Effect of Chain Architecture on the Structure, Dynamics, and Rheology of Thermoresponsive Poloxamer Hydrogels and Associated Blends

Abstract

Poloxamers, ABA triblock polymers composed of a poly(propylene oxide) (PPO) midblock (B) and poly(ethylene oxide) end blocks (A), are widely studied for biomedical applications. Aqueous poloxamer 407 (P407) undergoes a solution-to-gel transition with increasing temperature, driven by the formation and ordering of micelles onto periodic lattices; however, the gel temperature and resulting modulus have limited tunability. Here, reverse P407 (RP407), a BAB polymer of the same composition and molar mass but with an inverted architecture, is synthesized via anionic polymerization. The micellization and gelation temperatures of RP407 are higher than those of P407, and the PPO end blocks allow for intermicelle bridging; however, both single-component solutions favor body-centered cubic (BCC) packings. Furthermore, aqueous RP407 displays a "soft-gel" region with interesting rheological behavior, including viscoelastic aging and thermal hysteresis. Combining P407 and RP407 yields solutions with intermediate transition temperatures and alters the micelle size and packing. While the singlecomponent solutions produce BCC packings, the blends form close-packed structures and larger micelles of higher aggregation numbers. Blends of P407 with an analogous AB diblock (E 111 P 32 ) display similar behavior, whereas RP407/diblock blends form intermediate-sized BCC-packed micelles. These differences in packing and aggregation alter the local environments within the gels, which could have implications for applications such as drug delivery and protein stabilization.

Effect of Acetaminophen on Poloxamer 407 Micelles and Hydrogels: The Relationship between Structural and Physical Properties

“…All SAXS profiles exhibited Bragg peaks derived from the micelle packing phase. Various micelle packing structures, including a face-centered cubic (FCC) structure and a body-centered cubic (BCC) structure, have been reported for poloxamer gels. ,, The structure of ordered micelle packing can be characterized based on the relative peak position ( q / q 0 ) of each peak position q with respect to the fundamental peak position q 0 . Table S1 shows the relative peak positions of FCC and BCC structures and the Miller index ( hkl ) of the corresponding lattice planes.…”

“…It should be mentioned that the gel strength of P407 ( G′ at 40 °C) decreased with increasing ACE concentration (Figure ). White et al reported the transition of micelle packing structure from FCC to BCC in 25 wt % P407 gels accompanied by a slight increase in P407 gel strength. In the present study, the micelle packing structure of ACE-loaded P407 gels changed from FCC to BCC, although the gel strength was weakened with increasing ACE concentration.…”

“…The nanostructure of in situ gel composed of glycerol monooleate is changed from inverse cubic to inverse hexagonal structures by adding medium-chain triglyceride, which affects the mechanical strength and drug release behavior of the gels . In poloxamer gels, the structural changes of poloxamer micelle packing by adding other polymers have been well studied. , Adding reverse poloxamer (PPO–PEO–PPO) to P407 changes the micelle packing structure of P407 gels . There are a few reports that investigated the effect of the addition of small molecules on poloxamer micelle packing. , Meznarich et al showed the structural change of P407 micelle packing by adding methylparaben and dexamethasone.…”

The Method of Direct and Reverse Phase Portraits as a Tool for Systematizing the Results of Studies of Phase Transitions in Solutions of Thermosensitive Polymers

“…The reverse poloxamer (RP407) showed improved gelation properties compared to P407, which is relevant for applications such as drug delivery and protein stabilization. Mixing P407 and RP407 altered the size and packing of micelles, providing customized gelation behavior for various biomedical applications [ 104 ].…”