Biodegradable nanofibrous polymeric substrates for generating elastic and flexible electronics

Abstract

Biodegradable nanofibrous polymeric substrates are used to fabricate suturable, elastic, and flexible electronics and sensors. The fibrous microstructure of the substrate makes it permeable to gas and liquid and facilitates the patterning process. As a proof-of-principle, temperature and strain sensors are fabricated on this elastic substrate and tested in vitro. The proposed system can be implemented in the field of bioresorbable electronics and the emerging area of smart wound dressings.

Keywords: biodegradable electronics; elastic devices; implantable sensors; nanofibrous substrates; wound dressings.

Figure 1

Fabrication and characterizations of PGS-PCL substrate-based electronics. (a) Schematic of the electrospinning setup used for fabricating sheets with uniform thickness (i,ii) and fabricating a conductive pattern by screen printing of silver ink on a substrate using a shadow mask (iii). (b) Representative SEM images of typical PGS-PCL electrospun sheets (with the ratio of 1:1), side view (i) and top view (ii). (c) A representative image of patterned electrospun sheet with a zoomed in micrograph showing the preservation of the PGS-PCL microstructure after the patterning process. (d) Representative strain-stress curves for a typical PGS-PCL elctrospun sheet and a sheet containing a conductive pattern. (e) Electrical resistance of different pattern that indicates repeatability of the pattern formation on the surface of electrospun sheet (at least n = 6 independent measurements).

Figure 2

Elasticity and flexibility of the fiber-based electronic circuits. (a) Variation of the electrical conductivity of the serpentine line as a function of mechanical strain. (i) Images show the setup used for stretching the sample and measuring its tensile mechanical properties while monitoring its electrical resistance. (ii) The values of electrical resistance of the stretched patterns (R) nondimensionalized with the values in the unstretched condition (R₀); the presented results are the average of (at least n = 6) independent measurement. (b) Effect of cyclic load on the electrical resistance (i) and stress-strain curve (ii) of the fabricated pattern; the device was stretched by 4% of its original length and then released to its original length with a rate of 1 cycle/minute. (c) Schematic diagram of patterned silver on sheet and wrapping around curved surface with different curvature radii (top) and the ratio of the measured electrical resistance after cyclic load (R) to the initial electrical resistance (R₀) of patterned silver on electrospun sheet versus the curve diameter to which the sheet is turned (bottom).

Figure 3

Electrical resistance of the fabricated devices in various environmental conditions. (a) The effect of media on the measured electrical resistance of serpentine lines patterned on the surface of PGS-PCL sheets; air represent the dry condition. (b) The electrical resistance of a coil patterned on the surface of an electrospun sheet inside cell media and incubator at 37 °C coil seeded with 3T3 cells over 14 days. (c) Images showing the degradation of the device inside a solution of 0.5 M NaOH. (i) a typical device connected to grips for measuring its electrical resistance; (ii) image of a typical conductive pattern on the surface of an electrospun sheet before degradation. (iii) the image of the same structure after complete degradation of the polymeric substrate which left behind the conductive pattern. (d,f) Electrical resistance (R) of the patterned electrodes over 14 days in 0.5 mM NaOH and PBS nondimensionalized with respect to their original resistance after fabrication (R₀); the results are the average of n = 6 independent measurements. (e,g) Mass loss of the device over 14 day in 0.5 mM NaOH and PBS; the results are the average of n = 6 independent measurements.

Figure 4

Application of the PGS-PCL platform in functionalized wound patches. (a) The use of the platform as a bioresorbable temperature sensor and heater (i, ii). As a heater the device was covered with a temperature sensitive film (thermometer strip) and electrical voltage was applied to the conductive pattern which was used as a resistor to generate heat. The schematic of the system is shown (i) along with an image of the temperature sensitive film indicating “N” sign associated with 37 °C (iii); in the case of temperature sensor, the device was mounted on the surface of a heater and the conductive pattern was connected to a multimeter to measure its electrical resistance while the surface temperature was simultaneously measured with a T-type thermocouple (iv). The resistance in different temperatures (R) is nondimensionalized with respect to the resistance at 37 °C (R₃₇). (b) Fe₃O₄ paste screen-printed onto PGS-PCL sheets to create circular patterns in ordered arrangements. The patterned substrate was clamped to a micro-manipulator and was placed on top of a polyimide-insulated copper coil connected to an impedance analyzer. The variation in the resonant frequency of the coil was measured and correlated to the substrate strain.