Leonid Ionov

Self-folding all-polymer thermoresponsive microcapsules

We design partially biodegradable thermoresponsive self-folding capsules capable of controlled capture and release of cells. The proof of principle is demonstrated on the example of star-like patterned polycaprolactone-poly(N-isopropylacrylamide) bilayers, which reversibly encapsulate/release yeast cells in response to a temperature signal.

Shape-programmed folding of stimuli-responsive polymer bilayers.

We investigated the folding of rectangular stimuli-responsive hydrogel-based polymer bilayers with different aspect ratios and relative thicknesses placed on a substrate. It was found that long-side rolling dominates at high aspect ratios (ratio of length to width) when the width is comparable to the circumference of the formed tubes, which corresponds to a small actuation strain. Rolling from all sides occurs for higher actuation, namely when the width and length considerably exceed the deformed circumference. In the case of moderate actuation, when both the width and length are comparable to the deformed circumference, diagonal rolling is observed. Short-side rolling was observed very rarely and in combination with diagonal rolling. On the basis of experimental observations, finite-element modeling and energetic considerations, we argued that bilayers placed on a substrate start to roll from corners due to quicker diffusion of water. Rolling from the long-side starts later but dominates at high aspect ratios, in agreement with energetic considerations. We have shown experimentally and by modeling that the main reasons causing a variety of rolling scenarios are (i) non-homogenous swelling due to the presence of the substrate and (ii) adhesion of the polymer to the substrate.

Soft microorigami: self-folding polymer films

Fabrication of 3D objects using folding of thin films is a novel and very attractive research field. The manuscript overviews recent advances in development and application of polymer films, which are able to fold and form 3D structures.

Unusual and Superfast Temperature‐Triggered Actuators

A superfast actuator based on a bilayer fibrous mat shows folding/unfolding and the formation of 3D structures in a fraction of a second. The actuation is reversible for many cycles without losing its form and size, with unfolding at room temperature and folding above 35 °C. The system is promising for making 3D bioscaffolds, electrodes, and micro-/macroactuators.

Temperature Controlled Encapsulation and Release Using Partially Biodegradable Thermo-magneto-sensitive Self-rolling Tubes

We suggest a new approach for controlled encapsulation and release of microparticles, cells and drugs using thin bilayer films of thermoresponsive and biodegradable polymers, which are able to form self-rolling tubes. The magnetic nanoparticles are incorporated in the thermoresponsive layer in order to provide the microtubes sensitivity to magnetic field. We demonstrate reversible rolling and unrolling of the polymer films, reversible capture and release of microparticles in response to change of temperature as well as manipulation of particle-loaded microtubes using external magnetic field. The suggested approach can be successfully implemented for controlled delivery of drugs and cells in living organisms as well as to design scaffolds for tissue engineering.

Fully Biodegradable Self-Rolled Polymer Tubes: A Candidate for Tissue Engineering Scaffolds

We report an approach for the fabrication of fully biodegradable self-rolled tubes based on patterned polysuccinimide/polycaprolactone bilayers. These polymers are biocompatible, biodegradable, produced industrially, and are already approved for biomedical purposes. Both polycaprolactone and polysuccinimide are hydrophobic and intrinsically water-insoluble. Polysuccinimide, however, hydrolyzes in physiological buffer environment yielding water-swellable polyaspartic acid that causes the rolling of the polymer bilayer and formation of tubes. We demonstrate the possibility to encapsulate yeast cells using self-rolled tubes.

Water-Repellent Textile via Decorating Fibers with Amphiphilic Janus Particles

We investigated morphology and wetting properties of textiles modified by chemically immobilized amphiphilic micrometer and submicrometer large Janus particles. The Janus particles bind by their reactive side to the textile surface, while their hydrophobic side faces the environment. It was found that the character of immobilization of the Janus particles on textile depends on their size: larger particles bind between fibers, while smaller ones bind to the fiber surface. In both cases, immobilization of Janus particles results in the hydrophobization of the hydrophilic textile surface. Finally, we demonstrated that submicrometer large Janus particles are very efficient for the design of water-repellent textiles.

Stimuli-Responsive Microjets with Reconfigurable Shape

Flexible thermoresponsive polymeric microjets are formed by the self-folding of polymeric layers containing a thin Pt film used as catalyst for self-propulsion in solutions containing hydrogen peroxide. The flexible microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows microjets to rapidly start and stop multiple times by controlling the radius of curvature of the microjet. This work opens many possibilities in the field of artificial nanodevices, for fundamental studies on self-propulsion at the microscale, and also for biorelated applications.

Synthesis of robust raspberry-like particles using polymer brushes.

Synthesis of chemically and mechanically robust raspberry-like particles as well as wetting properties of coatings based on them is reported. The raspberry-like particles were prepared by immobilization of silica nanoparticles on the surface of silica microparticles coated by poly(glycidyl methacrylate) brush layer. The raspberry-like particles retain their structure after ultrasonication and exposure to organic solvents that allows their use as substrates for immobilization on polymers. Fabrication ultrahydrophobic surfaces using raspberry-like particles with immobilized poly(pentafluorostyrene) was also demonstrated.

Actively-moving materials based on stimuli-responsive polymers

This review addresses recent developments in actively moving materials based on stimuli-responsive polymers on the scale from single molecules to polymer networks. The examples of application of stimuli-responsive polymers for design of actuators, sensors, active elements in microfluidic devices, materials with switchable optical properties as well as biomaterials are discussed. Emphasis is given to biohybrid materials consisting of synthetic and living components as well as stimuli-responsive materials inspired by nature.