PDMS-based antimicrobial surfaces for healthcare applications

This thesis describes two types of approaches for reducing the incidence of hospital-acquired infections (HAIs), which are chemical approaches that inactivate bacteria that adhere to the surface i.e. bactericidal activity and physical approaches that inhibit initial bacterial attachment to the surface i.e. anti-biofouling activity. Specifically, the antimicrobial polydimethylsiloxane (PDMS)-based systems detailed in this thesis are: (i) photosensitizer, crystal violet (CV),-coated PDMS for both medical device and hospital touch surface applications, (ii) crystal violet-coated, zinc oxide nanoparticle-encapsulated PDMS for hospital touch surface applications, (iii) superhydrophobic antibacterial copper coated PDMS films via aerosol assisted chemical vapour deposition (AACVD) for hospital touch surface applications and (iv) slippery copper-coated PDMS films to prevent biofilm formation on medical devices. The materials were characterized using techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis absorbance spectroscopy, water-contact angle measurement and microbiology tests. Functional testing indicated that CV-coated samples were suitable for targeted applications and showed potent light-activated antimicrobial activity when tested against model Gram-positive bacteria, Staphylococcus aureus, and Gram-negative bacteria, Escherichia coli, associated with hospital-acquired infections, with > 4 log reduction in viable bacterial numbers observed. On the other hand, CVD modified samples demonstrated highly significant antibacterial activity against both bacteria (> 4 log reduction in bacterial numbers) under dark conditions. Moreover, they resulted in a significant reduction in bacterial cell adhesion compared to PDMS and glass controls. However, superhydrophobic materials accumulated biofilm of both bacteria over a 2-day period while slippery materials significantly prevented biofilm formation over the same period. The novel and highly efficacious antibacterial materials reported in this thesis show a very strong potential to be utilized in hospital environments for reducing the incidence of HAIs

Bioinspired Design of Wetting and Anti-Wetting Surfaces via Thiol-ene Photopolymerization

Surface wettability is known to have a profound influence in both academic study and industrial application of materials. Superhydrophobic surfaces, with a static contact angle higher than 150° and a contact angle hysteresis lower than 10°, have received continued attention for their broad applications, such as self-cleaning, antifogging and frosting, and drag reduction. The continuous development of materials and approaches that used to create superhydrophobic surfaces has led to further exploration of coatings with other desirable properties such as superamphiphobicity, mechanical robustness and thermal stability. In this work, coatings with super wetting and super anti-wetting properties were designed and fabricated by tailoring the chemical composition and the morphology of the surface in an effort to expand the application and to improve the mechanical property of the coatings. In the first study, a superamphiphobic coating was prepared by spray deposition and followed up UV-polymerization of a hybrid organic-inorganic thiol-ene precursor. The combination of dual-scale roughness and low surface energy materials led to surfaces with strong water/ oil repellency and self-cleaning properties. In the second study, a superhydrophilic and superoleophobic membrane for oil/water separation applications was developed. The textured membrane morphology enhanced the hydrophilic and oleophobic properties of the surface. The efficiency of the superhydrophilic/superoleophobic membrane on oil/water separation was demonstrated by emulsion and dye contained emulsion separation studies. In the third study, a superhydrophobic surface was prepared with porogen leaching approach in an effort to reduce the loading level of NPs. The microphase separation and porogen leaching process resulted in microscale roughness. NPs migration from bulk to interphase led to the formation of nanoscale roughness. The combination of micro- and nano-scale feature provides the surface with superhydrophobicity with 50 wt.% reduced NPs loading level

Biomimetic lubricant-infused titania nanoparticle surfaces via layer-by-layer deposition to control biofouling

Lubricant-infused surfaces have attracted a lot of attention in antifouling applications. Previously, lubricant-infused surfaces fabricated by a layer-by-layer process involved two or more polyelectrolytes and needed post-treatments to generate pores. Here, the paper proposes a layer-by-layer sol-gel process to prepare a lubricant-infused surface. This process only involves a single material and without any post-treatment. The nanostructured titania layers were layer-by-layer assembled onto 316L stainless steel substrates by immersing the substrates into a titanium (IV) butoxide ethanol solution. The titania layers were subsequently surface-functionalized by fluorinated silanes and infiltrated with fluorinated lubricant to form lubricant-infused nanoparticle surfaces. The physicochemical properties of the lubricant-infused nanoparticle surfaces dominated the antifouling performance. These results give some insight into the construction of lubricant-infused nanoparticle surfaces with desirable liquid repellency and antifouling properties via a layer-by-layer sol-gel process

Recent Developments and Practical Feasibility of Polymer-Based Antifouling Coatings

While nature has optimized its antifouling strategies over millions of years, synthetic antifouling coatings have not yet reached technological maturity. For an antifouling coating to become technically feasible, it should fulfill many requirements: high effectiveness, long-term stability, durability, ecofriendliness, large-scale applicability, and more. It is therefore not surprising that the search for the perfect antifouling coating has been going on for decades. With the discovery of metal-based antifouling paints in the 1970s, fouling was thought to be a problem of the past, yet its untargeted toxicity led to serious ecological concern, and its use became prohibited. As a response, research shifted focus toward a biocompatible alternative: polymer-based antifouling coatings. This has resulted in numerous advanced and innovative antifouling strategies, including fouling-resistant, fouling-release, and fouling-degrading coatings. Here, these novel and exciting discoveries are highlighted while simultaneously assessing their antifouling performance and practical feasibility

Recent Developments and Practical Feasibility of Polymer-Based Antifouling Coatings

While nature has optimized its antifouling strategies over millions of years, synthetic antifouling coatings have not yet reached technological maturity. For an antifouling coating to become technically feasible, it should fulfill many requirements: high effectiveness, long-term stability, durability, ecofriendliness, large-scale applicability, and more. It is therefore not surprising that the search for the perfect antifouling coating has been going on for decades. With the discovery of metal-based antifouling paints in the 1970s, fouling was thought to be a problem of the past, yet its untargeted toxicity led to serious ecological concern, and its use became prohibited. As a response, research shifted focus toward a biocompatible alternative: polymer-based antifouling coatings. This has resulted in numerous advanced and innovative antifouling strategies, including fouling-resistant, fouling-release, and fouling-degrading coatings. Here, these novel and exciting discoveries are highlighted while simultaneously assessing their antifouling performance and practical feasibility

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field

Effects of Nanoparticles on Friction Reduction in Fluid Flow

The interaction between a flowing fluid and the solid surfaces over which it flows is fundamental to determining the resistance to flow offered by the solid. This interaction is commonly described as friction or drag in fluid mechanics and is the basis for the no-slip boundary condition in fluid dynamics. The slip behaviour of the fluid near the solid boundary, commonly quantified as the "slip length," is often used to quantify friction reduction. Nanoparticles (NPs) have been proposed to influence the fluid flow in reservoirs through several mechanisms, including modifying the slip behaviour of a fluid. This thesis investigates whether coating the surface of channels in glass micromodels with silica NPs affects the slip length of oil flow and water flow. Silica NPs with different shapes, surface coating and charges were tested to understand how the nature of these nanomaterials can affect friction. In-line coating, immersion, and spin coating were evaluated to determine how effectively each method coated the surface of the channel with NPs. Particle deposition was evaluated by water droplet contact angle measurement, scanning electron microscope (SEM) imaging, and elemental analysis. A uniform, crack-free, and stable distribution of NPs on the surface was observed using spin coating. Hydrophilic silica NP coating affected water differently from oil, causing a reduction in friction while oil flooding but an increase in friction for water. On the other hand, partially hydrophobic silica NPs reduced the friction for both water and oil flooding. The fundamental understanding of how NPs can be used as friction reducers for oil production will open new opportunities for designing low-energy and more sustainable oil production methods

Improving tribomechanical properties of polymeric nanocomposite coatings

Low friction, high wear resistance and strong adhesion in polymeric coatings employed in a variety of industrial and domestic processes such as in ball bearings, water repellent surfaces, antiadhesive coatings, and anticorrosion systems are of significant interest for energy saving and durability purposes. Even small increases in friction can have implications on energy efficiency, life time expectancy and performance of such coatings

Wear Resistant Polydopamine/PTFE Nanoparticle Composite Coating for Dry Lubrication Applications

This dissertation presents an investigation into the effect of nanoparticle fillers and a polydopamine adhesive primer on the tribological performance of thin PTFE films. The principal objective of this investigation was to reduce wear in PTFE films, an issue which precludes the use of PTFE films in tribological applications requiring high durability. The friction and wear of the composite films were evaluated using a ball-on-flat configuration in linear reciprocating motion. It was found that the use of a polydopamine adhesive primer reduces the wear of PTFE films more than 600 times. X-ray photoelectron spectroscopy (XPS) results show that a tenacious layer of PTFE remains adhered to the polydopamine primer, which enables the durability of the polydopamine/PTFE film. Furthermore, the combination of a polydopamine primer, Cu nanoparticle fillers in the PTFE film, and optimal fabrication processes provided a collective effect that increased the wear life of PTFE films by more than 940 times. Because of the relatively low thickness of the film, it shows great potential for use in applications where durable, thin films are desirable

Surface Engineering for Phase Change Heat Transfer: A Review

Among numerous challenges to meet the rising global energy demand in a sustainable manner, improving phase change heat transfer has been at the forefront of engineering research for decades. The high heat transfer rates associated with phase change heat transfer are essential to energy and industry applications; but phase change is also inherently associated with poor thermodynamic efficiencies at low heat flux, and violent instabilities at high heat flux. Engineers have tried since the 1930's to fabricate solid surfaces that improve phase change heat transfer. The development of micro and nanotechnologies has made feasible the high-resolution control of surface texture and chemistry over length scales ranging from molecular levels to centimeters. This paper reviews the fabrication techniques available for metallic and silicon-based surfaces, considering sintered and polymeric coatings. The influence of such surfaces in multiphase processes of high practical interest, e.g., boiling, condensation, freezing, and the associated physical phenomena are reviewed. The case is made that while engineers are in principle able to manufacture surfaces with optimum nucleation or thermofluid transport characteristics, more theoretical and experimental efforts are needed to guide the design and cost-effective fabrication of surfaces that not only satisfy the existing technological needs, but also catalyze new discoveries