Improvement in the elasticity and toughness of polymeric materials is an important issue in the fabrication of polymeric materials. However, solving this issue is challenging because of the trade-off between toughness and elasticity. Herein, citric acid-modified cellulose (CAC) was introduced as a filler into movable cross-linked polymeric materials, in which cyclic molecules move along the polymer chain. The resulting CAC/polymer composite materials contained both reversible and movable cross-links. The reversible cross-links were hydrogen bonds formed between the carboxyl group of acrylic acid units (AA; in the polymer chain) and the CAC filler. The movable cross-links were formed by a cyclic molecule along the polymer chain. This combination of reversible and movable cross-links resulted in the high toughness of the composite materials against an applied stress. The CAC/polymer composite materials with 3 wt % CAC increased the Young’s modulus by 1.6 times and maintained the toughness compared to the original elastomer without the CAC. The CAC/polymer composite materials without CAC or the AA unit did not show this increase. Dynamic viscoelasticity measurements revealed the relationship between the relaxation modes and the toughness of the CAC/polymer composite materials. Upon combining the appropriate unit ratio of movable and reversible cross-links, the CAC/polymer composite materials exhibited the highest Young’s modulus and toughness. The design of the CAC/polymer composite materials improved the toughness with a high Young’s modulus.

Hydrogels are biocompatible polymer networks; however, they have the disadvantage of having poor mechanical properties. Herein, the mechanical properties of host−guest hydrogels were increased by adding a filler and incorporating other noncovalent interactions. Cellulose was added as a filler to the hydrogels to afford a composite. Citric acid-modified cellulose (CAC) with many carboxyl groups was used instead of conventional cellulose. The preparation began with mixing an acrylamide-based αCD host polymer (p-αCD) and a dodecanoic acid guest polymer (p-AADA) to form supramolecular hydrogels (p-αCD/p-AADA). However, when CAC was directly added to p-αCD/p-AADA to form biocomposite hydrogels (p-αCD/p-AADA/CAC), it showed weaker mechanical properties than p-αCD/p-AADA itself. This was caused by the strong intramolecular hydrogen bonding (Hbonding) within the CAC, which prevented the CAC reinforcing p-αCD/p-AADA in p-αCD/p-AADA/CAC. Then, calcium chloride solution (CaCl 2 ) was used to form calcium ion (Ca 2+ ) complexes between the CAC and p-αCD/p-AADA. This approach successfully created supramolecular biocomposite hydrogels assisted by Ca 2+ complexes (p-αCD/p-AADA/CAC/Ca 2+ ) with improved mechanical properties relative to p-αCD/p-AADA hydrogels; the toughness was increased 6-fold, from 1 to 6 MJ/m 3 . The mechanical properties were improved because of the disruption of the intramolecular H-bonding within the CAC by Ca 2+ and subsequent complex formation between the carboxyl groups of CAC and p-AADA. This mechanism is a new approach for improving the mechanical properties of hydrogels that can be broadly applied as biomaterials.