Levitating objects .... with sound!

It has been known for 100 years that sound waves can exert a force (the acoustic radiation pressure effect) but not until now has this principle been used to manipulate physical objects.

I'll keep this post pretty short because the maths involved is pretty obscene but for those who are slightly masochistic and would like to take a look, the paper by Foresti et al. was published yesterday in PNAS and can be viewed here.

The basic principle used here is there is an emitting platform (that as the name suggests emits the sound wave) and then placed opposite that, there is a reflecting platform and these platforms are placed at particular places based on some complex math. The figure below is a diagram of the apparatus taken directly from the paper.

Setup of droplet manipulator (Foresti et al. (2013)

I won't get into it but take my word that the design of this system and the calculations involved is an example of some beautifully thought out elegant science and props to those involved in its development.

Now, it's all very well to make an object levitate using a sound wave, but they go one step further and actually move the object with these sound waves which again has some pretty complex equations behind it. The sound emitting mechanism is made with piezoelectric crystals, which shrink or stretch depending on the voltage applied to them and hence can alter the sound wave produced quite finely and accurately.

As a proof of principle they did several awesome things! First, I will show you the video of them moving and mixing droplets of water seen in the video below:

Then as true scientists, they wanted to make this useful for something very important to most scientists ... Making coffee ... Check it out:

Yep, they are mixing a granule of instant coffee and water in thin-air to make a drop of coffee! That video is slowed down by 100-times so you can see the fine details.

Next they took a step larger:

I don't know about you, but I find that pretty incredible!

The applications for this are not as wide-ranging as you might think unfortunately. The object being levitated and the sound waves have a very intimate relationship, the diameter of the object needs to half of the wavelength of the soundwave, so big objects are out of the question at this stage. However, it does have some exciting applications for chemistry as many chemical reactions and science experiments are influenced by the chemistry of being on the surface of something so we can now investigate questions free from surface interference.

So aside from making coffee in mid-air, the benefits of this amazing technology remain to be reaped by scientists ... For now.


Foresti D., Nabavi M., Klingauf M., Ferrari A. & Poulikakos D. (2013). Acoustophoretic contactless transport and handling of matter in air, Proceedings of the National Academy of Sciences, 110 (31) 12549-12554. DOI: 10.1073/pnas.1301860110

How to grow a liver in a petri dish and save lives

Liver donors are extremely rare - In 2011, 5,805 liver transplants were completed in the US and that same year, 2,938 people died waiting for one. Needless to say, an area that needs attention. In a first of a kind study by Takebe et al. published in Nature this week we may be a step closer to solving this problem.

The group has used human stem cells (I'll go into how towards the end) to create what they have dubbed 'liver buds', that is basically miniature human livers (about 4mm in diameter). They have then taken these liver buds and surgically implanted them into mice. The surgically implanted buds were able to substantially prolong the life of mice with liver failure! This is itself is a pretty amazing feat of science! Taking some human cells, growing a mini liver, throwing into an animal with liver failure and they live longer!

The liver buds not only prolonged the lives of these mice but incorporated themselves with the mouses blood system and continued to grow after the implantation. The buds took on many features of a fully-functional liver such as producing and sending out liver-specific proteins and signals. The figure below shows the implanted bud (in the dotted area) gaining blood vessels over time (shown by the increase in red in the dotted area).

Figure showing vascularization of liver buds (reproduced from Takebe et al. (2013))

These mini livers were the result of combining 3 types of human stem cell. First, pluripotent stem cells were converted into cells that are programmed to express liver specific genes (this is done by given the cells signals that trick them into thinking they're growing in a liver). Next, they combined these liver-specific cells with some endothelial cells (the kind of cells that make your blood vessels) and some mesenchymal stem cells (these can make bone, cartilage and fat). Over time, these groups of cells interacted and self-organized into the liver buds seen above. Below is an illustration of the process of creating the liver buds (panel A) but also a visualization of them forming over time (panel B). You can see how they start as a large smear and as time progresses they come together in an organized fashion.

Figure showing A) An illustration of the methodology of the experiment and B) showing the formation of the liver buds over time. (Reproduced from Takebe et al. (2013))

The figure below is what is called a "survival curve" which illustrates the rate of death of the mice in different conditions. Every vertical drop in the line is a mouse (or mice) dying. So a flat line means the group is surviving, a rapidly decreasing line shows they a dying.

There are only two lines you need to worry about. The dotted line at the very bottom is the group of mice that had the procedure done but didn't have a bud implanted (the control group), and the solid black line at the top is the group of mice that had the procedure done and did have the liver bud implanted.

Survival curve (reproduced from Takebe et al. (2013))

This shows that when the mice don't have the treatment, over a 30-day period, they die fairly rapidly. However, when they receive the bud implants, over the 30-day period, only ONE mouse died!

I don't know about you but I find that pretty amazing and VERY exciting. Of course as with most first of a kind studies, it needs to be replicated and further studies done but the implications this has for not only those with liver damage, but with any organ damage is huge and every exciting.

PS. For those of you who do not belong to an institution and cannot view the original article there is a summary here.