Chirality-Enabled Liquid Crystalline Physical Gels with High Modulus but Low Driving Voltage

Mechanical Properties of Cement-Based Gel Composites Reinforced by Plant Fiber: A Review

Plant fibers (PFs) have been increasingly employed in cement-based gel composites (CCs) on account of their excellent mechanical properties, toughness and sustainability. Researchers have engaged in a lot of studies on plant fiber-reinforced cement-based gel composites (PFRCCs). Based on these studies, the chemical components and mechanical characteristics of PFs are summed up in this review. In addition, the modification methods for matrices and PFs are also discussed. The mechanical properties of PFRCCs, including static and dynamic properties, are reviewed. Predictive equations for the mechanical properties of PFRCCs are summarized in this paper. In the end, the characteristics of the interface transition zones between PFs and CCs are analyzed. According to the results of previous studies, the addition of PFs can enhance the flexural strength and tensile strength of CCs, but it can have an uncertain effect on compressive strength. The elastic modulus and fracture behavior of PFRCCs increases with the addition of PFs. At the same time, modification methods have been proved to be useful in reducing the degradation of PFs in CCs. Generally speaking, PFRCCs are new building materials which have extensive application prospects. The aim of this review is to help researchers understand the mechanical properties of PFRCCs and to promote the application of PFRCCs in future projects.

Graphene oxide-doped chiral dextro-hydrogel promotes peripheral nerve repair through M2 polarization of macrophages

Dextro-chirality is reported to specifically promote the proliferation and survival of neural cells. However, applying this unique performance to nerve repair remains a great challenge. Graphite oxide (GO)-phenylalanine derivative hydrogel system was constructed through doping 5% GO into self-assembly dextro- or levo-hydrogels (named as dextro and levo group, respectively), which exhibited identical physical and chemical properties, cyto-compatibility, and mirror-symmetrical chirality. In vivo experiments using rat sciatic nerve repair models showed that the functional recovery and histological restoration of regenerating nerves in the dextro group were significantly improved, approaching that of autograft implantation. The doped GO promoted M2 polarization of macrophages, increasing the expression of platelet-derived growth factor BB chain and vascular endothelial growth factor, thereby improving angiogenesis in regenerating nerves. A mechanism is proposed for the facilitated nerve repair through the synergistic effect of GO and dextro-hydrogel, involving dextro-chirality selection of neural cells and GO-induced M2 polarization, which promotes microvascular regeneration and myelination. This study showcases the immense potential of chirality in addressing neurological issues by providing a compelling demonstration of the development of effective therapies that leverage the unique matrix chirality selection of nerve cells to promote peripheral nerve regeneration.

Balancing Compatibility and Gelability for High-Performance Cholesteric Liquid Crystalline Physical Gels

Liquid crystalline physical gels (LCPGs) have attracted increasing interest because of their mechanical properties and stimulus-response behaviors. However, due to their gelator properties such as thermal stability, gelation capability, and compatibility in liquid crystals, development of LCPGs with high performances still remains a huge challenging task. Herein, four novel gelators ((l)-PH, (d)-PH, (l)-P2H, and (d)-P2H) based on 1,4-benzenedicarboxamide phenylalanine derivatives containing one or two ethylene glycol groups have been designed and synthesized. It is found that the ethylene glycol group plays a significant role in improving the compatibility between the gelator and the liquid crystal. All of the prepared compounds can form stable LCPGs in P0616A. In particular, the storage modulus of LCPG with 9.0 wt % of (l)-PH with one ethylene glycol unit is higher than 10⁶ Pa, which is similar to SmC gels and advantageous over previously reported nematic LCPGs. Furthermore, the prepared gels display a strong Cotton effect with hand-preferred twisted fiber networks and the self-assembled aggregates of (l)-PH can induce P0616A to form a cholesteric fingerprint structure. Thus, these low molecular weight gelators provide a strategy to construct high-performance cholesteric LCPGs for the realization of LC device applications.

Muscle-Mimetic Highly Tough, Conductive, and Stretchable Poly(ionic liquid) Liquid Crystalline Ionogels with Ultrafast Self-Healing, Super Adhesive, and Remarkable Shape Memory Properties

Here, we report a simple method for preparing muscle-mimetic highly tough, conductive, and stretchable liquid crystalline ionogels which contains only one poly(ionic liquid) (PIL) in an ionic liquid via in situ free radical photohomopolymerization by using nitrogen gas instead of air atmosphere. Due to eliminating the inhibition caused by dissolved oxygen, the polymerization under nitrogen gas has much higher molecular weight, lower critical sol-gel concentration, and stronger mechanical properties. More importantly, benefiting from the unique loofah-like microstructures along with the strong internal ionic interactions, entanglements of long PIL chains and liquid crystalline domains, the ionogels show special optical anisotropic, superstretchability (>8000%), high fracture strength (up to 16.52 MPa), high toughness (up to 39.22 MJ/m³), and have ultrafast self-healing, ultrastrong adhesive, and excellent shape memory properties. Due to its excellent stretchability and good conductive-strain responsiveness, the as-prepared ionogel can be easily applied for high-performance flexible and wearable sensors for motion detecting. Therefore, this paper provides an effective route and developed method to generate highly stretchable conductive liquid crystalline ionogels/elastomers that can be used in widespread flexible and wearable electronics.

Amplifying inorganic chirality using liquid crystals

Chiral inorganic nanostructures have drawn extensive attention thanks to their unique physical properties as well as multidisciplinary applications. Amplifying inorganic chirality using liquid crystals (LCs) is an efficient way to enhance the parented inorganic asymmetry owing to chirality transfer. Herein, the universal synthetic methods and structural characterizations of chiral inorganic-doped LC hybrids are introduced. Additionally, the current progress and status of recent experiment and theory research about chiral interactions between inorganic nanomaterials (e.g. metal, semiconductor, perovskite, and magnetic oxide) and LCs are summarized in this review. We further present representative applications of these new hybrids in the area of encryption, sensing, optics, etc. Finally, we provide perspectives on this field in terms of material variety, new synthesis, and future practice. It is envisaged that LCs will act as a pivotal part in the amplification of inorganic chirality with versatile applications.

Direct Visualization of Chiral Amplification of Chiral Aggregation Induced Emission Molecules in Nematic Liquid Crystals

Chiral amplification in liquid crystals (LCs) is a well-known strategy. However, current knowledge about the underlying mechanism was still lacking; in particular, how it was realized at the nano scale still remained to be revealed. Here, we provide systematical exploration of chiral amplification of chiral aggregation induced emission (AIE) molecules in LCs from direct visualization of their co-assemblies at the nano scale to theoretical calculation of the molecular packing modes on a single molecular level. Using AFM imaging,we directly visualized the co-assembly formed by chiral AIE molecules/LCs at the nano scale: the chiral AIE molecules self-assembled into helical fibers to serve as the helical template for LCs to bind, while the LCs helically bound to the helical fibers to form the co-assembly, giving the morphology of pearled necklaces or thick rods. Theoretical calculation suggested that chiral AIE molecules were packed into left-handed helical fibers with a large volume of empty space between neighboring molecules, which provided the binding cites for LCs. Structural analysis showed that the π-π stacking between aromatic groups from LCs and TPE groups and the σ-π hyperconjugation between LC aromatic groups and cholesterol aliphatic groups play an important role in stabilizing the binding of LCs in the confined space on the surface of the helical assemblies.

Light regulation and long-lived stability of RGB colors in cholesteric liquid crystal physical gels via a mixing strategy

Photo-responsive cholesteric liquid crystals (CLCs) have attracted much attention due to the dynamic tunability of their unique helical superstructure. However, it is still a challenge to endow the mechanical properties and to regulate the reflection colors at the same time. In this work, a simple strategy is developed for the construction of thermo-responsive CLC physical gels via the direct mixing of photo-responsive dopants and a gelator with nematic LCs. The reflection colors of CLCs and the mechanical properties of gels can be independently regulated due to the separation of the photo-responsive chiral group from the gelator. In addition, the CLC reflection colors can be regulated via visible light in the range of RGB with long-lived thermal stability. Finally, the information storage properties of this kind of CLC gel have been investigated.

Ultra-low switching reverse mode liquid crystal gels

This research investigates the electro-optical properties of reverse mode liquid crystal gel (LC-gel) scattering films. The LC-gel has been fabricated through the fibrous self-assembly of the gelator 12-hydroxydodecanoic acid (G12) and mesogen monomer (RM257) in nematic LC HTW106700-100 (HTW). Adding RM257 monomer improves the transparency in the OFF state and enhances scattering effects in the ON state. Moreover, an extremely low switching voltage (∼ 1 V) is demonstrated.

Mechanically Stable C2-Phenylalanine Hybrid Hydrogels for Manipulating Cell Adhesion

Tuning of the viscoelastic properties of supramolecular hydrogels to be used as biological material substrates in tissue engineering has become significantly relevant in recent years due to their ability to influence cell fate. In the quest to enhance the stability and mechanical properties of a derived C2-phenylalanine gelator (LPF), derivatives of the polysaccharide dextran were incorporated as additives to promote hydrogen bonding and π-π stacking with the gelator. Dextran was esterified to yield carboxymethyl dextran (CMDH), which was subsequently amidated to furnish amino dextran (AD), the resulting hybrid hydrogels were denoted as LPF-AD_x and LPF-CMDH_x, where x represents the amount of AD and CMDH (mg). The LPF gelator interacted with the carboxyl and amino functional groups of the CMDH and AD, respectively, through hydrogen bonding and π-π stacking, resulting in mechanically stable hydrogels. Morphological studies revealed that the hybrid hydrogels were formed as a result of dense highly branched thin and broad fibers for LPF-AD and LPF-CMDH, respectively. Rheological studies confirmed the superiority of the hybrid hydrogels over the neat hydrogel, where LPF-CMDH₃ exhibited the best mechanical properties with an improved elastic modulus of 11 654 Pa over 1518 and 140 Pa for LPF-AD_4.5 and LPF, respectively. The adhesion and spreading behavior of NIH 3T3 fibroblast cells were significantly improved on the LPF-CMDH₃ substrate owing to their enhanced mechanical properties. The tuning of the mechanical properties of the therein hydrogels via the facile incorporation of biodegradable and biocompatible functionalized additives opens up avenues for strengthening the supposed weak supramolecular gelators and hence increasing their potential of being employed largely in the field of tissue engineering.