Solar cell polymers with multiplied electrical output


One challenge in improving the efficiency of solar cells is that some of the absorbed light energy is lost as heat. So scientists have been looking to design materials that can convert more of that energy into useful electricity. Now a team from the U.S. Department of Energy’s Brookhaven National Laboratory and Columbia University has paired up polymers that recover some of that lost energy by producing two electrical charge carriers per unit of light instead of the usual one.

Solar cell polymers with multiplied electrical output

“Critically, we show how this multiplication process can be made efficient on a single molecular polymer chain,” said physicist Matthew Sfeir, who led the research at Brookhaven Lab’s Center for Functional Nanomaterials, a DOE Office of Science User Facility. Having the two charges on the same molecule means the light-absorbing, energy-producing don’t have to be arrayed as perfect crystals to produce extra electrical charges. Instead, the self-contained materials work efficiently when dissolved in liquids, which opens the way for a wide range of industrial scale manufacturing processes, including “printing” solar-energy-producing material like ink.

The research is published as an Advance Online Publication in Nature Materials, January 12, 2015.

The concept of producing two charges from one unit of light is called “.” (Think of the fission that splits a single biological cell into two when cells multiply.) Devices based on this multiplication concept have the potential to break through the upper limit on the efficiency of so-called single junction , which is currently around 34 percent. The challenges go beyond doubling the electrical output of the solar cell materials, because these materials must be incorporated into actual current-producing devices. But the hope is that the more-efficient current-generating materials could be added on to existing solar cell materials and device structures, or spark new types of solar cell designs.

Most singlet fission materials explored so far result in twin charge carriers being produced on separate molecules. These only work well when the material is in a crystalline film with long-range order, where strong coupling results in an additional charge being produced on a neighboring molecule. Producing such high quality crystalline films and integrating them with solar cell manufacturing complicates the process.

Producing the twin charges on a single polymer molecule, in contrast, results in a material that’s compatible with a much wider variety of industrial processes.

The materials were designed and synthesized by a Columbia University team led by Professor Luis Campos, and analyzed at Brookhaven using specialized tools at the CFN and in the Chemistry Department. For Sfeir and Campos, the most fascinating part of the interdisciplinary project was exploring the electronic and chemical requirements that enable this multiplication process to occur efficiently.

“We expect a significant leap in the development of third-generation, hot-carrier solar cells,” said Campos. “This approach is especially promising because the materials’ design is modular and amenable to current synthetic strategies that are being explored in second-generation .”

Details of the materials’ analysis

At the CFN, Sfeir and Erik Busby (a postdoctoral fellow) used time-resolved optical spectroscopy to induce and quantify singlet fission in the various polymer compositions using a single laser photon. Xiaoyang Zhu of Columbia helped to understand the data and interpret results.

“We put light energy into a material with a laser pulse and watch what happens to that energy using a series of weaker light pulses – somewhat analogous to taking snapshots using a camera with a very fast shutter,” Sfeir said.

The team also studied the same process using “pulse radiolysis” in collaboration with John Miller, who runs the Laser-Electron Accelerator Facility.

“The differences observed between these two experiments allowed us to unambiguously identify singlet fission as the primary process responsible for the production of these twin charges,” Sfeir said.

With Qin Wu, the team also used a powerful computer cluster at the CFN to model these materials and understand the design requirements that were necessary for singlet fission to take place.

“The ideas for this project and supervision of the work were really shared between Brookhaven and Columbia,” Sfeir said. “It’s a great example of the kind of collaborative work that takes place at DOE user facilities like the CFN.”

The next steps for the CFN-Columbia team will be to test a large class of materials using the design framework they’ve identified, and then integrate some of these carbon-based polymer materials into functioning solar cells.

“Even though we have demonstrated the concept of multiplication in single molecules, the next challenge is to show we can harness the extra excitations in an operating device. This may be in conventional bulk type solar cells, or in third-generation concepts based on other inorganic (non-carbon) nanomaterials. The dream is to build hot-carrier solar cells that could be fully assembled using solution processing of our organic singlet fission materials.”

Advertisements

Supercomputers reveal strange, stress-induced transformations in world’s thinnest materials.


Interested in an ultra-fast, unbreakable, and flexible smart phone that recharges in a matter of seconds? Monolayer materials may make it possible. These atom-thin sheets—including the famed super material graphene—feature exceptional and untapped mechanical and electronic properties. But to fully exploit these atomically tailored wonder materials, scientists must pry free the secrets of how and why theybend and break under stress.

Supercomputers reveal strange, stress-induced transformations in world's thinnest materials

 Fortunately, researchers have now pinpointed the breaking mechanism of several monolayer  hundreds of times stronger than steel with exotic properties that could revolutionize everything from armor to electronics. A Columbia University team used supercomputers at the U.S. Department of Energy’s Brookhaven National Laboratory to simulate and probe quantum mechanical processes that would be extremely difficult to explore experimentally.

They discovered that straining the materials induced a novel phase transition—a restructuring in their near-perfect crystalline structures that leads to instability and failure. Surprisingly, the phenomenon persisted across several different materials with disparate electronic properties, suggesting that monolayers may have intrinsic instabilities to be either overcome or exploited. The results were published in the journal Physical Review B.

“Our calculations exposed these monolayer materials’ fundamental shifts in structure and character when stressed,” said study coauthor and Columbia University Ph.D. candidate Eric Isaacs. “To see the beautiful patterns exhibited by these materials at their breaking points for the first time was enormously exciting—and important for future applications.”

The team virtually examined this exotic phase transition in boron nitride, molybdenum disulfide, and graphane—all promising monolayer materials.

Simulated Shattering

Monolayer materials experience strain on atomic scales, demanding different investigative expertise than that of the average demolition crew. Isaacs and his collaborators turned to a mathematical framework called density functional theory (DFT) to describe the quantum mechanical processes unfolding in the materials.

“DFT lets us study materials directly from fundamental laws of physics, the results of which can be directly compared to experimental data,” said Chris Marianetti, a professor of materials science at Columbia University and coauthor of the study. “We supply the fundamental constants and the material’s nuclei, and using DFT we can closely approximate real characteristics of the material under different conditions.”

In this study, DFT calculations revealed the materials’ atomic structures, stress values, vibrational properties, and whether they acted as metals, semiconductors, or insulators under strain. Toggling between or sustaining those conductive properties are particularly important for future applications in microelectronics.

Supercomputers reveal strange, stress-induced transformations in world's thinnest materials
IBM supercomputer Blue Gene/Q, the latest addition to the New York Center for Computational Sciences.

“Testing all the different atomic configurations for each material under strain boils down to a tremendous amount of computation,” Isaacs said. “Without the highly parallel supercomputing resources and expertise at Brookhaven, it would have been nearly impossible to pinpoint this transition in strained monolayers.”

Twisted Atomic Half-Pipe

Everything breaks under enough stress, of course, but not everything meaningfully transforms along the way. A bending oak branch, for example, doesn’t enter a strange transition phase as it creeps toward its breaking point—it simply snaps. Monolayer materials, it turns out, play by very different rules.

Within the honeycomb-like lattices of monolayers like graphene, boron nitride, and graphane, the atoms rapidly vibrate in place. Different vibrational states, which dictate many of the mechanical properties of the material, are called “modes.” As the perfect hexagonal structures of such monolayers are strained, they enter a subtle “soft mode”—the vibrating atoms slip free of their original configurations and distort towards new structures as the materials break.

“Imagine a skateboarder in a half-pipe,” Isaacs said. “Normally, the skater glides back and forth but remains centered over the bottom. But if we twist and deform that half-pipe enough, the skateboarder rolls out and never returns—that’s like this soft mode where the vibrating atoms move away from their positions in the lattice.”

Softly Breaking

The researchers found that this vibrational soft mode caused lingering, unstable distortions in most of the known monolayer materials. In the case of graphene, boron nitride, and graphane, the backbone of the perfect crystalline lattice distorted toward isolated hexagonal rings. The soft mode distortion ended up breaking graphene, , and molybdenum disulfide.

As the monolayers were strained, the energetic cost of changing the bond lengths became significantly weaker—in other words, under enough stress, the emergent soft mode encourages the atoms to rearrange themselves into unstable configurations. This in turn dictates how one might control that strain and tune monolayer performance.

“Our work demonstrates that the soft mode failure mechanism is not unique to graphene and suggests it might be an intrinsic feature of monolayer materials,” Isaacs said.

Monolayer Renovations

Armed with this knowledge, researchers may now be able to figure out how to delay the onset of the newly characterized instabilities and improve the strength of existing monolayers. Beyond that, scientists may even be able to engineer new ultra-strong materials that anticipate and overcome the soft mode weakness.

“Beyond the thrill of the discovery, this work is immediately useful to a large community of researchers excited to learn about and exploit graphene and its cousins,” Isaacs said. “For example, we’ve been working with Columbia experimentalists who use a technique called ‘nanoindentation’ to experimentally measure some of what we simulated.”

Key Takeaways

  • Graphene and other monolayer materials feature exotic electronic and —atomically thin, ultra light, and stronger than steel. But how do these promising materials transform and fail under strain?
  • What did the scientists learn? They pinpointed the breaking points and failure mechanisms for these atom-thin super materials. When stressed, so-called “soft mode” instabilities emerge that cause characteristic atomic reconfigurations—surprisingly, this behavior persisted across different monolayer materials.
  • How did they do it? Using quantum mechanical laws and supercomputers, they simulated the atomic structure and vibrational modes of materials under different degrees of duress. Scientists strained and stressed these monolayer materials to the point of breaking—all virtually.
  • What’s the impact? Everything from microelectronics to powerful, lightweight armor might be advanced by understanding how monolayer materials perform under stress.

Human stem cells converted to functional lung cells.


For the first time, scientists have succeeded in transforming human stem cells into functional lung and airway cells. The advance, reported by Columbia University Medical Center (CUMC) researchers, has significant potential for modeling lung disease, screening drugs, studying human lung development, and, ultimately, generating lung tissue for transplantation. The study was published today in the journal Nature Biotechnology.

“Researchers have had relative success in turning human stem cells into heart cells, pancreatic beta cells, intestinal cells, liver cells, and nerve cells, raising all sorts of possibilities for regenerative medicine,” said study leader Hans-Willem Snoeck, MD, PhD, professor of medicine (in microbiology & immunology) and affiliated with the Columbia Center for Translational Immunology and the Columbia Stem Cell Initiative. “Now, we are finally able to make lung and airway cells. This is important because lung transplants have a particularly poor prognosis. Although any clinical application is still many years away, we can begin thinking about making autologous lung transplants — that is, transplants that use a patient’s own skin cells to generate functional lung tissue.”

The research builds on Dr. Snoeck’s 2011 discovery of a set of chemical factors that can turn human embryonic stem (ES) cells or human induced pluripotent stem (iPS) cells into anterior foregut endoderm — precursors of lung and airway cells. (Human iPS cells closely resemble human ES cells but are generated from skin cells, by coaxing them into taking a developmental step backwards. Human iPS cells can then be stimulated to differentiate into specialized cells — offering researchers an alternative to human ES cells.)

In the current study, Dr. Snoeck and his colleagues found new factors that can complete the transformation of human ES or iPS cells into functional lung epithelial cells (cells that cover the lung surface). The resultant cells were found to express markers of at least six types of lung and airway epithelial cells, particularly markers of type 2 alveolar epithelial cells. Type 2 cells are important because they produce surfactant, a substance critical to maintain the lung alveoli, where gas exchange takes place; they also participate in repair of the lung after injury and damage.

The findings have implications for the study of a number of lung diseases, including idiopathic pulmonary fibrosis (IPF), in which type 2 alveolar epithelial cells are thought to play a central role. “No one knows what causes the disease, and there’s no way to treat it,” says Dr. Snoeck. “Using this technology, researchers will finally be able to create laboratory models of IPF, study the disease at the molecular level, and screen drugs for possible treatments or cures.”

“In the longer term, we hope to use this technology to make an autologous lung graft,” Dr. Snoeck said. “This would entail taking a lung from a donor; removing all the lung cells, leaving only the lung scaffold; and seeding the scaffold with new lung cells derived from the patient. In this way, rejection problems could be avoided.” Dr. Snoeck is investigating this approach in collaboration with researchers in the Columbia University Department of Biomedical Engineering.

“I am excited about this collaboration with Hans Snoeck, integrating stem cell science with bioengineering in the search for new treatments for lung disease,” said Gordana Vunjak-Novakovic, PhD, co-author of the paper and Mikati Foundation Professor of Biomedical Engineering at Columbia’s Engineering School and professor of medical sciences at Columbia University College of Physicians and Surgeons.

 

Better catalyst for solar-powered hydrogen production.


Hydrogen is a “green” fuel that burns cleanly and can generate electricity via fuel cells. One way to sustainably produce hydrogen is by splitting water molecules using the renewable power of sunlight, but scientists are still learning how to control and optimize this reaction with catalysts. At the National Synchrotron Light Source, a research group has determined key structural information about a potential catalyst, taking a step toward designing an ideal material for the job.

https://i2.wp.com/cdn.physorg.com/newman/gfx/news/2013/designingabe.jpg

Due to the mechanical and electrical complexity of the water-splitting reaction, there are many requirements in order for a catalyst to perform optimally. Scientists must understand not only a candidate’s local but also its structure over longer ranges – particularly the nanoscale, which tends to be a good indicator of a material’s electronic behavior and therefore its overall .

Scientists are increasingly focusing on a particular group of catalysts: cobalt-based thin films. These films are created via electrodeposition from aqueous solutions of cobalt mixed with an electrolyte. In this study, researchers from Columbia University, Harvard University, and Brookhaven Lab used x-rays to better understand the intermediate-range nanoscale structure of one of these films. They also investigated the structural differences between films grown using two electrolytes: phosphate, a negative phosphorous-oxygen ion, and borate, negative a boron-oxygen ion. The resulting films are denoted CoPi and CoBi, respectively.

X-ray scattering data from the CoPi and CoBi samples, taken at NSLS beamline X7B, indicate that both are nanocrystalline. This means that they consist of nanoscale grains, each ranging from about 1.5 to 3 nanometers (nm) in size with an ordered molecular structure. Aside from this, there are clear and important differences.

The CoBi films consist of 3-4 nm cobalate (cobalt–oxygen) clusters that stack neatly up to three layers deep. The CoPi films consist of significantly smaller clusters that do not stack in an ordered way.

These structural differences seem to tie into the films’ catalytic activity. Electrochemical data show that, as film thickness increased, the CoBi films were more active than CoPi and ultimately displayed a “significantly superior” performance. These findings suggest that the increase in CoBi film thickness also increases the effective surface area available for catalysis, while at the same time preserving the charge-transport properties of the films.

“Our results show a concrete difference between CoBi and CoPi, thus allowing the first insight into a tangible structure-function correlation,” said Harvard chemist and professor Daniel Nocera.

Stem Cells Converted Into Lung Tissue.


Lung transplant recipients have a relatively low 10 year survival rate of about 28%. Cellular rejection of the donor organ occurs about 90% of the time, which brings additional obstacles for the patient and doctors. This might be about to change, as functional lung tissue has been created from human stem cells. The research comes from Hans-Willem Snoeck from the Columbia Center for Translational Immunology and was published in the current edition of Nature Biotechnology.

A couple of years ago, Dr. Snoeck was able to convert stem cells into the precursor endoderm cells that can eventually differentiate into lung cells. This was done with human embryonic stem cells as well as human induced pluripotent stem cells, which involve a bit more work but are easier to come by. Those precursor cells were shown to actually differentiate into six different respiratory tissues, including the coveted type II alveolar cells. which facilitate gas exchange and produce surfactant.

Type 2 alveolar cells, also called pneumocytes, are responsible for producing surfactant, the compound that allows the lungs to remain inflated with air. These type II cells also aid in gas exchange and lung repair.

The lung tissue produced by stem cells could give researchers a unique perspective to study the tissue and learn more about how lung diseases originate. This could lead to better treatment options for lung diseases.

If treatments do not work and transplant becomes inevitable, physicians can use the patient’s own cells to provide a new disease-free organ. This eliminates both the potential for cellular rejection as well as the stress of waiting on the transplant list. To make a replacement lung, researchers would first remove the patient’s lung and decellularize it, leaving only a cartilaginous scaffold. The stem cells would then be used to coat the scaffold and regrow functional tissue to be put back into the patient.

Though it is a long way from getting implanted into a human body, these results are exciting. A patent has been filed by Columbia University for their technique of converting induced pluripotent stem cells into the functional tissue.

Nanomechanical FM transmitter is smallest yet.


Researchers at Columbia University in the US have built the smallest frequency-modulated (FM) radio transmitter ever. Based on a graphene nanomechanical system (NEMS), the device oscillates at a frequency of 100 MHz. It could find use in a variety of applications, including sensing tiny masses and on-chip signal processing. It also represents an important first step towards the development of advanced wireless technology and the design of ultrathin mobile phones, says team co-leader James Hone.

“Our device is much smaller than any other radio-signal source ever made and, importantly, can be put on the same chip that is used for data processing,” he explains.

Graphene is a sheet of carbon atoms arranged in a honeycomb-like lattice that is just one atom thick. Since its discovery in 2004, this “wonder material” has continued to amaze scientists with its growing list of unique electronic and mechanical properties, which include high electrical conductivity and exceptional strength. Indeed, some researchers believe that graphene might even replace silicon as the electronic industry’s material of choice in the future.

Ideal for making NEMS

Graphene is ideal for making NEMS – which are scaled-down versions of the microelectromechanical systems (MEMS) that are routinely employed in vibration-sensing applications. The new device made by Hone and colleagues is a NEMS version of a common electronic component known as a voltage-controlled oscillator (VCO) and generates a frequency-modulated (FM) signal of about 100 MHz. This frequency lies exactly in the middle of the FM radio band (87.7–108 MHz) and the researchers say that they have already succeeded in using low-frequency music signals to modulate the 100 MHz carrier signal from their graphene NEMS and recover the signals again using an ordinary FM receiver.

While graphene NEMS might not replace conventional radio transmitters yet, they will certainly be used in many other wireless signal-processing applications. Although electrical circuits have been continuously shrinking over the last few decades (as described by Moore’s law), there are still some types of devices – especially those involved in creating and processing radio-frequency (RF) signals – that are notoriously difficult to miniaturize, explains team co-leader Kenneth Shepard. Called off-chip components because they cannot be integrated with miniaturized devices, they require a lot of space and electrical power, and their frequency cannot be easily tuned.

Graphene NEMS offer a solution to this problem because they are very small – the active area is only a few microns across – and they can potentially be integrated directly onto conventional CMOS chips. Most importantly, it is easy to tune their frequency thanks to graphene’s exceptional strength.

Adjusting the tension

The Columbia researchers made their devices by contacting graphene sheets to source and drain electrodes and freely suspending the sheets over metal gates. In this configuration, the graphene functions like the skin of a drum. A DC gate voltage pulls the graphene down towards the gate and this adjusts the tension and, therefore, the mechanical resonance frequency, explains Hone. A radio-frequency signal on the gate drives sheet vibrations. “Finally, we apply a DC bias across the graphene and when the graphene vibrates it acts as a transistor whose gate capacitance is constantly changing – and it is this that creates an RF source–drain current,” he says.

The team studied the vibrational properties of the device at room temperature in a vacuum chamber. “To make an oscillator, we first adjust the signal gain to just above unity (using a variable amplifier) and the phase to zero (using a phase shifter) at the resonance frequency,” says Hone. “We then connect the output to the gate. This creates a closed loop that amplifies random thermal vibrations and makes the device oscillate.”

The researchers say they are now busy looking at how to put their devices directly onto integrated circuits that already contain all the necessary drive and readout circuitry. They also hope to improve the performance of their oscillators and reduce device noise.

Graphene the perfect material for a Lunar Elevator.


Scientists at Columbia University conducted a study which revealed that graphene retains most of its mechanical properties even when it has been stitched together from small fragments. This discovery may have been the first step toward large scale manufacture of carbon nanotubes, which could be essential in the manufacturing of the first space elevator, light – strong materials, and flexible electronics.

Lunar Elevator

At the present moment, a practical breakthrough in the construction of a lunar elevator has not been realized. However, many scientists have performed experiments which show it will be possible through use of graphene. In these experiments, they have measured the strength of the microscopic carbon nanotube and proved it can indeed support the construction of such elevators.

The space elevator ribbon is constructed out of carbon nanotubes, which are at least 100 times stronger than steel but have flexibility equal to that of plastic. Scientists will only be able to make the ribbon to be used in the space elevator if they manage to make fibers out of carbon nanotubes. In the recent experiments, the materials that were involved were neither strong nor flexible enough to form such a ribbon.

Graphene ribbons have a very high tensile strength and very high elastic modulus, theoretically they are said to make the process of building a space elevator easy. There are two major ways that a lunar elevator ribbon can be built: in the first case a long carbon tube ideally several meters long will be braided into a rope like structure, and in the second case a shorter nanotube will be placed in a selected polymer matrix.

So far graphene is the ideal material for construction of the ribbon, the carbon-carbon bond in graphene is at least 0.142 nm. Scientists have proved that two sheets of graphene are held together by much stronger van de Waals forces than bulk Graphene.

Baldness cure a ‘step closer’


Scientists say they have moved a step closer to banishing bald spots and reversing receding hairlines after human hair was grown in the laboratory.

Bald man combing scalp

A joint UK and US team was able to create new hairs from tissue samples.

Far more research is needed, but the group said its technique had the “potential to transform” the treatment of hair loss.

The study results were published in the journal Proceedings of the National Academy of Sciences.

There are baldness therapies including drugs to slow the loss of hairs, and transplants, which move hair from the back of the head to cover bald spots.

“Yeah I think it [baldness] will eventually be treatable, absolutely.”

Prof Colin Jahoda, Durham University

The scientists at the University of Durham, in the UK, and Columbia University Medical Centre, in the US, were trying to actually grow new hairs.

Their plan was to start with material taken from the base of a hair and use it to grow many new hairs.

Tricky feat

But human hair has been tricky to grow despite successes in animal studies.

Whenever human tissue was taken from the dermal papillae, the cells which form the base of each hair follicle, the cells would transform into skin instead of growing new hairs.

However, the group found that by clumping the cells together in “3D spheroids” they would keep their hairy identity.

Tissue was taken from seven people and grown in 3D spheroids. These were then transplanted into human skin which had been grafted on to the backs of mice.

Hair follicle
Cells were taken from the base of a follicle and used to grow new hairs

After six weeks, new hair follicles formed in five out of the seven cases and some new tiny hairs began to form.

Prof Colin Jahoda, from Durham University, told the BBC a cure for baldness was possible but it was too soon for men to be hanging up the toupee.

“It’s closer, but it’s still some way away because in terms of what people want cosmetically they’re looking for re-growth of hair that’s the same shape, the same size, as long as before, the same angle. Some of these are almost engineering solutions.

“Yeah I think it [baldness] will eventually be treatable, absolutely.”

He added: “It’s hard to say exactly how long that would take, but the fact that we’ve done it now should reawaken interest.”

Any future therapy would involve transplanting cells which have been grown in the laboratory so safety is a concern.

There would be a risk of infection and the cells could become abnormal, or even cancerous, while being grown.

Baldness cures may not be the first application of the research. Prof Jahoda believes the findings will be used to improve the quality of skin grafts used after severe burns.

Prof Angela Christiano, from Columbia University, said: “This approach has the potential to transform the medical treatment of hair loss.

“Current hair-loss medications tend to slow the loss of hair follicles or potentially stimulate the growth of existing hairs, but they do not create new hair follicles.

“Our method, in contrast, has the potential to actually grow new follicles using a patient’s own cells.”

A Possible Cure for Baldness, in 3D.


 
Set the ball rolling. Human skin cells grown on a flat culture remain dispersed and unable to induce the formation of hair follicles (left). But in a 3D culture, the cells form spheres that can coax new hair follicle growth (right).

Christiano lab, Columbia University

Set the ball rolling. Human skin cells grown on a flat culture remain dispersed and unable to induce the formation of hair follicles (left). But in a 3D culture, the cells form spheres that can coax new hair follicle growth (right).

Scientists have successfully grown new hair follicles from the skin cells of balding men. While the research team hasn’t yet shown whether the structures, which produce strands of hair on our bodies, are fully functional and usable for transplants onto a scalp, experts say the discovery is a significant step toward finding new treatments for hair loss.

“Their work is very elegant and extremely rigorous,” says Radhika Atit, a skin biologist at Case Western Reserve University in Cleveland, Ohio, who was not involved in the new study. “This is a big technical advance.”

Balding occurs when hair follicles stop producing new strands of hair in any area of the body. Now, taking drugs that prevent or slow the hair loss or transplanting hair follicles from one area of the body to another are the only viable treatments. Producing new hair follicles in the lab has not been an option—at least for human patients. In mice, researchers have shown that if they isolate dermal papilla cells, which surround hair follicles in the skin, grow them in petri dishes to produce new cells, and then put the cells back in the mouse, new hair follicles will develop. But when dermal papilla cells from humans are put into dishes in the lab, they lose their ability to induce the formation of new follicles.

Angela Christiano, a skin researcher at Columbia University who has discovered genes related to hair loss, recently brainstormed potential solutions to the problem with her colleagues. They noticed that while the dermal papilla cells from mice naturally formed large clumps in culture, the human cells didn’t. “We began thinking that maybe if we could get the human cells to aggregate like the mouse cells, that might be a step toward getting them to form new follicles,” Christiano says.

Her team decided to try a cell-growing approach, called 3D cultures, that’s been successful for other types of cells that need to form complex structures as they grow. The researchers collected dermal papilla cells from seven volunteers who had been diagnosed with male-pattern baldness. Rather than stick the isolated cells on a flat culture dish, they mixed the cells with liquid, then let the mixture hang in tiny droplets from a plastic lid, like condensation on the roof of a container. Because the cells inside the droplets are free-floating, the technique allows them to contact each other in every direction, as they would in the human body, rather than only touch side to side as they do in a flat dish. In the droplets, the cells behaved differently; as they divided to form new cells, they clumped into what the researchers call “spheroids”—balls of about 3000 cells.

To test whether the new spheroids were a better mimic for functional dermal papilla cells than those that had been grown in typical dishes, Christiano and her team determined what genes were turned on and off in different sets of dermal papilla cells. In cells grown on flat culture dishes, the expression of thousands of genes didn’t match up with their normal patterns, explaining why the cells from those dishes had been unable to generate new hair follicles. But in the 3D cultures, 22% of those genes had been restored to their correct on or off state.

The researchers then took 10 to 15 of the spheroids that had formed from each donor and sandwiched them between two layers of human skin that were grafted onto mice. Six weeks later,spheroids from five of the seven donors had coaxed the skin cells around them to start rearranging, forming the telltale shape of a hair follicle, the team reports online today in the Proceedings of the National Academy of Sciences. In two cases, hairs were even seen beginning to extend from the follicles, though the researchers didn’t continue the initial experiment for long enough to test whether the hairs were fully normal in terms of their ability to regrow.

Using one’s own cells to generate new follicles is useful because hair color and thickness will match perfectly with the rest of someone’s head of hair, Christiano notes. And with the new tissue culture technique, clinicians would be able to take just a few dermal papilla cells from a balding patient and expand the number of hair follicles available for transplant, rather than only be able to move follicles around. “Using this technique could change the number of people who would be eligible for hair transplants,” Christiano says.

The success of the approach is exciting, but the real breakthrough for other researchers in the field is the new data on gene expression in dermal papilla cells, says George Cotsarelis, a dermatologist at the University of Pennsylvania. The full readout of what genes are on and off in dermal papilla cells has never been collected before, so researchers now have a new list of thousands of genes to study further that may play key roles in hair follicle development. “It could have implications for not just hair, but treating wounds and scarring,” he says.

The spheroids capable of producing hair follicles could also be used as a new way to test drugs for their ability to restore follicle function, Atit says. “This is a better model system to use for drug testing than a two-dimensional plate.”