Physicochemical properties and toxicity of soluble polypyrrole: A study of its potential for biomedical applications

Polypyrrole is one of the most promising polymers for biomedical applications, and its low solubility in most common solvents led to the development of soluble forms of this conducting polymer. In this study, the physicochemical properties and the in vivo toxicity of soluble polypyrrole were evaluated, aiming to validate its potential for biomedical applications. The pH, density, and miscibility in different solvents were determined in two soluble polypyrrole samples synthesized on different dates. Two nonclinical studies on the toxicity of soluble polypyrrole were conducted with Swiss mice distributed into groups according to the dose administered. The single-dose toxicity study (acute toxicity) consisted of a single intraperitoneal application of a soluble polypyrrole solution at the doses of 500 and 1,000 mg/kg, followed by observation during 14 days. The repeated-dose toxicity study lasted for 28 days with daily intraperitoneal applications of the soluble polypyrrole solution, at the doses of 250, 500, and 1,000 mg/kg. Parameters such as mortality, behavioral screening, water and ration intake, body mass evolution, organ indices, and the macroscopic evaluation of the organs were observed in both studies. Additionally, hematological and histopathological analyses were performed in the repeated-dose toxicity study. In the acute toxicity study, no mortality was verified during the 14 days of observation at any of the doses tested, indicating that soluble polypyrrole has an LD₅₀>1,000 mg/kg. The main alterations observed in the repeated-dose toxicity study involved the liver changes, such as in the increase of its relative weight, the presence of necrosis, and granulomatous inflammation. Considering the high doses administered and the time of application, the results indicate low toxicity of soluble polypyrrole when administered by the intraperitoneal route.