We propose a surface wettability guided assembly (SWGA) approach for high throughput formations of droplets [1]. The SWGA technique is based upon stamping glass slides with PDMS templates to micro-pattern surfaces with predefined hydrophilic and hydrophobic regions. Here, we introduce three applications of droplets by SWGA: i) Tissue engineering. SWGA is used to rapidly bioengineer thousands of heterogeneous cell niches in 3D microgel arrays with quantitative controls over physical, chemical cues and cell populations. Assembly of cell niches on the wettability patterned surface is demonstrated with chemical gradient, cell density gradient and orthogonal gradients of chemical concentration and cell density over individual microgels. We also show spatial organization of heterogeneous cell populations in individual microgels and assembly of a hydrogel sheet with spatially-defined chemical distribution; ii) Earth-on-a-chip. With SWGA technique, a new concept of “earth-on-a-chip” is realized, which enables rapid generating thousands of heterogeneous microearth arrays to study the soil–microbe system and their biogeochemical effects in a precisely controlled microenvironment. We demonstrate utilities of this platform technology by recapitulating natural biogeochemical phenomenon on a chip, including soil colloid assembly, microscale transport of soil organic matter/microbes during wet-dry cycles of soil formation, microbe deposition on  soil/clay mineral, microbial regulated carbon-nitrogen cycling, providing new insights into biogeochemical processes at the microscale; iii) Micro/nano-fabriaction. By SWGA, gold nanoparticles solution self-confines into pre-defined geometries according to the hydrophilic regions. Then, the monodispersed nanoparticles self-assemble into well-defined circuits by coffee-ring-effect. Submicron-height and submicron to microns-width circuit arrays with various structures are precisely generated by varying the PDMS nanofilm patterns. Thousands of circuits with different geometries can be self-assembled simultaneously within 1 min. We belive that this SWGA platform technology may have wide applications in chemistry, biomedicine and engineering.