Improving Thermal Stability of Enzymatic Micromotors by a Temperature‐Sensitive Smart Polymeric Shell

Abstract

Enzyme-powered micromotors using biocompatible substances as fuel are promising candidates in biomedical applications due to their potential autonomous movement in biological fluid and supreme biocompatibility. However, the inherent fragility of enzymes in complex environment hinders their application in practice. Herein, the smart temperatureresponsive poly(N-isopropylacrylamide) (PNIPAM) is introduced to SiO 2 @urease micromotors to increase the stability of the enzyme engine by the confinement effect derived from shrinkage of PNIPAM at temperatures above its lower critical solution temperature (LCST). As a result, the structure transformation and subunit dissociation of the enzyme are suppressed, leading to improved thermal stability of the urease engine. A systematic comparison of PNIPAM protected and bare SiO 2 @urease micromotors after thermal treatments at identical temperatures for various time intervals has clearly revealed the enhancement of stability against thermal deformation by PNIPAM integration. This work, paving a way to the development of thermally stable enzyme-powered micromotors, can greatly raise the prospect of the intelligent micromachines toward practical biomedical applications.

Enzyme-powered micro- and nano-motors: key parameters for an application-oriented design

“…37 Additionally, other methods of enzyme protection reported are based on polymeric coatings like PEG, 82,84 tannic acid 94 or PNIPAM. 90…”

“…64 Surprisingly, fully coated motors functionalized with this method showed self-propulsion. 13,16,19,26,85,90,106 Thus, since the Janus structure has not been engineered on the particle, other ways of asymmetry must take place on the motors.…”

“…4C) that consumes urea (CO(NH 2 ) 2 ) and releases ammonium ions (NH 4 + ) and bicarbonate (CO 3 2À ). 14,[20][21][22]31,34,36,39,44,60,[70][71][72][73][74][78][79][80][81]83,84,86,89,90,92,93,99,[117][118][119][120]129 Interestingly, a study of urease-powered micromotors shows that the gradient of ionic products may be responsible for the self-propulsion, 84 an ionic self-diffusiophoretic mechanism that has been further supported by theoretical models. 82,136 This was proved by the decreasing speed of urease micromotors aer exposing them to different ionic compounds.…”

“…78,81–87 Silica allows for easy spherical formation and surface modification, as well as biocompatibility and molecule encapsulation inside mesopores making this material promising for clinical translation. 88 Hence, it is combined with polymers to additionally confer these properties, for example silica with polystyrene (PS-SiO 2 ) 89 , poly(sodium styrene sulfonate) (PSS-SiO 2 ), 57 PNIPAM (PNIPAM-SiO 2 ) 90 or other combinations of increasing complexity like silica with polydopamine, poly( l -lysine) and poly(ethylene glycol) (SiO 2 -PDA-PLL-PEG) 91 .…”

“…There are examples of spherical shapes where instead of forcing asymmetry, active motion was produced by fully covering with enzymes the surface of rigid spheres, 13,14,16,31,34,57,60,65,85 porous spheres 71–76,78,80,96,125 and hollow spheres, 21,22,78,79,81–84,87,90,93 as well as embedding the enzymes inside the structure. 61 However, the full coverage of most of these spherical structures was not analyzed in detail.…”