BIOPLASMAS & PLASMAS WITH LIQUIDS - Joint Conference of COST ACTIONS TD1208 “Electrical discharges with liquids for future
applications” & MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology, Bertinoro, Italy, 13th-17th September 2015
Protein Adsorption Affected by Plasma-Deposited Vertical Chemical
Gradient Structures
Noémi E. Blanchard1, Manfred Heuberger1, Dirk Hegemann1
1
Empa, Swiss Federal Laboratories for Materials Science and Technology,
Advanced Fibers, Lerchenfeldstrasse 5, St.Gallen, 9014, Switzerland
Plasma polymerization is widely used to generate functional coatings. Nanometer-sized vertical chemical
gradients represent a novel type of such films which are enabled thanks to a high process control during
deposition [1]. Such structures are expected to influence the adsorption/desorption behavior of amphiphilic
molecules and proteins. Vertical chemical gradients were thus generated using plasma polymerization of
hexamethyldisiloxane (HMDSO). A more hydrophilic base layer (SiOx with x < 2) was produced from
O2/HMDSO discharges. A gradient structure was subsequently obtained by gradually removing the oxygen
from the plasma resulting in a hydrophobic PDMS-like pHMDSO surface layer with a thickness of a few
nanometers. The gradients were characterized by XPS and contact angle measurements.
Protein adsorption kinetics were measured with the Transmission Interferometric Adsorption Sensor
(TInAS), an optical technique providing high mass resolution and reasonable sampling rates. It was found
that, compared to the single layers (hydrophilic SiOx or hydrophobic pHMDSO), less bovine serum albumin
(BSA) adsorbs on the vertical chemical gradients and, in addition, also the adsorption kinetics were slower
(Fig. 1). Hence, the vertical chemical gradient greatly influences the adsorption of BSA which is discussed by
water structuring in the sub-surface layer, i.e. within the hydrophobic-to-hydrophilic gradient. Neutron
reflectometry measurements indeed revealed the hydration of hydrophobic pHMDSO films. Such vertical
chemical gradient coatings thus become interesting for their reduced protein adsorption and are also
envisaged as controlled drug release systems and for their sorption properties of amphiphilic molecules.
Fig 1: Adsorption of proteins (BSA) on single layers made of SiO x and pHMDSO and on the vertical
chemical gradient structure followed by TInAS. The right hand side shows a sketch of the possible protein
configuration on the individual surfaces.
[1] N.E. Blanchard, B. Hanselmann, J. Drosten, M. Heuberger and D. Hegemann, Plasma Process. Polym. 12
(2015) 32.