Controlling the shape of 3D microstructures by temperature and light

Hippler, Marc; Blasco, Eva; Qu, Jingyuan; Tanaka, Motomu; Barner‐Kowollik, Christopher; Wegener, Martin; Bastmeyer, Martin

doi:10.1038/s41467-018-08175-w

Cited by 235 publications

(265 citation statements)

References 41 publications

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“…A trivial way to achieve single‐phase mechanically graded structures is to use different laser powers and exposure times to affect the degree of crosslinking ( Figure a–c), yet, care must be taken as different exposures also affect the resolution of the system …”

Section: Homogeneous Materialsmentioning

confidence: 99%

“…The drawback of these systems is that all the processes are diffusion controlled and thus slow (unless thin structures are built). On this same line, recently Hippler et al designed a series of microactuators of poly( N ‐isopropylacrylamide) which relied on the different swelling behavior expected on different degrees of crosslinking: by varying the laser power, the authors achieved a sort of gray‐scale lithography and were able to induce different degrees of crosslink in the structure, which would respond differently upon heating, causing deformation.…”

Section: Homogeneous Materialsmentioning

confidence: 99%

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Functional Materials for Two‐Photon Polymerization in Microfabrication

Carlotti

Mattoli

2019

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176

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The creation of 3D micro and nanostructures is of particular interest in the fields of photonics, [3] microelectromechanical systems (MEMS), [4] metamaterials, [5] micro/ nanofluidics, [6] cellular proliferation, and differentiation. [7] To create 3D objects of arbitrary shape, 3D printing techniques offer many versatile solutions. [8] Among these, direct laser writing (DLW) allows for the simple preparation of (sub)micrometric objects and patterns with a resolution that can go below 100 nm. [9][10][11] DLW is an additive manufacturing technique based on twophoton polymerization (2PP). To produce a structure, a fs-pulsed long-wavelength laser is focused, by means of optical elements, in a photosensitive resin which is able to crosslink (negative photoresist) or decompose (positive photoresist) under an energetic radiation but that is also transparent at the laser wavelength: if the intensity of the excitation radiation is high enough-as it is the case in the focus-the resin can undergo two (or more)-photon absorption and polymerize (or decompose). [12] Such multiphotons absorption phenomena are nonlinear and the cross-section of the different materials scales with the square (or higher) of the intensity of the radiation. For these reasons, the laser beam can enter the photoresist without being absorbed and trigger the photochemical process(es) only in a small volume around the focus. This volume is named "voxel" being the 3D analogue of a 2D pixel. [13] The absorption probability outside of the voxel is small, thus suppressing the propagation of the reaction and resulting in fine resolution. By moving around the voxel, one can obtain complex 3D structures that can be isolated after developing. [14,15] More than two decades have passed since DLW was proposed [16] and much progress has been made in terms of improving feature size and resolution, [9,[17][18][19][20][21] enlarging the library of materials that can be used, [22][23][24][25] and the possible applications of these finely controlled structures. [6,[25][26][27][28] The research on functional materials-here intended as materials that can be employed in 2PP and show peculiar features that encourage their use in particular applications-has propelled the field of micro/nanostructuring forward by promoting the interdisciplinarity between chemistry, physics, biology, and material science. [26] In this review, we will summarize and critically discuss the different functional materials proposed in the literature, dividing them and confronting them according to their preparation and their application (Figure 1; Table 1). We start the main body discussing the properties and applications of nanocomposite resists used in 2PP. In the second part, Direct laser writing methods based on two-photon polymerization (2PP) are powerful tools for the on-demand printing of precise and complex 3D architectures at the micro and nanometer scale. While much progress was made to increase the resolution and the feature size throughout the years, by carefully designing a material, one...

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Section: Homogeneous Materialsmentioning

confidence: 99%

Section: Homogeneous Materialsmentioning

confidence: 99%

Functional Materials for Two‐Photon Polymerization in Microfabrication

Carlotti

Mattoli

2019

Small

176

126

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“…Photore sponsive hydrogels have been demonstrated as excellent scaf folds for soft actuators, healing materials, adaptive surfaces, dynamic cell microenvironments, and drug release. [148] Photoresponsive hydro gels will continue to advance applications across different fields and further broaden our understanding of dynamic systems. To expand their practical applications, there are several key challenges that need to be resolved.…”

Section: Discussionmentioning

confidence: 99%

Design and Applications of Photoresponsive Hydrogels

2019

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materials with diverse applications in var ious fields due to their tunable chemistry structure and physical properties as well as excellent biocompatibility. [2][3][4][5] Hydrogel research has evolved from static mate rials to smart ones, whose structures and property show responsiveness to external stimuli, including temperature, pH, light, electric or magnetic fields, and the pres ence of enzymes or ion concentrations. [6][7][8][9][10][11] This unprecedented level of control over material properties has driven both med ical and industrial fields into the realm of possibility: controlled drug delivery, [12] chemical sensors, [13] soft actuators or robotics, [14][15][16] or scaffolds for dynamic 3D cell culture. [17] Photoresponsiveness is attractive due to the inherent advan tages of light as stimulus. Light is non invasive and allows remote manipulation of materials without requiring additional reagents, thus, with limited byproducts. Modulation of irradiation parameters, such as light intensity and irradiation time, permits the pre cise control of irradiation dosage, thereby, the degree of photo reactions. Spatial control can be achieved in both 2D and 3D, and temporal control is possible by simply turning the respec tive light source on or off. Wavelengthselective photo chemical reactions can be used for orthogonal photomediation of hydrogel properties. [18] Photoresponsive hydrogels, as externally tunable materials, strongly contribute to the field of soft smart materials in regard to the abovementioned applications. [19] In this review, we elaborate on the design and the emerging appli cations of photoresponsive hydrogels. A comprehensive review about utilizing light for the formation of hydrogels is given by Mi and coworkers. [20] First, we discuss responsive modes and photochemical mechanisms of photoresponsive hydrogels. Fol lowing this, we highlight their applications for dynamic cell environments, smart biointerfaces, controlled drug delivery, photodriven actuators, and lighthealing materials. The review concludes with an outlook on the challenges and potential future approaches for photo responsive hydrogels. Light as Stimulus for Hydrogels Macroscopic Hydrogel PhotoresponsesThe interaction of light with photoresponsive hydrogels can result in different responses, some of which are observable with the bare eye. Those include hydrogel formation or degradation, network contraction or expansion, and chemical modifications in the network, which then have an immediate consequence on Hydrogels are the most relevant biochemical scaffold due to their tunable properties, inherent biocompatibility, and similarity with tissue and cell environments. Over the past decade, hydrogels have developed from static materials to "smart" responsive materials adapting to various stimuli, such as pH, temperature, chemical, electrical, or light. Light stimulation is particularly interesting for many applications because of the capability of contact-free remote manipulation of biomaterial properties and inherent spatial and t...

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“…In order to further expand the repertoire of applications of DLW, new photoresists have to be designed that directly impart functionality onto the structures emerging from the writing process . Our group has been pursuing this goal, producing resists that, e.g., lead to conductive, stimuli‐responsive, and erasable structures . The mechanical properties of microstructures are critical for their application, especially when used as cell scaffolds .…”

Section: Methodsmentioning

confidence: 99%

Tailoring the Mechanical Properties of 3D Microstructures Using Visible Light Post‐Manufacturing

et al. 2019

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the laser, where the square of the optical intensity exceeds the threshold needed to initiate polymerization. In this way, very small feature sizes of less than 100 nm can be achieved. [3,4] Microstructures pre pared via DLW have for example been used in microfluidic chips, [5,6] metama terials, [7] or as 3D microscaffolds for cell and tissue engineering. [8] Commercial resist mixtures are available that are well suited for the rapid generation of stable structures. However, when using standard resists, the resulting microstructures are static. In order to further expand the rep ertoire of applications of DLW, new photo resists have to be designed that directly impart functionality onto the structures emerging from the writing process. [9] Our group has been pursuing this goal, pro ducing resists that, e.g., lead to conduc tive, [10] stimuliresponsive, [11] and erasable structures. [12] The mechanical properties of microstructures are critical for their application, especially when used as cell scaf folds. [13] The mechanical properties of microstructures created via DLW can certainly be tuned by careful adjustment of the writing parameters (i.e., laser power and scan speed), but only to a limited extent. [14] Herein, we present the first photoresist for DLW that is capable of generating microstructures whose mechanical properties can be adjusted postwriting, solely The photochemistry of anthracene, a new class of photoresist for direct laser writing, is used to enable visible-light-gated control over the mechanical properties of 3D microstructures post-manufacturing. The mechanical and viscoelastic properties (hardness, complex elastic modulus, and loss factor) of the microstructures are measured over the course of irradiation via dynamic mechanical analysis on the nanoscale. Irradiation of the microstructures leads to a strong hardening and stiffening effect due to the generation of additional crosslinks through the photodimerization of the anthracene functionalities. A relationship between the loss of fluorescence-a consequence of the photodimerization-and changes in the mechanical properties isestablished. The fluorescence thus serves as a proxy read-out for the mechanical properties. These photoresponsive microstructures can potentially be used as "mechanical blank slates": their mechanical properties can be readily adjusted using visible light to serve the demands of different applications and read out using their fluorescence. 3D MicrostructuresDirect laser writing (DLW) is the only manufacturing tech nique capable of producing truly 3D structures on the micro scopic scale. [1] What differentiates DLW from conventional 3Dprinting techniques is the fact that it exploits twophoton absorption (TPA) to initiate polymerizations. While single photon absorption (SPA) is proportional to the optical inten sity, TPA is proportional to the square of the optical intensity. [2] Thus, polymerization will only take place in the focal volume of

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Controlling the shape of 3D microstructures by temperature and light

Cited by 235 publications

References 41 publications

Functional Materials for Two‐Photon Polymerization in Microfabrication

Functional Materials for Two‐Photon Polymerization in Microfabrication

Design and Applications of Photoresponsive Hydrogels

Tailoring the Mechanical Properties of 3D Microstructures Using Visible Light Post‐Manufacturing

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