Liquid crystal elastomer composite materials and methods of preparing the same

Abstract

A liquid crystal elastomer composite material having well dispersed gold nanorods and a high temperature thermal initiator incorporated therein is described. Shape change in the liquid crystal elastomer composite material may be induced by activating the gold nanorods with near infrared light. Shape change in the liquid crystal elastomer may be made permanent by activating the high temperature thermal initiator with heat generated by the activated gold nanorods. Upon activation of the high temperature thermal initiator, free radicals are generated that cause bond rearrangement in the liquid crystal elastomer network and lead to shape change permanence. Methods of preparing fully functionalized gold nanorods that are non-aggregated and highly dispersed are also disclosed.

Description

LIQUID CRYSTAL ELASTOMER COMPOSITE MATERIALS AND METHODS OF PREPARING THE SAMESTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with government support under grant number F30HL 16407, awarded by the National Institutes of Health, and grant number FA9550-21 -1-0771 , awarded by the Air Force Office of Scientific Research. The government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATION(S)

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 562,162, filed March 6, 2024, and to U.S. Provisional Patent Application No. 63 / 670,402, filed July 12, 2024. Both of these U.S. Provisional Patent Applications are incorporated herein by reference in their entirety.BACKGROUND

[0003] Liquid crystalline elastomers (LCEs) are stimuli-responsive materials that transduce an input energy into a mechanical response. LCE composites prepared with photothermal agents, such as nanoinclusions, are a means to realize wireless, remote, and local control of LCE deformation upon application of light. Gold nanorods (AuNRs) are a type of photothermal nanoinclusion capable of converting optical energy into heat from within the LCE matrix in which they are dispersed, resulting in rapid heating and high strain rates upon irradiation with light. AuNRs are ideal photothermal agents due to a very high molar extinction coefficient and near-unity photothermal conversion efficiency.

[0004] AuNRs convert optical energy to heat through a surface plasmon resonance (SPR) mechanism in which the conductive band electrons oscillate in resonance with a specific wavelength of light and generate heat via a series of photophysical processes. The longitudinal SPR (LSPR), dictated by the aspect ratio of the AuNR, is stronger than that of the transverse SPR and five to six orders of magnitude larger than that of dye molecules.

[0005] Unfortunately, currently known methods of manufacturing LCEs with AuNR inclusions tend to result in AuNR aggregation within the LCE matrix, which has a negative impact on the performance of the LCE material as a stimuli-responsive material. More specifically, aggregation of AuNRs limits their photothermal effect. For example, AuNRs with an aspect ratio of ~4:1 absorb near-infrared (NIR) light with peak absorption around ~800 nm, which induces an oscillation of electrons that generates heat rapidly. Yet if two 4:1 AuNRs are stuck together along their long axis, they behave as a single AuNR with half the aspect ratio (2:1 ), and therefore will not absorb 800 nm light. When using a laser diode to induce the photothermal effect, aggregation of AuNRs causes poor photothermal efficiency, requiring much higher light doses to achieve heating. In some applications of LCE materials (e.g., biomedical applications), laser power must be limited to prevent tissue heating, so high efficiency is required. Furthermore, LCE aggregation can affect mechanical properties of the LCE network. In the case of LCEs, aggregates of AuNRs will cause a defect in the alignment of liquid crystalline mesogens and therefore a decrease in the total actuation strain and the strain rate of the LCE undergoing a thermotropic phase transition.

[0006] There have been a few reports detailing attempts at surface functionalization of AuNRs with neutral / inert or hydrophobic monomers to improve the interactions between AuNRs and LCEs, and more specifically, to try and minimize AuNR aggregation within LCEs. These processes generally aim to replace cetyltrimethylammonium bromide (CTAB) (a surfactant used in the creation of the AuNRs) with thiol-term inated molecules. However, these processes generally yield only incomplete functionalization of the AuNRs, which results in aggregation of AuNRs either in solution and / or after mixing with prepolymers. Any CTAB left on the surface of the AuNRs will induce phase separation with the prepolymers, while incomplete functionalization increases likelihood for irreversible aggregation while in solution.

[0007] Another issue faced with respect to LCE-AuNR composite materials is adapting these materials for use in different applications, with particular focus on biomedical applications for LCE-AuNR composite materials. A first issue that is presented when attempting to adapt LCE-AuNR composite materials for biomedical application is managing the power level of the stimulus used to activate the LCE-AuNR composite material. Forexample, if the LCE-AuNR is used in a subcutaneous implant, the intensity of a photostimulus used to activate the LCE-AuNR must be managed so as to ensure that the subject’s skin and / or underlying tissue is not damaged when applying the photostimulus. Another issue that may need to be addressed in certain biomedical applications of LCE- AuNR composite materials is providing permanence or semi-permanence with respect to the induced shape change in the LCE-AuNR composite material. Certain biomedical applications may benefit from induced shape change in LCE-AuNR composite materials being permanent rather than reversible. A primary example is in the case of a biomedical device implanted in an infant or child still undergoing growth. If the device cannot be permanently expanded as the patient grows, then further surgeries will be required to remove the outgrown implant and replace it with a larger implant. Such repeated surgeries are invasive and potentially life-threatening, and so a need exists for implantable devices where an LCE-AuNR composite material can be induced into permanent shape change to increase the size of the implantable device as a patient grows.SUMMARY

[0008] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary, and the foregoing Background, is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

[0009] In some embodiments, a liquid crystal elastomer composite material is described, the liquid crystal elastomer composite material including a liquid crystal elastomer network having dynamic allyl dithiol bonds incorporated therein; a photothermal agent dispersed throughout the liquid crystal elastomer network; and a thermal initiator incorporated into the liquid crystal elastomer composite material. In some embodiments, the photothermal agent includes gold nanorods, such as fully functionalized gold nanorods that are non-aggregated and well dispersed in the liquid crystal elastomer. When photoactuated, the gold nanorods can produce heat that cause shape change in the liquid crystal elastomer network. In some embodiments, the thermal initiator includes a high temperature thermal initiator that generates free radicals when exposed to hightemperatures. The generation of free radicals upon actuation of the thermal initiator can initiate bond rearrangement in the liquid crystal elastomer network and provide permanence of shape change in the liquid crystal elastomer.

[0010] In some embodiments, a method of preparing surface-functionalized gold nanorods is described, the method including a step of suspending a plurality of gold nanorods in a first solution to thereby provide a first mixture, and a step of sonicating the first mixture immediately following preparation of the first mixture. In some embodiments, the side surfaces of the gold nanorods suspended in the first solution are coated in cetyltrimethylammonium and the end surfaces of the gold nanorods are functionalized with methoxy polyethylene glycol) thiol. In some embodiments, the first solution comprises a mixture of ethanol, deionized water, and methoxy poly(ethylene glycol) thiol. The step of sonicating the first mixture generally results in replacement of all cetyltrimethylammonium on the side surfaces of the gold nanorods with methoxy polyethylene glycol) thiol such that all surfaces of the gold nanorods are functionalized with methoxy poly(ethylene glycol) thiol.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Non-limiting and non-exhaustive embodiments of the disclosed technology, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0012] Figure 1 is an illustration of a mechanism for preparing fully functionalized gold nanorods configured in accordance with various embodiments described herein.

[0013] Figure 2 is a flow chart illustrating a method for preparing fully functionalized gold nanorods configured in accordance with various embodiments described herein.

[0014] Figure 3 is an illustration of an LCE-AuNR composite material undergoing permanent shape change, the LCE-AuNR composition material being configured in accordance with various embodiments described herein.DETAILED DESCRIPTION

[0015] Embodiments are described more fully below with reference to the accompanying Figures, which form a part hereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense.

[0016] In a first aspect of the technology described herein, a method of preparing surface-functionalized gold nanorods (AuNRs) is aimed at providing a plurality of gold nanorods that are and remain individual, non-aggregated gold nanorods when dispersed within a liquid crystalline polymer network to thereby provide an improved LCE-AuNR composite material. This method is beneficial due at least to the present difficulty in preparing non-aggregated gold nanorods and the negative impact on LCE-AuNR performance when the AuNRs are aggregated and not well dispersed in the LCE matrix. Much of the difficulty in providing non-aggregated gold nanorods derives from the predominant process and materials used for generating gold nanorods. More specifically, gold nanorods are typically generated using a seed-mediated process in aqueous solution stabilized by the surfactant cetyltrimethylammonium bromide (CTAB). While CTAB can be at least somewhat effective for preventing AuNR aggregation, it is not miscible with hydrophobic monomers typically used in the fabrication of liquid crystalline elastomers. As such, mixing of CTAB-stabilized AuNRs with these monomers results in undesirable phase separation. An alternate route is therefore needed to provide non-aggregated AuNRs that are also suitable for use in fabricating LCE-AuNR composite materials and which remain non-aggregated and well dispersed when incorporated in an LCE network.

[0017] AuNRs generated with the seed-mediated process described previously are typically covered on all surfaces with CTAB. This is shown in Figure 1 , wherein AuNR 100 is covered in CTAB 110. The CTAB covers all side surfaces 101 and the end surfaces 102 of AuNR 100. In embodiments of a method described herein, the CTAB 110 is replaced on all surfaces of the AuNR 100 with thiol-term inated molecules 120. The method generallyrequires a two step or two pot process such that the CTAB 110 at end surfaces 102 of the AuNR 100 is first replaced with the thiol-terminated molecules 120, after which the CTAB 110 at side surfaces 101 of the AuNR 100 is replaced with the thiol-terminated molecules 120 to ultimately provide an AuNR 100 that is functionalized on all surfaces with the thiol- terminated molecules 120. In so doing, non-aggregated AuNRs are provided in a form that is suitable for use in subsequent fabrication of LCE-AuNR composite materials.

[0018] The two pot process described herein differs from and improves on previously known one-pot methods focused on functionalizing CTAB-covered AuNR with thiol- terminated molecules. In previously known one-pot methods, a high concentration of a thiol- terminated molecule (e.g., methoxy poly(ethylene glycol) thiol (mPEG-SH)) is added to a solution of AuNRs in which the CTAB concentration is above the critical micelle concentration (CMC). This one pot method ultimately results in incomplete functionalization of the AuNRs (i.e. , not all CTAB is replaced by mPEG-SH). Any CTAB left on the surface of the AuNR will induce phase separation with the prepolymers, while incomplete functionalization increases the likelihood for irreversible aggregation while in solution.

[0019] With reference to Figure 2, a method 200 of preparing surface-functionalized gold nanorods according to various embodiments described herein generally includes step 210 of suspending a plurality of partially functionalized gold nanorods in a first solution to thereby provide a first mixture, wherein the first solution comprises a mixture of ethanol, deionized water, and a thiol-terminated molecule, and a step 220 of sonicating the first mixture immediately following preparation of the first mixture. The sonication carried out in step 220 of method 200 generally results in replacement of all cetyltrimethylammonium on the side surfaces of the gold nanorods with the thiol-terminated molecules such that all surfaces of the gold nanorods are functionalized with the thiol-terminated molecule.

[0020] Step 210 of method 200 generally calls for providing a plurality of partially functionalized gold nanorods such that these partially functionalized nanorods can then be suspended in the first solution as part of carrying out step 210. The partially functionalized gold nanorods generally refer to gold nanorods where the side surfaces of the gold nanorods are coated in CTAB but the ends of the gold nanorods are functionalized with a thiol- terminated molecule such as mPEG-SH. While mPEG-SH is used herein as the exemplarythiol-terminated molecule, it should be appreciated that any other suitable thiol-term inated molecules may be used in the methods described herein. The middle gold nanorod 100 shown in Figure 1 generally illustrates a partially functionalized gold nanorod 100, where CTAB 110 is present on the side surfaces 101 the gold nanorod 100 and thiol-terminated molecules 120 are present on the end surfaces 102 of the gold nanorod 100.

[0021] The partially functionalized gold nanorods are generally prepared by methods known in the art. For example, AuNRs produced by the seed-mediated method previously mentioned generally provide AuNRS covered on all surfaces by CTAB. In one exemplary process for partially functionalizing the AuNRs, the AuNRs are first sonicated in a water bath sonicator for ~30 minutes to ensure dispersion. 1 mL of 1 .1 mM solution of mPEG-SH (MW: 800) sonicated in deionized water for about 5 minutes is then prepared. Next, 100 pL of AuNR is added to 900 pL of mPEG-SH and vortexed. This mixture contains a -SH concentration of 1 mM, an AuNR concentration of 0.5-1 nM, and a CTAB concentration of 1 mM. By dropping the CTAB concentration to the CMC, the bilayer that normally stabilizes the AuNR is disrupted, and the thiols can more easily penetrate the CTAB layer to bind to the surface of the AuNR. However, because of the continued presence of CTAB in solution, the AuNR is not fully functionalized with the thiol. More specifically, CTAB is generally retained along the side surfaces of the AuNR and the thiols are mostly bound to the ends of the gold nanorods, thus providing the partially functionalized gold nanorods required for step 210 in method 200 and illustrated in Figure 1.

[0022] Once partially functionalized AuNRs are provided, step 210 can proceed by suspending the plurality of partially functionalized gold nanorods in a first solution to thereby provide a first mixture. The first solution generally comprises a mixture of ethanol, deionized water, and mPEG-SH. In some embodiments, the first solution is prepared by first mixing together a 90% ethanol and 10% sonicated deionized water mixture, which is then combined with mPEG-SH at a desired concentration to provide the first solution. In some embodiments, the amount of mPEG-SH used in preparing the first solution is selected to provide a large excess of mPEG-SH relative to the number of thiols that could theoretically bind to the surface the AuNRs which will be added to the first solution, taking into account both the quantity and surface area of the AuNRs to be suspended in the first solution. Inone example, the concentration of mPEG-SH used in the first solution is calculated to provide a ~50 fold excess of thiols than could theoretically be bound to the quantity of AuNRs used in the first solution.

[0023] In some embodiments, prior to suspending the partially functionalized AuNRs in the first solution, the partially functionalized AuNRS may be centrifuged (such as at 14,800 rpm for 15 minutes), after which the supernatant is discarded and the AuNRs are suspended in the first solution.

[0024] In step 210, combining the partially functionalized AuNRs with the first solution to prepare the first mixture causes the remaining CTAB to be removed from the side surfaces of the AuNRs because the ethanol component of the first solution is an effective solvent for CTAB. However, this sudden removal of CTAB can cause aggregation of AuNRs absent further processing steps, and thus method 200 further includes step 220 wherein, immediately following preparation of the first mixture, the first mixture is sonicated. Sonication can be carried out for any suitable period of time that results in the AuNRs becoming fully functionalized with the thiol-term inated molecule, though in some embodiments, sonication is carried out for about two hours. Immediate sonication prevents AuNR aggregation after removal of CTAB, and allows sufficient time for the mPEG-SH component of the first mixture to fully cover the surface of the AuNR that has been stripped of CTAB by the ethanol. Referring back to Figure, 1 , the final gold nanorod 100 of the illustrated sequence depicts a fully functionalized gold nanorod 100 where both the side surfaces 101 and the end surfaces 102 are functionalized with thiol-term inated molecules 120.

[0025] Following sonication, the method 200 may optionally include an additional step of centrifuging the first mixture, discarding the supernatant, and collecting the now fully functionalized and non-aggregated AuNRs.

[0026] Once the fully functionalized AuNRs are prepared according to method 200, the AuNRs may be resuspended in dichloromethane (DCM), and the AuNRs will remain dispersed and non-aggregated. This allows the prepared functionalized AuNRs to be stored prior to use in, e.g., LCE-AuNR composite material formation. In some embodiments, method 200 results in greater than 70% of the gold nanorods suspended in the DCM beingindividual, isolated gold nanorods that are not touching or bound to one or more other gold nanorods. In some embodiments, greater than 80% or greater than 90% individual nanorods is achieved by the method 200. For gold nanorods suspended in DCM that are not isolated, the majority of non-isolated gold nanorods are in pairs of two, and aggregation beyond groups of two gold nanorods is generally not exhibited. When these AuNRs are used in the formation of LCE-AuNR composite materials as discussed in greater detail below, the AuNRs retain their non-aggregation such that similar or identical levels of individual gold nanorods are exhibited in the LCE-AuNR composite material. That is to say, LCE-AuNR composite material prepared using the fully functionalized AuNR described herein may include greater than 70% individual gold nanorods.

[0027] When the fully functionalized AuNRs are used in preparation of an LCE-AuNR composite material, the process for preparing the LCE with well dispersed, non-aggregated AuNRs generally follows known LCE formation processing steps. For example, LCE-AuNR composite material may be prepared using a conventional two-step polymerization reaction. In the first reaction, thiol-term inated liquid crystalline oligomers are generated through a base-catalyzed thiol-Michael addition reaction between mesogenic diacrylates and a molar excess of a low-molecular weight dithiol (e.g., BMEE). In one non-limiting example, C6BAPE and C3M are used in the first reaction to prepare the thiol-term inated LC oligomers for the second LCE-forming reaction.

[0028] In the second LCE-forming reaction, the thiol-terminated LC oligomers from the first reaction are combined with crosslinker(s), initiator(s), and DCM to form a mixture that is subsequently combined with the mixture of AuNR in DCM described previously. After combining the two mixtures, DCM is removed from the mixture, such as by rotary evaporation with continued sonication such that the mixture remains homogenous during solvent evaporation. The mixture may then be fully dried, such as by placing the mixture in a vacuum oven overnight. LCE-AuNR composite material may then prepared be subjecting the mixture to polymerization, such photopolymerization. In one example, films of LCE- AuNR may be prepared in the polydomain orientation via photopolymerization. Due to the full functionalization of AuNR prior to use in preparing the LCE-AuNR composite material, the AuNR remains highly dispersed as single nanorods in the LCE-AuNR compositematerial, with few or no nanorod pairs. This method also results in the AuNRs being homogenously distributed throughout the thickness of the LCE-AunR composite material with no evidence of surface segregation.

[0029] In another exemplary LCE formation process, AuNRs dispersed in DCM can be directly added to polymerized LCNs / LCEs. In this example, LCNs / LCEs are formed in a similar manner as described above, with the exception that AuNRs are not added prior to polymerization. When AuNRs are added after polymerization, DCM is used to swell the polymer network, increasing the mesh size and allowing the AuNRs to infiltrate the network. After swelling to equilibrium, the polymer network is placed in a vacuum oven overnight to remove all of the DCM. The AuNRs remain trapped in the network, but may have a more heterogeneous distribution, as the solvent evaporation from the edges of the polymer may draw AuNRs towards the edge of the polymer. Regardless, this is another method for introducing dispersed AuNRs into polymer networks that are not compatible with the method described previously for oligomers.

[0030] As noted above, the LCE formation process generally involves mixing one or more initiators with the oligomers as part of the LCE formation process so that initiators are present in the mixture to induce the polymerization reaction used to form the LCE network and / or so that initiators and / or agents are incorporated into the formed LCE material for inducing LCE shape change. In the case of incorporating AuNRs in the LCE composite material, the AuNRs serve as photothermal agents for inducing shape change in the LCE material. As described previously, when exposed to certain light wavelengths, the AuNRs generate heat, which heat can then induce shape change in the LCE material. In some embodiments, NIR light is a preferred stimulus for shape change of LCEs, and the AuNRs may be designed so as to be actuatable by exposure to NIR light, e.g., by tailoring the aspect ratio of the AuNRs during seed-mediated process. NIR light as the AuNR stimulus may be especially useful in biomedical applications of the LCE-AuNR material, such as biomedical implants. NIR light in the wavelength range from 700-900 nm can penetrate several millimeters into tissues and is generally safe to cells and tissues. Experimentation on 3D- printed LCE-AuNRs actuated by NIR exhibited efficient photothermal heating and rapid, fullthickness actuation. Photothermal efficiency is critical to a NIR-responsive implant, as lightattenuation through tissue necessitates the use of higher light intensities to obtain the same degree of photothermal heating and thus shape change. In some embodiments, the high dispersion of AuNRs achieved by the methods described herein allows for use of a relatively low concentration of AuNRs in an implant to achieve the same photothermal heating rate as in less dispersed, higher concentration exampled. Furthermore, because of this low concentration of AuNRs, the NIR light can penetrate through the full thickness of the LCE- AuNR resulting in this full-thickness actuation. This is in contrast to previous reports in which AuNR aggregation (or surface segregation) resulted in most of the NIR light being absorbed on the incident side, and as a result the material generating a thermal gradient and bends instead of actuating linearly.

[0031] In another embodiment described herein, an LCE-AuNR composite material is described wherein at least a thermal initiator (in addition to and different from the AuNR photothermal agent) is included in the composite material. The presence of a thermal initiator in the LCE composite material potentially expands the uses for the composite material into new applications, such as certain biomedical applications requiring permeance or semi-permeance in LCE shape change. Accordingly, in some embodiments, the LCE composite material described herein generally includes an LCE network, a photothermal agent (which may be in the form of individual fully functionalized AuNRs as described previously) dispersed throughout the LCE network, and a thermal initiator incorporated into the LCE composite material. In some embodiments, the photothermal agent and the thermal initiator are selected such that, when exposed to certain light wavelengths (e.g., NIR), the photothermal agent heats the LCE network to a first temperature that induces a shape change in the LCE network, while the thermal initiator, when exposed to a second temperature that is greater than the first temperature, generates radicals and thereby induces chemical reactions within the LCE that can lead to permanence in LCE shape change.

[0032] The LCE network that forms the base of the LCE composite material described herein may be any suitable LCE network, including, but not limited to, the LCE network previously described wherein C6BAPE and C3M serve as the primary oligomers in the formation of the LCE network. The LCE network further comprises a dynamic bonds, suchas, but not limited to, dynamic allyl sulfide bonds, which, as described in greater detail below, may allow for permanent or semi-permanent shape change in the LCE. The ability to achieve permanent shape change may expand the applications of the LCE material, such as to biomedical applications not previously contemplated.

[0033] The dynamic bonds incorporated into the LCE network may be any dynamic bonds suitable for inclusion in an LCE network and that, when exposed to free radicals, exhibit reversible bond exchange and / or addition. In one not limiting example, the dynamic bonds are allyl sulfide bonds incorporated into the LCE network, which may be covalent adaptable allyl sulfide bonds capable of radical-medicated addition-fragmentation chain transfer (AFT). In some embodiments, these dynamic allyl sulfide bonds are incorporated into the LCE network by including allyl dithiol (ADT) in the mixture of oligomers used to form the LCE network. For example, a portion of the dithiol BMEE used in the first reaction step of the LCE formation process can replaced with ADT to thereby incorporate dynamic allyl sulfide bonds in the LCE network.

[0034] The thermal initiator included in the LCE composite material described herein is preferably a high temperature thermal initiator that, upon exposure to the required high temperatures, generates the free radicals necessary to induce allyl sulfide bond exchange. By high temperature it is meant that the temperature that induces the generation of free radicals by the thermal initiator is at least higher than the temperature that induces shape change in the LCE network. In some embodiments, the high temperature thermal initiator is selected from those thermal initiators capable of generating free radicals when exposed to a temperature higher than about 100°C. One non-limiting example of a suitable high temperature thermal initiator is 2,2'-Azobis(N-butyl-2-methylpropionamide) (VAm-110).

[0035] The synergistic effect of using a photothermal agent together with a high temperature thermal initiator within the same LCE material, especially with respect to safely achieving shape change permanence in an implantable device comprising the LCE material, can be exemplified by considering a case where fully functionalized and well dispersed AuNRs are engineered to be actuatable upon exposure to NIR and used in conjunction with VAm-110 configured to generate radicals when exposed to temperatures above 100°C. In this example, NIR as a stimulus will cause AuNRs in the implanted LCE material to generateheat and ultimately increase the bulk temperature within the LCE material to between 45 and 50°C. This bulk material temperature is safe for the patient and successfully induces shape change in the LCE. At the same time, the activation of AuNRs by NIR results in the AuNRs generating temperatures above 100°C at a localized level, thereby actuating VAm- 110 located in close proximity to the AuNRs to generate free radicals. Critically, this local generation of heat is self-contained within the material system and isolated from cellular contact, and therefor does not endanger the patient. The generated free radicals serve to induce bond rearrangement in the dynamic allyl sulfide bonds, which results in rendering permanent the shape change in the LCE induced by the AuNR raising the bulk temperature of the material. Finally, it is noted that the VAm-110 is stable at body temperatures and at the bulk material temperature after AuNR activation, thus meaning the VAm-110 will not deteriorate within the LCE-AuNR material once implanted.

[0036] With reference to Figure 3, an illustration of achieving shape change permanence in an LCE-AuNR material including dynamic allyl sulfide bonds and a high temperature thermal initiator is provided. The configuration and mechanism illustrated in Figure 3 may be suitable for various implantable biomedical devices, of which one nonlimiting example is a pulmonary artery band (PAB). In some embodiments, it is possible for the implantable biomedical device to be made entirely of this LCE-AuNR material, while in other embodiments, the LCE-AuNR material is component of the implantable biomedical device. As shown in Figure 3, the LCE-AuNR material 300 may be 3D printed such that the material has LCE alignment in the short axis. Localized NIR irradiation 310 in the middle (lengthwise) of the material 300 induces LCE shape change via activating the AuNRs to increase the bulk temperature of the material to between 45 and 50°C. This results in the material 300 narrowing in the targeted area and elongating overall to thereby become elongated material 300’. At the same time, localized free radical generation resulting from AuNRs heating the thermal initiators to above 100°C will fix the network in the new geometry via AFT. Thus, even after removal of the localized NIR irradiation 310, the elongated material 300’ retains its elongation.

[0037] While not shown in Figure 3, the material 300 can be expanded multiple times by changing the region that is irradiated. Furthermore, since the liquid crystalline order doesnot fall to near zero at 50 °C, liquid crystalline order will remain in the reprogrammed network and may allow for repeated irradiation of the same spot to obtain an even greater degree of elongation.

[0038] While this disclosure has focused primarily on gold nanrods, it should be appreciated that other gold nanoinclusions are also suitable for use in the methods and materials described herein. For example, the gold nanoinclusions may have other shapes besides rod shapes. These gold nanoinclusions (having any shape) may be fully functionalized and incorporated into an LCE network using the same methods as described herein.

[0039] Additionally, while this disclosure has focused primarily on gold nanorods, it should be appreciated that other photothermally responsive elements may be used in conjunction with or as a replacement to gold nanorods in the LCE network, including in an LCE network specifically adapted for use in an implantable biomedical device capable of permanent shape change. In one non limiting example, an alternative to gold nanorods that may be used as a photothermal agent in an LCE network is polydopamine.

[0040] Furthermore, while this disclosure has focused primarily on LCE networks, it should be appreciated that the technology described herein may be equally applicable to other polymer networks. In some embodiments, the technology described herein is applicable to any polymer network provided that the polymer network is generally compatible with DCM (e.g., the pre-polymer solution can be dissolved in DCM or the polymer network can be swollen in DCM after polymerization).

[0041] From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

[0042] Although the technology has been described in language that is specific to certain structures and materials, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and materials described. Rather, the specific aspects are described as forms of implementing the claimed invention.Because many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

[0043] Unless otherwise indicated, all number or expressions, such as those expressing dimensions, physical characteristics, etc., used in the specification (other than the claims) are understood as modified in all instances by the term "approximately". At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter recited in the specification or claims which is modified by the term "approximately" should at least be construed in light of the number of recited significant digits and by applying rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass and provide support for claims that recite any and all sub-ranges or any and all individual values subsumed therein. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all sub-ranges or individual values that are between and / or inclusive of the minimum value of 1 and the maximum value of 10; that is, all sub-ranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

Claims

CLAIMSWhat is claimed is:1 . A liquid crystal elastomer composite material, comprising: a liquid crystal elastomer network having dynamic bonds incorporated therein; a photothermal agent dispersed throughout the liquid crystal elastomer network; and a thermal initiator incorporated into the liquid crystal elastomer composite material.

2. The liquid crystal elastomer composite material of claim 1 , wherein the dynamic bonds comprise allyl dithiol dynamic bonds.

3. The liquid crystal elastomer composite material of claim 1 , wherein the photothermal agent comprises gold nanorods.

4. The liquid crystal elastomer composite material of claim 1 , wherein the temperature at which the thermal initiator is induced to generate radicals is greater than the bulk polymer temperature of the liquid crystal elastomer composite material during photothermal actuation of the liquid crystal elastomer composite material.

5. The liquid crystal elastomer composite material of claim 4, wherein the temperature at which the thermal initiator induces generation of radicals is greater than about 100°C.

6. The liquid crystal elastomer composite material of claim 1, wherein the thermal initiator comprises 2,2'-Azobis(N-butyl-2-methylpropionamide) (VAm-110).

7. The liquid crystal elastomer composite material of claim 1 , wherein the photothermal agent is configured to generate heat upon application of near infrared light to the liquid crystal elastomer composite material, and wherein the thermal initiator is configured to generate radicals upon application of heat generated by the photothermal agent to the thermal initiator.

8. The liquid crystal elastomer composite material of claim 1 , wherein the entire surface of the gold nanorods is functionalized with thiol-term inated molecules.

9. The liquid crystal elastomer composite material of claim 8, wherein the thiol- terminated molecule comprises methoxy poly(ethylene glycol) thiol (mPEG-SH).

10. The liquid crystal elastomer composite material of claim 1 , wherein greater than 80% of the gold nanorods dispersed throughout the liquid crystal elastomer network are individual, non-aggregated gold nanorods.

11. The liquid crystal elastomer composite material of claim 1 , wherein the liquid crystal elastomer composite material is incorporated into an implantable biomedical device.

12. The liquid crystal elastomer composite material of claim 11 , wherein the implantable biomedical device consists of or consists essentially of the liquid crystal elastomer composite material.

13. A method of preparing surface-functionalized gold nanorods, comprising: suspending a plurality of gold nanorods in a first solution to thereby provide a first mixture, wherein: the side surfaces of the gold nanorods are coated in cetyltrimethylammonium and the end surfaces of the gold nanorods are functionalized with a thiol-term inated molecule; and the first solution comprises a mixture of ethanol, deionized water, and thiol- term inated molecule; and immediately following preparation of the first mixture, sonicating the first mixture; wherein sonicating the first mixture results in replacement of all cetyltrimethylammonium on the side surfaces of the gold nanorods with thiol-term inated molecule such that all surfaces of the gold nanorods are functionalized with thiol-term inated molecule.

14. The method of claim 13, further comprising: following sonication of the first mixture, mixing the gold nanorods with liquid crystal oligomers to thereby provide a second mixture; and polymerizing the second mixture to thereby prepare a liquid crystal elastomer network having gold nanorods dispersed therein; wherein greater than 80% of the gold nanorods dispersed in the liquid crystal elastomer network are individual, non-aggregated gold nanorods.

15. The method of claim 13, wherein the thiol-term inated molecule comprises methoxy polyethylene glycol) thiol (mPEG-SH).

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