Minimal oxidation and inflammogenicity of pristine graphene with residence in the lung

Abstract

Two-dimensional graphitic carbon, graphene, is a new form of nanomaterial with great potential in a wide variety of applications. It is therefore crucial to investigate the behaviour of graphene in biological systems to assess potential adverse effects that might follow from inhalation exposure. In this study we focussed on medium-term effects of graphene in lung tissue by investigating the pulmonary inflammation 6 weeks after pharyngeal aspiration of unoxidised multilayered graphene platelets (GPs) in mice and assessed their biopersistence in the lung tissue using Raman spectroscopy. Additionally, GP degradation in vitro was examined after horseradish peroxidase (HRP) treatment up to 1 week. Building on our previous report showing acute inflammation in mice lungs at 1 day, pristine GP showed minimal inflammation in mouse lungs after 6 weeks even though no degradation of GP in lung tissue was observed and large deposits of GP were evident in the lungs. Raman analysis of GP in tissue sections showed minimal oxidation, and in vitro examinations of enzymatic oxidation of GP via HRP and H₂O₂ showed only slight increases in I_D/I_G ratio and the appearance of the Raman D' band at 1620 cm⁻¹ (surrogates of graphene oxidation). Our results showing non-inflammogenicity at medium time points have important implications in the hazard identification of GPs following inhalation exposure and for their use in biomedical applications. Additionally, the biopersistence of pristine GP in vivo with no associated inflammation could open the way to applications in tissue engineering and drug delivery.

Keywords::

• pristine graphene
• oxidation
• horseradish peroxidase
• biodegradation
• lung inflammogenicity

Acknowledgements

We are grateful to O. Nerushev, A. Gromov and K. Fisher for technical support with the Raman spectrometer and chemical oxidation of GPs.

Author contributions

AS, KD and CJC initiated, designed, directed and performed all experiments (excluding AFM) and took responsibility for planning and writing the manuscript. FAM contributed to design the experiments and write the manuscript. AS, AA, VK and KS prepared samples for AFM experiments and performed AFM measurements and analysis.

Funding sources

The research was funded by the Colt Foundation (AS and KD), The Department of Health (FAM), EaStCHEM and Leverhulme Trust (CJC) and Eric Birse Charitable Trust and Materials, Physics and Nanosciences COST Action MP1106 (AA,VK and KS).