Thermally induced gelable polymer networks for living cell encapsulation

We report the encapsulation of MIN6 cells, a pancreatic β-cell line, using thermally induced gelable materials. This strategy uses aqueous solvent and mild temperatures during encapsulation, thereby minimizing adverse effects on cell function and viability. Using a 2:1 mixture of PNIPAAm-PEG-PNIPAAm tri-block copolymer and PNIPAAm homopolymer that exhibit reversible sol-to-gel transition at ∼30°C, gels were formed that exhibit mechanical integrity, and are stable in H2O, PBS and complete DMEM with negligible mass loss at 37°C for 60 days. MTT assays showed undetectable cytotoxicity of the polymers towards MIN6 cells. A simple microencapsulation process was developed using vertical co-extrusion and a 37°C capsule collection bath containing a paraffin layer above DMEM. Spherical capsules with diameters ranging from 500 to 900 µm were formed. SEM images of freeze-dried capsules with PBS as the core solution showed homogenous gel capsule membranes. Confocal microscopy revealed that the encapsulated cells tended to form small aggregates over 5 days, and staining for live and dead cells showed high viability post-encapsulation. A static glucose challenge with day-5 cultured microencapsulated cells exhibited glucose-dependent insulin secretion comparable to controls of free MIN6 cells grown in monolayers. These results demonstrate the potential use of these thermo-responsive polymers as cell encapsulation membranes. Biotechnol. Bioeng. 2007;96: 146–155. © 2006 Wiley Periodicals, Inc.