Engineered tissue micro-rings fabricated from aggregated fibroblasts and microfibres for a bottom-up tissue engineering approach

Tissue rings with incorporated microscaffolds have been engineered as promising building blocks for constructing biological tubes from the bottom up. However, the microscaffolds available for incorporation are very limited at present. In this paper we provide an efficient strategy to first incorporate microfluidic spun Ca-alginate microfibres encapsulating magnetic nanoparticles into self-assembled fibroblast micro-rings. Based on the surface modification, microfibres with a size of ∼40 μm allowed fibroblasts to spread and proliferate along the long axis. The optimal cell seeding density was obtained by evaluating the degree of coverage of fibroblasts on microfibres after 3 days of culture. Then we designed a magnetically guided culture apparatus with multiple annular micro-wells to facilitate cell-driven assembly of microfibres. A manipulation strategy dependent on surface tension was used to pattern microfibres along the micro-wells prior to cell seeding, and magnetic attraction further kept the patterned microfibres from being deposited in the micro-wells during cultivation. Within 3 days of culture, microfibre-incorporated tissue micro-rings were formed in the micro-wells. Quantitative analysis of the formation process revealed liquid-like aggregating behaviours, and incorporated microfibres showed the potential to promote the directed organization of cells in tissue micro-rings. Furthermore, magnetically driven manipulation was used robotically to assemble the micro-rings on a micropillar inserted into the centre of the culture apparatus. After 5 days of culture to allow cell fusion, a biological tubular microstructure was achieved. Microfluidic spinning can generate fibres with a variety of shapes, geometries, and compositions; therefore, our proposed method greatly enriches the variety of microscaffolds available for incorporation into tissue rings to engineer complex artificial organs for tissue engineering and regenerative medicine.