Scientists looking for a treatment for a dangerous liver virus have found new ways to study it in the laboratory.
For the first time, a US team managed to watch the progress of a rare strain of hepatitis C among liver cells kept alive in a lab dish.
In the journal, the Proceedings of the National Academy of Sciences, they say it could lead to easier drug testing.
However, a UK expert said the method needed to work with more common hepatitis strains.
Hundreds of millions of people worldwide are thought to be infected with hepatitis C.
For most, it is an asymptomatic infection, but a small percentage, often many years later, develop liver cancer or failure.
One of the obstacles to the disease's study is that while many types of human cells can be grown successfully in the laboratory, liver cells have always been problematic.
After a very short while in a lab dish, the cells normally change or "differentiate" into forms which no longer behave in the same way.
The researchers from Massachusetts Institute of Technology (MIT) were able to extend their useful life by weeks by using a lab dish with a tiny pattern on its base.
This directed the cells to exactly the right place, and allowed other types of cells, called fibroblasts, to align with the liver cells.
This was important because fibroblasts are known to support the growth of liver cells.
Professor Sangeeta Bhatia, who led the research alongside scientists from Rockefeller University in New York, said: "If you just put cells on a surface in an unorganised way, they lose their function very quickly - if you specify which cells sit next to each other, you can extend the lifetime of the cells and help them maintain their function."
In addition, the team managed to infect their cells with a strain of hepatitis C, opening the opportunity for potential drugs to be tested over a two or three-week period.
William Rosenberg, a professor of hepatology at University College London, said that the research represented a "significant advance".
He added: "This is a tool which can be used to study hepatitis C in more detail, and with greater accuracy, than existing culture systems."
However, the cells were infected with a strain of hepatitis C responsible for a very small number of very severe cases of the illness, and Professor Roger Williams, also from University College London.
He said that the success would have to be repeated using more common strains.
"What they have managed to do is interesting, but this is a very unusual strain, and patients with this form of 'fulminant hepatitis' are very different to those with other strains of the virus."