Natural
fibers with functionalities have attracted considerable
attention. However, developing facile and versatile strategies to
modify natural fibers is still a challenge. In this study, cotton
fibers, the most widely used natural fibers, were partially oxidized
by sodium periodate in aqueous solution, to give oxidized cotton fibers
containing multiple aldehyde groups on their surface. Then poly(hexamethylene
guanidine) was chemically grafted onto the oxidized cotton fibers
forming Schiff bases between the terminal amines of poly(hexamethylene
guanidine) and the aldehyde groups of oxidized cotton fibers. Finally,
carbon–nitrogen double bonds were reduced by sodium cyanoborohydride,
to bound poly(hexamethylene guanidine) covalently to the surface of
cotton fibers. These functionalized fibers show strong and persistent
antibacterial activity: complete inhibition against Escherichia coli and Staphylococcus
aureus was maintained even after 1000 consecutive
washing in distilled water. On the other hand, cotton fibers with
only physically adsorbed poly(hexamethylene guanidine) lost their
antibacterial activity entirely after a few washes. According to Cell
Counting Kit-8 assay and hemolytic analysis, toxicity did not significantly
increase after chemical modification. Attributing to the hydrophilicity
of poly(hexamethylene guanidine) coatings, the modified cotton fibers
were also more hygroscopic compared to untreated cotton fibers, which
can improve the comfort of the fabrics made of modified cotton fibers.
This study provides a facile and versatile strategy to prepare modified
polysaccharide natural fibers with durable antibacterial activity,
biosecurity, and comfortable touch.
Poly(ethylene glycol) (PEG) is widely used for covalent conjugation with therapeutic molecules to prolong their biocirculation time. This effect can be further improved by increasing the molecular weight of PEG. However, because of the lack of effective degradation mechanisms, PEG with a molecular mass over 10 kDa is hardly excreted from the body, thus accumulating in the liver and kidneys which increases the risk of toxicity. Herein, biodegradable PEGs were synthesized by linking PEG backbones with ester bonds through the polycondensation of PEG diols and dicarboxylic acids. To overcome the difficulties in synthesis of high molecular weight products by traditional esterification strategies, a novel carboxyl-ester transesterification mechanism was developed to produce biodegradable PEGs with a molecular weight up to 112.6 kDa. It was confirmed that these biodegradable PEGs show comparable characteristics of nondegradable PEGs with similar molecular weights, but they can be metabolized after the cleavage of ester bonds.
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