We design and construct artificial intelligent cell (A.I. cell) with microfluidic droplets. Our A.I. cells demonstrate morphological and functional mimics of mammalian cells. In detail, the shape and size of microfluidic droplets resemble mammalian cells; and the central biochemical reactions of cells, i.e., transcription and translation, function well in our A.I. cells.
1. Fabrication of microfluidic device
Microfluidics has recently emerged as a robust platform for the formation of microdroplets. Monodisperse aqueous droplets in oil are formed and manipulated with microfluidic device. These droplets are in the nL-pL range and can be considered as completely isolated reaction chambers. Microdroplets can be generated at rates in excess of thousands per second. The power of microfluidics to prepare droplets lies in the formation of uniform droplets, fine control of the shape, size and monodispersity. First we designed microfluidic patterns using AutoCAD and fabricated masters with patterns on silicon wafer in clean room. Afterwards, we used elastomeric polymer, Polydimethylsiloxane (PDMS), as stamps to replicate the patterns on master, known as soft lithography technology. Before sealing PDMS pad with microfluidic channels on class slides, we punched holes at the inlets and outlets of the channels. To prepared droplets, we designed flow focusing patterns. Mineral oil was the continuous phase. Syringe pumps were employed to control the fluid speed of aqueous and oil phases. Through tuning the fluid speeds, surfactant concentration in oil, we obtained stable droplets with excellent monodispersity.
2. Design and construction of in vitro transcription and translation (IVTT)
Transcription and translation are the central biochemical reactions in living systems, which are universally preserved in all life formats, such as in modern cells. Therefore, in vitro transcription and translation (IVTT) provides a powerful experimental model for exploring events in our A.I. cells. In IVTT system, the plasmid DNA encoded with functional genes was designed and constructed first; with incubation with cell lysates, DNA was transcribed to RNA, which was afterwards translated to proteins. Our IVTT contains two parts: cell lysates and plasmid DNA.
3. Design and construction of DNA molecules
We varied the sequences of reporter genes in pRSET vector and got different plasmids, including pRSET-GFP, pRSET-YFP and pRSET-CFP. With incubation those plasmids with cell lysate, accordingly we produced GFP, YFP and CFP in IVTT.
4. Design and construction of A.I. cells
We used the microfluidic device to prepare microdroplets, with encapsulation of IVTT in droplets, generating A.I. cells. To obtain stable A.I. cells with fine monodispersity, we optimized the dimension of microfluidic channels, the flow rate of cell lysate and oil phase, as well as the concentration of surfactant in oil. To avoid IVTT reactions during the formation of A.I. cells, we controlled the temperature at 4 °C, afterwards incubated A.I. cells at 37 °C to initiate the reactions.