X-ray Photoelectron Spectroscopy (XPS) for Biomaterials-Medical / Health Care - Pharmaceuticals

Biomaterials are designed to function in a hydrated environment, which presents a challenge when using X-ray photoelectron spectroscopy (XPS) instruments that typically operate under ultra-high vacuum (UHV) conditions.

Biomaterials are intended to interact with living systems and are often required to maintain their functionality in a hydrated state. This conflict between the need for a hydrated environment and the requirement for UHV conditions has posed a significant obstacle in studying the surface chemistry of biomaterials using XPS techniques.

Recent development from Kratos of a cryo-stage for the AXIS Supra⁺ has allowed the preparation of hydrated samples by fast-freezing. This process vitrifies the water in the sample conserving spatial structure followed by XPS sample analysis at liquid nitrogen temperature.  The technique of fast-freezing was developed by Drs. Shchukarev and Ramstedt at UMEA, Sweden. They comment that ‘The biosample analysis started after we developed cryo-methods for the studies of mineral suspensions. This was driven by an interest to study bio-geo chemistry. We determined that we could interpret the data in terms of the electric double layer and the behaviour of the minerals in suspension. Having worked with these carefully prepared frozen samples, we collaborated with Laura Leone to study bacteria surfaces. We undertook a similar approach to the mineral samples, determining the coordination and double electric layer information. As we looked at these types of samples more carefully, it was apparent that we could gain information on the composition of bacteria cell walls. The freezing stabilised the sample, retained the water and was less disruptive than previous freeze-drying techniques. We have also concluded that the cryo-sample preparation is less time consuming and maintains better sample cleanliness than the freeze-dry approach.

In a recently published paper, Kjaervik et al. present an informative ‘comparative study of Near Ambient Pressure (NAP) and cryo- XPS for the investigation of surface chemistry of the bacterial cell-envelope’ [1]. The authors conclude that both methods allow for analysis of the hydrated bacterial cell-envelope of intact bacterial cells, with some advantages being apparent for the cryo-XPS approach 

[1] M. Kjærvik, M. Ramstedt, K. Schwibbert, P.M. Dietrich and W.E.S. Unger (2021), Front. Chem. 9:666161, Surface analysis of bio-materials. DOI: 10.3389/fchem.2021.666161