The determination of functional groups on complex polymer surfaces by X-ray photoelectron spectroscopy (XPS) can be improved considerably by derivatization reactions. Simple polymers containing hydroxyl groups or amino groups were investigated as reference materials for the derivatization with trifluoroacetic anhydride (TFAA).Poly(vinyl alcohol) (PVA), poly(hydroxyethyl methacrylate) (PHEMA), poly(vinyl butyral) (PVB), poly(allylamine) (PAAm), and poly(diallyl amine) (PDAAm) were derivatized using TFAA and analyzed with XPS. Polyethylene (PE) was used as an independent external reference for the binding energy (BE). Applying this procedure, the BE scales of all measurements were referenced to the carbon atoms of PE. It was found that the BE of the CF 3 component in the C1s region is different when bonded as an acetate or as an amide. The CF 3 BE is also influenced by the density of these groups in the polymer molecule. In TFAA-PVA, where every second main chain carbon atom carries a trifluoroacetate (TFAc) group, the BE is 294.3 eV while in TFAA-PVB with only isolated groups, the BE is 293.6 eV. The BE of the CF 3 component in the trifluoroacetamides (TFAAms) prepared from PAAm and PDAAm was found to be 292.5 and 292.3 eV, respectively. Compared with the analog fluorine free compounds, the BE is shifted toward higher values also for the ester carbon atom, the amide carbon atom, and the carbon atom to which the ester or amide is bonded.The data suggest that the gas phase reaction of TFAA with a polymer surface is diffusion limited. The actual ester or amide formation is a fast reaction and runs as a wave into the surface.

A single-step process to polymer nanofiber meshes that possess biofunctional peptide segments on their surfaces is described here, which requires a standard electrospinning setup only. Spinning a homogeneous mixture composed of a valuable polymer-peptide conjugate (poly(lactic acid)-block-CGGRGDS) and a biocompatible commodity poly(lactic-co-glycolic acid) (PLGA) leads to nonwovens where the bioactive peptide part is enriched up to 11 times on their fiber surface. This is determined by X-ray photoelectron spectroscopy (XPS). The surface accessibility of the peptide is proved on the macroscale by contact angle measurements comparing pure PLGA fibers with GRGDS-functionalized fiber meshes as well as on the nanoscale by probing electrostatic interaction between CGGRGDS surface functionalities and a colloidal silica probe via atomic force microscopy (AFM). Ultimately, bioavailability and bioactivity of the peptides on the fiber surfaces are demonstrated, showing that the meshes promote adhesion and migration of fibroblasts in comparison to pure PLGA meshes. The one-step production of hydrophilic PLGA-based fibers could be exploited to electrospin into living cell culture without indication of toxic adverse effects on cell proliferation. This might be useful for directly production of cell-loaded scaffolds or biohybrid materials.

The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces, amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90% of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between the amino siloxane's amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the derivatization reaction cannot be unequivocally derived. However, 1-3% of the total carbon atoms in the surface layer were found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially lower than the total amount of amino groups present at the surface.

A modular strategy toward (bio)functional nanofiber meshes by electrospinning is described. In contrast to commonly established, multistep protocols or complex spinning setups, a straightforward single-step procedure is investigated to obtain polymer nanofibers with pentafluorophenyl (Pfp)-activated esters on the surface. The aim was to electrospin, for the first time, poly(pentafluorophenyl methacrylate) (PPfpMA) and PPfpMA/poly(ε-caprolactone) (PCL) blends, resulting in reactive nanofibers with fiber surfaces that can be functionalized with suitable bioactive entities. While PPfpMA fibers are brittle the spinning of PCL/PPfpMA blends leads to improved mechanical stability of the obtained fabrics. The effective introduction of surface functionalities onto the fibers was proven by both model compounds and bioactive monosaccharides. The Pfp-activated esters are enriched at the fiber surfaces and react cleanly with nucleophiles such as 2-aminoethanol, aminofluorescein, or amino-functionalized monosaccharides to generate a robust amide anchor. The attachment of functional entities releases a Pfp group that allows for monitoring of the functionalization reaction with UV/vis spectroscopy. X-ray photoelectron spectroscopy (XPS) and contact angle measurements indicate effective introduction of functionalities to the fiber surfaces, and fluorescence microscopy suggests a homogeneous distribution of amino functional fluorescence markers on the meshes. The bioavailability of the introduced carbohydrates is shown by macrophage stimulation experiments using PCL/PPfpMA fiber meshes, which are functionalized with 2-aminoethyl-R-D-mannopyranoside or β-D-galactopyranoside. Meshes functionalized with mannose specifically enhance the cytokine production of macrophages when costimulated with lipopolysaccharides compared to galactose-or aminoethanol-functionalized PCL/PPfpMA fiber mat controls.

A first inter‐laboratory comparison was conducted to demonstrate and document the capability of interested laboratories to measure the fraction of COH species on a plasma oxidised poly(propylene) sample by using a chemical derivatisation XPS approach. This report presents the results from that inter‐laboratory comparison and includes the data received for the measured values and their associated standard deviations of laboratory means, at a 95% confidence level. The measurements were guided by a protocol developed within the group before and summarised shortly in the paper. Standard deviations that may characterise the state‐of‐the‐art for the nominally simple and rather often practised case of TFAA chemical derivatisation XPS of COH species on a plasma oxidised polyolefin surface are calculated following ISO 5725‐2:1994. The main conclusion is that the associated degree of equivalence reached by the participating laboratories in this comparison is still low. Further research to improve chemical derivatisation XPS protocols is mandatory.