Poster O7 - Surface Modified Electrospun Soft PDMS Fibers for Stretchable Bioelectronic Applications

Introduction: PDMS is a widely used elastomeric material known for its flexibility and biocompatibility, making it suitable for various biomedical and engineering applications [1]. However, its hydrophobic nature can limit its interactions with biological substances and fluidic applications. The introduction of PEG, a hydrophilic polymer, into PDMS addresses this challenge by imparting improved hydrophilicity, biocompatibility, and functional versatility to the material [2]. This surface modification technique holds great promise in advancing the performance of PDMS in fields such as tissue engineering, drug delivery, and biosensor development. Notably, the surface modification of PDMS using PEG does not interfere with its capacity to be patterned with conductive ink. Herein, we present the integration of PEG with electrospun PDMS fibers with systematic studies of hydrophilicity applications as an epidermal electronic device.

Materials and

Methods: Sylgard 184 silicone elastomer kit (PDMS) was purchased from Ellsworth Adhesives (Germantown, WI). Dimethylsiloxane (60-70% Ethylene Oxide) Block Copolymer (PEG BCP) MW 600, 20 cSt was purchased from Gelest (Morrisville, PA). Polyvinylpyrrolidone (PVP) and Tetrahydrofuran (THF) were purchased from ThermoFisher Scientific (Waltham, MA). Intexar PE874 Stretchable Silver Conductor was purchased from Dupont (Wilmington, DE). Liquid Bandage was purchased from New-Skin (Cedar Knolls, NJ). PDMS fibers were created using the MSK-NFES-3 benchtop electrospinning unit. After fiber deposition, fiber mats were cured in an oven at 100 ⁰C for 24 hours; then the PVP sheath was removed by soaking fiber mats in ethanol for 20 minutes. The systematic study of PDMS-PEG was investigated with 10:1 and 30:1 elastomeric base to cure ratios of PDMS. PEG BCP was added to PDMS mixtures in weight percentages (w/v) of 1% and 2% with added THF in weight percentages (w/v) of 10%, 15%, and 20%. The stretchability and adhesion strength of the PDMS-PEG and PDMS fiber mats at different concentrations (n = 8) was assessed using the ESM303 Mark 10 with a 25-force gauge at a 0.5 mm/min strain rate. The circuit was printed on a PDMS-PEG sample containing 2% BCP and 15% THF using the Voltera V-One Desktop PCB Printer (Waterloo, ON). The circuit was printed using a needle height of 0.17mm, extrusion rate of +27, and cured at 130℃ for 15 minutes. Liquid bandage was used to adhere the Surface Mount LED Chip (DigiKey, River Falls, MN) to the end of the conductive circuit.

Results, Conclusions, and Discussions: PEG BCP reportedly enhances the Si-O group in PDMS, resulting in a more hydrophilic surface due to an increase in a silicon oxide (SiOx) rich layer; this explains the decrease in WCA with increasing additions of PEG (Figure 1A). When we further observe the mechanical properties of the fiber mat groups, we see a decrease in stress and strain of the PDMS-PEG groups compared to the pure PDMS (Figure 1B). The pure PDMS fiber mat, 1% PDMS-PEG fiber mat, and 2% PDMS-PEG fiber mat yield a max percent strain before fracture of 563.20%, 308.80%, and 189.60%, respectively. Based on this trend, the stretchability of PDMS fibers decreases approximately 1.725 times per 1% addition of PEG. Pure PDMS fiber mats have an adhesion force of 19.21 kPa, while the 1% and 2% PDMS-PEG fiber mats have an adhesion force of 2.62 kPa and 1.64 kPa, respectively (Figure 1C). PDMS-PEG fiber mats have similar adhesion loads to commercially available wound dressings such as Allevyn Adhesives and Mepilex Border [3]. The PDMS-PEG fiber mat, through Van der Waals forces, even with its low adhesion strength, maintains contact with the stratum corneum under stretching, twisting, and compression motions of the skin. A conductive circuit made with stretchable ink can be printed directly onto a PDMS-PEG sample containing 2% BCP and 15% THF. The fiber mat and conductive circuit can be seen in Figure 1D adhering to the skin and lighting up an LED, demonstrating applications with flexible biosensors despite its softer mechanical properties. Incorporating PEG BCP into PDMS fiber mats enhances hydrophilicity and alters mechanical properties. PDMS-PEG samples show a lower stress and strain and adhesion force compared to pure PDMS samples. Despite softer mechanical properties the PDMS-PEG samples maintain adhesion to the skin while stretching, twisting, and compression. Additionally, the softer mechanical properties do not affect the ability to pattern the fiber mats with conductive circuits. Furthermore, the integration of stretchable conductive circuits onto PDMS-PEG samples enables the development of flexible biosensors, as demonstrated by the successful illumination of an LED on skin.

Acknowledgements (Optional): This research is supported by the National Science Foundation (NSF CAREER; CBET #2238173).