Hydrolyzable Polyureas Bearing Hindered Urea Bonds

Hydrolyzable polymers are widely used materials that have found numerous applications in biomedical, agricultural, plastic, and packaging industrials. They usually contain ester and other hydrolyzable bonds, such as anhydride, acetal, ketal, or imine, in their backbone structures. Here, we report the first design of hydrolyzable polyureas bearing dynamic hindered urea bonds (HUBs) that can reversibly dissociate to bulky amines and isocyanates, the latter of which can be further hydrolyzed by water, driving the equilibrium to facilitate the degradation of polyureas. Polyureas bearing 1-<i>tert</i>-butyl-1-ethylurea bonds that show high dynamicity (high bond dissociation rate), in the form of either linear polymers or cross-linked gels, can be completely degraded by water under mild conditions. Given the simplicity and low cost for the production of polyureas by simply mixing multifunctional bulky amines and isocyanates, the versatility of the structures, and the tunability of the degradation profiles of HUB-bearing polyureas, these materials are potentially of very broad applications

Drug-Initiated, Controlled Ring-Opening Polymerization for the Synthesis of Polymer–Drug Conjugates

Paclitaxel, a polyol chemotherapeutic agent, was covalently conjugated through its 2′-OH to polylactide with 100% regioselectivity via controlled polymerization of lactide mediated by paclitaxel/(BDI-II)­ZnN­(TMS)₂ (BDI-II = 2-((2,6-diisopropylphenyl)­amino)-4-((2,6-diisopropylphenyl)­imino)-2-pentene). The steric bulk of the substituents on the <i>N</i>-aryl groups of the BDI ligand drastically affected the regiochemistry of coordination of the metal catalysts to paclitaxel and the subsequent ring-opening polymerization of lactide. The drug-initiated, controlled polymerization of lactide was extended, again with 100% regioselectivity, to docetaxel, a chemotherapeutic agent that is even more structurally complex than paclitaxel. Regioselective incorporation of paclitaxel (or docetaxel) to other biopolymers (i.e., poly­(δ-valerolactone), poly­(trimethylene carbonate), and poly­(ε-caprolactone)) was also achieved through drug/(BDI-II)­ZnN­(TMS)₂-mediated controlled polymerization. These drug–polylactide conjugates with precisely controlled structures are expected to be excellent building blocks for drug delivery, coating, and controlled-release applications

Water-Soluble Poly(l‑serine)s with Elongated and Charged Side-Chains: Synthesis, Conformations, and Cell-Penetrating Properties

Water-soluble poly­(l-serine)­s bearing long side-chain with terminal charge groups were synthesized via ring-opening polymerization of <i>O</i>-pentenyl-l-serine <i>N</i>-carboxyanhydride followed by thiol–ene reactions. These side-chain modified poly­(l-serine)­s adopt β-sheet conformation in aqueous solution with excellent stability against changes in pH and temperature. These water-soluble poly­(l-serine) derivatives with charged side-chain functional groups and stable β-sheet conformations showed membrane-penetrating capabilities in different cell lines with low cytotoxicity

Trigger-Responsive Poly(β-amino ester) Hydrogels

Water-soluble, acrylate-terminated poly­(β-amino esters) with built-in trigger-responsive domains were synthesized through Michael addition of trigger-responsive diacrylates and primary amines. They were used as macromolecular precursors for photoinitiated cross-linking reactions to prepare trigger-responsive hydrogels for protein encapsulation. The encapsulated proteins could be rapidly released upon external triggering

Algorithm 4: Similarity computation algorithm based on random walk.

<p>Algorithm 4: Similarity computation algorithm based on random walk.</p

Collaboration network of scientists at the Santa Fe Institute.

<p>(a) The ground truth community structure; (b) The community structure detected by the proposed algorithm; (c) The community structure obtained by Fast<i>Q</i>; (d) The community structure aggregated from 30 results of LPA; (e) The first-level community structure extracted by Infohiermap; (f) The second-level community structure extracted by Infohiermap; (g) The community structure identified by PPC.</p

A simple two-community network.

<p>If the nodes are selected according to their degree values, only node will be selected, and community will be ignored. However, using the <i>score</i> value in conjunction with degree value of every node in the network as the condition, we will select node (or ) from the network at least, which means that the selected nodes can cover all of the ground truth communities. (The different node shapes and shades indicate different communities, the black lines are the edges within communities, and the light-gray connections represent the edges across different communities. This illustration style is also applied in the following figures.)</p

Zachary's karate club network.

<p>(a) The ground truth community structure; (b) The community structure extracted by the proposed algorithm; (c) The community structure extracted by Fast<i>Q</i>; (d) The community structure aggregated from 30 community structures extracted by LPA; (e) The community structure detected by Infohiermap; (f) The community structure identified by PPC.</p

The evolutions of the three metrics on the scientist collaboration network.

<p>The evolutions of the three metrics on the scientist collaboration network.</p

Statistical information of the networks.

<p>Statistical information of the networks.</p