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. 2021 Sep 30;13(19):3365. doi: 10.3390/polym13193365

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© 2021 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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Optical images (a,b), scanning electron microscope (SEM) images (c) of BC samples and ultrastructural transmission electron microscopy (TEM) images (d) of BC samples [24,27,28].