Alginate/PEO-PPO-PEO Composite Hydrogels with Thermally-Active Plasticity

Abstract

Stimuli-responsive hydrogels with high strength and toughness have received significant interest in recent years. Here, we report thermally active composite hydrogels comprising alginate and one of two poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. Temperature-sensitive structural and mechanical changes are probed using calorimetry, neutron scattering, shear rheology, unconfined compression, and fracture. Below the lower gelation temperature, LGT, the mechanical properties are dominated by alginate. As the LGT is reached, the contribution of PEO-PPO-PEO to the mechanical properties is activated, resulting in order-of-magnitude increases in elastic modulus. Under compression, we show the evolution of plasticity for the composite hydrogels as the LGT is approached and surpassed, resulting in dramatic increases in fracture stress compared to neat alginate hydrogels. Plasticity was observed above the LGT and may be attributed to restructuring from the sliding of packed micelles and strain-hardening due to stress concentration on alginate cross-links and junction zones, ultimately leading to fracture.

Temperature‐dependent structure and compressive mechanical behavior of alginate/polyethylene oxide–poly(propylene oxide)–poly(ethylene oxide) hydrogels

“…Alginate hydrogels were prepared using a calcium ion release method that was previously reported (Quah et al, ; White et al, ). Concentrations of 0.5, 0.75, and 1.0% (w/v) alginate were prepared by first dissolving the respective amounts of sodium alginate in water and stirring for 24 hr.…”

“…However, alginate‐based materials do not display thermoresponsive gelation behavior, and the rheological properties are not strongly dependent upon temperature. Previously, we demonstrated thermoreversible capabilities in an alginate‐F127 multicomponent hydrogels and reported the mechanical properties of these materials in low‐amplitude oscillatory shear (Quah, Smith, Preston, Laughlin, & Bhatia, ; White, Saffer, & Bhatia, ). Some of these formulations exhibited an increase in the storage modulus, G ′, at physiological temperatures (~36–40°C) of up to 100× greater than room temperature (~20–25°C).…”

Reductant-triggered rapid self-gelation and biological functionalization of hydrogels

“…After the LVR, G′ increases slightly with the shear strain until it reaches the critical strain of rupture, indicating a more rapidly rising stress relative to increasing straina hardening behavior (Fig. Strain hardening properties are frequently observed in biopolymer gels 42,43 and interpenetrating networks (IPNs), 44,45 where weak crosslinks break up for the sake of dissipating energy. In the figure, the upturn of G″ is even more significant.…”

“…5b). 42,43 The dynamic disulfide bonds play a key role in energy dissipation, and are possibly responsible for the large rupture strain and strain hardening behavior observed in the synthesized hydrogels. Strain hardening properties are frequently observed in biopolymer gels 42,43 and interpenetrating networks (IPNs), 44,45 where weak crosslinks break up for the sake of dissipating energy.…”

A self-regulating antimicrobial model based on the ion-exchange stimuli

“…, leading to an ordered conformational structure called ''egg-box'' array. The property of Alg hydrogels being sensitive to pH and calcium ions showed potential applications in the field of intelligent DDSs [20][21][22][23][24][25][26][27][28]. However, few studies about the controlling release of nano-silver regulated by the intelligent response of Alg have been reported in the field of antimicrobial wound dressing.…”