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Scientific article
English

In Vitro Monitoring of Poly(ortho ester) Degradation by Electron Paramagnetic Resonance Imaging

Contributors

Capancioni, Sergio Pietro; Schwach-Abdellaoui, Khadija; Kloeti, Werner; Herrmann, Werner; Brosig, Holger; Borchert, Hans-Hubert; Heller, Jorge; Gurny, Robert

Published in

Macromolecules, vol. 36, no. 16, p. 6135-6141

Publication date

2003

Abstract

Electron paramagnetic resonance (EPR) imaging was applied to investigate further the in vitro degradation process of poly(ortho esters) containing 30 mol % lactic acid units in the polymer backbone (POE[70]LA[30]) and developed for controlled drug delivery. The objective of this study was the direct and continuous determination of pH values inside the degrading POE[70]LA[30]. pH-sensitive nitroxide spin probes 4-amino-2,2,5,5-tetramethyl-3-imidazoline-1-yloxy, 2,2,3,4,5,5-hexamethylimidazolidine-1-yloxy, and 2,2,4,5,5-pentamethyl-3-imidazoline-1-yloxy were calibrated in buffer solutions in order to cover a pH range between 1.0 and 8.0. Nitroxide spin probes were incorporated in POE[70]LA[30], and polymer samples were incubated in 0.1 M phosphate buffer (pH 7.4) at 37 °C. At selected times, polymer samples were removed for the determination of pH values inside the eroding POE[70]LA[30] by EPR at a frequency of 9.4 GHz. EPR imaging showed that the in vitro degradation of POE[70]LA[30] followed a two-phase process: in the first week of incubation, diffusion of water, and in consequence polymer degradation, were limited to the surface of the hydrophobic POE[70]LA[30] where pH values between 6.0 and 7.4 were measured. After 1 week of incubation, water diffused into the core of the sample, allowing the determination of pH values inside the eroding POE[70]LA[30] until complete erosion. Results indicated the formation of a pH gradient, with the most acidic environment inside the eroding sample where the lowest pH value of 3.8 was measured and higher pH at the surface. It was also possible to observe a polymer erosion front moving down within the polymer matrix in the course of time. The pH value of 3.8 measured inside the degrading POE[70]LA[30] remained constant until polymer samples disintegrated at day 23, where no EPR signal was detectable. In conclusion, EPR imaging allows the noninvasive spatially resolved observation of pH changes within POE[70]LA[30], and results confirmed that the in vitro erosion mechanism of POE[70]LA[30] was neither bulk erosion nor pure surface erosion.

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UNIGE research groups

Citation (ISO format)

CAPANCIONI, Sergio Pietro et al. In Vitro Monitoring of Poly(ortho ester) Degradation by Electron Paramagnetic Resonance Imaging. In: Macromolecules, 2003, vol. 36, n° 16, p. 6135–6141. doi: 10.1021/ma034365q

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Article (Published version)

Identifiers

Additional URL for this publication

http://pubs.acs.org/cgi-bin/article.cgi/mamobx/2003/36/i16/pdf/ma034365q.pdf

Journal ISSN

0024-9297
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Technical informations

Creation

06/10/2009 11:58:58

First validation

06/10/2009 11:58:58

Update

14/03/2023 15:16:06

Status update

14/03/2023 15:16:06

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