Liquid-liquid phase separation (LLPS) has emerged as a central principle of subcellular organization. While membraneless condensates composition and function are increasingly understood, how cells control their biophysical properties  (size, number, morphology…) remains unclear. To address this, I developed a method to build artificial condensates in living cells, combining the control of in vitro reconstitution with a cellular context. These condensates, formed by multivalent proteins, could be enriched with RNA via a specific RNA-binding protein. Imaging revealed that RNA accumulated at condensate surfaces, and quantification highlighted a correlation between RNA surface density and condensate size and morphology. A second line of work explored how molecular motors influence condensates, focusing on their subcellular localization through motor protein interactions. Artificial motor-functionalized condensates robustly localized to microtubule ends and enabled targeted RNA recruitment, providing a tool to study the role of mRNA localization. I will also quickly introduce my most recent work investigating LLPSbased DNA hydrogels, their biophysical control, and their potential biological and technological applications.