Short description:
In order to obtain nanosized liposomes using a continuous-flow microfluidics method as MHF, an appropriate geometry had to be constructed. Therefore, for the current study a three-inlet and one outlet design has been used for both experimental and numerical approaches. The geometry consists on a microchannel with a squared cross-section of      100 x 100 μm.

Figure 1: 3D model of the microchannel with 3 inputs (A, B1, B2) and one output (C), with detail of the structured discretization of the computational domain.

The numerical 3D geometry and the structured orthogonal mesh has been generated using GAMBIT pre-processor, consisting of 629400 hexahedral finite volumes (Figure 1).
The 3D pressure-driven flow in the microchannel configuration has been simulated using the FLUENT CFD commercial package. The code computes the isothermal laminar flows of the Newtonian working fluids, with double precision and with 10-10 convergence criterion. The initial numerical simulations were performed using a constant flow rate for inlet A and varying the equal flow rate for inlets B1 and B2, in a range of flow rate ratios (FRR) of 1 to 20. The solution containing the dissolved lipids introduced in inlet A has the same dynamic viscosity as the aqueous solution introduced from inlets B1 and B2, η ≈ 10-3 Pa∙s, therefore the test fluid had the water material characteristics. Gold nanoparticles were numerically injected at the cross junction to simulate the formation of liposomes (Figure 3).

Results: The stream of lipids from the solution introduced from inlet A is hydrodynamically focused by the two buffer streams at the cross junction of the microchannel (Figure 2).
The flow rates of the lipids solution and the buffer streams are adjusted to control the width of the self-assembling liposomes stream, controlling at the same time their size (Figure 4).

Figure 2: Velocity distributions (Ia÷d) and pressure distributions (IIa÷d) with streamtraces for a median plane in the cross-section area.

Figure 3: 3D nano-particles distributions and median plane pathlines distributions (IIIa÷d) in the cross-section area.

Figure 4: Example of main stream dimensions for flow rate ratio of 1:8.