Protein adsorption is one of the key parameters influencing the biocompatibility of medical device materials. This study investigates serum protein adsorption and bacterial attachment on polymer coatings deposited using an atmospheric pressure plasma jet system. The adsorption of bovine serum albumin and bovine fibrinogen (Fg) onto siloxane and fluorinated siloxane elastomeric coatings that exhibit water contact angles (θ) ranging from superhydrophilic (θ < 5°) to superhydrophobic (θ > 150°) were investigated. Protein interactions were evaluated in situ under dynamic flow conditions by spectroscopic ellipsometry. Superhydrophilic coatings showed lower levels of protein adsorption when compared with hydrophobic siloxane coatings, where preferential adsorption was shown to occur. Reduced levels of protein adsorption were also observed on fluorinated siloxane copolymer coatings exhibiting hydrophobic wetting behaviour. The lower levels of protein adsorption observed on these surfaces indicated that the presence of fluorocarbon groups have the effect of reducing surface affinity for protein attachment. Analysis of superhydrophobic siloxane and fluorosiloxane surfaces showed minimal indication of protein adsorption. This was confirmed by bacterial attachment studies using a Staphylococcus aureus strain known to bind specifically to Fg, which showed almost no attachment to the superhydrophobic coating after protein adsorption experiments. These results showed the superhydrophobic surfaces to exhibit antimicrobial properties and significantly reduce protein adsorption.

The particle size of polymethylhydrogen siloxane (PHMS) and hexamethyldisiloxane (HMDSO) droplets nebulised into an atmospheric pressure plasma was investigated using laser particle imaging. At low precursor flow rates the volatile HMDSO monomer is shown to be vapourised by the nebulisation process and no discrete aerosol droplets enter the plasma. This results in a standard gas phase PECVD process. As the precursor flow rate increases, liquid aerosol droplets are detected in the plasma. The diameter and number of droplets is largely unaffected by exposure to the plasma and intact droplets exit the plasma and impact directly on the substrate. The change in precursor flow is found to significantly alter the surface morphology of the deposited coatings with minimal impact upon the coating chemistry.

In this study surfaces exhibiting a nano-structured morphology have been creating in a single step deposition process using an atmospheric pressure plasma jet. Plasma polymerized coatings were deposited from a HMDSO monomer which was introduced into a He/N 2 plasma in the form of aerosolized droplets. By controlling the plasma discharge regime and monomer flow rate, the surface morphology was altered to create surfaces exhibiting an aligned fibrous morphology or a surface consisting of spherical agglomerates. Optical emission spectroscopy showed variation in photon emission energy depending on the He/N 2 ratio. Both thermal imaging and numerical simulations indicate that vaporization of the monomer occurs, which facilitates monomer polymerization in the gas phase and subsequent particulate nucleation. XPS analysis identified a higher amount of carbon bound siloxy species at regions where greater particulate formation was observed on the substrate. Cross-sectional SEM and He-ion imaging indicate that the formation of fibrous structures is associated with localized surface charging, which gives rise to selective agglomeration of semi-amorphous particulates which become aligned on the substrate. Modeling of droplet behavior in the plasma indicates that under conditions of higher monomer flow rate, saturation within the plasma occurs which facilitates nucleation of particulates, while experimental and modeling results indicate surface driven growth mechanisms are more likely to occur at lower precursor flow rates.

This work directly compares vapour and liquid aerosol states for the deposition of perfluorocarbon coatings using an atmospheric pressure, non‐thermal equilibrium plasma jet system. The objective of the study is to evaluate how the physical state of the precursor (gas or liquid), influences the fragmentation of the monomer molecules in the plasma and the subsequent coating properties. Specifically the effect of gas or liquid aerosol precursor feed on the ability to achieve a soft plasma polymerization (SPP) is assessed with a view to producing a coating that exhibits minimal fragmentation, while being well cross‐linked. The precursor (perfluoro‐1‐decene) was introduced into a helium plasma and coatings deposited at rates of up to 50 nm · min−1. The deposited coatings were examined using XPS, FTIR, contact angle and ellipsometric measurements. These indicated that a controlled polymerization reaction through the vinyl group of the monomer had taken place in the case of the gas deposited samples with only minor fragmentation of the functional perfluoro chain. Furthermore, a high level of cross‐linking was achieved and the perfluorocarbon coatings were stable to a toluene wash. In contrast, while coatings deposited using the liquid deposition technique showed good retention of monomer molecular structure, they exhibited poor stability when immersed in toluene. This is attributed to lower levels of cross‐linking of the liquid precursor in the plasma, compared with coatings deposited using the gaseous precursor technique. magnified image

Plasma polymerised PEO‐like films were deposited from tetraethylene glycol dimethyl ether (TEGDME) and diethylene glycol vinyl ether (DEGVE) using an atmospheric plasma jet. Films formed from TEGDME with COC retention >50% showed anti‐fouling properties, while DEGVE films with COC >60% did not. TEGDME films deposited at higher monomer flow rates had a lower density and more amorphous phases in the polymer network. Consequently, these films more readily facilitate penetration and binding of water to their surface in comparison to the denser DEGVE films. The difference in fouling properties identified through this comparative study has shown that % COC retention may not alone be an indication of non‐fouling behaviour. Other factors such as polymer network structure may also play a crucial role in the prevention of surface fouling.