Novel polypyrrole derivatives to enhance conductive polymer-tissue interactions

Abstract

Developing materials that interact effectively with surrounding tissue is a major obstacle in sensor and drug delivery research. The body's natural immune response prevents foreign objects from easily integrating with an organism. Without an intimate link between a biomedical device and the proximate environment, reliable measurements or delivery of molecules is not possible. Many of the current materials used for biomedical applications are centered on inert substances and polymers that degrade in the body but have limited functional capabilities. This thesis work addresses the need to develop materials that are capable of interacting in biological environments. Polypyrrole (PPy) is a conducting polymer that is a promising biomaterial for drug delivery and sensing applications. Because PPy is a polymer that can be made in degradable forms and because it can be stimulated electrically, it is an interactive platform for biomedical applications. By accomplishing the following research objectives, this thesis work could help develop an effective polymeric paradigm for tissue interactions: 1) Develop a new method to effectively micro-pattern electrodeposited polymers and metals for in vivo devices 2) Determine the optimal synthesis conditions of the conductive polymer, PPy, for sensor and implant applications.

(cont.) 3) Fabricate PPy tubes to be used as nerve guides to promote nerve regeneration 4) Modify PPy for neurotrophic factor drug delivery devices and antibody-based sensing applications Through the use of standard microfabrication techniques, the patterning template upon which PPy is electrodeposited can be controlled precisely. By utilizing the growth mechanism of PPy on these templates, three-dimensional polymer objects can be created. Being able to micropattern the PPy and release the polymer generates the ability to create implants and devices that are completely erodible in the body. To develop the optimum conditions for sensor and drug delivery applications, PPy implants were fabricated and implanted into rat cortical tissue. Compared to similar Teflon implants, the electrically conductive PPy had preferable characteristics for material integration in the cortex. Additionally, PPy tubes have been designed and promoted peripheral nerve growth after tissue injury. By controlling the shape and morphology of PPy, the polymer implants formed an interactive bridge with their biological environment. By incorporating bioactive molecules into the PPy matrix, materials for externally controlled drug release and sensing devices can be designed.

(cont.) Drug delivery was demonstrated through the integration of nerve growth factor (NGF), a neurotrophic factor, into the PPy followed by triggered pulsatile release. Such neurotrophic factors can be used to promote neural growth in peripheral and central nervous system injury. Because PPy is easily modifiable through the use of dopants and control of its shape, PPy provides a flexible platform for novel polymeric-tissue interactions.