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.