Denis P. Dowling

Bio: Denis P. Dowling is an academic researcher from University College Dublin. The author has contributed to research in topics: Atmospheric-pressure plasma & Coating. The author has an hindex of 36, co-authored 234 publications receiving 4936 citations. Previous affiliations of Denis P. Dowling include National University of Ireland & Lucideon.

Fabrication of Continuous Carbon, Glass and Kevlar fibre reinforced polymer composites using Additive Manufacturing

Abstract: This study evaluates the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. The fibre reinforced nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength per fibre volume. Its tensile strength values were up to 6.3 times higher than those obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 22.5%, with higher fibre contents (up to 33%), yielding only minor increases in strength.

Effect of Surface Wettability and Topography on the Adhesion of Osteosarcoma Cells on Plasma-modified Polystyrene

Abstract: Biomaterials interact with the biological environment at their surface, making accurate biophysical characterization of the surface crucially important for understanding subsequent biological effects. In this study, the surface of polystyrene (PS) was systematically altered in order to determine the effect of plasma treatment and surface roughness on cell adhesion and spreading. Surfaces with water contact angle from hydrophilic (12°) to superhydrophobic (155°) were obtained through a combination of modifying surface roughness (R (a)), the deposition of siloxane coatings and the fluorination of the PS surface. R (a) values in the range of 19-2365 nm were obtained by grinding the PS surface. The nanometer-thick siloxane coatings were deposited using an atmospheric pressure plasma system, while the fluorination of the PS was carried out using a low-pressure radio frequency (RF) plasma. The siloxane coatings were obtained using a liquid poly(dimethylsiloxane) precursor that was nebulized into helium or helium/oxygen plasmas. Water contact angles in the range of 12-122° were obtained with these coatings. Cell adhesion studies were carried out using human MG63 osteosarcoma cells. It was observed that higher polymer surface roughness enhanced cell adhesion, but had a negative effect on cell spreading. Optimum cell adhesion was observed at ∼64° for the siloxane coatings, with a decrease in adhesion observed for the more hydrophilic and hydrophobic coatings. This decrease in cell adhesion with an increase in hydrophobicity was also observed for the fluorinated PS surfaces with water contact angles in the range of 110-155°.

Anti-bacterial silver coatings exhibiting enhanced activity through the addition of platinum

Abstract: Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn+. This study evaluates the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series platinum is more active than silver and therefore Pt enhances Ag+ ion formation through galvanic action. In order to evaluate this, potential step (chronoamperometric) experiments were performed on silver/platinum alloys containing 0.5 and 3.0% Pt. The resulting current–time curves demonstrated that Ag+ formation increased with platinum addition by up to 100%. A magnetron sputtering target was fabricated consisting of 1% Pt in a Ag matrix. This was used to sputter Pt/Ag coatings with thicknesses in the range 5–12 nm onto silicone and polyurethane substrates. The bacterial adhesion and bactericidal effects of the coated polymers was assessed using Straphylococcus epidermidis and the cytotoxicity using fibroblast cells. The addition of 1% Pt was found to significantly enhance the anti-bacterial effectiveness of the Ag coatings. Up to a 2 log reduction in bacterial adhesion was achieved for 5 nm thick Ag/1% Pt coatings on silicone, which did not exhibit cytotoxicity.

Evaluation of Protein Adsorption on Atmospheric Plasma Deposited Coatings Exhibiting Superhydrophilic to Superhydrophobic Properties

Abstract: 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 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.

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).