Microneedles are a type of biomedical device consisting of microscale needles that can penetrate the skin's stratum corneum to deliver therapeutic molecules. They offer advantages over traditional methods, including better medication adherence, ease of use, and painless self-administration. Microneedles can vary in shape, size, and composition, and their design must consider factors such as delivery location, material, and manufacturing process. They have been used in various applications, including drug and vaccine delivery, cosmetics, therapy, diagnostics, tissue engineering, sample extraction, cancer research, and wound healing. Microneedles can be categorized into solid, coated, dissolving, hollow, and hydrogel-forming types. Solid microneedles create temporary micro-holes in the skin, allowing drug delivery through topical formulations. Coated microneedles release drugs upon insertion, with the coating dissolving after application. Dissolving microneedles are made from water-soluble materials and dissolve upon contact with interstitial fluid, enabling drug release. Hollow microneedles allow direct drug delivery into the skin, while hydrogel-forming microneedles use a polymer matrix to control drug release. Microneedle design involves parameters such as length, needle-to-needle spacing, tip diameter, tip angle, and aspect ratio. These factors influence penetration depth, drug delivery efficiency, and patient comfort. For example, longer microneedles can penetrate deeper but may cause more pain, while smaller tip diameters improve penetration. The aspect ratio, defined as the ratio of length to base diameter, affects mechanical properties and penetration efficiency. Microneedle fabrication methods include MEMS, micromolding, laser cutting, laser ablation, and drawing-based methods. MEMS techniques allow precise manufacturing of complex structures, while micromolding is cost-effective and suitable for various materials. Laser cutting and ablation are used for metal and polymer microneedles, while drawing-based methods enable the production of basic structures like conical or hollow needles. Atomized spraying and injection molding are also used for dissolving microneedles, offering advantages in mass production and controlled drug delivery. Overall, microneedles offer a versatile and efficient method for drug delivery and other medical applications, with ongoing research aimed at improving their design, fabrication, and functionality.Microneedles are a type of biomedical device consisting of microscale needles that can penetrate the skin's stratum corneum to deliver therapeutic molecules. They offer advantages over traditional methods, including better medication adherence, ease of use, and painless self-administration. Microneedles can vary in shape, size, and composition, and their design must consider factors such as delivery location, material, and manufacturing process. They have been used in various applications, including drug and vaccine delivery, cosmetics, therapy, diagnostics, tissue engineering, sample extraction, cancer research, and wound healing. Microneedles can be categorized into solid, coated, dissolving, hollow, and hydrogel-forming types. Solid microneedles create temporary micro-holes in the skin, allowing drug delivery through topical formulations. Coated microneedles release drugs upon insertion, with the coating dissolving after application. Dissolving microneedles are made from water-soluble materials and dissolve upon contact with interstitial fluid, enabling drug release. Hollow microneedles allow direct drug delivery into the skin, while hydrogel-forming microneedles use a polymer matrix to control drug release. Microneedle design involves parameters such as length, needle-to-needle spacing, tip diameter, tip angle, and aspect ratio. These factors influence penetration depth, drug delivery efficiency, and patient comfort. For example, longer microneedles can penetrate deeper but may cause more pain, while smaller tip diameters improve penetration. The aspect ratio, defined as the ratio of length to base diameter, affects mechanical properties and penetration efficiency. Microneedle fabrication methods include MEMS, micromolding, laser cutting, laser ablation, and drawing-based methods. MEMS techniques allow precise manufacturing of complex structures, while micromolding is cost-effective and suitable for various materials. Laser cutting and ablation are used for metal and polymer microneedles, while drawing-based methods enable the production of basic structures like conical or hollow needles. Atomized spraying and injection molding are also used for dissolving microneedles, offering advantages in mass production and controlled drug delivery. Overall, microneedles offer a versatile and efficient method for drug delivery and other medical applications, with ongoing research aimed at improving their design, fabrication, and functionality.