The aim of bio-engineering is to transpose the advanced concepts and tools of physics, chemistry, optics or mechanical engineering to the life sciences in order to improve understanding and develop more effective diagnoses and treatments. École Polytechnique has made this field one of its priorities for the coming decades. In 2018, with the Institut Pasteur and in collaboration with the CNRS, the French national research agency, it set up a joint team to work on "physical microfluidics and bio-engineering" with a view to developing new approaches in biology based on microfluidics for individualized cell handling and study. X's team, which has been developing such cell handling tools for several years, is contributing its expertise in fluid mechanics and engineering to provide answers to the questions posed by researchers at the Institut Pasteur in the fields of biology and health. One of the projects concerns understanding the appearance of resistance to antibiotics in individual cells. This project deals with a highly topical global issue, that of the loss of effectiveness of antibiotics. Other research projects are seeking to understand the response of an individual cell to a controlled modification in its local environment, which will provide a better understanding of the heterogeneity of the responses to a given drug within a population. The field of bio-engineering also interests the researchers in X's Solid Mechanics Laboratory who are studying tissue engineering, which involves regenerating or replacing organs with cultured tissues, obtained from our own cells. However, since at the present time it is difficult to grow substitute tissues that immediately have the right properties, mechanical properties in particular, the researchers at Polytechnique have developed an innovative device for observing the behavior of fibers in mechanical tests. The results obtained are opening up the way for new interpretations of the mechanical perception of tissues and could eventually make it possible to provide the mechanical stresses needed for tissue to reconstitute.