In silico design and 3D printing of microfluidic chips for the preparation of size-controllable siRNA nanocomplexes

Small interfering RNA (siRNA) is regarded as one of the most powerful tools for the treatment of various diseases by downregulating the expression of aberrant proteins. Delivery vehicle is often necessary for getting siRNA into the cells. Nanocomplex using polyamidoamine (PAMAM) is regarded a promising approach for the delivery of siRNA. The size of siRNA nanocomplexes is a critical attribute in order to achieve high gene silencing efficiency in vivo. Microfluidics provides advantages in the preparation of siRNA nanocomplexes due to better reproducibility and a potential for more robust process control. The mixing efficiency of siRNA and PAMAM is different in microfluidics systems with different geometries, therefore, resulting in nanocomplexes with varying size attributes. In this study, hydrodynamic flow focusing microfluidic chips with different channel designs, i.e. diameters/widths, channel shapes (cylindrical/rectangular) and inter-channel spacings were optimized in silico and rapidly prototyped using 3D printing and finally, used for production of siRNA nanocomplexes. The fluid mixing inside the microfluidic chips was simulated using the finite element method (FEM) with the single-phase laminar flow interface in connection with the transport of diluted species interface. The digital design and optimization of microfluidic chips showed consistency with experimental results. It was concluded that the size of siRNA nanocomplexes can be controlled by adjusting the channel geometry of the microfluidic chips and the simulation with FEM could be used to facilitate the design and optimization of microfluidic chips in order to produce nanocomplexes with desirable attributes.