This summer I have the privilege of working in Western Washington University’s Chemistry lab under the supervision of Dr. Amanda Murphy. Her research involves creating silk-conducting polymer (CP) composites that can act as artificial muscle; these films are more flexible in vivo than current conducting polymers which are brittle and do not last long. When a silk film is chemically modified so that one side is active, ions diffuse across the film, causing expansion during oxidation and contraction during reduction. Dr. Murphy hopes to create silk-CPs that have increased durability, electrical conductivity, and stability.
Dr. Murphy’s lab has been experimenting with three CPs: poly(pyrrole) (Ppy), poly(3,4-ethylenedioxythiphene) (PEDOT), and poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH). The first layer of CP is chemically deposited onto the surface of the silk films, and an additional layer of CP is deposited using either electropolymerization or chemical polymerization. Electropolymerization techniques yield better results in regards to conductivity and occur in a dopant-monomer solution; the dopant (NaDBS or pTSA) allows for cation exchange. The chemical deposition of CPs onto silk films creates an interpenetrating network (IPN) which prevents delamination. After creating silk-CP IPNs between the conducting polymer and silk fibroin (from cocoons), her research students test the electrochemical properties of the silk-CP composites by performing cyclic voltammetry and four-point probe conductivity measurements to test resistivity.
There are many different aspects to this “artificial muscle” project, and I will be working on repelling proteins from accumulating on the surface of the silk-CP composites in vivo; protein accumulation hinders the ion exchange of the silk-CP composites. The first week in the lab, I was trained in every procedure relevant to my experiment.
I isolated and purified silk fibers from cocoons to make a silk solution. I cast this onto silicon sheets to create films. Once I acid-modified the films, I was able to deposit polymerized Ppy onto them. This produced a silk-Ppy composite that was electrically conducting. I prepared the silk films for electropolymerization by making them into electrodes. I electropolymerized these electrodes in a dopant-monomer solution (NaDBS as the dopant; Ppy, EDOT, or EDOT-OH as the monomer) and performed four-point probe conductivity tests to ensure that the resistivities were within the appropriate range. I repeated this procedure with the two other CPs.
To prevent protein-binding on the silk devices, I synthesized an oligo- or polyethylene glycol monomer, EDOT-EG4, or more specifically, EDOT-O-PEG; the literature shows that this monomer repels proteins. Currently, I am waiting to perform Nuclear magnetic resonance spectroscopy (NMR) to determine how pure the EDOT-O-PEG is. I will be synthesizing silk-EDOT-O-PEG composites and measuring their impact on protein accumulation and will be performing tests to determine a ratio of EDOT-EG4 to EDOT-OH for optimal conductivity and protein repulsion.
I am excited about working on a project that is so important; the thought that I am directly contributing to scientific progress drives me every day in the lab. Through this internship, I have seen instruments and techniques I have never engaged with in a chemistry lab. I believe my work has a purpose, and I am looking forward to everything I will learn in the next few weeks.