Biomechanical Engineering

Empa Industry Cooperation Research Consulting Services Expertise Technology Transfer Biomechanical Engineering Empa Industry Cooperation Biomechani...
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Empa Industry Cooperation Research Consulting Services Expertise Technology Transfer

Biomechanical Engineering

Empa Industry Cooperation Biomechanical Engineering

Contents Implants 4 6 8 9 10

Metallic Implants – Surface Functionalizing and Corrosion Metallic Implants – Failure Analysis and Characterization Metal-Metal and Metal-Ceramic Joints for Biomedical Applications Novel Polymeric Biomaterials Novel Implants and Implant Surfaces

12

Novel Scaffolds for Medical Applications

14 15

A Wireless Sensor for Measuring Implant Deformation Cell-based Biosensors

16

Designing an Optimized Body Protector

18

Computational Biomechanics

20 21

Experimental Biomechanics Artificial Muscles

22 23 24 26 28 29 30

Super-resolved Images of Cell Structures Thermal Imaging of Implanting Processes 3D High Resolution Imaging of Bone Structures by FIB X-Ray Tomography of Bones, Implants and Cellular Materials Deformation Analysis of Implants and Bones with Interferometry Confocal Laser Scanning Microscopy (CLSM) and Transmission Electron Microscopy (TEM) Imaging Surface Analysis in the Nanometer Range

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Empa – Bridge between Science and Business

Tissues Sensors

Protectors Modeling Testing / Devices

Imaging / Analysis

Cooperation & Technology Transfer

Head of Program «Materials for Health and Performance»

Markus Rüedi +41 71 274 72 48 [email protected]

Biomechanical Engineering Empa has been conducting research in the area of biomechanical engineering for many years. This brochure provides an overview of our services and activities in this important area of medical technology. With our know-how and superior infrastructure, we can support your organization through the development of highly innovative products and systems. We offer various clearly defined services and consultations, simulations of materials and structures as well as joint research projects. We strive to contribute to increasing the innovative edge of our industrial partners, especially by allowing SMEs (small and medium sized enterprises) without R&D facilities to participate in innovative developments. It is Empa’s utmost goal to build a bridge from research to practical application. With our help, you will be able to implement novel ideas faster and successfully launch them on the market. In this respect, Empa researchers and specialists from multiple disciplines can support you in this endeavor. Should you have specific questions or a general inquiry, we invite you to contact our specialists and look forward to helping you elaborate goal-directed solutions.

Metallic Implants – Surface Functionalization and Corrosion 4

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Upon implantation in the human body, metallic implants are subject to electrochemical reactions on their surfaces inducing release of ionic species. Characterization of the materials’ in vitro reactivity can be used to deepen our understanding of the degradation processes in order to avoid implant failure and to enable new implant materials development. Macro- and micro-electrochemical methods allow investigation of uniform and localized corrosion susceptibility and its relation to material microstructure. A major difference to classical corrosion investigations is the complexity of the physiological media with the presence of proteins (and cells). Solution chemistry at the implant site is thus a prime influence on degradation mechanisms. Besides being used as an analytical tool, electrochemical methods also help to functionalize implant surfaces by growing tailored anodic oxide layers or via the deposition of specific coatings.

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1b

Corrosion analysis on implant surfaces 1a

Electrochemical microcell analysis of a medical screw 1b

Mg alloy stent 1c

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100 Slow reaction: Uniform corrosion

log Z [Ω.cm-2]

Corrosion rates and types for Mg alloy characterized by Electrochemical Impedance Spectroscopy (EIS)

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Fast reaction: Localized corrosion

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40 20

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1 -2

-1

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2 log ω

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-20

phase angle

1c

Dr Patrik Schmutz + 41 44 823 48 45 [email protected]

Electrochemical characterization of corrosion susceptibility can be performed macroscopically – i.e. on bulk material – or directly on critical areas of the implants using the microcell technique (Fig.1a). Metallic implant degradation (stainless steel, Co alloys) is mainly the result of localized corrosion related to the microstructure and/or surface treatments. Crevice and galvanic corrosion induced by the complex implant geometries and dissimilar material used can be investigated in in vitro experimental setups. For instance, the release of «toxic» ions into the solution can be monitored long before implant failure occurs. Corrosion can also be desired, especially when degradable implants with defined dissolution rate are aimed at (Fig.1b).

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It is possible to analyze uniform and localized corrosion processes by Electrochemical Impedance Spectroscopy (EIS; Fig. 1c) and to develop alloys exhibiting a «controlled» degradation rate. Electrochemistry can be further used, for example, to grow porous oxide films improving the corrosion resistance of Mg alloys (Fig. 2a) or to functionalize Ti and enhance cell attachment to the surface (Fig. 2b).

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Surface functionaliziation 2a

Focussed Ion Beam (FIB) section of anodic oxide on Mg alloy: The oxide layer provides initial temporary corrosion protection 2b

Porous anodic oxide to promote cell adhesion on a Ti surface 2b

Metallic Implants – Failure Analysis and Characterization 6

Metallic implants that have failed represent « sources of data» where the information is stored within specific features of the fractured area, on the implant surface or in its microstructure. These data can be read and interpreted using suitable characterization methods such as Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), microstructure analysis, corrosion investigation and mechanical tests. Combining all this information allows a reconstruction of the failure history and, ultimately, the development of improved implants.

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Macroscopic documentation 1a

Perpendicular fracture surface within the thread 1b

Stepped fracture origin with «beach» marks typical for fatigue

scrystalline «feather-like structure» for stress corrosion cracking, intergranular «crows feet structure» for hydrogen embrittlement, etc. can be identified. In-depth crack propagation is further analyzed on metallographic sections (Fig. 3). The transgranular, intergranular or branched nature of the crack gives additional indications on the failure mechanism. Specific investigations of the corrosion products using EPMA reveal local aggressive environmental conditions. Putting all pieces of the puzzle together helps to obtain a complete picture of the failure process.

During the investigation of implant failure cases a systematic experimental procedure is necessary to guarantee a detailed understanding of failure mechanism. With macroscopic documentation of the broken part (Fig. 1a), first hints concerning type (ductile or brittle), initiation site(s) and fracture mode can be determined (Fig. 1b). Based on these assumptions a more detailed microscopic characterization of the initiation site(s) is performed by means of SEM. Microscopic features on the fractured surface like striations for fatigue (Fig. 2), tran-

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4 mm

Oliver von Trzebiatowski + 41 44 823 41 36 [email protected] Dr Kilian Wasmer +41 33 228 29 71 [email protected]

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Fatigue fracture with striation pattern

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SEM images 3a

Surface crack parallel to the fracture origin 3b

Branched crack indicating corrosive attack

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Metal-Metal and Metal-Ceramic Joints for Biomedical Applications 8

Titanium and titanium alloys such as Ti-6Al-4V are widely used in medical or implant technology because they combine appropriate mechanical properties with corrosion resistance and biocompatibility. Some applications require joined components, whereby the joining partners can be of the same or of dissimilar materials e.g. a combination of titanium and Al2O3-ceramics. Since both good corrosion properties as well as biocompatibility must be guaranteed, appropriate joining technologies have to be applied.

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In order to produce reliable components, joining of titanium must be performed in a very clean shielding gas atmosphere or under high vacuum conditions in order to prevent reactions with elements like oxygen or nitrogen. Diffusion bonding can be used to produce titanium-titanium joints. The joining partners are placed in a high vacuum furnace, which is heated to temperatures between 1150 and 1200 degree Celsius. At this temperature, atoms from one joining partner can easily diffuse to the other partner, hereby forming a tight joint. The advantage of this technology is that no other material

Ti mesh on a Ti plate, produced by diffusion bonding

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Al2O3-Ti-6Al-4V joints after active brazing in the high vacuum furnace

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Al2O3

Ti-6Al-4V

Dr Christian Leinenbach +41 44 823 45 18 [email protected]

is introduced between the joining partners which can affect the corrosion properties. Figure 1 shows a mesh of commercially pure titanium, which was bonded to a titanium plate. Such joints are used, among others, for hip prostheses in order to improve bone ingrowth. Titanium-ceramic joints can be produced by active brazing using special filler metals. With this method heliumtight joints could be produced at Empa. Figure 2 shows Al2O3-Ti-6Al-4V joints after brazing in the high vacuum furnace.

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Dr Manfred Zinn

Novel Polymeric Biomaterials New biomaterials are required for particular medical applications, for which – besides biocompatibility – degradation and subsequent regeneration of deficient tissue are equally important. These biomaterials are designed to stimulate specific cellular responses at the molecular level and at the same time to be resorbable. They are capable of supporting the body’s self-healing mechanisms by prompting cells to initiate tissue repair processes. Polymeric and bio- degradable systems used in today’s medicine are mainly based on poly(lactic acid), poly(glycolic acid) and their co-polymers. Other biodegradable polymers are currently under development, however, have not yet been granted approval by health authorities. Biomaterials research at Empa is focused on polymeric materials that originate from microbial synthesis. One of our prime candidates is poly([R]-hydroxyalkanoate) (PHA) (Fig. 1), a class of biodegradable and biocompatible polyesters, with many potential applications in

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+41 71 274 76 98 [email protected]

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biomedicine such as heart valve scaffolds, pulmonary conduits, sutures, screws, bone plates, repair patches, stents and scaffolds for tissue engineering and tissue regeneration. Generally, PHA – an intracellular carbon and energy storage compound for bacteria – is composed of mainly 3-, 4-, or rarely 5-hydroxy fatty acid monomers, which form linear isotactic polyesters. The polymers may be tailored during biosynthesis to carry functional groups (e.g. double bonds) in their side chains. Such functional groups allow further diversification of physical properties of PHA through chemical modification. Special bioreactor systems (Fig. 2) have been developed for the reproducible synthesis of PHA. The purity of PHA is a crucial factor for sophisticated applications and depends on the bacterial production strain as well as on biosynthesis and extraction procedures (Fig. 3). 3

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General structure of poly([R]-hydroxyalkanoate) 2

R

H OH

m

Accurate production techniques are applied to produce PHA in a reproducible way 3

m=1-3

n

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Purity and properties of PHA depend on the appropriate processing after biosynthesis

Novel Implants and Implant Surfaces 10

Once implanted, the fate of the implant depends on two in factors: the interaction between host cells and the implant surface and on cell population dynamics and competition between various cell types at the implant surface. These extremely complex processes in various ways influence, both the host cells and the implanted material.

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Lab impressions

To produce novel implantable devices and to optimize existing strategies, sophisticated cell culture techniques are currently developed and/or improved. These range from the isolation, propagation and phenotyping of specific primary cells over the use of gene constructs as tool to monitor cytoskeletal changes and the state of cell differentiation all the way to time-lapse analysis of cell migration, functional state and cell population dynamics in single and mixed cell type cultures. Accordingly, we aim at identifying critical features of the implant surface affecting cell functionality and, subsequently, at steering the reaction of the cells contacting the implant surface in a favorable direction. Based on our knowledge of cellmaterial interactions, we are currently developing unique implants such as neuroimplants, bone-related implants, biosensors and nanoimplants (e.g. nanocarriers for drug delivery).

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Investigation of cell-cell interactions using osteocarcoma and fibroblast cells labelled by DiO (green) or DiI (red), respectively

100 µm

Dr Arie Bruinink +41 71 274 76 95 [email protected] Dr Katharina Maniura +41 71 274 74 47 [email protected]

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Human bone cells on a metallic surface exhibiting hemisphere structures: Hemispheres have a diameter of 30 µm and are about 15 µm high. The culture was stained for actin (green) and vinculin (red) 5a

Cultured embryonic chicken spinal cord neurons growing on a partially structured surface (3 µm high and 10 µm wide ridges with 10 µm interridge spacings)

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The trajectories of the growth cone dislocation were monitored for 96 hours. To visualize the neurons on the non-transparent surface, spinal cord neurons were transfected in ovo with a modified RFP-plasmid vector

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Novel Scaffolds for Medical Applications 12

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Lab impressions

Tissue defects resulting from disease (e.g. tumors) or injury (e.g. accidents) pose a considerable clinical challenge. The regeneration of such defects may be partly promoted, and enhanced, by introducing biocompatible supporting structures – a scaffold. The development of such scaffolds as backbones directly supporting tissue regeneration is a highly challenging task.

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Tissue engineering is a novel and promising scientific discipline targeting de novo tissue regeneration. Inductive tissue engineering aims at the delivery of cell-seeded scaffolds to diseased or injured sites. The shape and architecture of these scaffolds is dictated by the histological nature, size and shape of the defect (e.g. a 2D membrane for skin regeneration or a 3D foam or textile for bone

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repair). In vitro, both the initial reaction and the fate of cells seeded onto these scaffolds are influenced by various factors including (i), the chemical and physical characteristics of the scaffold (ii), the heterogeneity of the cell culture (i.e., different cell types) and (iii), culture conditions (e.g. bioreactor setup and nutritional factors). We aim at optimizing theses scaffolds thereby inducing and

Dr Arie Bruinink +41 71 274 76 95 [email protected]

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Human bone marrow cells seeded on a polyamide knit

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4 µm

maintaining favorable cell reactions such as viability, scaffold invasion and phenotype maintenance. To achieve these objectives, our group utilizes well-established and newly developed, state-of-the-art biological tools (e.g. molecular biology, immuno-cytochemistry, live time-lapse monitoring of cell motility).

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Human bone marrow cells on a PET woven. Nuclei of the cells were labelled using BrdU (5-Brom-2-desoxyuridin)(proliferating cells, bright blue) and DAPI (2-(4-carbamimidoylphenyl)-1H-indol-6-carboximidamid) (all cells, dark blue)

Dr Jürg Neuenschwander

A Wireless Sensor for Measuring Implant Deformation 14

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Wireless sensor (WIPSS) and its ultrasound-based read-out unit

In order to monitor the deformations of orthopedic implants, a novel sensor is currently being developed in collaboration with the Institute of Micro- and Nanosystems at ETH Zurich. The system consists of an implantable passive strain sensor (WIPSS) and an ultrasound-based read-out unit. The measured strain is displayed by a varying amount of fluid in a microchannel integrated into the sensor. By means of a novel ultrasound technology the fill level of the microchannel is determined, which in turn enables the calculation of the strain. The sensor is completely manufactured of biocompatible or even bioresorbable polymer material.

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Linear relation between ultrasonic signal AM and fill level of the microchannel. The measurements are in very good agreement with the simulations

+41 44 823 43 20 [email protected]

The strain measured by the WIPSS will be read-out through human tissue by means of non-invasive ultrasound. The attenuation properties of the tissue require the use of ultrasound pulse frequencies in the range of 5 megahertz. At these (low) frequencies the microchannel appears as a blurred spot in a 3D ultrasound image and therefore a straightforward determination of the fill level is not feasible. This situation has led to a new read-out principle based on a linear relation between the fill level and the area integration of a C-scan of the microchannel. Additionally, a calibration reflector inside the WIPSS is intended to provide a defined echo, which will be used to compensate amplitude variations of the ultrasound signals caused by the tissue that covers the WIPSS. Extensive in vitro ultrasound experiments as well as numerical simulations of the wave propagation were carried out in order to test the read-out method. Experiments with tissue mimicking materials agree very well with theoretical results.

Evaluation

Ultrasound transducer

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1.0 Simulation Lin. Fit Measurement

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Tissue

Fractured bone

AM (normalized)

Implant

0.8

0.6

WIPSS

0.4 Patient

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50 Fill level [%]

100

Dr Arie Bruinink +41 71 274 76 95 [email protected] Dr Katharina Maniura +41 71 274 74 47 [email protected]

Cell-based Biosensors Discovering novel compounds and materials for biomedical applications and assessing their toxic potential entails an ever-increasing price tag. It is, therefore, critical that pre-clinical in vitro methodologies are optimized whereby, as a result, potential in vivo (human subjects) pharmacological and toxicological potencies can be predicted. This may greatly accelerate decision making in the early stages of drug development and support the monitoring of product quality. 1

As the smallest living entities of an organism, cells are capable of reacting with high sensitivity to single and multiple stimuli (e.g. particles, drugs, hormones, etc.). This reaction, the mechanisms involved and the ensuing effects can be evaluated with appropriate tools like cell-based biosensors. Developing cell-based biosensors to measure cytotoxicity is highly dependent on the type of test (on-line monitoring or single measurement), the targeted cell type (e.g. nerve cells, mesenchymal stem cells) and the measured parameter(s). In our lab we focus on the development of new biosensors to characterize the effects of nanomaterials and drugs, which potentially affect nerve cell, soft tissue (fibroblast) and bone progenitor cell differentiation. Currently, the investigated parameters comprise cell forces transmitted to substrates, electrophysiological activity and single gene activity.

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Lightmicroscopy analysis of a cell culture

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Millivolts

Recordings of the electrical activity of an embryonic chicken spinal cord neuron and muscle cell coculture (green: muscle cells; red: neurons) on MEA surface 3

Biochip with Multi-Electrode Array (MEA) including cell culture tissue 4

Time (sec)

Fibroblasts (green) with nuclei (blue) on structured surface consisting of an array of pillars (red)

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10 µm

20 µm

Designing an Optimized Body Protector 16

Our society is experiencing a growing awareness and desire for protection against mechanical influences as evidenced, e.g. by the increasing popularity of ski helmets and back protectors. Because these protectors are worn on the body, factors such as weight and flexibility as well as thermal comfort and ergonomy are often crucial for consumer decisions. For the developer of such protection systems, the challenge to design light, effective, attractive body protectors depends upon access to reliable measurements and expertise.

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The high-speed image sequence shows a measurement of an artificial hip model (from left top to right top) to evaluate the effectiveness of a hip protector under realistic conditions. The measurement was taken with a high-speed camera

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For all body protectors, two critical aspects influence the desired level of protection: The applied forces have to be reduced – absorbed – in time and space, and mechanical energy is converted to heat. For this reason, there are limitations to the freedom to design such protectors. Generally, two types of elements are employed: • Polymer foam, which combines the functions of a spring and of a damping element, so that the force of the impact is reduced and its energy partially dissipated • A polymer shell, which redistributes a localized force over a larger area For any specific application, the construction of a protector can vary depending, e.g. on the part of the body being protected, the type of mechanical influence of concern, and the expected velocity. The challenge for the manufacturer is how to reduce weight and cost and simultaneously offer excellent protection and comfort. Impacts in the real world occur within milliseconds and require a measurement procedure, which offers reference data under such dynamic conditions,

Dr Paul Brühwiler +41 71 274 77 67 [email protected]

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Drop test for hip protectors with an instrumented falling mass on the anatomically-shaped hip model. The protector is positioned with accessory underwear

and which allows an understanding of the mechanics. At Empa, we have the know-how to characterize the shock absorption capacity of material samples or complete protectors, as well as the experience to provide expert advice. Finally, ideas can be tested in simulations before being converted to prototypes, thereby (potentially) saving valuable time.

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Impact Analysis and Development of Protectors For impact analyses of the effects of protection, Empa’s fall test laboratory is located in a 12 meter high room, designed specifically for such tests. It houses a range of fall test equipment, which can flexibly be applied to study dynamic impacts using free or guided falling masses reaching impact speeds of up to 50 kilometer per hour. The impact velocity, the deceleration of the falling mass and the impact force can all be registered at high precision. If needed, complex experiments can be filmed with a highspeed camera. A special drop test for dynamic failure of ropes and yarns is also available, offering a highlyresolved measurement of the stress-strain relation during the fall. For a realistic analysis of the protection offered by hip protectors, an anatomically-structured hip model has been developed, which measures forces transmitted to the femoral neck in a drop test simulating the forces experienced by a falling person.

Frontal view of the hip model. The hip consists of an artificial pelvis made of aluminium, linked by a ball-and-socket joint to an anatomically-shaped steel femur. The femur is embedded in silicone, which simulates the damping and load-dispersal effect of the surrounding tissue. A triaxial load sensor is integrated in the neck of the femur to measure the axial and cross-sectional force components in response to external impact forces on the hip

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The great trochanter (femur) consists of the long shank and the short neck, which carries the ball of the hip joint. In the neck region, the bone is not particularly strong. In case of age-related decalcification of the bones (osteoporosis) the risk of fracture increases dramatically (see insert). Such fractures are problematic because of the long duration of treatment and the high likelihood of complications

Computational Biomechanics 18

Numerical simulation of the human musculo-skeletal system is a method to evaluate the internal loads within joints as well as the kinematics of the different segments. Finite Element Analysis is then used to design new prostheses; it also helps to predict deformations and stresses in the implant as well as in the surrounding biological tissues. Using «Rigid Multi-Body Simulations» of the musculoskeletal system we can, for instance, predict muscle and reaction forces in the different segments and joints for any given movement.

With the help of Finite Element Analysis (FEA) we can model trauma implants, instruments, joint replacements, dental implants, bones and soft tissues. Both geometrical (contact with friction) and material nonlinearities can be considered. FEA results yield stress and strain distributions, deformations and contact forces. Both topology and shape of medical devices can also be optimized using numerical modeling. Moreover, we can render 3D modelings – for instance of bones – based on Computed Tomography (CT) scans.

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Response of a lumbar spine model, in which individual vertebrae are connected with non-linear elastic joints and springs when loaded by a pure moment

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Person equipped with markers for motion capture (left) and model of the human musculoskeletal system (right) Software: Adams® and LifeMOD® 3

Artificial hip joint implant, femoral head, lumbar spine, functional spinal unit, lateral femoral nail and bone plate Software: Abaqus® and Ansys®

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Bernhard Weisse +41 44 823 48 10 [email protected]

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Optimized shape of the chamfer between the conical bore and the bottom of the bore hole of a hip joint ball head Software: CAO by Mattheck

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Lateral image of a long bone (equine radius; left) and surface model of the bone based on gray values for bone material density (right)

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lCT-scan slice: diaphysis (top), corresponding density profile measured left to right (center), and longitudinal section of the FE model using Young’s modulus distribution derived from the density profile (bottom) Software: Materialise/Mimics®

Bernhard Weisse

Experimental Biomechanics 20 1

Measurement of service loads on sports articles (e.g. bicycles, skis, kickboards) or rehabilitation accessories (e.g. crutch, wheel chair) 2

Static, creep, wear and fatigue tests as well as durability tests using variable load levels can be performed with up to four channels simultaneously

Once an orthopaedic implant has been developed it must be tested extensively to fulfil numerous safety and performance standards as well as customer specifications. The laboratory «Mechanical Systems Engineering» performs mechanical tests of such implants accompanied by deformation and strain measurements. For complex applications special test facilities may be required and can be developed at Empa. The laboratory has a long-term experience in performing mechanical experiments on structures using force, displacement and strain measurement sensors (strain gage or contact-free such as laser or video extensometer). Implants may be tested in physiological solution at 37 degree Celsius in order to simulate in vivo conditions.

The laboratory is accredited in accordance with DIN EN ISO/IEC 17025: Mechanical testing of metallic materials, structural components and constructions (STS053 ). All used test machines and devices are categorized in precision class 1. Test simulators are developed to allow specific loadings and motions according to customer specifications. Empa’s Workshop team provides support in sketching construction plans and in manufacturing the test facilities. The laboratory also hosts special test facilities for impact characterization with optional recording by highspeed video camera and subsequent video tracking and for analyzing the mechanical properties of soft tissues.

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3-point bending test set-up for equine radius bone 4

High-speed video image of the crack propagation in a long bone, which was hit by an impact (top), and a biopolymer augmented bone specimen used for compression test in the range of a few Newtons (bottom) 5

Tension test on a sheep calcaneus tendon: The grips were optimized to assure the muscular side fixation

+41 44 823 48 10 [email protected]

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Dr Gabor Kovacs +41 44 823 40 63 [email protected]

Artificial Muscles

21 Smart materials that respond to external stimuli by changing their shape or size such as electro-active polymers (EAP) may find uses as muscle-like actuators in the not too distant future. The actual performance of EAP-based actuators is in the range of load and strain produced by real muscles. Driven by the tremendous advances in computer science and computational power, virtual environments play an important role in many fields, such as in interactive product designs, medical education and telesurgery. A qualified virtual world allows the user to interact with the virtual environment by addressing all his/ her senses. However, haptic interfaces providing touch sensations to the user are not yet satisfying.

At Empa, we develop a portable force feedback device, which provides satisfying touch sensations to the operator, is powerful, lightweight, and non-obstructive by employing new actuation technologies that have high power density, fast response and low cost. EAP Actuator Bundles as muscular implants The first arm wrestling match between a human and a robotic arm driven by EAP was held at the EAPAD conference in 2005. The primary objective was to demonstrate the potential of the EAP actuator technology for applications in the field of robotics and bioengineering. The robot presented by Empa was driven by a system of rolled dielectric elastomer actuators.

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Arrangement of EAP actuators in an arm prosthesis 2

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Empa EAP robotic arm participating at the arm wrestling competition 3

Spring-rolled actuator used for surgical simulators 4

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EAP production

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Dr Erwin Hack

Super-resolved Images of Cell Structures 22

In a microscope the imaging resolution at a given magnification is limited by the point spread function (PSF) of the objective. The PSF can introduce artefacts in the image that impede a meaningful interpretation. Liquid crystal arrays allow the manipulation of both the phase and the amplitude of light. If properly used in combination with a lens, sharper images can thus be obtained.

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Comparison of conventional imaging (left) and super-resolved imaging (right) of rice-grains 1

+41 44 823 42 73 [email protected]

In collaboration with the EU Joint Research Centre in Ispra (IT), we are developing methods to integrate programmable super-resolution pupil filters based on liquid crystal arrays into a microscope. This will allow identifying and eliminating artefacts introduced by the imaging process. The system will be applied to high-resolution imaging of cells in cell culture in order to localize and image (sub)cellular structures. Such a tool will be invaluable for label-free real-time monitoring of cells exposed to test substances. Figure 1 shows the effect of a super-resolution pupil filter on the imaging of an array of rice grains. The image appears sharper, and a higher number of individual grains become visible.

Dr Erwin Hack

Thermal Imaging of Implanting Processes

+41 44 823 42 73 [email protected]

23

Many processes of implanting or fixing prostheses develop a substantial amount of heat. It is of great importance to optimize these processes in order not to exceed certain temperature limits that could harm the surrounding biological tissue. To assess such processes in a time-resolved manner infrared imaging of the implantation process is of great help. To immobilize fractured bones or to mount a fixation device onto a fractured bone various types of screws or pin-like implants are used. The surface of polymeric or polymer-coated implants can be melted by ultrasonic excitation and provide a solid junction between bone and implant (BoneWelding® Technology, patented by WoodWelding SA, Switzerland). Figure 1 shows the increase in temperature due to the fixation of a polymeric implant into a bone model. From the temperature distribution seen at the surface of the model system, the maximum temperature can be calculated as a function of various process parameters.

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Temperature distribution during ultrasonic implantation of a polymeric model implant into a bone sample (Ø 3.5 mm, measured at 2 mm from the implant surface) Copyright WW Technology AG

3D High Resolution Imaging of Bone Structures by FIB 24

Focused Ion Beam (FIB) tomography allows 3D analyses and visualization of bone structures with a spatial resolution down to 20 nanometers. Small features like bone cells and their connecting canaliculus system can be extracted from a stack of Scanning Electron Microscope (SEM) images using image processing techniques.

Deeper insight in the canaliculus (tubes of about 100 nm in diameter) intercellular network topology of osteocytes (bone cells) is crucial to study metabolism and growth of bone. FIB is a well suited instrument to perform high resolution data acquisition for such studies, but has the disadvantage of destroying the sample in the process. The ion source mills the bone slice by slice while a SEM is grabbing an image snapshot of the current view.

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Two cross-sectional images of a mouse bone; two slices at different depths showing a bone cell and a number of canaliculi

Figure 1 shows two example images at different depths captured during the milling process. X-ray Micro Computer Tomography (XMT) as an alternative, non-destructive 3D image acquisition method does not achieve the same resolution as FIB (≈ 500 nm instead of 20 nm or less with FIB). FIB and XMT techniques can, however, complement each other in analyzing the hierarchical structure of bone.

Dr Urs Sennhauser +41 44 823 41 73 [email protected] Jürgen Hofmann +41 44 823 45 73 [email protected]

25 Consecutive cross-sectional images can be aligned and stacked to yield a 3D tomogram. Specialized hybrid image preprocessing methods have to cope with typical FIB artefacts like waterfall or local electrostatic charging effects. Figure 2 shows a 3D segmentation of a bone cell with canaliculus network. We are focused on the development of advanced quantitative analysis methods,

which are applicable to gather the geometry and topology of bone structures and generate appropriate 3D (CAD) models. These models can then be used for further numerical evaluations and simulations.

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Section of bone cell and its associated canaliculus network

200 nm

X-Ray Tomography of Bones, Implants and Cellular Materials 26

3D imaging of cellular materials is a key issue in biomechanics. Multiscale X-ray Computed Tomography (CT) covering the macro-, meso- and microscale supports the development of advanced materials in biomedical sciences. The imaging process includes the beam hardening corrected tomography scan, surface rendering, segmentation and quantitative morphological analysis. 3D imaging with X-rays can also be performed under mechanical load. Empa has at its disposal systems for macroscale X-ray tomography (down to 3 µm) and experience in using synchrotronendstations for mesoscale tomography.

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In situ loading device at the SLS 2

Bone before (left) and after loading (right)

We have developed an in situ mechanical loading device for the non-destructive investigation of fatigue, elastic and plastic behavior, microcrack formation and fracture mechanisms of biological and technical microstructures with a resolution of 1 micrometer in all dimensions by using synchrotron radiation tomographic microscopy at PSI’s Swiss Light Source (SLS).

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Peter Wyss +41 44 823 43 19 [email protected]

27 3

3D X-ray imaging of dense foams at the border of macro- to mesoscale: This image shows an orthogonal reslicing of a high density cermet foam sample (1200 x 1200 x 600 µm), scanned with a microfocus system with a digital resolution of 2 µm. The resolution will soon be enhanced to 0.5 µm, yielding an effective resolution for medium contrast items in the range of 3 µm. This offers interesting possibilities for biomechanical research and morphological analysis. Synchrotron endstations with sufficient energy for such large samples are very rare

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Metal artifacts are a major problem in medical CT. They are due to strongly attenuating objects (e.g. implants, dental amalgam, medical equipments, etc.) in the scanning plane. The reduction of metal artifacts is also an important issue in modern forensic medicine where the quality of CT images can be lowered by fragments of bullets or other projectiles. We are currently evaluating the potential qualitative and quantitative improvement brought by a Metal Artifact Reduction (MAR) technique coupled with a dedicated reconstruction algorithm. First simulations of a 120 kiloelectron volt head scan

show that the streaks generated by metallic parts with high Z number (copper, lead) are strong and make any post-processing task such as tissue segmentation a real challenge. The involvement of a more elaborate clustering/segmentation algorithm using a priori anatomical information is envisaged.

Deformation Analysis of Implants and Bones with Interferometry 28

Prostheses pose a challenge in design and implantation since they have to transfer load and be biocompatible at the same time. Consequently, Finite Element (FE) models will have to include the mechanical design as well as parameters of biological and biocompatible materials. Results from FE simulations must often be validated by measurements during the optimization of the implant design. We characterize the mechanical and thermal parameters of materials as well as the deformation behavior of biomechanical devices, e.g. of a bone-endoprosthesiscompound, by 3D (Digital Speckle Pattern Interferometry, DSPI). DSPI is a non-contacting imaging laser tech-

1

Comparison of DSPI measurement (left) and FE simulation results (right) of a bone-endoprosthesis-compound. Colored and grey level fringes give lines of equal displacement orthogonal to the load

1

Dr Erwin Hack +41 44 823 42 73 [email protected]

nique to measure surface deformations with a resolution of a few tens of nanometer. By illuminating the object from several different directions, all components of the displacement vector can be calculated. Figure 1 shows the comparison of an FE simulation with the laser measurement of the lateral displacement (bending) of a hip prosthesis made of carbon-fiber reinforced polymer (CFRP) that is implanted into a model femur. A quantitative analysis shows a good agreement between simulation and measurement, thus validating the FE analysis. From comparative measurements on a common Ti implant and on a bone model the suitability of the CFRP implant to transfer load in a more natural way could be proven.

Confocal Laser Scanning Microscopy (CLSM) and Transmission Electron Microscopy (TEM) Imaging

Dr Jean-Pierre Kaiser +41 71 274 76 89 [email protected] Liliane Diener +41 71 274 76 81 [email protected]

29

1

1

Confocal Laser Scanning Microscopy

2

Probe under the microscope

CLSM and TEM are important tools in understanding biological processes at the cellular and subcellular scale. By using TEM, valuable information on the substrate surface and cell structure can be obtained. The CLSM, including time-lapse imaging, on the other hand enables monitoring processes occurring at both cellular (cell migration) and subcellular (spatial modification of the cytoarchitecture) scale.

2

Dr Roland Hauert +41 44 823 45 58 [email protected]

Surface Analysis in the Nanometer Range 30

The surface or, more precisely, the topmost atomic layer is decisive for the surface chemical behavior of a material, which controls effects like adhesion, wetting, bioreactions, heterogeneous catalysis, etc. The presence of residuals or contaminants at a surface can have a crucial influence on desired applications or the lifetime of a work piece.

1

1

AES: The light areas show the Niobium-oxide distribution on the surface of a TiAlNb implant

We offer surface-related problem solving solutions, from single measurements to complex research projects. Surface analysis will mainly be performed using X-ray Photoelectron Spectroscopy (XPS), Auger Electron Microscopy (AES), and Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) or other adequate analytical techniques depending on the problem at hand. Typical problems related to surfaces are: • Adhesion problems • Coating delamination • Inadequate wetting • Surface contaminations • Surface activation of polymers • Contaminations and quality control of surfaces

2

XPS: Si2p photoelectron signal from different silicon oxide layers on Si(111). The attenuation of the Si substrate signal by the increasing oxide thickness can clearly be seen

2

3 16

ToF-SIMS: Positive ion distribution shows the almost complete removal of an nm-thick organic film from a Ti/Si patterned substrate after applying an electric potential. The high surface sensitivity of ToF-SIMS reveals the presence of thin overlayers. Bright areas indicate higher concentrations of the species

14 Intensity [1000 counts/ sec.]

3

+

(c) Ti m/z 48

(a)

SiO2

Si

Si

10 10 µm µm

Ti

Si

Ti

12 10 7 nm Si-ox. / Si +

8

+

(b) Si m/z 28

(d) C2H50 m/z 45

Si

Si

6 nm Si-ox. / Si 6 4

4 nm Si-ox. / Si

Ti

2 2 nm Si-ox. / Si 10 µm

0 116 114 112 110 108 106 104 102 100 98 Binding Energy [eV]

96

94

10 µm

Ti

Empa – Bridge between Science and Business Whether you seek support for developing new products and processes, optimizing an existing technology, clarifying open questions and solving problems in the field of sustainable material science, or raising the level of professional know-how, Empa scientists stand ready to help meet the challenges you may face, offering their knowledge, ideas, experience and all the necessary technical equipment in-house.

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Bärbel Selm +41 44 823 44 44 [email protected]

31

Research and Development Cooperation In cooperation with Empa – as a strong partner or through the use of one of its networks – you can make your R&D ideas become reality. Research agreements clearly define the tasks allotted to each individual partner and regulate the ownership, exploitation and publication rights to the research results (inventions, know-how etc.). Frequently such projects are long term cooperations for specific developments, and are supported by national or international funding (SNSF, CTI, EU etc.). Technology Transfer Empa ensures that its innovative developments and ideas quickly reach Swiss industrial firms for practical implementation through an efficient science and technology transfer process. Technology transfer represents an important contribution to the business development of small and medium sized enterprises (SMEs). Our aim is to help turn innovative ideas into marketable products. In doing so, we place emphasis on maintaining our researchers’ rights to publish results by registering the intellectual property rights to their work as soon as possible. At the same time we ensure that our partners’ needs for industrial confidentiality are not unnecessarily compromised.

Benefit from our expertise and experience in numerous ways. The choice is yours: • Cooperative research projects • Technical and expert professional services • Technology transfer • Support for start-ups and spin-offs • Continuous education

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The Empa portal – your point of entry to access Empa’s know-how

Empa

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www.empa.ch

Empa is an interdisciplinary research and service institution within the ETH Domain covering selected fields of materials science and technology development including important environmental issues. Empa’s R&D activities focus on the requirements of industry and the needs of society, thus linking research to engineering, and science to industry and society. As a result, Empa is capable of providing its partners with customized services and solutions that not only enhance their innovative edge, but also help to improve the quality of life for the public at large. Safety, reliability and sustainability of materials and systems are cross-sectional topics and a hallmark of all Empa activities. As such, Empa plays a key role in Switzerland’s research and innovation landscape. Empa brings its competencies to bear in the areas of knowledge dissemination, technology transfer, different levels of teaching and continuous formation, thus transforming knowledge and inventions into marketable innovations. Empa’s PORTAL is the «one-stop shopping» access point for interested customers and partners looking for innovative solutions and collaborative research efforts in materials science and technology.

Contact [email protected] Phone +41 44 823 44 44 www.empa.ch/ portal

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