Special Issue "3D Microfabrication Unleashed: Emerging Applications and New Manufacturing Concepts"

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (31 August 2020).

Special Issue Editor

Dr. Angelo Accardo
E-Mail Website
Guest Editor
Department of Precision and Microsystems Engineering (PME), Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands
Interests: two-photon polymerization; stereolithography; 3D scaffolds; neuroscience; biomimetics

Special Issue Information

Dear colleagues,

The bloom of 3D microfabrication technologies has opened a new era for the prototyping of 3D micro- and nanostructured devices addressing a heterogeneous range of applications. Among these techniques, we find top–down approaches, involving extrusion-based systems (e.g., fused deposition modeling, bioprinting, ink-jet printing) and light-assisted ones (e.g., stereolithography, two-photon polymerization, selective laser sintering) as well as bottom–up strategies (e.g., gas foaming, electrospinning, freeze drying). By exploiting these protocols, it is possible to manufacture objects from the nm- to the cm-scale constituted by single or multiple materials (e.g., polymers, metals, ceramics). The use of 3D fabrication has therefore proven to be a valuable alternative to conventional 2D fabrication approaches in terms of fast-prototyping, cost effectiveness, and reduction of manufacturing steps.

Accordingly, this Special Issue invites contributions (original research papers, review articles, and brief communications) on novel methodological developments in 3D microfabrication. We seek to provide a comprehensive collection with a focus on manufacturing processes, functional materials, and relevant applications, including but not limited to organ-on-chip, microfluidics, optoelectronic structures, energy harvesting devices, and microrobotics, revealing the unlimited potential of this fabrication paradigm.

Asst. Prof. Dr. Angelo Accardo
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • 3D/4D printing
  • cell scaffolds
  • microfluidics
  • energy harvesting
  • optoelectronics
  • microrobotics
  • rapid prototyping

Published Papers (3 papers)

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Research

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Article
Fabrication of Tapered 3D Microstructure Arrays Using Dual-Exposure Lithography (DEL)
Micromachines 2020, 11(10), 903; https://doi.org/10.3390/mi11100903 - 29 Sep 2020
Cited by 4 | Viewed by 1176
Abstract
Three-dimensional (3D) microstructure arrays (MSAs) have been widely used in material science and biomedical applications by providing superhydrophobic surfaces, cell-interactive topography, and optical diffraction. These properties are tunable through the engineering of microstructure shapes, dimensions, tapering, and aspect ratios. However, the current fabrication [...] Read more.
Three-dimensional (3D) microstructure arrays (MSAs) have been widely used in material science and biomedical applications by providing superhydrophobic surfaces, cell-interactive topography, and optical diffraction. These properties are tunable through the engineering of microstructure shapes, dimensions, tapering, and aspect ratios. However, the current fabrication methods are often too complex, expensive, or low-throughput. Here, we present a cost-effective approach to fabricating tapered 3D MSAs using dual-exposure lithography (DEL) and soft lithography. DEL used a strip-patterned film mask to expose the SU-8 photoresist twice. The mask was re-oriented between exposures (90° or 45°), forming an array of dual-exposed areas. The intensity distribution from both exposures overlapped and created an array of 3D overcut micro-pockets in the unexposed regions. These micro-pockets were replicated to DEL-MSAs in polydimethylsiloxane (PDMS). The shape and dimension of DEL-MSAs were tuned by varying the DEL parameters (e.g., exposure energy, inter-exposure wait time, and the photomask re-orientation angle). Further, we characterized various properties of our DEL-MSAs and studied the impact of their shape and dimension. All DEL-MSAs showed optical diffraction capability and increased hydrophobicity compared to plain PDMS surface. The hydrophobicity and diffraction angles were tunable based on the MSA shape and aspect ratio. Among the five MSAs fabricated, the two tallest DEL-MSAs demonstrated superhydrophobicity (contact angles >150°). Further, these tallest structures also demonstrated patterning proteins (with ~6–7 μm resolution), and mammalian cells, through microcontact printing and direct culturing, respectively. Our DEL method is simple, scalable, and cost-effective to fabricate structure-tunable microstructures for anti-wetting, optical-, and bio-applications. Full article
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Communication
Powder Filling and Sintering of 3D In-chip Solenoid Coils with High Aspect Ratio Structure
Micromachines 2020, 11(3), 328; https://doi.org/10.3390/mi11030328 - 22 Mar 2020
Viewed by 897
Abstract
In this study, a 3D coil embedded in a silicon substrate including densely distributed through-silicon vias (TSVs) was fabricated via a rapid metal powder sintering process. The filling and sintering methods for microdevices were evaluated, and the effects of powder types were compared. [...] Read more.
In this study, a 3D coil embedded in a silicon substrate including densely distributed through-silicon vias (TSVs) was fabricated via a rapid metal powder sintering process. The filling and sintering methods for microdevices were evaluated, and the effects of powder types were compared. The parameters influencing the properties and processing speed were analyzed. The results showed that the pre-alloyed powder exhibited the best uniformity and stability when the experiment used two or more types of powders to avoid the segregation effect. The smaller the particle diameter, the better the inductive performance will be. The entire structure can be sintered near the melting point of the alloy, and increasing the temperature increases strength, while resulting in low resistivity. Finally, an 800-µm-high coil was fabricated. This process does not need surface metallization and seed layer formation. The forming process involves only sintering instead of slowly growing copper with a tiny current. Therefore, this process has advantages, such as a process time of 7 h, corresponding to an 84% reduction compared to current electroplating processes (45 h), and a 543% efficiency improvement. Thus, this process is more efficient, controllable, stable, and suitable for mass production of devices with flexible dimensions. Full article
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Review

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Review
Engineered Microgels—Their Manufacturing and Biomedical Applications
Micromachines 2021, 12(1), 45; https://doi.org/10.3390/mi12010045 - 01 Jan 2021
Cited by 2 | Viewed by 1021
Abstract
Microgels are hydrogel particles with diameters in the micrometer scale that can be fabricated in different shapes and sizes. Microgels are increasingly used for biomedical applications and for biofabrication due to their interesting features, such as injectability, modularity, porosity and tunability in respect [...] Read more.
Microgels are hydrogel particles with diameters in the micrometer scale that can be fabricated in different shapes and sizes. Microgels are increasingly used for biomedical applications and for biofabrication due to their interesting features, such as injectability, modularity, porosity and tunability in respect to size, shape and mechanical properties. Fabrication methods of microgels are divided into two categories, following a top-down or bottom-up approach. Each approach has its own advantages and disadvantages and requires certain sets of materials and equipments. In this review, we discuss fabrication methods of both top-down and bottom-up approaches and point to their advantages as well as their limitations, with more focus on the bottom-up approaches. In addition, the use of microgels for a variety of biomedical applications will be discussed, including microgels for the delivery of therapeutic agents and microgels as cell carriers for the fabrication of 3D bioprinted cell-laden constructs. Microgels made from well-defined synthetic materials with a focus on rationally designed ultrashort peptides are also discussed, because they have been demonstrated to serve as an attractive alternative to much less defined naturally derived materials. Here, we will emphasize the potential and properties of ultrashort self-assembling peptides related to microgels. Full article
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