Contents
1. Introduction Page No.
2. Dynamic Surface Antifouling (DSAF) Strategy Page No.
3. Degradable Polymer Page No.
3.1. Degradable Polyurethanes Page No.
3.2 Degradable Polyacrylates Page No.
4. Conclusions Page No.
1. Introduction
Marine biofouling referring to the accumulation of marine
microorganisms, animals, and plants has great adverse impacts on marine
industries.[1] Biofouling on ship increases its
weight and navigation resistance, resulting in additional fuel
consumption. It also accelerates the corrosion of metal, thereby
shortening the service life of marine facility.[2]Biofouling can block seawater pipelines of nuclear power plants,
reducing the cooling efficiency or even slowing down the
generators.[3] In aquaculture, biofouling can
block the mesh, decreasing the oxygen and nutrients in breeding cages,
thereby lowering the production.[4] On the other
hand, fouling organisms on vessels can migrate from one sea area to
another and affect the ecosystem.[5] Anyhow,
marine antifouling is of great economic and environmental importance.
However, due to the wide variety of biofouling and complex marine
environment, developing efficient and eco-friendly antifouling materials
and techniques remains a challenge.
In the past decades, some antifouling approaches including coatings,
mechanical treatment, electrolyzing seawater, and ultrasonic cleaning
have been developed. Among them, using antifouling coatings is the most
convenient, efficient and economic.[6] The
so-called self-polishing copolymer (SPC) coating containing tributyltin
(TBT) can efficiently prevent the settlement and growth of biofouling.
However, due to the toxicity to non-target creatures, it was banned by
the International Marine Organization in 2008.[7]Since then, development of eco-friendly and effective antifouling
coatings has been an urgent task.
In recent years, cuprous oxide SPC coatings, fouling release
coatings,[8] protein-resistant
polymers,[9] amphiphilic
polymers,[10] and biomimetic
polymers[11] have been prepared. While they have
some effectiveness in certain scenarios, they exhibit poor antifouling
performance on static conditions with short service life. Moreover, they
are unable to degrade and form marine microplastics once they are
released into the ocean.[12]
Based on a ten-year experience in marine antifouling, we put forward the
strategy of Dynamic Surface Antifouling (DSAF), a changeable surface can
renew itself in seawater and thus weaken the adhesion of fouling
organism.[13] Alone this line, we developed high
performance antifouling materials based on biodegradable polymers. Due
to the degradation of the main polymer chain, the surface renewing is
not driven by external force, so they still have good antifouling
ability even under static conditions. They are also eco-friendly since
such degradation yields low molecular weight molecules instead of
microplastics. In this paper, we present the synthesis, structures and
properties of DSAF polymers.
2. Dynamic Surface Antifouling (DSAF) Strategy
Biofouling formation on a submerged surface is a multi-step process
involving the initial attachment of fouling organisms, secretion of
biological adhesives, and subsequent growth. DSAF polymer can renew its
surface and significantly reduce the contact time between microorganisms
and coating surface, which is not conducive to the adhesion of
biofouling.
We investigated the movement trajectory of bacteria by using digital
holographic microscopy (DHM) to understand DSAF
mechanism.[14,15] DSAF surface was constructed by
biodegradable copolymer (poly(CL-co-HL) of ε-caprolactone (CL) and
δ-hexalactone (HL). The degradation rate that characterizes the change
of the coating surface was determined by quartz crystal microbalance
with dissipation (QCM-D). Clearly, the degradation rate increased with
HL content in the range we investigated.
The adhesion of Pseudomonas sp. (P. sp. ) orEscherichia coli (E coli. ) on the coating surface was
monitored by recording and reconstructing bacterial behavior with DHM.
Subdiffusive motion of the bacteria near the surface was observed before
irreversible adhesion.[16] The mean square
displacement (MSD) of bacteria indicated that a higher degradation rate
diminished the bacterial coverage (10%-20%) and the probability of
subdiffusive motion on coating surface (Figure 1a). Accordingly, a
dynamic surface with a certain change rate can significantly hinder the
adhesion of bacteria.
Atomic force microscopy (AFM) observation showed the adhesion force
(γ ) of bacteria on dynamic surface. We can see that γsignificantly decreased as the surface self-renewal rate increased
(Figure 1b). Clearly, the self-renewal surface based on degradable
polymer can reduce adhesion strength of bacteria, thereby preventing
bacteria from irreversible adhesion so that they had to escape from the
surface (Figure 1c). DSAF surface can keep dynamic or changeable in
seawater with the ongoing hydrolytic and enzymatic degradation.