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DOE OSTI2026

Coarse-Grained Simulations of Polyrotaxane Hydrogels under Quiescent and Shear Conditions

Cyclodextrin-based polyrotaxanes (PR) form hydrogels in water through cyclodextrin (CD) aggregation and crystallization. These networks can break under shear flows, making them versatile platforms for extrusion-based 3D printing. To optimize the material properties of 3D-printed PR gels, a microscopic understanding of the structural evolution during 3D printing is necessary. Here, we employ coarse-grained (CG) simulations to reveal the PR assembly process at the molecular level. Our simulations reproduce the experimental crystal morphologies of PR at varying concentrations and chain lengths under quiescent conditions. Using nonequilibrium simulations, we show shear flow ruptures crystalline domain connectivity in PR gels and stacks the lamellae in the gradient direction, allowing the materials to flow during 3D printing. After the cessation of flow, the anisotropic crystal alignment and absence of available dangling PR diminish the intercrystal connectivity. The printed materials are therefore mechanically weaker than the pristine hydrogels, in agreement with experimental results. Nonetheless, by relating the microscopic structural evolution with viscoelastic properties of PR gels and solutions, we elucidate how flow conditions and sample composition affect the 3D printing performance of PR hydrogels.

Smith, Cameron D. [Dartmouth College, Hanover, NH ↗

DOE OSTI2023

3D-printed ketoenamine crosslinked polyrotaxane hydrogels and their mechanochromic responsiveness

A ketoenamine-based dynamic covalent crosslinker was introduced here to α-cyclodextrin-based polypseudorotaxanes, forming viscoelastic hydrogels for direct-ink-write 3D printing. The irreversible enol–keto tautomerization imparts high chemical stability to the extensively crosslinked polyrotaxane hydrogels, which showed mechanochromic responsiveness in the presence of the integrated fluorophores.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Material properties and applications of mechanically interlocked polymers

Mechanically interlocked polymers (MIPs), such as polyrotaxanes and polycatenanes, are polymer architectures that incorporate a mechanical bond. In a polyrotaxane, the mechanical bond is the result of a linear dumbbell component threaded through a ring, while in a polycatenane, it is the consequence of interlocked ring components. Furthermore, the interlocked nature of these architectures can result in high degrees of conformational freedom and mobility of their components, which can give rise to unique property profiles. In recent years the synthesis and studies of a range of MIPs has allowed researchers to build an initial understanding of how incorporating mechanical bonds within a polymer structure impacts its material properties. This review focuses on the understanding of these structure-property relationships with an outlook toward their applications, specifically focusing on four main classes of MIPs: polyrotaxanes, slide-ring gels, daisy-chain polymers, and polycatenanes.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Conductive and anti-freezing hydrogels constructed by pseudo-slide-ring networks

In this work, stretchable, tough, and anti-freezing hydrogels were prepared using partially carboxymethylated polyrotaxanes and polyacrylamides. The carboxylic acid groups of α-cyclodextrins in the polyrotaxane and the amide groups in polyacrylamide are hydrogen-bonded, affording a pseudo-slide-ring network, greatly enhancing the hydrogels’ macroscale mechanical properties, anti-freezing features, and electrical conductivity for the fabrication of a cold-temperature strain sensor.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Reinforced double-threaded slide-ring networks for accelerated hydrogel discovery and 3D printing

Traditionally, slide-ring gels are stretchable but soft as a result of an elasticity-stretchability trade-off. Herein, we introduce a new approach to breaking this trade-off and creating reinforced slide-ring networks with mobile crosslinkers. Our approach involves the construction of a polyethylene glycol double-threaded γ-cyclodextrin-based pro-slide-ring crosslinker that serves as a modular component for 3D printing and copolymerization. The resulting crystalline-domain-reinforced slide-ring hydrogels, or CrysDoS-gels, exhibit both high elasticity and high stretchability. The modular synthesis allows for high-throughput synthesis of CrysDoS-gels, generating a large amount of data for structure-property analysis. Here, by employing data science techniques, such as machine learning and linear regression, not only were we able to identify which chemical components influence the mechanical properties of CrysDoS-gels, but this analysis also aided in the discovery of better-performing CrysDoS-gels. Finally, we demonstrate the potential application of the newly discovered CrysDoS-gels as sensing devices by 3D printing them as stress sensors with high sensitivity and a broad detection range.

3D-printing↗