Shape Memory Polyurethane Microcapsules with Active Deformation

Abstract

From smart self-tightening sutures and expandable stents to morphing airplane wings, shape memory structures are increasingly present in our daily life. The lack of methods for synthesizing intricate structures from them on the micron and sub-micron level, however is stopping the field from developing. In particular, the methods for synthesis of the shape memory polymers and structures at this scale and the effect of new geometries remain unexplored. Here we describe the synthesis of shape-memory polyurethane (PU) capsules accomplished by interfacial polymerization of emulsified droplets. The emulsified droplets contain the monomers for the hard segments, while the continuous aqueous phase contains the soft segments. A tri-functional chemical crosslinker for shape-memory PU synthesis was utilized to eliminate creep and improve recovery ratios of the final capsules. We observe an anomalous dependence of the recovery ratio with the amount of programmed strain compared to previous shape-memory polymers. We develop quantitative characterization methods and theory to show that when dealing with thin shell objects, alternative parameters to quantify recovery ratios are needed. We show that while achieving 94-99% area recovery ratios, linear capsule recovery ratios can be as low as 70%. This quantification method allows us to convert from observed linear aspect ratios in capsules to find out unrecovered area strain and stress. The hollow structure of 2 the capsules grants high internal volume for some applications (e.g. drug delivery) which benefits from much higher loading of active ingredients than polymeric particles. The methods we developed for the capsule synthesis and programming could be easily scaled up for larger volume applications.

Preparation and performance of chlorfenapyr microcapsules with a degradable polylactide-based polyurethane wall material

“…3(c), some incomplete capsule particles were found, which clearly demonstrated the core/shell structure of the microcapsules. 39,40 In order to further verify whether chlorfenapyr is encapsulated in microcapsules, an element mapping analysis was performed using EDS. As shown in Fig.…”

Materials and Schemes of Multimodal Reconfigurable Micro/Nanomachines and Robots: Review and Perspective

“…One such potential mechanism could be the micro/nanoscale shape‐memory effects in alloys or polymers induced by heat or external magnetic fields. [ 80–82 ] Given a suitable stimulus, a shape‐memory material exhibits a reversible change of shape. Shape‐memory materials in the macroscale are already commercialized and applied in areas such as civil infrastructure, airline and aerospace, and dental industries.…”

Shape Memory Polymer Fibers: Materials, Structures, and Applications

“…Shape memory polymers (SMPs) are important active deformation materials. Under the excitation of thermal, electrical, light, magnetic, microwave and other external environment, SMPs can remember the temporary shape and return to the initial state [1][2][3][4]. This ability of sensing environmental changes makes SMPs more widely used in aerospace, smart fabrics, biomedicine, intelligent robots, flexible substrates, optics and smart tools, as well as electronic information carriers [5][6][7][8][9][10].…”