Host-defense peptides
(HDPs) are produced by eukaryotes to defend
against bacterial infection, and diverse synthetic polymers have recently
been explored as mimics of these natural peptides. HDPs are rich in
both hydrophobic and cationic amino acid residues, and most HDP-mimetic
polymers have therefore contained binary combinations of hydrophobic
and cationic subunits. However, HDP-mimetic polymers rarely duplicate
the hydrophobic surface and cationic charge density found among HDPs
(HuK.23750051Macromolecules2013461908); the charge and hydrophobicity are generally higher among the polymers.
Statistical analysis of HDP sequences (WangG.18957441Nucleic
Acids Res.200937D933) has revealed that serine (polar but uncharged)
is a very common HDP constituent and that glycine is more prevalent
among HDPs than among proteins in general. These observations prompted
us to prepare and evaluate ternary nylon-3 copolymers that contain
a modestly polar but uncharged subunit, either serine-like or glycine-like,
along with a hydrophobic subunit and a cationic subunit. Starting
from binary hydrophobic–cationic copolymers that were previously
shown to be highly active against bacteria but also highly hemolytic,
we found that replacing a small proportion of the hydrophobic subunit
with either of the polar, uncharged subunits can diminish the hemolytic
activity with minimal impact on the antibacterial activity. These
results indicate that the incorporation of polar, uncharged subunits
may be generally useful for optimizing the biological activity profiles
of antimicrobial polymers. In the context of HDP evolution, our findings
suggest that there is a selective advantage to retaining polar, uncharged
residues in natural antimicrobial peptides.
Rapid response and strong mechanical properties are desired for smart materials used in soft actuators. A bioinspired hybrid hydrogel actuator was designed and prepared by series combination of three trunks of tough polymer-clay hydrogels to accomplish the comprehensive actuation of "extension-grasp-retraction" like a fishing rod. The hydrogels with thermo-creep and thermo-shrinking features were successively irradiated by near-infrared (NIR) to execute extension and retraction, respectively. The GO in the hydrogels absorbed the NIR energy and transformed it into thermo-energy rapidly and effectively. The hydrogel with adhesion or magnetic force was adopted as the "hook" of the hybrid hydrogel actuator for grasping object. The hook of the hybrid hydrogel actuator was replaceable according to applications, even with functional materials other than hydrogels. This study provides an innovative concept to explore new soft actuators through combining response hydrogels and programming the same stimulus.
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