Interfacial Self‐Assembly of Amphiphilic Dual Temperature Responsive Actuating Janus Particles

Abstract

Amphiphilic Janus particles feature the combination of two different functional materials in one single colloid, as well as the possibility of self‐assembly at interfaces into complex superstructures. In this article, the self‐assembly of dual temperature responsive amphiphilic Janus particles at liquid–liquid interfaces and their subsequent conversion into an actuating layer‐shaped surface are presented. These microparticles are produced in a capillaries based continuous flow microfluidic device by photoinitiated radical polymerization. The hydrophobic part of the Janus particles contains a liquid crystalline elastomer (LCE), which performs a strong actuation up to 95% during the nematic–isotropic phase transition. The other side consists of a p(NIPAAm) hydrogel, which features volumetric expansions up to 280% below the lower critical solution temperature. A multistep molding process is developed to uniformly align the Janus particles at a toluene/water boundary surface and to embed the particles into a hydrogel matrix. A particle covered hydrogel layer is obtained, which features a collective actuation of the rod‐like LCE parts on the surface and a bundling of the resulting forces during the phase transition.

Microfluidic Synthesis of Liquid Crystalline Elastomer Particle Transport Systems which Can Be Remote‐Controlled Magnetically

“…Our results demonstrate the successful 2D magnetic guidance of magnetic LCE particles and this should be applicable also to the previously described microfluidically synthesized Janus‐particles or LCE tubes . In this way, the versatile internal actuations–which were demonstrated before–could be complemented with precisely controlled external movements.…”

Thermally-Induced Actuations of Stimuli-Responsive, Bicompartmental Nanofibers for Decoupled Drug Release

“…Importantly, temperature-dependent, decoupled drug release profiles from the two different, chemically crosslinked polymer compartments of these BCNFs, with precisely engineered nanoscale compartmentalization, can be potentially useful for temporally multi-modal drug delivery reservoirs and functional nanofibers with actuation at the nanoscale, for tissue engineering and regenerative medicine. Future work should focus on fabrication of directionally aligned BCNFs, which would have great potential for temperature-responsive bending hydrogels as actuating cell sheets with oriented cell growth via spatio-selective cell-surface interactions and also as soft actuator-based robotic systems (Stoychev et al, 2013; Wang et al, 2013; Stoychev and Ionov, 2016; Hessberger et al, 2018).…”

“…Specifically, multi-compartmental polymer microcylinders and nanofibers with compositional anisotropy showed controlled shape reconfigurations and reversible anisotropic actuations, depending on environmental stimuli including ultrasound, solvent exchange, temperature, pH, and ionic strength (Lendlein et al, 2001; Chen et al, 2010; Lee et al, 2012; Liu et al, 2012; Qi et al, 2016). These stimuli-triggered, swelling-deswelling properties of each compartment occurred to different degrees via volume change, which was largely affected by hydrophilicity-hydrophobicity and conformational changes of the polymers (Okeyoshi et al, 2008; Rockwood et al, 2008; Okuzaki et al, 2011; Saha et al, 2012; Stoychev and Ionov, 2016; Hessberger et al, 2018).…”

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli‐Responsive Systems

“…Seminal examples of hydrogel‐based actuators are highlighted below. A dual‐thermoresponsive material was reported by Hessberger et al, composed of amphiphilic Janus hydrogel rods with a LC elastomer tail and a PNIPAAm head 17. When added to a toluene–water mixture, these Janus rods self‐assembled at the liquid–liquid interface with the PNIPAAm‐based heads pointing toward the lower aqueous layer.…”