Ionotropic Gelation Fronts in Sodium Carboxymethyl Cellulose for Hydrogel Particle Formation

Abstract

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a model anionic polyelectrolyte, with Fe3+ cations in water. Gelation front kinetics are first established using 1D microfluidic experiments, and effective diffusive coefficients are found to increase with Fe3+ concentration and decrease with NaCMC concentrations. We use Fourier Transform Infrared Spectroscopy (FTIR) to elucidate the Fe3+-NaCMC gelation mechanism and small angle neutron scattering (SANS) to spatio-temporally resolve the solution-to-network structure during front propagation. We find that the polyelectrolyte chain cross-section remains largely unperturbed by gelation and identify three hierarchical structural features at larger length scales. Equipped with the understanding of gelation mechanism and kinetics, using microfluidics, we illustrate the fabrication of range of HMP particles with prescribed morphologies.

Carboxymethyl Cellulose Hydrogel from Biomass Waste of Oil Palm Empty Fruit Bunch Using Calcium Chloride as Crosslinking Agent

“…This could be due to the fact that crosslinking only involved the substitution of Na + with Ca 2+ from CaCl 2 as the crosslinking agent. There was only slight shifting in the wavenumber after Ca 2+ ionic crosslinking on the CMC chain from 1589 cm −1 to a lower wavenumber (1585 cm −1 ) and 1413 cm −1 to a higher wavenumber (1423 cm −1 ) due to the bidentate of the carboxylate group to Ca 2+ [ 29 ]. In addition, both peaks showed less intensity after the ionic crosslinking reaction compared to the CMC, which reflects the decrement of the crystalline nature of the hydrogel [ 30 ].…”

Insights into the Gelation Mechanism of Metal-Coordinated Hydrogels by Paramagnetic NMR Spectroscopy and Molecular Dynamics

“…∼1735 cm −1 , indicative of the presence of monodentate binding of the Fe 3+ cation under the investigated conditions. 17 Long-Range Ordering of CMC−Fe 3+ Hydrogel. The structural long-range order of CMC in the absence and in the presence of Fe 3+ ions has been characterized using the PXRD technique (Figure 3c).…”

“…15 In addition, the weak nature of the reversible ionic interactions between metal ions and CMC chains might donate temperature-and pH-responsive properties to the 3D gel network. 15 One of the key features of CMC is its chelating property and the resulting ability to form 3D gel structures at a pH close to neutrality in the presence of bivalent 16 (i.e., Zn 2+ ) and trivalent 17 (i.e., Fe 3+ ) metal cations. In particular, iron crosslinking can be used to induce redox-controlled structural changes of the hydrogel promoted by the interconversion of Fe 2+ and Fe 3+ ions.…”

“…17 A tetrahedral coordination and a bidentate chelating mode were assigned to Fe 3+ ions in a complex with CMC via Fourier transform infrared (FT-IR) characterization. 17 Yet, relatively little is known about the mechanisms of the mutable metal-coordinated bonds occurring in CMC−Fe 3+ hydrogels. Specifically, structural information about the complexes' formation and the influence of the metal ions on the polysaccharide structure and its interaction with water molecules are still missing.…”

Cellulose-Based Hydrogels and Aerogels Embedded with Silver Nanoparticles: Preparation and Characterization

“…More examples of the applications of cellulose-based hydrogels and aerogels can be found in recent reviews [ 26 , 27 , 28 ]. The use of hydrogels and aerogels as containers for functional nanoparticles represents an especially popular trend [ 29 , 30 ].…”