Exploration of plasma-enhanced chemical vapor deposition as a method for thin-film fabrication with biological applications

Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD)

Densely sintered aluminum oxide (α-Al2O3) is chemically and biologically inert. To improve the interaction with biomolecules and cells, its surface has to be modified prior to use in biomedical applications. In this study, we compared two deposition techniques for adhesion promoting SiOx films to facilitate the coupling of stable organosilane monolayers on monolithic α-alumina; physical vapor deposition (PVD) by thermal evaporation and plasma enhanced chemical vapor deposition (PE-CVD). We also investigated the influence of etching on the formation of silanol surface groups using hydrogen peroxide and sulfuric acid solutions. The film characteristics, that is, surface morphology and surface chemistry, as well as the film stability and its adhesion properties under accelerated aging conditions were characterized by means of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and tensile strength tests. Differences in surface functionalization were investigated via two model organosilanes as well as the cell-cytotoxicity and viability on murine fibroblasts and human mesenchymal stromal cells (hMSC). We found that both SiOx interfaces did not affect the cell viability of both cell types. No significant differences between both films with regard to their interfacial tensile strength were detected, although failure mode analyses revealed a higher interfacial stability of the PE-CVD films compared to the PVD films. Twenty-eight day exposure to simulated body fluid (SBF) at 37 °C revealed a partial delamination of the thermally deposited PVD films whereas the PE-CVD films stayed largely intact. SiOx layers deposited by both PVD and PE-CVD may thus serve as viable adhesion-promoters for subsequent organosilane coupling agent binding to α-alumina. However, PE-CVD appears to be favorable for long-term direct film exposure to aqueous solutions.

Mechanically Robust Plasma-Activated Interfaces Optimized for Vascular Stent Applications

The long-term performance of many medical implants is limited by the use of inherently incompatible and bioinert materials. Metallic alloys, ceramics, and polymers commonly used in cardiovascular devices encourage clot formation and fail to promote the appropriate molecular signaling required for complete implant integration. Surface coating strategies have been proposed for these materials, but coronary stents are particularly problematic as the large surface deformations they experience in deployment require a mechanically robust coating interface. Here, we demonstrate a single-step ion-assisted plasma deposition process to tailor plasma-activated interfaces to meet current clinical demands for vascular implants. Using a process control-feedback strategy which predicts crucial coating growth mechanisms by adopting a suitable macroscopic plasma description in combination with noninvasive plasma diagnostics, we describe the optimal conditions to generate highly reproducible, industry-scalable stent coatings. These interfaces are mechanically robust, resisting delamination even upon plastic deformation of the underlying material, and were developed in consideration of the need for hemocompatibility and the capacity for biomolecule immobilization. Our optimized coating conditions combine the best mechanical properties with strong covalent attachment capacity and excellent blood compatibility in initial testing with plasma and whole blood, demonstrating the potential for improved vascular stent coatings.

Microphase-Separated PE/PEO Thin Films Prepared by Plasma-Assisted Vapor Phase Deposition

Immiscible polymer blends tend to undergo phase separation with the formation of nanoscale architecture which can be used in a variety of applications. Different wet-chemistry techniques already exist to fix the resultant polymeric structure in predictable manner. In this work, an all-dry and plasma-based strategy is proposed to fabricate thin films of microphase-separated polyolefin/polyether blends. This is achieved by directing (-CH2-)100 and (-CH2-CH2-O-)25 oligomer fluxes produced by vacuum thermal decomposition of poly(ethylene) and poly(ethylene oxide) onto silicon substrates through the zone of the glow discharge. The strategy enables mixing of thermodynamically incompatible macromolecules at the molecular level, whereas electron-impact-initiated radicals serve as cross-linkers to arrest the subsequent phase separation at the nanoscale. The mechanism of the phase separation as well as the morphology of the films is found to depend on the ratio between the oligomeric fluxes. For polyolefin-rich mixtures, polyether molecules self-organize by nucleation and growth into spherical domains with average height of 22 nm and average diameter of 170 nm. For equinumerous fluxes and for mixtures with the prevalence of polyethers, spinodal decomposition is detected that results in the formation of bicontinuous structures with the characteristic domain size and spacing ranging between 5 × 10(1) -7 × 10(1) nm and 3 × 10(2)-4 × 10(2) nm, respectively. The method is shown to produce films with tunable wettability and biologically nonfouling properties.

Enhanced osteoblast adhesion on amino-functionalized titanium surfaces through combined plasma enhanced chemical vapor deposition (PECVD) method

A combined PECVD method has been developed to introduce amino-groups onto titanium implants for the better improvement of osseointegration.

Synthesis of ultrathin poly(methyl methacrylate) model coatings bound via organosilanes to zinc and investigation of their delamination kinetics

Polymer coatings are widely used to protect metals from corrosion. Coating adhesion to the base material is critical for good protection, but coatings may fail because of cathodic delamination. Most of the experimental studies on cathodic delamination use polymers to study the corrosion behavior under conditions where the interfacial chemistry at the metal(oxide)/polymer interface is not well-defined. Here, ultrathin linear and cross-linked poly(methyl methacrylate) [PMMA] coatings that are covalently bound to oxide-covered zinc via a silane linker have been prepared. For preparation, zinc was functionalized with vinyltrimethoxysilane (VTS), yielding a vinyl monomer-covered surface. These samples were subjected to thermally initiated free radical polymerization in the presence of methyl methacrylate (MMA) to yield surface-bound ultrathin PMMA films of 10-20 nm thickness, bound to the surface via Zn-O-Si bonds. A similar preparation was also carried out in the presence of different amounts of the cross-linkers ethylene glycol diacrylate and hexanediol diacrylate. Functionalized and polymer-coated zinc samples were characterized by infrared (IR) spectroscopy, secondary ion mass spectrometry (SIMS), ellipsometry, and X-ray photoelectron spectroscopy (XPS). Coating stability toward cathodic delamination has been evaluated by scanning Kelvin probe (SKP) experiments. In all cases, the covalently linked coatings show lower delamination rates of 0.02-0.2 mm h(-1) than coatings attached to the surface without covalent bonds (rates ∼10 mm h(-1)). Samples with a higher fraction of cross-linker delaminate slower, with rates down to 0.03-0.04 mm h(-1), compared to ∼0.3 mm h(-1) without cross-linker. Samples with longer hydrophobic alkyl chains also delaminate slower, with the lowest observed delamination rate of 0.028 mm h(-1) using hexanediol diacrylate. For the coatings studied here, delamination kinetics is not diffusion limited, but the rate is controlled by a chemical reaction. Several possibilities for the nature of this reaction are discussed; radical side reactions of the oxygen reduction are the most likely path of deadhesion.

Development of antimicrobial coatings by atmospheric pressure plasma using a guanidine-based precursor

Antimicrobial coatings deposited onto ultra high molecular weight polyethylene (UHMWPE) films were investigated using an atmospheric pressure - plasma enhanced chemical vapor deposition (AP-PECVD) process. Varying concentrations of a guanidine-based liquid precursor, 1,1,3,3-tetramethylguanidine, were used, and different deposition conditions were studied. Attenuated total reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS) were used to study the chemical structure and elemental composition of the coatings. Conformity, morphology, and coating thickness were assessed through SEM and AFM. Optimal AP-PECVD parameters were chosen and applied to deposit guanidine coatings onto woven fabrics. The coatings exhibited high antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) based on a modified-AATCC 100 test standard, where 2-5 log reductions were achieved.