| Recently,the demand for bioelectronic devices of health monitoring is growing rapidly,especially for the flexible electronic skins attached to the human body.It has bright application prospects in many fields such as artificial prostheses and wearable devices.However,most materials currently used for flexible bioelectronic devices such as polycarbonate(PC),polyethylene terephthalate(PET)cannot take the biocompatibility,biodegradability,flexibility and stretch ability of the material into account at the same time.Due to its excellent air permeability,biocompatibility,mechanical compliance and degradability,naturally sourced silk fibroin(SF)has become an excellent substitute for these synthetic materials,and it is easy to be processed into various forms.However,the pure SF membrane is fragile and has poor chemical stability,so it is necessary to modify the SF membrane.In addition,most current fabrication techniques for flexible electronics are not compatible with SF and the conventional technology is transfer printing,which greatly limits their applications.As a mask-free,cost-effective and precise technology,ink-jet printing technology can simplify the fabrication process of flexible electronic devices with little effort.In this work,SF is the main material,then ink-jet printing and electrodeposition technology are used to prepare electrodes,which are assembled into a pressure sensor with biocompatibility,super flexibility and sensitivity.The research results are as follows:(1)PU was added into the SF solution to promote the crystallization of SF by solution blending method.The SF molecules form aggregates and were evenly dispersed in the PU network to form new cross-linking points,thereby building a new cross-linking network,which greatly improved the stretch ability of the SF-PU film(strain ε=255%).The SF-PU film exhibited high transparent(>90%),and can endure heat treatment(160℃)and are more flexible.(2)Based on this robust membrane,an ink-jet printing technique was introduced to successfully fabricate various patterned electrodes on SF-PU.And the effects of different heat treatment time,heat treatment temperature,number of printing layers,and heat treatment methods on silver electrodes were explored.At the same time,since the resistance of ink-jet printed granular silver is much higher than that of bulk silver(1.6 μΩ/cm),in order to further increase the stability and conductivity of the ink-jet printing electrodes,Ni was electrodeposited on the printed electrode and the influence of different electrodeposition currents density and electrodeposition time on the nickel electrode was discussed,and an electrode of less than 0.01 Ω/cm was obtained,which performed well during the bending tests.(3)The SF-PU printed with patterned electrodes is applied to a resistive pressure sensor.The result shows that the device has a good response time(75 ms),the sensitivity is 0.0169 kPa-1 in the pressure range of 0-16 kPa,and the sensitivity is 0.0021 kPa-1 when the pressure is higher than 16 kPa,showing super sensitive characteristics.Based on the electrodes,a palm-shaped protein-based electronic skin array integrated with 20 resistive pressure sensors was constructed.It can sense the pressure of different parts of the palm under different ball-holding position and monitor the pressure distribution precisely.This work provides a feasible manufacturing technology on protein substrates,which is conducive to the development of protein flexible electronic devices. |
