Key Takeaways & Executive Findings
- •• Metallic microneedles (MMNs) offer superior mechanical properties, machinability, and biocompatibility compared to silicon, polymer, and ceramic counterparts, enabling painless and efficient skin penetration. • MMNs are classified by structure (in-plane/out-of-plane) and internal/surface design (solid, hollow, coated, porous), each tailored for specific applications. • Fabrication technologies for MMNs include cutting tool machining, non-traditional machining, etching, hot-forming, and additive manufacturing, each with distinct advantages and limitations. • MMNs show significant promise in drug delivery, disease diagnosis, and cosmetology, but challenges remain in fabrication scalability, cost, and long-term safety, guiding future research directions.
Abstract
Microneedle (MN) is a medical device containing an array of needles with a micrometer-scale. It can penetrate the human stratum corneum painlessly and efficiently for treatment and diagnosis purposes. Currently, the materials commonly used to manufacture MNs include silicon, polymers, ceramics and metals. Metallic MNs (MMNs) have drawn significant attention owing to its superior mechanical properties, machinability, and biocompatibility. This paper is a state-of-the-art review of the structure, fabrication technologies, and applications of MMNs. According to the relative position of the axis of MN and the plane of the substrate, MMNs can be divided into in-plane and out-of-plane. Solid, hollow, coated and porous MMNs are also employed to characterize their internal and surface structures. Until now, numerous fabrication technologies, including cutting tool machining, non-traditional machining, etching, hot-forming, and additive manufacturing, have been used to fabricate MMNs. The recent advances in the application of MMNs in drug delivery, disease diagnosis, and cosmetology are also discussed in-depth. Finally, the shortcomings in the fabrication and application of MMNs and future directions for development are highlighted.
1. Introduction
Microneedle (MN) as a medical device is composed of micron-sized arrays of tip protrusions [1, 2]. As a novel transdermal drug delivery technique, MNs can pierce the stratum corneum to form microchannels reaching the epidermis and even the upper dermis without touching the nerve fibers and blood vessels in the dermis [3]. The first-pass metabolism of the traditional delivery method of oral ingestion is avoided by MNs drug delivery [4]. The pain and infection risk of hypodermic injection delivery can also be reduced by MNs [5–7]. Moreover, MNs can increase the drug delivery efficiency and the drug types compared to traditional transdermal drug delivery [8–10]. Besides, MNs have great potential in disease diagnosis [11–13] and cosmetology [14].
Due to the inherent viscoelastic properties of the skin, the MNs have to possess sufficient strength and stiffness. Furthermore, they have to be sharp, thin, and long enough to penetrate the stratum corneum and to reach the epidermis and even the dermis [15–17] without breaking or bending during insertion [18–23]. It is therefore challenging to design and manufacture MNs that meet the aforementioned requirements.
The material of the MNs has a strong influence on the mechanical properties [24]. Until recently, most of the MNs have been made using silicon, polymer, ceramic, and metal [25–28]. The first MN device was built using silicon [29], and photolithography (LIGA) has been extensively employed to fabricate silicon MNs with a very high dimension and shape accuracy [30, 31]. However, silicon possesses low fracture toughness, posing the risk of leaving debris of silicon in tissue in the case of fracture [24, 32]. Polymer MNs are biocompatible, degradable, and sufficiently tough, but easily undergo buckling failure during insertion due to their low strength [33]. Ceramic MNs are employed because of their excellent chemical stability, compression resistance, and biocompatibility [34]. However, they can also experience a brittle fracture like silica MNs [35]. Compared with other materials, metallic MNs have superior mechanical properties, including high strength, hardness, and toughness, which allow them to have precise insertion capabilities. Moreover, because of these features, they can penetrate through the skin without being fractured or buckled, even in the case of the formation of larger microchannels or higher porosity [8, 36]. Therefore, metallic mater
Loading authentic research manuscript (Pages 1–5)...
Zhishan Yuan, Hongzhao Zhang, Wentao Hu, Xiao Yu, Si Qin, Chengyong Wang, Fenglin Zhang (2025). State-of-the-art Review of Metallic Microneedles: Structure, Fabrication, and Application. Chinese Journal of Mechanical Engineering. https://doi.org/10.1186/s10033-025-01188-9
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What are metallic microneedles (MMNs) and why are they advantageous?
Metallic microneedles are micron-sized needle arrays made from metals, offering superior mechanical strength, hardness, and toughness compared to silicon, polymer, or ceramic microneedles. This allows them to penetrate the skin painlessly and efficiently without breaking or buckling, making them ideal for drug delivery, diagnosis, and cosmetic applications.
How are metallic microneedles classified?
MMNs are classified based on the orientation relative to the substrate (in-plane or out-of-plane) and their internal/surface structure (solid, hollow, coated, or porous). Each type serves specific purposes, such as enhanced drug loading or continuous fluid extraction.
What fabrication technologies are used for metallic microneedles?
Fabrication methods include cutting tool machining, non-traditional machining (e.g., EDM, laser), etching, hot-forming, and additive manufacturing (3D printing). Each technique offers different trade-offs in precision, cost, scalability, and material compatibility.
What are the main applications of metallic microneedles?
MMNs are primarily used in transdermal drug delivery, disease diagnosis (e.g., interstitial fluid sampling), and cosmetology (e.g., anti-aging treatments). Their robust mechanical properties enable reliable skin penetration and controlled release or extraction.
What are the current challenges and future directions for metallic microneedles?
Challenges include high fabrication costs, limited scalability, potential metal ion release, and regulatory hurdles. Future research focuses on developing cost-effective manufacturing methods, improving biocompatibility, and integrating smart features like sensors for personalized medicine.
Related Technical Papers & Translations
Direct Repair of the Crystal Structure and Coating Surface of Spent LiFePO4 Materials Enables Superfast Li-Ion Migration
The rapid accumulation of spent LiFePO4 (LFP) cathodes from retired lithium-ion batteries necessitates the development of effective and environmental-friendly recycling strategies. In this context, direct regeneration has emerged as a promising approach for reclaiming LFP cathode materials, offering a streamlined pathway to restore their electrochemical functionality. We report an integrated regeneration protocol that simultaneously repairs the degraded crystal structure and reconstructs the damaged carbon coating in spent LFP. The regenerated cathode material had superfast lithium-ion diffusion kinetics and a stable cathode–electrolyte interface, giving a remarkable rate capability with specific capacities of 122 mAh g−1 at 5C and 106 mAh g−1 at 10C (1C = 170 mA g−1). It also maintained capacities of 110.7 mAh g−1 (5C) and 84.1 mAh g−1 (10C) after 400 cycles. It could be used in harsh environments and could be stably cycled at subzero temperatures (−10 and −20 °C) and in solid-state electrolyte batteries. Life cycle assessment combined with economic evaluation using the EverBatt model reveals that this direct regeneration approach has high economic and environmental benefits.
Oxide Semiconductor for Advanced Memory Architectures: Atomic Layer Deposition, Key Requirement and Challenges
Oxide semiconductors (OSs), introduced by the Hosono group in the early 2000s, have evolved from display backplane materials to promising candidates for advanced memory and logic devices. The exceptionally low leakage current of OSs and compatibility with three-dimensional (3D) architectures have recently sparked renewed interest in their use in semiconductor applications. This review begins by exploring the unique material properties of OSs, which fundamentally originate from their distinct electronic band structure. Subsequently, we focus on atomic layer deposition (ALD), a core technique for growing excellent OS films, covering both basic and advanced processes compatible with 3D scaling. The basic surface reaction mechanisms—adsorption and reaction—and their roles in film growth are introduced. Furthermore, material design strategies, such as cation selection, crystallinity control, anion doping, and heterostructure engineering, are discussed. We also highlight challenges in memory applications, including contact resistance, hydrogen instability, and lack of p-type materials, and discuss the feasibility of ALD-grown OSs as potential solutions. Lastly, we provide an outlook on the role of ALD-grown OSs in memory technologies. This review bridges material fundamentals and device-level requirements, offering a comprehensive perspective on the potential of ALD-driven OSs for next-generation semiconductor memory devices.
Laser powder bed fusion of biodegradable Zn-4Cu alloy: Processing, microstructure and properties
Zn's natural degradability and biocompatibility make it a promising candidate for implants, however, its mechanical properties remain insufficient for bone applications. In this study, the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion (LPBF). Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed. Under optimized conditions of 100 W and 100 mm/s, high-density (99.58%) Zn-Cu alloys with improved hardness (68.2HV) and yield strength (160 MPa) were achieved. These improvements are attributed to solid solution strengthening, segregation strengthening, and grain refinement. The Zn-Cu alloys also demonstrated favorable degradation behavior, with a rate of 0.16 mm/year. This degradation is primarily driven by micro-galvanic corrosion between the CuZn5 phase and Zn matrix, along with refined grains and increased grain boundary density. This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.