pH‐Based Regulation of Hydrogel Mechanical Properties Through Mussel‐Inspired Chemistry and Processing

Abstract

The mechanical holdfast of the mussel, the byssus, is processed at acidic pH yet functions at alkaline pH. Byssi are enriched in Fe3+ and catechol-containing proteins, species with chemical interactions that vary widely over the pH range of byssal processing. Currently, the link between pH, Fe3+-catechol reactions, and mechanical function are poorly understood. Herein, we describe how pH influences the mechanical performance of materials formed by reacting synthetic catechol polymers with Fe3+. Processing Fe3+-catechol polymer materials through a mussel-mimetic acidic-to-alkaline pH change leads to mechanically tough materials based on a covalent network fortified by sacrificial Fe3+-catechol coordination bonds. Our findings offer the first direct evidence of Fe3+-induced covalent cross-linking of catechol polymers, reveal additional insight into the pH dependence and mechanical role of Fe3+- catechol interactions in mussel byssi, and illustrate the wide range of physical properties accessible in synthetic materials through mimicry of mussel protein chemistry and processing.

Bioadhesive hydrogels demonstrating pH-independent and ultrafast gelation promote gastric ulcer healing in pigs

“…Consistent with previous reports showing that the formation of HA-Cat hydrogels depends on the pH (33,34), a 2% HA-Cat solution formed a hydrogel in 30 min at pH 7, but the process required a much longer time (about 3 hours) at pH 2. When the molar ratio of the oxidation agent (NaIO 4 ) to Cat was decreased from 1:1 to 0.1:1, the HA-Cat precursor solution was unable to form a hydrogel (Fig.…”

Bioadhesive hydrogels demonstrating pH-independent and ultrafast gelation promote gastric ulcer healing in pigs

“…Consistent with previous reports showing that the formation of HA-Cat hydrogels depends on the pH (33,34), a 2% HA-Cat solution formed a hydrogel in 30 min at pH 7, but the process required a much longer time (about 3 hours) at pH 2. When the molar ratio of the oxidation agent (NaIO 4 ) to Cat was decreased from 1:1 to 0.1:1, the HA-Cat precursor solution was unable to form a hydrogel (Fig.…”

Bioinspired Metal–Ligand Networks with Enhanced Stability and Performance: Facile Preparation of Hydroxypyridinone (HOPO)-Functionalized Materials

“… 45 , 51 , 55 , 59 As visually demonstrated in Figure 3 , disk samples of HOPO and catechol functionalized networks were transferred from acidic storage solutions (1 mM HCl) to basic, aqueous solutions buffered at pH 9 (KOH and 0.2 M bicine) for 24 h, imaged, and then returned to acidic solution. Catechol samples displayed characteristic color changes related to quinone formation and oxidative coupling, 10 , 51 , 67 while no appreciable changes were observed for HOPO-functionalized materials, consistent with prior studies. 51 , 55 This difference in visual appearance between catechol and HOPO systems after base mediated oxidation was further illustrated by FTIR measurements at 24 and 72 h, and via comparison with the FTIR spectra of control, pristine samples and via comparison to controls oxidized with sodium periodate (NaIO 4 ) ( Figure S5 ).…”

Quantitative Correlation between Bound Water and Mechanical Stress Relaxation in Dehydrated Metal-Coordinate Polymer Networks

“…Consistent with these comparisons, the bis -Ni–histidine-coordinate cross-linked hydrogels with only metal-coordinate cross-links show even faster relaxation (Figure c) and a higher loss factor (Figure d) than 1:3 hydrogels at the same tested pH 10. These observations confirm the dynamic nature of metal-coordinate cross-links in contrast to the permanent covalent cross-links and tunable viscoelasticity of the hydrogels, as demonstrated previously by Barret et al Thus, these metal-coordinate networks serve as a good controllable platform for testing the dehydration effects on the dynamic behaviors transitioned from their wet hydrogel state to the dehydrated xerogel state.…”

Bioadhesive hydrogels demonstrating pH-independent and ultrafast gelation promote gastric ulcer healing in pigs

“…Consistent with previous reports showing that the formation of HA-Cat hydrogels depends on the pH (33,34), a 2% HA-Cat solution formed a hydrogel in 30 min at pH 7, but the process required a much longer time (about 3 hours) at pH 2. When the molar ratio of the oxidation agent (NaIO 4 ) to Cat was decreased from 1:1 to 0.1:1, the HA-Cat precursor solution was unable to form a hydrogel (Fig.…”

Bioinspired Metal–Ligand Networks with Enhanced Stability and Performance: Facile Preparation of Hydroxypyridinone (HOPO)-Functionalized Materials

“… 45 , 51 , 55 , 59 As visually demonstrated in Figure 3 , disk samples of HOPO and catechol functionalized networks were transferred from acidic storage solutions (1 mM HCl) to basic, aqueous solutions buffered at pH 9 (KOH and 0.2 M bicine) for 24 h, imaged, and then returned to acidic solution. Catechol samples displayed characteristic color changes related to quinone formation and oxidative coupling, 10 , 51 , 67 while no appreciable changes were observed for HOPO-functionalized materials, consistent with prior studies. 51 , 55 This difference in visual appearance between catechol and HOPO systems after base mediated oxidation was further illustrated by FTIR measurements at 24 and 72 h, and via comparison with the FTIR spectra of control, pristine samples and via comparison to controls oxidized with sodium periodate (NaIO 4 ) ( Figure S5 ).…”

Quantitative Correlation between Bound Water and Mechanical Stress Relaxation in Dehydrated Metal-Coordinate Polymer Networks

“…Consistent with these comparisons, the bis -Ni–histidine-coordinate cross-linked hydrogels with only metal-coordinate cross-links show even faster relaxation (Figure c) and a higher loss factor (Figure d) than 1:3 hydrogels at the same tested pH 10. These observations confirm the dynamic nature of metal-coordinate cross-links in contrast to the permanent covalent cross-links and tunable viscoelasticity of the hydrogels, as demonstrated previously by Barret et al Thus, these metal-coordinate networks serve as a good controllable platform for testing the dehydration effects on the dynamic behaviors transitioned from their wet hydrogel state to the dehydrated xerogel state.…”

Bioadhesive hydrogels demonstrating pH-independent and ultrafast gelation promote gastric ulcer healing in pigs

“…Consistent with previous reports showing that the formation of HA-Cat hydrogels depends on the pH (33,34), a 2% HA-Cat solution formed a hydrogel in 30 min at pH 7, but the process required a much longer time (about 3 hours) at pH 2. When the molar ratio of the oxidation agent (NaIO 4 ) to Cat was decreased from 1:1 to 0.1:1, the HA-Cat precursor solution was unable to form a hydrogel (Fig.…”

Bioinspired Metal–Ligand Networks with Enhanced Stability and Performance: Facile Preparation of Hydroxypyridinone (HOPO)-Functionalized Materials

“… 45 , 51 , 55 , 59 As visually demonstrated in Figure 3 , disk samples of HOPO and catechol functionalized networks were transferred from acidic storage solutions (1 mM HCl) to basic, aqueous solutions buffered at pH 9 (KOH and 0.2 M bicine) for 24 h, imaged, and then returned to acidic solution. Catechol samples displayed characteristic color changes related to quinone formation and oxidative coupling, 10 , 51 , 67 while no appreciable changes were observed for HOPO-functionalized materials, consistent with prior studies. 51 , 55 This difference in visual appearance between catechol and HOPO systems after base mediated oxidation was further illustrated by FTIR measurements at 24 and 72 h, and via comparison with the FTIR spectra of control, pristine samples and via comparison to controls oxidized with sodium periodate (NaIO 4 ) ( Figure S5 ).…”

Quantitative Correlation between Bound Water and Mechanical Stress Relaxation in Dehydrated Metal-Coordinate Polymer Networks

“…Consistent with these comparisons, the bis -Ni–histidine-coordinate cross-linked hydrogels with only metal-coordinate cross-links show even faster relaxation (Figure c) and a higher loss factor (Figure d) than 1:3 hydrogels at the same tested pH 10. These observations confirm the dynamic nature of metal-coordinate cross-links in contrast to the permanent covalent cross-links and tunable viscoelasticity of the hydrogels, as demonstrated previously by Barret et al Thus, these metal-coordinate networks serve as a good controllable platform for testing the dehydration effects on the dynamic behaviors transitioned from their wet hydrogel state to the dehydrated xerogel state.…”