Microcapsules with intrinsic barium radiopacity for immunoprotection and X-ray/CT imaging of pancreatic islet cells

Biomaterials. 2012 Jun;33(18):4681-9. doi: 10.1016/j.biomaterials.2012.03.008. Epub 2012 Mar 22.


Microencapsulation is a commonly used technique for immunoprotection of engrafted therapeutic cells. We investigated a library of capsule formulations to determine the most optimal formulation for pancreatic beta islet cell transplantation, using barium as the gelating ion and clinical-grade protamine sulfate (PS) as a new cationic capsule cross-linker. Barium-gelated alginate/PS/alginate microcapsules (APSA, diameter = 444 ± 21 μm) proved to be mechanically stronger and supported a higher cell viability as compared to conventional alginate/poly-l-lysine/alginate (APLLA) capsules. Human pancreatic islets encapsulated inside APSA capsules, gelated with 20 mm barium as optimal concentration, exhibited a sustained morphological integrity, viability, and functionality for at least 3-4 weeks in vitro, with secreted human C-peptide levels of 0.2-160 pg/ml/islet. Unlike APLLA capsules that are gelled with calcium, barium-APSA capsules are intrinsically radiopaque and, when engrafted into mice, could be readily imaged in vivo with micro-computed tomography (CT). Without the need of adding contrast agents, these capsules offer a clinically applicable alternative for simultaneous immunoprotection and real-time, non-invasive X-ray/CT monitoring of engrafted cells during and after in vivo administration.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alginates / chemistry
  • Animals
  • Barium / chemistry*
  • Capsules / chemistry*
  • Cell Line, Tumor
  • Cells, Cultured
  • Humans
  • In Vitro Techniques
  • Islets of Langerhans / diagnostic imaging*
  • Mice
  • Polylysine / analogs & derivatives
  • Polylysine / chemistry
  • Tomography, X-Ray Computed / methods*


  • Alginates
  • Capsules
  • alginate-polylysine-alginate
  • Barium
  • Polylysine