Microfabrication Research Articles

Synthesis of Hydrogel-Based Microgels and Nanogels Toward Therapeutic and Biomedical Applications

Hydrogel is one of the most prominent biomaterials in therapeutic and biomedical engineering, benefiting from its biocompatibility, chemical/physical tunability, and wide versatility to various fabrication techniques. One remarkable advance in the latest hydrogel research is the micro/nanofabrication technologies, which utilize unique mechanical and chemical properties of hydrogel, various chemical reaction mechanisms, and multidisciplinary approaches to realize innovative systems at these size scales. This review reports a comprehensive overview on the latest advances in fabrication of hydrogel-based micro- and nano-systems with an emphasis on their biomedical and therapeutic applications. Challenges and prospects are discussed from the material, fabrication, and system design perspectives to develop effective, personalized, and versatile hydrogel-based therapies.

Ultrafast chirality-dependent dynamics from helicity-resolved transient absorption spectroscopy.

Chirality, a pervasive phenomenon in nature, is widely studied across diverse fields including the origins of life, chemical catalysis, drug discovery, and physical optoelectronics. The investigations of natural chiral materials have been constrained by their intrinsically weak chiral effects. Recently, significant progress has been made in the fabrication and assembly of low-dimensional micro and nanoscale chiral materials and their architectures, leading to the discovery of novel optoelectronic phenomena such as circularly polarized light emission, spin and charge flip, advocating great potential for applications in quantum information, quantum computing, and biosensing. Despite these advancements, the fundamental mechanisms underlying the generation, propagation, and amplification of chirality in low-dimensional chiral materials and architectures remain largely unexplored. To tackle these challenges, we focus on employing ultrafast spectroscopy to investigate the dynamics of chirality evolution, with the aim of attaining a more profound understanding of the microscopic mechanisms governing chirality generation and amplification. This review thus provides a comprehensive overview of the chiral micro-/nano-materials, including two-dimensional transition metal dichalcogenides (TMDs), chiral halide perovskites, and chiral metasurfaces, with a particular emphasis on the physical mechanism. This review further explores the advancements made by ultrafast chiral spectroscopy research, thereby paving the way for innovative devices in chiral photonics and optoelectronics.

Light-Programmable g-C3N4 Microrobots with Negative Photogravitaxis for Photocatalytic Antibiotic Degradation.

Microrobots enhance contact with pollutants through their movement and flow-induced mixing, substantially improving wastewater treatment efficiency beyond traditional diffusion-limited methods. g-C3N4 is an affordable and environmentally friendly photocatalyst that has been extensively researched in various fields such as biomedicine and environmental remediation. However, compared to other photocatalytic materials like TiO2 and ZnO, which are widely used in the fabrication of micro- and nanorobots, research on g-C3N4 for these applications is still in its early stages. This work presents microrobots entirely based on g-C3N4 microtubes, which can initiate autonomous movement when exposed to ultraviolet and visible light. We observed distinct motion behaviors of the microrobots under light irradiation of different wavelengths. Specifically, under ultraviolet light, the microrobots exhibit negative photogravitaxis, while under visible light, they demonstrate a combination of 3-dimensional motion and 2-dimensional motion. Therefore, the wavelength of the light can be used for programming the motion style of the microrobots and subsequently their application. We show that the microrobots can effectively degrade the antibiotic tetracycline, displaying their potential for antibiotic removal. This exploration of autonomous motion behaviors under different wavelength conditions helps to expand research on g-C3N4-based microrobots and their potential for environmental remediation.

Shedding Light on the Mid‐Infrared Complex Refractive Index of Anodic Aluminum Oxide

AbstractIn the current scientific landscape, the understanding of optical properties in the mid‐infrared (mid‐IR) range (3–30 µm) is crucial in simulations and models to explore the potential of materials for various applications. However, due to the challenges associated with mid‐IR characterization, accurate refractive index (n) and extinction coefficient (κ) data are often lacking in the literature. This study addresses this gap by investigating the mid‐IR n and κ spectra of anodic aluminum oxide (AAO) nanostructures anodized under different conditions, using two distinct approaches: IR ellipsometry and a theoretical model based on multilayer reflection and effective medium. The results demonstrate a strong agreement: the anodizing conditions have a significant influence on the optical properties of the AAO nanostructures. These differences enable accurate simulations of the emissivity spectra of AAO nanostructures on Al foils, which align closely with experimental measurements. This theoretical approximation is versatile and extensible to a broad range of materials. Different materials are tested, namely, a sapphire, a polycarbonate film, and a polyethylene terephthalate (PET) film achieving a useful qualitative description. This study paves the way for a novel approach in the engineering of new micro and nano‐optical materials, facilitating their evaluation for suitability in mid‐IR applications.

Near-Field Direct Writing Based on Piezoelectric Micromotion for the Programmable Manufacturing of Serpentine Structures

Serpentine microstructures offer excellent physical properties, making them highly promising in applications in stretchable electronics and tissue engineering. However, existing fabrication methods, such as electrospinning and lithography, face significant challenges in producing microscale serpentine structures that are cost-effective, efficient, and controllable. These methods often struggle with achieving precise control over fiber morphology and scalability. In this study, we developed a near-field direct writing (NFDW) technique incorporating piezoelectric micromotion to enable the precise fabrication of serpentine micro-/nanofibers by incorporating micromotion control with macroscopic movement. Modifying the fiber structure allowed for adjustments to the mechanical properties, including tunable extensibility and distinct characteristics. Through the control of the frequency and amplitude of the piezoelectric signal, the printing errors were reduced to below 9.48% in the cycle length direction and 6.33% in the peak height direction. A predictive model for the geometrical extensibility of serpentine structures was derived from Legendre’s incomplete elliptic integral of the second kind and incorporated an error correction factor, which significantly reduced the calculation errors in predicting geometric elongation, by 95.85%. The relationship between microstructure bending and biomimetic non-linear mechanical behavior was explored through tensile testing. By controlling the input electrical signals, highly ordered serpentine microstructures were successfully fabricated, demonstrating potential for use in biomimetic mechanical scaffolds.

Non-Fourier thermal spike effect on nanocrystalline Cu phase engineering

The thermal spike effect dominates rapid heating and quenching at the nanoscale in ion beam assisted materials surface phase engineering. This phenomenon often leads to the formation of metastable nanocrystalline phases in the resulting micro-/nanostructures. However, such a non-equilibrium process cannot be accurately described by the conventional Fourier thermal spike model. In this study, a non-Fourier model is proposed to elucidate the dynamics of heat diffusion in sub-keV Cu ion beam sputter deposition. The effects of beam density and energy on the non-equilibrium thermal and stress fields are quantitatively investigated. The influence of high stress field on nanocrystalline Cu phase content is also studied. It is found that the energetic Cu ion beams produce a rapidly oscillating stress field with a maximum of ∼ 10 GPa within 50 ps, which significantly constrains the growth of nanocrystalline Cu phase at a threshold of ∼ 4 GPa. This understanding provides new insights into the formation of metastable nanocrystalline phases in the fabrication and modification of surface micro-/nanostructures using ion beam assisted techniques.

A Novel View on the Electrochemical Nucleation and Growth of Metals and Alloys By Local Electrochemistry and Correlative Electron Microscopy

Electrochemical deposition offers the opportunity for precise control, scalability, cost-effectiveness, and environmental friendliness, making it the preferred method for synthesizing (nano)materials for various applications [1]. Yet, this requires a comprehensive understanding of the formation of a new solid phase on a foreign substrate, particularly in its early stages. The formation of nuclei on a substrate are critical steps determining the physicochemical properties of the deposit, which are inherently influenced by the surface properties of the substrate. The in-depth experimental assessment of the process is very challenging due to the random nature of initiation events (nucleation), the heterogeneity of surfaces and the (very) fast kinetics across several length scales. For all that, our understanding of the mechanisms involved is inaccurate and incomplete [2].This process is commonly examined by electrochemical characterization, coupled with ex-situ (post-mortem) evaluation of the deposits. When coupling this standard approach with TEM compatible substrates, it has brought valuable evidence of non-classical growth pathways, which need to be fully understood to fine-tune size, shape and composition of nanostructured materials [3,4]. Yet, it does not capture the influence of the heterogeneous nature of the surface where EN&G proceeds, nor the dynamics before, during and after nucleation [5].Over the past years, our group has been tackling these challenges by combining (high-throughput) local electrochemistry by Scanning Electrochemical Cell Microscopy (SECCM), with ex-situ and in-situ electron microscopy and data-centric analyses to study the electrochemical nucleation and growth of metals, and more recently alloys, on carbon surfaces [6-8]. This correlative microscopy approach enables unambiguous correlations and clears the path towards a better understanding of the electrochemical response at the local scale.In this contribution, we show how both overpotential and surface state significantly influence the probability of nucleation. Experiments with varying probe sizes demonstrate that the nucleation rate distribution is also influenced by the electrode's area. Our derived analytical model successfully fits experimental current transients, revealing an excellent correlation between the number of active sites inferred from the model and the number of nanoparticles observed by FESEM. [9] Systematic understanding of correlations among nucleation, growth and structure of deposits, and the accurate depiction of the current transients, are the cornerstones of precise electrochemical manufacturing of micro- and nanostructures.Furthermore, our integrated scanning microscopy approach offers a robust framework for generating rich experimental data, laying the foundation for future investigations. These are the bridge connecting the microscopic world to macroscopic outcomes, shedding light on how surface heterogeneities influence nucleation rates and electrodeposit properties.

Ultrawide Spectrum Metallic Plane Blackbody with Extremely High Absorption from 0.2 to 25 µm.

A plane blackbody serves as a standard radiation source, providing a precise quantitative relationship between input radiation and the output of infrared detectors, which is essential component of space infrared remote sensing instruments. However, current plane blackbodies fabricated by coating or surface structuring are unable to achieve uniform and stable high absorption in the ultrawide spectral range spanning the UV-VIS-NIR-MIR. Here, a femtosecond laser "V"- scanning method is proposed for the fabrication of cross-scale multi-layered micro- and nanocomposite structures on copper surfaces to realize ultrawide spectrum metallic plane blackbody with high absorption. The structures consist of a micrometer cone-tip structure with a depth-to-width ratio of 7:1 (period 30 µm, depth 210 µm), an oxide layer with a thickness of more than 2 µm, and nanoparticles of different sizes, achieving uniform high absorption rates exceeding 99% in the localized spectral range of 400-700 nm and over 98% from the UV to MIR range of 200 nm to 25 µm. This strategy offers a generalized approach to enhance surface light absorption, with significant application potential in infrared calibration, passive radiation cooling, and stray light suppression.

Development platform for UV-NIL processes using polymer masters produced by laser ablation and photolithography

Ultraviolet nanoimprint lithography (UV-NIL) is a versatile and cost-effective technique for the fabrication of micro- and nanostructures by copying master patterns in a planar or a roll-to-roll process through curing of a liquid UV-sensitive precursor. For applications with a high pattern complexity, new UV-NIL process chains must be specified. Master fabrication is a challenging part of the development and often cannot be accomplished using a single master fabrication technique. Therefore, an approach combining different patterning fabrication techniques is developed here for polymer masters using laser direct writing and photolithography. The polymer masters produced in this way are molded into inverse silicone stamps that are used for roll-to-roll replication into an acrylate formulation. To fit the required roller size for large-area UV-NIL, several submasters with micrometer-sized dot and line gratings and prism arrays, which have been patterned by these different techniques, are assembled to final size of ∼200 × 600 mm2 with an absolute precision of better than 50 µm. The size of the submasters allows the use of standard laboratory equipment for patterning and direct writing, thus enabling the fabrication of micro- and even nanostructures when electron-beam writing is utilized. In this way, the effort, time, and costs for the fabrication of masters for UV-NIL processes are reduced, enabling further development for particular structures and applications. Using this approach, patterns fabricated with different laboratory tools are finally replicated by UV-NIL in an acrylate formulation, demonstrating the high quality of the whole process chain.

Deciphering Spatially-Resolved Electrochemical Nucleation and Growth Kinetics by Correlative Multimicroscopy.

The study employs a multimicroscopy approach, combining Scanning Electrochemical Cell Microscopy (SECCM) and Field Emission Scanning Electron Microscopy (FESEM), to investigate electrochemical nucleation and growth (EN&G). Cu nanoparticles (NPs) are meticulously electrodeposited on glassy carbon (GC), to perform co-located characterization, supported by analytical modeling and statistical analysis. The findings reveal clear correlations between electrochemical descriptors (i-t transients) and physical descriptors (NPs size and distribution), offering valuable insights into nucleation kinetics, influenced by varied overpotentials, surface state, and electrode's area. Analysis of the stochasticity of nucleation reveals intriguing temporal distributions, indicating an increased likelihood of nucleation with higher overpotential and larger electrode's area. Notably, the local surface state significantly influences nucleation site number and activity, leading to spatial differences in nucleation rates unaccounted for in macroscopic experiments. The updated analytical model for EN&G current transients, considering SECCM geometry, shows excellent agreement with FESEM measurements, facilitating the calculation of active sites within individual regions. These results deepen the understanding of EN&G phenomena from a new perspective, and lay the groundwork for further theoretical advancements, showcasing the great potential of current experimental methods in advancing precise electrochemical manufacturing of micro- and nanostructures.

Formation of tunable diamond micro- and nanopillars for field effect enhancement applications

We developed a process for the fabrication of tunable single crystal diamond micro- and nanopillars, with tip widths ranging from 40 to 460 nm, densities ranging from 0.5 to 53.5 pillars/μm2, and heights greater than 4.5 μm. A self-assembled Au nanodot ensemble etch mask was formed from an annealed Au thin film. The nanodot diameter and density can be tuned using the initial film thickness. The pillars were etched from the nanodot mask using an RIE O2 plasma, which has infinite selectivity for the diamond when applied at low RF powers (50 W). Finally, the pillars can be sharpened to ∼40 nm tip widths by annealing in air at 650 °C. These pillars can be used for applications such as field effect enhancement of diamond photocathode devices, enhancement of optical emission from N-V centers, and antireflective coatings.

Closed-Form Solution for Scale-Dependent Frequencies of Shear Deformable Cellular Microplates Coated by Piezoelectric Polymeric Skins Consisting of FG Distributed CNTs

In this work, a rectangular cellular microplate is taken into consideration which is embedded between two functionally graded carbon nanotube-reinforced composite layers that have the piezoelectric ability. Different patterns for the carbon nanotube dispersion are considered. Moreover, an external electrical voltage is applied to them. The displacements are described based on a higher-order shear deformation theory which is called hyperbolic theory and the size influence is captured via the modified couple stress formulations. The governing motion equations are then derived using the variational technique and Hamilton’s principle. Then, for simply supported edge conditions, a closed-form solution is provided. Next, it turns to validate the results in simpler states, and after that, the effect of the most prominent parameters on the results is investigated. It is observed that by increasing the external applied voltage to the face sheets, the frequencies are reduced. Also, the natural frequencies have a tendency to decrease as the dimensionless material length scale parameter increases. This study’s outcomes may help design and manufacture micro-/nano-electro systems, sensors and actuators, small-scale devices, and other engineering structures.

Micro‐ and nanorobots from magnetic particles: Fabrication, control, and applications

AbstractMagnetic microparticles (MPs) and nanoparticles (NPs) have long been used as ideal miniaturized delivery and detection platforms. Their use as micro‐ and nanorobots (MNRs) is also emerging in the recent years with the help of more dedicated external magnetic field manipulations. In this review, we summarize the research progress on magnetic micro‐ and nanoparticle (MNP)‐based MNRs. First, the fabrication of micro‐ and nanorobots from either template‐assisted NP doping methods or directly synthesized MPs is summarized. The external driving torque sources for both types of MNRs are analyzed, and their propulsion control under low Reynolds number flows is discussed by evaluating symmetry breaking mechanisms and interparticle interactions. Subsequently, the use of these MNRs as scientific models, bioimaging agents, active delivery, and treatment platforms (drug and cell delivery, and sterilization), and biomedical diagnostics has also been reviewed. Finally, the perspective of MNPs‐based MNRs was outlined, including challenges and future directions.

Diamond etching with near-zero micromasking

The outstanding material properties of single-crystal diamond have been the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. Etching and patterning diamond have proven challenging due to the hardness and chemical resistance of the material. In this work, the patterned etching process of single-crystal diamond has been investigated using the inductively coupled plasma etching technique. In order to avoid the micromasking phenomenon caused by the metal mask, this paper adopts the Ar/O2–Ar/Cl2/BCl3 two-step cycle etching process and investigates the effect of the Cl2/BCl3 gas ratio on the bottom morphology of single-crystal diamond grid grooves. A theoretical explanation is provided for the use of chlorine-based gases to eliminate micromasking and achieve a smooth etching surface. Finally, an Ar/O₂-Ar/Cl₂/BCl3 cyclic etching process for patterning single-crystal diamond with near-zero micromasking has been developed.

Nature-inspired approach for enhancing the fracture performance of 3D printed strain-hardening cementitious composites (3DP-SHCC)

3D printing technology enhances design flexibility, enables the creation of complex geometrical structures, facilitates rapid prototyping, and allows the fabrication of micro- and macroscopic structures. This study investigates the use of 3D concrete printing to create Bouligand structures inspired by mantis shrimp. Bouligand-printed strain-hardening cementitious composites (SHCC) with different pitch angles (15°, 30°, 45°, 60°, 75°, and 90°) are fabricated and compared with traditional parallel-printed and mold-cast SHCC. The fracture behavior of these specimens is investigated through three-point bending tests on notched beams. The results reveal that Bouligand-printed specimens exhibit enhanced flexural strength, fracture energy, and fracture toughness, ranging from 0.97 to 1.29 times, 0.99 to 1.63 times and 0.87 to 1.47 times that of the mold-cast specimens, respectively. Bouligand-printed specimens with a pitch angle of 30° exhibits the highest flexural strength, fracture energy, and fracture toughness. The Bouligand-printed SHCC enhance toughness through the synergistic effects of crack twisting and bridging. A finite element model integrating cohesive elements with the concrete plastic damage model is developed to numerically replicate the experimental process. This study highlights the potential of 3D concrete printing for the fabrication of biomimetic concrete structures with superior fracture performance.

Optimizing Hot Embossing of Poly(methyl methacrylate) Microfluidic Chip

Microfluidic research become a more important research field in mechanical and bioengineering fields. The application of microfluidic positively relates to the ability to manufacture micro or precision. Nowadays, the manufacturing in this area is aimed at around 100-500 µm. Here, a hot embossing method is reported to realize microchannel with height and width dimensions of 150-300 µm and 600-800 µm, respectively. This study also shows that the margin factor between the mould/dies to the realized dimension is 50-70% and 5-7% for height and width, respectively.

Site-Selective Biofunctionalization of 3D Microstructures Via Direct Ink Writing.

Two-photon lithography has revolutionized multi-photon 3D laser printing, enabling precise fabrication of micro- and nanoscale structures. Despite many advancements, challenges still persist, particularly in biofunctionalization of 3D microstructures. This study introduces a novel approach combining two-photon lithography with scanning probe lithography for post-functionalization of 3D microstructures overcoming limitations in achieving spatially controlled biomolecule distribution. The method utilizes a diverse range of biomolecule inks, including phospholipids, and two different proteins, introducing high spatial resolution and distinct functionalization on separate areas of the same microstructure. The surfaces of 3D microstructures are treated using bovine serum albumin and/or 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) to enhance ink retention. The study further demonstrates different strategies to create binding sites for cells by integrating different biomolecules, showcasing the potential for customized 3D cell microenvironments. Specific cell adhesion onto functionalized 3D microscaffolds is demonstrated, which paves the way for diverse applications in tissue engineering, biointerfacing with electronic devices and biomimetic modeling.

Multiobjective Optimization Strategy for Enhancing the Efficiency and Quality of Organic Thin-Film Manufacturing with Electrohydrodynamic Atomization Coating.

Electrohydrodynamic atomization coating technology is well-suited for micro-/nanoscale thin-film additive manufacturing. However, there are still some challenges in quality control and parameter adjustment during the coating process. Especially when coating on nonconductive and nonhydrophilic substrates, film quality and thickness uniformity are difficult to control. This paper proposes an optimization strategy for enhancing the efficiency and quality of thin-film manufacturing on nonconductive, nonhydrophilic glass substrates. In this paper, a visual inspection system was developed for in situ inspection and identification of droplet deposition states in the substrate surface. Then, the statistical relationship between the operating parameters and the quality of the deposition state was analyzed by response surface methodology. On this basis, machine learning models and intelligent recommendation frameworks for small data sets were developed to rapidly optimize operating parameters and improve the quality of thin-film coating. Optimization strategy developed by applying the principles of statistical modeling, analysis of variance, and global optimization are more efficient and less costly than traditional parameter screening methods. The experimental results show that optimum deposition quality can be obtained with the recommended operating parameters. And, validation results show a 12.8% improvement in film thickness uniformity. At the same time, no mura defects appeared on the thin-film surface. The proposed optimization strategy can improve the efficiency and quality of additive manufacturing of micro and nano thin films and is beneficial for advancing industrial applications of the electrohydrodynamic atomization coating.

The Design and Analysis of the Fabrication of Micro- and Nanoscale Surface Structures and Their Performance Applications from a Bionic Perspective.

This paper comprehensively discusses the fabrication of bionic-based ultrafast laser micro-nano-multiscale surface structures and their performance analysis. It explores the functionality of biological surface structures and the high adaptability achieved through optimized self-organized biomaterials with multilayered structures. This study details the applications of ultrafast laser technology in biomimetic designs, particularly in preparing high-precision, wear-resistant, hydrophobic, and antireflective micro- and nanostructures on metal surfaces. Advances in the fabrications of laser surface structures are analyzed, comparing top-down and bottom-up processing methods and femtosecond laser direct writing. This research investigates selective absorption properties of surface structures at different scales for various light wavelengths, achieving coloring or stealth effects. Applications in dirt-resistant, self-cleaning, biomimetic optical, friction-resistant, and biocompatible surfaces are presented, demonstrating potential in biomedical care, water-vapor harvesting, and droplet manipulation. This paper concludes by highlighting research frontiers, theoretical and technological challenges, and the high-precision capabilities of femtosecond laser technology in related fields.

The Second Laser Revolution in Chemistry: Emerging Laser Technologies for Precise Fabrication of Multifunctional Nanomaterials and Nanostructures

AbstractThe use of photons to directly or indirectly drive chemical reactions has revolutionized the field of nanomaterial synthesis resulting in appearance of new sustainable laser chemistry methods for manufacturing of micro‐ and nanostructures. The incident laser radiation triggers a complex interplay between the chemical and physical processes at the interface between the solid surface and the liquid or gas environment. In such a multi‐parameter system, the precise control over the resulting nanostructures is not possible without deep understanding of both environment‐affected chemical and physical processes. The present review intends to provide detailed systematization of these processes surveying both well‐established and emerging laser technologies for production of advanced nanostructures and nanomaterials. Both gases and liquids are considered as potential reacting environments affecting the fabrication process, while subtractive and additive manufacturing methods are analyzed. Finally, the prospects and emerging applications of such technologies are discussed.