News Column

Patent Application Titled "Functionalized Silicones with Polyalkylene Oxide Side Chains" Published Online

August 26, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- According to news reporting originating from Washington, D.C., by NewsRx journalists, a patent application by the inventors Webster, Dean C. (Fargo, ND); Bodkhe, Rajan B. (Woodbury, MN), filed on June 15, 2012, was made available online on August 14, 2014 (see also NDSU Research Foundation).

The assignee for this patent application is NDSU Research Foundation.

Reporters obtained the following quote from the background information supplied by the inventors: "Surfaces having non-fouling characteristics facilitate the development of advanced materials for use in biomedical and marine applications.

"In medical applications, a major problem associated with implanted and blood contact biomaterials is the triggering of a number of undesired responses including inflammation, infection, thrombosis, fibrosis, allergy, and biomaterial induced cancer. These unwanted responses are triggered with the rapid accumulation of a large number of blood plasma proteins when the materials come in contact with blood (Wyszogrodzka and Haag, Biomacromolecules 2009 10:1043-1054; Castner and Ratner, Surf Sci. 2002 500:28-60; Ratner and Bryant, Annu. Rev. Biomed. Eng. 2004 6:41-75).

"In marine environments, surfaces become fouled rapidly due to biofouling. Biofouling is the unwanted accumulation of microorganism, plants, algae and animals on artificial structures immersed in water, such as sea, river or lake water. Biofilm formation, which involves adhesion of bacteria and diatoms, is the first step in the process of biofouling. The specific or nonspecific recognition of adsorbed organic material by bacteria is the main driving force for their adhesion (Iguerb et al., Langmuir 2008 24:12272-12281; Geesey, Curr. Opin. Microbiol. 2001 4:296-300). Bacteria use exopolymers and a protein matrix to cement themselves to a surface. Although adhesion of organisms to the surface is complicated, marine organisms attach to surfaces by a primary mechanism that involves wetting of the surface by secretion of a protein or glycoprotein adhesive (Iguerb et al., Langmuir 2008 24:12272-12281).

"Materials can be modified with a surface coating to become protein resistant (Ostuni et al., Langmuir 2003 19:1861-1872; Hester et al., Macromolecules 2002 35:7652-7661; Griesser et al., Smart Mat. Struct. 2002 11:652). Materials containing PEG self-assembled monolayers (SAM) are commercially available and are prominent protein resistant materials (Wyszogrodzka and Haag, Biomacromolecules 2009 10:1043-1054; Szleifer, Curr. Opin. Solid State Mater. Sci. 1997 2:337-344). However, the SAM approach is not suitable for broad practical use. Improved protein-resistant coatings and surface modifications are of broad continuing interest in many technological, industrial and medical fields."

In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventors' summary information for this patent application: "The present invention provides novel amphiphilic polymers, compositions, formulations, coatings and surface modifications that are effective to reduce or eliminate the attachment of biological materials, organic matter, or organisms to surfaces, particularly surfaces in contact with water or in aqueous environments. Generally, the polymers and coatings of the invention are termed 'anti-fouling' for their ability to reduce or prevent adhesion of biological or organic matter such as proteins, bacteria, and the like to the coated surfaces.

"More particularly, the present invention provides an amphiphilic silicone polymer that includes a hydrophobic component, such as a polysiloxane or a polysiloxane/polylactone copolymer, and a hydrophilic component, such as a polyalkylene glycol. The hydrophilic component is grafted onto the polysiloxane backbone, preferably via a thioether linkage. Polysiloxanes have many desirable properties such as low glass transition temperature, hydrophobicity, UV stability and high chain flexibility, and may be modified to provide more desirable mechanical or industrial properties according to their intended use. Polyalkylene glycols, such as polyethylene glycols (PEG), are of interest due to their protein resistant, nontoxic and nonimmunogenic properties.

"Surface coverage by a grafted polymer is important for the ability of a polymer layer to prevent protein adsorption (Prime and Whitesides, J. Am. Chem. Soc. 1993 115:10714-10721; Szleifer, Curr. Opin. Solid State Mater. Sci. 1997 2:337-344). Hence, the present invention incorporates a protein resistant material like PEG into the polymer, with control over the amount of PEG on the surface. The anti-fouling polymer of the invention is amphiphilic, containing both hydrophobic and hydrophilic components. When used as or incorporated into a coating that is applied to the surface of a material, both hydrophilic and hydrophobic moieties are preferably present at the coating surface. It is well known that the lowest surface energy components of a solvent cast block copolymer preferentially segregate to the surface (Patel et al., Macromolecules 1988 21:2689-96; Smith et al., Macromolecules 1992 25:2575-81). By attaching a hydrophilic polymer or oligomer to a low surface energy polymer or oligomer such as polysiloxane, the hydrophilic component will be forced to segregate to the surface of the material along with the low surface energy polymer, resulting in an amphiphilic surface.

"The polymers of the present invention are thus well suited for use in anti-fouling coating systems, either alone, incorporated into other polymers, or in combination with other polymers. The amphiphilic silicone polymer of the invention can, for example, be incorporated into a polyurethane (PU) to yield a siloxane-polyurethane fouling-release coating. Siloxane-polyurethane fouling-release coatings represent a non-toxic approach to combat biofouling and have already showed promising results in laboratory assays against a number of diverse marine organisms (U.S. Pat. No. 7,799,434; U.S. Pat. Appl. 20100280148). A siloxane-polyurethane system overcomes the drawback of durability and toughness associated with commercially available silicone elastomer fouling-release coatings. See, e.g., Yebra et al., Prog. Org. Coat. 2004 50:75-104. Polyurethanes are widely used as biomaterials due to their biocompatibility and toughness.

"Formation of a polyurethane coating having an amphiphilic surface can, for example, be accomplished by first synthesizing siloxane polymers with terminal amine functionality and pendant PEG chains, then incorporating these PEGylated siloxane polymers into a thermoset PU system. The resulting polyurethane coatings can be characterized for their surface properties using water contact angle (WCA), confocal Raman microscopy (CRM), and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, as illustrated in Example 1. The fouling-release performance of the coatings was tested in the laboratory using a suite of relevant marine fouling organisms. The low surface energy siloxane can aid in bringing PEG chains to the surface, and the terminal amine functionality can react with polyurethane so that it is incorporated into the coating system. Therefore, the surface of the material will be amphiphilic while the PU bulk will give toughness to the system.

"Additionally, the method of the invention permits synthesis of amphiphilic coatings with compositional control over hydrophilic and hydrophobic components, thereby facilitating the synthesis of a wide variety of polymers that can be used to more broadly resist marine biofouling. The synthetic approach described herein allows for precise control over the number of hydrophilic PEG chains, siloxane and PEG chain lengths, and terminal amine functionality for further reaction. The amount of surface coverage by the PEG chains can be varied by changing the number and amount of pendant PEG chains.

"Fouling-release coatings do not necessarily deter the attachment of marine organisms, but allow only a weak bond to form between marine organisms and the surface. Weakly attached organisms are 'released' by the application of hydrodynamic forces such as a ship moving through the water. However, marine organisms exhibit different responses to various surface characteristics, thereby complicating efforts to combat biofouling. As an example, two types of marine algae, Ulva linza and Navicula incerta show exactly the opposite behavior with respect to adhesion to hydrophobic or hydrophilic surfaces. The green alga Ulva linza adheres weakly to hydrophobic surfaces, while the diaton Nacvicula incerta adheres strongly to hydrophobic surfaces including silicone elastomers (Finlay et al., Biofouling 2008 24:219-225; Holland et al., Biofouling 2004 20:323-329). Hydrophobic coatings based on polydimethylsiloxane (PDMS) and fluorinated block copolymers are efficient in release of Ulva while hydrophilic coatings based on block copolymers containing polyethylene glycol showed extremely good release performance against diatoms (Krishnan et al., Biomacromolecules 2006 7:1449-1462; Gudipati et al., Langmuir 2005 21:3044-3053; Krishnan et al., Langmuir 2006 22:5075-5086). An amphiphilic coating is expected to be effective in reducing adhesion of a broad variety of marine organisms as illustrated by the two different marine algae discussed above.

"Accordingly, in one aspect, the present invention provides a polymer, preferably an amphiphilic graft polymer, that includes a polymeric silicone backbone, such as a polysiloxane backbone, and a plurality of hydrophilic polymeric pendant side chains that are linked to the silicone backbone through a thioether linkage. Optionally, the polymeric silicone backbone includes a reactive functional end group at one or both of its ends. In another embodiment, the polymer of the invention includes a polymeric silicone backbone, such as a polysiloxane backbone, that includes a reactive functional end group at one or both ends; and a plurality of hydrophilic polymeric pendant side chains. In this embodiment of the amphiphilic polymer, the hydrophilic polymeric pendant side changes may, but need not, be linked to the silicone backbone through a thioether linkage. The reactive functional end group, when present, is preferably an alkyl amine. The amphiphilic polymer of the invention is preferably prepared by the process of reacting a polyvinylsiloxane with a hydrophilic polymeric monothiol.

"In a preferred embodiment of the amphiphilic polymer, the polymeric silicone backbone is formed from polydimethylsiloxane. Alternatively or additionally, the polymeric silicone backbone may be a copolymer of siloxane and lactone constituent units.

"In a preferred embodiment of the amphiphilic polymer, the hydrophilic polymeric pendant side chains of the amphiphilic polymer include polyalkylene glycol, more preferably, polyethylene glycol.

"In another aspect, the invention includes a polyurethane that incorporates the amphiphilic polymer as described herein.

"In yet another aspect, the invention includes a composition, coating, film, adhesive, gel, oil or lubricant that includes a polymer as described herein. The invention further includes an article that includes said composition, coating, film, adhesive, gel, oil or lubricant, as well as an article having a surface coated with any of the polymers described herein.

"In yet another aspect, the invention provides a method for making an amphiphilic polymer that includes combining a hydrophilic polymeric monothiol reactant and a polyvinylsiloxane reactant in the presence of a catalyst for a time and under conditions to yield an amphiphilic polymer characterized by a polysiloxane backbone and a plurality of hydrophilic polymeric pendant side chains. Optionally, the monothiol is supplied in molar excess. The polyvinylsiloxane reactant is preferably a linear polyvinylsiloxane that has a reactive functional group at one or both ends. Also included in the invention is an amphiphilic polymer prepared by the method of the invention.

"In yet another aspect, the invention provides a method for making a polyvinylsiloxane that includes reacting a vinylated cyclic siloxane with at least one of a cyclic siloxane and a linear siloxane, in the presence of a catalyst under conditions and for a time sufficient to yield the polyvinylsiloxane. Preferably, the linear siloxane has one or two functional reactive end groups, such as an alkyl amine, and the polyvinylsiloxane product includes the functional reactive end group(s). Also included is a polyvinylsiloxane prepared by the method of the invention.

BRIEF DESCRIPTION OF THE FIGURES

"FIG. 1 shows an .sup.1H NMR spectra of (A) PEG tosylate, (B) PEG thioacetate (C) SH-PEG in CDCl.sub.3.

"FIG. 2 shows an .sup.1H NMR spectrum of siloxane-PEG copolymer.

"FIG. 3 shows a confocal Raman spectrum of surface of 10K-50% AF-20% coating showing the presence of Si--O--Si, C--S and PEG groups on the surface.

"FIG. 4 shows an ATR-FTIR spectra of coating 10K-50% AF-20%.

"FIG. 5 shows surface topography of 10K-50% PEG-20% coating made using drawdown. The image size is 20.times.20 .mu.m.

"FIG. 6 shows the water contact angle (WCA) of PDMS-PEG and PDMS coatings. The WCA value is a mean of three replicate measurements and the error bar represents one standard deviation from the mean.

"FIG. 7 shows the surface energy (SE) of PDMS-A and PDMS as made coatings and after one month of DI water immersion and one month of DI water immersion then one week of artificial sea water (ASW) immersion. SE was calculated using WCA and MI contact angle using Owens-Wendt method.

"FIG. 8 shows retention of C. lytica biofilm. The values shown are a mean of three replicate measurements and the error bar represents one standard deviation from the mean.

"FIG. 9 shows C. lytica removal at water jet pressure of 138 kPa from PDMS-PEG and PDMS coating compared with the standard coatings. The values shown are a mean of three replicate measurements and the error bar represents one standard deviation from the mean.

"FIG. 10 shows attachment of N. incerta to the coatings surface quantified by fluorescence intensity. The values shown are a mean of three replicate measurements and the error bar represents one standard deviation from the mean. The fluorescence value reported is directly proportional to the amount of algal cells attached to the coating surfaces.

"FIG. 11 shows N. incerta removal at water jet pressure of 138 kPa for PDMS-PEG and PDMS coatings compared with the standard coatings. The values shown are a mean of three replicate measurements and the error bar represents one standard deviation from the mean.

"FIG. 12 shows biomass of Ulva sporeling before jetting presented as RFU values measured as extracted chlorophyll. Each point is the mean of 6 replicates. Error bars show 95% confidence limits.

"FIG. 13 shows a percentage removal of Ulva sporelings after 7 days growth using an impact pressure of 111 kPa with the spin-jet. Each point is the mean of 6 replicates. Error bars show 95% confidence limits derived from arcsine transformed data."

For more information, see this patent application: Webster, Dean C.; Bodkhe, Rajan B. Functionalized Silicones with Polyalkylene Oxide Side Chains. Filed June 15, 2012 and posted August 14, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2078&p=42&f=G&l=50&d=PG01&S1=20140807.PD.&OS=PD/20140807&RS=PD/20140807

Keywords for this news article include: Polyenes, Silicones, Siloxanes, Polyvinyls, Hydrocarbons, Vinyl Compounds, Biomacromolecules, Organic Chemicals, Organosilicon Compounds, NDSU Research Foundation.

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Source: Life Science Weekly


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