Bacterial adhesion and colonization are common occurrences that cause problems in a variety of settings. Surface hydrophilization has been popular in recent years as a new approach to preventing microbial colonization. Because a tightly bound layer of water acts as an energetic and physical barrier that effectively resists biological contamination processes, such as protein attachment, initial bacterial attachment, and subsequent biofilm formation, surface hydration layers induced by hydrophilic polymers can impart biological contamination resistance to surfaces.
Several hydrophilic polymers, such as poly(ethylene glycol) (PEG) and amphoteric-containing polymers, have been used as candidates for the creation of hydrophilic anti-biofouling coatings. Hydrophilic polymers, on the other hand, cannot be employed as coatings on their own due to their water solubility and poor mechanical durability. Alfa Chemistry employs numerous strategies to improve the durability of hydrophilic polymer. We concentrate on the most recent advancements in anti-biofouling coatings based on hydrophilic polymers, with a focus on mechanical durability.
3D-Grafted Coatings
Grafting hydrophilic polymers onto mechanically and chemically tough hydrophobic coatings is a common method for achieving targeted surface hydrophilicity and biological contamination resistance. Alfa Chemistry grafts poly(ethylene oxide) (PEO) into a cross-linked poly(2-vinyl pyridine) (P2VP) network using a new 3D grafting process that involves a reaction between PEO and the alkyl halogen groups in the P2VP pyridine ring. Due to the chemical potential gradient, when the PEO brushes on the surface are destroyed, the underlying PEO chain segments stored in the matrix spontaneously float out of the surface. In comparison to the usual scheme, the 3D grafted surface has a fourfold increase in durability under physiological settings.
Fig 1. Schematic illustration of the 3D grafting of PEO into the P2VP polymer matrix and the self-healing process after the PEO segments are separated from the surface. (Lewis A. L, et al. 2000)
Hierarchical Spheres-Based Coatings
Alfa Chemistry constructed a self-healing underwater coating through the assembly of layered microgel spheres. n Isopropylacrylamide (NIPAM), methacrylic acid (MAA), and poly(ethylene glycol) diacrylate (PEGDA) were first used to fabricate microgel spheres (MS), and then silica nanoparticles were added to obtain graded microgel spheres (HMS). Then, PMPS-b-(PHEMA-co-PMPC) hydrophilic block copolymer was grafted onto silica nanoparticles on HMS to achieve modified graded microgel spheres (MHMS). MHMS were subsequently spin-coated onto glass substrates and allowed to self-assemble, and then thermosetting acrylic polyurethane resins were spin-coated onto the MHMS layers to obtain durable biofouling-resistant coatings.
This coating maintains its underwater superoleophobicity even under the challenges of highly acidic or alkaline environments. Its remarkable self-healing properties are attributed to the swelling of MHMS and the replenishment of the surface by the hydrophilic copolymer when immersed in water.
Inorganic Nanoparticles-Reinforced Coatings
Hydrophilic polymer-grafted nanoparticles have been widely studied and applied as an easy-to-modify and highly versatile platform. Alfa Chemistry designs polymer shell structures around inorganic nanomaterials for combined durability and surface hydrophilicity. To generate superoleophobic and anti-biofouling coatings, we cast methacryloyloxypropyltrimethoxysilane (MPS)-SiO2/PNIPAM (N-isopropylacrylamide) hybrid nanoparticles (HNS) into epoxy resin (ER) adhesives by casting layer. In the intermediate layer, the ER serves as a physical support for hybrid nanoparticles and their hierarchical structure.
PEG, another commonly used hydrophilic polymer, can also be grafted onto silica nanoparticles. Examples include SiO2-PEG based acrylic polyurethane (APU) coatings for durable outdoor antifouling applications.
Fig 2. Synthetic route and preparation of the durable underwater superoleophobic coating. (Hu J, et al. 2019)
Hydrolysis-Based Coatings
A new strategy is an eco-friendly hydrolyzable anti-biofouling polyurethane coating with poly (lactic acid) chain segments and natural antifouling agents. Biogenic PLA is used to build hydrolyzable chain segments in polyurethane for self-renewal. In addition a natural anti-biofouling agent, butenolactone, was incorporated into the coating to obtain synergistic anti-biofouling properties. The long-term durability of the coating was tested in a real marine environment for 3 months. The control PVC coating was heavily covered by marine organisms, while only 7% of the new polyurethane coating was covered by biofouling.
Layer-by-Layer Assembled Surfaces
Layer-by-layer (LbL) assemblies for the fabrication of multilayer films are receiving increasing attention due to their simplicity and precise control of surface composition and thickness. We use this technique to prepare amphoteric polymer surfaces on a variety of substrates, including stainless steel, textiles, and wood, for durable corrosion and biofouling-resistant applications.
Fig 3. Schematic illustration of the layer-by-layer assembled zwitterionic coated surface. (Huang Z, et al. 2020)
PEG films can also be easily deposited on a variety of substrates through polydopamine-mediated bonding. Layer-by-layer assembly proves the simplicity required to achieve higher thicknesses by depositing alternating component layers compared to other common methods for fabricating multilayer films with long-lasting durability.
Semi-Interpenetrating Network-Based Coatings
We also investigated semi-interpenetrating polymer networks (SIPNs) consisting of one or more networks with interpenetrating linear polymers for anti-biofouling and water purification applications. SIPN provides an easily tunable structure for enhanced mechanical and chemical stability of hydrophilic polymers.
Alfa Chemistry copolymerized sulfobetaine methacrylate (SBMA) and acrylamide (Am) monomers with the crosslinker N,N'-methylenebisacrylamide (MBA) to form SIPN by in situ free-radical polymerization with PVA. The mechanical properties of charged SIPN were determined by tensile. The mechanical properties of the charged SIPN were determined by tensile strength tests, and the tensile strength and elastic modulus were significantly increased after the addition of the PVA network, indicating that PVA enhanced the mechanical properties of the coating.
References
- Lewis A. L, et al. (2000). "Phosphorylcholine-Based Polymers and Their Use in The Prevention of Biofouling." Colloids Surf B: Biointerfaces. 18: 261-275.
- Hu J, et al. (2019). "A New Anti-Biofilm Strategy of Enabling Arbitrary Surfaces of Materials and Devices with Robust Bacterial Anti-Adhesion via A Spraying Modified Microsphere Method." J Mater Chem A. 7: 26039-26052.
- Huang Z, et al. (2020). "Networked Zwitterionic Durable An Tibacterial Surfaces." ACS Appl Bio Mater. 3: 911-919.
