Enhancing the Diffusion Channels of Silica-Alginate Capsules for Microbial Encapsulation

Silica-alginate capsule (G-0) has recently been used in fermentation processes to encapsulate microbial cells for several benefits, including facilitating continuous flow processes and simplifying cell recovery and reuse. However, these conventional silica-coated alginate capsules suffer from poor diffusion channels, which are critical for efficiently transporting substrates and products. This study aimed to develop a novel method for producing silica-coated alginate capsules with improved diffusion channels (G-3). The Ca-alginate capsule was fabricated via a simple dripping method, where a solution of calcium chloride (CaCl₂) and carboxymethylcellulose (CMC) was dripped into an alginate solution. For the traditional silica coating (G-0), the alginate capsule was mixed with a silica source (hydrolyzed 3-aminopropyl triethoxysilane) under specific conditions. In the modified method, glucose was introduced as a pore-forming agent (PFA), with varying amounts (0.75, 1.5, and 3 g) resulting in capsules labeled G-0.75, G-1.5, and G-3, respectively. The diffusion coefficient for G-3 was found to be the highest, for example, at 313.15 K, it was calculated as $\left(7.77\pm 0.57\right)\times {10}^{-3}m{m}^2/\min$ compared to $\left(3.04\pm 0.09\right)\times {10}^{-3}m{m}^2/\min$ for G-0. This finding highlights the effectiveness of PFA in enhancing membrane porosity and diffusivity, which is promising for microbial cell immobilization where mass transfer is a significant concern.