SEM characterization of gelatin-ionic liquid functional polymers

Abstract

ION JELLY^® patented technology is based on the cross-linking of Ionic Liquids (ILs) with Gelatin that results in a viscous gel that can be molded into a film or a block, and solidifies by cooling below 35 ºC . The outcome of this combination is a transparent, light and flexible conductive polymer that adapts perfectly to a great variety of surfaces. Some of the key properties of ION JELLY^® are: high stability up to 180ºC, large electrochemical window and bio-compatibility. Taking in consideration the attractive attributes of ILs, that provide a stable and friendly environment for the enzymes, where they retain their catalytic activity, combined with the morphologic advantage of gelatin, we have decided to study this new protein-ionic-based material regarding water content, swelling behaviour, and structural morphology by scanning electron microscopy (SEM).

The properties of [emim][EtSO₄] and [bmim][N(CN)₂] ION JELLY^® films were compared with those of solely gelatin. Thin films were prepared with different amounts of water or phosphate buffer and left to maturate in a controlled atmosphere for 4 days. Swelling was carried out in water at 4ºC and films were lyophilized afterwards. SEM images of ION JELLY^® and gelatin films were obtained prior and after these steps.

ION JELLY^® films were rubbery while gelatin films were glassy. Water-made ION JELLY^® had completely smooth surfaces, just like gelatin, but buffer-made ION JELLY^® exhibited salt crystals on the surface, as well as some superficial pores (Figure 1). Free water content in [emim][EtSO₄] ION JELLY^® was found to be greater than [bmim][N(CN)₂] ION JELLY^® and gelatin.

The swelling ratio of both types of ION JELLY^® was close to 100%, while gelatin swelled 8 times more. The swollen lyophilized gelatin films formed a heterogeneous and highly porous network (Figure 2), while ION JELLY^® films were more homogeneous with a lower degree of porosity (Figure 3).

These results showed that ION JELLY^® is a polymer with a more tightly bound structure than gelatin. This material allows water to penetrate, but possesses a higher rigidity that prevents too much mobility of the polymeric chains. Considering that it’s a biocompatible polymer, lyophilized swollen ION JELLY^® could have potential applications as a scaffold for biological material.

Financial support received from the Portuguese Science and Technology foundation (Fundação para a Ciência e Tecnologia) under the grants SFRH/BD/77568/2011, PTDC/EBB-BIO/114288/2009, PTDC/EBB-BI/099237/2008 and SFRH/BPD/41175/2007 and Projecto Estratégico IBB: PEst – OE/EQB/LA0023/2011