From Molecular Machines to Stimuli‐Responsive Materials

Abstract

Shape-memory effects and mechanical actuations can be indeed generated from objects of various chemical nature [3][4][5] (e.g., metallic alloys, ceramics, liquid crystals, or polymers), and they are often supported by a combination of bottom-up and top-down structural engineering techniques going from surfaces to 3D materials (e.g., supramolecular self-assembly, photopatterning, microfluidics, or inkjet printing). [6,7] Various stimuli can generate their response (e.g., molecules, temperature, light, electrical potential, or mechanical stress) and their functioning principles vary largely from one system to another, involving a number of physical phenomena which can take place at the (macro)molecular level and which are transferred toward higher length scales (e.g., polarity, solubility-such as lower critical solution temperature (LCST), osmotic pressure, surface energy, or phase transition). It should also be mentioned that bio-inspiration is often a driving force in the design of such artificial materials as many smart mechano-active systems with adaptable properties are found in nature (e.g., stiffness change of sea cucumber, adaptive toughness of spider silk, closure of mimosa leaves when touched, or opening of seed pods). [8][9][10] Since the early 2000s, exciting opportunities have emerged in the scientific community for making use of artificial molecular machines as the elementary responsive building blocks in new types of stimuli-responsive materials. This approach is fundamentally disruptive compared to the others developed so far, because it aims to exploit precisely controlled mechanical motions at molecular level (produced by the machines), and to amplify them in collective mechanical motions taking place at larger dimensions up to the material's length scale. The most prominent example of what could be potentially achieved in the far future by such artificial materials is also found in nature, in the form of striated muscle tissue. In muscles, by using adenosine triphosphate (ATP) as chemical fuel, millions of myosin motors, which individually cycle hundreds of few nanometers scale actuations, are able to pull synchronously on sliding actin filaments and to produce micrometric contractions of sarcomeric units. Further hierarchical organizations of sarcomeres in bundled fibrils and fibers result in a macroscopic contraction of the muscle. At that point, and before describing selected examples of (much simpler) artificial systems, it is important for the readers who would not be familiar with molecular machines to first introduce more precisely terms and notions which define their nature and actuation principles. Artificial molecular machines are able to produce and exploit precise nanoscale actuations in response to chemical or physical triggers. Recent scientific efforts have been devoted to the integration, orientation, and interfacing of large assemblies of molecular machines in order to harness their collective actuations at larger length scale and up to the generation of macroscopic motions. Maki...

Aggregation‐induced emission systems involving supramolecular assembly

“…Supramolecular assembling processes, driven by noncovalent intermolecular interactions including hydrogen bonding, electrostatic interactions, hydrophobic forces, metal coordination, Van der Waals forces, and π–π stacking are seminal for the creation of well‐ordered architectures beyond molecular level built with fundamental building blocks, following the “bottom‐up” approaches. [ 6,7 ] Due to the dynamic and directional nature of the noncovalent driving forces, supramolecular assemblies are endowed with intriguing properties, such as good reversibility and stimuli‐responsiveness, whereby the assembling processes can be adjusted by varying the basic molecular modules and/or exerting external actuations. Till today, a large number of AIEgen‐containing supramolecular assemblies have been reported varying from simple complexes to sophisticated supramolecular ensembles, demonstrating adjustable features in various aspects including luminescence intensities, emission colors, and assembly morphologies, which relate closely to the altered strength or binding modes of supramolecular complexation.…”

A bio‐inspired gelatin‐based pH‐ and thermal‐sensitive magnetic hydrogel for in vitro chemo/hyperthermia treatment of breast cancer cells

“…[19][20][21] Amongst, pH-and thermal-responsive DDSs have received more attention owing to their simplicities as well as abnormal microenvironment condition of tumoral tissues (lower pH and higher temperature values) in comparison with healthy tissues that resulted to targeted release of encapsulated cargo. [22][23][24][25] On the other hand, the integration of magnetic nanoparticles (MNPs) into hydrogelbased DDSs lead to easy isolation in target area, remote control ability under a magnetic field and application in diagnosis through magnetic resonance imaging (MRI). [26][27][28][29] In addition, such DDS can be applied in hyperthermia therapy as a synergic approach for chemotherapy.…”

Structural properties of contractile gels based on light-driven molecular motors: a small-angle neutron and X-ray study

“…The integration of molecular motors in polymer systems is of particular interest to design stimuliresponsive materials capable of generating out-of-equilibrium functions by mechanical transduction. 1 First inspiration can be found in nature where muscles integrate biomolecular 2,3 motors (myosin heads) capable of out-of-equilibrium pulling collective motions into a biopolymers network (actin and myosin filaments) when supplied with adenosine triphosphate (ATP) external energy. 4 This sliding filament mechanism is amplified up to the macroscopic scale resulting in highly efficient muscular contraction and extension.…”

“…In particular, various molecular switches working at thermodynamic equilibrium have been integrated into polymer systems in order to amplify their collective nanoactuations across increasing length scales. 5,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] However, the integration of more complex molecular motors, 1,5,22,23 which are able to produce an increasing work on their environment by functioning out-of-equilibrium, are still very scarce. Using Feringa's light-driven rotary motors [24][25][26] , we have recently developed motor-polymer conjugates capable of unidirectional rotation under irradiation and acting as dynamic reticulation nodes into polyethylene glycol (PEG)-based chemical gels.…”