The Effects of Monomer, Crosslinking Agent, and Filler Concentrations on the Viscoelastic and Swelling Properties of Poly(methacrylic acid) Hydrogels: A Comparison

Abstract

The present work aims at comparatively studying the effects of the concentrations of a monomer (10–30 wt% based on the whole hydrogel composition), crosslinking agent (1–3 mol% based on the monomer), and reinforcing agent (montmorillonite–MMT, 1–3 wt.% based on the whole hydrogel composition) on the swelling and viscoelastic properties of the crosslinked hydrogels prepared from methacrylic acid (MAA) and N,N′-methylenebisacrylamide (BIS) in the presence of K2S2O8 in aqueous solution. The viscoelastic measurements, carried out on the as-prepared hydrogels, showed that the monomer concentration had the largest impact, its three-time enhancement causing a 30-fold increase in the storage modulus, as compared with only a fivefold increase in the case of the crosslinking agent and 1.5-fold increase for MMT in response to a similar threefold concentration increase. Swelling studies, performed at three pH values, revealed that the water absorption of the hydrogels decreased with increasing concentration of both the monomer and crosslinking agent, with the amplitude of the effect of concentration modification being similar at pH 5.4 and 7.4 in both cases, but very different at pH 1.2. Further, it was shown that the increased pH differently influenced the swelling degree in the case of the hydrogel series in which the concentrations of the monomer and crosslinking agent were varied. In contrast to the effect of the monomer and crosslinking agent concentrations, the increase in the MMT amount in the hydrogel resulted in an increased swelling degree at pH 5.4 and 7.4, while at pH 1.2, a slight decrease in the water absorption was noticed. The hydrogel crosslinking density determinations revealed that this parameter was most affected by the increase in the monomer concentration.

Adjusting Some Properties of Poly(methacrylic acid) (Nano)Composite Hydrogels by Means of Silicon-Containing Inorganic Fillers

“…In a strong acidic environment (pH 1.2), the reinforced hydrogels swelled less than H, most likely because of the slight crosslinking effect of the fillers [ 44 ]. The additional crosslinking effect induced by the filler could be best identified at this pH because no COO − groups formed due to the basicity of the medium or the reinforcing agent being present ( Figure 1 ) [ 43 , 45 , 58 ]. An estimation of the structural parameters of the hydrogels at this pH (Equations (2)–(5)) showed an increase in the crosslinking density ( ) as a function of the filler (H < HMt < HXLG ≈ HXLS < HHDK ≈ HFS, Table 3 ), probably determined by the number of additional PMAA network-reinforcing agent interactions.…”

“…Laponite XLG and Laponite XLS (BYK Additives & Instruments, kindly donated by Cosichem & Analytical, Romania), the two commercial brands of hydrophilic pyrogenic silica (fumed silica, FS, Sigma and HDK N20 pyrogenic silica, HDK, Wacker Silicones), methacrylic acid (MAA, Jansen Chemistry, 99%), N,N’-methylenebisacrylamide (BIS, 99%, Sigma Aldrich), ammonium persulfate (APS, Sigma Aldrich, 98%), methylene blue (MB, Loba Chemie, 95%), and crystal violet (CV, Loba Chemie, 96%) were used as received. Unmodified montmorillonite (Mt, Cloisite Na, a gift from Southern Clay Products Inc. Gonzales, TX, USA) was purified by the method previously described [ 43 ]. The characteristics of both reinforcing agents in water and their aqueous dispersions, determined by us, are displayed in Table 1 .…”

“…[ 40 ]. Composite hydrogels based on poly(methacrylic acid) (PMAA) were obtained by reinforcing hydrogels with different types of clays: bentonite [ 41 ], Mt [ 42 , 43 , 44 ], modified Mt [ 11 ], Lap [ 45 , 46 ], kaolin [ 47 ], gold nanoparticles [ 48 ], pyrogenic silica [ 17 ], and carbon nanotubes [ 49 ]. By introducing different nanoparticles into the PMAA matrix, properties such as the mechanical and thermal ones, and water absorption have been improved.…”

Development of Statistically Optimized Chemically Cross-Linked Hydrogel for the Sustained-Release Delivery of Favipiravir

“…In the current study, results depict that, with the increase in crosslinker concentration, the swelling index of the hydrogel ultimately decreased. However, Ninciuleanu et al reported that with the increase in MBA concentration (crosslinker), the swelling degree of the hydrogel increased due to the higher crosslinking density [26]. The water absorption capacity of the hydrogel was lower as a result of more crosslinking agent.…”

Tuning the Properties of PNIPAm-Based Hydrogel Scaffolds for Cartilage Tissue Engineering

“…Hence, such a process can affect cell spreading, migration, proliferation, and differentiation, thus impacting tissue regeneration. The rate of degradation can be tuned by altering the ratio of crosslinker to monomer during synthesis [ 61 ]. In PNIPAm-based copolymeric scaffold synthesis, degradation time can be regulated by tuning the ratio of PNIPAm polymer to another polymer [ 62 ].…”