DEPARTURE INTO THE UNKNOWN

How Christof Wöll and Hartmut Gliemann are pioneering a new molecular platform technology.

What if you had an idea for a shelving system that was better than commercially available shelving? How do you sell a system that is suitable for all possible room sizes, loads and volumes and has many additional functions, but is still not produced because the sheer number of ways in which the system can be used makes its usefulness for different applications seem abstract?

Professor Christof Wöll, Hartmut Gliemann, and their team at the Institute for Functional Interfaces at KIT are working on a kind of molecular construction kit that enables a wide range of applications. Now it is a matter of actually implementing the large number of product ideas. Metal-organic framework compounds, so-called MOFs, are highly porous lattice structures that are already being manufactured on a large scale for gas storage and sold commercially in the form of powders. MOFs are crystalline materials made from metallic junctions and organic bonding elements. They are characterized by a very large specific surface area. MOFs absorb other molecules like a sponge and have so far been used primarily in the storage of gases: When the gas enters the solid, it attaches to the pore walls and is thus liquefied to a certain extent. The density increases significantly as a result, and considerably more molecules can be stored in the same volume. In addition to this conventional use as gas storage, MOFs are currently being tested for a number of much more sophisticated products. However, powders are not suitable for many of these new uses, and new methods for producing MOFs therefore urgently need to be developed. The interdisciplinary research team led by physicist Christof Wöll has been working on MOF coatings since 2009 and has managed to develop the completely new class of SURMOFs during this time.

"Innovations are real products for meaningful use, into which completely new technological approaches have flowed. Our task in the innovation process is to provide food for thought, to think around corners and to create the technological basis for this."

Professor Christof Wöll and Hartmut Gliemann

These 'Surface Mounted Metal-Organic Frameworks' grow layer by layer on a solid substrate. The layer-by-layer structure and the combination of different base materials for nodes and connectors in the frameworks allow the structures to be varied within wide limits and thus tailored to specific applications. "We are thus intelligently building storage facilities in which molecules can not only be stored but also identified and, if necessary, further processed. The properties of the SURMOFs can be modified even further. We have, so to speak, developed a nanoscale construction kit from which you can build practically anything you have in mind," explains scientist Hartmut Gliemann.

Now, as with the construction kit, it depends on imagination and fantasy how SURMOFs with new properties can be made from the construction elements. According to Christof Wöll, there are a number of ideas: "The application potential of metal-organic framework structures can only be vaguely guessed at today. The task now is to exploit the diversity of molecules known from chemistry as building blocks to develop new materials with new application potential that could revolutionize organic electronics, sensor technology, catalysis, medical technology or logical storage materials, for example."

For example, SURMOFs could be used to optimize combustion processes by serving as heat-stable, gas-selective prefilters for gas sensors. Pollutants in liquids and the air could be detected and removed more precisely than before. However, interesting applications are also emerging in pharmaceuticals and medical technology. "We can provide the scaffolds at their uppermost layer with flaps that can be opened and closed using light," says Gliemann. This enables the targeted release of stored molecules, such as drugs. For example, active ingredients such as antibiotics could be targeted to specific parts of the body and then released exactly where they are needed.

The researchers are also working on optimizing the SURMOF technology for medical applications and adapting it to the conditions prevailing there. Artificial body parts, such as hip and knee joints or pacemakers, must be antimicrobially coated and impregnated with medical agents to prevent inflammation and to prevent the implant from being rejected by the human body. "In this context, it is important that the scaffold structures are free of toxic components and subsequently degrade in the body without leaving any residue. We have explicitly developed SURMOFs further for this purpose," says Professor Wöll.

The technology is used in KIT laboratories; the research team has developed an automated production process and can react quickly to individual requirements. Nevertheless, the scientists face a hurdle in bringing their ideas to market, says Gliemann: "We know a lot about the basics of the technology, but we need industry to turn it into a real innovation. SURMOF types can be designed specifically for real-world problems. These prototypes can then be further developed together until useful products emerge that have real novelty and added value." The scientists see their SURMOFs as a platform technology, comparable to plastic or Teflon: "It wasn't the PET bottle that was developed, but initially just the plastic material, which was then used to realize countless applications and products. It wasn't the inventors of the material who came up with all these ideas about what could be made from a new base material, but industry with its practical problems," says Wöll. Such developments can take time, but he and his colleagues would like to take the first steps within the next five years: "Our goal is to develop gas sensors and solar cells based on SURMOFs to market maturity together with a partner from industry."

MOFs, SURMOFs and SURGEL

MOFs are crystalline materials made of metallic junctions and organic connecting elements. They have an enormously large surface area and are highly porous. MOFs are suitable, among other things, for storing gas in the tank of natural gas- or hydrogen-powered automobiles, but also for storing the greenhouse gases carbon dioxide and methane. Other applications are in the fields of material separation, catalysis and sensor technology. The right MOF can be tailored for any application; they are usually available as powders. In the past ten years, more than 20,000 different representatives of this material class have already been characterized in detail.

In contrast, the SURMOFs invented at KIT are not in powder form but thin MOF layers built on solid substrates and structurally perfect. The pore size of these new metal-organic framework compounds is currently already up to three times three nanometers. This means that the pores already offer space for small proteins. SURMOFs open up completely new areas of application compared to the MOFs used to date.

SURGEL is a further development of SURMOFs at KIT. It is a gel primarily for biomedical use consisting of organic building blocks crosslinked with each other by means of click chemistry. Compared to conventional polymer coatings, this gel is characterized by the fact that the pore size of the layer can be specifically adapted to the bioactive substances to be embedded, for example pharmaceutical agents.

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