Dissolving Microneedles as Skin Allergy Test Device

Tiny titans- unravelling the potential of polysaccharides and proteins based dissolving microneedles in drug delivery and theranostics: A comprehensive review

In recent years, microneedles (MNs) have emerged as a promising alternative to traditional drug delivery systems in transdermal drug delivery. The use of MNs has demonstrated significant potential in improving patient acceptance and convenience while avoiding the invasiveness of traditional injections. Dissolving, solid, hollow, coated, and hydrogel microneedles are among the various types studied for drug delivery. Dissolving microneedles (DMNs), in particular, have gained attention for their safety, painlessness, patient convenience, and high delivery efficiency. This comprehensive review primarily focuses on different types of microneedles, fabrication methods, and materials used in fabrication of DMNs such as hyaluronic acid, chitosan, alginate, gelatin, collagen, silk fibroin, albumin, cellulose and starch, to list a few. The review also provides an exhaustive discussion on the applications of DMNs, including the delivery of vaccines, cosmetic agents, contraceptives, hormone and genes, and other therapeutic applications like for treating cancer, skin diseases, and diabetes, among others, are covered in this review. Additionally, this review highlights some of the DMN systems that are presently undergoing clinical trials. Finally, the review discusses current advances and trends in DMNs, as well as future prospective directions for this ground-breaking technology in drug delivery.

Biomaterial-based delivery platforms for transdermal immunotherapy

Nowadays, immunotherapy is one of the most essential treatments for various diseases and a broad spectrum of disorders are assumed to be treated by altering the function of the immune system. For this reason, immunotherapy has attracted a great deal of attention and numerous studies on different approaches for immunotherapies have been investigated, using multiple biomaterials and carriers, from nanoparticles (NPs) to microneedles (MNs). In this review, the immunotherapy strategies, biomaterials, devices, and diseases supposed to be treated by immunotherapeutic strategies are reviewed. Several transdermal therapeutic methods, including semisolids, skin patches, chemical, and physical skin penetration enhancers, are discussed. MNs are the most frequent devices implemented in transdermal immunotherapy of cancers (e.g., melanoma, squamous cell carcinoma, cervical, and breast cancer), infectious (e.g., COVID-19), allergic and autoimmune disorders (e.g., Duchenne's muscular dystrophy and Pollinosis). The biomaterials used in transdermal immunotherapy vary in shape, size, and sensitivity to external stimuli (e.g., magnetic field, photo, redox, pH, thermal, and even multi-stimuli-responsive) were reported. Correspondingly, vesicle-based NPs, including niosomes, transferosomes, ethosomes, microemulsions, transfersomes, and exosomes, are also discussed. In addition, transdermal immunotherapy using vaccines has been reviewed for Ebola, Neisseria gonorrhoeae, Hepatitis B virus, Influenza virus, respiratory syncytial virus, Hand-foot-and-mouth disease, and Tetanus.

Dissolvable polymer microneedles for drug delivery and diagnostics

Dissolvable transdermal microneedles (μND) are promising micro-devices used to transport a wide selection of active compounds into the skin. To provide an effective therapeutic outcome, μNDs must pierce the human stratum corneum (~10 to 20 μm), without rupturing or bending during penetration, then release their cargo at the predetermined area and time. The ability of dissolvable μND arrays/patches to sufficiently pierce the skin is a crucial requirement, which depends on the material composition, μND geometry and fabrication techniques. This comprehensive review not only provides contemporary knowledge on the μND design approaches, but also the materials science facilitating these delivery systems and the opportunities these advanced materials can provide to enhance clinical outcomes.

Dissolving microneedles: Applications and growing therapeutic potential

Microneedles are a rapidly developing method for the transdermal delivery of therapeutic compounds. All types of microneedles, whether solid, hollow, coated, or dissolving function by penetrating the stratum corneum layer of the skin producing a microchannel through which therapeutic agents may be delivered. To date, coated and hollow microneedles have been the most successful, despite suffering from issues such as poor drug loading capabilities and blocked pores. Dissolving microneedles, on the other hand, have superior drug loading as well as other positive attributes that make it an ideal delivery system, including simple methods of fabrication and disposal, and abundantly available materials. Indeed, dissolvable microneedles can even be fabricated entirely from the therapeutic agent itself thus eliminating the requirement for additional excipients. This focused review presents the recent developments and trends of dissolving microneedles as well as potential future directions. The advantages, and disadvantages of dissolving microneedles as well as fabrication materials and methods are discussed. The potential applications of dissolving microneedles as a drug delivery system in different therapeutic areas in both research literature and clinical trials is highlighted. Applications including the delivery of cosmetics, vaccine delivery, diagnosis and monitoring, cancer, pain and inflammation, diabetes, hair and scalp disorders and inflammatory skin diseases are presented. The current trends observed in the microneedle landscape with particular emphasis on contemporary clinical trials and commercial successes as well as barriers impeding microneedle development and commercialisation are also discussed.

An overview of microneedle applications, materials, and fabrication methods

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics - so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

A systematic review of carbohydrate-based microneedles: current status and future prospects

Microneedles (MNs) are minimally invasive tridimensional biomedical devices that bypass the skin barrier resulting in systemic and localized pharmacological effects. Historically, biomaterials such as carbohydrates, due to their physicochemical properties, have been used widely to fabricate MNs. Owing to their broad spectrum of functional groups, carbohydrates permit designing and engineering with tunable properties and functionalities. This has led the carbohydrate-based microarrays possessing the great potential to take a futuristic step in detecting, drug delivery, and retorting to biologicals. In this review, the crucial and extensive summary of carbohydrates such as hyaluronic acid, chitin, chitosan, chondroitin sulfate, cellulose, and starch has been discussed systematically, using PRISMA guidelines. It also discusses different approaches for drug delivery and the mechanical properties of biomaterial-based MNs, till date, progress has been achieved in clinical translation of carbohydrate-based MNs, and regulatory requirements for their commercialization. In conclusion, it describes a brief perspective on the future prospects of carbohydrate-based MNs referred to as the new class of topical drug delivery systems.

Microvascular effects of microneedles with subsequent histamin application in the skin prick test

BACKGROUND

Since decades, histamin applications are routinely performed in skin prick tests using a lancet. However, this technique is associated with various drawbacks.

MATERIALS AND METHODS

In healthy human subjects, we investigated the effects of microneedle-enhanced histamin delivery (wheal size, erythema size) in the skin microvasculature using polarized light spectroscopy imaging (Tissue Viability imaging, TiVi). Histamin was applied on microneedle-pretreated skin or on -untreated skin, to assess the microvascular response in the local skin.

RESULTS

In our results, histamin was delivered more rapidly into the skin after microneedle pretreatment compared to passive diffusion, visible as wheal and erythema.

CONCLUSION

The here presented technique might be useful for a personalized drug-testing system in the future.

Microvascular effects of microneedle application

BACKGROUND

The efficiency of transdermal drug delivery may be increased by pretreating the skin with microneedles, but distinct effects of microneedles and the microneedle-enhanced delivery of vasoactive drugs on the skin microvasculature are still not well investigated.

MATERIALS AND METHODS

In eight healthy human subjects, we measured the microvascular response to microneedle-induced microtraumas in the skin microvasculature using polarized light spectroscopy imaging (Tissue Viability imaging, TiVi). The microvascular response was assessed for up to 48 hours for three microneedle sizes (300 µm, 500 µm, and 750 µm) and for different pressures and application times.

RESULTS

In our results, microneedle application increased the local red blood cell (RBC) concentration for up to 24 hours dependent on the needle lengths, applied time, and force.

CONCLUSION

Optimization of microneedles size, pressure, and application time should be taken into account for future protocols for drug delivery and experimental provocations.

Dissolving Microneedle Arrays with Optimized Needle Geometry for Transcutaneous Immunization

In this study, the feasibility of transcutaneous immunization using different needle-geometries dissolving microneedle array (DMNA) were investigated as drug carriers for ovalbumin (OVA) preparations. A two-step molding process was used in which needles were loaded with OVA. The microneedles displayed a geometry and dimensions consistent with the main molds. DMNA with different needle-geometries were compared and characterized. Drug loading of the prepared DMNAs reached ~100 μg measured via BCA assay. The stability of OVA in the DMNAs was investigated by SDS-PAGE electrophoresis and showed that the OVA encapsulated in the DMNAs was stable during preparation. The immune responses induced by the DMNAs and hypodermic needle-based injections were compared through in vivo immunoglobulin G (IgG) production assays. OVA-loaded DMNAs also induced stronger immune responses compared to hypodermic needle-based injections. In conclusion, these results suggest that: (1) the needle-morphology of DMNAs influences their mechanical properties, insertion capacity, and dissolution, thus affecting the immune response; (2) Cone-DMNAs are optimal for transcutaneous immunization. These data provide a theoretical basis for the use of transcutaneous immunization of DMNAs for vaccine development.

A compendium of current developments on polysaccharide and protein-based microneedles

Microneedles (MNs), i.e. minimally invasive three-dimensional microstructures that penetrate the stratum corneum inducing relatively little or no pain, have been studied as appealing therapeutic vehicles for transdermal drug delivery. Over the last years, the fabrication of MNs using biopolymers, such as polysaccharides and proteins, has sparked the imagination of scientists due to their recognized biocompatibility, biodegradability, ease of fabrication and sustainable character. Owing to their wide range of functional groups, polysaccharides and proteins enable the design and preparation of materials with tunable properties and functionalities. Therefore, these biopolymer-based MNs take a revolutionary step offering great potential not only in drug administration, but also in sensing and response to physiological stimuli. In this review, a critical and comprehensive overview of the polysaccharides and proteins employed in the design and engineering of MNs will be given. The strategies adopted for their preparation, their advantages and disadvantages will be also detailed. In addition, the potential and challenges of using these matrices to deliver drugs, vaccines and other molecules will be discussed. Finally, this appraisal ends with a perspective on the possibilities and challenges in research and development of polysaccharide and protein MNs, envisioning the future advances and clinical translation of these platforms as the next generation of drug delivery systems.

Advances in the Design of Transdermal Microneedles for Diagnostic and Monitoring Applications

Due to their intrinsic advantages over classical hypodermic needles, microneedles have received much attention over the last two decades and will likely soon appear in clinics. Although the vast majority of research is focused on designing microneedles for the painless delivery of drugs, their applications for diagnostic purposes have also provided promising results. In this paper, the main advances in the field of microneedles for diagnostic and patient monitoring purposes are introduced and critically discussed.

Functionalized microneedles for continuous glucose monitoring

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