Development of a new method for the coating of elastomers with zwitterionic materials

Author

Pérez Balaguer, Dario  

Abstract

In this thesis, a new method for the coating of elastomers with polymer hydrogels is proposed. These hydrogels are made of zwitterionic materials. Zwitterionic materials are materials formed of zwitterions, molecules that contain both positively-charged functional groups and negatively-charged functional groups, but whose total electric charge is neutral. These types of materials present ultra-low-fouling properties, which means that they avoid the adsorption of proteins onto their surface. For that reason, they are an ideal material to coat elastomers, polymers commonly used in the development of medical implants, since they prevent the triggering of the immune response system. The main problem behind the coating of elastomers is that they are extremely hard to coat for various reasons: the coating needs to be flexible and elastic and it is extremely difficult to attach other materials onto them since they lack reactive groups in their chemical structure and their surface is very smooth. Therefore, the zwitterionic material cannot directly get attached to the elastomer. To make it possible, a multilayer strategy is developed. First, the substrate polydimethylsiloxane (PDMS) is coated with polydopamine (pDA), which provides reactive amine groups. Then, the cross-linker ethylene glycol dimethacrylate (EGDMA), is attached to the polydopamine layer through aza-Michael addition, based on the conjugate addition of nitrogen to α β, unsaturated esters. Last, the zwitterionic material sulfobetaine methacrylate (SBMA) is attached while being polymerized onto the EGDMA layer.
All the layers have undergone an optimization process to get the maximum amount of material attached to the surface. Moreover, in the attachment of SBMA, it was also considered to add a certain amount of EGDMA in conjunction with SBMA. Doing that, one can obtain a hydrogel instead of spare chains grafted and the properties may dier. Once the samples are coated, the properties of the coating are analyzed. For that, several techniques and instruments are used: 

1. Fourier-transform infrared spectroscopy (FTIR): to analyze the chemical structure of the coating.
2. Water contact angle (WCA) measurements: to measure the wetting properties of the surface.
3. Laser microscopy: to analyze the roughness and thickness from the substrate and the different layers conforming to the coating.
4. Stretching: to verify the flexibility and elasticity of the coating when the samples are stretched up to100%.
5. Adhesion tests: to measure the stability of the coating.

Finally, in order to demonstrate the reproducibility of our method, it has been applied to other elastomers and flexible materials like NuSil, Ecoflex, and Mold Max.

Director

Pena-Francesch, Abdon
Borrós i Gómez, Salvador

Degree

IQS SE - Master’s Degree in Chemical Engineering

Date

2020-09-04