Introduction:
Conductive polymers are of great interest to regenerate tissues conducting electric signals. Recently, matrices containing polypyrrole (PPy) have been reported for tissue engineering of nervous, bone and muscle tissues1. However, production of 3D PPy-based scaffolds is rather difficult because pyrrole is water insoluble, while the polymer melting point exceeds its thermal destruction temperature. Moreover, scaffolds fabricated from pyrrole as a single component are fragile, which limits their application for tissue engineering. Therefore, a new simple technique to fabricate matrices containing PPy is needed. The current study was aimed at preparation of composite macroporous polyvinyl alcohol (PVA) hydrogels with entrapped PPy fragments by novel simple technique, evaluation of their physicochemical properties and estimation of their ability to support cell growth in vitro.

Material and Methods:
The composite PVA-PPy were prepared using a two-stage procedure. First, PVA-based cryostructures containing PPy fragments were obtained by oxidative polymerization of pyrrole in water-frozen PVA solutions. At the second stage, PVA was covalently cross-linked by heat treatment at 100℃ and the structure of freeze-dried cryostructures was fixed. Cytotoxicity of the PVA-PPy hydrogels was evaluated using an extraction test. Mouse fibroblasts (L929) were used as a model cell line for this study. Morphology and spreading of the cells were studied by confocal laser scanning microscopy.

Results:
The obtained hydrogel samples varied in PPy content (2.5–20 wt. %) and in a time of heat treatment (60–120 min). Swelling behavior of the hydrogel samples was found to decrease with an increase in PPy content and an enhancement of heating time. Extraction test was used for evaluation of cytotoxicity of the PVA-PPy hydrogels. Extracts were obtained after previous incubation of the hydrogels samples in Dulbecco’s modified Eagle medium (DMEM) supplemented with 10% FBS for 24 h. Then, the cells were cultured in the extracts for 24 h, and then cell viability was determined by MTT-test. It was shown that all obtained hydrogel samples were non-cytotoxic. Additionally, human osteosarcoma cells (HOS) were cultured in the hydrogels for 7 days. Morphology and spreading of the cells were studied by confocal laser scanning microscopy in 24 h. The hydrogel samples heated at 100℃ for 90 min were optimal for cell adhesion, spreading and proliferation.

Conclusions:
The composite macroporous polyvinyl alcohol hydrogels with the entrapped polypyrrole fragments could be promising for tissue engineering.

Conflicts of interest:
The authors declare that they have no conflict of interest in the publication of this article. The authors have no conflicts of interest to report in this work. Abstract was not submitted elsewhere and was first published here.

Funding:
This study was partly supported by Russian Science Foundation (grant: 22-13-00261) and MSU Program of Development.