05) with increased dose of subcutaneous injection of HBsAg and intradermal delivery of dMN, but the opposite effect was observed in Lipo-dMN. The possible mechanism for this observation may be the increased cellular uptake of liposomes by BMDCs upon long-term incubation. In summary, this study presents a promising approach to enhance HBsAg vaccination efficacy through the synergistic combination of liposomes and dissolvable microneedles at reduced vaccine doses.

Fabrication and Evaluation of Dissolving Hyaluronic Acid Microneedle Patches for Minimally Invasive Transdermal Drug Delivery by Nanoimprinting

Transdermal drug delivery minimizes pain and provides a controlled, stable release of drugs, but its effectiveness is limited by the skin's natural barriers. Microneedles overcome this problem, enabling minimally invasive drug delivery. Microneedle patches (MNPs) with 80 µm-tall needles composed of hyaluronic acid (HA) were developed and evaluated for their formability, structural integrity, dissolution rate, skin penetration ability, and drug transmission capacity. The influence of the molecular weight of HA on these properties was also investigated. MNPs made from low-molecular-weight HA (30 kDa-50 kDa) demonstrated 12.5 times superior drug permeability in ex vivo human skin compared to needleless patches (NLPs). Furthermore, in the same test, low-molecular-weight HA MNPs had 1.7 times higher drug permeability than high-molecular-weight HA MNPs, suggesting superior transdermal administration. The molecular weight of HA significantly influenced its solubility and permeability, highlighting the potential effectiveness of MNPs as drug delivery systems. Puncture tests demonstrated a penetration depth of 50-60 µm, indicating minimal nerve irritation in the dermis and effective drug delivery to the superficial dermal layer. These results present a manufacturing technique for MNPs incorporating model drug compounds and highlight their potential as a novel and minimally invasive drug delivery method for the biomedical applications of soft gels.

What Is the Optimal Geometry of Dissolving Microneedle Arrays? A Literature Review

The application of dissolving microneedle arrays (DMNAs) is an emerging trend in drug and vaccine delivery as an alternative for hypodermic needles or other less convenient drug administration methods. The major benefits include, amongst others, that no trained healthcare personnel is required and that the recipient experiences hardly any pain during administration. However, for a successful drug or vaccine delivery from the DMNA, the microneedles should be inserted intact into the skin. A successful penetration into the upper skin layers may be challenging because of the elastic nature of the skin; therefore, a minimum insertion force is required to overcome the total resistance force of the skin. In addition, the microneedles need to stay intact, which requires a certain mechanical strength, and be able to resist the required insertion force. In addition to the type of material with which the DMNAs are produced, the geometry of the DMNAs will also have a profound effect, not only on the mechanical strength but also on the number of insertions and penetration depth into the skin. In this review, the effects of shape, aspect ratio, length, width of the base, tip diameter and angle, and spacing of DMNAs on the aforementioned effect parameters were evaluated to answer the following question: 'What is the optimal geometry of dissolving microneedle arrays?'.

Modelling Hollow Microneedle-Mediated Drug Delivery in Skin Considering Drug Binding

Background/Objectives: Microneedle(MN)-based drug delivery is one of the potential approaches to overcome the limitations of oral and hypodermic needle delivery. An in silico model has been developed for hollow microneedle (HMN)-based drug delivery in the skin and its subsequent absorption in the blood and tissue compartments in the presence of interstitial flow. The drug's reversible specific saturable binding to its receptors and the kinetics of reversible absorption across the blood and tissue compartments have been taken into account. Methods: The governing equations representing the flow of interstitial fluid, the transport of verapamil in the viable skin and the concentrations in the blood and tissue compartments are solved using combined Marker and Cell and Immersed Boundary Methods to gain a quantitative understanding of the model under consideration. Results: The viscoelastic skin is predicted to impede the transport of verapamil in the viable skin and, hence, reduce the concentrations of all forms in the blood and the tissue compartments. The findings reveal that a higher mean concentration in the viable skin is not always associated with a longer MN length. Simulations also predict that the concentrations of verapamil in the blood and bound verapamil in the tissue compartment rise with decreasing tip diameters. In contrast, the concentration of free verapamil in the tissue increases with increasing injection velocities. Conclusions: The novelty of this study includes verapamil metabolism in two-dimensional viscoelastic irregular viable skin and the nonlinear, specific, saturable, and reversible binding of verapamil in the tissue compartment. The tip diameter and the drug's injection velocity are thought to serve as regulatory parameters for the effectiveness and efficacy of MN-mediated therapy if the MN is robust enough to sustain the force needed to penetrate a wider tip into the skin.

Swellable Biopolymer Composite Microneedle Patch for Pain-Free Collection of Interstitial Fluid to Analyze Multiple Biomolecules

Sampling of interstitial fluid (ISF) using microneedle (MN) patch offers a pain-free minimally invasive alternative to syringe needle-based blood sample collection. However, there is a challenge in the development of MN patch that provides swelling behavior with sufficient mechanical strength for skin penetration. Here, we report fabrication of MN patch made of biopolymer composite containing iota-carrageenan, gelatin, and polyethylene glycol. Calcium chloride was used as a crosslinker to improve mechanical strength. MN patch was characterized for integrity, swelling behavior, mechanical strength, aspiration of fluid from agarose gel, and the excised porcine ear skin. An array of 361 MNs was able to aspirate 36 ± 5 and 14 ± 1 μL fluid after application in agarose gel matrix and the ex vivo porcine skin model, respectively. MN patch applied in vivo rat model for 30 min resulted in the collection of ISF containing 267 ± 128 mg/dL, 24 ± 13 mg/dL, and 0.6 ± 0.4 mIU/mL of glucose, uric acid and thyroid stimulating hormone (TSH), respectively. The concentration of glucose, uric acid, and TSH in rat blood was found to be 199 ± 47 mg/dL, 8.4 ± 6 mg/dL, and 1.1 ± 0.6 mIU/mL at the same time. Furthermore, MN patch applied on the forearm of 10 healthy human volunteers for 30 min was able to aspirate 32 ± 14 μL of ISF. The concentration of glucose, uric acid, and TSH determined from ISF samples of human volunteers was 64 ± 25 mg/dL, 4.2 ± 4.1 mg/dL, and 0.16 ± 0.08 mIU/mL, respectively. The visual analogue scale (VAS) pain score after MN application was lower compared with hypodermic syringe needle insertion. Taken together, biopolymer composite-based swellable MN patch can be developed for collection of ISF for simultaneous determination of multiple biomolecules in a minimally invasive manner.

Physical stimuli-responsive polymeric patches for healthcare

Many chronic diseases have become severe public health problems with the development of society. A safe and efficient healthcare method is to utilize physical stimulus-responsive polymer patches, which may respond to physical stimuli, including light, electric current, temperature, magnetic field, mechanical force, and ultrasound. Under certain physical stimuli, these patches have been widely used in therapy for diabetes, cancer, wounds, hair loss, obesity, and heart diseases since they could realize controllable treatment and reduce the risks of side effects. This review sketches the design principles of polymer patches, including composition, properties, and performances. Besides, control methods of using different kinds of physical stimuli were introduced. Then, the fabrication methods and characterization of patches were explored. Furthermore, recent applications of these patches in the biomedical field were demonstrated. Finally, we discussed the challenges and prospects for its clinical translation. We anticipate that physical stimulus-responsive polymer patches will open up new avenues for healthcare by acting as a platform with multiple functions.

Comparison of the efficacy of combination treatment of microneedling and topical Bleomycin with cryotherapy for the management of hand and foot refractory warts

Several studies have looked into the effectiveness of bleomycin treatment for warts using various injection methods, such as intralesional injection, multiple puncture technique, jet injection, and moonlet needle prick method, in various concentrations and doses. However, injection methods have been linked to acute pain and bleeding. The purpose of this study is to examine the efficacy of microneedling combination with topical bleomycin and cryotherapy in the treatment of resistant warts on the hands and feet. This randomized clinical trial, conducted at Sina Hospital in Tabriz, involved 90 patients with treatment-resistant warts on their hands and feet. Treatment measures were repeated every two weeks in treatment-resistant patients who did not react to four cryotherapy sessions or whose lesions remained stable for six months. Each wart lesion was randomly assigned to one of two treatment groups: topical bleomycin with microneedling or cryotherapy. The effectiveness of the treatment in weeks 2, 4, 6, and 8 with PGA and PaGA, the amount of clearance, and side effects were evaluated in each session and the 8th week. Pain during therapy was assessed using a visual analog scale (VAS) ranging from 0 to 10. The patients' mean age was 33.65 ± 12.24 years, with 63.3% being female. A total of 186 resistant wart lesions were treated, with 98 (52.7%) situated in the palmar region and 88 (47.3%) in the plantar region. In palm lesions, the bleomycin micro-needling group had a considerably greater clearance rate than the cryotherapy group (86.4% vs. 61.9%; p = 0.001). In foot lesions, the bleomycin microneedling group had a greater clearance rate than the cryotherapy group, although there was no statistically significant difference (69.6% vs. 54.2%; p = 0.209). In the eighth week following the intervention, the number of lesions and the diameter of warts on the palms and feet decreased significantly in the bleomycin microneedling group when compared to the cryotherapy group. Bleomycin microneedling had no adverse effects; however, in patients undergoing cryotherapy, local pain, blisters, and scars were noted. Bleomycin microneedling has a higher therapeutic efficiency than cryotherapy for treating refractory hand and foot warts, and it removes lesions more effectively. In addition, this therapeutic method is safer and has fewer side effects than cryotherapy.

A systematic review of microneedles technology in drug delivery through a bibliometric and patent overview

The transdermal drug delivery (TDD) route has gathered considerable attention for its potential to improve therapeutic efficacy while minimizing systemic side effects. Among transdermal technologies, microneedle (MN) devices have proven to be a promising approach that combines the advantages of traditional needle injections and non-invasive topical applications. This review provides a comprehensive analysis of progress in transdermal drug delivery systems (TDDS) via MN from 2000 to 2023, integrating bibliometric analysis and patent landscape to present a multi-faceted perspective on the evolution of this technology. The study identifies key trends, challenges, and opportunities in the research, implementation, and commercialization of MN tools through a systematic examination of scientific literature and an extensive investigation of global patent databases. The study of bibliometric trends reveals the leading experts, organizations, companies, and countries contributing to this field, collaboration networks, and the thematic evolution of research topics. The patent analysis offers insights into innovative trajectories, key players, and geographical distribution of intellectual property. This review resumes the latest advancements in MN devices and provides a strategic outlook that can guide future research directions, promote partnerships, and inform stakeholders involved in the development of TDDS.

Advancements in microneedle technology: current status and next-generation innovations

Microneedle technology is a pivotal component of third-generation transdermal drug delivery systems featuring tiny needles that create temporary microscopic channels in the stratum corneum which facilitate drug penetration in the dermis. This review offers a detailed examination of the current types of microneedles, including solid, coated, dissolving, hollow, and swelling microneedles, along with their preparation techniques as well as their benefits and challenges. Use of 3D printing technology is especially gaining significant attention due to its ability to achieve the high dimensional accuracy required for precise fabrication. Additionally, its customisability presents significant potential for exploring new designs and creating personalised microneedles products. Furthermore, this review explores next generation microneedles, especially stimuli-responsive microneedle, bioinspired microneedle and microneedles combined with other transdermal technology like sonophoresis, electroporation and iontophoresis. Regulatory aspects, characterisation techniques, safety considerations, and cost factors have also been addressed which are crucial for translation from lab to the market.

Claes K, Blondeel P, Monstrey S, Dorpe JV, Van Vlierberghe S. Photo-crosslinkable polyester microneedles as sustained drug release systems toward hypertrophic scar treatment

Burn injuries can result in a significant inflammatory response, often leading to hypertrophic scarring (HTS). Local drug therapies e.g. corticoid injections are advised to treat HTS, although they are invasive, operator-dependent, extremely painful and do not permit extended drug release. Polymer-based microneedle (MN) arrays can offer a viable alternative to standard care, while allowing for direct, painless dermal drug delivery with tailorable drug release profile. In the current study, we synthesized photo-crosslinkable, acrylate-endcapped urethane-based poly(ε-caprolactone) (AUP-PCL) toward the fabrication of MNs. Physico-chemical characterization (1H-NMR, evaluation of swelling, gel fraction) of the developed polymer was performed and confirmed successful acrylation of PCL-diol. Subsequently, AUP-PCL, and commercially available PCL-based microneedle arrays were fabricated for comparative evaluation of the constructs. Hydrocortisone was chosen as model drug. To enhance the drug release efficiency of the MNs, Brij®35, a nonionic surfactant was exploited. The thermal properties of the MNs were evaluated via differential scanning calorimetry. Compression testing of the arrays confirmed that the MNs stay intact upon applying a load of 7 N, which correlates to the standard dermal insertion force of MNs. The drug release profile of the arrays was evaluated, suggesting that the developed PCL arrays can offer efficient drug delivery for up to two days, while the AUP-PCL arrays can provide a release up to three weeks. Finally, the insertion of MN arrays into skin samples was performed, followed by histological analysis demonstrating the AUP-PCL MNs outperforming the PCL arrays upon providing pyramidical-shaped perforations through the epidermal layer of the skin.

Microneedles with Implantable Tip-Accumulated Therapeutics for the Long-Term Management of Psoriasis

Methotrexate is successfully used as the gold standard for managing moderate-to-severe psoriasis. However, the low bioavailability and short half-life of the oral pills and the invasiveness of the parenteral injections make these suboptimal therapeutic options. Microneedles, bridging the advantages of the former forms, are successfully used to deliver methotrexate for different therapeutic purposes. However, the utilized dissolving microneedles demand frequent administration, potentially compromising patients' compliance. Additionally, the high toxicity of methotrexate prompts a quest for safer alternatives. Phloretin, a natural compound with confirmed antipsoriatic potential, emerges as a promising candidate. Herein, microneedle patches with separable, slow-degrading tips are developed for the sustained delivery of methotrexate and phloretin, as a comprehensive solution for long-term psoriasis management. Both compounds are individually loaded at varying doses and display sustained-release profiles. The developed microneedle patches demonstrate high mechanical strength, favorable drug delivery efficiency, and remarkable antipsoriatic potential both in vitro in keratinocytes and in vivo in a psoriasis mouse model. Comparative analysis with two subcutaneous injections reveals a similar antipsoriatic efficacy with a single patch of either compound, with prominent phloretin safety. Therefore, the developed patches present a superior alternative to methotrexate's current marketed forms and provide a viable alternative (phloretin) with comparable antipsoriatic efficacy and higher safety.

Optimizing CNC milling parameters for manufacturing of ultra-sharp tip microneedle with various tip angles

Microneedle technology has emerged as an advanced method for transdermal drug delivery, which focuses on diverse fabrication techniques to develop microneedles with various models and geometries. This study explores the application of Computer Numerical Control (CNC) milling technology to create microneedle master molds with extremely sharp tips. We examined the effects of two key machining parameters, feed rate and ramp angle, on the tip sharpness of the microneedles. Our results showed that increasing both the feed rate and ramp angle could significantly reduce machining time. However, a higher feed rate also led to larger tip diameters and notable tip defects. Conversely, changes in the ramp angle at a constant feed rate had minimal impact on tip size. We identified an optimal condition balancing cutting time and tip sharpness at a feed rate of 100 mm/min and a ramp angle of 1.5°. Additionally, we assessed the CNC's capability to produce needles with different tip angles. The findings confirm that needles with varying tip angles maintained tip diameters below 10 μm, with needles having a 50° tip angle exhibiting the sharpest tips at approximately 3.3 μm. Further compression, insertion and diffusion tests were conducted to evaluate the performance of needles with different geometries.

Innovative freeze-drying technique in the fabrication of dissolving microneedle patch: Enhancing transdermal drug delivery efficiency

Microneedle patch (MNP) has become a hot research topic in the field of transdermal drug delivery due to its ability to overcome the stratum corneum barrier. Among the various types of microneedles, dissolving microneedles represent one of the most promising transdermal delivery methods. However, the most used method for preparing dissolving microneedles, namely microfabrication, suffers from issues such as long drying time, susceptibility to humidity, and large batch-to-batch variability, which limit the development of dissolving microneedles. In this study, we report for the first time a method for preparing dissolving microneedles using freeze-drying technology. We screened substrates suitable for freeze-dried microneedle patch (FD-MNP) and used coating technology to enhance the mechanical strength of FD-MNP, allowing them to meet the requirements for skin penetration. We successfully prepared FD-MNP using hyaluronic acid as the substrate and insulin as the model drug. Scanning electron microscopy revealed that the microneedles had a porous structure. After coating, the mechanical strength of the microneedles was 0.61 N/Needle, and skin penetration rate was 97%, with a penetration depth of 215 μm. The tips of the FD-MNP dissolved completely within approximately 60 s after skin penetration, which is much faster than conventional MNP (180 s). In vitro transdermal experiments showed that the FD-MNP shortened the lag time for transdermal delivery of rhodamine 123 and insulin compared to conventional MNP, indicating a faster transdermal delivery rate. Pharmacological experiments showed that the FD-MNP lowered mouse blood glucose levels more effectively than conventional MNP, with a relative pharmacological availability of 96.59 ± 2.84%, higher than that of conventional MNP (84.34 ± 3.87%), P = 0.0095. After storage under 40℃ for two months, the insulin content within the FD-MNP remained high at 95.27 ± 4.46%, which was much higher than that of conventional MNP (58.73 ± 3.71%), P < 0.0001. In conclusion, freeze-drying technology is a highly valuable method for preparing dissolving microneedles with potential applications in transdermal drug delivery.

Development and optimization of hydrogel-forming microneedles fabricated with 3d-printed molds for enhanced dermal diclofenac sodium delivery: a comprehensive in vitro, ex vivo, and in vivo study

With the developing manufacturing technologies, the use of 3D printers in microneedle production is becoming widespread. Hydrogel-forming microneedles (HFMs), a variant of microneedles, demonstrate distinctive features such as a high loading capacity and controlled drug release. In this study, the conical microneedle master molds with approximately 500 μm needle height and 250 μm base diameter were created using a Stereolithography (SLA) 3D printer and were utilized to fabricate composite HFMs containing diclofenac sodium. Using Box-Behnken Design, the effects of different polymers on swelling index and mechanical strength of the developed HFMs were evaluated. The optimum HFMs were selected according to experimental design results with the aim of the highest mechanical strength with varying swelling indexes, which was needed to use 20% Gantrez S97 and 0.1% (F22), 0.42% (F23), and 1% (F24) hyaluronic acid. The skin penetration and drug release properties of the optimum formulations were assessed. Ex vivo studies were conducted on formulations to determine drug penetration and accumulation. F24, which has the highest mechanical strength and optimized swelling index, achieved the highest drug accumulation in the skin tissue (17.70 ± 3.66%). All optimum HFMs were found to be non-cytotoxic by the MTT cell viability test (> 70% cell viability). In in vivo studies, the efficacy of the F24 was assessed for the treatment of xylene-induced ear edema by contrasting it to the conventional dosage form. It was revealed that HFMs might be an improved replacement for conventional dosage forms in terms of dermal diseases such as actinic keratosis.

Iontophoresis and electroporation-assisted microneedles: advancements and therapeutic potentials in transdermal drug delivery

Transdermal drug delivery (TDD) using electrically assisted microneedle (MN) systems has emerged as a promising alternative to traditional drug administration routes. This review explores recent advancements in this technology across various therapeutic applications. Integrating iontophoresis (IP) and electroporation (EP) with MN technology has shown significant potential in improving treatment outcomes for various conditions. Studies demonstrate their effectiveness in enhancing vaccine and DNA delivery, improving diabetes management, and increasing efficacy in dermatological applications. The technology has also exhibited promise in delivering nonsteroidal anti-inflammatory drugs (NSAIDs), treating multiple sclerosis, and advancing obesity and cancer therapy. These systems offer improved drug permeation, targeted delivery, and enhanced therapeutic effects. While challenges remain, including safety concerns and technological limitations, ongoing research focuses on optimizing these systems for broader clinical applications. The future of electrically assisted MN technologies in TDD appears promising, with potential advancements in personalized medicine, smart monitoring systems, and expanded therapeutic applications.

Optimizing Solid Microneedle Design: A Comprehensive ML-Augmented DOE Approach

Microneedles (MNs), that is, a matrix of micrometer-scale needles, have diverse applications in drug delivery, skincare therapy, and health monitoring. MNs offer a minimally invasive alternative to hypodermic needles, characterized by rapid and painless procedures, cost-effective fabrication methods, and reduced tissue damage. This study explores four MN designs, cone-shaped, tapered cone-shaped, pyramidal with a square base, and pyramidal with a triangular-shaped base, and their optimization based on predefined criteria. The workflow encompasses three loading conditions: compressive load during insertion, critical buckling load, and bending loading resulting from incorrect insertion. Geometric parameters such as base radius/width, tip radius/width, height, and tapered angle tip influence the output criteria, namely, total deformation, critical buckling loads, factor of safety (FOS), and bending stress. The comprehensive framework employing a design of experiment approach within the ANSYS workbench toolbox establishes a mathematical model and a response surface fitting model. The resulting regression model, sensitivity chart, and response curve are used to create a multiobjective optimization problem that helps achieve an optimized MN geometrical design across the introduced four shapes, integrating machine learning (ML) techniques. This study contributes valuable insights into a potential ML-augmented optimization framework for MNs via needle designs to stay durable for various physiologically relevant conditions.

The Design Features, Quality by Design Approach, Characterization, Therapeutic Applications, and Clinical Considerations of Transdermal Drug Delivery Systems-A Comprehensive Review

Transdermal drug delivery systems (TDDSs) are designed to administer a consistent and effective dose of an active pharmaceutical ingredient (API) through the patient's skin. These pharmaceutical preparations are self-contained, discrete dosage forms designed to be placed topically on intact skin to release the active component at a controlled rate by penetrating the skin barriers. The API provides the continuous and prolonged administration of a substance at a consistent rate. TDDSs, or transdermal drug delivery systems, have gained significant attention as a non-invasive method of administering APIs to vulnerable patient populations, such as pediatric and geriatric patients. This approach is considered easy to administer and helps overcome the bioavailability issues associated with conventional drug delivery, which can be hindered by poor absorption and metabolism. A TDDS has various advantages compared to conventional methods of drug administration. It is less intrusive, more patient-friendly, and can circumvent first pass metabolism, as well as the corrosive acidic environment of the stomach, that happens when drugs are taken orally. Various approaches have been developed to enhance the transdermal permeability of different medicinal compounds. Recent improvements in TDDSs have enabled the accurate administration of APIs to their target sites by enhancing their penetration through the stratum corneum (SC), hence boosting the bioavailability of drugs throughout the body. Popular physical penetration augmentation methods covered in this review article include thermophoresis, iontophoresis, magnetophoresis, sonophoresis, needle-free injections, and microneedles. This review seeks to provide a concise overview of several methods employed in the production of TDDSs, as well as their evaluation, therapeutic uses, clinical considerations, and the current advancements intended to enhance the transdermal administration of drugs. These advancements have resulted in the development of intelligent, biodegradable, and highly efficient TDDSs.

Fabrication of Poly Lactic-co-Glycolic Acid Microneedles for Sustained Delivery of Lipophilic Peptide-Carfilzomib

Transdermal drug delivery (TDD) is an attractive route of administration, providing several advantages, especially over oral and parenteral routes. However, TDD is significantly restricted due to the barrier imposed by the uppermost layer of the skin, the stratum corneum (SC). Microneedles is a physical enhancement technique that efficiently pierces the SC and facilitates the delivery of both lipophilic and hydrophilic molecules. Dissolving microneedles is a commonly used type that is fabricated utilizing various biodegradable and biocompatible polymers, such as polylactic acid, polyglycolic acid, or poly(lactide-co-glycolide) (PLGA). Such polymers also promote the prolonged release of the drug due to the slow degradation of the polymer matrix following its insertion. We selected carfilzomib, a small therapeutic peptide (MW: 719.924 g/mol, log P 4.19), as a model drug to fabricate a microneedle-based sustained delivery system. This study is a proof-of-concept investigation in which we fabricated PLGA microneedles using four types of PLGA (50-2A, 50-5A, 75-5A, and 50-7P) to evaluate the feasibility of long-acting transdermal delivery of carfilzomib. Micromolding technique was used to fabricate the PLGA microneedles and characterization tests, including Fourier transform infrared spectroscopy, insertion capability using the skin simulant Parafilm model, histological evaluation, scanning electron microscopy, and confocal microscopy were conducted. In vitro release and permeation testing were conducted in vertical Franz diffusion cells. N-methyl pyrrolidone was utilized as the organic solvent and microneedles were solidified in controlled conditions, which led to good mechanical strength. Both in vitro release and permeation testing showed sustained profiles of carfilzomib over 7 days. The release and permeation were significantly influenced by the molecular weight of PLGA and the lipophilic properties of carfilzomib.

State-of-the-art strategies to enhance the mechanical properties of microneedles

Microneedles (MNs) have gained increasing attention in the biomedical field, owing to their notable advantages over injectable and transdermal preparations. The mechanical properties of MNs are the key to determine whether MNs can puncture the skin for efficient drug delivery and therapeutic purposes. However, there is still lacking of a systemic summary on how to improve the mechanical properties of MNs. Herein, this review mainly analyzes the key factors affecting the mechanical properties of MNs from the theoretical point of view and puts forward improvement approaches. First, we analyzed the major stresses exerted on the MNs during skin puncture and described general methods to evaluate the mechanical properties of MNs. We then provided detail examples to elucidate how the physicochemical properties of single polymer, formulation compositions, and geometric parameters affected the mechanical properties of MNs. Overall, the mechanical strength of MNs can be enhanced by tuning the crosslinking density, crystallinity degree, and molecular weight of single polymer, introducing polysaccharides and nano-microparticles as reinforcers to form complex with polymer, and optimizing the geometric parameters of MNs. Therefore, this review will provide critical guidance on how to fabricate MNs with robust mechanical strength for successful transdermal drug delivery.

Microneedles as a potential platform for improving antibiotic delivery to bacterial infections

Bacterial infections are mainly managed by the administration of antibiotics, which are either cytotoxic or cytostatic to microbes. In some cases, it is inconvenient to treat infections caused by bacteria using the traditional oral route for antibiotic administration. This can be due to the limited oral bioavailability of antibiotics, their gastrointestinal tract (GIT) adverse effects, and the increased possibility of the appearance of resistant strains. In addition, the fact that many populations are needle-phobic restricts the switch from the oral to the parenteral route. Furthermore, poor drug permeation throughout the stratum corneum of topically applied antibiotics causes low systemic bioavailability. Therefore, microneedles (MNs) have emerged as viable medicinal devices for the delivery of antibiotics, either for local or systemic effects. MNs represent a minimally invasive, painless way of administration that can be self-administered by the patient without the need of medical professionals. This review has specifically focused on MNs as a promising approach for the delivery of antibiotics; it has discussed the different types of MNs, their advantages, and possible limitations for the delivery of antibiotics. Recent studies on the incorporation of antibiotics into various types of MNs, either for topical or transdermal delivery are highlighted, and finally, we present the conclusion and future perspectives.

Design of poly(vinyl pyrrolidone) and poly(ethylene glycol) microneedle arrays for delivering glycosaminoglycan, chondroitin sulfate, and hyaluronic acid

Osteoarthritis (OA) is a prevalent joint disorder characterized by cartilage and bone degradation. Medical therapies like glucosaminoglycan (GAG), chondroitin sulfate (CS), and hyaluronic acid (HA) aim to preserve joint function and reduce inflammation but may cause side effects when administered orally or via injection. Microneedle arrays (MNAs) offer a localized drug delivery method that reduces side effects. Thus, this study aims to demonstrate the feasibility of delivering GAG, CS, and HA using microneedles in vitro. An optimal needle geometry is crucial for the successful application of MNA. To address this, here we employ a multi-objective optimization framework using the non-dominated sorting genetic algorithm II (NSGA-II) to determine the ideal MNA design, focusing on preventing needle failure. Then, a three-step fabrication approach is followed to fabricate the MNAs. First, the master (male) molds are fabricated from poly(methyl methacrylate) using mechanical micromachining based on optimized needle geometry. Second, a micro-molding with Polydimethylsiloxane (PDMS) is used for the fabrication of production (female) molds. In the last step, the MNAs were fabricated by microcasting the hydrogels using the production molds. Light microscopy (LIMI) confirms the accuracy of the MNAs manufactured, and in vitro skin insertion tests demonstrate failure-free needle insertion. Subsequently, we confirmed the biocompatibility of MNAs by evaluating their impact on the L929 fibroblast cell line, human chondrocytes, and osteoblasts.

Converting Short-Acting Insulin into Thermo-Stable Longer-Acting Insulin Using Multi-Layer Detachable Microneedles

The detachable dissolving microneedles (DDMNs) feature an array of needles capable of being separated from the base sheet during administration. Here they were fabricated to address delivery efficiency and storage stability of insulin. The constructed insulin-DDMN is multi-layered, with 1) a hard tip cover layer; 2) a layer of regular short-acting insulin (RI) mixed with hyaluronic acid (HA) and sorbitol (Sor) which occupies the taper tip region of the needles; 3) a barrier layer situated above the RI layer; and 4) a fast-dissolving layer connecting the barrier layer to the base sheet. RI entrapped in DDMNs exhibited enhanced thermal stability; it could be stored at 40 °C for 35 days without losing significant biological activity. Differential scanning calorimetric analysis revealed that the HA-Sor matrix could improve the denaturation temperature of the RI from lower than room temperature to 186 °C. Tests in ex vivo porcine skin demonstrated RI delivery efficiency of 91±1.59 %. Experiments with diabetic rats revealed sustained release of RI, i.e., when compared to subcutaneous injection with the same RI dose, RI-DDMNs produced slower absorption of insulin into blood circulation, delayed onset of hypoglycemic effect, longer serum insulin half-life, and longer hypoglycemic duration.

Machine Learning Assists in the Design and Application of Microneedles

Microneedles (MNs), characterized by their micron-sized sharp tips, can painlessly penetrate the skin and have shown significant potential in disease treatment and biosensing. With the development of artificial intelligence (AI), the design and application of MNs have experienced substantial innovation aided by machine learning (ML). This review begins with a brief introduction to the concept of ML and its current stage of development. Subsequently, the design principles and fabrication methods of MNs are explored, demonstrating the critical role of ML in optimizing their design and preparation. Integration between ML and the applications of MNs in therapy and sensing were further discussed. Finally, we outline the challenges and prospects of machine learning-assisted MN technology, aiming to advance its practical application and development in the field of smart diagnosis and treatment.

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.

Acrylated adhesive proteinic microneedle patch for local drug delivery and stable device implantation

Microneedle patches have been developed as favorable platforms for delivery systems, such as the locoregional application of therapeutic drugs, and implantation systems, such as electronic devices on visceral tissue surfaces. However, the challenge lies in finding materials that can achieve both biocompatibility and stable fixation on the target tissue. To address this issue, utilizing a biocompatible adhesive biomaterial allows the flat part of the patch to adhere as well, enabling double-sided adhesion for greater versatility. In this work, we propose an adhesive microneedle patch based on mussel adhesive protein (MAP) with enhanced mechanical strength via ultraviolet-induced polyacrylate crosslinking and Coomassie brilliant blue molecules. The strong wet tissue adhesive and biocompatible nature of engineered acrylated-MAP resulted in the development of a versatile wet adhesive microneedle patch system for in vivo usage. In a mouse tumor model, this microneedle patch effectively delivered anticancer drugs while simultaneously sealing the skin wound. Additionally, in an application of rat subcutaneous implantation, an electronic circuit was stably anchored using a double-sided wet adhesive microneedle patch, and its signal location underneath the skin did not change over time. Thus, the proposed acrylated-MAP-based wet adhesive microneedle patch system holds great promise for biomedical applications, paving the way for advancements in drug delivery therapeutics, tissue engineering, and implantable electronic medical devices.

Investigating Laser Ablation Process Parameters for the Fabrication of Customized Microneedle Arrays for Therapeutic Applications

Microneedles are an innovation in the field of medicine that have the potential to revolutionize drug delivery, diagnostics, and cosmetic treatments. This innovation provides a minimally invasive means to deliver drugs, vaccines, and other therapeutic substances into the skin. This research investigates the design and manufacture of customized microneedle arrays using laser ablation. Laser ablation was performed using an ytterbium laser on a polymethyl methacrylate (PMMA) substrate to create a mold for casting polydimethylsiloxane (PDMS) microneedles. An experimental design was conducted to evaluate the effect of process parameters including laser pulse power, pulse width, pulse repetition, interval between pulses, and laser profile on the desired geometry of the microneedles. The analysis of variance (ANOVA) model showed that lasing interval, laser power, and pulse width had the highest influence on the output metrics (diameter and height) of the microneedle. The microneedle dimensions showed an increase with higher pulse width and vice versa with an increase in pulse interval. A response surface model indicated that the laser pulse width and interval (independent variables) significantly affect the response diameter and height (dependent variable). A predictive model was generated to predict the microneedle topology and aspect ratio varying from 0.8 to 1.5 based on the variation in critical input process parameters. This research lays the foundation for the design and fabrication of customized microneedles based on variations in specific input parameters for therapeutic applications in dermal sensors, drug delivery, and vaccine delivery.

Polymeric Microneedles Enhance Transdermal Delivery of Therapeutics

This research presents the efficacy of polymeric microneedles in improving the transdermal permeation of methotrexate across human skin. These microneedles were fabricated from PLGA Expansorb® 50-2A and 50-8A and subjected to comprehensive characterization via scanning electron microscopy, Fourier-transform infrared spectroscopy, and mechanical analysis. We developed and assessed a methotrexate hydrogel for physicochemical and rheological properties. Dye binding, histological examinations, and assessments of skin integrity demonstrated the effective microporation of the skin by PLGA microneedles. We measured the dimensions of microchannels in the skin using scanning electron microscopy, pore uniformity analysis, and confocal microscopy. The skin permeation and disposition of methotrexate were researched in vitro. PLGA 50-8A microneedles appeared significantly longer, sharper, and more mechanically uniform than PLGA 50-2A needles. PLGA 50-8A needles generated substantially more microchannels, as well as deeper, larger, and more uniform channels in the skin than PLGA 50-2A needles. Microneedle insertion substantially reduced skin electrical resistance, accompanied by an elevation in transepidermal water loss values. PLGA 50-8A microneedle treatment provided a significantly higher cumulative delivery, flux, diffusion coefficient, permeability coefficient, and predicted steady-state plasma concentration; however, there was a shorter lag time than for PLGA 50-2A needles, base-treated, and untreated groups (p < 0.05). Conclusively, skin microporation using polymeric microneedles significantly improved the transdermal delivery of methotrexate.

Dissolvable microneedles in the skin: Determination the impact of barrier disruption and dry skin on dissolution

Dissolvable microneedles (DMNs), fabricated from biocompatible materials that dissolve in both water and skin have gained popularity in dermatology. However, limited research exists on their application in compromised skin conditions. This study compares the hyaluronic acid-based DMNs penetration, formation of microchannels, dissolution, and diffusion kinetics in intact, barrier-disrupted (tape stripped), and dry (acetone-treated) porcine ear skin ex vivo. After DMNs application, comprehensive investigations including dermoscopy, stereomicroscope, skin hydration, transepidermal water loss (TEWL), optical coherence tomography (OCT), reflectance confocal laser scanning microscopy (RCLSM), confocal Raman micro-spectroscopy (CRM), two-photon tomography combined with fluorescence lifetime imaging (TPT-FLIM), histology, and scanning electron microscopy (SEM) were conducted. The 400 µm long DMNs successfully penetrated the skin to depths of ≈200 µm for dry skin and ≈200-290 µm for barrier-disrupted skin. Although DMNs fully inserted into all skin conditions, their dissolution rates were high in barrier-disrupted and low in dry skin, as observed through stereomicroscopy and TPT-FLIM. The dissolved polymer exhibited a more significant expansion in barrier-disrupted skin compared to intact skin, with the smallest increase observed in dry skin. Elevated TEWL and reduced skin hydration levels were evident in barrier-disrupted and dry skins compared to intact skin. OCT and RCLSM revealed noticeable skin indentation and pronounced microchannel areas, particularly in barrier-disrupted and dry skin. Additional confirmation of DMN effects on the skin and substance dissolution was obtained through histology, SEM, and CRM techniques. This study highlights the impact of skin condition on DMN effectiveness, emphasizing the importance of considering dissolvability and dissolution rates of needle materials, primarily composed of hyaluronic acid, for optimizing DMN-based drug delivery.

Diagnostic, Therapeutic, and Theranostic Multifunctional Microneedles

Microneedles (MNs) have maintained their popularity in therapeutic and diagnostic medical applications throughout the past decade. MNs are originally designed to gently puncture the stratum corneum layer of the skin and have lately evolved into intelligent devices with functions including bodily fluid extraction, biosensing, and drug administration. MNs offer limited invasiveness, ease of application, and minimal discomfort. Initially manufactured solely from metals, MNs are now available in polymer-based varieties. MNs can be used to create systems that deliver drugs and chemicals uniformly, collect bodily fluids, and are stimulus-sensitive. Although these advancements are favorable in terms of biocompatibility and production costs, they are insufficient for the therapeutic use of MNs. This is the first comprehensive review that discusses individual MN functions toward the evolution and development of smart and multifunctional MNs for a variety of novel and impactful future applications. The study examines fabrication techniques, application purposes, and experimental details of MN constructs that perform multiple functions concurrently, including sensing, drug-molecule release, sampling, and remote communication capabilities. It is highly likely that in the near future, MN-based smart devices will be a useful and important component of standard medical practice for different applications.

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.

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.

Evaluation of 3D-Printed Solid Microneedles Coated with Electrosprayed Polymeric Nanoparticles for Simultaneous Delivery of Rivastigmine and N-Acetyl Cysteine

In the current study, coated microneedle arrays were fabricated by means of digital light processing (DLP) printing. Three different shapes were designed, printed, and coated with PLGA particles containing two different actives. Rivastigmine (RIV) and N-acetyl-cysteine (NAC) were coformulated via electrohydrodynamic atomization (EHDA), and they were incorporated into the PLGA particles. The two actives are administered as a combined therapy for Alzheimer's disease. The printed arrays were evaluated regarding their ability to penetrate skin and their mechanical properties. Optical microscopy and scanning electron microscopy (SEM) were employed to further characterize the microneedle structure. Confocal laser microscopy studies were conducted to construct 3D imaging of the coating and to simulate the diffusion of the particles through artificial skin samples. Permeation studies were performed to investigate the transport of the drugs across human skin ex vivo. Subsequently, a series of tape strippings were performed in an attempt to examine the deposition of the APIs on and within the skin. Light microscopy and histological studies revealed no drastic effects on the membrane integrity of the stratum corneum. Finally, the cytocompatibility of the microneedles and their precursors was evaluated by measuring cell viability (MTT assay and live/dead staining) and membrane damages followed by LDH release.

A Bibliometric Analysis of Publications on Cadavers: A Study Based on Web of Science Data From 1978 to 2023

This study aimed to investigate the significance of publications examining the effectiveness of cadaver studies in the field of medicine with the method of bibliometric analysis, which emerged in the 1950s, offers the opportunity to conduct a detailed analysis of a specific subject, just like a systematic literature review or meta-analysis. Also, it aimed to enlighten the content of cadaver studies in the last half-century and to present a perspective for the future. In the study, an advanced search was conducted on the Web of Science Core Collection database on August 1, 2023, using the keywords "cadaver," "cadaver study," "cadaveric dissection." Review articles were excluded from the study. There were determined 34554 documents. The documents were transferred to the VOSviewer software program. In this way, the authors made detailed analyses of authors, keywords, journals, organizations, institutions, and countries and created scientific maps. The United States was one of the most important countries in terms of research. Generally, the use of cadaver terms in documents belongs to surgery, anatomy, and transplantation journals. Anatomy, cadaver, biomechanics, ultrasound, and computed tomography were the top 5 most frequently used keywords with cadaver term. The findings of our study showed that cadaver studies are used in many fields of medical science. However, clinical studies, including advanced imaging techniques, draw attention to the developing technology. Along with the powerful institutions of the United States, its great contributions to publications stand out.

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

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

MgO@polydopamine Nanoparticle-Loaded Photothermal Microneedle Patches Combined with Chitosan Gel Dressings for the Treatment of Infectious Wounds

As for wound drug delivery, microneedles (MNs) have attracted wide attention. However, while effective at increasing the depth of drug delivery, traditional MNs often have limited drug loads and have difficulty penetrating scabs on wounds. Herein, we develop a drug delivery system combining MgO@polydopamine (MgO@PDA) nanoparticle-loaded photothermal MN patches and chitosan (CS) gel to inhibit the formation of scabs and deliver sufficient drugs into deep tissue. When inserted into the wound, the MN system can keep the wound bed moist and weakly acidic to inhibit the formation of scabs and accelerate wound closure. The released MgO@PDA nanoparticles from both the tips and the backing layer, which immensely increase the drug load, continuously release Mg2+ in the moist, weakly acidic wound bed, promoting tissue migration and the formation of microvessels. MgO@PDA nanoparticles show excellent antibacterial activity under near-infrared irradiation synergized with the CS gel, and the PDA coating can also overcome the adverse effects of oxidative stress. Through in vitro and in vivo experiments, the MN system showed remarkable antibacterial, antioxidant, anti-inflammatory, and pro-angiogenic effects, indicating its potential in the treatment of infectious wounds.

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.

Integration of polysaccharide electrospun nanofibers with microneedle arrays promotes wound regeneration: A review

Utilizing electrospun nanofibers and microneedle arrays in wound regeneration has been practiced for several years. Researchers have recently asserted that using multiple methods concurrently might enhance efficiency, despite the inherent strengths and weaknesses of each individual approach. The combination of microneedle arrays with electrospun nanofibers has the potential to create a drug delivery system and wound healing method that offer improved efficiency and accuracy in targeting. The use of microneedles with nanofibers allows for precise administration of pharmaceuticals due to the microneedles' capacity to pierce the skin and the nanofibers' role as a drug reservoir, resulting in a progressive release of drugs over a certain period of time. Electrospun nanofibers have the ability to imitate the extracellular matrix and provide a framework for cellular growth and tissue rejuvenation, while microneedle arrays show potential for enhancing tissue regeneration and enhancing the efficacy of wound healing. The integration of electrospun nanofibers with microneedle arrays may be customized to effectively tackle particular obstacles in the fields of wound healing and drug delivery. However, some issues must be addressed before this paradigm may be fully integrated into clinical settings, including but not limited to ensuring the safety and sterilization of these products for transdermal use, optimizing manufacturing methods and characterization of developed products, larger-scale production, optimizing storage conditions, and evaluating the inclusion of multiple therapeutic and antimicrobial agents to increase the synergistic effects in the wound healing process. This research examines the combination of microneedle arrays with electrospun nanofibers to enhance the delivery of drugs and promote wound healing. It explores various kinds of microneedle arrays, the materials and processes used, and current developments in their integration with electrospun nanofibers.

Rapidly Dissolving Trans-scleral Microneedles for Intraocular Delivery of Cyclosporine A

Cyclosporine A (CsA) is a cyclic peptide immunosuppressant drug that is beneficial in the treatment of various ocular diseases. However, its ocular bioavailability in the posterior eye is limited due to its poor aqueous solubility. Conventional CsA formulations such as a solution or emulsion permeate poorly across the eye due to various static and dynamic barriers of the eye. Dissolvable microneedle (MN)-based patches can be used to overcome barrier properties and, thus, enhance the ocular bioavailability of CsA in the posterior eye. CsA-loaded dissolvable MN patches were fabricated using polyvinylpyrrolidone (PVP) and characterized for MN uniformity and sharpness using SEM. Further characterization for its failure force, penetration force, and depth of penetration were analyzed using a texture analyzer. Finally, the dissolution time, ex vivo permeation, and ocular distribution of cyclosporine were determined in isolated porcine eyes. PVP MNs were sharp, uniform with good mechanical properties, and dissolved within 5 min. Ocular distribution of CsA in a whole porcine eye perfusion model showed a significant increase of CsA levels in various posterior segment ocular tissues as compared to a topically applied ophthalmic emulsion (Restasis®) (P < 0.001). Dissolving MNs of CsA were prepared, and the MN arrays can deliver CsA to the back of the eye offering potential for treating various inflammatory diseases.