Tracking nanoparticle movement deep inside our lungs

Lung disease is the third leading cause of deaths worldwide, according to a study by the World Health Organization. The respiratory system is prone to numerous diseases like asthma, bronchitis, pneumonia, and cancer. Many of these are caused by nanoparticles that deposit on the inner surfaces in our lungs.

• How does our breathing pattern affect the transport and deposition of these nanoparticles?
• Does our breathing rate during different activities like sleeping, running or walking have any significant effect on this?
• What are the differences in the breathing profiles of healthy persons and those with diseases?
• Can predicting nanoparticle movement in the lung help combat lung disease?

These are some of the questions that Chitresh Bhargava, a research scholar with the IITB-Monash Research Academy, is seeking answers to as part of his PhD project titled ‘Deep in the Lung: Nanoparticles transport and deposition in alveolar flows’.

“The transfer of desirable (drugs) or undesirable aerosols (pollutants) in the lung occurs with the exchange of oxygen and carbon dioxide in small sacs known as alveoli (more than 300 million in number). Understanding the transport and deposition of such nanoparticles is of deep interest to me,” says Chitresh. “It enables us to study health effects — both from the point of view of potential risks due to pollutants and safety to pharmaceutical drug delivery.”

Previous studies suggest that factors such as the particle size and carrier airflow pattern determine the deposition fraction in regions such as nasal pharyngeal, bronchioles and alveoli. “It has been reported that a fine particle size (approximately 20 nm) has a deposition fraction of 90% in the alveoli”, which suggests that diffusion is the main mechanism of particle deposition. However, studies reveal that diffusion cannot be the only reason. Convective transport plays a vital role as well in the transport of particles along the conducting airways.”

During his research, Chitresh will simulate and analyze fluid flow and particle deposition in various complex alveolar models of the pulmonary tract through computational fluid dynamics (CFD). “In a series of studies, we will employ the CFD approach as it allows us to consider flows that are very difficult to model experimentally even for very small particles. However, CFD has not yet been used extensively to study alveolar deposition. Limitations such as failure to incorporate the accurate shape of the alveoli, expansion-contraction of the alveoli during breathing, and the impact of breathing rate on the transport and deposition of aerosols have influenced us to work on a more accurate method to track particles in the alveoli.”

Airflow simulation in an alveolated duct 3D model for Reynolds number 0.01. The streamline profile shows re-circulation of air in alveoli

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars like Chitresh study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Says Prof Murali Sastry, CEO of the IITB-Monash Research Academy, “Extensive research is being conducted to ascertain new drugs and drug delivery systems for pulmonary delivery that are more efficient and safe. It is first important, though, to understand the mechanism of transport and deposition of the particulate matter in the human lung rather than directly switching to the drug delivery system for treatment of a number of diseases. Thus, the prediction of the particle deposition in the human pulmonary tract is of vital importance to evaluate the risks associated with exposure to air pollutants. We hope Chitresh’s research will lead to a novel understanding of transport and deposition mechanisms that occur in alveolar flows, which, in turn, will help us all breathe a little easier!”