Carboxybetaine functionalized nanosilicas as protein resistant surface coatings

Materials with protein resistant properties are increasingly sought after for their potential application as low-fouling surface coatings. Hydrophilic coatings with improved resistance to protein fouling have been prepared from zwitterionic carboxybetaine (CB) functionalized silica nanoparticles (SiNPs). The authors report three methods of coating preparation via direct tethering of CB to predeposited particle films, a two-step surface functionalization process, and deposition of CB functionalized particle dispersions. The pH at which aqueous CB solutions were prepared and reacted to SiNPs was found to drastically influence the mechanism of CB attachment and affect the protein resistance of the resultant coatings. Depending on the method of coating preparation, protein binding to functionalized particle coatings was reduced by up to 94% compared to unfunctionalized SiNP control surfaces. As a result, all three methods offer simple and scalable fabrication routes for the generation of hydrophilic, zwitterionic interfaces with improved inhibition to protein fouling.

Zwitterion Functionalized Silica Nanoparticle Coatings: The Effect of Particle Size on Protein, Bacteria, and Fungal Spore Adhesion

The negative impacts that arise from biological fouling of surfaces have driven the development of coatings with unique physical and chemical properties that are able to prevent interactions with fouling species. Here, we report on low-fouling hydrophilic coatings presenting nanoscaled features prepared from different size silica nanoparticles (SiNPs) functionalized with zwitterionic chemistries. Zwitterionic sulfobetaine siloxane (SB) was reacted to SiNPs ranging in size from 7 to 75 nm. Particle stability and grafting density were confirmed using dynamic light scattering and thermogravimetric analysis. Thin coatings of nanoparticles were prepared by spin-coating aqueous particle suspensions. The resulting coatings were characterized using scanning electron microscopy, atomic force microscopy, and contact angle goniometry. SB functionalized particle coatings displayed increased hydrophilicity compared to unmodified particle coating controls while increasing particle size correlated with increased coating roughness and increased surface area. Coatings of zwitterated particles demonstrated a high degree of nonspecific protein resistance, as measured by quartz crystal microgravimetry. Adsorption of bovine serum albumin and hydrophobin proteins were reduced by up to 91 and 94%, respectively. Adhesion of bacteria ( Escherichia coli) to zwitterion modified particle coatings were also significantly reduced over both short and long-term assays. Maximum reductions of 97% and 94% were achieved over 2 and 24 h assay periods, respectively. For unmodified particle coatings, protein adsorption and bacterial adhesion were generally reduced with increasing particle size. Adhesion of fungal spores to SB modified SiNP coatings was also reduced, however no clear trends in relation to particle size were demonstrated.

Hydration Layer Structure of Biofouling-Resistant Nanoparticles

Hydrophilic surface chemistries can strongly bind water to produce surfaces that are highly resistant to protein adsorption and fouling. The interfacial bound water and its distinct properties have intrigued researchers for decades, yet the relationship between the water three-dimensional structure and function in antifouling coatings remains elusive. Here, we use hydrophilic, epoxy organosilane modified silica nanoparticles to demonstrate cheap, robust, and practically applied coatings that we discover have broad-ranging, ultralow fouling properties when challenged by various proteins, bacteria, and fungal spores. To understand their excellent antifouling properties, frequency modulation-atomic force microscopy is used to directly observe the interfacial water structure at subatomic resolution, which we validate using all-atom molecular dynamic simulations that strikingly predict similar structures of water layers on the original and ultralow fouling surfaces. The convergence of experimental and modeling data reveals that suitably spaced, flexible chains with hydrophilic groups interact with water molecules to produce a connective, quasi-stable layer, consisting of dynamic interfacial water, that provides a basis for antifouling performance of ultrathin, hydrophilic surface chemistries.

Silica Nanoparticles Functionalized with Zwitterionic Sulfobetaine Siloxane for Application as a Versatile Antifouling Coating System

The growing need to develop surfaces able to effectively resist biological fouling has resulted in the widespread investigation of nanomaterials with potential antifouling properties. However, the preparation of effective antifouling coatings is limited by the availability of reactive surface functional groups and our ability to carefully control and organize chemistries at a materials' interface. Here, we present two methods of preparing hydrophilic low-fouling surface coatings through reaction of silica-nanoparticle suspensions and predeposited silica-nanoparticle films with zwitterionic sulfobetaine (SB). Silica-nanoparticle suspensions were functionalized with SB across three pH conditions and deposited as thin films via a simple spin-coating process to generate hydrophilic antifouling coatings. In addition, coatings of predeposited silica nanoparticles were surface functionalized via exposure to zwitterionic solutions. Quartz crystal microgravimetry with dissipation monitoring was employed as a high throughput technique for monitoring and optimizing reaction to the silica-nanoparticle surfaces. Functionalization of nanoparticle films was rapid and could be achieved over a wide pH range and at low zwitterion concentrations. All functionalized particle surfaces presented a high degree of wettability and resulted in large reductions in adsorption of bovine serum albumin protein. Particle coatings also showed a reduction in adhesion of fungal spores (Epicoccum nigrum) and bacteria (Escherichia coli) by up to 87 and 96%, respectively. These results indicate the potential for functionalized nanosilicas to be further developed as versatile fouling-resistant coatings for widespread coating applications.

In vitro partial relipidation of apolipoproteins in plasma

In vitro recombination of lipids with apolipoproteins is achieved when a concentrated solution of plasma lipids in petroleum ether is mixed with delipidated plasma. Combination of phospholipids and unesterified fatty acids are observed in amounts comparable with those originally present in the native unextracted plasma; triglycerides combine partially and cholesterol only slightly. On agarose gel immunoelectrophoresis, a component in the delipidated plasma which is reactive with high density lipoprotein antibodies migrates more slowly than high density lipoprotein in the undelipidated control plasma. However, the component reacting with low density lipoprotein antibodies in the delipidated plasma moves more rapidly than low density lipoprotein in the native plasma. These changes are reversed by recombination of lipid with delipidated plasma. All lipids present in the plasma phase after relipidation travel with the lipoproteins during zonal electrophoresis. The apparent concentrations of proteins reacting with high density and low density lipoprotein antibodies decrease when no lipid is present in plasma on assay by single radial immunodiffusion and immunoelectrophoresis, using commercially available lipoprotein antibodies. On relipidation, full immunochemical properties of high density lipoprotein are restored, but relipidated low density lipoprotein exhibits only partial immunochemical restoration.

A solvent system for delipidation of plasma or serum without protein precipitation

A technique has been developed which attains in 30 minutes complete removal of triglyceride, cholesterol, phospholipid, and unesterified fatty acids from plasma without protein denaturation. Plasma is agitated at room temperature with a mixture of butanol and di-isopropyl either in a 40:60 (v/v) ratio. The plasma proteins, including the apolipoproteins, remain in solution in the aqueous phase, while the organic phase contains the dissolved lipids. The phases can easily be separated by low speed centrifugation. Different lipids are simultaneously extracted, but the rate of extraction is most rapid for unesterified fatty acids, followed by triglyceride, cholesterol, and phospholipid at, respectively, decreasing rates. Selective extraction of unesterified fatty acids, triglyceride and total cholesterol can be achieved by di-isopropyl ether alone. Ionic strength and pH are not altered by these procedures.

Changes in electrophoretic mobilities of alpha-and beta-lipoproteins as a result of plasma delipidation

A two-phase system containing the ternary mixture butanol/disopropyl ether/plasma in different proportions yields ordered delipidation of alpha-lipoproteins, pre-beta-lipoproteins- and beta-lipoproteins in plasma, as quantitated by densitometry after electrophoresis. As a consequence of delipidation the electrophoretic mobilities of pre-beta-lipoproteins and beta-lipoprotein increased, that of alpha-lipoprotein decreased.

Changes in electrophoretic mobilities of alpha-and beta-lipoproteins as a result of plasma delipidation

A two-phase system containing the ternary mixture butanol/disopropyl ether/plasma in different proportions yields ordered delipidation of alpha-lipoproteins, pre-beta-lipoproteins- and beta-lipoproteins in plasma, as quantitated by densitometry after electrophoresis. As a consequence of delipidation the electrophoretic mobilities of pre-beta-lipoproteins and beta-lipoprotein increased, that of alpha-lipoprotein decreased.

The relationship of red cell membrane lipid content to red cell morphology and survival in patients with liver disease

The relationship of red blood cell (RBC) membrane lipid content to RBC morphology and survival was studied in patients with liver diseases. An increase in RBC cholesterol and phospholipid was detected in most patients with hepatocellular disease or cholestatic jaundice but the alteration in RBC lipid content did not correlate with RBC survival. The main abnormality of RBC morphology observed was the presence of macrocytes and target cells. In a small proportion of patients (approximately 3%) with severe hepatocellular disease, significant numbers of severely deformed ("spur") cells were seen. In these patients haemolysis was moderately severe and the RBC lipid profile showed increased membrane cholesterol without a concomitant increase in phospholipids. It is concluded that only in patients with "spur" cell anaemia do the morphological alterations lead to premature removal of cells from the circulation. The cause of the shortened RBC survival in jaundiced patients without "spur" cells remains to be determined.