Graphene in biomedicine

The May editorial of Nature Materials discusses the recent launch of a Work Package on Biomedical Technologies by the Graphene Flagship, and highlighted the questions that researchers in the field will try to answer in the next few years.

Among the different applications being currently explored for graphene and other 2D materials, diagnostic and therapeutic medical tools certainly have huge commercial potential. However, will the performance and fabrication costs of graphene-based devices ever be able to compete with those of Silicon lab-on-chips, metallic electrodes for brain stimulation and flexible neural recording sensors based on organic semiconductors or other materials?

A sensible approach to answer this riddle is trying to understand which physical and chemical properties of graphene can make the difference in such applications. For instance, membranes of monolayer graphene are ion-impermeable, yet they can be patterned to create nanopores that allow the controlled transport of ionic currents, polymer chains and DNA molecules. These architectures have been studied for DNA sequencing applications, although several practical challenges remain to be solved.  Graphene can also be easily functionalized , which may prove advantageous for the fabrication of efficient drug delivery systems. Single or few layers of graphene or graphene oxide could be used as carriers that immobilize drugs on their surface and release them only in proximity to a specific target in the body.  First, however, it’s essential to understand how cells and organs react to graphene, and it seems now clear that systematic studies on how  the biocompatibility of 2D materials is affected by their size, structural integrity and chemical functionalization will be required to address this point.

As a final example, it is worth mentioning that also the electronic properties of graphene may be leveraged to realize advanced biomedical devices. A high charge mobility improves the sensing performance of transistors used to record the electrical activity of neurons, and indeed  flexible graphene transistors that detect the action potential generated by cell cultures with sensitivity comparable with Silicon transistors have been recently reported. Scaling up this technology and translating it into in vivo applications — for example to realize devices able to record the brain activity from more than 1,000,000 neurons simultaneously, as required by a recent call for proposals from DARPA — is a massive engineering challenge that will certainly need much more work, and it is not clear at this stage if graphene will be the winning solution in bioelectronics on the long term.

For those interested in learning more about the potential of graphene in biomedicine, Nature Materials, Nature Physics and the Graphene Flagship are organising a Nature Symposium on Biomedical Applications during the Graphene Week conference coming next June. Stay tuned.

 

Luigi Martiradonna (Nature Materials)

Into the fold

Graphene boasts a number of exceptional properties, but arguably its best feature may be its form as a strong and flexible sheet of material. After all, the ancient art of origami teaches us that an infinite range of shapes can be created by folding up paper-like sheets like graphene. 3D is the new 2D: folding techniques may be employed for bottom-up fabrication of intricate 3D nanostructures or for assembling flat-packed devices that can unfold where or when needed.

A square twist mechanical switch

A square twist mechanical switch: recently shown possible due to hidden degrees of freedom.
From Nature Materials 14, 389–393 (2015) “Origami structures with a critical transition to bistability arising from hidden degrees of freedom”.

Origami-led concepts have already inspired the design of numerous soft devices made from 2D polymer sheets such as miniature robots that self-assemble and become mobile by folding and unfolding. Recently, mechanical metamaterials were constructed, using a paper folding technique called snapology, that can smoothly change shape from a flat sheet to a voluminous block of material, and back.

In recent years, the bug of origami-inspired design has also caught among graphene researchers as the possibilities seem endless. Controlled crumpling and folding of graphene can produce new types of 3D nanostructures of interest for flexible electrodes in batteries and supercapacitors. In another strand of research, scientists have unleashed the power of kirigami – origami with cutting – to make super-stretchable, ultrathin graphene electrodes that could be used in biomedical applications. In a more classic origami demonstration, graphene oxide paper sheets can self-fold into boxes that could be used as miniature containers that open and close on demand. Proposals also exist for folding single layer graphene into thin but robust nanocages for high-density molecular storage.

Astoundingly, new discoveries are still made in origami research as the mechanics of folding materials yields new surprises and previously unknown geometries (see figure). Graphene researchers may want to pay attention as the inspiration for the next breakthrough in graphene materials may be found in novel geometries enabled by the art of paper folding.

 

Liesbeth Venema (Senior Editor, Nature)

 

The capacity of graphene’s market

Since graphene was first isolated in 2004, the initial research buzz around it focussed unsurprisingly on its remarkable physical properties, such as Klein tunnelling, observed in these atomic layers. Then, research in material and device aspects started to claim its role on centre-stage, in the quest to explore graphene’s potential applications in commercial products. A plethora of graphene materials have since been developed for applications in areas as diverse as biomedical sensors and energy storage.

When talking about graphene applications electronics might come to mind, since banking on, for example, graphene’s high electron mobility seems a no-brainer. However, the R&D timescale of electronic products are incredibly long, and limited by – for one – the lack of industrially scalable production of high-quality monolayer material. Thus, it comes to little surprise that the first commercial applications of graphene materials included tennis rackets instead, which bank on the lightweight and robustness of less-electronically-pristine graphene. Rackets are now being joined by bicycle tyres, in which the addition of graphene materials improves their mechanical properties, such as grip and durability, and heat dissipation. If we look at products that are a little bit less sporty but more mainstream, we find the graphene-coated LEDs recently developed at the University of Manchester (almost) on shop shelves. A bulb can be yours for a mere £15, and promises to reduce electricity consumption and last longer than conventional LED bulbs.

Graphene has thus started trickling down production lines and reaching us customers. But how pervasive will its presence be in the coming years? In which market areas, if any, will the ‘graphene revolution’ really happen? A recent market research identifies key areas in which graphene is expected to have significant commercial impact over the next 10 years and forecast the size of the global market. Keeping in mind that the market for graphene products has been estimated to be $1.5m in 2015, the projections for 2020 ($310.4m) and 2025 ($2.1b) are plainly mind-blowing. The report predicts a mean annual growth rate over the next decade of over 46%, and singles out capacitor applications as the workhorse of the graphene industry, with a growth rate of 65.7% over the period, followed suit by structural materials, with a growth rate of 37.8%. Other applications considered include communications, data storage, thermal management, displays, solar cells, sensing and imaging.

It is still early days for graphene products, but their future shines bright. On our part, we hope that advances enabled by this wonder material will also impact possibly less remunerative, but equally important, applications such as water desalination and purification.

 

Elisa De Ranieri (Senior Editor, Nature Energy)

Disclaimer: the editors of Flatchat in no way endorse any of the commercially available graphene-products mentioned in the article.

 

Focus on 2D

It was only a few years ago that the field of ‘2D’ materials for photonics applications was completely dominated by one material. It is this material that, in 2004, Andre Geim and Kostya Novoselov famously peeled atomically thin flakes of from a lump of graphite using ‘sticky tape’. The material is of course graphene. However, graphene is no longer alone; there is now an extended family of related materials emerging, each bringing their own unique properties to the table for researchers to put to work.

In addition to materials based on carbon (graphene and graphyne), this family now includes thin films based on boron (borophene), germanium (germanene), silicon (silicene), tin (stanene), phosphorus (phosphorene) and hexagonal boron nitride. And, this is list is far from complete.

To highlight these emerging systems the April 2016 issue of Nature Photonics is a Focus Issue on 2D materials, with an emphasis on those with properties readily exploitable for optics applications.

As highlighted in the editorial, we have a review from Kin Fai Mak and Jie Shan on the transition metal dichalcogenides (TMDCs), like molybdenum disulfide and tungsten diselenide. Zhipei Sun, Amos Martinez and Feng Wang review optical modulators based on 2D materials such as graphene, TMDCs, black phosphorus and heterostructure combinations. Fengnian Xia from Yale University explains in his Interview why other materials such as black phosphorus and silicene are receiving interest from an optical point of view. We’ve also got Commentary from Andres Castellanos-Gomez, who explains the excitement around graphene and also delves into silicene and hexagonal boron nitride. By coincidence we even have three research papers in the same issue related to 2D materials. One is on the nature of the bandgap of hexagonal boron nitride, another is on ultrafast switching of infrared plasmons in graphene and the last shows the existence of plasmon modes on the edges of graphene cavities.

While there is good reason to be excited about these areas of research there are a lot of hopes being discussed and promises being made in the current literature and of course only time will tell how much of this comes to fruition. Castellanos-Gomez cautioned in his commentary that while the excitement is justified, we are in a stage of experimental infancy in terms of practical exploitation. In any case, we expect much to come from the field and hope this Focus Issue on 2D materials helps fan the fire.

 
David Pile (Senior Editor, Nature Photonics)

 

Flat out

Welcome to “Flatchat,” a new blog from the editors of several journals within the Nature family, handling manuscripts on graphene and 2D materials. And you can probably guess what this blog will be about!

Graphene made an impressive entry a few years back, with the Nobel Prize in Physics awarded to Andre Geim and Konstantin Novoselov from the University of Manchester in 2010 and hasn’t left the spotlight since. On the contrary, other materials – equally thin – joined the team, like transition metal dichalcogenides. At the moment, a very large community of researchers across a number of disciplines is looking to uncover the fundamental properties and reveal the potential of this family of materials for applications. Our aim for this blog is to bring exciting news about these endeavours to you.

In particular, we aim to discuss here, first of all, interesting papers published in various scientific journals, and covering all aspects of undergoing research on graphene and 2D materials. We will also bring you news from the conferences we occasionally attend: on the talks, the posters, the trends.. We will also discuss news pieces covering the science of 2D materials, published books, blogs, websites or any other relevant media outlet that catches our attention.

Above all, we are hoping for this blog to become a communication platform with our readers, so please feel free to leave comments below the entries, if you wish to contact us. Entries will be added regularly in this space, so make sure you check this page occasionally to see what we and the 2D materials community are up to!

 

Elisa de Ranieri (Senior Editor, Nature Energy)

Luke Fleet (Senior Editor, Nature Physics)

Maria Maragkou (Associate Editor, Nature Materials)

Luigi Martiradonna (Senior Editor, Nature Materials)

Silvia Milana (Associate Editor, Nature Communications)

Giulia Pacchioni (Associate Editor, Nature Reviews Materials)

Liesbeth Venema (Senior Editor, Nature)