The states of water in tryptophan grafted hydroxypropyl methylcellulose hydrogels and their effect on the adsorption of methylene blue and rhodamine B

Cellulose Dissolution, Modification, and the Derived Hydrogel: A Review

The cellulose-based hydrogel has occupied a pivotal position in almost all walks of life. However, the native cellulose can not be directly used for preparing hydrogel due to the complex non-covalent interactions. Some literature has discussed the dissolution and modification of cellulose but has yet to address the influence of the pretreatment on the as-prepared hydrogels. Firstly, the "touching" of cellulose by derived and non-derived solvents was introduced, namely, the dissolution of cellulose. Secondly, the "conversion" of functional groups on the cellulose surface by special routes, which is the modification of cellulose. The above-mentioned two parts were intended to explain the changes in physicochemical properties of cellulose by these routes and their influences on the subsequent hydrogel preparation. Finally, the "reinforcement" of cellulose-based hydrogels by physical and chemical techniques was summarized, viz., improving the mechanical properties of cellulose-based hydrogels and the changes in the multi-level structure of the interior of cellulose-based hydrogels.

The effect of the molecular structure of hydroxypropyl methylcellulose on the states of water, wettability, and swelling properties of cryogels prepared with and without CaO2

Hydroxypropyl methylcellulose (HPMC) belongs to the cellulose ether family that has hydroxyl groups substituted by hydrophobic methyl groups (DS) and hydrophilic hydroxypropyl groups (MS). Herein, the interactions between water molecules and cryogels prepared with HPMC in the presence and absence of a linear nonionic surfactant, as well as CaO₂ microparticles, which react with water producing O₂, were systematically investigated by sorption experiments and Time-Domain Nuclear Magnetic Resonance. Regardless of the DS and MS, most water molecules presented transverse relaxation time t2 typical of intermediate water and a small population of more tightly bound water. HPMC cryogels with the highest DS of 1.9 presented the slowest swelling rate of 0.519 ± 0.053 g_water/(g.s) and the highest contact angle values 85.250^o ± 0.004^o, providing the best conditions for a slow reaction between CaO₂ and water. The presence of surfactant favored hydrophobic interactions that allowed the polar head of the surfactant to be exposed to the medium, resulting in a higher swelling rate and lower contact angle values. The HPMC with the highest MS presented the fastest swelling rate and the lowest contact angle. These findings are relevant for the formulations and reactions, where tuning the swelling kinetics is crucial for the final application.

Rheological and mechanical properties of hydroxypropyl methylcellulose-based hydrogels and cryogels controlled by AOT and SDS micelles

HYPOTHESIS

The type and concentration of surfactants affect the rheological behavior of hydroxypropyl methylcellulose (HPMC) chains in hydrogels, influencing the microstructure and mechanical properties of HPMC cryogels.

EXPERIMENTS

Hydrogels and cryogels containing HPMC, AOT (bis (2-ethylhexyl) sodium sulfosuccinate or dioctyl sulfosuccinate salt sodium, two C8 chains and sulfosuccinate head group), SDS (sodium dodecyl sulfate, one C12 chain and sulfate head group), and sodium sulfate (salt, no hydrophobic chain) at different concentrations were investigated using small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), rheological measurements, and compressive tests.

FINDINGS

SDS micelles bound to the HPMC chains building "bead necklaces", increasing considerably the storage modulus G' values of the hydrogels and the compressive modulus E values of the corresponding cryogels. The dangling SDS micelles promoted multiple junction points among the HPMC chains. AOT micelles and HPMC chains did not form "bead necklaces". Although AOT increased the G' values of the hydrogels, the resulting cryogels were softer than pure HPMC cryogels. The AOT micelles are probably embedded between HPMC chains. The AOT short double chains rendered softness and low friction to the cryogel cell walls. Therefore, this work demonstrated that the structure of the surfactant tail can tune the rheological behavior of HPMC hydrogels and hence the microstructure of the resulting cryogels.

Intrinsic-water desorption induced thermomechanical response of hydrogels

We report an interplay between the desorption of intrinsic water and relaxation of polymer chains resulting in an unusual thermomechanical response of a hydrogel, wherein the elastic modulus increases in a certain temperature range followed by a sharp decrease with a further increase in temperature. We establish that, in a hydrogel, the desorption of disparate water types having distinct binding energy affects the consolidation and relaxation behaviour of the matrix, which in turn affects the mechanical properties at different temperature ranges. Using temperature-dependent dielectric relaxation spectroscopy and nanoindentation techniques, the chain dynamics and mechanical properties are investigated.

Vanillin crosslinked chitosan films: The states of water and the effect of carriers on curcumin uptake

In this work, chitosan chains were crosslinked with different contents of vanillin (Van), characterized and loaded with curcumin (CUR), a hydrophobic drug. Sodium dodecyl sulfate (SDS), Tween 20® (T20) and β-cyclodextrin (βCD) were used as curcumin carriers. Films prepared with Van 20 % yielded gel content of 70 %, swelling degree of ~23 g_water/g, bound water and capillary water, as revealed by Time-Domain Nuclear Magnetic Resonance measurements. Films prepared with higher Van contents showed small swelling degree (< 1.6 g_water/g) and hydrophobicity, making them inadequate for drug loading. UV-Vis and fluorescence spectroscopic studies indicated that Van 20 % combined with SDS and SDS/βCD presented the highest CUR uptake (~3.0 mg/g), favored by electrostatic interactions and hydrophobic interactions. CHI and Van 20 % films did not present any cytotoxicity in human neuroblastoma SH-SY5Y cells. At pH 1.0 the films were completely soluble, pointing to their potential application as gastric delivery systems for hydrophobic drugs. Chemical compounds studied in the manuscript: Chitosan, vanillin, curcumin, β-cyclodextrin, sodium dodecyl sulfate, polyethylene glycol sorbitan monolaurate.

Crosslinkers for polysaccharides and proteins: Synthesis conditions, mechanisms, and crosslinking efficiency, a review

Polysaccharides and proteins are important macromolecules for developing hydrogels devoted to biomedical applications. Chemical hydrogels offer chemical, mechanical, and dimensional stability than physical hydrogels due to the chemical bonds among the chains mediated by crosslinkers. There are many crosslinkers to synthesize polysaccharides and proteins based on hydrogels. In this review, we revisited the crosslinking reaction mechanisms between synthetic or natural crosslinkers and polysaccharides or proteins. The selected synthetic crosslinkers were glutaraldehyde, carbodiimide, boric acid, sodium trimetaphosphate, N,N'-methylene bisacrylamide, and polycarboxylic acid, whereas the selected natural crosslinkers included transglutaminase, tyrosinase, horseradish peroxidase, laccase, sortase A, genipin, vanillin, tannic acid, and phytic acid. No less important are the reactions involving click chemistry and the macromolecular crosslinkers for polysaccharides and proteins. Literature examples of polysaccharides or proteins crosslinked by the different strategies were presented along with the corresponding highlights. The general mechanism involved in chemical crosslinking mediated by gamma and UV radiation was discussed, with particular attention to materials commonly used in digital light processing. The evaluation of crosslinking efficiency by gravimetric measurements, rheology, and spectroscopic techniques was presented. Finally, we presented the challenges and opportunities to create safe chemical hydrogels for biomedical applications.

Synthesis of Sodium Carboxymethyl Cellulose/Poly(acrylic acid) Microgels via Visible-Light-Triggered Polymerization as a Self-Sedimentary Cationic Basic Dye Adsorbent

In this study, sodium carboxymethyl cellulose/poly(acrylic acid) (CMC/PAA) microgels were successfully synthesized via visible-light-triggered free-radical polymerization to remove methylene blue (MB) from water. The microgels had a loose and porous 3-D network structure, exhibiting excellent adsorption performance. The equilibrium adsorption capacity and the removal efficiency of the microgels reached approximately 1479 mg/g and 97%, respectively, when the initial concentration of MB was 300 mg/L. The adsorption kinetics was well described by the pseudo-second-order model, and the adsorption isotherms followed the Langmuir isothermal model. Notably, CMC/PAA microgels could naturally settle and be separated from the MB solution. Furthermore, the recovery efficiency of the regenerated CMC/PAA microgels reached approximately 94% after five adsorption-desorption cycles. Therefore, the microgels could be used as promising adsorbents due to the advantages of high adsorption capacity, fast removal rate, and reusability.

Hydroxypropyl methylcellulose: Physicochemical properties and ocular drug delivery formulations

Hydroxypropyl methylcellulose (HPMC) is a cellulose ether widely used in drug formulations due to its biocompatibility, uncharged nature, solubility in water and thermoplastic behavior. Particularly for ocular and ophthalmic formulations, HPMC is applied as viscosity enhancer agent in eye drops, gelling agent in injections, and polymeric matrix in films, filaments and inserts. The different therapeutic approaches are necessary due to the complex anatomic structure of the eye. The natural ocular barriers and the low drug permeation into the circulatory system make the drug administration challenging. This review presents the eye anatomy and the usual local routes of drugs administration, which are facilitated by the physicochemical properties of HPMC. The relationship between chemical structure and physicochemical properties of HPMC is displayed. The different types of formulations (local application) including HPMC for ocular drug delivery are discussed with basis on recent literature reports and patents.