Biomaterials
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BIOMATERIALS Research in the Department of Biomaterials The Department of Biomaterials focuses on interdisci- New Methods for Analysis of Biomaterials plinary research in the field of biological and bio- Studying hierarchical biomaterials requires state-of-the-art mimetic materials. The emphasis is on under- experimental equipment, but there is also some need for the standing how the mechanical or other physical development of new approaches. Scanning methods based properties are governed by structure and compo- on the diffraction of synchrotron radiation, as well as the sition (see Fig. 1). Furthermore, research on nat- technique of small-angle x-ray scattering (SAXS) are continu- ural materials (such as bone or wood) has poten- ously developed to improve the characterization of hierarchi- tial applications in many fields. First, design con- cal biomaterials. Further technical improvement is expected cepts for new materials may be improved by from a dedicated scanning set-up which is currently being learning from Nature. Second, the understanding installed at the synchrotron BESSY in Berlin. of basic mechanisms by which the structure of bone or connective tissue is optimised opens the way for Plant Biomechanics Biotemplating studying diseases and, thus, for contributing to diagnosis (Ingo Burgert) (Oskar Paris) and development of treatment strategies. A third option is to use structures grown by Nature and transform them by phys- Mechanobiology Biomimetic Materials ical or chemical treatment into technically relevant materials (Richard Weinkamer) (Peter Fratzl) (biotemplating). Given the complexity of natural materials, new approaches for structural characterisation are needed. Mineralized Tissues Bone Research Some of these are further developed in the Department, in (Himadri S. Gupta) (Peter Fratzl) particular for studying hierarchical structures. Scanning Diffraction Beamline Hierarchical Structure of Natural Materials (Oskar Paris) The development of metals and alloys with increasing strength has been a constant trigger for the technical development of Fig. 2: Research groups in the Department of Biomaterials with our societies. Interestingly, Nature does not use metals as respective group leaders structural materials at all. Practically all biological materials are based on polymers and polymer-mineral composites. The Research Strategy required mechanical performance is obtained by an intelligent The research on biomaterials is currently concentrated in structure which is hierarchical and optimised at all levels. seven research groups as sketched in Fig. 2. Three groups (left column in Fig. 2) deal with “understanding” (see Fig. 1) Hierarchical Biological Understand the mechanical properties of biological materials and their Structure Materials (experiment and adaptation to external stimulus. Three more groups (right col- macro – micro – nano modelling) umn in Fig. 2) concentrate on more applied goals, relating to Mineralized Tissue the development of new materials, on the one hand, and to (bone, dentin, enamel, …) medical problems in bone research, on the other. Finally, a (Mechanical) Copy Plant Bodies Behaviour (biotemplating) seventh group is dedicated to the development of a new (wood, …) micro-focus beamline for scanning x-ray scattering applica- Connective Tissue tions at the BESSY synchrotron in Berlin. More detailed goals Functional (collagen, cartilage, …) Mimic of the different research groups are outlined below. Adaptation … (biomimetic materials) Plant Biomechanics Fig. 1: General research goals in the Department of Biomaterials The main goals are: · To understand plant tissue as a fibre composite in relation Mechanical Adaptation of Biomaterials to its mechanical adaptation; It is also well-known that biological materials constantly adapt · To understand the nano-structure and mechanical properties to changing mechanical needs. This is achieved by a strain- of the plant cell wall; sensing mechanism, which in most biological systems is not · To obtain basic knowledge on structure-property relation- fully elucidated. In the case of bone, for instance, spe- ships in plants for transfer to technical systems. cialized cells are thought to act as strain sensors and to be at the centre of a feed-back loop, called Mineralized Tissues bone remodelling cycle, where damaged The main goals are: bone is removed and replaced by new · To understand how bone and related calcified tissues are material. This process is crucial designed at the micro- and nano- levels to fulfil their for the tissue's capability of load-bearing and structural requirements; mechanical adaptation · To develop a theoretical formulation that relates the and self-repair. mechanical properties of mineralized tissues to their struc- ture at the sub-micron level. 26 Mechanobiology The main goals are: · To understand and predict the adaptation of materials to mechanical requirements by means of numerical simulation; · To improve the understanding of the biological response of natural tissues to mechanical stimulus and the associated feedback mechanisms by means of theoretical analysis. (a) (b) (c) (d) Biotemplating The main goals are: · To take natural tissues as scaffolds or moulds for the creation of novel engineering materials with improved mechanical and functional properties; Gustav Klimt (1862-1918): (a) normal, (b) bisphosphonate, (c) parathyroid hormone, (d) NaF · To preserve and/or replicate the hierarchical structure of Three ages of a women, 1905 the biological tissues down to the nanometer regime during the conversion process. Fig. 3: Various treatment strategies of osteoporosis investigated with back-scattered electron microscopy in collaboration with the Ludwig- Biomimetic Materials Boltzmann Institute of Osteology in Vienna, Austria (courtesy, The main goals are: Dr. Paul Roschger) · To use the building principles of natural hierarchical com- posites, such as bone, collagen or the plant cell wall, to improve existing materials by shaping and structuring. Peter Fratzl · Current work includes: Biomimetic polymer-mineral Director of the Department composites; Designed porous scaffolds with optimised of Biomaterials mechanical properties; Novel precious metal-based bio- nano-catalysts; synthesis of hydroxyapatite naoparticles with special shapes. Bone and Mineral Research This group works in close collaboration with external medical research groups and its main goals are: · To study clinical problems related to bone material quality in various bone diseases, such as osteoporosis or brittle bone disease, · To establish the effect of genotype on bone material in ani- mal models and for genetic diseases, · To develop new physical methodology for assessing bone material quality. Scanning Diffraction Beamline The main goals are: · To develop a microfocus synchrotron beamline for scanning x-ray scattering applications, in col- laboration with BESSY and the Federal Institute for Materials Research (BAM), the idea being to use the small-angle and/or diffraction signal to image a specimen with micrometer resolution; · To develop high-throughput tech- nology for online data analysis, to deal with the enormous amount of data collected in scanning diffraction applications; · To implement a platform for the study of biological specimens (in particular cryo-sections). 27 BIOLOGICAL MATERIALS Calcified Tissue Structure and Mechanics Structural Adaptation and Mechanisms Fibrillar Level Deformation Mechanisms in of Deformation in Calcified Tissues Mineralized Tendons and Bone The general aim of this group is to elucidate For partially mineralized avian tendons for low (< 1–2%) how the various structural features of natu- macroscopic strains, the fibril level deformation follows the ral calcified tissues (bone, tendon, cartilage) applied external stress, for larger strains, an unexpected relate to their mechanical behavior [1]. biphasic behavior is observed, where a portion of the fibrils Specifically, three types of tissues were relax back to their unstressed state while the remainder elon- addressed. (a) Mineralized cartilage, which is the gate to much larger strains, while maintaining macroscopic crucial interface between subchondral bone and cohesion (Fig. 2b). By combining the results with fractograph- Himadri Shikhar Gupta 26.06.1973 articular cartilage in articulating joints; (b) Parallel fibered ic analysis using scanning electron microscopy, we find that 1991-1996: M.Sc. in Physics mineralized collagen from tendon and bone, in order to eluci- the mineralized tendon consists, at the micrometer level, of a (Indian Institute of Technology, date mechanical deformation mechanisms at the fibril level; heterogeneously mineralized group of unmineralized and Kanpur, India) (c) And single osteons, the basic building block of compact fully mineralized fiber bundles of 2 – 4 micron diameter. Our 1996-2000: PhD, Physics (Department bone, comprising layers of lamellar bone around a blood ves- results are interpreted in terms of two-fiber composite model of Physics and Astronomy, Rutgers, The sel. The aim was to resolve their intra-lamellar structure in (Fig. 2b), inset) in which the highly mineralized fibers account State University of New Jersey, New terms of the orientation, size, shape and crystallographic for the macroscopic stiffness and the lowly mineralized fibers Brunswick, New Jersey, USA) structure of the nanometer size crystallites in relation to the the high work to fracture [2]. In contrast, our more recent Thesis: Phase Segregation and Alloying