Development of a microchannel emulsification process for pancreatic beta cell encapsulation.

In this study, we developed a high-throughput microchannel emulsification process to encapsulate pancreatic beta cells in monodisperse alginate beads. The process builds on a stirred emulsification and internal gelation method previously adapted to pancreatic cell encapsulation. Alginate bead production was achieved by flowing a 0.5-2.5% alginate solution with cells and CaCO3 across a 1-mm thick polytetrafluoroethylene plate with 700 × 200 µm rectangular straight-through channels. Alginate beads ranging from 1.5-3 mm in diameter were obtained at production rates exceeding 140 mL/hr per microchannel. Compared to the stirred emulsification process, the microchannel emulsification beads had a narrower size distribution and demonstrated enhanced compressive burst strength. Both microchannel and stirred emulsification beads exhibited homogeneous profiles of 0.7% alginate concentration using an initial alginate solution concentration of 1.5%. Encapsulated beta cell viability of 89 ± 2% based on live/dead staining was achieved by minimizing the bead residence time in the acidified organic phase fluid. Microchannel emulsification is a promising method for clinical-scale pancreatic beta cell encapsulation as well as other applications in the pharmaceutical, food, and cosmetic industries.

Mammalian Cell Encapsulation in Alginate Beads Using a Simple Stirred Vessel.

Cell encapsulation in alginate beads has been used for immobilized cell culture in vitro as well as for immunoisolation in vivo. Pancreatic islet encapsulation has been studied extensively as a means to increase islet survival in allogeneic or xenogeneic transplants. Alginate encapsulation is commonly achieved by nozzle extrusion and external gelation. Using this method, cell-containing alginate droplets formed at the tip of nozzles fall into a solution containing divalent cations that cause ionotropic alginate gelation as they diffuse into the droplets. The requirement for droplet formation at the nozzle tip limits the volumetric throughput and alginate concentration that can be achieved. This video describes a scalable emulsification method to encapsulate mammalian cells in 0.5% to 10% alginate with 70% to 90% cell survival. By this alternative method, alginate droplets containing cells and calcium carbonate are emulsified in mineral oil, followed by a decrease in pH leading to internal calcium release and ionotropic alginate gelation. The current method allows the production of alginate beads within 20 min of emulsification. The equipment required for the encapsulation step consists in simple stirred vessels available to most laboratories.

Magnetic Resonance Imaging of Alginate Beads Containing Pancreatic Beta Cells and Paramagnetic Nanoparticles.

Microencapsulation is being investigated as a means to avoid rejection of transplanted pancreatic islets. Monitoring bead distribution and stability in vivo is an important step toward improving microencapsulated islet transplantation strategies. Islet co-encapsulation with gadolinium-labeled mesoporous silica nanoparticles (Gd-MSNs) could allow bead visualization while immobilizing and limiting the potential internalization of the contrast agent. The porous nature of the MSNs could also be used to locally release anti-inflammatory, angiogenic, or anti-apoptotic factors. Mouse insulinoma 6 (MIN6) beta cells were co-encapsulated with Gd-MSNs in alginate beads produced by emulsification and internal gelation. Gd-MSN alginate beads appeared brighter in T1-weighted imaging sequences (detection threshold of 0.016 mM Gd; relaxometric ratio r2/r1 = 1.45) than beads without Gd-MSNs. No leaching of Gd3+ from the hydrogels was detected over the course of 3 months. MIN6 cells co-encapsulated with Gd-MSNs were viable without significant differences in cell growth rate compared to encapsulated controls without Gd-MSNs. This study paves the way for microencapsulated islet tracking via MRI using co-encapsulated paramagnetic nanomaterials.