Shawn A. Sapp

Novel Degradable Co-polymers of Polypyrrole Support Cell Proliferation and Enhance Neurite Out-Growth with Electrical Stimulation

Synthetic polymers such as polypyrrole (PPy) are gaining significance in neural studies because of their conductive properties. We evaluated two novel biodegradable block co-polymers of PPy with poly(ε-caprolactone) (PCL) and poly(ethyl cyanoacrylate) (PECA) for nerve regeneration applications. PPy–PCL and PPy–PECA co-polymers can be processed from solvent-based colloidal dispersions and have essentially the same or greater conductivity (32 S/cm for PPy–PCL, 19 S/cm for PPy–PECA) compared to the PPy homo-polymer (22 S/cm). The PPy portions of the co-polymers permit electrical stimulation whereas the PCL or PECA blocks enable degradation by hydrolysis. For in vitro tests, films were prepared on polycarbonate sheets by air brushing layers of dispersions and pressing the films. We characterized the films for hydrolytic degradation, electrical conductivity, cell proliferation and neurite extension. The co-polymers were sufficient to carry out electrical stimulation of cells without the requirement of a metallic conductor underneath the co-polymer film. In vitro electrical stimulation of PPy–PCL significantly increased the number of PC12 cells bearing neurites compared to unstimulated PPy–PCL. For in vivo experiments, the PPy co-polymers were coated onto the inner walls of nerve guidance channels (NGCs) made of the commercially available non-conducting biodegradable polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV). The NGCs were implanted in a 10 mm defect made in the sciatic nerve of rats, and harvested after 8 weeks. Histological staining showed axonal growth. The studies indicated that these new conducting degradable biomaterials have good biocompatibility and support proliferation and growth of PC12 cells in vitro (with and without electrical stimulation) and neurons in vivo (without electrical stimulation).

Electric field stimulation through a biodegradable polypyrrole-co-polycaprolactone substrate enhances neural cell growth

Nerve guidance conduits (NGCs) are FDA-approved devices used to bridge gaps across severed nerve cables and help direct axons sprouting from the proximal end toward the distal stump. In this article, we present the development of a novel electrically conductive, biodegradable NGC made from a polypyrrole-block-polycaprolactone (PPy-PCL) copolymer material laminated with poly(lactic-co-glycolic acid) (PLGA). The PPy-PCL has a bulk conductivity ranging 10-20 S/cm and loses 40 wt % after 7 months under physiologic conditions. Dorsal root ganglia (DRG) grown on flat PPy-PCL/PLGA material exposed to direct current electric fields (EF) of 100 mV/cm for 2 h increased axon growth by 13% (± 2%) toward either electrode of a 2-electrode setup, compared with control grown on identical substrates without EF exposure. Alternating current increased axon growth by 21% (±3%) without an observable directional preference, compared with the same control group. The results from this study demonstrate PLGA-coated PPy-PCL is a unique biodegradable material that can deliver substrate EF stimulation to improve axon growth for peripheral nerve repair.

New Conducting and Semiconducting Polymers for Organic Photovoltaics

In the emerging field of low-cost printed electronics there is a lack of solvent processable conducting and semiconducting materials with highly tuned and known electronic properties. Currently the best performing conductors and semiconductors are not sufficient to produce truly printable, cost competitive organic photovoltaics (OPVs). TDA Research, Inc. (TDA) has been investigating a new class of solvent processable intrinsically conducting polymers for use as charge transport and transparent conducting layers in organic electronic devices. We have also begun the manufacture of electron-deficient semiconducting polymers that may prove to be excellent acceptors in bulk hetero-junction OPVs. This paper presents a summary of the materials characterization conducted on TDAs new electronic materials and how these may address several of the pressing issues preventing the realization of low-cost, printed solar cells and flexible electronics devices.