Hofmeister‐Effect‐Guided Ionohydrogel Design as Printable Bioelectronic Devices

Abstract

Bioelectronic platforms convert biological signals into electrical signals by utilizing biocatalysts that provide tools to monitor the activity of cells and tissues. Traditional conducting materials such as solid conductors and conducting polymers are confronted with a great challenge in sophisticated production processes and mismatch at biological tissues–machine interfaces. Furthermore, the biocatalyst, the key functional component in the electron‐transfer reaction for bio‐signal detection denatures easily in an ionic conductive solution. Herein, a bionic strategy is elaborately developed to synthesize an ionohydrogel bioelectronic platform that possesses extracellular‐matrix‐like habitat by employing hydrated ionic liquids (HILs) as ionic solvent and bioprotectant. This strategy realizes an integration of ionic and enzymatic electronic circuits and minimization of the disparities between tissues and artificial machines. The Hofmeister effect of HILs on enzyme proteins and polymer chains ensures the high bioactivity of the enzymes and greatly improves the mechanical properties of the ionohydrogels. Moreover, hydrogen bonds formed by ILs, water, and polymer chains greatly improve the water‐retention of the ionohydrogel and give it more practical significance. Consequently, the promising ionohydrogel is partly printed and fabricated into wearable devices as a pain‐free humoral components monitor and a wireless motion‐sensor.

Adaptive Ionogel Paint from Room‐Temperature Autonomous Polymerization of α‐Thioctic Acid for Stretchable and Healable Electronics

“…[ 25,26,49–52 ] The 90° peeling tests were performed to evaluate the adhesion energy of polyTA ionogel on different substrates (Figure 4c). The measured adhesion energy ranges from 53 to 428 J m −2 with the substrates of glass, porcine skin, polyethylene (PE), PE terephthalate (PET), and copper (Figure 4d), much higher than hydrogel paint based on coupling agent‐modification [ 18 ] and comparable to a few reported adhesive hydrogels, [ 20,50,53 ] ionohydrogels, [ 31 ] and ionic elastomers. [ 54,55 ] Since all the substrates are smooth and the peeling forces are very stable in the steady state, the adhesion damage should occur mainly due to interfacial failure.…”

“…It is noticeable that, [EMI][ES] and [EMI][DCA] have been frequently used as the organic solvents for preparing polyacrylic acid‐based stretchable ionogels via forming moderate H‐bonds with carboxylic acid groups. [ 15,31,35,36 ] To verify the existence of such H‐bond in the case of polyTA ionogel (as illustrated in Figure a), we performed ATR‐FTIR and 1 H NMR spectral comparison between different components. As shown in Figure 2b, clear evidence comes from the emergence of a new shoulder peak of v (COOH) at around 1734 cm −1 in polyTA ionogel, corresponding to a weakly H‐bonded COOH with [ES], while mainly strong dimeric H‐bonds exist in pure polyTA observed at 1703 cm −1 .…”

“…Inspired by these previous reports and above considerations, herein, by elaborately adjusting the internal interactions in polyTA elastomer, we report the facile preparation of ionogel paint from the room‐temperature autonomous polymerization of TA in the presence of a low‐toxic, air‐stable IL—1‐ethyl‐3‐methylimidazolium ethyl sulfate ([EMI][ES]). [ 31 ] [EMI][ES] well stabilizes the as‐polymerized polyTA with the aid of H‐bonds between [ES] and carboxylic acids, resulting in a highly transparent and superelastic ionogel that is readily dissolved in ethanol. Owing to the low surface tension of ethanol (γ ≈ 22.39 mN m −1 at 20 °C), the formed ionogel paint easily spreads on arbitrarily shaped solid surfaces, such as being casted on planar/nonplanar substrates or infiltrated into porous substrates with good adhesion and mechanical adaptability, rendering the substrates with excellent ionic conductivity and sensing abilities.…”

A mechanical, electrical dual autonomous self-healing multifunctional composite hydrogel

“…Meanwhile, the ionic circuits were achieved by the migration of cations and anions in hydrated ILs ​[ 31 ] to endow the hydrogel with good ionic conductivity [ 32 , 33 ]. Such ionic conductive hydrogel will have higher conductivity than the electron conductive hydrogel, prepared by composing the conductive polymer, because it has higher concentration of counterions as the charge carrier [ 34 ].…”

Regenerated hydrogel electrolyte towards an all-gel supercapacitor

“…For example, polyacrylamide (PAM)-based hydrogels exhibit good flexibility and water retention [13,14], while zwitterion hydrogels feature promising zwitterion conductivity [15][16][17], all of which offer an ideal platform for constructing flexible and self-healing electronics. Meanwhile, the expanding development of gel electrolytes from traditional aqueous gel electrolytes to non-aqueous gel electrolytes has served to facilitate significantly enhanced ion migration rates and mechanical properties of electrolytes, thereby greatly improving their electrochemical performance [18][19][20]. However, the synthesis routes for functional PAMbased hydrogels or zwitterion gel electrolytes feature complicated design and operation elements.…”