A Composite Microfiber for Biodegradable Stretchable Electronics

Abstract

Biodegradable stretchable electronics have demonstrated great potential for future applications in stretchable electronics and can be resorbed, dissolved, and disintegrated in the environment. Most biodegradable electronic devices have used flexible biodegradable materials, which have limited conformality in wearable and implantable devices. Here, we report a biodegradable, biocompatible, and stretchable composite microfiber of poly(glycerol sebacate) (PGS) and polyvinyl alcohol (PVA) for transient stretchable device applications. Compositing high-strength PVA with stretchable and biodegradable PGS with poor processability, formability, and mechanical strength overcomes the limits of pure PGS. As an application, the stretchable microfiber-based strain sensor developed by the incorporation of Au nanoparticles (AuNPs) into a composite microfiber showed stable current response under cyclic and dynamic stretching at 30% strain. The sensor also showed the ability to monitor the strain produced by tapping, bending, and stretching of the finger, knee, and esophagus. The biodegradable and stretchable composite materials of PGS with additive PVA have great potential for use in transient and environmentally friendly stretchable electronics with reduced environmental footprint.

Keywords: biodegradable; microfiber; poly(glycerol sebacate); poly(vinyl alcohol); stretchable electronics; transient electronics.

Figure 1

Schematic and characteristics of biodegradable microfiber. (a) Representation of PGS:PVA composite microfiber. Hydrogen bonding is shown by the dotted lines between the PGS and PVA in the composite. (b) FT-IR spectra of the prepared composite solutions at various ratios of PGS:PVA (2:1, 2:1.5 and 2:2 (v/v)). (c) A cross-sectional FE-SEM image of a microfiber with a diameter of about 350 µm. The scale bar is 10 µm. (d) The photograph shows the uniform length of the fabricated microfibers. (e) The photograph demonstrates the conformity of the microfiber to a human finger.

Figure 2

Mechanical properties of the biodegradable microfiber. (a) Stress-strain curves of the microfibers with varying loading ratios of PGS:PVA (2:1, 2:1.5, 2:2 (v/v)). (b) Strength, (c) Young’s modulus, and (d) toughness of the biodegradable microfibers with various loading ratios of PGS:PVA (2:1, 2:1.5, 2:2 (v/v)). (e) Creep test of a microfiber at a loading ratio of 2:1.5 under a hanging weight of 30 g at room temperature. The initial length is measured before addition of the hanging weight, and the final length change is in terms of extension% measured after removal of the weight.

Figure 3

Biodegradability of the microfiber. The PVA microfiber and biodegradable PGS:PVA composite microfiber with a loading ratio of 2:1.5 were modified by incorporating FITC and Fluoresbrite^®dye, respectively, and the images were captured using a confocal microscope. (a) Biodegradability pattern of PVA (green) and PGS:PVA (red) microfibers from 0 to 28 days. The composite microfiber shows the fast degradation while stiff PVA shows slow degradation. After 28 days most of the the PVA and composite microfibers are degraded at set conditions. (b) Cell viability was assayed by LIVE/DEAD cell staining in the solution (live cells as green fluorescence and dead cells as red fluorescence) at an interval of 5 days. The scale bar is 20 µm. (c) Cell viability data evaluated by LIVE/DEAD cell staining. (d) Photographs of a 1cm long microfiber attached to skin with a cotton band-aid (left panel). After 24 h, the sample was removed (right panel) from the skin, and no redness or irritation was observed. After removing the microfiber there was no allergic reaction and no itching was reported by any of the four volunteers.

Figure 4

Demonstration of the biodegradable and stretchable strain sensor. (a) Schematic of AuNPs incorporated into PGS:PVA microfiber. (b) The current variation during cyclic stretching (100 stretch-release cycles) at 30% strain. (c) The current variation was recorded by the AuNP- incorporated strain sensor during tapping of the finger. The inset photograph shows the pressure applied by the finger on the strain sensor. (d) Response of the biodegradable strain sensor to bending and stretching of the knee. The inset is a photograph of the strain sensor attached conformally to the knee during bending and stretching. (e) The wearable strain sensor was attached to the esophagus, and current-time (I-T) response was measured during the movements. Inset photograph shows the strain sensor attached to the esophagus. (f) Response (I-T) of the wearable strain sensor to bending/relaxing of finger joints. The inset shows a photograph of microfiber-based stretchable strain sensors attached to the finger joints.