CHO immobilization in alginate/poly-l-lysine microcapsules: an understanding of potential and limitations

Abstract

Microencapsulation offers a unique potential for high cell density, high productivity mammalian cell cultures. However, for successful exploitation there is the need for microcapsules of defined size, properties and mechanical stability. Four types of alginate/poly-L-Lysine microcapsules, containing recombinant CHO cells, have been investigated: (a) 800 lm liquid core microcapsules, (b) 500 lm liquid core microcapsules, (c) 880 lm liquid core microcapsules with a double PLL membrane and (d) 740 lm semiliquid core microcapsules. With encapsulated cells a reduced growth rate was observed, however this was accompanied by a 2-3 fold higher specific production rate of the recombinant protein. Interestingly, the maximal intracapsular cell concentration was only 8.7 · 10 7 cell mL -1 , corresponding to a colonization of 20% of the microcapsule volume. The low level of colonization is unlikely to be due to diffusional limitations since reduction of microcapsule size had no effect.Measurement of cell leaching and mechanical properties showed that liquid core microcapsules are not suitable for continuous long-term cultures (>1 month). By contrast semi-liquid core microcapsules were stable over long periods with a constant level of cell colonization (u = 3%). This indicates that the alginate in the core plays a predominant role in determining the level of microcapsule colonization. This was confirmed by experiments showing reduced growth rates of batch suspension cultures of CHO cells in medium containing dissolved alginate. Removal of this alginate would therefore be expected to increase microcapsule colonization.

Progress technology in microencapsulation methods for cell therapy

“…In this respect, semi-liquid cores appear to be the best compromise. 128 Cells-core/shell capsules are an interesting alternative, but several questions pertaining to mechanical resistance (related to strength of the cell aggregates), the consequences of cell growth and death on the integrity of the immunoisolation barrier, and finally, long-term stability and performance need to be addressed.…”

“…19 It has been reported that the hydrogel network can reduce cell growth and protein production by exerting stress not present in liquid or semi-liquid capsules. [127][128][129] Moreover, diffusion of gases and nutrients is higher in liquid than in gel. The objectives of encapsulating mammalian cells in liquid-core microcapsules (Figure 2b) have been pursued with a wide range of techniques, from interfacial polymerization, interfacial precipitation to PEC membrane and sacrificial core methods (Table 5).…”

“…Although beneficial for cell growth, core liquifaction weakens mechanical resistance of the capsules. 128 Transient alginate scaffold beads have been promoted for the assembly of CS/pDADMAC PE shells. These co-called ''CellMAC'' capsules, after dissolution of the alginate bead scaffold, proved to display excellent mechanical properties and cell viability.…”

Whey Protein-Pullulan (WP/Pullulan) Polymer Blend for Preservation of Viability ofLactobacillus acidophilus

“…This could be attributed to the formation of a smooth structure within the microcapsule; free volume for the bacteria needed to proliferate inside the microcapsule was insufficient. [70] …”

The Application of Dielectric Spectroscopy and Biocalorimetry for the Monitoring of Biomass in Immobilized Mammalian Cell Cultures

“…On the other hand immobilized cultures do not require sophisticated equipment to retain the cells within the vessel. A simple mesh is sufficient to extract the spent media as represented in Figure 1B [5]. Mammalian cell cultures are highly complex and may vary from one culture to another.…”