ROS-responsive biomaterials alleviate the oxidative stress in tissue microenvironments, promoting tissue regeneration and disease therapy.

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Bottlebrush molecules are branched polymers with a long linear backbone densely grafted by many relatively short linear side chains. Such a unique molecular architecture enables bottlebrush polymers with properties and functions inaccessible by their linear counterparts. The existing understanding is that, in melts of bottlebrush polymers, the interbackbone distance decreases as the grafting density of side chains becomes smaller. Here, we experimentally discover a behavior opposite to all existing works: the interbackbone distance increases monotonically as the grafting density decreases. To explain these remarkable experimental findings, we develop a theory by accounting for the incompatibility between the backbone and side chains within a bottlebrush molecule. The backbone polymer folds into a cylindrical core with all grafting sites on its surface to reduce interfacial free energy. As the grafting density decreases, the backbone collapses; this process not only increases the diameter of the cylindrical core but also reduces the distance between grafting sites in space, such that the extension of side chains is not alleviated. Our discovery presents a paradigm-shifting understanding of the molecular structure of bottlebrush polymers.

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Paralytic shell sh toxins (PSTs) produced by certain marine dino agellates accumulate in lter-feeding marine bivalves. We used LC-MS/MS to detect and quantify 13 PSTs in 188 shell sh samples of 14 species collected from Shenzhen city's Buji seafood wholesale market from March 2019 to February 2020. Twenty-six of 188 shell sh samples (13.8%) were PST-positive, with highest values in samples of the Noble clam Chlamys nobilis (10/34, 29.4%). Samples originating from Nan'ao island among 11 source sites in China recorded the highest detected rate (7/17, 41.2%). Samples containing PSTs were concentrated in Spring and Winter, with the highest levels in March > December > January. Among PSTs detected, C1 was dominant. Acute dietary exposure assessments for Shenzhen residents were based on P 99 consumption data (139.2g/day) and maximum PST concentration for each shell sh species. The outcome for Chlamys nobilis was 2.4 ~ 3.7-fold higher than recommended ARfDs (0.5 ~ 0.7 µg STX eq./kg bw/day). Mean PST concentration (10.9 ~ 134.1 µg STX Eq. /kg), mean shell sh consumption (4.8 g/day) and P 99 consumption data were used to assess chronic dietary exposure. The results were lower than the recommended ARfDs. In conclusion, residents in Shenzhen are at risk for acute PST poisoning, while relatively safe from chronic PST exposure.