Endoscopic submucosal dissection is an established method for the removal of early cancers and large lesions from the gastrointestinal tract but is faced with the risk of perforation. To decrease this risk, a submucosal fluid cushion (SFC) is needed clinically by submucosal injection of saline and so on to lift and separate the lesion from the muscular layer. Some materials have been tried as the SFC so far with disadvantages. Here, we proposed a thermogel generated by the “block blend” strategy as an SFC. This system was composed of two amphiphilic block copolymers in water, so it was called a “block blend”. We synthesized two non-thermogellable copolymers poly­(d,l-lactide-co-glycolide)-b-poly­(ethylene glycol)-b-poly­(d,l-lactide-co-glycolide) and blended them in water to achieve a sol–gel transition upon heating in both pure water and physiological saline. We explored the internal structure of the resultant thermogel with transmission electron microscopy, three-dimensional light scattering, 13C NMR, fluorescence resonance energy transfer, and rheological measurements, which indicated a percolated micelle network. The biosafety of the synthesized copolymer was preliminarily confirmed in vitro. The main necessary functions as an SFC, namely, injectability of a sol and the maintained mucosal elevation as a gel after injection, were verified ex vivo. This study has revealed the internal structure of the block blend thermogel and illustrated its potential application as a biomaterial. This work might be stimulating for investigations and applications of intelligent materials with both injectability and thermogellability of tunable phase-transition temperatures.

Main observation and conclusion Ring‐opening polymerization (ROP) of cyclic esters in the presence of stannous octoate (Sn(Oct)2) is the main way to obtain biodegradable aliphatic polyesters, an important family of biodegradable polymers which have been widely used and still rapidly developed in the fields of biomedical polymers and environment‐friendly materials. The underlying mechanism is thought via a coordination‐insertion way, but the pathway is still open owing to the absence of direct experimental evidence. Herein, we inquire this issue through density functional theory (DFT) calculations. According to our DFT calculations and the following Curtin‐Hammett evaluation, the carbonyl oxygen has a significant advantage over the ester oxygen, and thus the ring is opened mainly through pathway A instead of pathway B. The stannous octoate is identified as a catalyst rather than an initiator. We eventually summarize the main stages during the whole polymerization of lactide.

Biodegradable polymers constitute an important class of new materials, in particular biomedical materials. While degradation has been studied extensively as a "destroy" factor of a material for many years, it is less investigated when treated as a "construction" factor to influence a material in a dynamic manner. Herein, we examined a hydrolyzable amphiphilic block copolymer and found significant reorganization of the condensed state of copolymers during degradation in water. The reorganization occurs, depending upon polymer composition and experimental condition, both mesoscopically and macroscopically, which we term as "degradation-influenced/induced self-assembly (DISA)". To this end, we developed dynamic Monte Carlo simulations by introduction of hydrolysis probability while keeping the chain microrelaxation modes. A series of dynamic Monte Carlo simulations of amphiphilic triblock copolymers was carried out in a selective solvent, and three types of DISA were revealed: micelle 1 to micelle 2, sol−gel 1 to sol−gel 2, and precipitate to sol−gel−precipitate. Subsequently, amphiphilic block copolymers poly(D,L-lactide)-bpoly(ethylene glycol)-b-poly(D,L-lactide) (PLA-PEG-PLA) were synthesized, and all of the three DISA types were confirmed in experiments of the aqueous systems of three copolymers of different block lengths. We found that the DISA was regulated by both the decrease of molecular weight (MW) and the increase of dispersity. Here the term "dispersity" emphasizes not only the conventional molecular weight distribution (MWD) of all species but also the more diversified components after degradation, which include blends of copolymers and the degradation-generated homopolymers and oligomers. We also employed fluorescence resonance energy transfer to confirm the percolated network of semibald micelles underlying the temperature-induced physical hydrogel in such systems. The present study illustrates that degradation can act as a new strategy to influence the hierarchical selfassembly of amphiphilic block copolymer chains.