Abstract
Controllable feature and size, good mechanical stability and intelligent release behavior is the capsule products relentless pursuit of the goal. In addition, to illustrate the quantitative relationship of structure and performance is also important for encapsulation technology development. In this study, the sphericity and size of millimeter-scale calcium sodium alginate capsules (mm-CaSA-Caps) with aqueous core were well tuned by manipulating the viscosity, surface tension, and density of CaCl2/carboxyl methyl cellulose (CMC) drops and sodium alginate (SA) solution. The well-tuned mm-CaSA-Caps showed significant mechanical and control-releasing property effects. The results showed that the prepared mm-CaSA-Caps were highly monodispersed with average diameter from 3.8 to 4.8 mm. The viscosity of the SA solution and the viscosity and surface tension of the CaCl2/CMC solution had significant effects on the mm-CaSA-Caps sphericity. Uniform and spherical mm-CaSA-Caps could be formed with high viscosity CaCl2/CMC solution (between 168.5 and 917.5 mPa·s), low viscosity SA solution (between 16.2 and 72.0 mPa·s) and decreased surface tension SA solution (by adding 0.01 wt.% poloxamer 407). The diameter of the mm-CaSA-Caps could be predicted by a modified Tate’s law, which correlated well with the experimental data. The Caps with sphericity factor (SF) < 0.07 had better mechanical stability, with the crushing force 2.91–15.5 times and the surface Young’s modulus 2.1–3.99 times higher than those of the non-spherical Caps (SF > 0.07). Meanwhile, the spherical Caps had a more even permeation rate, which was helpful in producing uniform and sustained releasing applications in foodstuff, medicine, agriculture and chemical industry.
Highlights
Fish-egg-like calcium sodium alginate (CaSA) matrix capsules (Caps) with an aqueous core at the millimeter scale prepared using the extrusion dripping method have been studied in food [1], agriculture [2] and biomedical industries [3,4]
Millimeter-scale calcium-alginate capsules were produced by the extrusion dripping method based on the ionotropic gelation principle
The viscosity and surface tension of Sodium alginate (SA) solution and CaCl2 /carboxyl methyl cellulose (CMC) solution were considered as major factors for tuning the shape of mm-CaSA-Caps
Summary
Fish-egg-like calcium sodium alginate (CaSA) matrix capsules (Caps) with an aqueous core at the millimeter scale prepared using the extrusion dripping method have been studied in food [1], agriculture [2] and biomedical industries [3,4]. For core-shell structures, CaCl2 droplets containing the active molecule and non-gelling polymer used to modulate viscosity and density are dropped into a SA bath to form the gel membrane in the interface of alginate molecules and calcium cations [8]. This inverted extrusion dripping method is popular due to its simple setup. It ensures that bioactive materials to be encapsulated never come into contact with the ionotropic gel-forming polymers and remain within their original environment [8] This method is more likely to obtain microcapsules within a narrow dimensional range and with high encapsulation efficiency, thereby proving a good choice for industrialized production [9]. The sphericity factor (SF) effect on the mechanical properties and permeability of mm-CaSA-Caps is discussed
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