Poly(ethylene glycol) Hydrogel Crosslinking Chemistries Identified via Atmospheric Solids Analysis Probe Mass Spectrometry

Abstract

Hydrogels are hydrophilic, crosslinked polymer networks that can absorb several times their own mass in water; they are frequently used in biomedical applications as a native tissue mimic. The characterization of hydrogels and other covalently crosslinked networks is often limited by their insolubility and infinite molecular weight conferred by crosslinking. In this study, chemically crosslinked hydrogel materials based on poly­(ethylene glycol) (PEG) have been characterized directly, without any sample preparation, by mild thermal degradation using atmospheric solids analysis probe mass spectrometry (ASAP-MS) coupled with ion mobility (IM) separation and tandem mass spectrometry (MS/MS) characterization of the degradants. The structural insight gained from these experiments is illustrated with the analysis of oxime-crosslinked PEG hydrogels formed by the click reaction between 4-arm PEG star polymers with either ketone or aminooxy end group functionalities and PEG dimethacrylate (PEGDMA) copolymeric hydrogel networks formed by photopolymerization of PEGDMA. The ASAP-MS, IM, and MS/MS methods were combined to identify the crosslinking chemistry and obtain precursor chemistry information retained in the end-group substituents of the thermal degradation products