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Since 30 years, liquid crystalline elastomers (LCEs) have been attracting the attention of many researchers thanks to their anisotropic molecular structure which allows them to build up artificial muscles. Possible applications span from soft robotics to biomedical or tunable optical devices. The power of thiol-yne click chemistry was recently demonstrated in the preparation of smart polymers, in particular LCEs, in which the mesogenic units are incorporated both in the main-chain and as pendant groups. To enrich the library of available LCE materials, in this work, several liquid crystalline dithiols and alkynes have been synthesized and copolymerized to obtain elastomers with different thermomechanical properties. The architecture of the main chain was found to play a prominent role in modulating the clearing point in a range of 60 °C, whereas only a minor contribution is given by the mesogens in the side chain. On the other hand, the mechanical response resulted highly sensitive to fine details of the side-chain structure. Accordingly, the present study not only improves the basic understanding of the chemical-physical properties of LCEs but paves the way to the preparation of multicomponent actuators able to deform in different temperature ranges, thus ultimately leading to complex soft robotic operations.

Light responsive shape-changing polymers are able to mimic the function of biological muscles accomplishing mechanical work in response to selected stimuli. A variety of manufacturing techniques and chemical processes can be employed to shape these materials to different length scales, from centimeter fibers and films to 3D printed micrometric objects trying to replicate biological functions and operations. Controlled deformations shown to mimick basic animal operations such as walking, swimming or grabbing objects, while also controlling the refractive index and the geometry of devices, opens up the potential to implement tunable optical properties. Another possibility is that of combining artificial polymers with cells or biological tissue (such as intact cardiac trabeculae) with the aim to improve tissue formation in vitro or to support the mechanical function of damaged biological muscles. Such versatility is afforded by chemistry. New customized liquid crystalline monomers are presented here that modulate material properties for different applications. The role of synthetic material composition is highlighted as we demonstrate how using apparently similar molecular formulations, that liquid crystalline polymers can be adapted to different technological and medical challenges.

Photopolymerization of customized materials became a well-established technique for micro- and nano-fabrication of photonic structures, and their optical properties as the refractive index should be precisely tailored to design specific photonic features. For this purpose, the refractive index determination in macroscopic samples is not exhaustive, and an in situ characterization is thus necessary at both the macro- and microscale to point out how different polymerization processes differently modulate the optical properties. In particular, we focus our attention on liquid crystalline networks (LCNs) that have been studied as birefringent materials whose tunable response is of interest for applications in different fields such as in robotics, biomedicine, and photonics. By tuning the molecular composition of LCN mixtures, e.g., modifying the cross-linker and dye amount inside the polymer network, the refractive index and the optical anisotropy of microscopic and macroscopic samples have been engineered and measured by a refractometer method under temperature variation or light actuation stimuli. Monitoring the refractive index at different length scales showed that two-photon polymerization increases the birefringence in microscopic structures, and the maximum variation of the optical anisotropy is achieved by a remote laser light stimulus.

Enhancing the resolution of 3D patterning techniques in functional soft polymers enlarges the application areas of responsive shape-changing materials, for tunable nanophotonics and nanorobotics. Thanks to the recent advances of polymer science, the palette of available materials for nanomanufacturing is becoming wider and wider--although the comprehension of their polymerization process by two-photon polymerization is still incomplete. In this work, both shrinking of the minimal polymerizable unit and a significant improvement of the mechanical stability of microstructured soft polymers, in particular of liquid crystalline networks, are demonstrated. To this aim, temperature control enhances the resolution and reduces the swelling of the polymerized structures, thus avoiding deviations of the final structure from the intended design. This fine control on the nanoscale features enables the use of soft responsive materials not only for bulky microelements, but also for high-resolution structures with more complex design.

Summary: Development of biological tissues in vitro is not a trivial task and requires the correct maturation of the selected cell line. To this aim, many attempts were done mainly by mimicking the biological environment using micro/nanopatterned or stimulated scaffolds. However, the obtainment of functional tissues in vitro is still far from being achieved. In contrast with the standard methods, we here present an easy approach for the maturation of myotubes toward the reproduction of muscular tissue. By using liquid crystalline networks with different stiffness and molecular alignment, we demonstrate how the material itself can give favorable interactions with myoblasts helping a correct differentiation. Electrophysiological studies demonstrate that myotubes obtained on these polymers have more adult-like morphology and better functional features with respect to those cultured on standard supports. The study opens to a platform for the differentiation of other cell lines in a simple and scalable way.

International audience; The study of evolutionarily optimized solutions of animals and plants is used in biologically inspired engineering to find inspiration for the development of better devices and technology. In nature, the morphology of living systems is responsible not only for the biological functions but frequently also for their appearance. A fascinating feature based on material architecture is that of structural coloration, which receives growing interest for the development of efficient reflective coatings, photonic devices, and optical sensors. [1-3] An inspiring example is provided by the nanoarchitecture of the butterfly wings. Among them, the color of Morpho menelaus [4-6] is mainly determined by the interaction of light with the wing's complex scale morphology that produces a brilliant blue structural color as a sum of multiple optical effects. A specific characteristic of this species is the low angular dependence of wing coloration that remains bluish over a wide range of viewing angles, in contrast to what is typically observed in many other structural colors. [7] This unique property motivated a profound exploration of the morphology of the wing scales that are constituted by nanostructured cover and ground scales. The scales are nanostructured in ridges with a lamellar structure

Polymeric matrices offer a wide and powerful platform for integrated photonics, complementary to the well-established silicon photonics technology. The possibility to integrate, on the same chip, different customized materials allows for many functionalities, like the ability to dynamically control the spectral properties of single optical components. Within this context, this Article reports on the fabrication and optical characterization of integrated photonic circuits for the telecom C-band, made of a combination of both rigid and tunable elastic polymers. By using a 3D photolithographic technique (direct laser writing), in a single-step process, every building block of the polymeric circuit is fabricated: straight and bent waveguides, grating couplers, and single and vertically coupled whispering gallery mode resonators designed in planar and vertical geometries. Using this platform, a new type of operation was introduced through true three-dimensional integration of tunable photonic components, made by liquid crystalline networks that can be actuated and controlled by a remote and non-invasive light stimulus. Depending on the architecture, it is possible to integrate them as elastic actuators or as constituents of the photonic cavity itself. The two strategies then exploit the optical induced deformation and variation of its refractive index, inducing a net red or blue shift of the cavity resonances, respectively. This work paves the way for light-tunable optical networks that combine different photonic components, made by glassy or shape-changing materials, in order to implement further photonic circuit requirements.

Quantum technologies could largely benefit from the control of quantum emitters in sub-micrometric size crystals. These are naturally prone to integration in hybrid devices, including heterostructures and complex photonic devices. Currently available quantum emitters in nanocrystals suffer from spectral instability, preventing their use as single-photon sources for most quantum optics operations. In this work we report on the performances of single-photon emission from organic nanocrystals (average size of hundreds of nm), made of anthracene (Ac) and doped with dibenzoterrylene (DBT) molecules. The source has hours-long photostability with respect to frequency and intensity, both at room and at cryogenic temperature. When cooled to 3 K, the 00-zero phonon line shows linewidth values (50 MHz) close to the lifetime limit. Such optical properties in a nanocrystalline environment recommend the proposed organic nanocrystals as single-photon sources for integrated photonic quantum technologies.

The ability to obtain 3D polymeric objects by a 2D-to-3D shape-shifting method is very appealing for polymer integration with different materials, from metals in electronic devices to cells in biological studies. Such functional reshaping can be achieved through self-folding driven by a strain pattern designed into the molecular network. Among polymeric materials, liquid crystalline networks (LCNs) present an anisotropic molecular structure that can be exploited to tailor internal strain, resulting in a natural non-planar geometry when prepared in the form of flat films. In this article, we analyze the influence of different molecular parameters of the monomers on the spontaneous shape of the polymeric films and their deformation under different stimuli, such as heating or light irradiation. Modifying the alkilic chains of the crosslinkers is a simple and highly effective way to increase the temperature sensitivity of the final actuator, while modifying ester orientation on the aromatic core interestingly acts on the bending direction. Combining such effects, we have demonstrated that LCN stripes made of different monomeric mixtures originate complex non-symmetric deformation under light activation, thus opening up new applications in photonic and robotics.

Light responsive liquid crystalline networks were prepared by photopolymerization of azobenzene-doped mesogen mixtures and applied for production of micro-actuators by a laser writing technique. Adjusting the cross-linker content was found to be an efficient and easy way to control the dynamics of light-induced deformation from the micro- up to the macro-meter length scales. Starting from a complete characterization of the response of millimeter-sized stripes under irradiation with different sources (LED and laser light), micro-structures based on different monomer mixtures were analyzed for micro-actuator preparation. Double stripes, able to perform a light driven asymmetric movement due to the different mixture properties, were created by a double step process through a laser writing system. These results are a simple demonstration of an optically activated non-reciprocal movement in the microscale by a chemical material manipulation. Moreover, we demonstrate a rapid actuator dynamics that allows a movement in the second time scale for macrostructures and a millisecond actuation in the microscale.

Rationale: Despite major advances in cardiovascular medicine, heart disease remains a leading cause of death worldwide. However, the field of tissue engineering has been growing exponentially in the last decade and restoring heart functionality is now an affordable target; yet, new materials are still needed for effectively provide rapid and long-lasting interventions. Liquid crystalline elastomers (LCEs) are biocompatible polymers able to reversibly change shape in response to a given stimulus and generate movement. Once stimulated, LCEs can produce tension or movement like a muscle. However, so far their application in biology was limited by slow response times and a modest possibility to modulate tension levels during activation. Objective: To develop suitable LCE-based materials to assist cardiac contraction. Methods and Results: Thanks to a quick, simple, and versatile synthetic approach, a palette of biocompatible acrylate-based light-responsive LCEs with different molecular composition was prepared and mechanically characterized. Out of this, the more compliant one was selected. This material was able to contract for some weeks when activated with very low light intensity within a physiological environment. Its contraction was modulated in terms of light intensity, stimulation frequency, and t on /t off ratio to fit different contraction amplitude/time courses, including those of the human heart. Finally, LCE strips were mounted in parallel with cardiac trabeculae, and we demonstrated their ability to improve muscular systolic function, with no impact on diastolic properties. Conclusions: Our results indicated LCEs are promising in assisting cardiac mechanical function and developing a new generation of contraction assist devices.

The ability to control cell alignment represents a fundamental requirement toward the production of tissue in vitro but also to create biohybrid materials presenting the functional properties of human organs. However, cell cultures on standard commercial supports do not provide a selective control on the cell organization morphology, and different techniques, such as the use of patterned or stimulated substrates, are developed to induce cellular alignment. In this work, a new approach toward in vitro muscular tissue morphogenesis is presented exploiting liquid crystalline networks. By using smooth polymeric films with planar homogeneous alignment, a certain degree of cellular order is observed in myoblast cultures with direction of higher cell alignment corresponding to the nematic director. The molecular organization inside the polymer determines such effects since no cell organization is observed using homeotropic or isotropic samples. These findings represent the first example of cellular alignment induced by the interaction with a nematic polymeric scaffold, setting the stage for new applications of liquid crystal polymers as active matter to control tissue growth.

Manipulating objects at the micro and nano scale is still an open fascinating challenge that scientists are addressing by proposing different approaches to obtain machines with basic or complex functions. Combining shape changing polymers that differently respond to optical stimuli on the basis of the molecular alignment, together with 3D structuration at the microscale (with nanometric features), we demonstrated synthetic microrobots entirely powered by light. The arbitrary design allowed to mimic diverse animal and even humanoid tasks as walking, grabbing or manipulating objects, even overcoming natural limitations present at such small scale. Liquid crystalline networks offer the possibility to perform different movements depending on their molecular alignment and, controlling by light their elastic deformation, wireless activation of micro-machines was obtained. We report here how tuning intrinsic parameters, as the lithographic ones, and an external setting as the actuation power, it is possible to induce diverse deformations and time responses. Such results can be exploited to tailor the working mechanism and actuation speed of different micro robots. Engineering a proper structural design and combining different time responding materials would generate not reciprocal motion, basic and necessary property to achieve swimming at the microscale. This first technical demonstration paves the way to a micro swimmer fueled by light.

The 1,3 dipolar cycloaddition reactions of three pentose-derived pyrroline N-oxides with mono- and disubstituted alkenes are reported. A strong dependence of the diastereoselectivity of the cycloadditions on the relative configuration of the nitrone stereocentres was observed. Further transformation of the reaction products allowed the synthesis of four new tetrahydroxylated indolizidines. Their activity as glycosidase inhibitors was evaluated against a panel of commercially available glycosidases. The specificity of inhibitory activity against amyloglucosidase and α-mannosidases depends on the configuration at C-2 of the indolizidine moiety.

Recent discoveries evidenced that many cells organize into well-aligned nematic domains, showing also their topological defects and suggesting the liquid crystalline order to be necessary for some biological functions. These evidences were described as the basis for the development of a new area of research in which polymeric liquid crystals were developed to exploit and promote cell adhesion and proliferation towards tissue regeneration. To address the requirements of tissue engineering, new biocompatible materials must be designed and synthesized to support cell adherence and growth together with nutrient transport under physiological condition. This Minireview presents a journey that, starting from the first discovery of liquid crystalline phases in biological (natural) materials with different structures and physical-chemical properties, will inform readers of the very recent application of liquid crystal polymeric materials as functional cell scaffolds to address current tissue engineering issues.

We report on organic nanocrystals doped with tunable concentration of fluorescent molecules, grown with an easy and inexpensive method and performing as bright and photostable single-photon sources at both room and cryogenic temperatures.

Materials of which the optical response is determined by their structure are of much interest both for their fundamental properties and applications. Examples range from simple gratings to photonic crystals. Obtaining control over the optical properties is of crucial importance in this context, and it is often attempted by electro-optical effect or by using magnetic fields. In this paper, we introduce the use of light to switch and tune the optical response of a structured material, exploiting a physical deformation induced by light itself. In this new strategy, light drives an elastic reshaping, which leads to different spectral properties and hence to a change in the optical response. This is made possible by the use of liquid crystalline networks structured by Direct Laser Writing. As a proof of concept, a grating structure with sub-millisecond time-response is demonstrated for optical beam steering exploiting an optically induced reversible shape-change. Experimental observations are combined with finite-element modeling to understand the actuation process dynamics and to obtain information on how to tune the time and the power response of this technology. This optical beam steerer serves as an example for achieving full optical control of light in broad range of structured optical materials.

In this contribution, we will report on a new adventure in the field of photonics, combining the optical control of photonic materials with that of true micro meter scale robotics. We will show how one can create complex photonic structures using polymers that respond to optical stimuli, and how this technology can be used to create moving elements, photonic skin, and even complete micro meter size robots that can walk and swim. Using light as the only source of energy. The materials that we have developed to that end can also be used to realize tunable photonic components that respond to light and adapt their photonic response on the basis of the illumination conditions.

A successful realisation of sub-20 nm features on silicon (Si) is becoming the focus of many technological studies, strongly influencing the future performance of modern integrated circuits. Although reactive ion etching (RIE), at both micrometric and nanometric scale has already been the target of many studies, a better understanding of the different mechanisms involved at sub-20 nm size etching is still required. In this work, we investigated the influence of the feature size on the etch rate of Si, performed by a cryogenic RIE process through cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer (DBC) masks with diameter ranging between 19-13 nm. A sensible decrease of the etch depth and etch rate was observed in the mask with the smallest feature size. For all the DBCs under investigation, we determined the process window useful for the correct transfer of the nanometric cylindrical pattern into a Si substrate. A structural and physicochemical investigation of the resulting nanostructured Si is reported in order to delineate the influence of various RIE pattern effects. Feature-size-dependent etch, or RIE-lag, is proved to significantly affect the obtained results.

Cardiomyocytes from human induced pluripotent stem cells (hiPSC-CMs) are the most promising human source with preserved genetic background of healthy individuals or patients. This study aimed to establish a systematic procedure for exploring development of hiPSC-CM functional output to predict genetic cardiomyopathy outcomes and identify molecular targets for therapy. Biomimetic substrates with microtopography and physiological stiffness can overcome the immaturity of hiPSC-CM function. We have developed a custom-made apparatus for simultaneous optical measurements of hiPSC-CM action potential and calcium transients to correlate these parameters at specific time points (day 60, 75 and 90 post differentiation) and under inotropic interventions. In later-stages, single hiPSC-CMs revealed prolonged action potential duration, increased calcium transient amplitude and shorter duration that closely resembled those of human adult cardiomyocytes from fresh ventricular tissue of patients. Thus, the major contribution of sarcoplasmic reticulum and positive inotropic response to &beta, adrenergic stimulation are time-dependent events underlying excitation contraction coupling (ECC) maturation of hiPSC-CM, biomimetic substrates can promote calcium-handling regulation towards adult-like kinetics. Simultaneous optical recordings of long-term cultured hiPSC-CMs on biomimetic substrates favor high-throughput electrophysiological analysis aimed at testing (mechanistic hypothesis on) disease progression and pharmacological interventions in patient-derived hiPSC-CMs.

In this article we demonstrate that a grating fabricated through nanoscale volumetric crosslinking of a liquid crystalline polymer enables remote polarization control over the diffracted channels. This functionality is a consequence of the responsivity of liquid crystal networks upon light stimuli. Tuning the photonic response of the device is obtained thanks to both a refractive index and a shape change of the grating elements induced by a molecular rearrangement under irradiation. In particular, the material anisotropy allows for nontrivial polarization state management over multiple beams. Absence of any liquid component and a time response down to 0.2 milliseconds make our device appealing in the fields of polarimetry and optical communications., Comment: 16 pages,8 figures, featured article in ALP

The synthesis of three tetrahydroxyindolizidines and one tetrahydroxypyrrolizidine related to natural hyacinthacines B and their biological evaluation as glycosidase inhibitors is reported. The target molecules were obtained through highly stereoselective cycloadditions between sugriched allylic and homoallylic alcohols. This allowed the installation of a methyl group at C5 – a common feature of many natural hyacinthacines – with high control over the stereoselectivity. The new compounds inhibit amyloglucosidase from Aspergillus niger and β-glucosidase from almonds. Compound 1 is a competitive inhibitor of amyloglucosidase and shows a fair selectivity towards this enzyme. The presence of C5-Me substitution in indolizidines 2 and 3 slightly diminishes the inhibitory activity towards amyloglucosidase whereas it improves the inhibitory properties towards β-glucosidase.

Grabbing and holding objects at the microscale is a complex function, even for microscopic living animals. Inspired by the hominid-type hand, a microscopic equivalent able to catch microelements is engineered. This microhand is light sensitive and can be either remotely controlled by optical illumination or can act autonomously and grab small particles on the basis of their optical properties. Since the energy is delivered optically, without the need for wires or batteries, the artificial hand can be shrunk down to the micrometer scale. Soft material is used, in particular, a custom-made liquid-crystal network that is patterned by a photolithographic technique. The elastic reshaping properties of this material allow finger movement, using environmental light as the only energy source. The hand can be either controlled externally (via the light field), or else the conditions in which it autonomously grabs a particle in its vicinity can be created. This microrobot has the unique feature that it can distinguish between particles of different colors and gray levels. The realization of this autonomous hand constitutes a crucial element in the development of microscopic creatures that can perform tasks without human intervention and self-organized automation at the micrometer scale.

Soft mobile microrobots whose deformation can be directly controlled by an external field can adapt to move in different environments. This is the case for the light-driven microrobots based on liquid-crystal elastomers (LCEs). Here we show that the soft microrobots can move through an agarose hydrogel by means of light-controlled travelling-wave motions. This is achieved by exploiting the inherent rise of the LCE temperature above the melting temperature of the agarose gel, which facilitates penetration of the microrobot through the hydrogel. The locomotion performance is investigated as a function of the travelling-wave parameters, showing that effective propulsion can be obtained by adapting the generated motion to the specific environmental conditions.

In this paper we investigate the potentials of liquid crystalline elastomer microstructures for the realization of optically tunable photonic microstructures. While certain limitations regarding the compromise between feature size and structure warping have been observed, it turns out that the simultaneous presence of a refractive index tuning effect and of a shape tuning effect intrinsic to the LCE material can be harnessed to design tunable photonic devices with unique behavior.

One of the main challenges in the development of microrobots, i.e. robots at the sub-millimeter scale, is the difficulty of adopting traditional solutions for power, control and, especially, actuation. As a result, most current microrobots are directly manipulated by external fields, and possess only a few passive degrees of freedom (DOFs). We have reported a strategy that enables embodiment, remote powering and control of a large number of DOFs in mobile soft microrobots. These consist of photo-responsive materials, such that the actuation of their soft continuous body can be selectively and dynamically controlled by structured light fields. Here we use finite-element modelling to evaluate the effective number of DOFs that are addressable in our microrobots. We also demonstrate that by this flexible approach different actuation patterns can be obtained, and thus different locomotion performances can be achieved within the very same microrobot. The reported results confirm the versatility of the proposed approach, which allows for easy application-specific optimization and online reconfiguration of the microrobot's behavior. Such versatility will enable advanced applications of robotics and automation at the micro scale.

An increasing interest in tunable photonic structures is growing within the photonic community. The usage of Liquid Crystalline Elastomer (LCE) structures in the micro-scale has been motivated by the potential to remotely control their properties. In order to design elastic photonic structures with a three-dimensional lithographic technique, an analysis of the different mixtures used in the micro-printing process is required. Previously reported LCE microstructures suffer damage and strong swelling as a limiting factor of resolution. In this article, we reported a detailed study on the writing process with four liquid crystalline photoresists, in which the percentage of crosslinker is gradually increased. The experiments reveal that exploiting the crosslinking degree is a possible means in which to obtain suspended lines with good resolution, quite good rigidity, and good elasticity, thereby preserving the possibility of deformation by light irradiation.

The 1,3 dipolar cycloaddition reactions of three pentose-derived pyrroline N-oxides with mono- and disubstituted alkenes are reported. A strong dependence of the diastereoselectivity of the cycloadditions on the relative configuration of the nitrone stereocentres was observed. Further transformation of the reaction products allowed the synthesis of four new tetrahydroxylated indolizidines. Their activity as glycosidase inhibitors was evaluated against a panel of commercially available glycosidases. The specificity of inhibitory activity against amyloglucosidase and α-mannosidases depends on the configuration at C-2 of the indolizidine moiety.