Facile Synthesis of Radial-Like Macroporous Superparamagnetic Chitosan Spheres with In-Situ Co-Precipitation and Gelation of Ferro-Gels

<div><p>Macroporous chitosan spheres encapsulating superparamagnetic iron oxide nanoparticles were synthesized by a facile and effective one-step fabrication process. Ferro-gels containing ferrous cations, ferric cations and chitosan were dropped into a sodium hydroxide solution through a syringe pump. In addition, a sodium hydroxide solution was employed for both gelation (chitosan) and co-precipitation (ferrous cations and ferric cations) of the ferro-gels. The results showed that the in-situ co-precipitation of ferro-ions gave rise to a radial morphology with non-spheroid macro pores (large cavities) inside the chitosan spheres. The particle size of iron oxide can be adjusted from 2.5 nm to 5.4 nm by tuning the concentration of the sodium hydroxide solution. Using Fourier Transform Infrared Spectroscopy and X-ray diffraction spectra, the synthesized nanoparticles were illustrated as Fe₃O₄ nanoparticles. In addition, the prepared macroporous chitosan spheres presented a super-paramagnetic behaviour at room temperature with a saturation magnetization value as high as ca. 18 emu/g. The cytotoxicity was estimated using cell viability by incubating doses (0∼1000 µg/mL) of the macroporous chitosan spheres. The result showed good viability (above 80%) with alginate chitosan particles below 1000 µg/mL, indicating that macroporous chitosan spheres were potentially useful for biomedical applications in the future.</p> </div

Characterization of the iron oxide-chitosan composite spheres.

<p>(a) FTIR spectra of chitosan spheres (gray line) and iron oxide nanoparticle-loaded chitosan spheres (black line). (b) X-ray diffraction pattern from iron oxides nanoparticle-loaded chitosan spheres prepared from the NaOH solutions with various concentrations.</p

Morphologies of the synthesyzed chitosan spheres.

<p>(a) An optical image of the iron oxide nanoparticles loaded chitosan spheres. (b) SEM images of chitosan spheres without (left) and with (right) iron oxide nanoparticles. (c) and (d) show the cross-section images of chitosan spheres (without iron oxide nanoparticles). Inset in (c) shows the sliced hemispheres of chitosan sphere. Inset in (d) shows details of the internal structure. (e) and (f) show the cross-section images of iron oxide nanoparticles loaded chitosan spheres.</p

Schematic of the formation process of macroporous chitosan spheres.

<p>Schematic of the formation process of macroporous chitosan spheres.</p

The relationships among the diameter of microfibers, width of observation channel and flow rate of continuous phase.

<p>The relationships among the diameter of microfibers, width of observation channel and flow rate of continuous phase.</p

Microfluidic chip.

<p>Expanded view (A) and a photo (B) of the microfluidic chip: 1, inlets of center channels; 2 and 3, inlets of side channels; 4, cross junction; 5, outlet; 6, observation channel; 7, bottom layer disk; 8, screw orifices; 9, the scale bar = 11 cm. (C) is the geometry of the microfluidic channels.</p

Microfiber formation.

<p>The diagram of the microfluidic system and photographs of observation positions. 1, 2 wt % CaCl₂ solution; 2, deionized water; 3, alginate solution; 4, sunflower seed oil; 5, observation channel; 6, microfibers. The formation of microfibers: A, photograph of the microfiber in the observation channel; B, Photograph of the second cross junction; C, photograph of the first cross junction.</p

Microfiber images.

<p>Microscopic images (A∼B, stained with Rhodamine B) and scanning electron microscopy images (C∼E) of microfibers.</p

Cell culture of microfibers.

<p>Proliferation of GBM cells in microfibers. A. GBM cells; B. microfiber without cells; C. GBM in microfibers at the 1st day; D. GBM in microfibers at the 7th day. Arrows indicate GBM cells.</p

Characteristics of the microfibers.

<p>(A) The hysteresis curve of the microfibers containing MIO nanoparticles. (B) Release profiles of diclofenac from MIO-loaded microfibers without magnetic stimulation as the control (▵), with 2 minutes stimulation at the 10th, 30th and 60th minute (▴), with a 10-minute stimulation after the 20th minutes (•) and with a continuous stimulation from the beginning (○).</p