the present application relates to nanoparticle bioengineering techniques were used to produce a non - toxic polypyrrole composition having two - dimensional and three - dimensional structures that can optionally be co - polymerized with carboxylic acid moieties to possess hydrophilicity . likewise , such polypyrrole / carboxylic acid structures may be further modified with neural growth factors to create treatment surfaces that can promote growth an differentiation of cells such as neurons .