Cold spray metal embedment: an innovative antifouling technology

The study demonstrates that embedment of copper particles into thermoplastic polymers (polymers) using cold spray technology is an effective deterrent against fouling organisms. Two polymers, high-density polyethylene (HDPE) and nylon were metallised with copper powder using cold spray technology. After 250 days in the field, Cu-embedded HDPE and copper plate controls were completely free of hard foulers compared to Cu-embedded nylon and polymer controls which were heavily fouled with both soft and hard fouling. Antifouling (AF) success is related to the interaction between the properties of the polymers (elastic modulus and hardness) and the cold spray process which affect particle embedment depth, and subsequently, the release of copper ions as determined by analytical techniques. Embedding metal using cold spray equipment is shown to be an effective AF technology for polymers, in particular those that are difficult to treat with standard AF coatings, with efficacy being a function of the interaction between the cold spray metal and the polymer recipient.     

Estimates of environmental loading from copper alloy materials

Abstract

Metal release rates were measured from four different copper alloy-based materials used by the aquaculture industry: copper sheet machined into a diamond mesh, copper alloy mesh (CAM), silicon bronze welded wire mesh, and copper sheeting, and compared with conventional nylon aquaculture net treated with a cuprous oxide antifouling (AF) coating. Release rates were measured in situ in San Diego Bay using a Navy-developed Dome enclosure system at nine different time points over one year. As expected, copper was the predominant metal released, followed by zinc and nickel, which were fractional components of the materials tested. Release rates followed a temporal trend similar to those observed with copper AF coatings applied to vessel hulls: an initial spike in copper release was followed by a decline to an asymptotic low. Leachate toxicity was consistent with prior studies and was directly related to the metal concentrations, indicating the alloys tested had no additional toxicity above pure metals.     

Assessment of the anti-biofouling potentials of a copper iodide-doped nylon mesh

We propose a copper iodide (CuI)-doped nylon mesh prepared using polyiodide ions as a precursor toward anti-biofouling polymer textile. The CuI-doped nylon mesh was subjected to the prevention of biofouling in marine environments. The attachment of the marine organisms was markedly inhibited on the CuI-doped nylon mesh surface until 249 days. Scanning electron microscopy-energy dispersive X-ray analysis indicated that copper compounds were maintained in the nylon mesh after the field experiment, although copper content in the nylon mesh was reduced. Therefore, the copper ions slowly dissolved from nylon mesh will contribute to the long-term prevention of biofouling. Furthermore, electron spin resonance analysis revealed the generation of reactive oxygen species (ROS) from CuI-doped nylon mesh after the field experiment. One of the possibilities for toxic action of copper ions will be the direct effect of Cu+ -induced ROS on biofilm forming on nylon mesh surface. The proposed polymer textile can be applied to fishing and aquafarming nets, mooring rope for ship, or silt fence to restrict polluted water in marine environments.     

Modification of polynucleotides by a fragment produced by enzymatic cleavage of S-(1, 2-dichlorovinyl)-L-cysteine

Polyribo- and polydeoxyribonucleotides were allowed to react with ³⁵S-(1,2-dichlorovinyl)-L-cysteine (DCVC) in presence of a bovine kidney lyase yielding products which were substituted to varying degrees with an alkylating thiovinyl fragment (AF) released from DCVC. Polydeoxyribonucleotides were more extensively substituted than polyribonucleotides. Double stranded homopolymer pairs were much less effective as acceptors of (AF) than single stranded polymers. Nucleotide substitution occurred only at the polymer level. Enzymatic hydrolysis of (AF)-substituted polymers yielded dinucleotides which contained an (AF) fragment apparently covalently linked in unknown fashion. (AF)-substituted polynucleotides had reduced ability to form helical complexes with complementary polynucleotides, as revealed by hypochromicity, melting transition and renaturation.     

Plasticization and crosslinking effects of acetone-formaldehyde and tannin resins on wheat protein-based natural polymers

Efficient plasticization and sufficient crosslinking were achieved by using an acetone-formaldehyde (AF) resin as an additive in the thermal processing of wheat protein-based natural polymers. The mobile AF resin and its strong intermolecular interactions with a wheat protein matrix produced sufficient flexibility for the plastics, while the covalent bonds formed between AF and the protein chains also caused the water-soluble resin to be retained in the materials under wet conditions. The mechanical properties of the materials were also enhanced as an additional benefit due to the formation of crosslinked networks through the polymer matrix. Tensile strength was further enhanced when using AF in conjunction with tannin resin (AFTR) in the systems as rigid aromatic structures were formed in the crosslinking segments. Different components in wheat proteins (WPs) or wheat gluten (WG) (e.g., proteins, residual starch and lipids) displayed different capabilities in interaction and reaction with the AFTR additives, and thus resulted in different performances when the ratio of these components varied in the materials. The application of the AFTR additives provides a feasible methodology to thermally process wheat protein-based natural polymers with improved mechanical performance and water-resistant properties.     

Synthesis and characterization of metal ion imprinted nano-porous polymer for the selective recognition of copper

Selective recognition of metal ions utilizing metal ion-imprinted polymers (MIIPs) received much importance in diverse fields owing to their high selectivity for the target metal ions. In the present study, a copper ion imprinted polymer was synthesized without an additional complexing ligand or complex with a broad aim to avoid the conventional extra metal ion complexing ligand during the synthesis of MIIP. The complete removal of the copper metal ion from the MIIP was confirmed by AAS and SEM–EDX. SEM image of the MIIP exhibited nano-patterns and it was also found to be entirely different from that of non-imprinted polymer and polymer with copper metal ions. BET surface area analysis revealed more surface area (47.96 m²/g) for the Cu(II)-MIIP than non-imprinted control polymer (41.43 m²/g). TGA result of polymer with copper metal ion indicated more char yield (18.41%) when compared to non-imprinted control polymer (8.3%) and Cu(II)-MIIP (less than 1%). FTIR study confirmed the complexation between Cu(II)-MIIP and Cu(II) metal ion through carbonyl oxygen of acryl amide. The Cu(II)-MIIP exhibited an imprinting efficiency of 2.0 and it was showing 8% interference from a mixture of Zn, Ni and Co ions. A potentiometric ion selective electrode devised with Cu(II)-MIIP showed more potential response for Cu(II) ion than that was fabricated from non-imprinted polymer.     

Chelating efficiency and thermal, mechanical and decay resistance performances of chitosan copper complex in wood-polymer composites

Wood–polymer composites (WPC) have been extensively used for building products, outdoor decking, automotive, packaging materials, and other applications. WPC is subject to fungal and termite attacks due to wood components enveloped in the thermoplastic matrix. Much effort has been made to improve decay resistance of WPC using zinc borate and other chemicals. In this study, chitosan copper complex (CCC) compounds were used as a potential preservative for wood–HDPE composites. CCC was formulated by reacting chitosan with copper salts under controlled conditions. Inductively coupled plasma (ICP) analytical results indicated that chitosan had high chelating efficiency with copper cations. CCC-treated wood–HDPE composites had a thermal behavior similar to untreated and zinc borate-treated wood–HDPE composites. Incorporation of CCC in wood–HDPE composites did not significantly influence board density of the resultant composites, but had a negative effect on tensile strength at high CCC concentration. In comparison with solid wood and the untreated wood–HDPE composites, 3% CCC-treated wood–HDPE composites significantly improved the decay resistance against white rot fungus Trametes versicolor and brown rot fungus Gloeophyllum trabeum. Especially, CCC-treated wood–HDPE composites were more effectively against the brown rot than the untreated and chitosan-treated wood–HDPE composites. Moreover, CCC-treated wood–HDPE composites performed well as zinc borate-treated wood–HDPE composites on fungal decay resistance. Accordingly, CCC can be effectively used as a preservative for WPC.     

A simple approach to prepare molecularly imprinted polymers from nylon‐6

A convenient and simple approach for the preparation of molecularly imprinted polymers (MIPs) based on polyamide (nylon‐6) was developed. The polymer matrix formation occurred during the transition of nylon from dissolved to solid state in the presence of template molecules in the initial solution. 2,2,2‐Trifluoroethanol (TFE) was chosen as a main solvent for the polyamide. It provides a high solubility of nylon and does not significantly change the structure of biopolymers. The alteration of the polymer matrix structure after the addition of different types of porogens in the nylon/TFE solution was investigated. The structured polymers in the form of films and microparticles were prepared in the chosen optimal conditions. Different model biomolecular templates (of low‐ and high‐molecular weight) were used for the preparation of MIPs, which were shown to specifically recognize these molecules upon binding experiments. The binding of the template molecules to MIPs was monitored using spectrophotometric, radioisotopic, or fluorometric detection. The selectivity coefficients of the MIPs were estimated to be 1.4–4.6 depending on the type of templates and conditions of the polymer matrix formation. Copyright © 2013 John Wiley & Sons, Ltd.     

Metal complexation of chitosan and its glutaraldehyde cross-linked derivative

The physicochemical characterization of metal complexed with chitosan (CS) and its glutaraldehyde cross-linked derivative (CSGA) was investigated. Seven metal ions from chromium through zinc of the first row of the transition metals were selected for complexation. Structural features pertinent to where and how metals bind into both polymers are our main interest. Studies using solid-state NMR spectroscopy and XRPD (X-ray powder diffraction) supported by ESR spectroscopy, ICP-OES (inductively couple plasma-optical emission spectroscopy) and far-FTIR spectroscopy for metal interaction with nitrogen sites at C-2 of the metal-polymer complexes were performed. Theoretical calculations of the metal-polymer ratio, the approximate charges on nitrogen for both amine and imino-linker, and the proton affinity between an alcohol group from the polymer and an amino/imino group are reported. A helical coiled chitosan model and a 2C1L (two-chitosans with one linker) model are proposed here. The metal uptake mechanism for both polymers is concluded to be absorption within the polymers, rather than adsorption on the polymer surface.     

Synthesis and characterization of biodegradable peptide-based polymers prepared by microwave-assisted click chemistry

In this study, the microwave-assisted copper(I)-catalyzed 1,3-dipolar cycloaddition reaction was used to synthesize peptide triazole-based polymers from two novel peptide-based monomers: azido-phenylalanyl-alanyl-lysyl-propargyl amide (1) and azido-phenylalanyl-alanyl-glycolyl-lysyl-propargyl amide (2). The selected monomers have sites for enzymatic degradation as well as for chemical hydrolysis to render the resulting polymer biodegradable. Depending on the monomer concentration in DMF, the molecular mass of the polymers could be tailored between 4.5 and 13.9 kDa (corresponding with 33-100 amino acid residues per polymer chain). As anticipated, both polymers can be enzymatically degraded by trypsin and chymotrypsin, whereas the ester bond in the polymer of 2 undergoes chemical hydrolysis under physiological conditions, as was shown by a ninhydrin-based colorimetric assay and MALDI-TOF analysis. In conclusion, the microwave-assisted copper(I)-catalyzed 1,3-dipolar cycloaddition reaction is an effective tool for synthesizing biodegradable peptide polymers, and it opens up new approaches toward the synthesis of (novel) designed biomedical materials.     

Metal-chelate affinity precipitation of proteins using responsive polymers

Affinity precipitation of proteins uses polymers capable of reversible soluble-insoluble transitions in response to small environmental changes (temperature, pH or solvent composition). Here we describe protocols for (i) the synthesis of responsive polymers with specific affinity to target proteins and (ii) the purification of proteins using these polymers. The purification is based on precipitation of the affinity complex between the protein and the polymer, which is induced by environmental changes. This separation strategy is simpler and more cost effective than conventional affinity column chromatography. Specifically, we describe the synthesis of thermoresponsive 1-vinylimidazole:N-isopropylacrylamide copolymers. The whole procedure takes 2-3 h when applied to purification of recombinant His-tag proteins or proteins with natural metal binding groups by means of metal chelate affinity precipitation. Optimization of the polymer composition and the type of chelating ions allows for target protein yields of 80% and higher.     

Quantification of Encapsulated Bioburden in Spacecraft Polymer Materials by Cultivation-Dependent and Molecular Methods

Bioburden encapsulated in spacecraft polymers (such as adhesives and coatings) poses a potential risk to jeopardize scientific exploration of other celestial bodies. This is particularly critical for spacecraft components intended for hard landing. So far, it remained unclear if polymers are indeed a source of microbial contamination. In addition, data with respect to survival of microbes during the embedding/polymerization process are sparse. In this study we developed testing strategies to quantitatively examine encapsulated bioburden in five different polymers used frequently and in large quantities on spaceflight hardware. As quantitative extraction of the bioburden from polymerized (solid) materials did not prove feasible, contaminants were extracted from uncured precursors. Cultivation-based analyses revealed <0.1–2.5 colony forming units (cfu) per cm³ polymer, whereas quantitative PCR-based detection of contaminants indicated considerably higher values, despite low DNA extraction efficiency. Results obtained from this approach reflect the most conservative proxy for encapsulated bioburden, as they give the maximum bioburden of the polymers irrespective of any additional physical and chemical stress occurring during polymerization. To address the latter issue, we deployed an embedding model to elucidate and monitor the physiological status of embedded Bacillus safensis spores in a cured polymer. Staining approaches using AlexaFluor succinimidyl ester 488 (AF488), propidium monoazide (PMA), CTC (5-cyano-2,3-diotolyl tetrazolium chloride) demonstrated that embedded spores retained integrity, germination and cultivation ability even after polymerization of the adhesive Scotch-Weld 2216 B/A. Using the methods presented here, we were able to estimate the worst case contribution of encapsulated bioburden in different polymers to the bioburden of spacecraft. We demonstrated that spores were not affected by polymerization processes. Besides Planetary Protection considerations, our results could prove useful for the manufacturing of food packaging, pharmacy industry and implant technology.     

Assessing the antifouling properties of cold-spray metal embedment using loading density gradients of metal particles

Particles of copper, bronze and zinc were embedded into a polymer using cold-spray technology to produce loading density gradients of metal particles. The gradients were used to identify the species with the highest tolerance to the release of copper and zinc ions. The gradients also established the minimum effective release rates (MERRs) of copper and zinc ions needed to prevent the recruitment of fouling under field conditions. Watersipora sp. and Simplaria pseudomilitaris had the highest tolerances to the release of metal ions. Copper and bronze gradient tubes were similar in their MERRs of copper ions against Watersipora sp. (0.058?g?m^?2?h^?1 and 0.054?g?m^?2?h^?1, respectively) and against S. pseudomilitaris (0.030?g?m^?2?h^?1 and 0.025?g?m^?2?h^?1, respectively). Zinc was not an effective antifoulant, with failure within two weeks. In conclusion, cold-spray gradients were effective in determining MERRs and these outcomes provide the basis for the development of cold-spray surfaces with pre-determined life-spans using controlled MERRs.     

Biomimetic calcium phosphate mineralization with multifunctional elastin-like recombinamers

Biomimetic hybrid materials based on a polymeric and an inorganic component such as calcium phosphate are potentially useful for bone repair. The current study reports on a new approach toward biomimetic hybrid materials using a set of recombinamers (recombinant protein materials obtained from a synthetic gene) as crystallization additive for calcium phosphate. The recombinamers contain elements from elastin, an elastic structural protein, and statherin, a salivary protein. Via genetic engineering, the basic elastin sequence was modified with the SN(A)15 domain of statherin, whose interaction with calcium phosphate is well-established. These new materials retain the biocompatibility, "smart" nature, and desired mechanical behavior of the elastin-like recombinamer (ELR) family. Mineralization in simulated body fluid (SBF) in the presence of these recombinamers reveals surprising differences. Two of the polymers inhibit calcium phosphate deposition (although they contain the statherin segment). In contrast, the third polymer, which has a triblock structure, efficiently controls the calcium phosphate formation, yielding spherical hydroxyapatite (HAP) nanoparticles with diameters from 1 to 3 nm after 1 week in SBF at 37 °C. However, at lower temperatures, no precipitation is observed with any of the polymers. The data thus suggest that the molecular design of ELRs containing statherin segments and the selection of an appropriate polymer structure are key parameters to obtain functional materials for the development of intelligent systems for hard tissue engineering and subsequent in vivo applications.     

Thermochemical study of amino acid imprinted polymer films

Molecularly imprinted polymers provide an alternative to traditional methods of amino acid analysis. The imprinted polymers are more robust and significantly less expensive than, for example, ELISA analysis. Amino acid imprinted nylon‐6 thin films were studied by differential scanning calorimetry and scanning electron microscopy. Endothermic peaks were observed for imprinted films at temperatures higher than that for pure nylon, indicating the formation of a more‐ordered, hydrogen bonded polymer. Removal of the amino acid from the imprinted film resulted in reversion to the peak observed for pure nylon‐6. Additives, β‐cyclodextrin and multiwalled carbon nanotubes, were added to the imprinted polymer solutions as a means to increase the porosity of the films. These studies resulted in alternative morphologies and calorimetric results that provide additional functionalities and applications for imprinted polymers. Copyright © 2015 John Wiley & Sons, Ltd.     

Copper transfer from the Cu(I) chaperone, CopZ, to the repressor, Zn(II)CopY: metal coordination environments and protein interactions

Extracellular copper regulates the DNA binding activity of the CopY repressor of Enterococcus hirae and thereby controls expression of the copper homeostatic genes encoded by the cop operon. CopY has a CxCxxxxCxC metal binding motif. CopZ, a copper chaperone belonging to a family of metallochaperones characterized by a MxCxxC metal binding motif, transfers copper to CopY. The copper binding stoichiometries of CopZ and CopY were determined by in vitro metal reconstitutions. The stoichiometries were found to be one copper(I) per CopZ and two copper(I) per CopY monomer. X-ray absorption studies suggested a mixture of two- and three-coordinate copper in Cu(I)CopZ, but a purely three-coordinate copper coordination with a Cu-Cu interaction for Cu(I)2CopY. The latter coordination is consistent with the formation of a compact binuclear Cu(I)-thiolate core in the CxCxxxxCxC binding motif of CopY. Displacement of zinc, by copper, from CopY was monitored with 2,4-pyridylazoresorcinol. Two copper(I) ions were required to release the single zinc(II) ion bound per CopY monomer. The specificity of copper transfer between CopZ and CopY was dependent on electrostatic interactions. Relative copper binding affinities of the proteins were investigated using the chelator, diethyldithiocarbamic acid (DDC). These data suggest that CopY has a higher affinity for copper than CopZ. However, this affinity difference is not the sole factor in the copper exchange; a charge-based interaction between the two proteins is required for the transfer reaction to proceed. Gain-of-function mutation of a CopZ homologue demonstrated the necessity of four lysine residues on the chaperone for the interaction with CopY. Taken together, these results suggest a mechanism for copper exchange between CopZ and CopY.     

Poly(ether urethane) networks from renewable resources as candidate biomaterials: synthesis and characterization

A series of poly(ether urethane) networks were synthesized from epoxidized methyl-oleate-based polyether polyol and 1,3-propandiol using l-lysine diisocyanate as a nontoxic coupling agent. Polyurethanes with different hard segment contents were prepared to tune the final properties of the materials. The polyurethanes were fully chemically and physically characterized, including water uptake and in vitro hydrolytic degradation measurements. The weight loss of the polyurethanes was traced, and the changes in the surface morphology with the degradation time were examined by scanning electron microscopy. The experimental results revealed that the hard segment content is the main factor that controls the physical, mechanical, and degradation properties of these polymers. The observed diversity in material properties suggests that these polyurethanes may be useful for a wide range of biomedical polymer applications.     

Effect of Drying Methods on Swelling,Erosion and Drug Release from Chitosan–Naproxen Sodium Complexes

The purpose of this research was to explore theapplication of ionic interactions between naproxen sodium (NS) and chitosan (CH) in complexes (NSC) prepared by tray drying (TD) and spray drying (SD) methods. Drug–polymer ratio (1:1) in the NSC was optimized on the basis of dialysis studies. The particulate systems of NSC were prepared by tray drying (TD) and spray drying (SD) methods. Release retarding polymers were added to the NSC and to the physical mixtures containing NS–CH and their effects on water uptake, matrix erosion and drug release at different pH were compared. Spray dried complexes (SDC) were spherical, free flowing, light and fine amorphous particles in contrast to the crystalline, hard, tenacious, irregularly shaped, denser tray dried complexes (TDC) with poor flowability. Differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) patterns confirm the conversion of crystalline to high energy amorphous phase suitable for ionic interactions in NSC. Presence of release retarding polymers, kappa carrageenan and hydroxypropylmethylcellulose (HPMC) in the NSC compacts retarded the drug release and improved the matrix integrity. Carrageenan matrices exhibited more retardation than HPMC tablets. FTIR patterns, erosion, swelling and drug release from matrices support ionic interactions between NS and CH in NSC. The reasons for retarded drug release from the chitosan matrices at acidic pH include poor solubility of drug at acidic pH, formation of a rate limiting polymer gel barrier along the periphery of matrices and the ionic interactions between oppositely charged moieties.     

Modeling and prediction of the mixed-mode retention mechanisms for puerarin and its analogues on n-octylamine modified poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monoliths

n-Octylamine modified poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (poly(GMA-co-EGDMA)) monoliths were prepared for the rapid screening and determination of puerarin content of a crude extract Radix puerariae. The mixed-mode retention mechanisms for puerarin and its analogues on n-octylamine modified monoliths were investigated using a variety of solvent systems, chromatographic evaluation and molecular dynamics (MDs) modeling. The equilibrated conformations between cross-linked polymers and target molecules were obtained from MD modeling. Both the polymer skeleton and functional groups played important roles in the recognition process. The cross-linker formed a structural network skeleton, in which recognition cavities were formed surrounded by functional groups. The polymer network structures provided good interaction access for isoflavones. The active groups recognized isoflavones by both intermolecular hydrogen bonding and hydrophobic interaction. The interaction energies and retention factors between polymers and target molecules were also evaluated and compared. A higher value of interaction energy corresponded to a higher value of retention factor. The potential of using modeling technology for predicting the chromatographic performances of target molecules was explored.     

Enzyme-based molecular imprinting with metals

Aromatic monomers with various functional groups were utilized in horseradish peroxidase-catalyzed polymerization reactions with metal ions Cu(II), Ni(II), and Fe(III) as imprinting templates. The approach described combines molecular imprinting with enzymatic free radical coupling. Selectivity in metal ion affinity between the various polymer products was assessed and found to depend on the metal used in the imprinting process using aniline, tyramine, and phenol as monomers. Selectivity in binding metals was found when polymers imprinted with copper, nickel, or iron were screened against the three metals, with preference for the metal used in the imprinting step. A model for the structural features of the putative imprinted polymers is proposed based on electron paramagnetic resonance, NMR, and IR analysis. Specific potential benefits to this imprinting method include reactivity with a wide range of aromatic monomers to provide more diverse options for molecular recognition with the target analyte and thus polymer products with higher selectivity, mild reaction conditions for the enzyme polymerization step to enable imprinting against labile substrates, imprinted polymeric products that contain conjugated backbones that could be suitable for electronics-based biosensor applications, and a potential for combinatorial selection to further enhance specificity.