Enhancing the Interface in Silk–Polypyrrole Composites through Chemical Modification of Silk Fibroin

Abstract

To produce conductive, biocompatible, and mechanically robust materials for use in bioelectrical applications, we have developed a new strategy to selectively incorporate poly(pyrrole) (Ppy) into constructs made from silk fibroin. Here, we demonstrate that covalent attachment of negatively charged, hydrophilic sulfonic acid groups to the silk protein can selectively promote pyrrole absorption and polymerization within the modified films to form a conductive, interpenetrating network of Ppy and silk that is incapable of delamination. To further increase the conductivity and long-term stability of the Ppy network, a variety of small molecule sulfonic acid dopants were utilized and the properties of these silk-conducting polymer composites were monitored over time. The composites were evaluated using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), optical microscopy, energy-dispersive X-ray (EDX) spectroscopy, cyclic voltammetry, a 4-point resistivity probe and mechanical testing. In addition, the performance was evaluated following exposure to several biologically relevant enzymes. Using this strategy, we were able to produce mechanically robust polymer electrodes with stable electrochemical performance and sheet resistivities on the order of 1 × 10(2) Ω/sq (conductivity ∼1 S/cm).

Durable Flexible Supercapacitors Utilizing the Multifunctional Role of Ionic Liquids

“…CPs are classified as "smart materials" because of their inherent abilitiy to accept ac ounter ion for chargeb alancew hen oxidized and to expel the counter ion when reduced.H owever, CPs suffer from a number of disadvantages:t hey are intractable, insoluble,a nd not thermoformable.T herefore,t heir processability is ac hallenge and restrictst heir direct usage in real-life applications flexibility is ar equirement. Alternatively,C Ps can be made flexible by grafting them on paper, [8] fabric, [9] or by modifying carbon electrodes such as graphene. [10] However, grafted polymers suffer from poor adherence to the surface of their host materials and inhomogeneity leading to non-uniform active surfaces.T herefore,s upercapacitors based on CPs face problems such as capacitance fade,incomplete electrode wetting, restrictions in the thickness of electrodes,m echanical stability, and usage of environmentally toxic chemicals.O n the other hand, metallic semiconducting free-standing flexible films are experimentally challenging and expensive to prepare on alarge scale.…”

Toward Biodegradable Mg–Air Bioelectric Batteries Composed of Silk Fibroin–Polypyrrole Film

“…After 10 days, SF-PPy film lost 65% of its original weight, much higher than that (8%) previously reported for PPy coating on both side of silk substrate. [21] The role of degradation obtained can be attributed to the low β-sheet content in SF obtained via water annealing treatment and the unique bilayer structure of SF-PPy film, which facilitated the enzyme to attack the silk film with cleavage sites available on the surface. After 13 days incubation, SF-PPy film could not keep its original form and crumbled into small fractions due to the degradation of silk substrate.…”

“…[20] A degradation profile of 8% mass loss after 10 days incubation in protease XIV solution (10 U mL -1 ) was reported. [21] Towards paving the way for a biocompatible and biodegradable battery, here we report a SFPPy film as an air cathode material in a Mg-air bio-battery. In this SF-PPy film the PPy layer was chemically coated onto one side of a silk film substrate.…”

Silk‐Based Biomaterials in Biomedical Textiles and Fiber‐Based Implants

“…Remero et al (2013) demonstrated that covalent attachment of negatively charged, hydrophilic sulfonic acid groups to silk protein can promote pyrrole absorption and polymerization to form conductive, interpenetrating networks of pyrrole and silk that did not delaminate. A variety of small molecule sulfonic acid dopants were utilized to further increase the conductivity and long-term stability of the Ppy network [230] . An engineered recombinant spider silk protein eADF4(C 16 ) was modified with the integrin recognition sequence arginine-glycine-aspartic acid (RGD) by genetic (fusing the genetic sequence encoding GRGDSPG) and chemical (using the cyclic peptide c(RGDfK)) approaches [231] .…”