Assessment of molecularly imprinted polymers as phosphate sorbents.

Phosphorus (P) is a non-renewable natural resource which is used extensively in agriculture as a fertilizer. Phosphate (PO43-) rocks are mined to meet growing agricultural demands induced by rising global populations. Much of the P used in agricultural fields finds its way into surface waters where it permanently resides, leading to devastating effects on the aquatic ecosystem through eutrophication of the waterbodies. This research was aimed at developing a sorbent that can engender a P reuse cycle by utilizing eutrophic surface waters as viable P sources (mines). The goal was to develop a sorbent which can selectively recover low concentration (≤100 P µg L-1) typical of eutrophic waters. Molecularly imprinted polymers (MIPs) were identified as a potential technology for accomplishing this goal. Three MIPs were screened for viability by assessing their sorption capacities. After the initial screening, one MIP was selected for further studies. The selected MIP was found to have partial PO43- selectivity and tunable P sorption capacity. Adjusting the template:monomer ratio resulted in an increase in P sorption capacity from ∼11 to ∼28 mg PO43--P g-1, making this MIP competitive with existing technologies. The MIP was characterized to understand the polymer chemistry and mechanisms of P-removal. The possible mechanisms of aqueous P removal by the MIP were identified as selective chemical binding to the imprinted recognition sites and electrostatic attraction.

Polymer Coating Materials and Their Fouling Release Activity: A Cheminformatics Approach to Predict Properties.

A novel cheminformatics-based approach has been employed to investigate a set of polymer coating materials designed to mitigate the accumulation of marine biofouling on surfaces immersed in the sea. Specifically, a set of 27 nontoxic, amphiphilic polysiloxane-based polymer coatings was synthesized using a combinatorial, high-throughput approach and characterized for fouling-release (FR) activity toward a number of relevant marine fouling organisms, including bacteria, microalgae, and adult barnacles. In order to model these complex systems adequately, a new computational technique was used in which all investigated polymer-based coating materials were considered as mixture systems comprising several compositional variables at a range of concentrations. By applying a combination of methodologies for mixture systems and a quantitative structure-activity relationship approach (QSAR), seven unique QSAR models were developed that were able to successfully predict the desired FR properties. Furthermore, the developed models identified several significant descriptors responsible for FR activity of investigated polymer-based coating materials, with correlation coefficients ranging from rtest2 = 0.63 to 0.94. The computational models derived from this study may serve as a powerful set of tools to predict optimal combinations of source components to produce amphiphilic polysiloxane-based coating systems with effective, broad-spectrum FR properties.

Combinatorial materials research applied to the development of new surface coatings XVI: fouling-release properties of amphiphilic polysiloxane coatings.

High-throughput methods were used to prepare and characterize the fouling-release (FR) properties of an array of amphiphilic polysiloxane-based coatings possessing systematic variations in composition. The coatings were derived from a silanol-terminated polydimethylsiloxane, a silanol-terminated polytrifluorpropylmethylsiloxane (CF3-PDMS), 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane (TMS-PEG), methyltriacetoxysilane and hexamethyldisilazane-treated fumed silica. The variables investigated were the concentration of TMS-PEG and the concentration of CF3-PDMS. In general, it was found that the TMS-PEG and the CF3-PDMS had a synergist effect on FR properties with these properties being enhanced by combining both compounds into the coating formulations. In addition, reattached adult barnacles removed from coatings possessing both TMS-PEG and relatively high levels of CF3-PDMS displayed atypical base-plate morphologies. The majority of the barnacles removed from these coatings exhibited a cupped or domed base-plate as compared to the flat base-plate observed for the control coating that did not contain TMS-PEG or CF3-PDMS. Coating surface analysis using water contact angle measurements indicated that the presence of CF3-PDMS facilitated migration of TMS-PEG to the coating/air interface during the film formation/curing process. In general, coatings containing both TMS-PEG and relatively high levels of CF3-PDMS possessed excellent FR properties.

Surface structures of PDMS incorporated with quaternary ammonium salts designed for antibiofouling and fouling release applications.

Poly(dimethylsiloxane) (PDMS) materials have been extensively shown to function as excellent fouling-release (FR) coatings in the marine environment. The incorporation of biocide moieties, such as quaternary ammonium salts (QAS), can impart additional antibiofouling properties to PDMS-based FR coating systems. In this study, the molecular surface structures of two different types of QAS-incorporated PDMS systems were investigated in different chemical environments using sum frequency generation vibrational spectroscopy (SFG). Specifically, a series of PDMS coatings containing either a QAS with a single ammonium salt group per molecule or a quaternary ammonium-functionalized polyhedral oligomeric silsesquioxane (Q-POSS) were measured with SFG in air, water, and artificial seawater (ASW) to investigate the relationships between the interfacial surface structures of these materials and their antifouling properties. Although previous studies have shown that the above-mentioned materials are promising contact-active antifouling coatings, slight variations of the QAS structure can lead to substantial differences in the antifouling performance. Indeed, the SFG results presented here indicated that the surface structures of these materials depend on several factors, such as the extent of quaternization, the molecular weight of the PDMS component, and the functional groups of the QAS used for incorporation into the PDMS matrix. It was concluded that in aqueous environments a lower extent of Q-POSS quaternization and the use of ethoxy (instead of methoxy) functional groups for QAS incorporation facilitated the extension of the alkyl chains away from the nitrogen atom of the QAS on the surface. The SFG results correlated well with the antifouling activity studies that indicated that the coatings exhibiting a lower concentration of longer alkyl chains protruding out of the surface can neutralize microorganisms more effectively, ultimately leading to better antifouling performance. Furthermore, the results of this study provide additional evidence that incorporated QAS exert their antimicrobial activity through a two-step interaction. The first step is the adsorption of the bacteria on the surface as a result of the electrostatic attraction between the negatively charged microorganisms and the positively charged QAS nitrogen atoms on the surface. The second step is the disruption of the cell membranes by the penetration of the QAS long, extended alkyl chains.

Iron nanoparticles coated with amphiphilic polysiloxane graft copolymers: dispersibility and contaminant treatability.

Amphiphilic polysiloxane graft copolymers (APGCs) were used as a delivery vehicle for nanoscale zerovalent iron (NZVI). The APGCs were designed to enable adsorption onto NZVI surfaces via carboxylic acid anchoring groups and polyethylene glycol (PEG) grafts were used to provide dispersibility in water. Degradation studies were conducted with trichloroethylene (TCE) as the model contaminant. TCE degradation rate with APGC-coated NZVI (CNZVI) was determined to be higher as compared to bare NZVI. The surface normalized degradation rate constants, k(SA) (Lm(2-) h(-1)), for TCE removal by CNZVI and bare NZVI ranged from 0.008 to 0.0760 to 007-0.016, respectively. Shelf life studies conducted over 12 months to access colloidal stability and 6 months to access TCE degradation indicated that colloidal stability and chemical reactivity of CNZVI remained more or less unchanged. The sedimentation characteristics of CNZVI under different ionic strength conditions (0-10 mM) did not change significantly. The steric nature of particle stabilization is expected to improve aquifer injection efficiency of the coated NZVI for groundwater remediation.

The effects of model polysiloxane and fouling-release coatings on embryonic development of a sea urchin (Arbacia punctulata) and a fish (Oryzias latipes).

In recent decades attention has focused on the development of non-toxic fouling-release coatings based on silicone polymers as an alternative to toxic antifouling coatings. As fouling-release coatings gain market share, they will contribute to environmental contamination by silicones. We report effects of eight model polysiloxane and three commercial foul-release coatings on embryonic development of sea urchins and fish, Japanese medaka. We used model coatings because they have known composition and commercially available components and molecules leaching from these coatings have been partially characterized. The commercial fouling-release coatings are purported to be non-toxic and components are proprietary. Our goal was to expose embryos of well studied model animals to the coatings to determine if the complex mixtures leaching from the coatings impact development. Urchins were chosen because development is rapid and embryos can enter the non-slip layer over surfaces. Medaka was chosen because the female deposits the sticky eggs onto the anal fin and then scrapes them off onto surfaces. Embryos were confined in water over coatings in 24 well plates. Fresh model coatings had no effect on urchin development while commercial fouling-release coatings inhibited development. Fish embryos had delayed hatching, increased mortality of hatchlings and dramatically decreased ability of hatchlings to inflate the swim bladder and reduced hatching success on all coatings. After one-month immersion of coatings in running seawater to simulate initial application in the marine environment, sea urchin embryos died when placed over model silicones. Effects of the commercial coatings were reduced but included retarded development. Effects on fish embryos over leached coating were reduced compared to those of fresh coating and included decreased hatching success, decreased hatchling survival and inability to inflate the swim bladder for commercial coatings. These findings suggest, similar to medical conclusions, compounds leaching from silicone coatings can impact development and the topic deserves study.

Combinatorial and high-throughput screening of materials libraries: review of state of the art.

Rational materials design based on prior knowledge is attractive because it promises to avoid time-consuming synthesis and testing of numerous materials candidates. However with the increase of complexity of materials, the scientific ability for the rational materials design becomes progressively limited. As a result of this complexity, combinatorial and high-throughput (CHT) experimentation in materials science has been recognized as a new scientific approach to generate new knowledge. This review demonstrates the broad applicability of CHT experimentation technologies in discovery and optimization of new materials. We discuss general principles of CHT materials screening, followed by the detailed discussion of high-throughput materials characterization approaches, advances in data analysis/mining, and new materials developments facilitated by CHT experimentation. We critically analyze results of materials development in the areas most impacted by the CHT approaches, such as catalysis, electronic and functional materials, polymer-based industrial coatings, sensing materials, and biomaterials.

Combinatorial materials research applied to the development of new surface coatings XV: an investigation of polysiloxane anti-fouling/fouling-release coatings containing tethered quaternary ammonium salt groups.

As part of ongoing efforts aimed at the development of extensive structure−property relationships for moisture-curable polysiloxane coatings containing tethered quaternary ammonium salt (QAS) moieties for potential application as environmental friendly coatings to combat marine biofouling, a combinatorial/high-throughput (C/HT) study was conducted that was focused on four different compositional variables. The coatings that were investigated were derived from solution blends of a silanol-terminated polydimethylsiloxane (HO-PDMS-OH), QAS-functional alkoxysilane, and methyltriacetoxysilane. The compositional variables investigated were alkoxysilane functionality of the QAS-functional silane, chain length of the monovalent alkyl group attached to the QAS nitrogen atom, concentration of the QAS-functional alkoxysilane, and molecular weight of the HO-PDMS-OH. Of these variables, the composition of the alkoxysilane functionality of the QAS-functional silane was a unique variable that had not been previously investigated. The antifouling (AF) and fouling-release (FR) characteristics of the 24 unique coating compositions were characterized using HT assays based on three different marine microorganisms, namely, the two bacteria, Cellulophaga lytica and Halomonas pacifica, and the diatom, Navicula incerta. Coatings surfaces were characterized by surface energy, water contact angle hysteresis, and atomic force microscopy (AFM). A wide variety of responses were obtained over the compositional space investigated. ANOVA analysis showed that the compositional variables and their interactions significantly influenced AF/FR behaviors toward individual marine microorganisms. It was also found that utilization of the ethoxysilane-functional QASs provided enhanced AF character compared to coatings based on methoxysilane-functional analogues. This was attributed to enhanced surface segregation of QAS groups at the coating-air interface and confirmed by phase images using AFM.

Compounds from silicones alter enzyme activity in curing barnacle glue and model enzymes.

BACKGROUND: Attachment strength of fouling organisms on silicone coatings is low. We hypothesized that low attachment strength on silicones is, in part, due to the interaction of surface available components with natural glues. Components could alter curing of glues through bulk changes or specifically through altered enzyme activity. METHODOLOGY/PRINCIPAL FINDINGS: GC-MS analysis of silicone coatings showed surface-available siloxanes when the coatings were gently rubbed with a cotton swab for 15 seconds or given a 30 second rinse with methanol. Mixtures of compounds were found on 2 commercial and 8 model silicone coatings. The hypothesis that silicone components alter glue curing enzymes was tested with curing barnacle glue and with commercial enzymes. In our model, barnacle glue curing involves trypsin-like serine protease(s), which activate enzymes and structural proteins, and a transglutaminase which cross-links glue proteins. Transglutaminase activity was significantly altered upon exposure of curing glue from individual barnacles to silicone eluates. Activity of purified trypsin and, to a greater extent, transglutaminase was significantly altered by relevant concentrations of silicone polymer constituents. CONCLUSIONS/SIGNIFICANCE: Surface-associated silicone compounds can disrupt glue curing and alter enzyme properties. Altered curing of natural glues has potential in fouling management.

Two Photon Polymerization-Micromolding of Polyethylene Glycol-Gentamicin Sulfate Microneedles.

The use of microneedles for transdermal drug delivery is limited due to the risk of infection associated with formation of channels through the stratum corneum layer of the epidermis. The risk of infection associated with use of microneedles may be reduced by imparting these devices with antimicrobial properties. In this study, a photopolymerization-micromolding technique was used to fabricate microneedle arrays from a photosensitive material containing polyethylene glycol 600 diacrylate, gentamicin sulfate, and a photoinitiator. Scanning electron microscopy indicated that the photopolymerization-micromolding process produced microneedle arrays that exhibited good microneedle-to-microneedle uniformity. An agar plating assay revealed that microneedles fabricated with polyethylene glycol 600 diacrylate containing 2 mg mL(-1) gentamicin sulfate inhibited growth of Staphylococcus aureus bacteria. Scanning electron microscopy revealed no platelet aggregation on the surfaces of platelet rich plasma-exposed undoped polyethylene glycol 600 diacrylate microneedles and gentamicin-doped polyethylene glycol 600 diacrylate microneedles. These efforts will enable wider adoption of microneedles for transdermal delivery of pharmacologic agents.

Novel, UV-curable coatings containing a tethered biocide: Synthesis, characterization, and antimicrobial activity.

Cationic, UV -curable coatings containing the tethered biocide, triclosan, were produced and their antimicrobial activity toward Staphylococcus epidermidis and Escherichia coli determined. Two polysiloxanes functionalized with both cycloaliphatic epoxy and triclosan were synthesized using hydrosilylation. The functionalized polysiloxanes, with varied concentration of pendant triclosan, were used to produce UV-curable coatings with reasonably good coating properties. Fourier transform (FT)-Raman spectroscopy showed that the tethered triclosan moieties self-concentrate on the coating surface. Using biological assays, it was determined that the coatings possessed nearly 100% antimicrobial activity toward the Gram-positive bacterium, S. epidermidis, without leaching toxic components. For the Gram-negative bacterium, E. coli, 60-80% reduction in biofilm retention was observed for all the coatings. Interestingly, the coatings were lesser effective in reducing E. coli cell viability suggesting that the tethered triclosan were able to substantially reduce the production of the biofilm extracellular matrix with minimal adverse affect on the bacterial cells attached to the coating surfaces. The high specificity of the coatings toward S. epidermidis indicates that a novel mode of contact-active antimicrobial activity was achieved through the disruption of processes unique to the Gram-positive cell wall. These novel UV-curable coatings have potential applications in inhibiting implantable biomedical device associated infections.

Atomic layer deposition-based functionalization of materials for medical and environmental health applications.

Nanoporous alumina membranes exhibit high pore densities, well-controlled and uniform pore sizes, as well as straight pores. Owing to these unusual properties, nanoporous alumina membranes are currently being considered for use in implantable sensor membranes and water purification membranes. Atomic layer deposition is a thin-film growth process that may be used to modify the pore size in a nanoporous alumina membrane while retaining a narrow pore distribution. In addition, films deposited by means of atomic layer deposition may impart improved biological functionality to nanoporous alumina membranes. In this study, zinc oxide coatings and platinum coatings were deposited on nanoporous alumina membranes by means of atomic layer deposition. PEGylated nanoporous alumina membranes were prepared by self-assembly of 1-mercaptoundec-11-yl hexa(ethylene glycol) on platinum-coated nanoporous alumina membranes. The pores of the PEGylated nanoporous alumina membranes remained free of fouling after exposure to human platelet-rich plasma; protein adsorption, fibrin networks and platelet aggregation were not observed on the coated membrane surface. Zinc oxide-coated nanoporous alumina membranes demonstrated activity against two waterborne pathogens, Escherichia coli and Staphylococcus aureus. The results of this work indicate that nanoporous alumina membranes may be modified using atomic layer deposition for use in a variety of medical and environmental health applications.

Antifouling and antimicrobial mechanism of tethered quaternary ammonium salts in a cross-linked poly(dimethylsiloxane) matrix studied using sum frequency generation vibrational spectroscopy.

Poly(dimethylsiloxane) (PDMS) materials containing chemically bound (''tethered'') quaternary ammonium salt (QAS) moieties are being developed as new contact-active antimicrobial coatings. Such coatings are designed to inhibit the growth of microorganisms on surfaces for a variety of applications which include ship hulls and biomedical devices. The antimicrobial activity of these coatings is a function of the molecular surface structure generated during film formation. Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a powerful technique to study polymer surface structures at the molecular level in different chemical environments. SFG was successfully used to characterize the surface structures of PDMS coatings containing tethered QAS moieties that possess systematic variations in QAS chemical composition in air, in water, and in a nutrient growth medium. The results indicated that the surface structure was largely dependent on the length of the alkyl chain attached to the nitrogen atom of the QAS moiety as well as the length of alkyl chain spanning between the nitrogen atom and silicon atom of the QAS moiety. The SFG results correlated well with the antimicrobial activity, providing a molecular interpretation of the activity. This research showed that SFG can be effectively used to aid in the development of new antimicrobial coating technologies by correlating the chemical structure of a coating surface to its antimicrobial activity.

Combinatorial materials research applied to the development of new surface coatings XIII: an investigation of polysiloxane antimicrobial coatings containing tethered quaternary ammonium salt groups.

High-throughput biological assays were used to develop structure - antimicrobial relationships for polysiloxane coatings containing chemically bound (tethered) quaternary ammonium salt (QAS) moieties. The QAS-functional polysiloxanes were derived from solution blends of a silanol-terminated polydimethylsiloxane, a trimethoxysilane-functional QAS (QAS-TMS), and methylacetoxysilane. Since the QAS moieties provide antimicrobial activity through interaction with the microorganism cell wall, most of the compositional variables that were investigated were associated with the chemical structure of the QAS-TMS. Twenty different QAS-TMS were synthesized for the study and the antimicrobial activity of sixty unique polysiloxane coatings derived from these QAS-TMS determined toward Escherichia coli , Staphylococcus aureus , and Candida albicans . The results of the study showed that essentially all of the compositional variables significantly influenced antimicrobial activity. Surface characterization of these moisture-cured coatings using atomic force microscopy as well as water contact angle and water contact angle hysteresis measurements indicated that the compositional variables significantly affected coating surface morphology and surface chemistry. Overall, compositional variables that produced heterogeneous surface morphologies provided the highest antimicrobial activity suggesting that the antimicrobial activity was primarily derived from the relationship between coating chemical composition and self-assembly of QAS moieties at the coating/air interface. Using data modeling software, a narrow region of the compositional space was identified that provided broad-spectrum antimicrobial activity.

Entrapment of iron nanoparticles in calcium alginate beads for groundwater remediation applications.

Zero-valent iron nanoparticles (nZVI) have been successfully entrapped in biopolymer, calcium (Ca)-alginate beads. The study has demonstrated the potential use of this technique in environmental remediation using nitrate as a model contaminant. Ca-alginate beads show promise as an entrapment medium for nZVI for possible use in groundwater remediation. Based on scanning electron microscopy images it can be inferred that the alginate gel cluster acts as a bridge that binds the nZVI particles together. Kinetic experiments with 100, 60, and 20mg NO(3)(-)-NL(-1) indicate that 50-73% nitrate-N removal was achieved with entrapped nZVI as compared to 55-73% with bare nZVI over a 2-h period. The controls ran simultaneously show little NO(3)(-)-N removal. Statistical analysis indicates that there was no significant difference between the reaction rates of bare and entrapped nZVI. The authors have shown for the first time that nZVI can be effectively entrapped in Ca-alginate beads and no significant decrease in the reactivity of nZVI toward the model contaminant (nitrate here) was observed after the entrapment.

Remediation of alachlor and atrazine contaminated water with zero-valent iron nanoparticles.

Zero-valent iron nanoparticles (nZVI, diameter < 90 nm, specific surface area = 25 m(2) g(-1)) have been used under anoxic conditions for the remediation of pesticides alachlor and atrazine in water. While alachlor (10, 20, 40 mg L(-1)) was reduced by 92-96% within 72 h, no degradation of atrazine was observed. The alachlor degradation reaction was found to obey first-order kinetics very closely. The reaction rate (35.5 x 10(-3)-43.0 x 10(-3) h(-1)) increased with increasing alachlor concentration. The results are in conformity with other researchers who worked on these pesticides but mostly with micro ZVI and iron filings. This is for the first time that alachlor has been degraded under reductive environment using nZVI. The authors contend that nZVI may prove to be a simple method for on-site treatment of high concentration pesticide rinse water (100 mg L(-1)) and for use in flooring materials in pesticide filling and storage stations.

Nitrate removal by entrapped zero-valent iron nanoparticles in calcium alginate.

Zero-valent iron nanoparticles (nZVI) were successfully entrapped in calcium alginate beads. The potential use of this technique in environmental remediation using nitrate as a model contaminant was investigated. Kinetics of nitrate degradation using bare nZVI (approximately 35 nm dia) and entrapped nZVI were compared. Calcium alginate beads show promise as the entrapment medium for nZVI for possible use in permeable reactive barriers for groundwater remediation. Based on scanning electron microscopy images it can be inferred that the alginate gel cluster acts as a bridge that binds the nZVI particles together. Kinetic experiments with 100, 60, and 20 mg NO3--N L(-1) indicate that 50-73% nitrate-N removal was achieved with entrapped nZVI as compared to 55-73% with bare nZVI over a 2 h period. The controls ran simultaneously show little or no NO3--N removal. Statistical analysis indicates that there was no significant difference between the reaction rates of bare and entrapped nZVI. The authors have shown for the first time that nZVI can be effectively entrapped in Ca-alginate beads and no significant decrease in the reactivity of nZVI toward the model contaminant (nitrate here) was observed after the entrapment.

Detection of tethered biocide moiety segregation to silicone surface using sum frequency generation vibrational spectroscopy.

Polymer surface properties are controlled by the molecular surface structures. Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a powerful technique to study polymer surface structures at the molecular level in different chemical environments. In this research, SFG has been used to study the surface segregation of biocide moieties derived from triclosan (TCS) and tetradecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride (C-14 QAS) that have been covalently bound to a poly(dimethylsiloxane) (PDMS) matrix. PDMS materials are being developed as coatings to control biofouling. This SFG study indicated that TCS-moieties segregate to the surface when the bulk concentration of TCS-moieties exceeds 8.75% by weight. Surface segregation of C-14 QAS moieties was detected after 5% by weight incorporation into a PDMS matrix. SFG results were found to correlate well with antifouling activity, providing a molecular interpretation of such results. This research showed that SFG can aid in the development of coatings for controlling biofouling by elucidating the chemical structure of the coating surface.

Combinatorial materials research applied to the development of new surface coatings X: a high-throughput electrochemical impedance spectroscopy method for screening organic coatings for corrosion inhibition.

The objective of the study was to develop a high-throughput electrochemical impedance spectroscopy (HT-EIS) method for rapid and quantitative evaluation of corrosion protective coatings. A 12-element, spatially addressable electrochemical platform was designed, fabricated, and validated. This platform was interfaced to a commercial EIS instrument through an automated electronic switching unit. The HT-EIS system enables four parallel EIS measurements to be run simultaneously, which significantly reduces characterization time compared to that of serial EIS measurements using a multiplexer. The performance of the HT-EIS system was validated using a series of model systems, including a Randles equivalent circuit, an electrochemical reaction (Ti/K4FeCN6, K3FeCN6), a highly uniform polymer film, and several polymer coatings. The results of the validation studies showed that the HT-EIS system enables a major reduction in characterization time and provides high quality data comparable to data obtained with conventional, single-cell EIS measurement systems.

Release characteristics of reattached barnacles to non-toxic silicone coatings.

Release mechanisms of barnacles (Amphibalanus amphitrite or Balanus amphitrite) reattached to platinum-cured silicone coatings were studied as a function of coating thickness (210-770 microm), elastic modulus (0.08-1.3 MPa), and shear rate (2-22 microm s(-1)). It was found that the shear stress of the reattached, live barnacles necessary to remove from the silicone coatings was controlled by the combined term (E/t)(0.5) of the elastic modulus (E) and thickness (t). As the ratio of the elastic modulus to coating thickness decreased, the barnacles were more readily removed from the silicone coatings, showing a similar release behavior to pseudobarnacles (epoxy glue). The barnacle mean shear stress ranged from 0.017 to 0.055 MPa whereas the pseudobarnacle mean shear stress ranged from 0.022 to 0.095 MPa.