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Unravelling respiratory microflows in silico and in vitro: novel paths for targeted pulmonary delivery in infants and young children

Periodic Reporting for period 4 - RespMicroFlows (Unravelling respiratory microflows in silico and in vitro: novel paths for targeted pulmonary delivery in infants and young children)

Reporting period: 2020-12-01 to 2021-05-31

Fundamental research on respiratory transport phenomena, and in particular approaches for pulmonary drug delivery, are overwhelmingly focused on efforts conducted in adults. Results are then typically translated (or scaled down) and adopted to children. Yet, children are not miniature adults: their distinct and developing lung structures and heterogeneous ventilation patterns set them aside from their parents. Whether concerned with inhalation aerosol therapies for topical delivery (e.g. asthma) or systemic delivery (e.g. vaccination), current methods and strategies for delivery face ongoing challenges with typically low yields in achieving optimal delivery of therapeutics (i.e. low deposition rates). Such delivery challenges are also true for liquid-based therapies such as surfactant replacement therapy (SRT) in treating pulmonary conditions of the newborn (e.g. infant respiratory distress syndrome).

To this day, the deposition of inhaled pharmaceutics in young children remains alarmingly low. While parents and the broader public may not be fully aware, the deposition efficiency of inhaled drugs in kids is typically less than 10% for a given dose. In particular, for diseases that require targeting deep alveolated airways (e.g. cystic fibrosis), lung deposition is further reduced to levels below 5%. In turn, low deposition efficiencies of inhaled aerosols often require treatments based on "flooding" the lungs with drugs to achieve sufficient drug deposition, and thus carrying the risk of local side effects including inflammation due to deposition “hot spots” and possible systemic side effects as a result of chronic drug therapy. In parallel to inhalation aerosols, liquid therapies are commonly instilled in premature babies suffering from infant respiratory distress syndrome (IRDS). Premature births (about 13 million births/year worldwide) contribute to >25% of global neonatal deaths and are often accompanied by a surfactant deficiency. Surfactant replacement therapy is the foremost strategy used to treat IRDS by instilling endotracheally a surfactant-laden bolus in the neonatal lungs. In many instances, however, the bolus has to be administered more than once to ensure reaching alveoli. Since data are frequently limited, the optimal method for surfactant delivery has yet to be proven.

RespMicroFlows sets out to radically revisit the challenges of pulmonary drug delivery in babies and young children. By developing advanced in silico numerical simulations together with in vitro platforms mimicking the respiratory airway environment, our efforts will not only deliver a gateway to reliably assess the outcomes of inhaling aerosols and predict deposition patterns in young populations, but furthermore we will unravel the fundamentals of liquid bolus transport to achieve optimal surfactant delivery strategies in premature neonates. By recreating cellular environments that capture underlying physiological functions, our advanced organ-on-chips will deliver both at true scale and in real time the first robust and reliable in vitro screening platforms of exogenous therapeutic materials in the context of inhaled aerosols and surfactant-laden installations. Combining advanced engineering-driven flow visualization solutions with strong foundations in transport phenomena, fluid dynamics and respiratory physiology, RespMicroFlows' ambitions are entrenched in delivering new paradigms in drug delivery
We have achieved significant and exciting progress during this first reporting period, with efforts reaching across all Pillars (I through III) of the research project and tackling specific Aims of the project. These have principally covered in silico pulmonary flow and aerosol transport models (Pillar I, Aim 1), in vitro microfluidic airway models (Pillar I & II) and capillary blood models (Pillar II, Aim 4) as well as approaches for therapeutic assessments (Pillar III, Aim 5). In addition, our dissemination activities include the publication of an overview article on the project goals (EU Research, Spring 2017).
The three main and concurrent avenues of research within the framework of our ERC project that run alongside consist of (i) in silico numerical simulations, (ii) in vitro lung-on-chip developments and (iii) engineered solutions for (i.e. medical devices) for targeted drug delivery to the lungs.

In silico simulations: We have just published this past month in silico results supporting a new approach and shift of thought in selecting aerosol sizes for upper airway targeting in the lungs of children, based on transport/particle aerodynamic determinants with age/growth (Das et al., PLoS One 2018). We now hope ito prove this further with in vitro experiments of aerosol deposition using 3D printed models.

In terms of our small-scale in vitro work (point ii above), we are developing some of the most advanced lung-on-chip platforms for pulmonary physiology, cytotoxicity and drug screening assays. Two hallmarks of our work are captured by a bronchiole-on-chip model and an acinus-on-chip model that combine anatomy, flow physiology and cell biology.

On the larger scales, we have delivered a new engineered solution to point target inhalation aerosols to the lungs using inhaled magnetic particles: our technique combines the use of a smart inhaler that delivers short pulse-aerosol boluses of specific particle size (combining SPION nanoparticles) with an external magnet and breath hold technique. This work is breaking away from any existing inhalation aerosol technique available and our in vitro experiments support the feasibility of such inhalation technique. We are now moving into ex vivo experiments to push forward the establishment of the technique.
Computational models of heterogeneous acinar structures (Hofemeier et al., Eur. J. Pharm. Sci. 2017)
Lung-on-chip model for aerosol deposition assays (Fishler et al., Journal of Biomechanics 2017)