Articular cartilage (AC) defects can lead to joint destruction and osteoarthritis, necessitating immediate intervention to prevent progressive cartilage degeneration. To support cartilage repair, hydrogels have been explored due to their structural similarity to the extracellular matrix (ECM), offering a hydrated microenvironment for chondrocytes that promotes cell adhesion and proliferation. Polyurethane (PU) is a promising candidate with adjustable mechanical properties, high biocompatibility, and degradability. Given the advantages of both hydrogels and PU for biomedical applications, functional degradable PU hydrogels present a potential solution for cartilage regeneration. This review summarizes the structure-property relationship and degradation mechanisms of PU hydrogels. Their advanced functionalities in cartilage repair are highlighted, including anti-inflammatory and antibacterial properties, controlled drug delivery, injectability, self-healing, and stimulus responsiveness. By reviewing recent advances and emerging technologies, this review provides valuable insights and a future outlook for the development of next-generation cartilage repair materials.

Polyurethanes that degrade via main-chain scission under ambient conditions were designed. Monomer precursors were synthesized via the Morita–Baylis–Hillman reaction of acrylates with terephthalaldehydic acid, followed by azidation. Subsequent Curtius rearrangement...

Programmable degradation is an important functionality for sustainable polymer materials; however, in conventional step polymerization of AA- and BB-type monomers, the polymer sequence itself has long lacked a clear and actionable definition. Polymers synthesized from AA- and BB-type monomers enable the incorporation of functional units directly into the polymer main chain, while inevitably featuring AA-BB connectivity; however, the concept of an "alternating" sequence has remained ambiguous. To address this fundamental limitation, we redefine sequence control in step polymerization by focusing on the connectivity unit rather than monomer composition. Using polyurethane as a representative model polymer, an AB-type monomer framework combined with dimeric species enables the explicit definition and practical implementation of (partially) alternating sequences. Incorporation of a photo-degradable monomer unit directly into the polymer backbone reveals pronounced sequence-dependent photo-degradability via main chain scission, which is drastically enhanced in alternating polymers, while thermal properties are likewise strongly influenced by polymer sequence. This work establishes the polymer sequence as an additional and actionable design parameter in polyurethanes as an example of step polymerization and provides a conceptual framework potentially applicable beyond polyurethanes to a broad range of AA/BB-based polymers. The utility of this framework for functional material development is demonstrated through sequence-controlled photo-degradation on the polymer main chain, offering a promising strategy toward sustainable polymer design.

ABSTRACT Since the discovery of carbon dots (CDs), the typical precursor combination of citric acid (CA)‐urea has been widely used in the scientific community to explore the formation mechanism and luminescence behavior of CDs. However, there have only been a few reports on the synthesis of CDs featuring aggregation‐induced emission (AIE) characteristics. In this study, CA and urea were used to synthesize hydrophilic red‐emissive carbon dots (R‐CDs) that exhibit blue fluorescence in water (dispersed state) and red fluorescence in DMF (aggregated state). The study reveals that the photoluminescence of R‐CDs is governed by π–π stacking interactions between solute molecules as well as solvent effects between solute and solvent molecules, leading to solvent‐responsive emission behavior. By tuning the solvent polarity, the intermolecular distance between R‐CDs can be adjusted, thereby influencing their photoluminescent properties. Taking advantage of the solvent‐responsive color change, anticounterfeiting printing and information encryption applications were designed. Moreover, by combining R‐CDs with poly(vinyl alcohol) (PVA), hydrogel‐based fluorescent information‐encoding materials were successfully fabricated.

A new photodegradable AB-type monomer (3-nitro,4-hydroxylmethyl benzoylazide) was developed for the synthesis of polyurethanes featuring a photodegradability, which could be finely controlled through copolymerization. Because of the o-nitrobenzyl alcohol framework on the monomer, the resulting polymer was decomposed by UV irradiation at 365 nm. Moreover, since the introduction of a nitro group on the AB-type monomer framework reduced the reactivity of the alcohol group and increased that of the isocyanate group, copolymerization with other monomers induced a certain preference of diad patterns, which would affect the photodegradability of polyurethanes. The results suggested the AB-type monomer protocol enables the synthesis of more precisely designed polyurethane structures than the conventional synthesis, i.e., by a polyaddition between diol and di-isocyanate.

AB-type monomers enable a more flexible molecular design of polyurethane synthesis than the conventional methods by the polyaddition of diol and di-isocyanate, that is, various side chain structures can be easily integrated on the former. Meanwhile, the impact of the substituent effect has not been clearly investigated on the synthesis and properties of polyurethanes from AB-type monomers despite its fundamental importance. Herein, we developed four new AB-type monomers exhibiting certain substituents to study the above issue. Interestingly, the introduction of a benzene ring to the side chain moiety did not significantly affect the thermal properties of the polyurethane compared with the corresponding polymer having an n-butyl substituent, while that to the main chain moiety drastically changed the reactivity of the monomer and the thermal properties of the resulting polymer. Moreover, a 2-ethylhexyl side chain structure increased the solubility and flexibility of the polyurethane framework while maintaining the high monomer reactivity at the same time, indicating it would work as a useful comonomer to increase the processability of rigid polymers.

Inspired by precisely designed protein synthesis from amino acids, we demonstrate precise polyurethane synthesis from novel AB-type monomers exhibiting side chain functionalities to implement an elaborate molecular/material design, which has been difficult to address by a conventional method. To realize this idea, we designed acylazide precursor monomers having alcohol moieties, which can transform into actual AB-type monomer species having isocyanate and alcohol groups by Curtius rearrangement. Polymers from the monomers afforded self-standing films that showed very different mechanical properties from conventional polyurethanes. The detailed kinetic analysis of the Curtius rearrangement and (co)polymerization studies revealed that the polyurethane backbone structure could be flexibly programmed by the choice or combination of monomers. Moreover, the resulting polymers were further functionalized by postpolymerization modification, enabling fine-tuning of their properties. Overall, the utility of this AB-type monomer protocol to implement tailored polyurethane synthesis is thoroughly studied.

Sliding graft copolymer (SGC) is a polyrotaxane (PR) composed of a poly(ethyelene glycol) (PEG) axle and α-cyclodextrins (α-CDs) substituted with polymer graft-chains. We have previously reported a sharp-endothermic phase transition of SGCs, which was expected due to the high mobility of graft chains by the mechanical linkage of PRs. To examine this hypothesis, SGCs with well-defined structures were prepared. PRs consisting of monoazidated α-CD and PEG were grafted with monomethoxy poly(ethylene glycos)s (mPEGs) via click chemistry. The SGC bearing shortest graft chains (mPEG750) did not exhibit endotherm, whereas those with side chains of mPEG2000 and mPEG4000 underwent endothermic phase transition. However, values of the transition temperatures and those of melting enthalpies were lower than those of unmodified mPEGs. Unlike our previous report, the SGCs synthesized here contained densely-packed α-CDs, which were capable of rotational movement but not translational movement. The endothermic peak observed for the present SGC is relatively broader than that observed for our previous SGC, which suggests that the mobility of α-CDs were critical to induce sharp-endothermic phase transition.

An orthogonal agent having both alcohol and acylazide groups was used to construct novel polyurethanes by a simple synthetic process. Ring-opening polymerization (ROP) of delta-valerolactone from the orthogonal agent afforded a crystalline polymer having acylazide initiation end, while that of delta-decanolactone resulted in an amorphous polymer. Since acylazide groups undergo thermally induced Curtius rearrangements to yield isocyanate groups, simple heating of above polymers gave macromonomers having both an isocyanate initiation end and an alcohol termination end, which afforded corresponding polyurethane by self-polyaddition in a bulk condition without any additives. Meanwhile, kinetic analysis of the Curtius rearrangement revealed that a quantitative conversion was reached within a short reaction time, for example at 110 degrees C for 30 min, or at 100 degrees C for 1 h. Moreover, obtained polyurethane species showed unique self-immolative type thermal degradation behavior. Considering the above, this orthogonal agent turned out to be useful to construct various polyurethane structures by a facile synthetic process, which would contribute to precise polymer synthesis and sequence defined polymer synthesis. image

Owing to their dynamic natures, rotaxane-based polymers are attractive motifs for developing stimuli-responsive materials. However, the accurate control of the rotaxane structure, which can be achieved via multistep synthesis, is key to utilizing the material. Concurrently, implementing a scale-up synthesis procedure to exploit the application potential of rotaxane-based polymers induces structural ambiguities, thereby presenting a significant trade-off between realizing inexpensive production and defined structures. To overcome this rotaxane-synthesis challenge, cyclodextrin (CD) can be employed as a promising alternative owing to its low production cost. Thus, this study presents an overview of the precise synthesis of CD-based rotaxane and its application to polymers to simultaneously ensure inexpensive production and realize defined structures.

Synthesis of polyurethane-type poly[3]rotaxanes is achieved by polyaddition between a cyclodextrin (CD)-based [3]rotaxane diol and various diisocyanate species, which provide a more defined structure compared to conventional polyrotaxane syntheses. In this study, hydroxyl groups on CDs of [3]rotaxane diol are initially acetylated, and deprotected after the polyaddition to introduce polyurethane backbone structure into polyrotaxane framework. Despite a relatively complicated chemical structure, [3]rotaxane diol monomer is successfully synthesized in a high yield (overall 67%) without any taxing purification process, which is beneficial for practical applications. The polymerization itself proceeds well under a standard polyaddition reaction condition to afford corresponding polyurethanes around 80% yield with Mn > 30 kDa. The poly[3]rotaxanes show different aggregation behavior or optical properties, whether or not acetyl groups are present, and are analyzed by XRD, SEM, and fluorescence measurements.

Herein, novel photoresponsive spiropyran (SP)-based P(DEGMA-co-SpMA) copolymers with variable percentages of SP fractions are synthesized. The SP group present in these polymers exhibited the abilities of reversible photoisomerism. Their photoresponsive, structural, and thermal properties have been investigated and compared using various characterization techniques. These light-responsive copolymers are found to exhibit photoswitchable glass transition temperature (Tg ), high thermal stability (Td > 250°C), instant photochromism as well as fluorescence upon exposure to UV light. It is demonstrated that the Tg of these synthesized polymers increased when irradiated with UV light (λ = 365 nm), as a consequence of the photoisomerization of incorporated SP groups into their merocyanine form. This increase in Tg is attributed to an increase in polarity and a decrease in the overall entropy of the polymeric system when it switches from the ring-closed SP form (less-ordered state) to the ring-opened merocyanine form (more-ordered state). Therefore, such polymers with a unique feature of phototunable glass transition temperatures provide the possibility to be integrated into functional materials for various photoresponsive applications.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Effects of primary amino group of methacrylamides on the polymerization and polymer pH- and thermosresponsiveness were investigated.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Main-chain scission of polymers induces a significant decrease in molecular weight and accompanying changes in physical properties and is important for applications in materials engineering, such as in photoresists and adhesive dismantling. In this study, we focused on methacrylates substituted with carbamate groups at the allylic positions for the purpose of developing a mechanism that efficiently cleaves the main chain in response to chemical stimuli. Dimethacrylates substituted with hydroxy groups at the allylic positions were synthesized by the Morita-Baylis-Hillman reaction of diacrylates and aldehydes. The polyaddition with diisocyanates afforded a series of poly(conjugated ester-urethane)s. These polymers underwent a conjugate substitution reaction with diethylamine or acetate anion at 25 °C, resulting in main-chain scission accompanied by decarboxylation. A side reaction by the re-attack of the liberated amine end to the methacrylate skeleton proceeded, whereas it was suppressed for the polymers with an allylic substitute of the phenyl group. Therefore, the methacrylate skeleton substituted with phenyl and carbamate groups at the allylic position is an excellent decomposition point that induces selective and quantitative main-chain scission with weak nucleophiles, such as carboxylate anions.

The Cover Feature illustrates the acylation reaction of cyclodextrin (CD)-based [3]rotaxane. In this reaction system, one [3]rotaxane has 36 hydroxyl groups on two CD units, and excess of methacryl anhydride was added, as shown on the background. However, approximately only one methacryl unit (highlighted by yellow color) was introduced to one CD ring when the reaction condition was properly designed, probably owing to the steric hindrance. As a result, the product could be used as a [3]rotaxane crosslinker to afford network polymer crosslinked by through-space bonding. Cover design by Yosuke Akae. More information can be found in the Research Article by Y. Akae and T. Takata.