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. 2023 Jun 19;9(6):501.
doi: 10.3390/gels9060501.

Synthesis and Characterization of Hydrogel Droplets Containing Magnetic Nano Particles, in a Microfluidic Flow-Focusing Chip

Fereshteh Moharramzadeh  1 , Seyyed Ali Seyyed Ebrahimi  1 , Vahid Zarghami  2 , Zahra Lalegani  1 , Bejan Hamawandi  3
Affiliations

Synthesis and Characterization of Hydrogel Droplets Containing Magnetic Nano Particles, in a Microfluidic Flow-Focusing Chip

Fereshteh Moharramzadeh et al. Gels. .

Abstract

Magnetic hybrid hydrogels have exhibited remarkable efficacy in various areas, particularly in the biomedical sciences, where these inventive substances exhibit intriguing prospects for controlled drug delivery, tissue engineering, magnetic separation, MRI contrast agents, hyperthermia, and thermal ablation. Additionally, droplet-based microfluidic technology enables the fabrication of microgels possessing monodisperse characteristics and controlled morphological shapes. Here, alginate microgels containing citrated magnetic nanoparticles (MNPs) were produced by a microfluidic flow-focusing system. Superparamagnetic magnetite nanoparticles with an average size of 29.1 ± 2.5 nm and saturation magnetization of 66.92 emu/g were synthesized via the co-precipitation method. The hydrodynamic size of MNPs was changed from 142 nm to 826.7 nm after the citrate group's attachment led to an increase in dispersion and the stability of the aqueous phase. A microfluidic flow-focusing chip was designed, and the mold was 3D printed by stereo lithographic technology. Depending on inlet fluid rates, monodisperse and polydisperse microgels in the range of 20-120 μm were produced. Different conditions of droplet generation in the microfluidic device (break-up) were discussed considering the model of rate-of-flow-controlled-breakup (squeezing). Practically, this study indicates guidelines for generating droplets with a predetermined size and polydispersity from liquids with well-defined macroscopic properties, utilizing a microfluidic flow-focusing device (MFFD). Fourier transform infrared spectrometer (FT-IR) results indicated a chemical attachment of citrate groups on MNPs and the existence of MNPs in the hydrogels. Magnetic hydrogel proliferation assay after 72 h showed a better rate of cell growth in comparison to the control group (p = 0.042).

Keywords: alginate; droplet; flow-focusing system; magnetic hydrogel; magnetite; microfluidic systems.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) FE-SEM image of magnetite NPs synthesized by the co-precipitation method, (b) M-H diagram of magnetite NPs synthesized by the co-precipitation method, (c) FT-IR spectra of trisodium citrate, magnetite NPs, and citrated magnetite NPs, and (d) hydrodynamic size of magnetite NPs before and after citration.
Figure 2
Figure 2
(a) Microscopic image of collected microgels produced in the spinal chip, (b) Optical microscope image of triple junction in microfluidic chip.
Figure 3
Figure 3
Different modes of droplet production in the microfluidic system, regarding the physical properties of phases that are constant in this study jetting mode (a,b), dripping mode (c,e,f) and satellite formation (d) were observed.
Figure 4
Figure 4
Microscopy image (in transmission mode) of: (a) non-uniform distribution of droplet sizes and (b) near uniform distribution of droplet sizes.
Figure 5
Figure 5
(a) M-H diagram of alginate microgels containing magnetite NPs, (b) FT-IR spectra of sodium alginate (S.Alg), alginate microgels (Alg.M.) and alginate microgels containing citrated magnetite NPs (Alg.MNP-Cit.M), and (c) ionic bonding interaction between Ca2+ and carboxylate groups in alginate hydrogels.
Figure 6
Figure 6
(a) Magnetite NPs biocompatibility before and after citration at different concentrations in the presence of human mesenchymal stem cells after 24 h (*: p < 0.05, **: p < 0.001); (b) biocompatibility test of alginate based microgels and their constituents after 1 day (*: p < 0.05 in comparison with control group); and (c) biocompatibility test of alginate based microgels and their constituents after 3 days. (*: p < 0.05).
Figure 7
Figure 7
3D view of designed models for microfluidic chip mold with: (a) spinal channel and (b) parallel channels.
Figure 8
Figure 8
Citration steps of Fe3O4 NPs: (a) after the addition of deionized water to the magnetic NPs and dispersion in an ultrasonic bath, (b) after the addition of sodium citrate and placing it in the oven, (c) after the addition of acetone and precipitation of citrated magnetic NPs, and (d) the attraction of citrated magnetic NPs to the magnet.
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