| The functional conductive hydrogels play a vital role in wearable devices,wound healing,and tissue engineering.With the excellent biocompatibility,agarose-based gels possess a higher practical application value.However,the agarose gel itself does not have the versatility of conductivity,tissue adhesion,stretchability,and self-healing,and the agarose chain molecules are rigid,resulting in weak mechanical properties of the gel and unable to meet the various application requirements.In order to solve the above problems,we designed and constructed an Agarose-Ag NWs conductive hydrogel system based on patterned silver nanowires?Ag NWs?,as well as a Glycerol-PDA-CNTs@agarose conductive gel system based on glycerol,polydopamine?PDA?,and single-walled carbon nanotubes?CNTs?.The processes and conditions of preparation are simple and mild,and the main conclusions of the study are as follows:?1?In the Agarose-Ag NWs conductive hydrogel system,Ag NWs with high aspect ratio were synthesized by polyol hydrothermal method,with a length of 50-100?m and a diameter of 60-80 nm.The size of Ag NWs is uniform,and the solution of Ag NWs possess a good stability.The conductive pattern of Ag NWs was prepared by the mask method,and its conductivity reached 4.1×10-4 S/cm,which was significantly better than the conductivity of the conductive hydrogel prepared by doping method at the same dosage.Pouring hot agarose solution to make the solution fully infiltrate Ag NWs.After transfer,agarose gel with conductive pattern of Ag NWs on the surface is successfully obtained.Furthermore,we successfully embedded the Ag NWs on the surface of the gel into the surface of the gel with infrared radiation treatment because of the heat-sensitive sol-gel conversion,which can be clearly observed under the scanning electron microscope,and further confirmed by the fatigue wear test that the Ag NWs embedded in the surface of the gel possesses better stability.The infrared radiation treatment time is too long will lead to excessive dehydration of the gel to form wrinkles,through regulation,determined that 10 minutes is the best treatment time.After then,we change the preparation concentration of Ag NWs,from 0 mg/mL to 50 mg/m L,and the conductivity of the hydrogels were measured using four-probe instrument.It can be seen that the conductivity of the gel is adjustable within the range of 10-6-10 S/cm,and the infrared radiation treatment has little effect on the conductivity of the gels with comparison,the maximum conductivity of the gel is only reduced from 3.31±0.84 S/cm to 1.85±0.47 S/cm.Finally,a biosensor based on the Agarose-Ag NWs conductive hydrogel is constructed for monitoring human joint movement,and the performance displays that the sensor possesses excellent sensitivity and stability,indicating that the gel has certain application prospects in the field of flexible wearable devices.?2?In the Glycerol-PDA-CNTs@agarose conductive gel system,a lower concentration?2 mM?of dopamine monomer was used to react with CNTs to form granular PDA particles on the surface of CNTs,and the water phase was successfully prepared.PDA-CNTs with medium dispersion and good stability,and the ZETA potential value is-32.8±0.8 mV.Observing the PDA-CNTs by SEM can clearly distinguish a single carbon tube.After mixing the agarose,glycerol and water,the Glycerol-PDA-CNTs@agarose conductive gel is prepared through a simple heating-cooling process,in which PDA-CNTs are randomly distributed inside the agarose gel,which can form a uniform and complete network-like structure to realize electrons transport.The electrical conductivity of the gel was measured by an electrochemical workstation,and it was found that its conductivity was positively correlated with the content of PDA-CNTs and negatively correlated with the content of glycerol.The conductivity of the gel could reach 0.32 S/m without glycerol,after adding 25 vol.%glycerol,the conductivity decreased to 0.12 S/m,because glycerol will hinder the electronic and ionic conduction in the system.In addition,the gel has rapid and efficient self-healing conductivity.The gel can still maintain 94.6±2.5%of the initial conductivity level after six cycles of incision-repair.The gel has accurate and stable deformation response performance,and it is a relationship between relative impedance?and the bending angle?within the bending deformation range from 0°to 90°.The function is?=0.15+0.38?+0.0015?2,which provides a theoretical basis for the construction of biosensors to detect human motion.The addition of an appropriate amount of glycerol?25 vol.%?gives the gel good and reversible adhesion properties.The maximum shear adhesion strength of the test substrates such as glass,aluminum and pigskin could reached to 1140 Pa,1510 Pa,and 1170 Pa,respectively.The mechanism of the adhesion performance may be the hydrogen bond and capillary force mediated by glycerol.The presence of glycerol also makes the gel possess anti-heating,anti-freezing,and moisture retention abilities.When the glycerol content is 25 vol.%,the relative mass can still be maintained at 39.2±0.5%after 168 h of exposure to the air for the reason that glycerol reduces the saturated vapor pressure of water and slows the rate of water evaporation.The nano-reinforcement effect of PDA-CNTs can increase the tensile strength,compressive strength,and shear recovery ability of the gel,and the mechanism is similar to the double network hydrogel.The glycerol promotes the relative movement of the backbone chains in the gel network,thereby greatly increasing the maximum elongation break rate from 13%to 115%of the gel,which solved the problem of rigidity and fragility of the agarose gel.After 2 days of co-culture with NIH3T3 cells,CCK-8 test and cell morphology observation showed that the gel possesses good affinity for cells,which was further proved by the epidermal stimulation test.The gel is non-toxic and has no obvious irritation,indicating that the good biocompatibility of the gels.Finally,the biosensor based on Glycerol-PDA-CNTs@agarose conductive gel can accurately monitor the bending movement of fingers,wrists,and elbows,as well as can be used to correct sitting posture.Compared with the Agarose-Ag NWs conductive hydrogel system,the Glycerol-PDA-CNTs@agarose conductive gel system has higher gel adhesion,stronger stretchability,and possesses anti-heating,anti-freezing,and moisture retention properties.But the Glycerol-PDA-CNTs@agarose conductive gel system is more complex and the preparation process are relatively more complicated.Compared to commercial conductive adhesives,Glycerol-PDA-CNTs@agarose conductive gel system shows the advantages of high biocompatibility and low price,but the conductivity and adhesion performance need to be further strengthened.All in all,Glycerol-PDA-CNTs@agarose conductive gel system has the significance of further research and improvement,and possesses the potential for commercial application. |
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