Droplet-Based Microfluidic Preparation of Shape-Variable Alginate Hydrogel Magnetic Micromotors.

Cheng Zhang,Xing Ma,Wenjun Chen,Yuduo Chen,Yong Wang

doi:10.3390/nano12010115

Abstract

This article introduces a facile droplet-based microfluidic method for the preparation of Fe3O4-incorporated alginate hydrogel magnetic micromotors with variable shapes. By using droplet-based microfluidics and water diffusion, monodisperse (quasi-)spherical microparticles of sodium alginate and Fe3O4 (Na-Alg/Fe3O4) are obtained. The diameter varies from 31.9 to 102.7 µm with the initial concentration of Na-Alginate in dispersed fluid ranging from 0.09 to 9 mg/mL. Calcium chloride (CaCl2) is used for gelation, immediately transforming Na-Alg/Fe3O4 microparticles into Ca-Alginate hydrogel microparticles incorporating Fe3O4 nanoparticles, i.e., Ca-Alg/Fe3O4 micromotors. Spherical, droplet-like, and worm-like shapes are yielded depending on the concentration of CaCl2, which is explained by crosslinking and anisotropic swelling during the gelation. The locomotion of Ca-Alg/Fe3O4 micromotors is activated by applying external magnetic fields. Under the rotating magnetic field (5 mT, 1–15 Hz), spherical Ca-Alg/Fe3O4 micromotors exhibit an average advancing velocity up to 158.2 ± 8.6 µm/s, whereas worm-like Ca-Alg/Fe3O4 micromotors could be rotated for potential advancing. Under the magnetic field gradient (3 T/m), droplet-like Ca-Alg/Fe3O4 micromotors are pulled forward with the average velocity of 70.7 ± 2.8 µm/s. This article provides an inspiring and timesaving approach for the preparation of shape-variable hydrogel micromotors without using complex patterns or sophisticated facilities, which holds potential for biomedical applications such as targeted drug delivery.

Highlights

Micromotors are microdevices capable of converting the energy from the environment into autonomous motion
Alginate hydrogel is synthesized through ionic crosslinking by divalent cations such as Ca2+. Combining these two points mentioned above in terms of the choice of the preparing method and material, here we describe a facile droplet-based microfluidic method for the preparation of alginate hydrogel magnetic micromotors
Droplet-based microfluidic experiments were performed with three different initial concentrations of Na-Alginate in dispersed fluid (Ci,Na-Alg ): 0.09, 0.9 and 9 mg/mL

Summary

Introduction

Micromotors are microdevices capable of converting the energy from the environment into autonomous motion. Various methods have been reported for the preparation of magnetic micromotors with different shapes. Spherical magnetic micromotors can be prepared via the template-assisted method with sputtering or incorporating magnetic materials [8,9,10]. Other shapes are produced by using a specific pattern [10,13] These methods require sophisticated facilities and are usually time-consuming. They are difficult to be replicated in normal laboratories. These micromotors are commonly composed of rigid materials which are not biodegradable in aqueous environments [14,15]. Facile fabrication methods are in demand for magnetic micromotors using soft biodegradable materials

Methods

Results

Conclusion