Whether a stem cell develops into bone or fat can be determined by the type of mould it is grown in, scientists at the University of Chicago have found.

The scientists placed human bone marrow cells into different shaped moulds, including star and flower shapes, circles, rectangles and pentagons. After treating the stem cells with the same kind of chemicals to encourage growth, they found that those grown in star-shaped moulds tended to develop into bone where as those in flower-shaped moulds matured into fat.

Professor Milan Mrksich from the University of Chicago, who led the study published in the Proceedings of the National Academy of Sciences (PNAS), concluded the presence of corners in the mould determined the cell type that the stem cells became. Moulds with sharp corners caused the cells to push against them and activated internal 'stress filaments.' This encouraged the development of long, strong filaments leading to the stem cells becoming bone. Moulds with round edges meanwhile encouraged the growth of softer filaments resulting in fat cells.

It is the first time that scientists have been able to show the role played by geometry in the development of stem cells.

'Cells change their geometries and mechanics throughout development and as they move through the body', Professor Christopher Chen, bioengineer at the University of Pennsylvania, who was not involved in the research, told New Scientist.

The research could lead to new ways of transforming stem cells into tissues for transplant in patients, for example. It also has the added bonus of using physical, not chemical, means to encourage stem cell development.