Some amphiphilic block copolymers exhibit sol–gel transition in water upon heating, which affords a promising injectable thermogel in clinic and an interesting soft matter system. While ABA-, BAB-, and AB-type block copolymers have all been reported, little is known about the comparative study of supermolecular structures of these polymer types in the physical hydrogels, which hinders the understanding of the universal mechanism of structural changes during thermogelling. Herein, a thermogellable aqueous system of ABA triblock copolymer poly­(d,l-lactide-co-glycolide)-b-poly­(ethylene glycol)-b-poly­(d,l-lactide-co-glycolide) was investigated by both experiments and computer simulations, with the corresponding AB diblock copolymer and BAB triblock copolymer as controls. The copolymers were synthesized via ring-opening polymerization, and their thermogelling behaviors in water were analyzed with transmission electron microscopy, three-dimensional dynamic light scattering, and so forth. Fluorescence resonance energy transfer, temperature-dependent 13C NMR, and rheological measurements were also carried out to investigate the internal structures and their evolutions during the sol–gel transition. A dynamic Monte Carlo simulation was operated to analyze the thermogelation further. We found two states with different structures in the thermogel window of the ABA block copolymer. The formation of a hydrophobic channel evolved from the semibald micelle was revealed as the key universal cue triggering the physical gelation for all types of thermogellable copolymers. Based on our structural studies, the molecular design principles for the thermogellable copolymers have been established.

As an injectable and biodegradable hydrogel, thermogels of amphiphilic block copolymers of polyester and polyether in water show great potential in biomedical fields. It is challenging to reveal the mechanism behind the reversed thermogelling with sol−gel transition upon heating. Herein, a computer simulation and corresponding experiments are combined to examine aqueous systems of amphiphilic diblock copolymer of methoxypoly(ethylene glycol) and poly(D,L-lactideco-glycolide). We synthesized the copolymer via ring-opening polymerization and characterized the thermogelling behavior of its aqueous solution by 3D dynamic light scattering and diffusing wave spectroscopy. Fluorescence resonance energy transfer and 13 C NMR spectroscopy etc. were also adopted to explore the structure change during thermogelation. A dynamic Monte Carlo simulation was performed for a corresponding multichain system. A new type of micelle, the semi-bald micelle, was first proposed as the precursor for thermogelling and was confirmed from both simulations and experiments. We demonstrate that the thermogel structure is a percolated micelle network with hydrophobic channels that evolved from the semi-bald micelles. The thermogelling mechanism is discussed at the chain level. On the basis of the mechanism study, we put forward the molecular design principle of the thermogels.

The new principle and technique to tune biodegradation rates of biomaterials is one of the keys to the development of regenerative medicine and next-generation biomaterials. Biodegradable stents are new-generation medical devices applied in percutaneous coronary intervention, etc. Recently, both corrodible metals and degradable polymers have drawn much attention in biodegradable stents or scaffolds. It is, however, a dilemma to achieve good mechanical properties and appropriate degradation profiles. Herein, we put forward a metal-polymer composite strategy to achieve both. Iron stents exhibit excellent mechanical properties but low corrosion rate in vivo. We hypothesized that coating of biodegradable aliphatic polyester could accelerate iron corrosion due to the acidic degradation products, etc. To demonstrate the feasibility of this composite material technique, we first conducted in vitro experiments to affirm that iron sheet corroded faster when covered by polylactide (PLA) coating. Then, we fabricated three-dimensional metal-polymer stents (MPS) and implanted the novel stents in the abdominal aorta of New Zealand white rabbits, setting metal-based stents (MBS) as a control. A series of in vivo experiments were performed, including measurements of residual mass and radial strength of the stents, histological analysis, micro-computed tomography, and optical coherence tomography imaging at the implantation site. The results showed that MPS could totally corrode in some cases, whereas iron struts of MBS in all cases remained several months after implantation. Corrosion rates of MPS could be easily regulated by adjusting the composition of PLA coatings.

Cartilage is difficult to self‐repair and it is more challenging to repair an osteochondral defects concerning both cartilage and subchondral bone. Herein, it is hypothesized that a bilayered porous scaffold composed of a biomimetic gelatin hydrogel may, despite no external seeding cells, induce osteochondral regeneration in vivo after being implanted into mammal joints. This idea is confirmed based on the successful continuous 3D‐printing of the bilayered scaffolds combined with the sol‐gel transition of the aqueous solution of a gelatin derivative (physical gelation) and photocrosslinking of the gelatin methacryloyl (gelMA) macromonomers (chemical gelation). At the direct printing step, a nascent physical hydrogel is extruded, taking advantage of non‐Newtonian and thermoresponsive rheological properties of this 3D‐printing ink. In particular, a series of crosslinked gelMA (GelMA) and GelMA‐hydroxyapatite bilayered hydrogel scaffolds are fabricated to evaluate the influence of the spacing of 3D‐printed filaments on osteochondral regeneration in a rabbit model. The moderately spaced scaffolds output excellent regeneration of cartilage with cartilaginous lacunae and formation of subchondral bone. Thus, tricky rheological behaviors of soft matter can be employed to improve 3D‐printing, and the bilayered hybrid scaffold resulting from the continuous 3D‐printing is promising as a biomaterial to regenerate articular cartilage.

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