Morphological characterization of bioerodible polymers. 3. Characterization of the erosion and intact zones in polyanhydrides using scanning electron microscopy

Mathiowitz, Edith; Jacob, Jules S.; Pekarek, Kathleen J.; Chickering, Donald E.

doi:10.1021/ma00077a010

Cited by 53 publications

(38 citation statements)

References 8 publications

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“…Comparing the MRI results of this study with the different mechanisms of polymer erosion published by Mathiowitz,22 it becomes evident that the erosion from P(CPP-SA) and PSA is neither bulk erosion nor pure surface erosion. The MRI results prove for the first time directly and noninvasively that these polyanhydrides erode according to a surface erosion front mechanism in vitro and in vivo.…”

Section: Discussionsupporting

confidence: 59%

Noninvasive in Vivo Monitoring of Drug Release and Polymer Erosion from Biodegradable Polymers by EPR Spectroscopy and NMR Imaging

Mäder¹,

Bačić²,

Domb³

et al. 1997

Journal of Pharmaceutical Sciences

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Biodegradable polymers have attracted much attention as implantable drug delivery systems. Uncertainty in extrapolating in vitro results to in vivo systems due to the difficulties of appropriate characterization in vivo, however, is a significant issue in the development of these systems. To circumvent this limitation, noninvasive magnetic resonance techniques, electron paramagnetic resonance (EPR) and magnetic resonance imaging (MRI), were applied to characterize drug release and polymer degradation in vitro and in vivo. MRI makes it possible to monitor water content, tablet shape, and response of the biological system such as edema and encapsulation. The results of the MRI experiments give the first direct proof in vivo of postulated mechanisms of polymer erosion. Using nitroxide radicals as model drug releasing compounds, information on the mechanism of drug release and microviscosity inside the implant can be obtained by means of 1.2 GHz EPR spectroscopy. To be able to attribute nitroxide mobility to a particular layer of the implant, sandwich-like tablets were manufactured, taking advantage of the distinct spectral features of nitroxides containing different isotopes of nitrogen (15N vs 14N). The use of both noninvasive methods to monitor processes in vivo leads to new insights in understanding the mechanisms of drug release and polymer degradation.

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Section: Discussionsupporting

confidence: 59%

Noninvasive in Vivo Monitoring of Drug Release and Polymer Erosion from Biodegradable Polymers by EPR Spectroscopy and NMR Imaging

Mäder¹,

Bačić²,

Domb³

et al. 1997

Journal of Pharmaceutical Sciences

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“…12 Hydrolysis of the surface of PLA copolymers due to erosion has been reported. 13 The surface was directly examined by scanning electron microscopy (SEM) 11,14 and atomic force microscopy (AFM)/SEM. 15 In recent years, mass spectrometry has been found to be a useful method for analyzing the chemical constituents and structure of biodegradable polymers.…”

Section: Introductionmentioning

confidence: 99%

Characterization of linear and cyclic polylactic acids and their solvolysis products by electrospray ionization mass spectrometry

et al. 2006

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Linear and cyclic polylactic acids (PLAs) were characterized using electrospray ionization mass spectrometry (ESI-MS) as part of our ongoing investigation of the hydrolysis mechanism of biodegradable polymers. The condensation oligomers of linear polylactic acid (LPLA) were synthesized by thermal dehydration of L-lactic acid. The trimer and tetramer base polymers of cyclic polylactic acid (CPLA) were obtained by cyclization reactions of lactic acid trimers and tetramers, respectively. In the ESI-MS/MS measurement, LPLA yielded three types of product ion series, while CPLA yielded only one type, from which the repeated units of CPLA were removed. The MS/MS spectrum of the NH4+ adduct ion for both cyclic and linear PLA showed loss of one ammonia molecule. The postsource decay (PSD) spectrum of CPLA by matrix-assisted laser desorption ionization (MALDI) mass spectrometry was similar to the ESI-MS/MS spectrum, while that of LPLA was different. In addition, the degradation of cyclic and linear PLAs by solvolysis was investigated. Solvolysis with anhydrous MeOH was quite feasible, but did not readily occur in the presence of even a small amount of water in the MeOH solvent.

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“…Erosion front formation (Fig. 3c) was proposed by Mathiowitz et al [6] as a typical erosion process for most conditions between these extremes, i.e. when degradation occurs in a finite outer region (erosion zone) of the polymer matrix.…”

Section: Synthetic Biodegradable Polymersmentioning

confidence: 89%

Surface perspectives in the biomedical applications of poly(α-hydroxy acid)s and their associated copolymers

Lee

Gardella

2002

Anal Bioanal Chem

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Impressive advances in biotechnology, bioengineering, and biomaterials with unique properties have led to increased interest in polymers and other novel materials in biological and biomedical research and development over the past two decades. Although biomaterials have already made an enormous impact in biomedical research and clinical practice, there is a need for better understanding of the surface and interfacial chemistry between tissue (or cells) and biomedical materials. This is because the detailed physicochemical events related to the biological response to the surface of materials still often remain obscure, even though surface properties are important determinants of biomedical material function. In this regard, data available in the literature show the complexity of the interactions (surface reorganization, non-specific/specific protein adsorption, and chemical reactions such as acid-base, ion pairing, ion exchange, hydrogen bonding, divalent-ion bridging) and the interrelationship between biological environments, interfacial properties, and surface functional groups responsible for the biological responses. Because of the multidisciplinary nature of surface and interfacial phenomena at the surface of biomedical polymers, this review focuses on several aspects of current work published on poly(alpha-hydroxy acid)s and their associated copolymers:surface structure-biomedical function relationships;physicochemical strategies for surface modification; and, finally,synthetic strategies to increase biocompatibility for specific in-vivo and/or in-vitro biomedical applications.

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Morphological characterization of bioerodible polymers. 3. Characterization of the erosion and intact zones in polyanhydrides using scanning electron microscopy

Cited by 53 publications

References 8 publications

Noninvasive in Vivo Monitoring of Drug Release and Polymer Erosion from Biodegradable Polymers by EPR Spectroscopy and NMR Imaging

Noninvasive in Vivo Monitoring of Drug Release and Polymer Erosion from Biodegradable Polymers by EPR Spectroscopy and NMR Imaging

Characterization of linear and cyclic polylactic acids and their solvolysis products by electrospray ionization mass spectrometry

Surface perspectives in the biomedical applications of poly(α-hydroxy acid)s and their associated copolymers

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