Coating Yeast Cells With Tunable Shell By Visible Light-induced Graft Polymerization And Preparation Of Self-propulsion Cells

Coating live cells with a shell layer not only enhances the stability of the cells themselves,but also improves their ability to withstand adverse external environments,which has been widely used in drug delivery,tissue engineering,cell therapy,and other fields.Nowadays,many methods such as layer by layer self-assembly,biomimetic mineralization,surface-initiated graft polymerization have been developed for coating cells with shells.However,most of these methods are not able to only modify a portion of cell surface.Compared to fully coated cells,partially coated cells can avoid completely occluding the cell surface,which is favorable for the inter cellular interaction and cell adhesion.In view of this background,we reported a new method of introducing full/partial coating on yeast cell surface by visible light induce controlled/living graft polymerization.The main research contents and achievements are as follows:1.A facile and mild strategy based on visible light induced graft polymerization was developed to prepare crosslinked shell on yeast cells.Firstly,polyethyleneimine(PEI)was absorbed to the surface of yeast cells by electrostatic interaction,and then the PEI modified yeast cells was sedimented on the surface of negatively charged glass slide to form monolayer.Then poly(polyethylene glycol diacrylate)was grafted onto the surface of yeast cells to form cross-linked shell by visible light irradiation of with thioxanthone catechol-O,O'-diacetic acid(TX CT)/PEI as initiation system.By using the controlled/living feature of this graft polymerization under visible light,secondary grafting polymerization of sodium acrylate monomer(AAS)on the surface of cross-linked shell was successfully achieved.Zeta potential,XPS,laser confocal microscopy(CLSM),Fourier transform infrared spectroscopy(FTIR),transmission electron microscopy(TEM)and scanning electron microscopy(SEM)were used to verify the successful introduction of crosslinked polymer shell and PAAS brushes.By means of fluorescein diacetate(FDA)staining and flow cytometry,it was found that the PEI modified,and cross-linked shell coated yeast cells could still maintain more than 99%viability.After introducing PAAS the viability of yeast cells was more than 86%.The effect of shell prepared under different light intensity and irradiation time on yeast cell.In contrast to native yeast cells,the results showed that the yeast cells coated with the grafted polymer shell had a maximum division lag of 25 hours under the li ght intensity of 15 mW/cm2 for 30 minutes.It confirmed that the polymer shell could retard the division of yeast cells effectively.The results of cell-lysis tests showed that the polymer shell had a typical protective effect on the cells.Under the light intensity of 15 mW/cm2 for 30 minutes,the viability of the grafted polymer shell after cell-lysis tests was about 35%higher than that of the free yeast cells.It is proved that grafting polymer shell on the surface of yeast cells can improve the viability of yeast cells in harsh external environment.2.Based on the above research,asymmetric coating of yeast cells was achieved by adjusting the light intensity and irradiation time,and yeast cells with self-propulsion property were prepared.It was found that the yeast cells partially coated with the polymer shell could be obtained under the light intensity of 6 mW/cm2 for irradiation of 35 minutes.The asymmetric modification of poly(PEGDA)and PAAS on yeast cell surface was confirmed by SEM,TEM and CLSM.Then urease was covalently conjugated to the carboxyl group of PAAS.In 0 mmol/L and 200 mmol/L urea solution,the average speed of urease modified yeast cells was 0.107 ?m/s and 4.45 ?m/s,respectively.The results demonstrated that yeast cells partially coated with urease exhibited excellent the self-propulsion.