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 systems , micro - sensing , and micro robotics . the actuators available to date can perform only simple actions , such as swelling / collapse in a hydrogel matrix , contraction / bending in one direction with the external field . although the recently developed techniques have enabled to fabricate microscopic scale actuating structures , 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 ) . these materials are capable of large deformation ( 20 - 400% ) under various types of external stimuli . 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 scale . lc monomers are synthesized with acrylate moiety , enabling a single - step photo - polymerization . this property gives access to different types of lithographic techniques  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 beam . dlw enables the creation of 3d free - form structures in lce without losing the molecular alignment . first , the resolution can reach the submicron scale , and the structures are truly 3d . previously reported lce micro fabrication methods , e.g. , masked exposure and replica molding , provided resolution down to around 10 m and only have 2d geometry . replica molding technique rarely gives sub - micron resolution and the structural quality is hard to control . thirdly , laser writing provides versatile options for local lc orientation at the microscopic scale . 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 , 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 . 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 . take out one microscope cover slide ( 3 cm in diameter ) , and clean it with acetone using lens tissues . 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 . place another microscope slide ( 1 cm in diameter ) on the top of the spacers . place a drop ( around 2 l ) of uv - curing glue on three different points respectively at the boundary of the upper glass . before the glue penetrates too much into the gap , use uv light to solidify the glue . place a drop ( around 10 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 . use glue to fix the cell on the sample holder and place it into the direct laser writing system . choose a 100x objective , and find the interface at the upper inner surface , followed by tilt correction on this surface . write the structures of designed ip - l grating patterns with a laser power and a scan speed of 6 mw and 60 m / sec , respectively . take out the cell , and immerse the sample in a 2-propanol bath without opening the cell , for 12 - 24 hr . take out the cell from the solvent , and dry it on the hot plate ( 50 c ) for 10 - 20 min . put the prepared mixture inside a glass bottle , and put it on a hot plate set at 70 - 80 c . wait until all the powder melts , add a magnetic stirrer , and mix the mixture for 1 hr ( 90 - 150 rpm ) . place a drop ( around 20 l ) of mixture on the edge of the smaller glass slide and wait until the liquid infiltrates into the cell . 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 . increase the temperature of the cell above 60 c by using a temperature controller on the microscope , then decrease the temperature ( 2 - 10 c per min ) , to measure the temperature range for lc phase . a good homogeneous nematic lc phase can be recognized by observing the image contrast inversion while rotating the sample every 45 with respect to the polarizer axis . 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 ) . 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 . write the lce structures by the use of dlw with a laser power and a scan speed of 4 mw and 60 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 m / sec by using 10x objective ( lce structure is fabricated throughout the entire sample thickness ) . take out the cell , and use a blade to open the cell removing the upper glass slide . 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 . observe light induced deformation by the optical microscope cmos camera ( frame rate 25.8 fps ) . use manual control of the micro - manipulation system ( figure 5 ) to put the glass tip at a position close to the lce microstructures . 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 . use a glass tip to pick up one lce microstructure , and hold it in the air . tune the laser to the high power ( > 100 mw ) , and observe the lce structure deform . take out one microscope cover slide ( 3 cm in diameter ) , and clean it with acetone using lens tissues . 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 . 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 . place a drop ( around 2 l ) of uv - curing glue on three different points respectively at the boundary of the upper glass . before the glue penetrates too much into the gap , use uv light to solidify the glue . place a drop ( around 10 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 . use glue to fix the cell on the sample holder and place it into the direct laser writing system . choose a 100x objective , and find the interface at the upper inner surface , followed by tilt correction on this surface . write the structures of designed ip - l grating patterns with a laser power and a scan speed of 6 mw and 60 m / sec , respectively . take out the cell , and immerse the sample in a 2-propanol bath without opening the cell , for 12 - 24 hr . take out the cell from the solvent , and dry it on the hot plate ( 50 c ) for 10 - 20 min . see the molecular composition in table 1 . put the prepared mixture inside a glass bottle , and put it on a hot plate set at 70 - 80 c . wait until all the powder melts , add a magnetic stirrer , and mix the mixture for 1 hr ( 90 - 150 rpm ) . place a drop ( around 20 l ) of mixture on the edge of the smaller glass slide and wait until the liquid infiltrates into the cell . 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 . increase the temperature of the cell above 60 c by using a temperature controller on the microscope , then decrease the temperature ( 2 - 10 c per min ) , to measure the temperature range for lc phase . a good homogeneous nematic lc phase can be recognized by observing the image contrast inversion while rotating the sample every 45 with respect to the polarizer axis . 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 ) . 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 . write the lce structures by the use of dlw with a laser power and a scan speed of 4 mw and 60 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 m / sec by using 10x objective ( lce structure is fabricated throughout the entire sample thickness ) . take out the cell , and use a blade to open the cell removing the upper glass slide . immerse the structures in a toluene bath for 5 min . 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 . observe light induced deformation by the optical microscope cmos camera ( frame rate 25.8 fps ) . use manual control of the micro - manipulation system ( figure 5 ) to put the glass tip at a position close to the lce microstructures . 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 . use a glass tip to pick up one lce microstructure , and hold it in the air . tune the laser to the high power ( > 100 mw ) , and observe the lce structure deform . 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  300  300 m travelling range for sample translation with a maximum speed of 100 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 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  100 m 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 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 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 ) . 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 . 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. 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 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 c with 0.5 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 m diameter and 20 m height . these cylinders are written on four differently orientated ip - l grating regions ( 1 m period ) . under light excitation , 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 direction . 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  40  20 m size lce stripe with two sections of alignment pattern was fabricated , as schematically shown in figure 7 ( a ) . 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 . 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  300  300 m travel range is used for the sample translation during laser exposure . 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 . 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 . 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 m diameter and 20 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 ) . a ) schematic of two sections of opposite 90 twisted alignments in a single lce stripe . b ) and c ) optical images of a 400 m long lce stripe bending in opposite directions under 532 nm laser illumination ( 3 w mm ) . please click here to view a larger version of this figure . 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 robots , and to open up a plethora of new strategies for the obtainment of light tunable devices . 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 , 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 . 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 ) 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 . third , the height of the structure is limited by the thickness of the cell and the objective working distance . in the laser writing system , 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 . 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 .
liquid crystalline elastomers ( lces ) are smart materials capable of reversible shape - change in response to external stimuli , and have attracted researchers ' 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 .