Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering

Department

Chemical Engineering

First Advisor

Samantha A. Meenach

Abstract

Electrically-responsive biomaterials such as conductive polymers and conductive hydrogels have piqued the interest of scientists for targeted payload delivery applications in recent years since generating electricity is easy. Conductive composite hydrogels are a specific class of hydrogel that can be designed to not only have mechanical properties similar to skin and soft tissue, but can also have electrical properties comparable to metals and organic semiconductors. These composite hydrogels have been considered for a wide range of technological applications. Conductive hydrogels can be fabricated to ensure that they exhibit: 1) excellent biocompatibility; 2) soft and tunable mechanical properties similar to biological tissue; 3) mixed electronic/ionic conductivity that promotes efficient signal transduction for delivering drugs to the tissue; 4) ability to create materials with well-controlled microstructure; and 5) ability to be loaded with wide range of molecular size molecules with different molecular charge; thereby making conductive hydrogels a stronger tool for targeted delivery applications.

This dissertation focuses on describing a novel method of creating hydrogel composites from the commercially available conductive polymer PEDOT (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate). The resulting method allows for fast production of conductive hydrogels, and does not need specific equipment. In this method of production, a wide range of mechanical properties can be achieved by altering hydrogel composition and production temperature without jeopardizing the electrical properties of the hydrogels by using conductive polymer. Additionally, this method could be employed for fabrication of conductive composite hydrogels with a variety of polymers and cross-linkers.

Chapter two provides an overview on electrically-responsive targeted delivery depots with respect to their release mechanisms from electrical stimulation, parameters affecting drug release with electricity, and current efforts on multi-drug delivery using electrically-responsive materials.

In chapter three, we explored the production and application of pAAc-PEDOT (poly acrylic acid-poly(3,4-ethylenedioxthiophene):polystyrene sulfonate) cryogels. Our goal was to develop soft, injectable, and conducting hydrogel-based electrode materials, and to characterize their sustained mechanical and electrical properties before and after sterilization and injection. Biocompatibility, cytotoxicity, and drug delivery capability of these cryogels were also investigated. pAAc-PEDOT cryogels were made at a subfreezing temperature to generate a macroporous structure within the gels. The resulting porous hydrogels exhibited enhanced mechanical properties. The cryogels exhibited softness (0.2-20 kPa), excellent toughness, and strain of failure, and could survive injection through 16-gauge needle. Additionally, these gels demonstrated the capability of recording alpha oscillations. Last but not least, these cryogels were found to be biocompatible and were capable of being loaded with and delivering proteins.

In chapter four, we investigated the integration of conductive hydrogels (alginate-PEDOT) with tripolar concentric ring electrodes (TCREs). Our goal was to develop hydrogel-integrated electrodes with isolated channels to improve the quality of recorded signals. To this end, we fabricated alginate-PEDOT hydrogels and explored their mechanical and electrical properties to identify an optimized hydrogel formulation. We also investigated the channel isolation of our proposed electrode design. Furthermore, we used our novel electrode to record neural activity and compared recorded signals of hydrogel TCREs with those of conductive paste.

Chapter five provides overall conclusions for this dissertation as well as comments on potential future work.

Available for download on Monday, April 12, 2021

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