The research leading to these results has received funding from the European Research Council under the European Union&#39;s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no [291349] on photonic micro robotics and from IIT SEED project Microswim. We also acknowledge support by the Ente Cassa di Risparmio di Firenze. We thank the entire Optics of Complex Systems group at LENS for feedback and discussions.

Note: This protocol contains three steps: IP-L grating preparation for LC molecular orientation, DLW in the LCE and light actuation characterization. The schematic of direct laser writing system is shown in Figure 1, while the micro-manipulation system is shown in Figure 5.
1. IP-L Grating Pattern Preparation
<ol>
	<li>Take out one microscope cover slide (3 cm in diameter), and clean it with acetone using lens tissues.</li>
	<li>Place some spacers (glass microspheres) with the help of a metal tip at 3 different points of the glass slide about 0.5 cm away from its center.</li>
	<li>Place another microscope slide (1 cm in diameter) on the top of the spacers. Use a tip to press gently on the top of the upper glass slide.</li>
	<li>Place a drop (around 2 &#181;l) of UV-curing glue on three different points respectively at the boundary of the upper glass.</li>
	<li>Before the glue penetrates too much into the gap, use UV light to solidify the glue. The cell is now formed.</li>
	<li>Place a drop (around 10 &#181;l) of IP-L resin on the boundary of the cell using a pipette. Wait for a few minutes until the liquid is infiltrated into the entire area of the cell.</li>
	<li>Use glue to fix the cell on the sample holder and place it into the direct laser writing system.</li>
	<li>Choose a 100X objective, and find the interface at the upper inner surface, followed by tilt correction on this surface.</li>
	<li>Write the structures of designed IP-L grating patterns with a laser power and a scan speed of 6 mW and 60 &#181;m/sec, respectively. The grating patterns are made by IP-L curve or straight lines.</li>
	<li>Repeat steps 1.8 &#38; 1.9 on the lower inner surface.</li>
	<li>Take out the cell, and immerse the sample in a 2-propanol bath without opening the cell, for 12 - 24 hr.</li>
	<li>Take out the cell from the solvent, and dry it on the hot plate (50 &#176;C) for 10 - 20 min.</li>
</ol>
2. LCE Microstructure Fabrication
<ol>
	<li>Measure ~300 mg monomer mixture on the balance. See the molecular composition in Table 1.</li>
	<li>Put the prepared mixture inside a glass bottle, and put it on a hot plate set at 70 - 80 &#176;C.</li>
	<li>Wait until all the powder melts, add a magnetic stirrer, and mix the mixture for 1 hr (90 - 150 rpm).</li>
	<li>Place the cell on the hot plate at 60 &#176;C.</li>
	<li>Place a drop (around 20 &#181;l) of mixture on the edge of the smaller glass slide and wait until the liquid infiltrates into the cell.</li>
	<li>Transfer the cell to the optical microscope with a crossed polarizer and a temperature controller. Keep everything in the dark during transfer, and put an orange filter before the illumination lamp to filter out the UV.</li>
	<li>Increase the temperature of the cell above 60 &#176;C by using a temperature controller on the microscope, then decrease the temperature (2 - 10 &#176;C per min), to measure the temperature range for LC phase. A mixture with different molecular composition has a different LC phase temperature. A good homogeneous nematic LC phase can be recognized by observing the image contrast inversion while rotating the sample every 45&#176; with respect to the polarizer axis.</li>
	<li>Fix the cell on the sample holder, place it into the DLW system, and set the temperature to reach the LC phase (measured in step 2.7).</li>
	<li>Find the interface at the lower inner surface and perform the tilt correction using a 100X objective, or a 10X objective without finding the interface.</li>
	<li>Write the LCE structures by the use of DLW with a laser power and a scan speed of 4 mW and 60 &#181;m/sec on the lower glass slide by using 100X objective. Otherwise, use with a laser power and a scan speed of 14 mW and 60 &#181;m/sec by using 10X objective (LCE structure is fabricated throughout the entire sample thickness).</li>
	<li>Take out the cell, and use a blade to open the cell removing the upper glass slide.</li>
	<li>Immerse the structures in a toluene bath for 5 min.</li>
	<li>Take out the sample, and dry in the air for 10 min.</li>
</ol>
3. Characterization of Light Actuation of LCE Microstructures
<ol>
	<li>Place the sample in the optical microscope (20X) and focus a laser beam (CW, 532 nm, 50 - 500 mW) by 10X objective on the structures.</li>
	<li>Observe light induced deformation by the optical microscope CMOS camera (frame rate 25.8 fps).</li>
	<li>Use manual control of the micro-manipulation system (Figure 5) to put the glass tip at a position close to the LCE microstructures.</li>
	<li>Switch on the laser at low power (~20 mW), in order to increase the temperature of the LCE (due to light absorption), and thus soften the structure.</li>
	<li>Use a glass tip to pick up one LCE microstructure, and hold it in the air. This process is needed to avoid the adhesion from glass surface.</li>
	<li>Tune the laser to the high power (&#62;100 mW), and observe the LCE structure deform.</li>
	<li>Record the light induced deformation with the microscope camera.</li>
</ol>

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The authors declare that they have no competing financial interests.

IP-L micro-grating orientation technique has been integrated with DLW to orientate liquid crystalline monomers. The subsequently laser-written LCE micro-structures can also be patterned with the designed alignment in the micro scale. This technique allows us to create compound LCE elements which can support multiple functionalities. With outstanding ability to create accurate 3D microstructures and control of actuation, we expect this technique to be used for creating elastomer based microscopic robots14, and to open up a plethora of new strategies for the obtainment of light tunable devices15.
There are two critical steps in the preparation. The first one is that the two glasses of the cell should be tightly glued (step 1.4, 1.5). The UV curing glue preserves the stability of the cell geometry during the development: the movement of a glass of the cell in respect to the other will result in a worst alignment of the LCE. Secondly, the laser writing speed during LCE structure writing should be as high as possible while 100X objective is chosen. Due to the strong swelling of the LCE during the laser writing process, the swelled structure would move out the designed position, thus affecting the quality of the fabricated actuators.
In some cases, the light induced deformability is observed to deteriorate in the structures. This could be due to the dye bleaching under high illumination intensity. Once the dye molecules have been switched off, the LCE structure behaves as a transparent medium, and the light absorption/light induced deformation is suppressed. A lower laser power would be safer for the actuation of LCE microstructures.
There are also some disadvantages of this method. Firstly, the whole process takes a relatively long time. In order to maintain the cell configuration, the first IP-L development process (made by immersing the sample in a solvent bath) is carried out in 2-proponal without opening the cell. The developing time thus depends on the cell size and the thickness of the gap, and usually takes 12 - 24 hours. Replacing the IP-L grating with other laser writable patterns, such as laser induced ablation pattern and laser induced chemically modified surface, could result in LC alignment and in a great reduction of the fabrication time. Second, LCE is a soft matter which always suffers adhesion on the glass substrate. Light induced deformation has been suppressed when the microstructures stick onto the surface. Third, the height of the structure is limited by the thickness of the cell and the objective working distance. In the laser writing system, the maximum height is around 100 &#181;m. Recently developed 3D printing techniques could be a good candidate for creating light actuated LCE structure from mesoscopic to macroscopic scale. However, maintaining the molecular orientation during polymerization could be the main issue of concern.
This technique is unique because allows one to obtain 3D free-form actuators at the truly microscale, which is not possible with other existing techniques. LCE microstructures may be patterned with different molecular orientations and functionalities. Implementation of such technique by further chemical engineering, will enable to make the actuators sensitive to other stimulus sources and will open up to develop efficient microrobots and soft photonic devices.

Microactuators are microscopic structures that can transmit external energy for the operation of another mechanism or system. Due to the compact size and remote control capability, they have been widely used in lab-on-chip systems1, micro-sensing2, and micro robotics3. The actuators available to date can perform only simple actions, such as swelling/collapse in a hydrogel matrix4, contraction/bending5 in one direction with the external field. Although the recently developed techniques have enabled to fabricate microscopic scale actuating structures6, it is still a big challenge to control these actuations in the same length scale. This paper reports a method to prepare 3D light activate microstructures with controllable actuation properties. The technique is based on direct laser writing (DLW), and it is demonstrated in liquid crystalline elastomers (LCEs).
LCEs are soft polymers combing the property of elastomer and liquid crystalline orientation. These materials are capable of large deformation (20 - 400%) under various types of external stimuli7. The advantage of using LCEs for microactuators is the convenience of engineering molecular order in the structures, which allows for controlling the actuation in the microscopic scale8. LC monomers are synthesized with acrylate moiety, enabling a single-step photo-polymerization. This property gives access to different types of lithographic techniques&#160;for fabrication of 3D microstructures. Azo-dyes as photo responsive molecules are linked to the polymer network by co-polymerization process. Such molecules combine their strong light response ability (trans to cis isomerization) with the light induced heating of the system affording light controlled deformation.
DLW is a technique to obtain polymer structures in a photosensitive material by spatial control of a focused laser beam9. DLW enables the creation of 3D free-form structures in LCE without losing the molecular alignment6. There are several advantages of DLW in the fabrication of LCE microactuators. First, the resolution can reach the submicron scale, and the structures are truly 3D6. Previously reported LCE micro fabrication methods, e.g., masked exposure10 and replica molding11, provided resolution down to around 10 &#181;m and only have 2D geometry. Secondly, DLW is a non-contact fabrication process. A suitable solvent can develop high quality structures maintaining the designed configuration. Replica molding technique rarely gives sub-micron resolution12 and the structural quality is hard to control. Thirdly, laser writing provides versatile options for local LC orientation at the microscopic scale8,13. Among various types of LC orientation techniques, rubbing is the most efficient way to orientate LC molecules and has been widely used in preparing of LCE thin film. This has been generally achieved by rubbing on polymer layers to generate microgrooves on the inner surfaces of a cell infiltrated by LC monomers. Due to the surface anchoring effect, such microgrooves are able to orientate the LC molecule along the groove direction. DLW enables the direct fabrication of those microgrooves on the selected region in the pre-designed direction with much higher accuracy. All these features make DLW a perfect, unique technique for fabrication and control of actuation in the microscopic scale.
Based on DLW, LCE microstructures may be patterned with different molecular orientations. With compound alignment within a single LCE structure, multifunctional actuations become possible. The method can be used for fabrication of LCE microactuators with any kind of LC monomer mixture. By further chemical engineering, it is possible to make the actuators sensitive to other stimulus sources, e.g., humidity or illumination at different wavelength.

<table><tbody><tr><td>Molecular: LC monomer</td><td>SYNTHON Chemicals GmbH &amp;amp; Co. KG</td><td>ST03866</td><td>~78 mol% in the mixture</td></tr><tr><td>Molecular: LC crosslinker</td><td>SYNTHON Chemicals GmbH &amp;amp; Co. KG</td><td>ST03021</td><td>20 mol% in the mixture</td></tr><tr><td>Molecular: Azo dye</td><td>Synthesis referring to Ref. 6</td><td></td><td>1 mol% in the mixture. Light sensitive component, can be excluded in the fabrication for heat driven actuators.</td></tr><tr><td>Molecular: Initiator</td><td>Sigma</td><td>Irgacure 369</td><td>1 - 2 mol% in the mixture</td></tr><tr><td>Spacer</td><td>Thermo scientific</td><td></td><td>Microsphere with diameter from 10 to 100 &amp;micro;m.</td></tr><tr><td>IP-L</td><td>Nanoscribe GmbH</td><td></td><td></td></tr><tr><td>UV curing glue</td><td>Homemade</td><td></td><td>IP-L with 1 wt% initiator (Irgacure 369)</td></tr><tr><td>Microscope cover slide</td><td>MENZEL-GL&amp;Auml;SER</td><td></td><td>Diameter: 1 or 3 mm, Thickness: 0.16 - 0.19 mm</td></tr><tr><td>UV LED lamp</td><td>Thorlabs</td><td>M385L2-C4</td><td>Wavelength: 385 &amp;#177; 10 nm</td></tr><tr><td>532 nm laser</td><td>Shanghai Dream Lasers</td><td>SDL-532-500T</td><td>500 mW laser</td></tr><tr><td>Direct Laser Writing system</td><td>Nanoscribe GmbH</td><td></td><td></td></tr><tr><td>Hot plate</td><td>Linkam Scientific Instruments Ltd.</td><td>PE120</td><td>Temperature range: -20 to 120 &amp;deg;C</td></tr><tr><td>Microscope</td><td>Zeiss</td><td>Axio Observer A1</td><td>With crossed polarizers</td></tr><tr><td>Micro-manipulator</td><td>Narishige</td><td>MHW-3</td><td></td></tr></tbody></table>

free-form light actuators &#8212; fabrication and control of actuation in microscopic scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Figure 1 shows the optical set up for laser writing. The system consists of a 780 nm fiber laser generating 130 fsec pulse at the repetition rate of 100 MHz. The laser beam is reflected into a telescope to adjust the beam profile to the optical microscope objective aperture where it is focused into the sample. On the microscope, a 3D piezo stage is installed with a 300 &#215; 300 &#215; 300 &#181;m3 travelling range for sample translation with a maximum speed of 100 &#181;m/sec at 2 nm resolution. Linearly polarized light from a red lamp illuminates the sample from the top, while the image is collected at the bottom by the same objective and reflected by a beam splitter into a CCD camera. Before the camera, another polarizer is used to obtain cross polarized illumination for enhanced contrast.
Figure 2 shows the scanning electron microscope (SEM) images of the laser written IP-L micrograting patterns (Step 1). The groove spacing is in the range of 400 - 1,200 nm, while the height of the grooves (top-to-valley) is around 700 nm. Grating patterns with different orientations can induce different LC alignments, depending on the desired actuation of the LCE element.
Figure 3 shows the LC monomer orientation induced by the IP-L grating patterns (Step 2.7). First, four kinds of micro-grating pattern with 100 &#215; 100 &#181;m2 size each were fabricated on opposite sides of a glass cell (schematically shown in Figure 3a). Due to the surface anchoring, the infiltrated LC monomers have been oriented along with the grating lines direction, thus exhibiting 45&#176; contrast inversion in the polarized optical microscope (POM) image (Figure 3b).
Figure 4 shows the SEM images of an LCE nano dot/line fabricated on IP-L grating networks with different orientation (Step 2.10). Within the grating network, the LCE structures become more confined, with much higher resistance to the development in toluene. A minimum width of the disconnected LCE has been measured to be ~300 nm, which is consistent with the resolution of DLW without the grating pattern. Another interesting approach for photonic application could be the realization of large scale periodic structure. Figure 4 (c, d) shows 2D LCE periodic structures within a micro-grating network. The alignments are well preserved inside these nanostructures, as shown in the inserted POM images of Figure 4 (c, d). However, light induced deformation could not be obtained in these nanostructures. This is because within the IP-L grating, the nano-LCE elements have been highly confined and adhesion prevents any visible deformation.
The micro manipulation system is based on a home-made reflected microscope and is shown schematically in Figure 5. A 10X objective is fixed on a lens tube placed on a vertically standing optical breadboard. A 730 nm IR LED light source is used for illumination through a non-polarized beam splitter. The reflected image is collected by the same objective and projected on the camera. A continuous solid state 532 nm laser is coupled into the objective by a long pass dichroic mirror (50% transmission and reflection at 567 nm) at an incidence angle of 45&#176;. A power meter measures the transmitted beam after the dichroic mirror for real time detection of laser power. A loosely focused laser spot of ~150 &#181;m diameter generates maximum illumination intensity of ~10 W/mm2. Laser intensity is controlled by a variable neutral density filter placed in front of the laser. Below the objective, a 3D manual translation stage is used for sample translation. A heating stage installed on the translation stage is used for precise control of the sample temperature in a range from -20 to 120 &#176;C with 0.5 &#176;C accuracy. Two glass tips mounted on two manual translation stages have been placed on the left and right sides, near the sample position. Structure micro manipulation can be realized by carefully moving the tips with the help of the translation stages.
To demonstrate the alignment and deformation correlation, we fabricate four LCE cylindrical structures with 60 &#181;m diameter and 20 &#181;m height. These cylinders are written on four differently orientated IP-L grating regions (1 &#181;m period). Under light excitation, the dyes inside the LCE absorb light energy and transfer it into the network. The LCE structures are heated up and then undergo phase transition (nematic to isotropic). Such phase transition is also helped by the trans to cis isomerization of the dye under the same light stimuli. Thus, the structures contract along the original LC alignment director and expand in the perpendicular direction7. Depending on different local alignments induced by the IP-L gratings, these structures deform along different directions, as shown in Figure 6 (Step 3.1).
This technique enables the creation of compound actuators, which contain more than one type of alignment in one single structure. A 400 &#215; 40 &#215; 20 &#181;m3 size LCE stripe with two sections of alignment pattern was fabricated, as schematically shown in Figure 7 (a). Those alignment sections contain each a 90&#176; twisted orientation in a different direction. The surface with parallel alignment contracts, while the one with perpendicular alignment expands under light illumination. The structure has been picked up by the micromanipulation system, and held in the air by a glass tip. Double bending was observed under light illumination (Step 3.3). A modulated laser beam (using an optical chopper) can induce cyclical deformations. LCE can respond following the laser modulation frequency (&#62;1k Hz). However, the deformation amplitude decreases with increasing frequency14.
<img alt="Figure 1" src="/files/ftp_upload/53744/53744fig1.jpg" /> 
Figure 1: Optical Set Up for Direct Laser Writing. A 780 nm laser beam (130 fsec pulse, repetition rate of 100 MHz) is coupled into a microscope and focused by an optical microscope objective into the sample. A 3D piezo stage with 300 &#215; 300 &#215; 300 &#181;m3 travel range is used for the sample translation during laser exposure. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53744/53744fig2.jpg" /> 
Figure 2: SEM Images of IP-L Micro-gratings. a) Unidirectional parallel line structure. b) Radial grating pattern. Scale bar: 10 &#181;m. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53744/53744fig3.jpg" /> 
Figure 3: IP-L Micro-grating Induce LC Orientation. a) Schematic of the micro-grating patterns designed for the LC orientation. b) POM image of the the LC orientation induced by the micrograting patterns. The scale bar is 50 &#181;m. The red color is due to the filter which prevents the photo-polymerization. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53744/53744fig4.jpg" /> 
Figure 4: SEM Images of LCE Nanostructures Embedded Inside IP-L Grating Networks. a) and b) Two micro-grating patterns were fabricated by DLW along different directions, while LCE nanodots are fabricated within the grating network. c) and d) Periodic LCE nano structures embedded within the same type of IP-L gratings. Insets are POM image of the structures. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53744/53744fig5.jpg" /> 
Figure 5: Schematic of the Micromanipulation Setup. A CW solid state 532 nm laser is coupled into a home-made microscope system. A 10X Objective is used for imaging and focusing the 532 nm laser for excitation. Two manual translation stages equipped with glass tip manipulators are used for sample micro-manipulation. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/53744/53744fig6.jpg" /> 
Figure 6: Light Actuation of LCE Micro-cylinders on Four Different IP-L Micrograting Regions with Different Orientations. a) Four LCE cylindrical structures with 60 &#181;m diameter and 20 &#181;m height, written on four differently orientated micro-grating regions. b) LCE cylinders deform along different axes (depending on the grating induced alignments) when exposed to a 532 nm laser radiation (10 W mm-2). Scale bar: 100 &#181;m. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/53744/53744fig7.jpg" /> 
Figure 7: Light-driven Deformation of LCE Microstructures with Multiple Molecular Alignments. a) Schematic of two sections of opposite 90&#176; twisted alignments in a single LCE stripe. b) and c) Optical images of a 400 &#181;m long LCE stripe bending in opposite directions under 532 nm laser illumination (3 W mm-2)8. <a href="https://www.jove.com/files/ftp_upload/53744/53744fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

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Research

JoVE Journal

Engineering

9.2K Views.  University of Florence. Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Video: Free-form Light Actuators — Fabrication and Control of Actuation in Microscopic Scale

Microfabricated Platforms for Mechanically Dynamic Cell Culture

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or fundamental cell biology studies is limited by current bioreactor technologies, which cannot simultaneously apply a variety of mechanical stimuli to cultured cells. In order to address this issue, we have developed a series of microfabricated platforms designed to screen for the effects of mechanical stimuli in a high-throughput format. In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and further demonstrate how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or ...

Bioengineering

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Chemistry

Fabrication of Soft Pneumatic Network Actuators with Oblique Chambers

Soft pneumatic network actuators have become one of the most promising actuation devices in soft robotics which benefits from their large bending deformation and low input. However, their monotonous bending motion form in two-dimensional (2-D) space keeps them away from wide applications. This paper presents a detailed fabrication method of soft pneumatic network actuators with oblique chambers, to explore their motions in three-dimensional (3-D) space. The design of oblique chambers enables actuators with tunable coupled bending and twisting capabilities, which gives them the possibility to move dexterously in flexible manipulators, to become biologically inspired robots and medical devices. The fabrication process is based on the molding method, including the silicone elastomer preparation, chamber and base parts fabrication, actuator assembly, tubing connections, checks for leaks, and actuator repair. The fabrication method guarantees the rapid manufacturing of a series of actuators with only a few modifications in the molds. The test results show the high quality of the actuators and their prominent bending and twisting capabilities. Experiments of the gripper demonstrate the advantages of the development in adapting to objects with different diameters and providing sufficient friction.

Here we present a fabrication method of soft pneumatic network actuators with oblique chambers. The actuators are capable of generating coupled bending and twisting motions, which broadens their application in soft robotics.

Soft pneumatic network actuators have become one of the most promising actuation devices in soft robotics which benefits from their large bending ...

Rapid Manufacturing of Thin Soft Pneumatic Actuators and Robots

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with an ultrathin form factor using a heat press and a laser cutter machine. The method starts with the lamination of thermoplastic polyurethane (TPU) sheets using a heat press for 10 min at the temperature of ~93 &#176;C. Next, the parameters of the laser cutter machine are optimized to produce a rectangular balloon with maximum burst pressure. Using the optimized parameters, the soft actuators are laser cut/welded three times sequentially. Next, a dispensing needle is attached to the actuator, allowing it to be inflated. The effect of geometrical parameters on the deflection of the actuator are studied systematically by varying the channel width and length. Finally, the performance of the actuator is characterized using an optical camera and a fluid dispenser. Conventional fabrication methods of soft pneumatic actuators based on silicone molding are time consuming (several hours). They also result in strong but bulky actuators, which limits the actuator&#8217;s applications. Moreover, microfabrication of thin pneumatic actuators is both time-consuming and expensive. The proposed manufacturing method in the current work resolves these issues by introducing a fast, simple, and cost-effective fabrication method of ultrathin pneumatic actuators.

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with a thin form factor. The fabrication method starts with lamination of thermoplastic polyurethane (TPU) sheets followed by laser cutting/welding of a two-dimensional pattern to form actuators and robots.

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with an ultrathin form factor using a heat press and a ...

Fabrication of Carbon-Based Ionic Electromechanically Active Soft Actuators

Ionic electromechanically active capacitive laminates are a type of smart material that move in response to electrical stimulation. Due to the soft, compliant and biomimetic nature of this deformation, actuators made of the laminate have received increasing interest in soft robotics and (bio)medical applications. However, methods to easily fabricate the active material in large (even industrial) quantities and with a high batch-to-batch and within-batch repeatability are needed to transfer the knowledge from laboratory to industry. This protocol describes a simple, industrially scalable and reproducible method for the fabrication of ionic carbon-based electromechanically active capacitive laminates and the preparation of actuators made thereof. The inclusion of a passive and chemically inert (insoluble) middle layer (e.g., a textile-reinforced polymer network or microporous Teflon) distinguishes the method from others. The protocol is divided into five steps: membrane preparation, electrode preparation, current collector attachment, cutting and shaping, and actuation. Following the protocol results in an active material that can, for example, compliantly grasp and hold a randomly shaped object as demonstrated in the article.

This article describes a fast and simple manufacturing process of ionic electromechanically active composite materials for actuators in biomedical, biomimetic and soft robotics applications. The key fabrication steps, their importance for the actuators&#39; final properties, and some of the main characterization techniques are described in detail.

Ionic electromechanically active capacitive laminates are a type of smart material that move in response to electrical stimulation. Due to the soft, ...

Fabrication and Implementation of a Reference-Free Traction Force Microscopy Platform

Quantifying cell-induced material deformation provides useful information concerning how cells sense and respond to the physical properties of their microenvironment. While many approaches exist for measuring cell-induced material strain, here we provide a methodology for monitoring strain with sub-micron resolution in a reference-free manner. Using a two-photon activated photolithographic patterning process, we demonstrate how to generate mechanically and bio-actively tunable synthetic substrates containing embedded arrays of fluorescent fiducial markers to easily measure three-dimensional (3D) material deformation profiles in response to surface tractions. Using these substrates, cell tension profiles can be mapped using a single 3D image stack of a cell of interest. Our goal with this methodology is to make traction force microscopy a more accessible and easier to implement tool for researchers studying cellular mechanotransduction processes, especially newcomers to the field.

This protocol provides instructions for implementing multiphoton lithography to fabricate three-dimensional arrays of fluorescent fiducial markers embedded in poly(ethylene glycol)-based hydrogels for use as reference-free, traction force microscopy platforms. Using these instructions, measurement of 3D material strain and calculation of cellular tractions is simplified to promote high-throughput traction force measurements.

Quantifying cell-induced material deformation provides useful information concerning how cells sense and respond to the physical properties of their ...

Using a Microfluidics Device for Mechanical Stimulation and High Resolution Imaging of C. elegans

One central goal of mechanobiology is to understand the reciprocal effect of mechanical stress on proteins and cells. Despite its importance, the influence of mechanical stress on cellular function is still poorly understood. In part, this knowledge gap exists because few tools enable simultaneous deformation of tissue and cells, imaging of cellular activity in live animals, and efficient restriction of motility in otherwise highly mobile model organisms, such as the nematode Caenorhabditis elegans. The small size of C. elegans makes them an excellent match to microfluidics-based research devices, and solutions for immobilization have been presented using microfluidic devices. Although these devices allow for high-resolution imaging, the animal is fully encased in polydimethylsiloxane (PDMS) and glass, limiting physical access for delivery of mechanical force or electrophysiological recordings. Recently, we created a device that integrates pneumatic actuators with a trapping design that is compatible with high-resolution fluorescence microscopy. The actuation channel is separated from the worm-trapping channel by a thin PDMS diaphragm. This diaphragm is deflected into the side of a worm by applying pressure from an external source. The device can target individual mechanosensitive neurons. The activation of these neurons is imaged at high-resolution with genetically-encoded calcium indicators. This article presents the general method using C. elegans strains expressing calcium-sensitive activity indicator (GCaMP6s) in their touch receptor neurons (TRNs). The method, however, is not limited to TRNs nor to calcium sensors as a probe, but can be expanded to other mechanically-sensitive cells or sensors.

Using a Microfluidics Device for Mechanical Stimulation and High Resolution Imaging of C. elegans

New tools for mechanobiology research are needed to understand how mechanical stress activates biochemical pathways and elicits biological responses. Here, we showcase a new method for selective mechanical stimulation of immobilized animals with a microfluidic trap allowing high-resolution imaging of cellular responses.

Free-form Light Actuators — Fabrication and Control of Actuation in Microscopic Scale

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