# The Impact of Physical Form on the Biocompatibility of Poly(3-hexylthiophene-2,5-diyl)

## TL;DR

This study shows that the physical form of a polymer affects its safety in biological systems, with nanoparticles being less biocompatible than films.

## Contribution

The novel comparison of P3HT films and nanoparticles reveals their differential biocompatibility with endothelial cells.

## Key findings

- P3HT films do not reduce the viability of bEnd.3 cells.
- P3HT nanoparticles lower cell viability by 20-30%, depending on the presence of PCBM.
- Light exposure does not affect the biocompatibility of P3HT-based materials.

## Abstract

Poly(3-hexylthiophene-2,5-diyl) (P3HT) is a semiconducting, electron donor polymer which, in addition to its intensive use in optoelectronic devices, is increasingly investigated in biological systems. However, there are conflicting reports about the biocompatibility of P3HT, and no direct comparison between P3HT films and P3HT nanoparticles has been conducted. In this context, we investigated the viability of bEnd.3 endothelial cells when such cells are grown onto P3HT films or incubated with P3HT nanoparticles and subjected to trains of moderate power density, relatively long light pulses. We observed that, while P3HT films do not decrease the viability of bEnd.3 cells at all, P3HT nanoparticles lower the viability of bEND.3 cells by ~20%, when the nanoparticles also contain [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as electron acceptor, and by ~30%, when the nanoparticles do not contain PCBM. Interestingly, the used photoexcitation protocol did not impact the biocompatibility of the P3HT-based materials. The obtained results reveal that (i). nanostructuring has a detrimental impact on the compatibility of P3HT with bEND.3 endothelial cells, and (ii). P3HT-based materials can be safely combined with light when used in biological systems because light, as used in the present study, does not alter the biocompatibility of such materials.