Temperature Responsive Hydrogels:Construction and Applications

Abstract

IntroductionAs a kind of smart materials, responsive hydrogels exhibit the rapidly responsive ability and sharp volume phase transitions according to the external stimuli from environment. Hydrogels demonstrate large-scale volumetric changes in response to small levels of stimuli. To the best of our knowledge, the most typical external stimuli factors related to responsive behaviors of smart hydrogels are pH [1][2][3][4][5], temperature [6][7][8], light [9][10][11] and multi-factors [12][13][14][15][16]. Additionally, the responsive hydrogels based on enzyme responsive [17,18], calcium responsive [19,20], glucose responsive [21,22], redox responsive [23,24], ionicstrength responsive [25,26], and chemical responsive [27] are also exhibited amazing responsive abilities. Among these insights, temperature responsive hydrogels are particularly important.This article gives an overview of the fundamentals of temperature responsive hydrogels. Some researches related to the construction methods, responsive mechanisms and applications of responsive hydrogels in the past few years are reviewed. Construction Method of Temperature Responsive HydrogelsThe temperature responsive hydrogels introduced in this section are mainly prepared based on the scaffolds of supramolecular assembled structure [28][29][30], hydrogel films [31] and hydrogel sphere [32,33]. Additionally, the temperature responsive hydrogels constructed employing the novel technics are also summarized [34][35][36]. Ritter and coworkers pioneered in construction of temperature responsive hydrogel using N-isopropylacrylamide as monomer [37]. As illustrated in Figure 1 based on the hostguest interaction between adamantyl group and cyclodextrin, the thermosensitive hydrogel 1 was prepared. Similarly, based on the host-guest interaction between D3-symmetric tris(spiroborate) cyclophane and [Ir(tpy) 2 ](PF 6 ) 3 complex, the assembled chain structure was obtained by Yamaguchi et al.[38]. Moreover, employing the host-guest interaction between cucurbit[8]uril and viologen/naphthoxy, a thermo-sensitive supramolecular polymer hydrogel 2 was prepared by Scherman and coworkers [39]. Typically, as the dynamic cross-link of CB[8]/viologen/naphthoxy, this hydrogel exhibited thermal reversibility. Additionally, the temperature responsive hydrogels based on hydrophobic interaction of dipeptides [40] and cyclic macromonomer crosslinking interaction [41] were also reported. Using a photo-crosslinkable benzophenone unit, Knoll and coworkers prepared the responsive hydrogel films by photo-cross-link method based on poly(N-isopropylacrylamide)(PNIPAM) copolymer [42]. To fabricate hydrogel nanoparticles with ultrafine nanosized hair, Yang's group developed a simple self-developed approach AbstractResponsive hydrogels have attracted researcher's special attentions. Up to now, a wide variety of responsive hydrogels are continuously constructed and the responsive mechanisms are deeply investigated. Typically, versatile responsive hydrogels with pH responsive, temperature responsive, ligh...

Nanoparticles

“…They demonstrated almost complete selectivity of release following stimulation with ultrasound. Similar hydrogels and polymers have been developed that are temperature [42][43][44] , pH [45][46][47][48] or light responsive [49][50][51] .…”

“…The heat range in which this occurs is referred to as the upper and lower critical solution temperatures [42][43][44] . Unfortunately, it can often be challenging to control temperature or photoenervation in-vivo so pH responsive polymers tend to be a bit more popular.…”

Recent advances in the synthesis of smart hydrogels

“…Furthermore, the diversified properties and applications of hydrogels have reasoned thousands of research articles focusing on various aspects. Numerous review articles on the different broad-spectrum are also found based on applications [49][50][51][52] and hydrogel types [53][54][55][56][57] . However, a critical review addressing the techniques to tailor different functional properties and governing mechanisms of responsive behavior are yet to be amassed into a single frame.…”

Functional organic dyes for health‐related applications

“…Since then, organic dyes have been applied as colorants in textiles dyeing, sensitizers in dye‐sensitized solar cells, emitting layer in organic light‐emitting diode, photovoltaic charge separation, and charge‐carrier transporter in field‐effect transistors 5 . With the development of dye stuff chemistry, the chemical structure‐optical property relationship has been elucidated for all kinds of dyes such as cyanine (Cy), rylene, and aggregation‐induced emission dye (AIEgen) 6‐8 . Encountering the vastly increasing biomedical demands, organic dyes have recently been applied for health‐related applications such as in vivo imaging, disease diagnosis, and treatment 9 .…”