Scientists have invented a new self-lubricating condom that becomes slippery on contact and could make using the contraceptive more pleasurable.

Their work, backed by the Bill and Melinda Gates Foundation, has resulted in a condom that stays slippery for more than 1,000 thrusts.

The scientists say that this could increase condom usage and cut down on sexually transmitted disease and unwanted pregnancies.

43% of those who took part in the study said such a condom would increase their condom usage.

Scientists have invented a new self-lubricating condom with money from Bill Gates, and it could cut down on sexually transmitted disease and unwanted pregnancies by making condoms more appealing to use.

The study, published in the Royal Society Open journal, describes how the rubber latex is coated with a thin layer of hydrophilic polymers that, upon contact with moisture, become slippery to the touch, making the lubricant last longer and removing the need to add more lubricant during sex.

It could last at least 1,000 thrusts without losing slipperiness and should be more comfortable than regular condoms.

The scientists, backed by the Bill and Melinda Gates Foundation, tested regular condoms with a shop-bought, water-based lubricant and found that they were initially slippery but became less so after around 600 thrusts.

Intercourse typically lasts for between 100 and 500 thrusts, the study said.

Researcher Prof Mark Grinstaff, from Boston University, told the BBC: "It feels a bit slimy when you handle it dry, but in the presence of water or natural fluids it becomes really slick. You only need a little bit of fluid to activate it."

Thirty-three men and women tested both types of condoms. Seventy-three percent rated the self-lubricating one more highly.

Of those that said they "never" use condoms, 86% said they would prefer an inherently slippery condom and 43% said that an inherently slippery condom would increase their condom usage.

Clinical trials with couples to see how the condoms compare in real-life settings could begin early next year, Grindstaff said.

A spin-off company from the university is now looking to develop a product for sale.