Background in fluid and cell transport: I have a strong background in fluid mechanics and soft matter physics. This is evident from my master’s degree from NTNU, my Ph.D. degree from the University of Oslo (UiO), and post-doctoral fellowships at Stanford University, UC Santa Barbara and UiO, see Fig.1.
Microfluidics: Microfluidic filtration: My Ph.D. research at UiO was a joint project with Sintef Digital aimed to characterize a commercial microfluidic filter. I used pressurized fluids to tune the microfluidic flow fields around special trilobite-shaped separation units, and I identified clog-free separation regimes for plastic particles and for live microalgae 1,2,3,4 . To describe the hydrodynamical interactions between the particles and the flow fields, I used a combination of micro Particle Image Velocimetry (?PIV) and Particle Tracking Velocimetry (PTV). The particle images were post-processed using an in-house made Matlab PIV-code.
Hydrodynamic Breadboard: These achievements inspired me to develop a construction base for modular microfluidic circuits (“The Hydrodynamic Breadboard” - inspired by the electrical analogue) that is inherently clog-free. Instead of using internal surfaces, it uses ‘virtual obstacles’ made of hydrodynamic flow structures. Specifically, these virtual obstacles are constructed by combinations of flow inlets (sources, ‘+’) and outlets (sinks, ‘-‘) that cannot be clogged because cells cannot adhere to them; Instead, they are deflected (Fig. 1). Bigger cells are deflected more, allowing separation by size.
The breadboard as teaching tool: During my post-doctoral fellowship at Stanford University, I was picked to lead a team of five graduate students in Bioengineering as part of a microfluidics manufacturing and laboratory class. In only ten weeks, the “Breadboard-team" created a hydrodynamic post that showed promising separation characteristics. To enable us to deploy Breadboards across the scientific community, I have an international pending patent5.
Interfacial dynamics:
I maintain a strong collaboration with the Fuller group at Stanford on problems involving gravitational Rayleigh-Taylor (R-T) instabilities in polymer solutions, miscible liquid drops, and drainage and de-wetting dynamics in thin-liquid films.
Our first study 6 recognizes that unstable concentration profiles can be induced in initially homogeneous materials through the action of evaporation, see Fig. 3a. By tuning the viscosity of polymer solutions (though tuning the concentration and molecular weight of the polymer), we were able to tune the onset of a R-T instability, which we predict by a simple scaling analysis. The onset time of the instability shows two limiting behaviors depending on the polymer diffusivity, see Fig. 3b. For high diffusivity polymers, the pluming time follows ?? 
as expected for diffusion stabilized systems. On the other hand, in low diffusivity polymers the pluming time follows a stronger concentration dependence, ?? ～ ?0?1. An effective interfacial tension, like those in immiscible systems, explains this strong concentration dependence.
The second study concerns the shape evolution of miscible (water) drops rising in more viscous liquids such as glycerol and corn syrup, see Fig. 4. The drops display different behavior depending on their transit time: early in their rise, the drops maintain a spherical shape and rise at a constant velocity (immiscible behavior), while at longer times, the drops become more oblate with the velocity decreasing as they start to mix with the ambient liquid through diffusion. We predict the transition between the immiscible behavior at “early times” and the miscible behavior at “late times” by a simple scaling parameter.
The last project [8] recognizes that contact lenses alter tear film stability due to the differences in surface properties as compared to the mucus layer of the eye. We characterize the effect of different surface coatings on the thin-film stability by using a dynamic thin-film interferometer developed in the group (see Fig.4). We reveal that despite the wide variations in wetting agent molecular properties like charge and polarity, the time to dewet.
50% of the contact lens linearly scales with the product of the receding contact angle (θr) and the contact angle hysteresis (cos θr ?cos θa). A corollary of this finding is the importance of minimizing contact angle hysteresis for effective wetting performance. Overall, we believe the methodology and results from this study provides a basis for identifying optimal wetting agents to minimize tear film dewetting and maximize patient comfort.
My main contribution to this project was conducting optical thin film interferometry experiments and reporting the obtained drainage and dewetting results directly to the scientific investigators at Johnson and Johnson, who sponsored this joint investigation.
[1] Mossige EJ, Jensen A, Mielnik MM, “An experimental characterization of a tunable separation device”, Microfluid. Nanofluid. 20, 160 (2016).
[2] Mossige EJ, Jensen A, Mielnik MM, “Separation and concentration without clogging using a high- throughput tunable filter”, Phys. Rev. Applied 9, 054007, 2018.
[3] Mossige EJ, Edvardsen B, Jensen A, Mielnik MM, “A tunable, microfluidic filter for clog-free concentration and separation of complex algal cells”, Microfluid. Nanofluid., 23(4), 2019.
[4] Mossige, EJ., & Jensen, A (2020). Clog-Free Trilobite Filtration: Tunable Flow Setup and Velocity Measurements. Micromachines, 11(10), 904. Invited contribution.
[5] Mossige EJ, Mathijssen AJTM, “Microfluidic device for hydrodynamic sorting and rheometry measurements of particles”. International patent. Application number: PCT/US2020/021216. Filed on: 3/14/2020.
[6] Mossige EJ, Chandran Suja V, Wheeler S, Islamov M, Fuller GG, 2020 “Evaporation induced Rayleigh- Taylor instabilities in aqueous polymer solutions”. Phil. Trans. R. Soc. A. 378: 20190533. Invited contribution to special issue in honor of Sir Gabriel Stokes’ 200th birthday.
[7] Mossige EJ, Chandran Suja V, Walls DJ, Fuller GG, “Dynamics of Freely Suspended Drops Translating through Miscible Environments”, Physics of Fluids, 33(3), 2021. DOI: 10.1063/5.0041536. Invited contribution to the special issue on ‘Kitchen Flows’ and featured in Physics of Fluids.
[8] Chandran Suja V, Verma A, Mossige EJ, Cui K, Xia V, Zhang Y, Sinha D, Joslin S, and Fuller GG (2022), “Dewetting Characteristics of Contact Lenses Coated with Wetting Agents”. Journal of Colloid and Interface Science, 614, 24-32.