Quantitative TOF-SIMS analysis of oligomeric degradation products at the surface of biodegradable poly(α-hydroxy acid)s

Abstract

This paper reports the development of a new method for quantification of the hydrolytic surface degradation kinetics of biodegradable poly(␣-hydroxy acid)s using time-of-flight secondary ion mass spectrometry (TOF-SIMS). We report results from static SIMS spectra of a series of poly(␣-hydroxy acid)s including poly(glycolic acid), poly( L -lactic acid), and random poly( D,L -lactic acid-co-glycolic acid) hydrolyzed in various buffer systems. The distribution of the most intense peak intensities of ions generated in high mass range of the spectrum reflects the intact degradation products (oligomeric hydrolysis products) of each biodegradable polymer. First, a detailed analysis of the oligomeric ions is given based on rearrangement of the intact hydrolysis products. The pattern of ions can distinguish both degradation-generated intact oligomers and their fragment ion peaks with a variety of combinations of each repeat unit. Then, the integration and summation of the area of all ion peaks with the same number of repeat units is proposed as a measurement that provides a more accurate MW average than the typically used method which counts only the most intense peak. The multiple ion summation method described in this paper would be practical in the improvement of quantitative TOF-SIMS studies as a better data reduction method, especially in the surface degradation kinetics of biodegradable polymers. , additives in a polymer [13], and detailed structural characterization [14,15] and quantitative analysis [16 -20] of polymers. Most TOF-SIMS spectra of polymers have been obtained in the mass range m/z Ͻ10,000 [5, 18 -20].Two main processes are observed in the TOF-SIMS spectra of polymers; these are the fragmentation of polymer chains and the desorption of intact oligomers. Fragmentation under ion bombardment in ultra-high vacuum (UHV) environment generates distinct fragmentation patterns that are unique to a given polymer. From the fragmentation patterns the mass of the repeat unit, terminal groups, side groups, and functional groups in a repeat unit can be determined [14,15]. Desorption of intact oligomers provides a direct measure of molecular weight distribution (MWD) from which a molecular weight average can be evaluated. According to the recent reports [21,22] on the comparison of mass spectrometric techniques, TOF-SIMS produced a result similar to electrospray ionization (ESI) and fast atom bombardment (FAB). They consistently showed lower MW averages compared with gel permeation chromatography (GPC)-deduced results, whereas

Time of flight secondary ion mass spectrometry surface and in-depth study of degradation of nanosheet poly(l-lactic acid) films

“…22,24,25,27 Given this idea, low-molecular-weight PLLA films have been chosen as a reference in order to reduce the hydrolysis time needed to obtain degradation information. Model system: PLLA 2 kDa films It has been our hypothesis in previous studies that, during the ToF-SIMS experiment, degradation product oligomers of hydrolysable polyesters are not able to desorb from the surface upon bombardment with primary ions until they reach a certain length that falls below the critical molecular weight of entanglement (M c ).…”

“…24,37 Briefly, for each polymer chain with n monomers, the sum of secondary ion signals that encompasses its total intensity consists of: In previous ToF-SIMS degradation studies, the MWD function of polyesters (PGA, PLLA, and PLGA) was calculated from oligomer signals in the high-mass region (m/z > 600 Da) in order to avoid the calculated average MW value to be skewed by counting lighter oligomer ions with higher intensities (low mass ions have higher ionization probability than heavier ions, which rise to the logarithmic signal decay characteristic of ToF-SIMS spectra). The total intensity of each oligomer was calculated using the multiple ion summation method.…”

“…[22][23][24][25][26][27][28][29][30] This methodology provides important information that is lost when the extent of polymer degradation is assessed by measuring the dissolved oligomer or monomer concentration in the treatment medium, since there are a series of chain scission events that need to occur in order for oligomers to be short enough to leave the matrix and solubilize. This technique has been successfully used by our research group to study the surface degradation behavior of poly a-hydroxy esters and polyanhydrides in macro-and microscale dimensions.…”

Review paper: Principles and Applications of Surface Analytical Techniques at the Vascular Interface

“…Although the common techniques used both in vitro and in vivo are XPS [97], FTIR microscopy [98], gas permeation chromatography (GPC), and static ion mass spectroscopy (SIMS) [53], imaging techniques such as SEM [99] has also been used to assess for degradation. Features of in vivo degradation using SEM include fissuring, interlocking, cracking, and surface grazing [100] and along with FTIR has been shown to detect in vivo degradation [101] of carbonate-based polyurethane grafts.…”

Helium Ion Microscopy with Secondary Ion Mass Spectrometry (HIM-SIMS) for the analysis and quantitation of polyolefins

“…[2][3][4][5] As such, research has primarily been focused on characterization of copolymers and polymer blends using ToF-SIMS. [6][7][8][9][10][11] ToF-SIMS has been used to investigate surface chemistry, interfaces, microscopic phases, and to quantitatively map surface specific polymers in blends including styrene-methyl methacrylate random copolymers, ethylene-propylene-diene terpolymers, and polypropylene/ethylene-propylene copolymer blends [12][13][14][15] as well as to determine the molecular weight for a variety of polymers including PE, PP, and polystyrene (PS). 16 The possibility to analyze and distinguish polymers in a blend with nanosized structures becomes increasingly important as properties and performance of such materials can depend on the interfacial segregation, phase separation, and phase coarsening, which can vary in size down to tens of nanometers.…”