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

Date Published: November 30, 2012

Publisher: Public Library of Science

Author(s): Chih-Hui Yang, Chih-Yu Wang, Keng-Shiang Huang, Chen-Sheng Yeh, Andrew H. -J. Wang, Wei-Ting Wang, Ming-Yu Lin, Yang Gan.


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.

Partial Text

Porous spheres have several, extremely valuable therapeutic and biotechnological applications [1], [2], including cell immobilization, drug delivery, and as a packing material in chromatography [3]–[6]. Macroporous structures are especially important to spheres to improve their performance [1], [2], [7]. For example, large pores can increase the drug permeability of the spheres in drug delivery, significantly increase their specific surface area, allow them to be used as culture systems for growing adherent cells, be used as water remediation in high diffusion rates, or be used in the separation of large biomolecules, etc [8]–[16].

Figure 2a shows a photograph of the prepared iron oxide-loaded chitosan spheres. It is evident that the spheres are uniform in size, measuring 2.67±0.08 mm in diameter. After the drying process, the spheres had shrunk by about 79%. The diameter of the spheres could be controlled from 1 to 5 mm (with a variation of less than 8%) by altering the size of the needles under the relative sample flow rate from 20 to 30 mL/hour. In the future, the diameter of the spheres could be made smaller by employing other conventional droplet generation methods, such as atomization (spraying), emulsification, coacervation, sonication, electrostatic droplets, microfluidic droplets, etc [35]–[38]. It is worth noting that the surface of the iron oxide-loaded chitosan sphere is more irregular than that of pure chitosan spheres (Fig. 2b). This finding gave us the motivation to explore the internal structure of the polymer spheres. The pure chitosan sphere (absence of iron oxide nanoparticles) possesses a compact intra structure (Figs. 2c and 2d). In contrast, to our surprise, the inner structure of the iron oxide-loaded chitosan sphere shows a radial-patterned-like, non-spheroid morphology of macro pores and interconnected large cavities, as shown in Figs. 2e and 2f.

Chitosan spheres with non-spheroid, radial-like macro pores were successfully obtained. By employing the in-situ co-precipitation for ferro-gels, the macro pores with radiating cavities were observed. The proposed method provides an alternative way for generating macroporous spheres. In addition, a sodium hydroxide solution was employed for both the gelation (chitosan) and co-precipitation (ferrous cations and ferric cations) of ferro-gels. The results show that the diameter of both the iron oxide nanoparticles and the chitosan were controllable. In addition, the prepared iron oxide nanoparticles loaded chitosan spheres present a superparamagnetic character with good viability (above 80% for chitosan spheres containing iron-oxide up to 1000 µg/mL), indicating that they are eco-friendly and can potentially be used in various biological and biomedical applications, such as magnetic-responsive drug delivery systems, scaffold for bone tissues, ultrasound contrast agent, targeted drug delivery vehicle, and for delivering tumor and/or thrombus destruction materials.