A review of recent advances in metal ion hydrogels: mechanism, properties and their biological applications

Abstract

In the past few decades, metal ion hydrogels have made great achievements in various aspects of the biological field. As an ion providing empty orbitals, metal ion was able to...

Hydrogels with electrically conductive nanomaterials for biomedical applications

“…24 The cross-linking mechanism is metal-ligand interaction where the metal ions form coordinate covalent bonds with chelating agents (N, O, S) in the polymer chain. 25 In high concentrations, the free metal ions contribute to the ionic conductivity of the hydrogel. 24 Zhang et al review the recent advances in metal ion hydrogels for biological applications.…”

“…24 Zhang et al review the recent advances in metal ion hydrogels for biological applications. 25 Non-ionic polymer chains may impair the ionic conductivity of hydrogels, compared to polyelectrolyte hydrogels. 26 Polyelectrolytes are polymers which contain ionic and/or ionizable groups in a substantial portion of their constitutional units.…”

Dynamic Cross-Linking Network Construction of Carboxymethyl Starch Enabling Temperature and Strain Bimodal Film Sensors

“…For these applications, bulk hydrogel materials, however, are not always well suited because the low surface area-to-volume ratio limits the diffusion of external stimuli inside the hydrogel bulk, lowering response or recovery levels , as a result. Reducing thickness of the bulk is an effective way of improving the responsive sensitivity , and is even able to broaden applications of ionic conductive hydrogels, for instance, in optical fields because of increased transparency . However, reducing the thickness is commonly against the stability of the bulk structure, especially as hydrogels are used as strain sensors undergoing repeated stretching, and also unconducive to the water retention because of the increase of surface area-to-volume ratio .…”

“…The as-prepared composite film/multilayer film (with bilayer or sandwich structure), as compared to the hydrogel bulk or sheet, is more suitable for sensing temperature and humidity alterations as a stretchable sensor. The substrate film well maintains the hydrogel structure and restrains water loss, guaranteeing service life of sensors and, on the other hand, can highly improve wearing comfort, and even acts as a protective layer of the skin against erosion when the ionic hydrogels contain high salt concentrations. It is more important that hydrogel thickness is highly reduced as the hydrogel is a coating layer, and the response and recovery speeds of the sensor are significantly improved in this case.…”

“…As-prepared film sensors were able to detect alterations of temperature or humidity, with good sensitivity, low limit of detection, and fast response, as well as good stability, and therefore revealed promising applications as wearable and multi-functional electronics. Thermal sensing capability of this type of sensors was mainly attributed to the physical changes in hydrogels, i.e., variation of capacitance or resistance arose from the thermal expansion effect (volume changes) or the formation of interfacial water layer, , instead of from the chemical changes of structures. In other words, the construction of temperature-sensitive units in the reported studies is limited to the changes of physical structures.…”