Research

Biomimetic Materials and Processes Biomineralization Morphosynthesis and Self-Organization Nonclassical Crystallization Process-Structure-Property Relationships

Biominerals, such as sea urchin spines and mollusk shells, are biogenically formed composite ceramics which show superb adaptation for given tasks. The 542 million years of evolution since the Cambrian explosion has rendered biominerals an immense source of inspiration for both material design and for the creation of ceramic materials at ambient temperature. The key step during genesis of these biogenic ceramics is the controlled solid-amorphous to crystalline transformation from a transient precursor to a highly co-oriented mosaic crystal. This solid-to-solid phase transformation is pseudomorphic, i.e. it proceeds with conservation of the macroscopic morphology of the mineral body which eventually leads to non-equilibrium shaped crystalline forms. Therefore, biominerals and biomineralization itself represents a huge source of inspiration for the synthesis of functional materials under morphological control. As of yet, the formation of ceramics at ambient conditions for anthropogenic ceramic materials is still in its infancy and Nature may guide us on this venture.

Fundamentals of Nucleation and Crystal Growth in Real Systems

Our research in biomimetic crystallization taught us that crystallization processes are not well understood for real systems; the classical models as given in 1920's work explicitly well for simple model systems (i.e. melts, NaCl, etc.). But already simple additives, such as polyacrylic acid, can strongly intervene in the crystallization process and trigger so-called Noncassical Crystallization processes. These processes i.e. oriented attachment, prenucleation cluster, and liquid-condensed mineral precursors (PILP) question our current understanding of crystal birth and growth. The third member of the nonclassical triumvirate is the so-called Polymer-Induced Liquid-Precursor Process (PILP), a process which has pronounced morphosynthetical potential. It proceeds in a colloid-mediated fashion via a liquid-phase amorphous intermediate. By addition of tiny amounts of poly-ionic polymers like poly-aspartate, poly-amines or selected biomineralization proteins, classical nucleation of a solid crystalline phase is suppressed which, in turn, promotes the formation of a liquid-condensed phase of mineral precursor. This unusual ion-enriched liquid-amorphous phase becomes the crucial agent of the precipitation reaction; the process of mineralization is converted from a solution crystallization process to a pseudomorphic solidification process. This change of pathway provides an efficient means to synthesize an impressive multitude of mineral morphologies, many of which mimic the features long considered enigmatic in biominerals.

Nacre forms via a nonclassical route

Intricate biomineralization processes in molluscs engineer hierarchical structures with meso-, nano- and atomic architectures that give the final composite material exceptional mechanical strength and optical iridescence on the macroscale. This multiscale biological assembly inspires new synthetic routes to complex materials. Our investigation of the prism–nacre interface reveals nanoscale details governing the onset of nacre formation using high-resolution scanning transmission electron microscopy. A wedge-polishing technique provides unprecedented, large-area specimens required to span the entire interface. Within this region, we find a transition from nanofibrillar aggregation to irregular early-nacre layers, to well-ordered mature nacre suggesting the assembly process is driven by aggregation of nanoparticles (~50–80 nm) within an organic matrix that arrange in fibre-like polycrystalline configurations. The particle number increases successively and, when critical packing is reached, they merge into early-nacre platelets. These results give new insights into nacre formation and particle-accretion mechanisms that may be common to many calcareous biominerals.

Get Open-Acess Article from Nature Communications

Read Press Releases on Phys.org or IDW

Tilting Biomimetic Crystals

Classical crystal exhibit smooth and flat facets, they do not tilt. Only few examples are known in which the facets or the crystallographic organization of crystals show twisting or tilting. Employing amorphous calcium carbonate films synthesized by the polymer-induced liquid-precursor (PILP) process, we are able to convert these films into flat cylindrulites with crystallographically complex features. By tuning the experimental parameters,  we can generate crystal lattice tilting similar to that found in calcareous biominerals. This contribution, recently published in CrystEngCom evidences the role of spherulitic growth mechanisms in pseudomorphic transformations of calcium carbonate and hints to a hidden role of spherultic processes in vivo.

This contribution is part of a special issue on Nanocrystal Formation and is featured by the outer cover page. Find the OpenAccess article online on CrystEngCom

The Wolf Pack

Pack News

01/01/0001 - Congratulations! Benedikt received poster price on the GISAS summerschool 2016!

01/01/0001 - Welcome to Dave Wallis Visiting Scientist from U Ox

04/07/2016 - Welcome to Clémence! Coming from Polytech Lyon, she joins us for an internship in collaboration with Prof. de Ligny.

03/02/2016 - Joe's paper is out!   Joe's Paper on crystal lattice tilting was accepted in CrystEngCom, see here!  

Pack Members

Prof. Dr. rer. nat.
Stephan E. Wolf
Mail CV

Stephan E. Wolf studied Chemistry (Diplom) at the Johannes-Gutenberg University of Mainz and obtained his PhD (Dr. rer. nat.) under the supervision of Prof. Dr. Wolfgang Tremel. His thesis with the title "Nonclassical Crystallization of Bivalent Metal Carbonates" was supported by a scholarship of the Konrad-Adenauer Foundation. After a short postdoc visit in the group of Prof. Dr. Rademann at the Humboldt University of Berlin, he received a DFG PostDoc scholarship and joined the CNRS Laboratoire Biogéoscience (UMR CNRS/uB 6282) and worked with Dir. Dr. Frédéric Marin at the University of Dijon on proteomic characterization of intracrystalline biomineralization proteins in bivalves. Then he joined as a reasearch associate the group of Lara A. Estroff in Cornell, in the Department of Materials Science and Engineering. With the aid of a repatriation grant, he came back to Germany as a visiting scientist at the Max-Planck Institute for Polymer Chemistry in the group of Prof. Dr. H.-J. Butt. Since February 2014, he is Assistant Professor for Biomimetic Materials and Processing at the Chair of Glass and Ceramics in the Department of Materials Science and Engineering of the Friedrich-Alexander-University Erlangen-Nürnberg. Shorty after, he received an Emmy-Noether Scholarship (1.24 Mio€, WO1712/3-1) by the German Research Foundation.

Dr.
Joe Harris
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Corinna F. Böhm MSc.
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Corinna F. Böhm has undertaken an apprenticeship as metallographer at the Max-Planck-Institute for Metal Research in Stuttgart, before she started her Forensic Science studies (Bachelor) at the Hochschule Bonn-Rhein-Sieg, the Victoria University Melbourne and the Hogeschool van Amsterdam. She continued her studies with the Elite Master's Programme in Advanced Materials and Processes at the Friedrich-Alexander-Universität Erlangen-Nürnberg, which she completed in our group with her Master´s Thesis "Influence of the Nano- and Microscale Structure on the Macroscopic Properties of Bivalve Shells". She is currently working on her PhD focussing on nanoscale properties of biominerals and biomimetic materials.


Benedikt Demmert MSc.
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Martina Schüßler MSc.
Mail

Huyen Trinh MSc
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Barbara Myszka MSc
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Simon Leupold BSc.
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Publications

If you need a authors copy of one of the publications, do not hesitate to drop me a line: stephan.e.wolf@fau.de

Selected Publications
Complete List of Articles
Complete List of Books and Book Chapters
  1. Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells
    Robert Hovden*, Stephan E. Wolf*, Megan E. Holtz, Frédéric Marin, David A. Muller and Lara A. Estroff (* equal contribution) in Nature Communications (2015) , Vol. 6, No. 10097. DOI:10.1038/ncomms10097.
    Abstract: Intricate biomineralization processes in molluscs engineer hierarchical structures with meso-, nano- and atomic architectures that give the final composite material exceptional mechanical strength and optical iridescence on the macroscale. This multiscale biological assembly inspires new synthetic routes to complex materials. Our investigation of the prism–nacre interface reveals nanoscale details governing the onset of nacre formation using high-resolution scanning transmission electron microscopy. A wedge-polishing technique provides unprecedented, large-area specimens required to span the entire interface. Within this region, we find a transition from nanofibrillar aggregation to irregular early-nacre layers, to well-ordered mature nacre suggesting the assembly process is driven by aggregation of nanoparticles (~50–80 nm) within an organic matrix that arrange in fibre-like polycrystalline configurations. The particle number increases successively and, when critical packing is reached, they merge into early-nacre platelets. These results give new insights into nacre formation and particle-accretion mechanisms that may be common to many calcareous biominerals.
  2. Strong Stabilization of Amorphous Calcium Carbonate Emulsion by Ovalbumin: Gaining Insight into the Mechanism of 'Polymer-Induced Liquid Precursor' Processes.
    Stephan E. Wolf, Jork Leiterer, Vitaliy Pipich, Raul Barrea, Franziska Emmerling and Wolfgang Tremel in J. Am. Chem. Soc. (2011) , Vol. 132, No. 32, pp. 1520-6. DOI:10.1021/ja202622g.
    Abstract: The impact of the ovo proteins ovalbumin and lysozyme—present in the first stage of egg shell formation—on the homogeneous formation of the liquid amorphous calcium carbonate (LACC) precursor, was studied by a combination of complementing methods: in situ WAXS, SANS, XANES, TEM, and immunogold labeling. Lysozyme (pI = 9.3) destabilizes the LACC emulsion whereas the glycoprotein ovalbumin (pI = 4.7) extends the lifespan of the emulsified state remarkably. In the light of the presented data: (a) Ovalbumin is shown to behave commensurable to the 'polymer-induced liquid precursor' (PILP) process proposed by Gower et al. Ovalbumin can be assumed to take a key role during eggshell formation where it serves as an effective stabilization agent for transient precursors and prevents undirected mineralization of the eggshell. (b) It is further shown that the emulsified LACC carries a negative surface charge and is electrostatically stabilized. (c) We propose that the liquid amorphous calcium carbonate is affected by polymers by depletion stabilization and de-emulsification rather than 'induced' by acidic proteins and polymers during a so-called polymer-induced liquid-precursor process. The original PILP coating effect, first reported by Gower et al., appears to be a result of a de-emulsification process of a stabilized LACC phase. The behavior of the liquid amorphous carbonate phase and the polymer-induced liquid-precursor phase itself can be well described by colloid chemical terms: electrostatic and depletion stabilization and de-emulsification by depletion destabilization.
  3. Formation of silicones mediated by the sponge enzyme silicatein-α
    Stephan E. Wolf, Ute Schlossmacher, Anna Pietuch, Bernd Mathiasch, Heinz-Christoph Schröder, Werner E G Müller and Wolfgang Tremel in Dalton Transact. (2010) , Vol. 39, pp. 9245-9. DOI:10.1039/B921640E. This article is part of a themed issue: New Horizon of Organosilicon Chemistry.
    Abstract: The sponge-restricted enzyme silicatein-α catalyzes in vivo silica formation from monomeric silicon compounds from sea water (i.e. silicic acid) and plays the pivotal role during synthesis of the siliceous sponge spicules. Recombinant silicatein-α, which was cloned from the demosponge Suberites domuncula (phylum Porifera), is shown to catalyze in vitro condensation of alkoxy silanes during a phase transfer reaction at neutral pH and ambient temperature to yield silicones like the straight-chained polydimethylsiloxane (PDMS). The reported condensation reaction is considered to be the first description of an enzymatically enhanced organometallic condensation reaction.
  4. Early homogenous amorphous precursor stages of calcium carbonate and subsequent crystal growth in levitated droplets.
    Stephan E. Wolf, Jork Leiterer and Michael Kappl, Franziska Emmerling and Wolfgang Tremel in J. Am. Chem. Soc. (2008) , Vol. 130, No. 37, pp. 12342-7. DOI:10.1021/ja800984y. Highlighted in Nachr. Chemie (2009).
    Abstract: An in situ study of the contact-free crystallization of calcium carbonate in acoustic levitated droplets is reported. The levitated droplet technique allows an in situ monitoring of the crystallization while avoiding any foreign phase boundaries that may influence the precipitation process by heterogeneous nucleation. The diffusion-controlled precipitation of CaCO3 at neutral pH starts in the initial step with the homogeneous formation of a stable, nanosized liquid-like amorphous calcium carbonate phase that undergoes in a subsequent step a solution-assisted transformation to calcite. Cryogenic scanning electron microscopy studies indicate that precipitation is not induced at the solution/air interface. Our findings demonstrate that a liquid-liquid phase separation occurs at the outset of the precipitation under diffusion-controlled conditions (typical for biomineral formation) with a slow increase of the supersaturation at neutral pH.
  5. Phase selection of calcium carbonate through the chirality of adsorbed amino acids.
    Stephan E. Wolf, Niklas Loges, Bernd Mathiasch, Martin Panthöfer, Ingo Mey, Andreas Janshoff and Wolfgang Tremel in Angew. Chem. Int. Ed. (2007) , Vol. 46, No. 29, pp. 5618-23. DOI:10.1002/anie.200700010. This is featured as a VIP paper.
    Abstract: On the phase of it: The phase selection of calcium carbonate (spheres: C gray, Ca green, O red) is determined by chiral amino acids (stick models) present during the crystallization. The interplay of composition and chirality of the crystal surfaces and additives leads to enantiospecific adsorption of the D and L amino acids on chiral surface steps. The resulting surface passivation creates a kinetic barrier, which controls the phase selection.

Get in touch

Looking for research opportunities, open positions, or just want to contact The Wolf Group?

General applications for postgraduate studentships and postdoc positions are welcome at any time of the year. Please send your application documents simply by email and refer to this website. We offer also throughout the year various topics for Master- and Bachelor theses, and also for internships and miniprojects. If you are interested to do your thesis or an internship with us, just drop me a mail and we will fix an appointment for discussion of the currently available research projects: stephan.e.wolf@fau.de

 

Prof. Dr. rer. nat. Stephan E. Wolf
Juniorprofessor for Biomimetic Materials and Processing
Department of Materials Science and Engineering
Institute of Glass and Ceramics  - https://www.glass-ceramics.tf.fau.de/
Friedrich-Alexander-University Erlangen-Nürnberg - https://www.fau.de/
Martensstr. 5, 91058 Erlangen, Germany
Fone +49 9131 85-27565
Fax   +49 9131 85-28311
stephan.e.wolf@fau.de