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Marine biofouling profoundly influences marine industries and activities. It slows the speed and increases the fuel consumption of ships, corrodes offshore platforms, and blocks seawater pipelines. The most effective and economical antifouling approach uses coatings. Fouling-release coatings (FRCs) with low surface free energy and high elasticity weakly adhere to marine organisms, so they can be readily removed by the water shear force. FRCs have attracted increasing interest because they are biocide-free and hence ecofriendly. However, traditional silicone-based FRCs have weak adhesion to substrates, low mechanical strength, and low fouling resistance, limiting their applications. In recent years, many attempts have been made to improve their mechanical properties and fouling resistance. This review deals with the progress in the construction of high-performance silicone-based fouling-release surfaces.

Surface stiffness plays a critical role in bacterial adhesion, but the mechanism is unclear since the bacterial motion before adhesion is overlooked. Herein, the three-dimensional (3D) motions of Escherichia coli and Pseudonomas sp. nov 776 onto poly(dimethylsiloxane) (PDMS) surfaces with varying stiffness before adhering were monitored by digital holographic microscopy (DHM). As Young's modulus (E) of the PDMS surface decreases from 278.1 to 3.4 MPa, the adhered E. coli and Pseudonomas sp. decrease in number by 40.4 and 34.9%, respectively. Atomic force microscopy (AFM) measurements show that the adhesion force of bacteria to the surface declines with the decreased surface stiffness. In contrast, a nontumbling mutant of adhered E. coli (HCB1414 with the adaptive function being partially deficient) decreases much less (by 18.4%). On the other hand, the tumble frequency (Ft) of E. coli HCB1 and flick frequency (Ff) of Pseudomonas sp. increase as the surface stiffness decreases, and the motion bias (Bθ) of Pseudomonas sp. also increases. These facts clearly indicate that the bacteria have adapted responses to the surface stiffness. RNA sequencing (RNA-seq) reveals that the downregulated Cph2 and CsrA as well as the upregulated GcvA of swimming E. coli HCB1 in bulk near the softer surface promote the bacterial motility.

Understanding the behavior of bacteria near biodegradable surfaces is critical for the development of biomedical and antibiofouling materials. By using digital holographic microscopy (DHM), we investigated the three-dimensional (3D) behavior of Escherichia coli and Pseudomonas sp. in lipase-containing aquatic environments near dynamic surfaces constructed by biodegradable poly(ε-caprolactone) (PCL)-based polymers in real time. As the enzymatic degradation rate increases, the percentage of near-surface subdiffusive bacteria and consequently, the irreversible adhesion decreases. Atomic force microscopy (AFM) measurements reveal that the adhesion force between bacteria and the surfaces decreases with an increasing degradation rate. In addition, the degradation products elicit a negative chemotactic response in E. coli, further driving them away from the dynamic surfaces through more frequent tumbling motion. Our study clearly demonstrates that bacterial adhesion can be reduced on dynamic surfaces formed by degradable polymers.

Protein resistance is the central issue in marine antibiofouling. We have prepared poly(ε-caprolactone) (PCL)-based polyurethane with 2-(dimethylamino) ethyl methacrylate (DEM) as pendant groups by a combination of the thiol-ene click reaction and the condensation reaction. By the use of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR), we have investigated the adsorption of fibrinogen, bovine serum albumin (BSA), and lysozyme on the polymer surface. The polymer exhibits protein resistance in seawater but not in fresh water because DEM pendant groups carry net neutral charges in the former. The evaluation of antibacterial adhesion of the polymer by using Micrococcus luteus demonstrates that the polymer can effectively inhibit the settlement of marine bacteria. Our studies also show that the polymer is degradable in marine environments.

We have developed a novel approach to introduce zwitterions into polyurethane for the preparation of antibiofouling coating. First, the thiol-ene click reaction between 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-mercapto-1,2-propanediol (TPG) is used to synthesize dihydroxy-terminated DMAEMA (DMA(OH)2) under UV catalysis. The product has been proved by gel permeation chromatography (GPC), Fourier transform infrared spectrum (FT-IR), proton nuclear magnetic resonance ((1)H NMR), and high resolution mass spectrometry (HRMS). DMA(OH)2 is then incorporated into polyurethane as side groups by polyaddition with diisocyanate and further reacts with 1,3-propane sultone to obtain the zwitterionic polyurethanes. The presence of sulfobetaine zwitterions side groups has been demonstrated by FT-IR and X-ray photoelectron spectroscopy (XPS). Thermal analysis indicates that the thermal stability is decreased with the increasing content of zwitterionions. The antibiofouling property of polyurethanes has been investigated by the measurement of adsorption of fibrinogen, bovine serum albumin (BSA), and lysozyme on the polyurethanes surface using quartz crystal microbalance with dissipation (QCM-D). The results show that the polyurethane coatings exhibit effective nonspecific protein resistance at higher content of zwitterionic side groups.

Segmented polyurethanes (PUs) containing poly(ethylene glycol) (PEG), poly(propylene glycol), or poly(dimethylsiloxane) soft segments have been prepared by two-step condensation polymerization. Atom force microscopy observation in air and solution indicates that the segmented PU forms a microphase separation on the surface. By use of quartz crystal microbalance with dissipation and surface plasmon resonance, we have investigated the adsorption of fibrinogen, bovine serum albumin, and lysozyme on a surface constructed by such a PU in aqueous solution in real time. Our results reveal that the protein resistance of the PUs arises from the hydrated PEG segments instead of microphase separation.