European XFEL elicits secrets from an important nanogel

Felix Lehmkühler at the instrument MID (Materials Imaging & Dynamics) of European XFEL where the experiments were done.
© European XFEL

An international team at the world’s largest X-ray laser European XFEL at Schenefeld near Hamburg has scrutinised the properties of an important nanogel that is often used in medicine to release drugs in a targeted and controlled manner at the desired location in a patient’s body. The team now published the results in the journal Science Advances.

An international team led by Felix Lehmkühler from Deutsches Elektronen-Synchrotron DESY in Hamburg has investigated the temperature induced swelling and collapsing of the polymer poly-N-isopropylacrylamide (PNIPAm) at European XFEL at Schenefeld near Hamburg. Due to its dynamic changes, PNIPAm is frequently used in medicine, e.g. for drug delivery, tissue engineering or sensorics.

Above 32 °C, PNIPAm changes from a hydrophilic to a hydrophobic state. As a consequence, the nanogel particles rapidly change their size by expelling water.
Above 32 °C, PNIPAm changes from a hydrophilic to a hydrophobic state. As a consequence, the nanogel particles rapidly change their size by expelling water. © Felix Lehmkühler

PNIPAm is typically dissolved in water. Above a certain temperature, the so-called lower critical solution temperature (LCST), which is around 32 °C, it changes from a hydrophilic, water-loving state to a hydrophobic, water-repellent state. As consequence, nanogel particles, as investigated by Lehmkühler and co-workers, rapidly change their size above that temperature by expelling water.

This feature is useful for a variety of applications, including the controlled release of drugs in a patient’s body, as a model system for proteins and in tissue engineering, the cultivation of organic tissue for medical applications, or as bio-compatible temperature sensors. However, it was very difficult so far to watch these rapid phase transitions experimentally, and therefore to optimize them for different applications. Therefore, the precise characterisation of the kinetics of the changes of the PNIPAm polymer with temperature is still a lively research topic.

Now, the fast sequence of X-ray pulses from the European XFEL enable researchers to investigate the rapid, temperature-dependent changes in the PNIPAm nanogel using a technique called X-ray Photon Correlation Spectroscopy (XPCS). “Due to the high repetition rate of the European XFEL, we can perform these measurements with high enough time resolution to follow the structure and motion of the nanogels”, says Johannes Möller, Instrument Scientist at the Materials Imaging and Dynamics (MID) instrument of European XFEL. The researchers studied particles of about 100 nanometre size, this is ten-millionths of a metre. The X-ray pulses were used both to heat the nanoparticles and to measure their structural changes via their dynamics, i.e. their movement in the surrounding water.

“With the help of the data obtained at the European XFEL, we have now been able to gain a better understanding of the swelling and collapsing of the polymer,” says Felix Lehmkühler, one of the leaders of the team. “In contrast to previous studies, that were limited to indirect measurements of the kinetics of swelling or collapsing, we found that the nanogel shrinks significantly faster in the range of 100 nanoseconds, but takes two to three orders of magnitude longer to swell”, explains Lehmkühler. The results could help researchers to further understand and improve the features of the polymer for different applications, such as the development of more efficient drug delivery systems.

About European XFEL:
European XFEL in the Hamburg area is an international research facility of superlatives: 27,000 X-ray flashes per second and a brilliance that is a billion times higher than that of the best conventional X-ray sources open up completely new opportunities for science. Research groups from around the world are able to map the atomic details of viruses, decipher the molecular composition of cells, take three-dimensional “photos” of the nanoworld, “film” chemical reactions, and study processes such as those occurring deep inside planets. The operation of the facility is entrusted to European XFEL, a non-profit company that cooperates closely with its main shareholder, the research centre DESY, and other organizations worldwide. European XFEL has a workforce of 500 employees and started user operation in September 2017. At present, 12 countries have signed the European XFEL convention: Denmark, France, Germany, Hungary, Italy, Poland, Russia, Slovakia, Spain, Sweden, Switzerland, and the United Kingdom. For more information on European XFEL go to

The team of researchers consisted of scientists from Deutsches Elektronen-Synchrotron (DESY), Germany, the University of Padua, Italy, The Hamburg Centre for Ultrafast Imaging, Germany, and, European X-Ray Free-Electron Laser Facility, Germany.

Original paper:
Real-time swelling-collapse kinetics of nanogels driven by XFEL pulses
DOI: 10.1126/sciadv.adm7876

More information, including a copy of the paper, can be found online at the Science Advances press package at

Wissenschaftliche Ansprechpartner:

Dr. Felix Lehmkuehler

Deutsches Elektronen-Synchrotron (Photon Science) Ein Forschungszentrum der
Helmholtz-Gemeinschaft Notkestr. 85 | 22607 Hamburg | Germany

phone: +49-40-8998-5671


Real-time swelling-collapse kinetics of nanogels driven by XFEL pulses
DOI: 10.1126/sciadv.adm7876

Media Contact

Gerhard Samulat Presse- und Öffentlichkeitsarbeit
European XFEL GmbH

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