Static and Dynamic Large Strain Properties of Methyl Cellulose Hydrogels

"Inverse" shape memory effect in energetic electron crosslinked methylcellulose hydrogels: Programming, demonstration and quantification

Shape memory hydrogels constitute a highly attractive materials class that bears enormous potential within a broad range of areas - from engineering to medicine. Within the present contribution we demonstrate that energetic electron crosslinked methylcellulose-only hydrogels exhibit an "inverse" shape memory effect that transforms from a secondary shape to its primary shape upon cooling. The primary shape can conveniently be "programmed" by application of energetic electrons. This intrinsically sterilizing processing approach promises to preserve the excellent FDA-approved biocompatibility of methylcellulose, particularly as it does not involve potentially hazardous crosslinkers or other reagents with medically adverse effects. While we observe the transformation behavior in a systematic study as function of synthesis parameters, we also address functional fatigue and quantify fixity, strain recovery as well as attainable actuator forces. With the latter being in the range of 0.1 N, our actuator elements might prove useful for biomedical applications.

Hyperelastic modeling of solid methyl cellulose hydrogel under quasi-static compression

Constitutive modeling of solid methyl cellulose (MC) hydrogels under quasi-static uniaxial compression is presented for a variety of compositions and test temperatures. Five constitutive models of varying complexity are examined, with the aim to identify the simplest accurate material representation. Due to the viscosity of the gel, the models were calibrated using compression tests only, with restrictions that ensure stability for other loading modes. It is found that of all the tested models, the second order polynomial constitutive model fulfills the requirements of simplicity and accuracy both for compression and predicted tension.

Chirality dependent inverse-melting and re-entrant gelation in α-cyclodextrin/1-phenylethylamine mixtures

Solutions of cyclohexakis-(1→4)-α-d-glucopyranosyl, α-cyclodextrin, αCD, in R-(+)-1-phenylethylamine, αCD/R-PEA, and S-(−)-1-phenylethylamine, αCD/S-PEA, display abnormal phase transitions that strongly depend on supramolecular diastereomeric interactions. While αCD/R-PEA mixtures show one sol–gel inverse-melting phase transition, αCD/S-PEA mixtures show temperature dependent gel–sol–gel re-entrant behavior. NMR, Raman spectroscopy, microscopy and X-ray scattering measurements reveal that hydrogen bond weakening in solution, as well as changes in crystal composition are responsible for entropy increase and gel formation upon heating.

Solutions of α-cyclodextrin in chiral 1-phenylethylamine display abnormal phase transitions. Depending on supramolecular diastereomeric interactions, inverse-melting and re-entrant gels are formed.

Impact-induced gelation in aqueous methylcellulose solutions

Inverse-freezing materials were known to solidify when heated – now a new stimulus is shown to induce this transition within microseconds’ timescales: mechanical impacts.