Effect of calcium neutralization on elastic and swelling properties of crosslinked poly(acrylic acid) - correlation to inhomogeneities and phase behaviour

Abstract

Abstract:Crosslinked hydrogels of poly(acrylic acid) neutralized with calcium hydroxide were synthesized using free radical co-polymerization. The effects of the amount added calcium on the elastic modulus and swelling properties of the gels and the correlation to phase behaviour and structural changes within the gels were studied using texture analysis, gravimetric analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and atomic force microscopy (AFM). It was found that the elastic modulus decreased nonlinearly with increasing amount of added calcium and that the swelling's dependence on the amount of added calcium was complicated. The maximum swelling increased with increasing amount of added calcium until a critical calcium content was reached, upon which the gels phase separated, with a strong decrease in swelling as a result. The changes in properties are explained by the fact that calcium affects the structure of the polymer network during synthesis and by the phase behaviour of the gels. Changes in the gel structure with the addition of calcium were detected with AFM. Furthermore, AFM revealed different phases on the nanometre scale for the sample with a calcium content around which phase separation is macroscopically observed. Finally, it was shown that the sulphur from the initiator potassium persulfate formed crystal like regions with high sulphur and calcium content upon drying of the hydrogels.

A novel dual-structure, self-healable, polysaccharide based hybrid nanogel for biomedical uses

“…Thus, the equilibrium swelling degree (ESD) of lyophilized composite hydrogels with the weight ratios CHC/SAL/glycerol ¼ 1/1.5/0, prepared using gelation media with different CaCl 2 concentrations, was determined in deionized water (di-water), cell culture medium (a-MEM + 10% FBS), and simulated body fluid (1.5SBF). The extent to which a gel swells is determined by the swelling pressure (p), which can be written: [62][63][64] p ¼ p mix + p ion + p e (5) where p mix is osmotic pressure from the dissolution of polymer chains, p ion is the osmotic pressure derived from counterions within the gel and p e is the elastic pressure derived from the deformation of the polymer network during swelling. [62][63][64] The term p e in the above equation is determined by the crosslinking density, where a high degree of crosslinking corresponds to a high elastic pressure opposing swelling.…”

“…The extent to which a gel swells is determined by the swelling pressure (p), which can be written: [62][63][64] p ¼ p mix + p ion + p e (5) where p mix is osmotic pressure from the dissolution of polymer chains, p ion is the osmotic pressure derived from counterions within the gel and p e is the elastic pressure derived from the deformation of the polymer network during swelling. [62][63][64] The term p e in the above equation is determined by the crosslinking density, where a high degree of crosslinking corresponds to a high elastic pressure opposing swelling. For the gels in this study the crosslinking should be dominated by the interaction between alginate and Ca 2+ .…”

The Alteration of the Gut Microbiome during Ramadan Offers a Novel Perspective on Ramadan Fasting: A Pilot Study

“…The Friedman test for multiple comparisons and the Wilcoxon test with Benjamini-Hochberg (BH) adjustment were used to discover the taxa with statistically significant differences among the groups. In addition, accessory and unique bacteria exclusively detected in the post-Ramadan groups were identified by core microbiome analysis using the "eulerr" [40], "microbiome" [35], and "microbiomeutilities" [41] R packages. To better understand, unassigned ASVs were removed and ASVs precisely assigned to genera were adopted.…”

Miscibility of poly(acrylic acid)/poly(methyl vinyl ketone) blend and in vitro application as drug carrier system

“…According to Calixto [25], PAA produces a hydrogel that is promising for topical drug delivery, allowing close contact with a biological substrate as well as enhancement of the local concentration gradient, where both factors may improve the biological performance of the drugs. In the last decade, various researchers have focused on developing new drug-carrier systems comprising nanogels based on PAA materials [26–28]. Müller et al [29] investigated the oral drug delivery application of mucus-penetrating papain combined with a PAA nanoparticle composite (PAPC).…”