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Synthesis of magnetic resonance–, X-ray– and ultrasound-visible alginate microcapsules for immunoisolation and noninvasive imaging of cellular therapeutics

Nature Protocols volume 6, pages 1142–1151 (2011)Cite this article

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Abstract

Cell therapy has the potential to treat or cure a wide variety of diseases. Non-invasive cell tracking techniques are, however, necessary to translate this approach to the clinical setting. This protocol details methods to create microcapsules that are visible by X-ray, ultrasound (US) or magnetic resonance (MR) for the encapsulation and immunoisolation of cellular therapeutics. Three steps are generally used to encapsulate cellular therapeutics in an alginate matrix: (i) droplets of cell-containing liquid alginate are extruded, using an electrostatic generator, through a needle tip into a solution containing a dissolved divalent cation salt to form a solid gel; (ii) the resulting gelled spheres are coated with polycations as a cross-linker; and (iii) these complexes are then incubated in a second solution of alginate to form a semipermeable membrane composed of an inner and an outer layer of alginate. The microcapsules can be rendered visible during the first step by adding contrast agents to the primary alginate layer. Such contrast agents include superparamagnetic iron oxide for detection by 1H MR imaging (MRI); the radiopaque agents barium or bismuth sulfate for detection by X-ray modalities; or perfluorocarbon emulsions for multimodal detection by 19F MRI, X-ray and US imaging. The entire synthesis can be completed within 2 h.

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Figure 1: Setup of capsule synthesis equipment.
Figure 2: Magnetocapsules.
Figure 3: Barium and bismuth X-Caps.
Figure 4: 19F MR imaging of perfluoropolyether (PFPE) microcapsules.
Figure 5: CT imaging of PFOB microcapsules.
Figure 6: Ultrasound imaging of PFOB microcapsules.

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Acknowledgements

The development of this synthesis protocol was supported by a Howard Hughes Medical Institute Research Training Grant (B.P.B.), NIH grants K08 EB004348 (A.A.), R01 HL073223 (D.L.K.), R01 EB007825, U54CA151838 (J.W.M.B.) and RO1 HL084186 (M.S.).

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Author notes

  1. Matthias Stuber

    Present address: Present address: Department of Radiology, Centre Hospitalier Universitaire Vaudois, Center for Biomedical Imaging (CIBM) and University of Lausanne, Lausanne, Switzerland.,

Authors and Affiliations

  1. Russell H. Morgan Department of Radiology, Division of Magnetic Resonance Research, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Brad P Barnett, Aravind Arepally, Matthias Stuber, Dian R Arifin, Dara L Kraitchman & Jeff W M Bulte

  2. Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Jeff W M Bulte

  3. Department of Chemical and Biomolecular Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Jeff W M Bulte

  4. Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Brad P Barnett, Dian R Arifin & Jeff W M Bulte

  5. Department of Molecular and Comparative Pathobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Dara L Kraitchman

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Contributions

B.P.B., A.A., D.R.A., M.S., D.L.K. and J.W.M.B. designed the experiments and analyzed the data. B.P.B., A.A., M.S. and D.L.K. conducted the experiments and collected data. B.P.B. and J.W.M.B. wrote the article.

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Correspondence to Jeff W M Bulte.

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The authors have a patent pending that describes the methods of composition and use of these capsules.

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Barnett, B., Arepally, A., Stuber, M. et al. Synthesis of magnetic resonance–, X-ray– and ultrasound-visible alginate microcapsules for immunoisolation and noninvasive imaging of cellular therapeutics. Nat Protoc 6, 1142–1151 (2011). https://doi.org/10.1038/nprot.2011.352

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