Speakers 2023

Lihi Adler-Abramovich
Tel Aviv University, Israel

The emerging demand for tissue engineering scaffolds capable of inducing bone regeneration using minimally invasive techniques prompts the need for the development of new biomaterials. One promising route is molecular self-assembly, a key direction in current nanotechnology and material science. In this approach, the physical properties of the formed supramolecular assemblies are directed by the inherent characteristics of the specific building blocks. Molecular co-assembly at varied stoichiometry substantially increases the structural and functional diversity of the formed assemblies, thus allowing tuning of their architecture and physical properties.

Here, in line with polymer chemistry paradigms, we applied a co-assembly approach using hydrogel-forming peptides, resulting in a synergistic modulation of their mechanical properties to form extraordinarily rigid hydrogels which supported osteogenic differentiation based on cells-mechanosensing. Furthermore, we designed a multi-component scaffold composed of polysaccharides, short self-assembling peptides, and bone minerals. We demonstrate the formation of a rigid, yet injectable and printable hydrogel without the addition of cross-linking agents. The formed composite hydrogel displays a nanofibrous structure, which mimics the extracellular matrix and exhibits thixotropic behavior and a high storage modulus. This composite scaffold can induce osteogenic differentiation and facilitate calcium mineralization.

This work provides a conceptual framework for the utilization of co-assembly strategies to push the limits of nanostructure physical properties obtained through self-assembly for the design of new biomaterials for tissue engineering and personalized medicine applications.

Annelise Barron
Stanford University, USA

Eva Blasco
Heidelberg University, Germany

4D microprinting has become a promising tool for the fabrication of dynamic microstructures opening new opportunities for the additive manufacturing of functional devices with high precision. During the last years, promising examples of defined 4D microstructures employing stimuli-responsive polymers have been shown using two-photon laser printing. Herein, we present our recent work on the field with emphasis on new printable polymeric materials. In particular, shape memory polymers as well as dynamic covalent polymer networks have been demonstrated to be excellent candidates for the preparation of “living” 4D microstructures with potential applications in micro and nanorobotics or biomedicine.

Uwe Bunz
Heidelberg University, Germany

Additive manufacturing (AM) reaching from the nano- to the macroscopic-regime is fundamentally a domain of physicists, mechanical engineers and coders, who provide the tools that transform CAD data of an imagined structure into reality.  The progress in disparate fields like micromachining, photolithography, DLW, 3D-printing, electrospinning, origami-type folding etc. has been achieved with a handful of commercially available elastomers, thermoplastic polymers and thermosets in addition to simple monomers monomers and photo initiators.

Yet, a multitude of properties other than mechanical ones are difficult to realize for objects made by AM, but bespoke inks (single or multicomponent) revolutionizes AM to give microscopic to macroscopic “plastic objects” with properties as disparate as (semi) conductivity, ultra-low shrinkage, displaying functional gradients of mechanical and optical properties, bio compatibility, and much more.

The creation of bespoke inks is the domain of synthetic chemistry. The inks have to play to the AM method used to deliver the exact function in fields ranging from inorganic and organic electronics, photonics, etc. to biological applications.  Together with the Korvink group we develop inks for near field electrospinning. Fairly conventional parameters such as viscosity, solubility and solvent choice already create a large parameter set of variables, the introduction of specific functional groups adds a layer of complexity together with the desired resolution and chemical composition but promises to deliver materials with outstanding properties with respect to mechanical, optical, sensory and biological applications.

Martina Delbianco

Max Planck Institute of Colloids and Interfaces, Germany

Polysaccharides are the most abundant organic materials in nature, yet correlations between their three-dimensional structures and macroscopic properties have not been established. With automated glycan assembly (AGA), we prepared well-defined oligo- and polysaccharides resembling natural as well as unnatural structures.[1] These synthetic glycans are ideal probes for the fundamental study of polysaccharides, shedding light on how the primary sequence affects the polysaccharide properties (i.e. solubility and crystallinity). Molecular dynamics simulations, NMR spectroscopy, and single molecule imaging allowed for the visualization of polysaccharides’ conformation and revealed that some polymers form helices while others adopt rod-like structures.[2] Modifications in specific positions of the oligosaccharide chains permitted to tune the three-dimensional structures and solubility of such compounds.[3] These synthetic oligosaccharides self-assembled into nanostructures of varying morphologies.[4] Differences in chain length, monomer modification, and aggregation methods yielded glycomaterials with distinct shapes and chirality, offering valuable models to study the aggregation of natural polysaccharides.

Makoto Fujita
University of Tokyo, Japan

Self-assembly of gigantic polyhedral complexes from a number of metal ions and small organic molecules will be discussed. The organic components can be either simple and rigid bridging ligands or oligopeptides that adopt fixed conformation when folded.

Frauke Gräter
Heidelberg University, Germany

Nature has evolved sophisticated molecular systems that sense mechanical force. They do so by specifically responding to the external force by a structural change or mechanochemical reaction. I will showcase systems inside and outside of the biological cell to highlight basic principles of molecular mechano-sensing and how one can engineer or mimic such systems. Examples will include protein unfolding and activation, force-dependent redox chemistry, and mechanoradicals in biomaterials.

Ian Hamley
University of Reading, UK

Peptides offer outstanding potential as bioactive and biocompatible nanomaterials that can be programmed with unique properties. I will review work from our group on peptides, lipopeptides (peptide amphiphiles) and polymer-peptide conjugates. This includes a diversity of designed or bio-inspired or bio-derived systems that self-assemble into micelles, vesicles, fibrils, nanotapes, and other nanostructures in solution and as hydro- or organo-gels. A remarkable range of biofunctionality has been demonstrated, including use as antimicrobial materials, scaffolds for regenerative medicine and tissue engineering, as amyloid functional materials and potential therapeutics, in gene delivery, and in other biomedical applications.

Stefan Hecht
Humboldt University of Berlin, Germany

The presentation will highlight xolography as a new and powerful volumetric 3D printing technique. It is based on the use of dual color photoinitiators that enable the precise confinement of the polymerization process into regions defined by two different light sources consisting of an UV/blue light sheet and an orthogonal visible light projector. The linear nature of the process in combination with the high-definition of the projection allow for rapid printing of homogeneous materials and complex multicomponent objects in high resolution without the need for support structures. Advantages and disadvantages as well as opportunities will be discussed.

Light-based additive manufacturing techniques offer various advantages based on their superior speed and resolution. Until now this great potential has not fully been harnessed due slow build rates and material inhomogeneities caused by point-wise or layered object generation common for methods including stereolithography and digital light processing. Volumetric 3D printing is the next evolutionary step to realize a fast and continuous printing process. However, both currently established methods, two-photon photopolymerization and computed axial lithography, suffer from low volume generation rates and limited resolution, respectively.

To overcome this limitation, we have developed xolography as a new and powerful volumetric 3D printing technique. It is based on the use of photoswitchable photoinitiators that require a sequence of two one-photon processes taking place at distinctly different wavelengths. Therefore, these dual color photoinitiators enable the precise confinement of the polymerization into regions defined by two different light sources consisting of an activating UV/blue light sheet and an orthogonal visible light projector. Since the crossing (x) light beams generate an entire (holos) object by this printing process, we refer to it as xolography. The linear nature of the process in combination with the high-definition of the projection allow for rapid printing of homogeneous materials and complex multicomponent objects in high resolution and without the need for support structures.

The presentation will highlight the action principle of xolography and discuss advantages and disadvantages with regard to build speed and resolution, object dimensions and complexity, as well as employable materials.

Nature 588, 620-624 (2020). DOI: 10.1038/s41586-020-3029-7

Ivan Huc
Ludwig-Maximilians-University, Germany

Aromatic oligoamides constitute a distinct and promising class of synthetic foldamers – oligomers that adopt stable folded conformations. Single helical structures are predictable, show unprecedented conformational stability, and constitute convenient building blocks to elaborate synthetic, very large (protein-sized) abiotic architectures[1] and peptide-foldamer hybrid structures.[2] They possess a high propensity to assemble into double, triple and quadruple helices, or to fold into sheet-like structures.[3] Cavities can be designed within such synthetic molecules that enable them to act as artificial receptors[4] and molecular motors.[5] Water soluble analogues of these foldamers show promise in protein recognition.[6] This lecture will give an overview of the design principles of these functional molecular architectures it will highlight recent developments and emphasize key methodologies.

1.   S. De, C. Chi, T. Granier, T. Qi, V. Maurizot, I. Huc, Nat. Chem., 2018, 10, 51.

2.   J. M. Rogers, S. Kwon, S. J. Dawson, P. K. Mandal, H. Suga, I. Huc., Nat. Chem., 2018, 10, 405

3. B. Gole, B. Kauffmann, A. Tron, V. Maurizot, N. McClenaghan, I. Huc, Y. Ferrand, J. Am. Chem. Soc. 2022, 144, 6894.

4. P. Mateus, N. Chandramouli, C. D. Mackereth, B. Kauffmann, Y. Ferrand, I. Huc, Angew. Chem. Int. Ed. 2020, 59, 5797.

5.  V. Koehler, A. Roy, I. Huc, Y. Ferrand, Acc. Chem. Res. 2022, 55, 1074.

6. K. Ziach, C. Chollet, V. Parissi, P. Prabhakaran, M. Marchivie, V. Corvaglia, P. Pratim Bose, K. Laxmi-Reddy, F. Godde, J.-M. Schmitter, S. Chaignepain, P. Pourquier, I. Huc, Nat. Chem., 2018, 10, 251.

.

Nicole Jung
Karlsruhe Institute of Technology (KIT), Germany

In the last decade, important progress was made with respect to scientific infrastructure, software tools, and methods that may change and improve the way scientists work in academia. While progress which depends on technical developments (in terms of software and hardware) was formerly reserved mostly to the chemistry industry, new developments based open source software, open hardware projects and open science in general are available to the whole community.

In this talk, examples for synergistic effects of systematic research data management, digitalization and automation in synthetic chemistry projects will be presented. It will be shown how the adaptation of currently manual processes to digital workflows can improve and accelerate scientific work, enabling the use of robotic systems in the end. Another focus will lie on the challenges of the community to use the potential of the new methods efficiently and in a sustainable way.

Laura Kiessling
Massachusetts Institute of Technology, USA

Milan Kivala
Heidelberg University, Germany

Triarylamines have in the meanwhile become ubiquitous in the area of organic electronics owing to their appreciable electron donor and hole transport properties. In our research we employ various structurally relatively simple triarylamines for the construction of unprecedented nitrogen-doped p-conjugated scaffolds upon introduction of different bridging moieties. In these compounds the nitrogen atom readily adopts a planar sp2-hybridized geometry to provide for efficient electronic communication with the surrounding p system. The resulting electron-rich compounds are highly attractive both as objects for fundamental studies and functional materials for diverse applications. Our recent achievements in this area will be presented herein.

Regine von Klitzing
Technical University of Darmstadt, Germany

Matthias Kühnhammer, Kevin Gräff, Sebastian Stock, Regine von Klitzing

Institute for Condensed Matter Physics, TU Darmstadt

Foams appear in many applications such as in personal care products, firefighting and food technology. An elegant tool to tune the foam stability is the addition of polymers of different charge, amphiphilicity or molecular architecture. An example, which will be addressed here are foams which are stabilized by stimuli-responsive microgels.

For understanding macroscopic foam properties, it is important to get deeper insight into the different length scales, i.e. the structuring of microgels at the air/water interface, in foam films, which separate the air bubbles from each other and (macroscopic) foams.  

The presentation will focus on microgels based on Poly-N-isopropylacrylamid (PNIPAM). Their stiffness and deformation at the air/liquid interface is controlled by the amount of cross-linker content which dominates the lateral pattern formation at the liquid interface.  A challenge for studies of microgel-stabilized foam films are their massive inhomogeneities, which makes it difficult to measure the respective foam film thickness.

To get insight into foam film properties, we use a camera based thin film pressure balance to study microgel-stabilized foam films in terms of disjoining pressure inside the foam films, drainage kinetics, and foam film stability. Film thickness profiles give insights into particle bridging, agglomeration and network formation in the foam films.

For a complete picture, small angle neutron scattering (SANS) measurements on macroscopic foams provide additional insights into the link between foams and single foam films.

Reference: M. Kühnhammer, K. Gräff, E. Loran, O. Soltwedel, O. Löhmann, H. Frielinghaus, R. von Klitzing, “Structure formation of PNIPAM microgels in foams and foam films”, Soft Matter, 2022, doi:10.1039/d2SM01021F.

Tuomas Knowles
University of Cambridge, UK

Mariana Kozlowska
Karlsruhe Institute of Technology (KIT), Germany

Polymerization of photoresists in 3D laser nanoprinting is triggered by the formation of radicals upon light activation of the photoinitiator with a specific wavelength. This process depends on a cascade of diverse preceding processes, such as multiphoton absorption, excited state absorption, internal conversion, radiative decay, nonradiative processes, e.g., intersystem crossing, etc. They often also compete with each other. Moreover, highly reactive excited states may induce diverse intermolecular reactions with photoresist components, demonstrating different 3D laser nanoprinting resolution and speed. Such processes cannot be fully understood by experiments alone. In my talk, I will reveal the molecular basis of the photoactivation and deactivation of photoinitiators from first principles calculations. I will explain key processes that control the reactivity of the photoresists and their mutual dependence, discuss mechanisms of radical formation, and demonstrate the efficiency of polymerization initiation by 7-diethylamino-3-thenoylcoumarin (DETC) photoinitiator.

Barbara Lechner
Technical University of Munich, Germany

Sub-nanometer metal clusters exhibit particular chemical and physical properties which often change non-monotonically with cluster size. Such clusters are used in heterogeneous catalysis, plasmonic devices, biosensors or coatings, to name just a few examples. We produce size-selected clusters and soft-land them on oxide supports to investigate the dynamics inherent to such systems experimentally and correlate functionality with structural dynamics. Pt clusters, for example, typically become encapsulated by reducible supports such as Fe3O4 or TiO2, altering the available active sites for catalytic reactions. Moreover, the cluster sinter by atom or cluster diffusion, depending on initial cluster size. By combining atomically resolved movie-rate scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy in pressures from ultra-high vacuum to near-ambient conditions, we investigate dynamic phenomena including cluster fluxionality, diffusion and sintering as well as support etching and growth, cation dynamics, and adsorbate spillover on a fundamental level.

Sijbren Otto
University of Groningen, Netherlands

How the immense complexity of living organisms has arisen is one of the most intriguing questions in contemporary science. We have started to explore experimentally how organization and function can emerge from complex molecular networks in aqueous solution.1 We focus on networks of molecules that can interconvert, to give mixtures that can change their composition in response to external or internal stimuli or internal processes. Noncovalent interactions within molecules in such mixtures can lead to the formation of foldamers.2,3 Molecular recognition between molecules in such mixtures leads to their mutual stabilization, which drives the synthesis of more of the privileged structures (Figure 1), giving rise to self-assembled materials. As the assembly process drives the synthesis of the very molecules that assemble, the resulting materials are self-synthesizing. Intriguingly, in this process the assembling molecules are replicating themselves, where replication is driven by self-recognition of these molecules in the dynamic network.4 The selection rules that dictate which (if any) replicator will emerge from such networks are starting to become clear.5 We have also witnessed spontaneous differentiation (a process akin to speciation as it occurs in biology) in a system made from a mixture of two building blocks.6 When such systems are operated under far-from-equilibrium flow conditions, adaptation of the materials to a changing environment can occur.

Materials that are able to catalyse reactions other than their own formation have also been obtained, representing a first step towards metabolism.7,8 Thus, the prospect of Darwinian evolution of purely synthetic molecules and materials is tantalizingly close and the prospect of synthesizing life de-novo is becoming increasingly realistic.

Ute Schepers
Karlsruhe Institute of Technology (KIT), Germany

Despite a remarkable progress of biofabrication techniques in tissue engineering, the development of extrudable bioinks that perform optimally at physiological temperatures remains a major challenge. Technologies such as light based printing technologies such as two photon based direct laser writing and DLP circumvent the problem. However, these technologies usually need sophisticated photoinitiators and are limited to their printing size. In order to enhance the survival of cells in 3D bioprinted objects functionalized biopolymers often based on extracellular matrix components are used.  The majority of these biopolymers and photocurable precursor solutions exhibit low viscosities at 37 °C, resulting in undesirable flows and loss of form prior to chemical crosslinking. Temperature-sensitive bioinks, such as gelatin methacryloyl (GelMA) or other gelatin and collagen based bioinks, can be deposited near their gelling point, but suffer from suboptimal temperature-induced pre-gelation, poor cell viability emerging from long holding times in the cooled cartridges, inefficient temperature transfer from the print bed, and discontinuous layer-by-layer fabrication. Recently we have developed  block polyelectrolyte additives serve as effective viscosity enhancers when added to non-extrudable precursor solutions. Rapid, electrostatic self-assembly of block polyelectrolytes into either micelles or interconnected networks provides a hydrogel scaffolding that forms nearly instantly, lends initial structural robustness upon deposition, and enhances shear and tensile strength of the deposited bioinks. Moreover, our approach enables continuous extrusion without the need of chemical crosslinking between individual layers, paving the way for fast biomanufacturing of human-scale tissue constructs with improved inter-layer bonding. In order to enhance vialbility of cells we also are heavily involved in the synthesis of novel cell friendly photoinitiators.

 

Christine Selhuber-Unkel
Heidelberg University, Germany

Rein Ulijn
Advanced Science Research Center, City University of New York, USA

We are interested in how functionality emerges from interactions and reactions between biomolecules, and subsequently how these functions can be incorporated into materials. Instead of using sequences known in biological systems, we use unbiased computational and experimental approaches to search and map the peptide sequence space for specific interactions and functions, with a focus on side chain, instead of backbone interactions. The talk will explore how to program molecular order and disorder through side chain interactions in short peptides, and how the conformations adopted by these peptides can be exploited to regulate interfacial assembly properties, and liquid-liquid phase separation. We will discuss chemo-mechanical peptide-crystals with connected soft and stiff domains, that change their properties upon changes in hydration states. The last part of the talk will focus on our progress in holistic study of mixtures of molecules that individually are simple and non-functional, but as components of complex interacting systems, however, they give rise to self-organization patterns that are dictated by the environmental conditions.  Collectively, we expect to identify insights that allow the repurposing of nature’s molecules to design new materials beyond those available through biology. 

Helma Wennemers
ETH Zürich, Switzerland

Self-assembly and selective recognition events involving proteins are critical in nature for the function of numerous different processes, for example, catalysis, signal transduction or the controlled formation of structural components such as bones. My group is intrigued by the question whether also peptides with significantly lower molecular weights compared to proteins can fulfill functions for which nature evolved large macromolecules. Specifically, we ask whether peptides can serve as effective asymmetric catalysts, templates for the controlled formation of metal nanoparticles,1 hierarchical supramolecular assemblies,2,3 and synthetic collagen-based assemblies.4,5

The lecture will focus on our research interests in supramolecular assemblies and their application in chemical biology and material sciences.

References

For examples, see:

  1. a) Corra, S.; Lewandowska, U.; Benetti, E. M.; Wennemers. H. Angew. Chem. Int. Ed., 2016, 55, 8542. b) Shoshan, M. S.; Vonderach, T.; Hattendorf, B.; Wennemers, H. Angew. Chem. Int. Ed. 2019, 58, 4901–4905.
  2. Lewandowska, U.; Zajaczkowski, W.; Corra, S.; Tanabe, J.; Borrmann, R.; Benetti, E. M.; Stappert, S.; Watanabe, K.; Ochs, N. A. K.; Schaeublin, R.; Li, C.; Yashima, E.; Pisula, W.; Müllen, K.; Wennemers, H. Nat. Chem., 2017, 9, 1068.
  3. T. Schnitzer, E. Paenurk, N. Trapp, R. Gershoni-Poranne, H. Wennemers,J. Am. Chem. Soc. 2021, 143, 644–648.
  4. Hentzen, N. B.; Smeenk, L. E. J.; Witek, J.; Riniker, S.; Wennemers, H. J. Am. Chem. Soc., 2017, 139, 12815.
  5. Fiala, T.; Barros, E. P.; Ebert, M.-O.; Ruijsenaars, E.; Riniker, S. Wennemers, H. J. Am. Chem. Soc. 2022, in press.

Christof Wöll
Karlsruhe Institute of Technology (KIT), Germany

Realizing molecular “Designer Solids” by programmed assembly of building units taken from libraries is a very appealing objective. Recently, metal-organic frameworks (MOFs) have attracted a huge interest in this context. Here, we will focus on MOF-based electrochemical, photoelectro-chemical, photovoltaic, and sensor devices. Internal interfaces in MOF heterostructures are also of interest with regard to photon-upconversion and the fabrication of diodes.

Since the fabrication of reliable and reproducible contacts to MOF-materials represent a major challenge, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on appropriately functionalized substrates. The resulting films are referred to as SURMOFs [1,2] and have very appealing properties in particular with regard to optical applications [3]. The fabrication of hetero-multilayers is rather straightforward with this lbl method. In this talk, we will describe the principles of SURMOF fabrication as well as the results of systematic investigations of electrical and photophysical properties exhibited by empty MOFs and after loading their pores with functional guests. We will close with discussing further applications [4] realized by loading MOFs with nanoparticles or quantum dots and by creating molecular solids lacking inversion symmetry for second harmonic generation (SHG).[5]

References:

[1] J. Liu, Ch. Wöll, Chem. Soc. Rev. 46, 5730-5770 (2017)
[2] L. Heinke, Ch. Wöll, Adv. Mater. 31 (26), 1970184 (2019)
[3] R. Haldar, L. Heinke, Ch. Wöll, Adv. Mater. 32, 1905, (2020)
[4] A. Chandresh, X. Liu, Ch. Wöll, L. Heinke, Adv. Sci., 8, 2001884 (2021)
[5] A. Nefedov, R. Haldar, Zh. Xu, H. Kühner, D. Hofmann, D. Goll, B. Sapotta, S. Hecht, M. Krstić, C. Rockstuhl, W. Wenzel, S. Bräse, P. Tegeder, E. Zojer, Ch. Wöll, Adv. Mater. 33, 2103287 (2021)

Omar Yaghi
University of California, USA

Reticular chemistry, linking of molecular building blocks by strong bonds to make crystalline extended structures, has led to ultra-porous metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Here, organic and inorganic (for MOFs), as well as just organic molecules are stitched together with covalent bonds (for COFs) to make crystalline, porous frameworks of high architectural and chemical robustness. This opened the way to carrying out chemistry on frameworks and chemically functionalizing the pores for water harvesting from air and carbon capture from air and flue gas. The chemistry to make these frameworks and their integration into machines capable of producing clean water and clean air will be presented.