Microencapsulation of carbon particles used as oxygen
sensors in EPR oximetry to stabilize their responsiveness to
oxygen in vitro and in vivo

1 Laboratory of Medicinal Chemistry and Radiopharmacy, Avenue Mounier 73.40, Université catholique
de Louvain, B-1200 Brussels, Belgium
2 Laboratory of Biomedical Magnetic Resonance, Avenue Hippocrate 10, Université catholique de
Louvain, B-1200 Brussels, Belgium
3 Illinois EPR Research Center, University of Illinois, Urbana-Champaign, IL, USA
4 EPR Research Center for the Study of Viable Biological Systems, Dartmouth Medical School,
Hanover, NH, USA

E-mail: Gallez@cmfa.ucl.ac.be

Received 17 August 2001
Published 14 November 2001

Abstract. The electron paramagnetic resonance (EPR) spectra of some paramagnetic materials exhibit a
pO2 (partial pressure of oxygen)-dependent linewidth. By recording the EPR linewidth in vivo using
low-frequency EPR spectrometers, it is possible to measure the partial pressure of oxygen in tissues. It
has been found, however, that some of the paramagnetic materials with optimal spectroscopic properties
in vitro may lose or change their responsiveness to oxygen in tissues. The aim of this study was to
microencapsulate paramagnetic particles by biopolymers in order to stabilize their responsiveness to
oxygen. Carbohydrate char particles (Bubinga) were encapsulated with different biopolymers: cellulose
acetate or cellulose triacetate, silicone and polyurethane. The performance of the materials was evaluated
in vitro and in vivo. X-band EPR spectroscopy was used to test the variation of the calibration curve
(EPR linewidth as a function of the pO2) after incubation in saline and after prolonged residence in
tissues. The stability of the responsiveness to pO2 in vivo was carried out by L-band EPR spectroscopy
using mice that received injection of the oxygen sensors in the muscles. After residence in saline and
prolonged residence in tissues, only the calibration curve of the silicone-coated (coating weight of 0.5%
(w/w)) paramagnetic materials remained unchanged, while those of oxygen sensors coated with cellulose
acetate, cellulose triacetate and polyurethane changed.

URL: stacks.iop.org/0031-9155/46/3323
DOI: 10.1088/0031-9155/46/12/317
PII: S0031-9155(01)27986-X