Reversible Thermosensitive Biodegradable Polymeric Actuators Based on Confined Crystallization

Abstract

We discovered a new and unexpected effect of reversible actuation of ultrathin semicrystalline polymer films. The principle was demonstrated on the example of thin polycaprolactone-gelatin bilayer films. These films are unfolded at room temperature, fold at temperature above polycaprolactone melting point, and unfold again at room temperature. The actuation is based on reversible switching of the structure of the hydrophobic polymer (polycaprolactone) upon melting and crystallization. We hypothesize that the origin of this unexpected behavior is the orientation of polycaprolactone chains parallel to the surface of the film, which is retained even after melting and crystallization of the polymer or the “crystallization memory effect”. In this way, the crystallization generates a directed force, which causes bending of the film. We used this effect for the design of new generation of fully biodegradable thermoresponsive polymeric actuators, which are highly desirable for bionano-technological applications such as reversible encapsulation of cells and design of swimmers.

Self‐Rolled Porous Hollow Tubes Made up of Biodegradable Polymers

“…The thermal transitions and degree of crystallinity of PLA remained the same even after putting in water at 40 °C, as determined by DSC and FTIR (Figures S1 and S2, Table S3, Supporting Information). Therefore, change in the crystallinity or melting of crystallites could not be the reason of causing shrinkage . It is known from the literature that, in several cases, the electrospun fibers are collected in an energetically unstable stretched state just after spinning and try to acquire the low‐energy unstretched conformation when heated near their glass transition temperature or come in contact with an appropriate solvent due to the chain movement .…”

“…Therefore, change in the crystallinity or melting of crystallites could not be the reason of causing shrinkage. [42] It is known from the literature that, in several cases, the electrospun fibers are collected in an energetically unstable stretched state just after spinning and try to acquire the low-energy unstretched conformation when heated near their glass transition temperature or come in contact with an appropriate solvent due to the chain movement. [3,8,43] The glass transition of electrospun PLA fibers is around 50 °C, as noted from DSC ( Figure S1, Supporting Information).…”

Stimulus-active polymer actuators for next-generation microfluidic devices

“…The advantages reported were (1) that the tendency of standard hydrogels to become brittle when stored under ambient conditions was reduced due to the low vapor pressure of the ionic liquid and the associated ability to plasticize the gel structure and (2) that the swelling and shrinking properties were improved considerably, which was demonstrated experimentally by means of an ionogelbased microvalve. Another interesting material effect used to realize a thermosensitive polymeric actuator was presented in [135]. The authors discovered a reversible actuation effect of poly(caprolactone) (PCL)-gelatin bilayer films upon temperature variation: the structure of the hydrophobic PCL switches reversibly upon melting and crystallization.…”

An Intriguing Method for Fabricating Arbitrarily Shaped “Matreshka” Hydrogels Using a Self-Healing Template

“…The idea is that a 3D object is obtained by folding, bending, or twisting a programmed 2D structure that consists of stimuli-responsive materials [16,17]. …”