Chengcheng Zhang

Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O– in pTMAO and water, and weaker interaction between O– and metal cations due to the strong repulsion from the N+ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.

Titanium and its alloys are widely used in aerospace, biomedicine, chemical industries, and other fields due to the excellent properties as high specific strength, strong corrosion resistance, and superior biocompatibility. With the development of mechanical industry, especially of aerospace, the higher fatigue performance of titanium alloys is demanded. Generally, fatigue cracking originates from the materials surface, so the surface roughness, residual stress, and microstructure in surface layer are believed to be the dominant factors in affecting the fatigue crack initiation and propagation, as well as the fatigue strength. Thus, by means of the mechanical surface enhancement techniques, the achievement of reducing the surface roughness, introducing the residual compressive stress, improving the surface microstructure and increasing the surface hardness could significantly enhance the fatigue strength. The effects of various mechanical surface treatments, such as deep rolling, shot peening, and laser shock peening, on surface integrity and fatigue properties of Ti-6Al-4V were reviewed in this article. By comparing surface roughness, hardness, residual stress, surface grain size, depth of grain refinement layer, fatigue properties at room and high temperatures, and residual stress relaxation during fatigue of different surface-treated Ti-6Al-4V, the advantages and the limitations of these surface treatments were identified and evaluated.

The benefits of incorporating amphiphilic properties into antifouling and fouling-release coatings are well-established. The use of sequence-defined peptides and peptoids in these coatings allows precise control over the spacing and chemistry of the amphiphilic groups, but amphiphilic peptoids have generally outperformed analogous peptides for reasons attributed to differences in backbone structure. The present work demonstrates that the superior properties of peptoids relative to peptides are primarily attributable to a lack of hydrogen bond donors rather than to their secondary structure. A new amphiphilic peptoid was designed containing functional groups similar to those typically found on a hydrogen-bonding peptide backbone. This peptoid and a non-hydrogen-bonding peptoid analogue were incorporated as side chains in PDMS-based polymer scaffolds. Bioassays with the soft algal fouling organisms Ulva linza and Navicula incerta indicate that hydrogen bonding largely determines the differences seen between similar peptide and peptoid species, while sum frequency generation vibrational spectroscopy suggests that the presence of hydrogen bond donors enhances interfacial water structuring. This reduced initial U. linza adhesion, but attached algae were more strongly bound by hydrogen-bonding interactions. Consequently, amphiphilic peptoid materials lacking hydrogen bond donors are better suited to resist marine fouling, with enhanced release of U. linza and similar performance against N. incerta relative to hydrogen-bonding analogues.