Challenges and limits of mechanical stability in 3D direct laser writing

Sedghamiz, Elaheh; Liu, Modan; Wenzel, Wolfgang

doi:10.1038/s41467-022-29749-9

Cited by 20 publications

(11 citation statements)

References 79 publications

(88 reference statements)

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“…between writing speed and material stiffness allows to simply control the mechanical properties of the microstructures and thus highlights the great potential of DLW as a fabrication technology for soft microactuators. [23] For the polymer resist used in this work, a range of writing speeds from 10 to 50 mm s −1 was suitable. Slower writing speeds resulted in microexplosions due to excessive energy input, while faster writing speeds did not cause polymerization at all.…”

Section: Resultsmentioning

confidence: 99%

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

Spratte

Geiger

Colombo

et al. 2022

Adv Materials Technologies

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based on a reversible phase transition at the lower critical solution temperature (LCST) due to a globule-to-coil transition. [8] Below the LCST the polymer is in a hydrophilic, hydrated state, while above the LCST it is in a hydrophobic state. In this state, the interactions of the polymer with itself lead to a higher gain in free energy than would be achieved by solvation energy. The volume of pNIPAM materials in the hydrated, swollen state is much higher than in the hydrophobic state, because water is integrated into the material in the hydrated state. [9] As the actuation of pNIPAM hydrogel is based on its water-dependent shrinkage and swelling, the actuation efficiency and the forces generated by pNIPAM-based actuators critically depend on the in-and outflow of water through the pores of the material. Therefore, the actuation effect, including actuation dynamics as well as stroke forces, can be improved by introducing pores into the material. [10,11] Whereas in previous studies template-assisted methods have proven highly suitable for introducing pores into hydrogels, they lack local microstructural control, while being excellent for structuring macroscopic samples with an interconnected structure. [10] For generating highly efficient pNIPAM-based microactuators, a precisely defined design is required and thus methods are needed that allow for their highly precise 3D structuring at the micrometer scale.The technology of additive nano-and micromanufacturing opens doors to novel and remarkable microengineering possibilities and even enables printing of simple 3D volumetric structures at small scales. [12] Direct laser writing (DLW) involving two-photon polymerization of photoresists is one of the additive manufacturing techniques that can be used to fabricate intricate and miniaturized 3D structures, as they are required for the fabrication of microactuators. By utilizing twophoton absorption and a femtosecond pulsed laser, this fabrication method allows to print in sub-micrometer resolution, even with several materials and on different types of substrates. [13,14] Direct laser writing has also proven highly suitable for fabricating 4D materials, i.e., responsive materials that change their properties due to an external stimulus. [15] For example, the shape of such materials could be controlled at the micrometer scale by temperature and light. [16] Thermoresponsive hydrogels such as poly(N-isopropylacrylamide) (pNIPAM) are highly interesting materials for generating soft actuator systems. Whereas the material has so far mostly been used in macroscopic systems, here it is demonstrated that pNIPAM is an excellent material for generating actuator systems at the micrometer scale. Two-photon direct laser writing is used to precisely structure thermoresponsive pNIPAM hydrogels at the micrometer scale based on a photosensitive resist. This study systematically shows that the surface-to-volume ratio of the microactuators is decisive to their actuation efficiency. The phase transition of the pNIPAM is also demonstrated...

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Section: Resultsmentioning

confidence: 99%

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

Spratte

Geiger

Colombo

et al. 2022

Adv Materials Technologies

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“…Laser-based 3D printing techniques are among the high-resolution 3D photolithography techniques for fabricating complex structures using ultrashort laser pulses. [87] A recent direct laser writing (DLW) technology called multi-photon polymerization (MPP) 3D printing can generate 3D objects with sub-100 nm resolution at scan speeds of 10 000 ms −1 . [88] The technique relies on nonlinear photon absorption by photopolymers to create tiny features in photosensitive material.…”

Section: Laser-based 3d Printing Techniques Of Photopolymersmentioning

confidence: 99%

Re‐Entrant Microstructures for Robust Liquid Repellent Surfaces

Nguyen

Kashaninejad

2023

Adv Materials Technologies

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nano-and microstructures on these surfaces. The anisotropic dewetting behavior of rice leaves and the self-cleaning ability of lotus leaves are two typical examples related to hydrophobicity. [3] In the past decades, a large number of biomimetic functional materials with controlled wettability has been explored for practical applications such as self-cleaning windows, [4] drag reduction, [5] surface treatment of medical devices, [6] waterproof clothes and textiles, [6] anti-corrosion, [7] anti-freezing, [8] heat transfer enhancement, [9] micro/ nanofluidic devices, [10] anti-biofouling surfaces, [11] and transparent self-cleaning surfaces for photovoltaics. [12] On the other hand, hydrophilic or water-loving surfaces are desired in some other applications, such as microfluidics, anti-fogging, liquid separation, or heat transfer. [13] Therefore, many efforts have been conducted to make controllable wetting structures. However, the stability of hydrophobic surface structures remains a significant difficulty, as they may become wet and lose the slip effect due to pollution, [14] air diffusion, [15] external pressure, [16] gravity, [17] vibrations, [16a,18] evaporation, [19] and impacts. [7b] Recently, it has been experimentally and theoretically discovered that the tip shape of pillars is a critical factor contributing to hydrophobic stability. Pillars with mushroom-like structures tend to improve this stability better than those with concave, spherical, or flat tips. [20] The underlying reason is that the net force directed upward competes with the internal pressure so that surfaces do not get wet, thanks to the tip formed on the top of the mushroom-like structure. [21] Oleophilic surfaces can attract oils or organic liquids. Oleophobicity refers to the property of surfaces with low affinity to oils. Oleophilic, oil-loving, surfaces have been known to have disastrous effects, for example, corrosion of oil pipelines, less self-cleaning ability of leaves, and swelling of elastomeric seals. [22] Therefore, we need omniphobic surface which could repel both polar and non-polar liquids. [23] Realizing the significance of superoleophobic surfaces, scientists developed surfaces with unusual patterns, such as re-entrant or negative-slope structures, to achieve a stable liquid-repellent state. [21a] The reentrant structure was first inspired by springtail, Figure 1. [24] The skin of this animal possesses an oil-repellent ability that protects its skin-breathing body against suffocation by complete Superhydrophobic surfaces have many interesting applications because of their self-cleaning, waterproof, anti-biofouling, anti-corrosion, and lowadhesion properties. Accordingly, numerous surfaces with hierarchical micro/ nanostructures are designed and engineered to achieve superhydrophobicity. However, these surfaces have two major problems. First, they lose superhydrophobic properties over time, primarily because of environmental conditions such as vibration, external pressure, evaporation, and pollution. Second, most su...

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“…In addition, the 2PLP process including TEMPO-methacrylate was also studied through Coarse-Grained Molecular dynamics (CGMD) simulation using the Kremer-Grest model of polymers, along with the dynamic recombination of covalent bonds [57][58][59][60] In particular, two formulations (Ink C5 and Ink C6) were simulated. Both inks contain the same cross-linker/ photoinitiator molar ratio (47:1), but a different TEMPO-methacrylate concentration.…”

Section: Optimizing Ink Formulation For Two-photon Laser Printing (2p...mentioning

confidence: 99%

Covalent Adaptable Microstructures via Combining Two‐Photon Laser Printing and Alkoxyamine Chemistry: Toward Living 3D Microstructures

Jia

Spiegel

Welle

et al. 2022

Adv Funct Materials

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Manufacturing programmable materials, whose mechanical properties can be adapted on demand, is highly desired for their application in areas ranging from robotics, to biomedicine, or microfluidics. Herein, the inclusion of dynamic and living bonds, such as alkoxyamines, in a printable formulation suitable for two‐photon 3D laser printing is exploited. On one hand, taking advantage of the dynamic covalent character of alkoxyamines, the nitroxide exchange reaction is investigated. As a consequence, a reduction of the Young´s Modulus by 50%, is measured by nanoindentation. On the other hand, due to its “living” characteristic, the chain extension becomes possible via nitroxide mediated polymerization. In particular, living nitroxide mediated polymerization of styrene results not only in a dramatic increase of the volume (≈8 times) of the 3D printed microstructure but also an increase of the Young's Modulus by two orders of magnitude (from 14 MPa to 2.7 GPa), while maintaining the shape including fine structural details. Thus, the approach introduces a new dimension by enabling to create microstructures with dynamically tunable size and mechanical properties.

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Challenges and limits of mechanical stability in 3D direct laser writing

Cited by 20 publications

References 79 publications

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

Re‐Entrant Microstructures for Robust Liquid Repellent Surfaces

Covalent Adaptable Microstructures via Combining Two‐Photon Laser Printing and Alkoxyamine Chemistry: Toward Living 3D Microstructures

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