Assessment by XPS and electrochemical techniques of two molecular organosilane films prepared on stainless-steel surfaces

Rationale Design for Anchoring Pendant Groups of Zwitterionic Polymeric Medical Coatings

A biocompatible and antifouling polymeric medical coating was developed through rational design for anchoring pendant groups for the modification of stainless steel. Zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) was copolymerized individually with three anchoring monomers of carboxyl acrylamides with different alkyl spacers, including acryloylglycine (2-AE), 6-acrylamidohexanoic acid (6-AH), and 11-acrylamidoundecanoic acid (11-AU). The carboxylic acid groups are responsible for the stable grafting of copolymers onto stainless steel via a coordinative interaction with metal oxides. Due to hydrophobic interaction and hydrogen bonding, the anchoring monomers enable the formation of self-assembling structures in solution and at a metallic interface, which can play an important role in the thin film formation and functionality of the coatings. Therefore, surface characterizations of anchoring monomers on stainless steel were conducted to analyze the packing density and strength of the intermolecular hydrogen bonds. The corresponding copolymers were synthesized, and their aggregate structures were assessed, showing micelle aggregation for copolymers with higher hydrophobic compositions. The synergistic effects of inter/intramolecular interactions and hydrophobicity of the anchoring monomers result in the diversity of the thickness, surface coverage, wettability, and friction of the polymeric coatings on stainless steel. More importantly, the antifouling properties of the coatings against bacteria and proteins were strongly correlated to thin film formation. Ultimately, the key lies in deciphering the molecular structure of the anchoring pendants in thin film formation and assessing the effectiveness of the coatings, which led to the development of medical coatings through the graft-onto approach.

Hot-Press-Assisted Adhesions between Polyimide Films and Titanium Plates Utilizing Coating Layers of Silane Coupling Agents

The development of low material-consuming adhesion techniques for different kinds of materials such as polymers and metals is important for the realization of sustainable societies. This study demonstrates that coating layers, expected to be formed as self-assembled monolayers, of silane coupling agents can act as adhesion layers at the polymer film-metal plate interfaces. Polyimide films were alkaline hydrolyzed to generate carboxy groups on their surfaces, whereas titanium plate surfaces were treated with the aminosilanes to form their coating layers thereon. These modified surfaces were placed in contact with each other and then hot pressed, which resulted in adhesion between them. An examination of the adhesion strength using lap shear tests and surface characterization of the prepared surfaces using X-ray photoelectron spectroscopy and other techniques indicated the formation of ionic bonds and/or amide bonds between the carboxy groups of the PI film surfaces and the amino groups immobilized on the titanium plate surfaces. The activation of the carboxy groups using N-hydroxysuccinimide resulted in adhesion obtaining a water-resistant property, which supported the increase in amide bond formation. On the basis of the results, the adhesion mechanism and the possible breaking points upon the breaking of adhesions are proposed.

Adlayer-mediated antibody immobilization to stainless steel for potential application to endothelial progenitor cell capture

This work describes the straightforward surface modification of 316L stainless steel with BTS, S-(11-trichlorosilylundecanyl)-benzenethiosulfonate, a thiol-reactive trichlorosilane cross-linker molecule designed to form intermediary coatings with subsequent biofunctionalization capability. The strategy is more specifically exemplified with the immobilization of intact antibodies and their Fab' fragments. Both surface derivatization steps are thoroughly characterized by means of X-ray photoelectron spectroscopy. The antigen binding capability of both types of biofunctionalized surfaces is subsequently assessed by fluorescence microscopy. It was determined that BTS adlayers achieve robust immobilization of both intact and fragmented antibodies, while preserving antigen binding activity. Another key finding was the observation that the Fab' fragment immobilization strategy would constitute a preferential option over that involving intact antibodies in the context of in vivo capture of endothelial progenitor cells in stent applications.

Understanding organic film behavior on alloy and metal oxides

Native oxide surfaces of stainless steel 316L and Nitinol alloys and their constituent metal oxides, namely nickel, chromium, molybdenum, manganese, iron, and titanium, were modified with long chain organic acids to better understand organic film formation. The adhesion and stability of films of octadecylphosphonic acid, octadecylhydroxamic acid, octadecylcarboxylic acid, and octadecylsulfonic acid on these substrates were examined in this study. The films formed on these surfaces were analyzed by diffuse reflectance infrared Fourier transform spectroscopy, contact angle goniometry, atomic force microscopy, and matrix-assisted laser desorption ionization mass spectrometry. The effect of the acidity of the organic moiety and substrate composition on the film characteristics and stability is discussed. Interestingly, on the alloy surfaces, the presence of less reactive metal sites does not inhibit film formation.

Surface Analysis by X-ray Photoelectron Spectroscopy of Sol−Gel Silica Modified with Covalently Bound Peptides

Chemical surface characterization of biologically modified sol-gel derived silica is critical but somewhat limited. This work demonstrates the ability of x-ray photoelectron spectroscopy (XPS) to characterize the surface chemistry of peptide modified sol-gel thin films based on the example of four different free peptide-silanes, denoted RGD, NID, KDI ,and YIG. The N 1s and C 1s peaks were found to be good fingerprints of the peptides, whereas O 1s overlapped with the signal of substrate oxygen and, therefore, the O 1s peak was not informative in the case of the thin films. The C 1s peak was fitted and the contribution of the residual hydrocarbons was sorted out. The curve-fitting procedure of the C 1s peak accounted for the different chemical states of carbon atoms in the peptide structure. The curve-fitting procedure was validated by analyzing free peptides in the powder form and was then applied to the characterization of the peptide-modified thin films. The XPS measured ratio between nitrogen and carbon for the peptide thin film was similar to the corresponding value calculated from the peptide structures. Angle resolved XPS confirmed the surface nature of peptides in modified thin films. The coverage and thickness of the peptides on the thin film surface depended on the peptide sequence. The coverage was in the range of 10% of a monolayer, and the layer thickness varied from 10 to 30 A. We believe that the different thicknesses and surface coverage are due to the local structure of the peptides, with the RGD and NID peptides taking a globule conformation and the YIG and KDI peptides adopting a more linear structure.

Self-assembled monolayers of alkanoic acids on the native oxide surface of SS316L by solution deposition

Stainless steel 316L is a widely used biomaterial substrate whose biocompatibility could be improved by surface modification. As a first step in this process, self-assembled monolayers of octanoic acid, octadecylcarboxylic acid, 16-hydroxyhexadecanoic acid, 12-aminododecanoic acid, and 1,12-dodecane dicarboxylic acid have been formed on the native oxide surface of stainless steel 316L by a simple, one-step solution deposition method. The ordering, close-packing, and coverage of the monolayers formed were characterized by diffuse reflectance infrared spectroscopy, contact angle measurements, and atomic force microscopy. The same procedure was applicable for all long alkyl chain carboxylic acids. This process formed chemically and mechanically stable monolayers. These carboxylic acids formed a bidentate bond with the stainless steel substrate. Robust chemical attachment of the acids to stainless steel through a simple process provides a stepping stone to improving the biocompatibility of stainless steel 316L.