Metabolic activity of CHO fibroblasts in HEMA–MMA microcapsules

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Abstract
Chinese hamster ovary (CHO) fibroblast cells were microencapsulated in polyacrylate membranes (HEMA-MMA: 75% HEMA) via an interfacial precipitation process. The CHO cells were observed to grow in large aggregates, attached to each other instead of to the capsule wall. When CHO cells were encapsulated at high density (4 × 106 cells/mL), the initial metabolic activity in microcapsules, as determined by the MTT assay, correlated with the polymer-cell extrusion ratio, presumably because of the dependence of encapsulation efficiency on the relative flow rates. However, there was a large variation in the metabolic activity among individual microcapsules throughout the present study. Capsules with low encapsulation efficiency (at a “seeding” density of 4 × 106 cells/mL) exhibited a rapid increase in the metabolic activity during the following week. When CHO cells were encapsulated at low density (4 × 105 cells/mL), there was only a small increase in the metabolic activity. Only a small fraction (∼5%) of the capsules exhibited a high level of metabolic activity and 40% of the capsules exhibited undetectable metabolic activity even after 2 weeks. We conclude that CHO cells, which served as model cells, survive the encapsulation process and retain an active metabolic state once enclosed by the HEMA-MMA membranes. However, the resultant microcapsules are extremely heterogeneous in the amount of retained metabolic activity.