Release Coatings Research Articles

Anti-Biofilm Performance of Three Natural Products against Initial Bacterial Attachment

Marine bacteria contribute significantly towards the fouling consortium, both directly (modern foul release coatings fail to prevent “slime” attachment) and indirectly (biofilms often excrete chemical cues that attract macrofouling settlement). This study assessed the natural product anti-biofilm performance of an extract of the seaweed, Chondrus crispus, and two isolated compounds from terrestrial sources, (+)-usnic acid and juglone, against two marine biofilm forming bacteria, Cobetia marina and Marinobacter hydrocarbonoclasticus. Bioassays were developed using quantitative imaging and fluorescent labelling to test the natural products over a range of concentrations against initial bacterial attachment. All natural products affected bacterial attachment; however, juglone demonstrated the best anti-biofilm performance against both bacterial species at a concentration range between 5–20 ppm. In addition, for the first time, a dose-dependent inhibition (hormetic) response was observed for natural products against marine biofilm forming bacteria.

Investigation of Silicone Oil Leaching in PDMS Fouling Release Coating by Confocal Laser Scanning Microscope

The silicone oil leachate in fouling release coatings has very important effect on inhabitting marine organism on ships hull and releasing of biofouling from it. For observing and testifying the leaching phenomenon of silicone oil in PMDS fouling release coating, the coating was designed and prepared consisting of 107 silicone gum, dimethyl silicone oil, tetraethylorthosilicate as crosslinked curing agent, multi-walled carbon nanotube as filler, dibutyltin dilaurate as catalyst. The confocal laser scanning microscopy (CLSM) LEXT OLS4000 was used to observe the morphology of the coating and silicone oil leachate. The results indicate that the dimethyl silicone oil can stably exist and distribute uniformly in PDMS coating. Regardless of between the coating and air or and seawater, silicone oil can leach on the interface. Silicone oil not only can leache faster on the interface between seawater and the coating than that between air and it, but also can easily form the continuous oil film because of the gravity of seawater.

Waterborne long alkyl chain branched copolymers used as release coatings synthesized by mini-emulsion polymerization

Waterborne long alkyl chain branched copolymers with excellent release performance for pressure-sensitive adhesive were synthesized via mini-emulsion polymerization. Dynamic light scattering, video-based contact angle measurement and electronic stripping testing were employed to characterize and analyze the structure and release properties of the resultant copolymers. The results showed that ultrasonic amplitude of 50% and ultrasonic duration of 15min were the optimum conditions for the preparation of a mini-emulsion containing long alkyl chain monomer stearyl methacrylate (SMA). The ultimate conversion of monomers declined with increasing SMA, while the hydrophobicity of the copolymers increased. Release strength testing illustrated that the optimum amount of SMA for release coating was 60%, taking the cost factor into account, and better release performance could be obtained by increasing the coating thickness.

Effects of molecular weight on permeability and microstructure of mixed ethyl-hydroxypropyl-cellulose films

Films of ethyl cellulose (EC) and water-soluble hydroxypropyl cellulose (HPC) can be used for extended release coatings in oral formulations. The permeability and microstructure of free EC/HPC films with 30% w/w HPC were studied to investigate effects of EC molecular weight. Phase separation during film spraying and subsequent HPC leaching after immersion in aqueous media cause pore formation in such films. It was found that sprayed films were porous throughout the bulk of the films after water immersion. The molecular weight affected HPC leaching, pore morphology and film permeability; increasing the molecular weight resulted in decreasing permeability. A model to distinguish the major factors contributing to diffusion retardation in porous films showed that the trend in permeability was determined predominantly by factors associated with the geometry and arrangement of pores, independent of the diffusing species. The film with the highest molecular weight did, however, show an additional contribution from pore wall/permeant interactions. In addition, rapid drying and increasing molecular weight resulted in smaller pores, which suggest that phase separation kinetics affects the final microstructure of EC/HPC films. Thus, the molecular weight influences the microstructural features of pores, which are crucial for mass transport in EC/HPC films.

Wettability and Surface Tension of Amphiphilic Polymer Films: Time‐Dependent Measurements of the Most Stable Contact Angle

AbstractThe wettability of new amphiphilic block copolymer films is studied by measuring different types of water contact angles (static, receding, advancing, and most stable). The most stable contact angles are used to calculate the surface tensions of the films following the recently developed Marmur–Valal correlation. Most stable contact angles of water in an air‐in‐water system are also measured to study the changes in surface tension over relatively long periods of immersion time. The new approach yields surface tension values that are higher than those calculated by previous methods. The results suggest that reconstruction of the surface takes place at short time scale and continues to occur at long time scale. The responsive character of the polymer films can have implications for their use as biofouling release coatings.

Fouling Release Coatings: A Nontoxic Alternative to Biocidal Antifouling Coatings

Fouling Release Coatings: A Nontoxic Alternative to Biocidal Antifouling Coatings

UV curing of epoxy functional hybrid silicones

AbstractSeveral epoxy difunctional hybrid alkylene‐silicone telomers with different silicone characters and organic spacers (linkers) were prepared via the platinum‐catalyzed polyhydrosilylation of α,ω‐dihydrosiloxanes and α,ω‐dienes. Thereafter, the resulting SiH‐terminated prepolymers were terminally functionalized with 4‐vinyl‐1,2‐epoxycyclohexane or allyl glycidyl ether. In the presence of a lipophilic cationic photoinitiator, the terminally epoxy‐functionalized hybrid alkylene–silicone telomers were photopolymerized to give crosslinked, soft, elastomeric, and transparent films. The progress of the photoinitiated cationic ring‐opening epoxide polymerizations was monitored using optical pyrometry. Potential applications for these novel photocurable epoxy‐functional telomers are as modifiers for UV curable coatings, printing inks, adhesives, and release coatings. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Use of fluoropolymer permanent release coatings for molded polyurethane foam production

The problem of adhesion of polyurethane foams to fluoropolymer permanent release mold coatings was studied. Two coatings, based on polytetrafluoroethylene (PTFE) and perfluoroalkoxy polymer (PFA) aqueous dispersions, respectively, were applied on aluminum plates, and the foam release performance evaluated. The PTFE coating displayed gradual loss of antiadhesion properties with consecutive exposure to the reactive mixture, which was associated with isocyanate surface penetration. Penetrant mass uptake experiments, performed on free films, indicated that PTFE retains about 10 times more isocyanate than PFA, probably because of its porous surface morphology. A synergistic effect was found by applying a very small quantity of a waterborne release agent on the PTFE coating, before every foam molding cycle. The release agent formed a protective barrier that minimized contact of the coating with the reactive mixture, allowing for stable and robust foam release performance. The problem of polyurea build-up, associated with the use of aqueous release agents, was not observed because of the small amounts of compound used.

Investigation of adhesion phenomena in thermoplastic polyurethane injection molding process

Adhesion is a serious problem when ejecting products from mold cavities in the injection molding process. This study developed a mechanism for measuring adhesion force in injection molding process. The apparatus measured and quantified adhesion force and engineers could use the measurements to understand the effectiveness of mold release agent and different adhesion release coatings. Three different surface roughness conditions (Ra = 0.01, 0.08, and 1.20 μm) without surface coating were compared and the results showed that the smallest adhesion force would be obtained when Ra = 0.08 μm. With Ra = 0.08 μm and 0.01 μm, it was found that single-layer CrN (chromium nitride) coating and modified CrN coating were effective in alleviating adhesion force whereas multi-layer CrN coating was not effective. In addition, the adhesion force was proportional to the ejection speed, melting temperature, and cooling time. Because thermoplastic polyurethane (TPU) behaves like a rubber-like material and is thus different from other stiff resin after cooling, the release of adhesion of TPU is time-dependent. Comparing the peak and integrated impulse values of the measured curve in continuous experiment, it was found that these two results were in good agreement with each other. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Ironing Out Alkene Hydrosilylation

Chemists could soon have a cheaper way to make silicone-based surfactants, fluids, release coatings, and pressure-sensitive adhesives, thanks to an iron catalyst that spurs alkene hydrosilylation r...

Turbulent boundary layer measurements over flat surfaces coated by nanostructured marine antifoulings

Whilst recent developments of nanotechnology are being exploited by chemists and marine biologists to understand how the completely environmentally friendly foul release coatings can control marine biofouling and how they can be developed further, the understanding of the hydrodynamic performances of these new generation coatings is being overlooked. This paper aims to investigate the relative boundary layer, roughness and drag characteristics of some novel nanostructured coatings, which were developed through a multi-European and multi-disciplined collaborative research project AMBIO (2010), within the framework of turbulent flows over rough surfaces. Zero-pressure-gradient, turbulent boundary layer flow measurements were conducted over flat surfaces coated with several newly developed nanostructured antifouling paints, along with some classic reference surfaces and a state-of-the-art commercial coating, in the Emerson Cavitation Tunnel (ECT) of Newcastle University. A large flat plane test bed that included interchangeable flat test sections was used for the experiments. The boundary layer data were collected with the aid of a two-dimensional DANTEC Laser Doppler Velocimetry (LDV) system. These measurements provided the main hydrodynamic properties of the newly developed nanostructured coatings including local skin friction coefficients, roughness functions and Reynolds stresses. The tests and subsequent analysis indicated the exceptionally good frictional properties of all coatings tested, in particular, the drag benefit of some new nanostructured coatings in the Reynolds number range investigated. The rapidly decreasing roughness function trends of AKZO19 and AKZO20 as the \( k_{s}^{ + } \) increases were remarkable along with the dissimilar roughness function character of all tested coatings to the well-known correlation curves warranting further research at higher Reynolds numbers. The wall similarity concept for the Reynolds stresses was only validated for the transitionally rough surfaces from \( (y + \varepsilon)^{ + } \approx 100 \) up to the end of the boundary layer.

Decreasing Bacterial Colonization of External Fixation Pins Through Nitric Oxide Release Coatings

Bacterial infection of the pin tract represents the most common complication associated with external fixation. This study was designed to evaluate the antibacterial activity of nitric oxide (NO)-releasing xerogel films applied to commercially pure titanium pins in a rat model. Pins were coated with xerogel solution through a dip-coating procedure. Half of the xerogel-coated implant pins were modified into NO donors and served as the NO-releasing group, whereas the remaining pins were left unmodified to serve as non-NO-releasing xerogel-coated controls. Acid-etched pins served as uncoated controls. Animal selection was randomized and every rat had one pin from each of the three groups randomly allocated to the third, fourth, or fifth tail vertebrae. Quantification of bacterial infection was performed 48 days postoperatively and the tissue-implant interface was inspected for clinical signs of infection on Days 14 and 28 postimplantation. Pin tract bacterial colony counts of the NO-releasing group (170,000 ± 181,000) were significantly lower than both the xerogel-coated group (677,000 ± 675,000) and the control group (1,181,000 ± 2,717,000) 48 days postoperatively (P < 0.05). No significant difference in colony counts was observed between the xerogel-coated group and the control group. The NO-releasing group also had significantly fewer clinical signs of infection than both the coated and the control groups on postoperative Day 28 (P < 0.05). The application of NO-releasing xerogel coatings can inhibit bacterial colonization of external fixation pins both during the initial postsurgical period and up to 48 days postimplantation.

Fabrication of nitric oxide-releasing polyurethane glucose sensor membranes

Despite clear evidence that polymeric nitric oxide (NO) release coatings reduce the foreign body response (FBR) and may thus improve the analytical performance of in vivo continuous glucose monitoring devices when used as sensor membranes, the compatibility of the NO release chemistry with that required for enzymatic glucose sensing remains unclear. Herein, we describe the fabrication and characterization of NO-releasing polyurethane sensor membranes using NO donor-modified silica vehicles embedded within the polymer. In addition to demonstrating tunable NO release as a function of the NO donor silica scaffold and polymer compositions and concentrations, we describe the impact of the NO release vehicle and its release kinetics on glucose sensor performance.

Design of multi-drug release coatings targeting infection and inflammation

Although infection and inflammation commonly coexist, there is a paucity of appropriate methods for concurrent localized delivery of antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) at appropriate concentrations and timescales. The commonly used therapeutic approach of systemic delivery of antibiotics and NSAIDs is associated with many complications, including rises in antibiotic resistant bacteria and severe gastrointestinal problems. As a potential solution, in this work we have assembled polymer multilayers to concurrently release therapeutic concentrations of an antibiotic, vancomycin, and an NSAID, diclofenac. Prior to film assembly, interactions between film components were thoroughly examined. Taking advantage of novel interactions found to exist between film components, several optimal film architectures were engineered using both dip and spray layer-by-layer assembly. A wide range of drug release profiles were obtained, with vancomycin delivery lasting from 4 hours to 2.3 days at final loadings of 13 to 30 μg/cm 2, while diclofenac released over 1.7 to 14 days at final loadings of 10 to 36 μg/cm 2. These drug release profiles have the potential to address a range of infection and inflammation requirements, from short term infection and inflammation eradication for trauma relief to infection prevention and long term inflammation mitigation from biomedical implants. Film-released vancomycin and diclofenac were found to be highly active against their respective targets in vitro, Staphylococcus aureus and cyclooxygenase. These films were also successfully applied to several medically relevant substrates, including intraocular lenses, bandages, and sutures, demonstrating potential for use as medical device coatings.

Lignin based controlled release coatings

Urea is a commonly used fertilizer. Due to its high water-solubility, misuse easily leads to excess nitrogen levels in the soil. The aim of this research was to develop an economically feasible and biodegradable slow-release coating for urea. For this purpose, lignin was selected as coating material. From four commercially available lignins, two lignosulfonates (Wafex P and Borresperce), a softwood kraft (Indulin AT) and soda flax lignin (Bioplast), the latter showed the best potential with respect to film forming properties. Bioplast dispersions up to a dry matter content of 50% are processable. However, high losses during processing resulted in thin coating layers on the urea granules. To reduce urea release, hydrophobic compounds and crosslinkers were added to the Bioplast dispersions. Addition of alkenyl succinic anhydride (ASA) significantly decreased the release of urea in water. However, complete release of urea still occurred within one hour, which can be explained by a low reactivity of the selected compounds towards lignin, too low percentages of applied coating or negative effects of the selected compounds on the film forming process. In addition, urea partly dissolves in the aqueous lignin dispersions due to its high water-solubility. This causes incorporation of urea in the lignin layer, which results in coatings with a low water resistance. This was improved by application of an inner coating layer with high dry matter content. In conclusion, lignin shows high potential as coating material. For industrial application, more insight in the film forming properties is desired.

Technology evaluation: Kollicoat IR

Introduction: Developments in industrial pharmacy are often linked to the discovery of pharmaceutical excipients. Although recently introduced as a material for immediate release coatings, Kollicoat IR already has other applications.Areas covered: In this review, the different properties and pharmaceutical applications of Kollicoat IR as an excipient are discussed. In the first part, the chemical structure and the physicochemical characteristics are examined. The second part is a presentation of the available Kollicoat IR products followed by a brief overview of the preclinical studies completed for its use as an instant release coating material.Expert opinion: Although the polymer was intended as an immediate release coating material for tablets, grafting PEG with polyvinyl alcohol to form this polymer provides physicochemical properties that lead to ever-broadening applications. Understanding its properties can lead to the development of a new use for Kollicoat IR. The addition of Kollicoat IR to an ethylcellulose or polyvinyl acetate tablet coat was successful at modifying the drug release rate. Designing a successful controlled release coat simply requires acknowledgment of the drug release mechanism from the mixture of polymers that includes Kollicoat IR. Moreover, the interaction between Kollicoat IR and poorly soluble drugs produces fast-dissolving solid dispersions prepared using hot stage extrusion, spray drying, or freeze drying.

Decreasing Bacterial Colonization of External Fixation Pins Through Nitric Oxide Release Coatings

Decreasing Bacterial Colonization of External Fixation Pins Through Nitric Oxide Release Coatings

A novel electrostatic dry powder coating process for pharmaceutical dosage forms: Immediate release coatings for tablets

An electrostatic dry powder coating process for pharmaceutical solid dosage forms was developed for the first time by electrostatic dry powder coating in a pan coater system. Two immediate release coating compositions with Opadry® AMB and Eudragit® EPO were successfully applied using this process. A liquid plasticizer was sprayed onto the surface of the tablet cores to increase the conductivity of tablet cores to enhance particle deposition, electrical resistivity reduced from greater than 1 × 10 13 Ω m to less than 1 × 10 9 Ω m, and to lower the glass transition temperature ( T g) of the coating polymer for film forming in the pan coater. The application of liquid plasticizer was followed by spraying charged coating particles using an electrostatic charging gun to enhance the uniform deposition on tablet surface. The coating particles were coalesced into a thin film by curing at an acceptable processing temperature as formation was confirmed by SEM micrographs. The results also show that the optimized dry powder coating process produces tablets with smooth surface, good coating uniformity and release profile that are comparable to that of the tablet cores. The data also suggest that this novel electrostatic dry powder coating technique is an alternative to aqueous- or solvent-based coating process for pharmaceutical products.

Controlled release nanoparticle-embedded coatings reduce the tissue reaction to neuroprostheses

Controlled release coatings were developed for neuroprostheses with the aim of combating the tissue reaction following implantation in the brain. The coatings consist of poly(propylene sulfide) drug-eluting nanoparticles embedded in a poly(ethylene oxide) matrix. The nanoparticles are loaded with dexamethasone, an anti-inflammatory drug known to have an effect on the cells activated during the damage caused by implantation. The nanoparticles are not affected by the coating process and the drug remains bioactive after it is released. The coating was applied to microfabricated cortical neuroprostheses consisting of platinum and polyimide. Coated drug-eluting devices were implanted in the cortex of rats. After implantation the matrix dissolves, exposing the electrode surfaces, while the nanoparticles remain in the vicinity of the tissue–implant interface. Using electrical impedance spectroscopy and comparative histology, a long-term decrease in the tissue response in comparison to control devices was observed. These coatings can therefore be used to increase the reliability and long-term efficacy of neuroprostheses.

Solventless visible light-curable coating: II. Drug release, mechanical strength and photostability

Solventless photocurable film coating was used to obtain modified release coatings. Different pore-forming agents were used to achieve immediate and sustained release of a blue dye contained in the coated pellets (non-pareil beads). A super-disintegrant, sodium starch glycolate, was used to obtain immediate release. When incorporated in the coating, this pore-former swelled and yielded large pores that demonstrated quick release of the marker dye while leaving behind the scaffold provided by the photocured polymer. Simple pore-formers (lactose and sodium chloride) dissolved away without swelling and provided a more sustained release profile. Release can be modified with the choice of material, number of layers and thickness of the coating. When release of sodium chloride and release of marker dye were simultaneously monitored, it was observed that at least 40–50% of the sodium chloride that was incorporated in the coating released before the dye was released through the coating showing that pore-formation preceded the release of the marker dye. The coupling factor between dye release and pore-formation was found to be dependent on the ratio of amount of solid pore-forming agent and volume of liquid monomer (S/L) of the coating. Also, studies demonstrate that the coating is photostable and can withstand handling stress.