Tuning structural durability of yeast‐encapsulating alginate gel beads with interpenetrating networks for sustained bioethanol production

Abstract

Microorganisms have become key components in many biotechnological processes to produce various chemicals and biofuels. The encapsulation of microbial cells in calcium cross-linked alginate gel beads has been extensively studied due to several advantages over using free cells. However, industrial use of alginate gel beads has been hampered by the low structural stability of the beads. In this study, we demonstrate that the incorporation of interpenetrating covalent cross-links in an ionically cross-linked alginate gel bead significantly enhances the bead's structural durability. The interpenetrating network (IPN) was prepared by first cross-linking alginate chemically modified with methacrylic groups, termed methacrylic alginate (MA), with calcium ions and subsequently conducting a photo cross-linking reaction. The resulting methacrylic alginate gel beads (IPN-MA) exhibited higher stiffness, ultimate strength and ultimate strain and also remained more stable in media either subjected to high shear or supplemented with chelating agents than calcium cross-linked alginate gel beads. Furthermore, yeast cells encapsulated in IPN-MA gel beads remained more metabolically active in ethanol production than those in calcium cross-linked alginate gel beads. Overall, the results of this study will be highly useful in designing encapsulation devices with improved structural durability for a broad array of prokaryotic and eukaryotic cells used in biochemical and industrial processes.

Matrices (re)loaded: Durability, viability, and fermentative capacity of yeast encapsulated in beads of different composition during long‐term fed‐batch culture

“…57 To investigate whether some bead types were more prone to swelling than others, bead diameter and mass were measured as a function of time. 57 To investigate whether some bead types were more prone to swelling than others, bead diameter and mass were measured as a function of time.…”

“…82 Regular changes in pH, from 5.8 to 4.6 over each 3.5-day feeding episode, were observed in this experiment and likely contributed to bead swelling. Swelling could also have been caused by gradual loss of calcium cations over time, 57 …”

“…52,53 Indeed, prior studies have shown that continuously fed encapsulated yeast produces ethanol at 88-100% efficiency for 1 week, 54 3 weeks, 55 and up to 3 months. 56 Thus, while multiple studies suggest that encapsulated cells could be re-used over several weeks, few 57,58 have explored whether and how different encapsulation matrices impact fermentation capacity and related parameters over longer time periods. 41 To fill these knowledge gaps, glucose consumption and ethanol production by S. cerevisiae were monitored over the course of 7 weeks, comparing the performance of cells in planktonic culture with cells encapsulated as~4 mm "beads" composed of four different matrices.…”

Photochemical Production of Interpenetrating Polymer Networks; Simultaneous Initiation of Radical and Cationic Polymerization Reactions

“…The high stiffness, the ultimate strength and strain, and the high stability of methacrylic alginate IPN gel beads are highly useful in designing encapsulation devices with improved structural durability for a broad array of prokaryotic and eukaryotic cells used in biochemical and industrial applications [84]. Photopolymerization provides a unique way to form an IPN gel in a fast and controllable manner usable for the direct photoencapsulation of cells.…”

A novel two‐species whole‐cell immobilization system composed of marine‐derived fungi and its application in wastewater treatment

“…Whole‐cell immobilization technology is receiving increased attention worldwide, which could be beneficial for applied goals such as biodegradation of mixed wastes and drug or fuel biosynthesis . Single species cells immobilized on various support matrices have been reported in the literature.…”