Artificial muscles and muscle tissues from photoresponsive fibers

Abstract

In one aspect, a liquid crystal elastomer actuator fiber includes a waveguide core. A shell of aligned azo-liquid crystal elastomer sheaths the waveguide core. An outer electrode shell sheaths the shell of aligned azo-liquid crystal elastomer.

Description

ARTIFICIAL MUSCLES AND MUSCLE TISSUES FROM PHOTORESPONSIVE FIBERSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a PCT application claiming benefit of priority from United States Provisional Patent Application Serial No. 63 / 604,15, entitled “Artificial Muscles and Muscle Tissues from Photoresponsive Fibers,” filed on November 29, 2023, all of which is incorporated herein by reference in its entirety for all purposes.STATEMENT OF FEDERALLY FUNDED RESEARCH OR SPONSORSHIP

[0002] This invention was made with government support under grant number N00014-22- 1-2447 P00001 awarded by the Department of Defense, Department of the Navy, and Office of Naval Research. The government has certain rights in the inventions.TECHNICAL FIELD

[0003] The present disclosure generally relates to robotics, and more specifically to photoresponsive fiber.BACKGROUND

[0004] Soft robotics represents an auspicious, multi-disciplinary paradigm for designing truly bioinspired robots. Along with the related disciplines of biorobotics, microrobotics, and activematter, soft robotics has demonstrated that utilizing soft materials and structures in robot design gives rise to machines that bypass many of the shortcomings that artificial machines currently face by enabling agents to appeal to the physical side of machine intelligence. For example, soft robots more easily adapt to the unstructured and dynamic nature of real-world environments than traditional rigid robots do. They can possess more complex and multifunctional behaviors, and their very bodies can participate in computation and control. However, despite over two decades of progress, a long-standing challenge in soft robotics is untethered operation. Tethers to offboard power and control are common throughout robotics, but they are notoriously prevalent in soft robotics. The inability to practically and effectively embody physical and computational intelligence within an untethered, freely locomoting material body will impede future efforts to realize soft, bioinspired machines that can continuously and autonomously perform tasks in real- world environments without human supervision.

[0005] The description provided in the background section should not be assumed to be prior art merely because it is mentioned in or associated with the background section. The background section may include information that describes one or more aspects of the subject technology.SUMMARY

[0006] In certain aspects, the disclosed technology provides a hybrid, multifunctional artificial muscle tissue design based on bundles of LCE-ionogel composite fibers. In certain aspects, individual fibers are comprised of a deformable, ionogel waveguide core embedded within an aligned, phototropic LCE shell, which contains photoresponsive azobenzene moieties. Thewaveguide enables the light required for optomechanical actuation to propagate along the length of the fiber, driving large-scale contractions that are difficult to achieve via conventional remote irradiation strategies. By ensheathing the entire fiber with another soft ionogel electrode, electric fields can be generated across the LCE shell to electrostatically drive rapid cis-trans isomerization of azobenzene groups to expedite reversibility. 3D printed bundles of fibers give rise to truly bioinspired, bulk artificial muscle tissues with distributed proprioception and actuation capabilities. The novel materials, artificial muscle designs, and hybrid optoelectronic actuation mechanism discussed below will afford high force generation, high actuation bandwidth, and high energy efficiency actuation for untethered soft machine locomotion in underwater and terrestrial scenarios. Moreover, the proposed artificial muscle tissues lay the foundation for neuromorphic control of untethered soft, bioinspired machines.

[0007] According to certain aspects of the present disclosure, a liquid crystal elastomer actuator fiber is provided. The liquid crystal elastomer actuator fiber includes a waveguide core. A shell of aligned azo-liquid crystal elastomer sheaths the waveguide core. An outer electrode shell sheaths the shell of aligned azo-liquid crystal elastomer. In certain aspects, the waveguide core is an ionogel waveguide core. In certain aspects, the waveguide core is transparent in ultraviolet light and blue light. In certain aspects, the waveguide core is formed from an ionic liquid. In certain aspects, the ionic liquid is one of l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, l-Butyl-3-methylimidazolium thiocyanate, and hexyltriphenylphosphonium di cyanamide. In certain aspects, the shell of aligned azo-liquid crystal elastomer is photoactuatable. In certainaspects, the shell of aligned azo-liquid crystal elastomer is photoactuatable from an extended state to a contracted state, wherein the shell of aligned azo-liquid crystal elastomer is / / ' / z / .s-azo-liquid crystal elastomer in the extended state and is cv.s-azo-liquid crystal elastomer in the contracted state.

[0008] According to certain aspects of the present disclosure, an artificial muscle is provided. The artificial muscle includes a plurality of liquid crystal elastomer actuator fibers, wherein each liquid crystal elastomer actuator fiber includes a waveguide core, a shell of aligned azo-liquid crystal elastomer sheathing the waveguide core, and an outer electrode shell sheathing the shell of aligned azo-liquid crystal elastomer. In certain aspects, the waveguide core is an ionogel waveguide core. In certain aspects, the waveguide core is transparent in ultraviolet light and blue light. In certain aspects, the waveguide core is formed from an ionic liquid. In certain aspects, the ionic liquid is one of l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, l-Butyl-3- methylimidazolium thiocyanate, and hexyltriphenylphosphonium dicyanamide. In certain aspects, the shell of aligned azo-liquid crystal elastomer is photoactuatable. In certain aspects, the shell of aligned azo-liquid crystal elastomer is photoactuatable from an extended state to a contracted state, wherein the shell of aligned azo-liquid crystal elastomer is Zrans-azo-liquid crystal elastomer in the extended state and is cv.s-azo-li uid crystal elastomer in the contracted state.

[0009] According to certain aspects of the present disclosure, method of fabricating a liquid crystal elastomer actuator fiber is provided. The method includes feeding an azo-LCE ink to a first inlet of a custom nozzle. The method includes feeding an ionogel waveguide ink to a second inlet ofthe custom nozzle. The method includes feeding an outer electrode shell ink to a third inlet of the custom nozzle. The method includes simultaneously extruding the azo-LCE ink, the ionogel waveguide ink, and the outer electrode shell ink through a first outlet of the custom nozzle, a second outlet of the custom nozzle, and a third outlet of the custom nozzle, respectively, wherein the first outlet of the custom nozzle is disposed between the second outlet and the third outlet. In certain aspects, the azo-LCE ink is photocrosslinkable. In certain aspects, the method further includes photocrosslinking the azo-LCE ink that is extruded. In certain aspects, the method further includes photopolymerizing the azo-LCE ink that is extruded. In certain aspects, the azo-LCE ink that is extruded is photopolymerized at a blue-green wavelength. In certain aspects, the azo-LCE ink is synthesized using one-pot, aza-Michael addition reactions.

[0010] It is understood that other configurations of the subject technology will become readily apparent to those skilled in the art from the following detailed description, wherein various configurations of the subject technology are shown and described by way of illustration. As will be realized, the subject technology is capable of other and different configurations and its several details are capable of modification in various other respects, all without departing from the scope of the subject technology. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are included to provide further understanding and are incorporated in and constitute a part of this specification, illustrate disclosed embodiments andtogether with the description serve to explain the principles of the disclosed embodiments. In the drawings:

[0012] FIG. 1 is a perspective diagram illustrating an artificial muscle comprising a plurality of photoactuatable LCEA fibers with an exploded view of a cross section of a photoactuatable LCEA fiber, in accordance with certain aspects of the disclosure.

[0013] FIG. 2 is a diagram illustrating an untethered soft robot with an artificial muscle comprising a plurality of photoactuable LCE fibers, and depicting a photoactuable LCEA fiber in an extended state and a contracted state, in accordance with certain aspects of the disclosure.

[0014] FIG. 3 is a diagram illustrating an artificial muscle comprising a plurality of photoactuable LCE fibers, and depicting a photoactuable LCEA fiber in an extended state and a contracted state, in accordance with certain aspects of the disclosure.

[0015] FIG. 4 is a diagram illustrating extrusion of an azo-LCE ink, an ionogel waveguide ink, and an outer electrode shell ink through a custom nozzle with an exploded view of a cross section of a photoactuatable LCEA fiber, in accordance with certain aspects of the disclosure.

[0016] FIG. 5 is a cross-sectional view of an end of the custom nozzle of FIG. 4, in accordance with certain aspects of the disclosure.

[0017] FIG. 6 is a diagram illustrating aza-Michael addition of mesogens into azo-LCE oligomers and reaction to form 3D printed liquid crystal elastomers, in accordance with certain aspects of the disclosure.

[0018] FIG. 7 is a front view of the custom nozzle of FIG. 4, in accordance with certain aspects ofthe disclosure.

[0019] FIG. 8 is a bottom end view of the custom nozzle of FIG. 7, in accordance with certain aspects of the disclosure.

[0020] FIG. 9 is a diagram illustrating a printing setup environment, in accordance with certain aspects of the disclosure.

[0021] FIG. 10 is a diagram illustrating a printing setup environment, in accordance with certain aspects of the disclosure.

[0022] FIG. 11 is perspective view of an untethered soft robotic quadruped, in accordance with certain aspects of the disclosure.

[0023] FIG. 12 is a diagram illustrating extrusion of a photoactuable LCEA fiber that is photocrosslinked with a lamp, in accordance with certain aspects of the disclosure.

[0024] FIG. 13 illustrates a chemical structure of l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0025] FIG. 14 illustrates a chemical structure of l-Butyl-3-methylimidazolium thiocyanate.

[0026] FIG. 15 illustrates a chemical structure of hexyltriphenylphosphonium di cyanamide.

[0027] FIG. 16 illustrates an eye mimic mechanically coupled to a skull via a plurality of photoactuable LCEA fibers, in accordance with certain aspects of the disclosure.

[0028] In one or more implementations, not all of the depicted components in each figure may be required, and one or more implementations may include additional components not shown in a figure. Variations in the arrangement and type of the components may be made without departingfrom the scope of the subject disclosure. Additional components, different components, or fewer components may be utilized within the scope of the subject disclosure.DETAILED DESCRIPTION

[0029] The detailed description set forth below is intended as a description of various implementations and is not intended to represent the only implementations in which the subject technology may be practiced. As those skilled in the art would realize, the described implementations may be modified in various different ways, all without departing from the scope of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0030] The disclosed technology provides an actuator design with an optoelectronic strategy for LCE actuation and represents a first embodiment of a phototropic LCE with integrated waveguides for improved actuation and control. The disclosed technology provides advantages in that it presents a strategy for fabricating truly bioinspired artificial muscle tissues. By extruding multiple individually-addressable artificial muscle fibers into larger artificial muscle tissues, the disclosed technology provides soft actuators with complex and distributed actuation and proprioceptive capabilities.

[0031] In certain aspects, the present disclosure provides soft artificial muscle tissues capable of high-power density, energy efficient actuation for untethered locomotion in soft machines. The soft artificial muscle tissues can be 3D printable and involve the design and fabrication of optoelectronically-stimulated, liquid crystal elastomer and ionogel composite fibers. Bundles ofindividually-addressable artificial muscle fibers are readily organized into large-scale artificial muscle tissues with distributed actuation and proprioceptive capabilities. The disclosed technology provides advantages over three key technological gaps for designing self-sensing artificial muscles for robust, reliable, and bioinspired locomotion in untethered soft machines. First, most traditional soft matter actuators suffer from key performance and hardware trade-offs. Liquid crystal elastomer actuators (LCEAs) are a popular option for driving high strain and high force actuation, but current varieties do not offer energy efficient performance. Phototropic LCEAs can theoretically offer a more energy efficient path to LCE actuation, but requirements for remote light sources and short penetration depths of incident optical stimuli are major barriers to their practical adoption. The disclosed technology provides photoactuated LCEA fibers with internal cores of deformable ionogel waveguides that facilitate propagation of light along the length of the fiber, achieving a more energy-efficient, high work capacity LCEA design. Second, LCEAs exhibit low actuation bandwidths, which limit their ability to facilitate practical locomotion speeds in untethered soft machines. The disclosed technology provides an energy efficient approach to electrostatically improve actuation bandwidth in phototropic LCEAs. Finally, in certain aspects, the disclosed technology 3D prints artificial muscle fibers into complete artificial muscle tissues and uses them to achieve untethered swimming and walking in soft machines. The disclosed technology introduces new materials and manufacturing methods to 3D print artificial muscle tissues and novel soft robot embodiments. The materials, 3D printing methods, and actuators described in the present disclosure can pioneer novel capabilities, for example, in applications ofbroad naval interest, spanning, robotics, wearable technologies, bioinspired materials, and more.

[0032] The disclosed materials and methods provide utility beyond just soft robotics. Soft actuators, printed sensors and ionogels, co-axial materials assembly, and self-sensing composites, for example, are required for emerging technologies in wearable devices for artificial / augmented reality systems (e.g., wearable tactile displays or clutches), active electronic textiles for mobility assistance or sensing, and future energy storage devices (e.g., stretchable / wearable batteries). The disclosed materials and manufacturing methods provide new forms, scientific insights, and energyefficient approaches to these applications.

[0033] With reference to FIGS. 1-3, the disclosed technology provides methods for 3D printing a photoactuatable LCEA fiber 10 with an internal core of a deformable, ionogel waveguide (e.g., waveguide core 12). The waveguide core 12 will facilitate propagation of UV light through the length of the artificial muscle fiber 10. The total internal reflection (TIR) can maximize artificial muscle fiber contraction. TIR is achieved when the refractive index, n, of the waveguide core is greater than the refractive indices of the non- actuated azo-LCE shell, TILCE. LCES are birefringent materials with nematic-director-dependent refractive indices that range from HLCE~1.4-1.7. An ionogel based on an ionic liquid (IL) is used as the deformable, internal waveguide (e.g., waveguide core 12) in the photoactuatable LCEA fiber 10 of an artificial muscle 14 because it can possess nn > TLLCE. ILS exhibit refractive indices of HIL~1.4-1.8. For example, the ionogel inks can be formulated from EMIM-ES, which has a 71EMIM-ES~1.48.

[0034] Phototropic LCEAs are used because thermotropic LCEAs and other thermomechanicalactuators have low energy efficiency. In certain aspects, an azobenzene-based phototropic LCE (azo-LCE) is used. A major barrier to adoption of conventional phototropic LCEAs and other AB- functionalized, optomechanical actuators is that they require external light sources for actuation and incident light stimuli does not deeply penetrate LCEAs. Moreover, phototropic LCEAs exhibit complex, highly dynamic, and non-intuitive deformation modes due to heterogeneous absorption and diffusion of light within the networks. Many challenges in phototropic LCEAs could be mitigated if internal optical waveguides could be routed throughout their bulk.

[0035] In certain aspects, the artificial muscle fiber (e.g., photoactuatable LCEA fiber 10) requires a coaxial design, where a shell of aligned azo-LCE 16 ensheathes the deformable ionogel waveguide core (e.g., waveguide core 12). Coaxial composite fibers and fibers of aligned LCEs can be manufactured from, but are not limited to, variations of electrospinning, melt spinning, and composite fiber drawing methods. More recently, direct extrusion of coaxial composite fibers has been achieved with DIW using core-shell nozzles. Multiple materials are extruded through coaxially assembled tubes or custom 3D printed nozzles. Designing nozzles that enable extrusion of thin shells is an important challenge. Coaxial nozzles are more easily made with high resolution 3D printing methods like stereolithography (SLA) or DPL. Core-shell extrusion has produced soft capacitive sensor fibers consisting of alternating electrolyte and elastomer dielectric layers; tough bioinspired lattice composites whose members consist of flexible thermoset cores surrounded by elastomeric and rigid thermoset shells; and fibrous dielectric elastomer actuator assemblies, where a conductive electrode core is encapsulated by an inner dielectric shell and an outer electrode shell.With reference to FIGS. 4-5, a 3D printed custom nozzle 18 for extruding the artificial muscle fiber 10 to rapidly produce designs with various core diameters and shell thicknesses is illustrated.

[0036] To print individual artificial muscle fibers (e.g., the LCEA fiber 10), the 3D print multishell-core nozzle 18 is configured to extrude filaments of azo-LCE ink 20 with cores of ionogel waveguide ink 22. In certain aspects, the nozzle 18 is configured to extrude an additional outer electrode shell 24. The outer electrode shell 24 is included to meet requirements for Aim 2. Minimizing both the thickness of the LCE shell (e.g., the LCEA fiber 10) and the diameter of the waveguide core 12 are key to achieving an optimal power density from the artificial muscle 14. If the LCE shell (e.g., the LCEA fiber 10) is too thick, the LCE will not fully contract since the UV light input will not penetrate the full thickness of the shell. If the waveguide core 12 - and thereby the overall diameter of the artificial muscle fiber 10 - is too large, then the volume fraction of azo- LCE is reduced, and the overall power density will drop as well. This tradeoff is analogous to battery design challenges, where the volume fraction of inactive materials reduces overall energy / power densities.

[0037] In certain aspects, the multi -shell -core nozzle 18 is 3D printed on a high resolution, 4K DPL printer (D4K Pro, EnvisionTEC) that provides, for example, X-Y resolution of 25pm and Z resolution of 1 pm. In other aspects, the core- shell nozzle 18 was achieved with a similar 3D printer providing, for example, X-Y and Z resolutions of 43 pm and 25pm, respectively. Nozzles printed with the lower resolution printer reliably yielded coaxial filaments with core diameters of ~400pm and shell thicknesses of ~100pm. In certain aspects, the multi-shell-core nozzle 18 is 3D printedwith waveguide diameters ranging from 0.1-0.5mm and shell outlets to achieve shell thicknesses of 0.05-0.2mm. The DPL printer also prints several tough, rigid photopolymer resins that will facilitate extrusion of our azo-LCE inks.

[0038] In certain aspects, the main-chain, LCE ink is designed to be shear-thinning, viscoelastic, and photocrosslinkable. Shear-thinning and viscoelastic behavior facilitates extrusion and alignment of the LCE ink. Meanwhile, the photocrosslinkable properties allow the nematic alignment to be fixed upon extrusion via exposure to UV light. In certain aspects, the azo-LCE ink will be synthesized via the oligomerization of reactive mesogens (RMs, e.g., RM82 or l,4-bis-[4- (6-acryloyloxy- hexyloxy)benzoyloxy]-2-methylbenzene) and RMs with azobenzene moieties (azo- RMs)using aza-Michael addition chemistry in one-pot, catalyst-free reactions. This modular oligomerization strategy readily allows for the tailoring of the ink’s rheological properties (i.e., by controlling reaction conditions to tune oligomer molecular weight, MW), the final LCE network’s mechanical properties (i.e., by setting the MW of the oligomer, which also acts as a crosslinker), and fractional composition of azo-RM. Moreover, important components like primary amine- containing chain extenders and spacers can be modularly swapped or introduced to tune LCE mechanical properties, glass transition temperature (Tg), and TNI. In other aspects, other chemistries for oligomerization (e.g., thiol-ene reactions, thiol-Michael addition, and cationic polymerization with terminal epoxide groups) can be used. The azo-LCE ink’s Tg, TNI, and any smectic-nematic transition temperatures with differential scanning calorimetry (DSC) are determined. A rheometer is used to characterize the ink’s rheological properties and NMR asneeded to determine end-group conversion on azo-LCE oligomers as well as MW.

[0039] The azo-LCE ink 20 aligns during extrusion when the appropriate rheological behaviors are achieved. The azo-LCE ink 20 is covalently crosslinked upon extrusion to ensure that the nematic director alignment is immediately fixed. AB moieties in the azo-LCE ink 20 absorbs the UV light and undergo trcms-cis isomerization. The bent molecular shape of AB’s cis configuration initiates a nematic- isotropic transition in the extruded azo-LCE ink 20, and the isotropic state will be photocrosslinked. This yields isotropic azo-LCEs that do not contract. Instead, the printed azo- LCE ink 20 is photopolymerize at blue-green wavelengths (450-570nm) to circumvent this challenge. A wavelength around 455nm is used for post-extrusion photopolymerization. This is the wavelength at which the c / .s-isomer of AB has maximum absorption for cis-trans isomerization. Thus, photocrosslinking in blue-green wavelengths ensures a well-aligned, 3D printed azo-LCE ink because the trans-AB isomer will be maintained. In certain aspects, the photoinitiator Irgacure 784 or 819 is used, which have absorption bands >400 nm. The azo-LCE printing is conducted under red lighting conditions to avoid crosslinking in ambient, visible light.

[0040] To determine appropriate parameters, the azo-LCE ink 20 is extruded at room temperature using traditional cylindrical nozzles and the 3D printed, multi-shell-core nozzle 18. Polarized optical microscopy (POM) with crossed polarizers are used to qualitatively assess azo-LCE alignment. The printed azo-LCEs’ order parameter is evaluated across all extrusion pressures, print speeds, and nozzle diameters using WAXS. TILCE for each specimen is determined with a spectroscopic ellipsometer for UV and green wavelengths.

[0041] Once riLCE is determined, an appropriately matched IL is determined or synthesized with n that enables TIR within the muscle fiber 10. Appropriate FS nanoparticle fillers are then identified for the selected / synthesized IL using the ionogel waveguide ink 22 design methods. ILs used in the ionogel waveguide ink 22 must be immiscible with the azo-LCE ink 20 to prevent swelling or other adverse side-effects that will result in the loss of nematic alignment. Printed azo- LCE specimens will be submerged in ILs identified as candidates for the ionogel waveguide ink 22 and analyzed for any changes of order parameter. While it is impossible to decide what exact rheological requirements are required for the waveguide ink before the azo-LCE ink is prepared, it has been shown that core-shell printing only requires the outer shell ink to be shear-thinning and viscoelastic; core inks can be low-viscosity Newtonian fluids. In certain aspects, the ionogel waveguide ink is a low-viscosity Newtonian fluid. In other aspects, the waveguide ink can be a neat, unmodified IL for the waveguide core 12. In addition to any characterization required for synthesizing an IL (e.g., NMR, DSC), a rheometer is used to characterize the waveguide ink’s rheological properties, refractometry to determine refractive index, and UV-vis spectroscopy to understand the optical properties of the waveguide.

[0042] azo-LCE ink 20 and ionogel waveguide ink 22 are extruded from the multi-shell-core nozzle 18 to obtain single artificial muscle fiber (e.g., the LCEA fiber 10). The dimensions of the printed fiber (e.g., the LCEA fiber 10) is analyzed in brightfield microscopy, and the influence of the fibers’ form will be investigated for various printing parameters (e.g., extrusion pressure and print speed) and nozzle designs. To prevent leaking of the ionogel waveguide ink 22, the fibers(e g., the LCEA fiber 10) can be extruded such that the start and end of extrusion involves azo-LCE extrusion only. Rigid polymer optical fibers (POFs) will be threaded into one end of the artificial muscle fibers (e.g., the LCEA fiber 10) after printing. The specific methods we will develop for this step will depend on the extruded fibers’ dimensions. However, other methods to interface electrode and thin wires into the artificial muscle fiber can be used. In certain aspects, inserting a rigid waveguide into the ionogel core will involve cutting one end of a printed artificial muscle fiber (e.g., the LCEA fiber 10) to expose the ionogel, manually threading the rigid POF into the core, and then sealing the fiber end with azo-LCE ink. The waveguide will be interfaced with an offboard high-power UV light source (e.g., a high-power UV LED or laser).

[0043] Reversibility is a key consideration in soft actuator design. Current methods of reversing LCE actuation in both thermotropic and phototropic varieties are energetically expensive and slow without additional hardware components. For example, thermotropic LCEAs must be cooled to a temperature below TNI to revert from a contracted to relaxed state. The previous works of thermotropic, liquid metal-LCEA composite fibers showed a low actuation bandwidth, with a maximum rate of ~0.025Hz at 35% strain in unloaded actuation. Reversing contraction in phototropic LCEAs is nontrivial and requires cis- trans isomerization of AB moieties. cis-trans isomerization is driven by thermal stimuli or exposure to visible light. Providing either of these stimuli to reverse actuation in azo-LCEs requires additional hardware that complicates untethered soft robot design.

[0044] In certain aspects, reversing phototropic LCE actuation is performed through electrostaticmechanisms. Prior investigations from the molecular electronics and nanomaterials communities have shown that electric fields can drive cis- trans isomerization of AB at a rate constant approaching five orders of magnitude higher than those associated with heat- or light-based strategies. High electric fields applied across the azo-LCE shell can expedite reversible contraction - that is, increase the actuation bandwidth of LCEs by at least one order of magnitude - by increasing the rate of cis-trans azo isomerization after contraction. To accomplish this, the ionically conductive waveguide core 12 is used as an internal electrode, and a second ionogel ink is used to extrude an external soft electrode (e.g., outer electrode shell 24) around the azo-LCE layer.

[0045] lonogels have relatively wide electrochemical windows (e.g., up to 6-7V), but many ILs / ionogels are hygroscopic. Water uptake results in hydrolysis at -1.23V, electrochemically decomposing the material. Prior works have showed that ionically conductive hydrogels can successfully be used as electrodes in transparent DEAs. Hydrogel electrodes support actuation voltages of nearly 20 kV, far above water’s electrochemical breakdown at 1.23V, without production of oxyhydrogen. Electrochemical breakdown does not occur at high actuation voltages because the voltage drop across the dielectric is much higher than the voltage associated with the electric double layer that forms at a metallic electrode and hydrogel electrode interface. The electrodes 26 will facilitate applied voltages up until the dielectric breakdown voltage of the azo- LCE, which will be in the range of 2-6 kV. Moreover, the electrode pair 26 comprised of the external ionogel electrode (e.g., the outer electrode shell 24) and internal ionogel waveguide (e.g.,the ionogel waveguide core 12) intrinsically provides proprioceptive self-sensing capabilities similar to those of DEAs and HASEL actuators.

[0046] The artificial muscle fiber’s (e.g., LCEA fiber 10) coaxial form uniquely enables opportunities for designing multifunctional LCE composites to address key challenges in LCE- based actuation. The electrostatic approach to reversing phototropic LCE contraction sidesteps the need for additional hardware otherwise needed to drive cis-trans isomerization by thermal or optical means. This further maintains the energy efficiency and high power density of the artificial muscle 14. Electrostatic control of AB moieties’ cis-trans isomerization in printed azo-LCE thin films are investigated in two planar testbeds. The testbeds will enable characterization of order parameter changes in azo-LCEs under high electric fields after UV exposure to proceed during finalization of the artificial muscle fibers 10. The artificial muscle fibers 10 are then printed ensheathed in outer ionogel electrode 24 and repeat experiments conducted on the planar testbeds.

[0047] Two planar testbeds are developed for investigating the electrostatic control of azo- moiety in azo-LCEs. The first testbed is an ionogel electrode-free, planar azo-LCE device. Using the azo- LCE ink candidates, 2D sheets of aligned phototropic LCEs are printed at thicknesses varying from 0.1-lmm. The films are sandwiched between two glass slides with transparent ITO electrodes. The second testbed comprises of a similar device, except the printed azo-LCE films are sandwiched between crosslinked ionogel electrode layers. The transparent electrodes are designed from polymerizable ionic liquid mixtures that can later be formulated into shear-thinning, viscoelastic ionogel inks. The ionogel electrodes of the second testbed are covalently crosslinkedto the azo-LCE by casting the ionogel formulation in a non-polymerized liquid state over the azo- LCE film and polymerizing to form a covalent interface.

[0048] Copper tape electrodes are fixed to the ITO / ionogel electrodes and apply electric fields across the azo-LCEA membrane. Capacitance is measured to ensure proper device performance. The first testbed serves as a control experiment; the second enables exploring electrostatic control of cis-trans isomerization via ionogel electrodes for the final, artificial muscle fiber design. Based on previous investigations of AB cis-trans isomerization by electric fields, the electric fields of 0.5-5 V / pm applied over the thickness of the azo-LCE layer will be required (i.e., 25-250V and 100-1000V for 50pm- and 200pm-thick azo-LCE layer, respectively). These operating voltages are much lower than those required for DEAs or HASEL actuators. They can be generated with miniature voltage amplifiers.

[0049] The azo-LCE films are exposed to UV light in the testbeds to initiate azo trans-cis isomerization. Then, electric fields of various amplitudes and frequencies are applied. Nematic disordering results from trans-cis AB isomerization stimulated by UV light. Any cis-trans AB conversion resulting from the applied electric fields are monitored with polarized optical microscopy (POM). In the first testbed, the rigid glass slides with ITO electrodes are restrict azo- LCE contraction. Thus, contractile strains and forces generated from optoelectronic actuation of the ionogel-azo-LCE composites from the second testbed are characterized on an Instron.

[0050] The external electrode ink 23 for the outer electrode shell 24 is formulated. Using ILs that are immiscible with the azo-LCE, a shear-thinning, viscoelastic ionogel ink is formulated usingfumed silica nanoparticles as a rheology modifier. Photocrosslinkable monomers and crosslinkers functionalized are added with acrylate moieties (e.g., acrylic acid (AA), PEG-DA) that covalently entrain the ionic liquid and bond to the azo- LCE shell. Well- studied acrylate-functionalized ILs are synthesized to create ionogel electrodes from polymerizable ILs (PILs). Ink designs are tailored to ensure that the ionogel electrode ink polymerizes at 455 nm without interfering with azo-LCE crosslinking. The inks are designed such that a covalently bonded interface forms between the electrode and azo-LCE shell. A controlled-stress rheometer is used to characterize the ionogel electrode ink’s rheological properties and characterize synthesis results using NMR as necessary.

[0051] An optoelectronic artificial muscle fiber (e.g., LCEA fiber 10) is extruded using the multi- shell-core nozzle 18. The fiber (e.g., LCEA fiber 10) consists of the coaxial architecture, where each fiber (e.g., LCEA fiber 10) is comprised of an azo-LCE shell (e.g., shell of aligned azo-LCE 16) sandwiched between an ionogel waveguide core 12 and an external ionogel electrode (e.g., outer electrode shell 24). The shell of aligned azo-LCE 16 is disposed between the ionogel waveguide core 12 and the outer electrode shell 24 such that the outer electrode shell 24 sheaths the shell of aligned azo-LCE, which in turn sheaths the ionogel waveguide core 12. A metallic wire is threaded into the waveguide core 12 and a metallic foil cuff is wrapped on the external electrode 24 to apply electric fields across the azo-LCE layer.

[0052] Fibers of varying architectural parameters (e.g., fiber length, azo-LCE shell thickness, waveguide core diameter, and outer electrode thickness) are printed and sweeped through electrical inputs (e.g., amplitude and frequency of the applied electric field). Using cameras and tensile loadcells, strain and contractile force are characterized for each architectural and electric field parameter. Actuation bandwidth is characterized for different optoelectronic actuation conditions. These characterization data will provide insights into the design parameters that yield optimal performance metrics.

[0053] Because the ionogel waveguide core 12 and outer electrode 24 provide intrinsic selfsensing capabilities, we will simultaneously measure the capacitance change across the azo-LCE shell is simultaneously measured and the resistance change along the length of the fiber 10 during all actuation characterizations. The same specialized readout electronics are used that were previously developed for measuring the resistance of ionogel sensors. Moreover, the ionogel waveguide and outer electrode are hygroscopic. Influence of water uptake on sensor performance is appropriately account for.

[0054] A critical tradeoff in any soft matter actuator or artificial muscle is designing actuators that are fast and large (i.e., for high force generation). For example, stimuli- and solvent- responsive soft actuators are limited by optical / thermal / mass transport constraints. Moreover, electrostatic soft actuators are, in principle, simple to scale in size, but fabrication limitations make this a tedious, and nontrivial endeavor. The artificial muscle fibers 10 are intentionally designed as mimics of individual, biological muscle fibers. Continuing with the bioinspired design, larger artificial muscles 14 are designed by assembling individual muscle fibers (e.g., LCEA fiber 10) together during printing. Thus, the disclosed scalable, high-throughput design approach enables true artificial muscle tissues (e.g., artificial muscle 14) comprised of multiple artificial musclefibers (e.g., the LCEA fiber 10) to be fabricated. The artificial tissues (e.g., artificial muscle 14) do not face the aforementioned size-speed tradeoff.

[0055] Another important feature of the design of the artificial muscle tissue (e.g., artificial muscle 14) is that each LCEA fiber 10 can be individually addressed and actuated like a single biological muscle fiber. Here, optical signals serve as analogs to pulse trains of actuation potentials from motor units. The intrinsic self- sensing capabilities provided by the ionogel features mimic muscle spindles or other proprioceptors. In short, the artificial muscle tissues (e.g., artificial muscle 14) possess true bioinspired, distributed actuation and proprioceptive capabilities. Finally, because individual artificial muscle tissues (e.g., artificial muscle 14) can be 3D printed, artificial muscle with complex structures found in nature, such as the deltoid and multipennate structures in vertebrate musculoskeletal systems, or the radial, oblique, and longitudinal assemblies of muscle fibers in cephalopods (e.g., the octopus tentacle) can be fabricated.

[0056] The disclosed multimaterial 3D printing capabilities and artificial muscle tissues (e.g., artificial muscle 14) are used to 3D print two important soft robotic systems capable of untethered locomotion. In certain aspects, a soft, iguana-inspired robot can be fabricated. Iguanas have muscular legs and tails which they use to walk / climb and swim, respectively. Untethered soft robots are fabricated to demonstrate fundamental walking and swimming capabilities with the artificial muscle 14, for example, a four-legged soft quadruped with supporting skeletal systems and an undulating, eel-inspired soft body.

[0057] Designing untethered soft robots requires that actuators, power supply, control scheme,and sensors be integrated in a manner that facilitates successful system-level performance. Untethered soft robots are generally burdened by bulky power and control hardware. The disclosed strategy for achieving untethered locomotion is inspired by soft untethered robots that embrace traditional hardware. Specifically, the untethered system is designed around the use of small lithium-ion batteries and miniature microcontrollers for the energy source and controller, respectively. A high-power UV LEDs and miniature, lightweight voltage amplifiers are used for optoelectronic stimulation of the artificial muscle tissues. While miniature voltage amplifiers have successfully supplied 7-10kV in (untethered) soft robots equipped with DEAs or HASEL actuators, the key challenge is designing optoelectronic artificial muscle tissues that can be powered by high-power UV LEDs, which the disclosed technology achieves.

[0058] UV LEDs provide a miniaturized, lightweight light source for actuating individual fibers 10 of the artificial muscle tissues 14. The maximum luminous intensity of commercially available miniature UV LEDs ranges from 10-25 mW. UV LED energy efficiencies are improving over time from their current values of 5- 20%. Still, these efficiencies are far improved compared to other LCE actuation strategies. Data regarding design-performance trade-offs previously determined are used to design muscle tissues (e.g., artificial muscle 14) whose individual fibers 10 can be addressed by a single LED. Arrays of high-power UV LEDs are developed to actuate larger artificial muscle tissues. Voltage amplifiers are considered for integration into each of the muscle fibers 10 for electrostatic reversal of contraction.

[0059] Antagonistic pairs of artificial muscle tissues are co-printed with rigid thermoset resins thatcan serve as lightweight, rigid skeletal features. Possible thermoset resins include, but are not limited to, photocrosslinkable or thermally curable epoxy or acrylate thermosets. For these efforts, the multimaterial printing methods discussed above are extensively used to print soft sensorized robots. Such printing methods and high-precision gantry enable DTW of four different materials. Individual muscle fiber ends are adhered to the skeletal thermoset features either by co-pattering a third, printable adhesive ink or by developing a thermoset resin for the skeletal features that can covalently bond to the azo-LCE ink or outer ionogel electrode during post-extrusion photopolymerization. Other printing methods to integrate printed features with other non-printed components are utilized and hybrid assembly methods to incorporate power and control hardware with the 3D printed soft robot bodies.

[0060] With the untethered soft robots designed, actuation patterns are developed for the artificial muscle tissues. The actuation patterns are quadruped and swimming soft robots, and focus is on algorithms that make optimal use of antagonistic muscle contraction and feedback from the distributed proprioceptive capabilities. Our ultimate goal is to incorporate distributed contact sensors throughout printed, untethered soft robot bodies and utilize deep learning techniques to enable closed-loop control, utilizing methods akin to those we have previously developed.

[0061] With reference to FIG. 3, photoactuation of the artificial muscle 14 is illustrated. The artificial muscle 14 can be photoactuated between an extended state and a contracted state. As illustrated in FIG. 3, the artificial muscle begins in the extended state and, when UV light is delivered, is photoactuated to the contracted state. When UV light is removed the artificial muscle14 reverses actuation from the contracted state to the extended state.

[0062] FIG. 6 depicts a diagram illustrating synthesization 30 of the azo-LCE ink 20. The azo- LCE ink 20 is synthesized using one-pot, aza-Michael addition reactions. The reaction yields main- chain azo-LCE oligomers. The mesogen in the azo-LCE ink 20 is RM82; the polymerizable azobenzene moiety, 4,4’-Bis[6-(acryloyloxy)hexyloxy]azobenzene, has been added at weight fractions of 0 - 25%. The reaction yields a thick, solvent-free ink of oligomers whose molecular weight provides shear-thinning, viscoelastic ink properties for extrusion. Actuation requires aligned mesogens. The ionogel waveguide ink 22 and outer electrode shell ink 23 can be formulated from poly(ionic liquids) (pILs) such as, but not limited to, l-ethyl-3-methyl imidazolium (3-sulfopropyl) acrylate (ES, a polyanionic pIL), -[2-acryloyloxyethyl]-3- butylimidazolium bis(trifluoromethane) sulfonimide (AT, a polycationic pIL), l-ethyl-3- methylimidazolium l-[3-acryloyloxypropylsulfonyl] - (trifluoromethane- sulfonyl)imide (ET, a more hydrophobic polyanionic pIL than ES), and other appropriate pILs. In other aspects, the ionogel waveguide ink 22 and outer electrode shell ink 23 can be formulated from ionic liquids (ILs) such as, but not limited to, an IL similar to AT that does not polymerize (liquid AT) and other appropriate ILs. The pILs are crosslinked for use as external electrodes. The pILs covalently bond to the azo-LCE inks when they are photocrosslinked together. This is essential for robust interfacing between the shell of aligned azo-LCE 16 and the external electrode shell (e.g., the outer electrode shell 24).

[0063] ES disrupts alignment of crosslinked LCEs over time, while alignment appears maintainedwhen the LCE is bonded to AT. Systematic studies are conducted using POM and WAXS to quantify how the order parameter of the extruded azo-LCE changes over time. This is an essential insight, which allows designing the ionogel inks for the waveguide core and outer electrode shells using AT. This result is the reason that “liquid AT” is a preferred waveguide IL.

[0064] Referring to FIGS. 7-8, the custom nozzle 18 can be 3D printed and configured to facilitate high-pressure extrusion (e.g., of at least 90 psi) of the azo-LCE ink 20. With reference to FIGS. 4- 5, as well, the custom nozzle 28 includes a first inlet 32, a second inlet 34, and a third inlet 36. In certain aspects, each of the first inlet 32, the second inlet 34, and the third inlet 36 are Leur-lock adapters. In other aspects, each of the first inlet 32, the second inlet 34, and the third inlet 36 are other appropriate adapters. As shown in the cross-section view of FIG. 5, a first conduit 38 extends between the first inlet 32 and a first outlet 40, a second conduit 42 extends between the second inlet 34 and a second outlet 44, and a third conduit 46 extends between the third inlet 36 and a third outlet 48. The second conduit 42 is disposed between the first conduit 38 and the third conduit 46.

[0065] FIGS. 9-10 illustrate a printing setup 50 for printing the photoactuatable LCEA fiber 10, which includes a curing station 52, such as, but not limited to an Omnicure S2000 “Elite,” a printing station 54, and a curing chamber 56.

[0066]

[0067] FIG. 11 illustrates an untethered soft robotic quadruped 58, which includes a plurality of legs 60 with each leg fabricated with the artificial muscle 14.

[0068] As discussed above, the photoactivatable LCEA fiber 10 is configured to linearly contract and can achieve actuation unattainable by external illumination. The photoactivatable LCEA fiber10 is also configured for reverse fiber actuation. Once actuated, the photoactuated fiber 10 can be reversed in multiple ways. For example, thermal energy, through direct heating or photothermal mechanisms, can be used to drive isomerization of the incorporated photoswitch back to its thermodynamically stable state, thereby causing network relaxation and fiber expansion. Illuminating the fiber with wavelengths that directly cause back isomerization of the incorporated photoswitch can similarly drive this fiber relaxation and expansion. In summary, direct thermal heating, photothermal heating, and photomechanical mechanisms can all be used to reverse fiber actuation.

[0069] The disclosed methods allow for several photoswitches to be used. Multiple photoswitches can be introduced into the liquid crystalline network to drive phototropic fiber actuation. Some of these are azobenzene-based photoswitches. This phototswitch is presented in all data unless otherwise noted. Beyond azobenzene photoswitches, fiber-based actuation can be achieved using arylazopyrazole photoswitches. This photoswitch was incorporated into the liquid crystalline network in the same manner as the azobenzene photoswitch discussed previously. Any number of photoswitches could be incorporated into our actuator and used to demonstrate fiber actuation via the disclosed approach.

[0070] In addition to the ionic liquids, other materials could be used as waveguide cores, such as, but not limited to, DOWSIL 9041, which have been shown to enable phototropic fiber actuation.

[0071] One limitation of most traditional soft actuators and shape-changing materials is that the stimulus necessary to drive actuation must be externally delivered from an external, exogenous source. While delivering external stimuli in a laboratory setting via a hot plate or UV lamp is straightforward, these methods are not practical for actuators designed for use in real-world devices in ordinary environments. Thermally addressable LCE systems have been introduced in other work. Addressable phototropic actuation, which provides many advantages over thermotropic actuation, however, has not been shown in contractile LCEs. Thus, in certain aspects, the disclosed technology utilizes photoactuatable LCE fibers with addressable actuation.

[0072] Creating a contractile, phototropic LCE actuator whose shape-changing behaviors depend on photoresponsive azobenzene moieties requires a method for uniform UV exposure and transcis azobenzene isomerization. Addressability requires the ability to address individual units within a larger collective or aggregate. The disclosed technology achieves an artificial muscle tissue by bundling multiple photoactuatable LCEs (e.g., photoactuatable LCEA fiber 10) together (e.g., the artificial muscle 14). These design requirements are achieved with a fiber geometry, where a photoactuatable LCE shell cladding (e.g., the shell of aligned azo-LCE 16) surrounds a high refractive index, soft waveguide core (e.g., ionogel waveguide core 12). As discussed above, custom core-shell nozzles (e.g., the custom nozzle 18) is 3D printed using, for example, a desktop digital light processing (DLP) printer (EnvisionTEC D4k). Using these nozzles (e.g., the custom nozzle 18), aligned LCEs (e.g., photoactuatable LCEA fiber 10) are printed into coaxial, multimaterial fibers using an extrusion-based direct ink writing method, as illustrated in FIG. 12.

[0073] In certain aspects, the custom nozzle 18 is printed using digital light processing (HTM 140V2, EnvisionTEK D4K) and subsequently coated in nail polish to prevent premature crosslinking of the printed materials. The dimensions of the custom nozzle 18 can vary, but typically produce an 800 «m IL core diameter (e.g., ionogel waveguide core 12), and 200 «m thick LCE shell (e.g., shell of aligned azo-LCE 16).

[0074] Prior to printing, the LCE ink (e.g., azo-LCE ink 20) is loaded into an amber colored 3cc syringe barrel (Nordson EFD, 7366092) to prevent premature crosslinking. The core ink (e.g., ionogel waveguide core 12) is loaded into a transparent 3cc syringe barrel (Nordson EFD, 7366095), as it contains no polymerizable groups. The IL ink barrel is then secured to the gantry and the core channel of the nozzle. The LCE ink barrel is loaded into a high-pressure adaptor (Nordson EFD, 7023590) and attached to the shell Luer lock of the nozzle.

[0075] In certain aspects, core-shell printing occurs at a rate of 0.75 - 1.2 mm / s, and fibers were photocrosslinked on the fly with a 525 nm lamp 72 (Kessil Lighting, PR160L-525). At the start and end of the print, the LCE was over extruded to ensure the IL was trapped within the core. After printing, fibers were additionally cured for a brief period of time before being stretched to 180% of their initial length for mechanical alignment purposes before a final crosslinking step.

[0076] Two materials are needed to fabricate LCE fibers (e.g., photoactuatable LCEA fiber 10). The first is the LCE (e.g., azo-LCE ink 20), which will serve as the photoactuating outer shell (e.g., the shell of aligned azo-LCE 16). In certain aspects, an azoLCE formulation is used. To achieve long fibers that uniformly actuate, a high refractive index HD) core material is ideal. However, thiscore material must also be transparent in the UV and blue light regimes so that the photoisomerization capabilities of azoLCE are preserved. In addition, it is critical that whatever core material is chosen does not interfere with the azoLCE mesogen ordering, as doing so would reduce actuation performance. The core should also be a liquid or soft gel to minimize the hydrostatic resistance during actuation, as a solid core would completely hinder contractile photoactuation. Taking these constraints into account, ionic liquids are a versatile class of materials with tunable properties and relative chemical inertness. Transparent ionic liquids have high (>1.60) refractive indices, satisfying three of the four design constraints considered.

[0077] The azo-LCE ink 20 includes variable refractive indices and can be, but is not limited to, l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide 62 (“[BMIM][TFSI]”) (see FIG. 13), l-Butyl-3-methylimidazolium thiocyanate 64 (“[BMIM][SCN]”) (see FIG. 14), and hexyltriphenylphosphonium di cyanamide 66 (“[P^s][N(CN)2]”) (see FIG. 15), and other appropriate ionic liquids with variable refractive indices. The refractive indices of [BMIM][TFSI], [BMIM][SCN], and [P6][N(CN)2] are 1.428, 1.538, and 1.610, respectively. [BMIM][SCN] is commercially available. [BMIM][TFSI] and [P 6][N(CN)2] are synthesized via a one-step ion exchange reaction. UV-Vis spectroscopy shows these ILs are relatively transparent beyond the 350 nm range, meaning they will not prevent photoactuation

[0078] To study whether the selected ILs interfere with azoLCE alignment, a wide-angle X-ray scattering (WAXS) is used to calculate the order parameter of samples before and after exposure to ILs. Specifically, printed azoLCE strips are submerged in the various ILs for four weeks. Twocontrols were also tested: air as a positive control, which should not disrupt order, and dichloromethane (DCM) as a negative control, which is known to swell LCEs and disrupt order.Measurements were taken every week, and five or six samples were tested for each solvent condition. As anticipated, DCM had the greatest detrimental effect on LCE ordering, reducing it by a factor of 50% over the study period. Submersion in [BMIM][TFSI], [BMIM][SCN], and air had a negligible effect on alignment over the period, while [P^e][N(CN)2] reduced the order parameter by approximately 25%. Despite this drop, the average order parameter after four weeks in [PPPp6][N(CN)2] was 0.26, which was still sufficient to observe thermotropic and phototropic actuation.

[0079] Based on these results, [BMIM][TFSI] and [P^6][N(CN)2] are selected for printing azoLCE fibers (e.g., photoactuatable LCEA fiber 10). [BMIM][SCN] was not tested inside a fiber due to known pathways of UV degradation, which would impact photoactuation performance. Both [BMIM][TFSI] and [Pp pe][N(CN)2] are liquids at room temperature, posing challenges for their extrudability. It is known that the rheology of ILs can be modified for DIW by adding filler materials such as fumed silica powders. However, adding solid fillers to the core will negatively impact actuation performance. While the low viscosity of [BMIM][TFSI] requires the use of a low wt% of fumed silica (2.8 wt%) to achieve a printable, soft gel, the high viscosity of neat [P PP6][N(CN)2] (~10 Pa s) means that it can be printed without any fillers. Both the azoLCE and [P,W6][N(CN)2] are extruded as viscous fluids, with loss modulus (G") greater than storage modulus (G) across the full stress range evaluated. In contrast, oscillatory amplitude sweeps showthat the [BMIM][TFSI] ink is printed as a soft gel with a yield stress, (ry), of 34 Pa, where ryis determined as the crossover point between G' and G '.

[0080] After printing, fibers are characterized at the molecular and macro scales using WAXS and micro-computed tomography (pCT). WAXS is performed on printed fibers with intact cores to determine the order parameter. ID and 2D WAXS plots are generated, and the order parameter is calculated based on previous methods to be 0.19. To perform pCT analysis, fibers are printed with a barium sulfate (BaSCh) filled IL core. BaSO4 acts as a radiopaque contrast agent and is used to help enhance the contrast between the azoLCE shell (e.g., shell of aligned azo-LCE 16) and IL core (e.g., ionogel waveguide core 12). pCT analysis shows fibers (e.g., photoactuatable LCEA fiber 10) to have a uniform geometry, with a core diameter of -800 pm, and a shell thickness of —150 pm.

[0081] The actuation performance of single azoLCE fibers was characterized using a combination of free- hanging strain measurements and isostrain force measurements. IL cores were illuminated via glass optical fibers inserted into the fiber. It is first investigated whether higher nD IL cores improved actuation performance. For short («20 mm) fibers, IL nD does not greatly influence actuation strain. However, for long (>30 mm) fibers, a higher nD IL leads to larger actuation strains. azoLCE fibers between 20-40 mm containing the high nD [PPPPe][N(CN)2] core display consistent actuation strains of 10%. Longer fibers show slightly decreased strains of 7%. In contrast, while fibers with a [BMIM][TFSI] core exhibit larger initial actuation strains (nearly 12% contraction for a 20 mm fiber), that strain quickly drops off as the fiber length increases. A 50 mm[BMIM][TFSI] fiber actuates less than 4%.

[0082] A [PpPP6][N(CN)2] actuating fiber shows that light propagates through its entirety. The isostrain actuation force as a function of fiber length is also quantified using DMA for the [PpPP6][N(CN)2] core, and plateaus for long fibers between 0.3 and 0.4 mN. Although this force output is small, the fiber geometry creates opportunities to combine multiple fibers into photoactuatable bundles that amplify force.

[0083] Bundling multiple fibers (e.g., photoactuatable LCEA fiber 10) together enables increased force output and opportunities for addressable actuation. Compared to a single 20 mm fiber with a force output of ~0.5 mN, a 7-fiber bundle exerts 3.5 mN of force, exhibiting a linear scaling behavior. In addition, the maximum actuation force due to internal illumination is greater than that due to external illumination. Internal illumination also circumvents the challenges of exogenous stimulus delivery, where the force during external illumination is highly sensitive to the distance between the light source to the fiber. While force output scales with the number of fibers in a bundle, strain will not. While the strain of a fiber bundle is slightly lower than that of a single fiber (9 vs 6%), this is due to the manual assembly of these bundles which results in imperfect coupling and fibers that are not completely taut before actuation. If fiber bundles are perfectly assembled, we would expect strain to be the same as that of a single fiber.

[0084] Not only can fibers (e.g., photoactuatable LCEA fiber 10) be bundled together to improve overall actuation performance, but they can also be bundled to create addressable motion. As illustrated in FIG. 16, the actuation of an eye mimic 68 placed within a skull model 70. Achievingsimilar actuation relying on external light would be impossible due to the placement of the fiber relative to the cranium. This actuation is only achievable using the addressable photoactuable fibers (e.g., photoactuatable LCEA fiber 10).

[0085] While phototropic LCEs have many benefits including high energy densities and, now, addressability, one significant limitation is the speed with which they relax to their original length. The half-life of the azobenzene ci -isomer is on the order of a few hours at room temperature, although additional stimuli, such as heat or longer- wavelength light, can increase the rate of isomerization and therefore the rate of azoLCE relaxation. In certain aspects, internal 450 nm light is used to quickly relax the [P^6][N(CN)2] core fibers back to their original length. Heat can be used to cause rapid restoration of a fiber’s original length.

[0086] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of thesubject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples.A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases.

[0087] A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Relational terms such as first and second and the like may be used to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for”.

[0088] While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of particular implementations of the subject matter. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0089] The subject matter of this specification has been described in terms of particular aspects, but other aspects can be implemented and are within the scope of the following claims. For example, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. The actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous.

[0090] The title, background, brief description of the drawings, abstract, and drawings are hereby incorporated into the disclosure and are provided as illustrative examples of the disclosure, not as restrictive descriptions. It is submitted with the understanding that they will not be used to limit the scope or meaning of the claims. In addition, in the detailed description, it can be seen that the description provides illustrative examples and the various features are grouped together in variousimplementations for the purpose of streamlining the disclosure. The method of disclosure is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, as the claims reflect, inventive subject matter lies in less than all features of a single disclosed configuration or operation. The claims are hereby incorporated into the detailed description, with each claim standing on its own as a separately claimed subject matter.

[0091] The claims are not intended to be limited to the aspects described herein, but are to be accorded the full scope consistent with the language claims and to encompass all legal equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirements of the applicable patent law, nor should they be interpreted in such a way.

Claims

WHAT IS CLAIMED IS1. A liquid crystal elastomer actuator fiber comprising: a waveguide core; a shell of aligned azo-liquid crystal elastomer sheathing the waveguide core; and an outer electrode shell sheathing the shell of aligned azo-liquid crystal elastomer.

2. The liquid crystal elastomer actuator fiber of Claim 1, wherein the waveguide core is an ionogel waveguide core.

3. The liquid crystal elastomer actuator fiber of Claim 1, wherein the waveguide core is transparent in ultraviolet light and blue light.

4. The liquid crystal elastomer actuator fiber of Claim 1, wherein the waveguide core is formed from an ionic liquid.

5. The liquid crystal elastomer actuator fiber of Claim 4, wherein the ionic liquid is one of l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, l-Butyl-3- methylimidazolium thiocyanate, and hexyltriphenylphosphonium dicyanamide.

6. The liquid crystal elastomer actuator fiber of Claim 1, wherein the shell of aligned azo-liquid crystal elastomer is photoactuatable.

7. The liquid crystal elastomer actuator fiber of Claim 6, wherein the shell of aligned azo-liquid crystal elastomer is photoactuatable from an extended state to a contracted state,wherein the shell of aligned azo-liquid crystal elastomer is Zra / zs-azo-liquid crystal elastomer in the extended state and is c / .s-azo-liquid crystal elastomer in the contracted state.

8. An artificial muscle comprising: a plurality of liquid crystal elastomer actuator fibers, wherein each liquid crystal elastomer actuator fiber comprises: a waveguide core; a shell of aligned azo-liquid crystal elastomer sheathing the waveguide core; and an outer electrode shell sheathing the shell of aligned azo-liquid crystal elastomer.

9. The artificial muscle of Claim 8, wherein the waveguide core is an ionogel waveguide core.

10. The artificial muscle of Claim 8, wherein the waveguide core is transparent in ultraviolet light and blue light.

11. The artificial muscle of Claim 8, wherein the waveguide core is formed from an ionic liquid.

12. The artificial muscle of Claim 11, wherein the ionic liquid is one of l-Butyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide, l-Butyl-3-methylimidazolium thiocyanate, and hexyltriphenylphosphonium dicyanamide.

13. The artificial muscle of Claim 8, wherein the shell of aligned azo-liquid crystal elastomer is photoactuatable.

14. The artificial muscle of Claim 13, wherein the shell of aligned azo-liquid crystal elastomer is photoactuatable from an extended state to a contracted state, wherein the shell of aligned azo-liquid crystal elastomer is / / z / / / .s-azo-liquid crystal elastomer in the extended state and is c / .s-azo-liquid crystal elastomer in the contracted state.

15. A method of fabricating a liquid crystal elastomer actuator fiber, the method comprising: feeding an azo-LCE ink to a first inlet of a custom nozzle; feeding an ionogel waveguide ink to a second inlet of the custom nozzle; feeding an outer electrode shell ink to a third inlet of the custom nozzle; and simultaneously extruding the azo-LCE ink, the ionogel waveguide ink, and the outer electrode shell ink through a first outlet of the custom nozzle, a second outlet of the custom nozzle, and a third outlet of the custom nozzle, respectively, wherein the first outlet of the custom nozzle is disposed between the second outlet and the third outlet.

16. The method of Claim 15, wherein the azo-LCE ink is photocrosslinkable.

17. The method of Claim 15, wherein the azo-LCE ink that is extruded is photocrosslinked.

18. The method of Claim 15, further comprising photopolymerizing the azo-LCE ink that is extruded.

19. The method of Claim 18, wherein the azo-LCE ink that is extruded is photopolymerized at a blue-green wavelength.

20. The method of Claim 15, wherein the azo-LCE ink is synthesized using one-pot, aza-Michael addition reactions.

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