skip to main content


Title: Techniques to characterize dynamics in biomaterials microenvironments: XPCS and microrheology of alginate/PEO–PPO–PEO hydrogels
Many recent studies have highlighted the timescale for stress relaxation of biomaterials on the microscale as an important factor in regulating a number of cell-material interactions, including cell spreading, proliferation, and differentiation. Relevant timescales on the order of 0.1–100 s have been suggested by several studies. While such timescales are accessible through conventional mechanical rheology, several biomaterials have heterogeneous structures, and stress relaxation mechanisms of the bulk material may not correspond to that experienced in the cellular microenvironment. Here we employ X-ray photon correlation spectroscopy (XPCS) to explore the temperature-dependent dynamics, relaxation time, and microrheology of multicomponent hydrogels comprising of commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in the bulk oscillatory shear rheology. At physiological temperatures, bulk rheology of these samples shows behavior characteristic of a soft solid, with G ′ > G ′′ and no crossover between G ′ and G ′′ over the measurable frequency range, indicating a relaxation time >125 s. By contrast, XPCS-based microrheology shows viscoelastic behavior at low frequencies, and XPCS-derived correlation functions show relaxation times ranging from 10–45 s on smaller length scales. Thus, we are able to use XPCS to effectively probe the viscoelasticity and relaxation behavior within the material microenvironments.  more » « less
Award ID(s):
1905547 1903189 1922639
PAR ID:
10272204
Author(s) / Creator(s):
; ; ; ; ; ; ;
Date Published:
Journal Name:
Soft Matter
Volume:
17
Issue:
6
ISSN:
1744-683X
Page Range / eLocation ID:
1685 to 1691
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Surface‐induced thrombosis is problematic in blood‐contacting devices composed of silicones or polyurethanes (PUs). Poly(ethylene oxide)‐silane amphiphiles (PEO‐SA) are previously shown effective as surface modifying additives (SMAs) in silicones for enhanced thromboresistance. This study investigates PEO‐SAs as SMAs in a PU at various concentrations: 5, 10, 25, 50, and 100 µmol g−1PU. PEO‐SA modified PUs are evaluated for their mechanical properties, water‐driven surface restructuring, and adhesion resistance against a human fibrinogen (HF) solution as well as whole human blood. Stability is assessed by monitoring hydrophilicity, water uptake, and mass loss following air‐ or aqueous‐conditioning. PEO‐SA modified PUs do not demonstrate plasticization, as evidenced by minimal changes in glass transition temperature, modulus, tensile strength, and percent strain at break. These also show a concentration‐dependent increase in hydrophilicity that is sustained following air‐ and aqueous‐conditioning for concentrations ≥25 µmol g−1. Additionally, water uptake and mass loss are minimal at all concentrations. Although protein resistance is not enhanced versus an HF solution, PEO‐SA modified PUs have significantly reduced protein adsorption and platelet adhesion from human blood at concentrations ≥10 µmol g−1. Overall, this study demonstrates the versatility of PEO‐SAs as SMAs in PU, which leads to enhanced and sustained hydrophilicity as well as thromboresistance.

     
    more » « less
  2. null (Ed.)
    Understanding and characterizing the influence of polymers and surfactants on rheology, application, and processing is critical for designing complex fluid formulations for enhanced oil recovery, pharmaceuticals, cosmetics, foods, inks, agricultural sprays, and coatings. It is well-established that the addition of anionic surfactant like sodium dodecyl sulfate (SDS) to an aqueous solution of an oppositely-charged or uncharged polymer like poly(ethylene oxide) (PEO) can result in the formation of the polymer–surfactant association complexes (P 0 S − ACs) and a non-monotonic concentration-dependent variation in zero shear viscosity. However, the extensional rheology response of polymer–surfactant mixtures remains relatively poorly understood, partially due to characterization challenges that arise for low viscosity, low elasticity fluids, even though the response to strong extensional flows impacts drop formation and many processing operations. In this article, we use the recently developed dripping-onto-substrate (DoS) rheometry protocols to characterize the pinching dynamics and extensional rheology response of aqueous P 0 S − solutions formulated with PEO (P 0 ) and SDS (S − ), respectively. We find the PEO–SDS mixtures display a significantly weaker concentration-dependent variation in the extensional relaxation time, filament lifespan, and extensional viscosity values than anticipated by the measured shear viscosity. 
    more » « less
  3. Because 3D batteries comprise solid polymer electrolytes (SPE) confined to high surface area porous scaffolds, the interplay between polymer confinement and interfacial interactions on total ionic conductivity must be understood. This paper investigates contributions to the structure-conductivity relationship in poly(ethylene oxide) (PEO)–lithium bis(trifluorosulfonylimide) (LiTFSI) complexes confined to microporous nickel scaffolds. For bulk and confined conditions, PEO crystallinity decreases as the salt concentration (Li+:EO (r) = 0.0.125, 0.0167, 0.025, 0.05) increases. For pure PEO and all r values except 0.05, PEO crystallinity under confinement is lower than in the bulk, whereas glass transition temperature remains statistically invariant. At 298 K (semicrystalline), total ionic conductivity under confinement is higher than in the bulk at r = 0.0167, but remains invariant at r = 0.05; however, at 350 K (amorphous), total ionic conductivity is higher than in the bulk for both salt concentrations. Time–of–flight secondary ion mass spectrometry indicates selective migration of ions towards the polymer–scaffold interface. In summary, for the 3D structure studied, polymer crystallinity, interfacial segregation, and tortuosity play an important role in determining total ionic conductivity and, ultimately, the emergence of 3D SPEs as energy storage materials. 
    more » « less
  4. Abstract Highlights

    Rheology of polyethylene oxide‐graphene composite precursors were studied.

    Shear and extensional rheology, and their correlations were investigated.

    Composition‐binder molecular weight‐yielding relationships were elucidated.

    Extensional relaxation regimes were identified with respect to composition.

    Results can be used to determine compositional ranges for different processes.

     
    more » « less
  5. Abstract

    We report the structural and mechanical behavior of multicomponent hydrogels comprising the commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in shear rheology. Here we explore the properties of these materials under compression and large deformations, relevant to applications such as wound dressings that require mechanical robustness. For gels with lower F127 concentration, we find that the stiffness of the gels can be ascribed to the alginate network, and that the Young's modulus and fracture stress do not strongly depend on temperatures. However, for gels with an F127 concentration of 30 wt %, the Young's modulus is enhanced at higher temperatures. Under large deformations, the fracture stress and fracture strain of the materials can be independently varied using the alginate and F127 concentrations, respectively; without the trade‐off in these properties that is often observed in rigid polymer networks. Small‐angle X‐ray scattering shows a power‐law dependence scattering intensity onqarising from the alginate network and scattering peaks consistent with rearranging micelles. For gels with lower F127 concentrations, we find a disordered–body‐centered cubic (BCC)‐face‐centered cubic (FCC) progression of states with temperature, and a BCC/FCC mixture for gels with higher F127 concentrations.

     
    more » « less