Soft Microorigami: Stimuli-Responsive Self-Folding Polymer Films
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Soft Microorigami: Stimuli-Responsive Self-Folding Polymer Films Leonid Ionov, Svetlana Zakharchenko, Georgi Stoychev, and Evgeni Sperling Leibniz Institute of Polymer Research Dresden, Hohe Str 6, 01069 Dresden
ABSTRACT Asymmetry is intrinsic to natural systems and is widely used by living organisms for efficient adaptation, mimicry and movement. Polymer bilayers are the example of synthetic asymmetric systems, which are able to generate macroscopic motion and fold by forming different 3D objects such as tubes and capsules. Similar to bimetal films, the polymer bilayer consist of two substances with different swelling properties. One polymer is non-swellable and hydrophobic. Another polymer is water-swellable hydrogel. The folding, which might occur in response to temperature or pH, is caused by swelling of the hydrogel layer. The formed tubes and capsules can be manipulated using magnetic field. Reversible folding and unfolding of the polymer films is applied for reversible capture and release of cells in response to change of temperature and other signals. This novel biomimetic approach can be used for controlled encapsulation and release of microparticles, cells and drugs as well as fabrication of 3D scaffolds for tissue engineering. INTRODUCTION Design of hollow 3D objects such as capsules and tubes is highly demanded for cells encapsulation, drug delivery, design of self-healing materials [1]. Most of the approaches for fabrication of capsules are based on the use of particles or fibers as templates, which are covered by functional materials. Hollow functional structures are, thus, formed after the removal of the core. Recently, use of self-folding films – thin films, which are able to form different 3D structures, was suggested as templateless alternative to the traditional templatebased approaches [2-3]. The main advantage of self-folding films the possibility to transfer pattern, which is created on the surface of the unfolded film, into inner and outer walls of the folded 3D structure [4-6]. Self-rolling films provide unique opportunities for encapsulation of small objects such as molecules or for larger ones such as particles and cells. This property is highly attractive for cell-delivery technology, food industry and tissue engineering. The main limitation comes, however, from non-biodegradability and non-biocompatibility of self-folding films, irreversibility of folding as well as from their sensitivity to stimuli in non-physiological ranges. In fact the number of stimuli which can be used to trigger folding of films are very limited. Cells are, for example, highly sensitive to even small changes of pH. Temperature appears to be the most suitable stimulus because cells readily withstand considerable changes of temperature. DISCUSSION We for first time developed self-rolling films which are able to reversibly roll and unroll in response to change of temperature in physiological range 30-37°C. For the demonstration of principle, bilayers of biodegradable and biocompatible polycaprolactone (PCL) and therm
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