Controlled Degradation and Erosion of Polyrotaxane Solids via the Formation of Multivalent Hydrogen Bonding in Water

Biodegradable polyrotaxanes (PRXs) are important scaffolds for the development of biomaterials. However, the degradation behavior of PRXs constructed via physical crosslinking remains largely unexplored. Herein, a degradable PRX exhibiting physical hydrogen bonds as crosslinks between α‐cyclodextrins (α‐CDs) as the cyclic molecules is synthesized by introducing hyperbranched polyglycerol (HPG) containing numerous terminal 1,2‐diols into the α‐CDs with an incorporation ratio of HPG (HPG/PRX) varying from 2 to 19 via anion ring‐opening polymerization of glycidol. Rheological analysis by a frequency sweep test reveals that a typical HPG‐PRX forms hydrogels by physical crosslinking via hydrogen bonding, whereas a low branched degree of HPG in HPG‐PRX weakens the physical crosslinking. The obtained gels recover their original shape upon pulling and releasing, which is consistent with a pulley effect. Degradation and erosion tests in water show that increasing the molecular weight of the introduced HPG changes the degradation behavior from bulk degradation to surface erosion. Owing to its controllable degradation or erosion by tuning the rate of water ingress according to the number of hydrogen bonds and the branched degree, this HPG‐modified PRX paves the way for the development of new biodegradable/erodible gels. Degradable polyrotaxane (PRX) gels exhibit physical hydrogen bonds as crosslinks between α‐cyclodextrins by introducing hyperbranched polyglycerol (HPG) containing branched 1,2‐diols into the α‐cyclodextrins.