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Ryan Clark
Ryan Clark

Principles Of Polymer Systems, Sixth Edition Download Pdf |VERIFIED|

Maintaining a balance between depth and breadth, the Sixth Edition of Principles of Polymer Systems continues to present an integrated approach to polymer science and engineering. A classic text in the field, the new edition offers a comprehensive exploration of polymers at a level geared toward upper-level undergraduates and beginning graduate stu

Principles of Polymer Systems, Sixth Edition download pdf

On the other hand, stimuli-responsive nanocarriers have shown the ability to control the release profile of drugs (as a triggered release) using external factors such as ultrasound [96], heat [97,98,99], magnetism [100, 101], light [102], pH [103], and ionic strength [104], which can improve the targeting and allow greater dosage control (Fig. 2). For example, superparamagnetic iron oxide nanoparticles are associated with polymeric nanocarriers [105] or lipids [106] to initially stimulate a controlled release system by the application of external magnetic field. In addition, Ulbrich et al. [107] revised recent achievements of drug delivery systems, in particular, on the basis of polymeric and magnetic nanoparticles, and also addressed the effect of covalently or noncovalently attached drugs for cancer cure [107]. Moreover, Au/Fe3O4@polymer nanoparticles have also been synthesized for the use in NIR-triggered chemo-photothermal therapy [108]. Therefore, hybrid nanocarriers are currently among the most promising tools for nanomedicine as they present a mixture of properties of different systems in a single system, thus ensuring materials with enhanced performance for both therapeutic and diagnostic applications (i.e., theranostic systems). Despite this, little is known about the real mechanisms of action and toxicity of drug delivery systems, which open opportunity for new studies. In addition, studies focusing on the synthesis of nanocarriers based on environmentally safe chemical reactions by implementing plant extracts and microorganisms have increased [10].

Discovering mechanisms governing organelle assembly is a fundamental pursuit in biology. The centriole is an evolutionarily conserved organelle with a signature 9-fold symmetrical chiral arrangement of microtubules imparted onto the cilium it templates. The first structure in nascent centrioles is a cartwheel, which comprises stacked 9-fold symmetrical SAS-6 ring polymers emerging orthogonal to a surface surrounding each resident centriole. The mechanisms through which SAS-6 polymerization ensures centriole organelle architecture remain elusive. We deploy photothermally-actuated off-resonance tapping high-speed atomic force microscopy to decipher surface SAS-6 self-assembly mechanisms. We show that the surface shifts the reaction equilibrium by 104 compared to solution. Moreover, coarse-grained molecular dynamics and atomic force microscopy reveal that the surface converts the inherent helical propensity of SAS-6 polymers into 9-fold rings with residual asymmetry, which may guide ring stacking and impart chiral features to centrioles and cilia. Overall, our work reveals fundamental design principles governing centriole assembly.

To understand how the fundamental SAS-6 building block can self-assemble into ring polymers with the correct symmetry and guide proper organelle architecture, it is necessary to quantitatively probe the properties of the SAS-6 surface polymerization reaction. Cell free assays have been transformative for revealing the fundamental features of other self-assembling cellular polymers, including microtubules, F-actin and FtsZ rings (reviewed in refs. 22,23,24). Understanding such fundamentals of polymer dynamics has proven critical not only for uncovering the self-organizing properties of the corresponding cytoskeletal networks, but also for revealing how these properties can be harnessed and modulated in the cellular context (reviewed in ref. 25). By analogy, unraveling the fundamental surface polymerization properties underlying SAS-6 ring assembly is expected to shed critical light on the structural principles governing biogenesis of centriole architecture.

Our work reveals that the presence of a surface makes two fundamental contributions at the onset of centriole assembly. First, the surface catalyzes SAS-6 self-assembly, shifting the equilibrium by a factor 104 from that in solution. This equilibrium shift provides a potential rationale for why SAS-6 ring polymers form exclusively on the torus of the resident centriole and not in the cytoplasm. Intriguingly, FRAP experiments in emerging centrioles of Drosophila embryos indicate that SAS-6 is incorporated into the cartwheel on the Asl torus, from the proximal end of the nascent organelle47, potentially reflecting the catalytic impact of such a surface. More generally, the equilibrium shift unveiled here reinforces the importance of the interplay between cytoplasmic and surface compartments in cellular diffusion-reaction systems (reviewed in48), as seen for instance with the catalytic effect of membranes in promoting assembly of macromolecular complexes such as pore forming toxins49,50. Our findings establish that these physico-chemical principles apply not only for interactions between cytosol and membranes, but also at the space scale of organelle assembly. In the cellular context, the torus surface is expected to efficiently restrict SAS-6 ring polymer assembly to that location. Given that this surface is parallel to the long axis of the resident centriole (see Fig. 1a), such surface-mediated catalysis could readily explain how the nascent centriole systematically emerges in an orthogonal fashion.

As opposed to the previously introduced corpora, a number of corpora have also been described that are more focused on chemistry and chemical entities rather than on biological aspects of chemical substances. They provided important lessons for the construction of the CHEMDNER corpus. Nevertheless they also showed crucial differences in scope, used document collections, availability (both of annotation guidelines together with the resulting corpus), format and size. Early attempts to build a chemical NER systems, due to the lack of a chemical entity text corpus, explored the use of lexical resources related to chemistry derived from the UMLS Metathesaurus, which was used for training and testing various methods [24]. Wren published a machine learning method trained on the chemical ChemID database and used it to find chemical entity mentions in PubMed abstracts. Due to the lack of an evaluation text corpus he could only assess the precision on a small sample of putative chemical names extracted automatically [25]. Another publication by Zhang described the use of chemical annotations done by the indexers of the National Library of Medicine (NLM) [26] as a proxy for evaluating a chemical entity recognition system. These annotations are only done at the document level without specifying the exact entity mention offsets within the abstract. The NLM indexers annotate topic-related chemical concepts and therefore the indexing is not exhaustive. This type of annotation only reflects the understanding of the topic by the individual indexer. The document indexing was based on terms of the MeSH tree associated with chemicals (Chemicals and Drugs branch and supplementary concept records called MeSH substances). Narayanaswamy and colleagues described a small corpus of 55 abstracts selected by a keyword search (using as query acetylates, acetylated and acetylation) that contained also a small number of chemical names [27]. The text corpus introduced in the article describing the ChemicalTagger system consisted in 50 paragraphs from the experimental sections of full text articles selected using a keyword search related to polymer synthesis. It is concerned with the annotation of chemical phrases rather than on chemical entity mentions and the associated link to the annotation guidelines was not functional anymore (broken link) [28]. The ChEBI Patent Gold Standard corpus was created as a joint effort between curators of the ChEBI database and the European Patent Office [29]. It involved the annotation of chemical entities in 40 patent documents (18,061 chemical entities, 47% of them were initially linked to ChEBI records). This corpus is publicly available but more details on the annotation criteria and process were not released together with the corpus. This corpus was generated manually without using any software to create pre-annotations. An updated version of this corpus was also published to increase the initial mapping of mentions by using an updated version of the ChEBI database (53.7% of ChEBI mapped chemical entities) [30]. A recent effort carried out by both academia and commercial teams resulted in a larger corpus of 200 patents annotated with chemical information [31]. These patents were automatically pre-annotated with chemical names and human curators revised and corrected mis-identified pre-annotations and added missing chemical mentions manually. The annotation guidelines used for constructing this corpus were partially based on the annotation guidelines that we have released for the CHEMDNER corpus, as detailed later in this manuscript. A relevant contribution to the development of chemical corpora was provided by the authors of the Sciborg corpus [32, 33] and the Chemistry PubMed corpus by Corbett et al. [33, 34] Unfortunately neither of these two corpora are publicly available, but the underlying annotation criteria shared by both datasets had a deep impact on the annotation guidelines prepared for the CHEMDNER corpus. The Sciborg corpus consisted of 42 full text chemistry research papers annotated manually with chemical compounds while the chemistry PubMed corpus by Corbett et al. consisted in an hand-annotated corpus of 500 PubMed abstracts selected using the query 'metabolism[Mesh] AND drug AND hasabstract'. Both corpora consisted in exhaustively annotated chemical texts done by chemists according to very detailed annotation rules (31 pages long guideline containing 93 rules, together with example cases [33]). Different annotation classes were defined to deal not only with chemical compounds but also with chemical reactions, chemical adjectives, enzymes and chemical prefixes. 350c69d7ab


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