Evaluation of biomedical materials and implants

Hip joint prostheses, bone cements or dental implants must withstand several million load cycles in the patient without failing due to material fatigue. Bone cements should not exhibit critical creep deformation under load. The mechanical properties of resorbable osteosynthesis plates should change in a defined manner during the degradation process. A micro bone screw should "grip" quickly and in a defined manner when screwed into the bone.

We characterize biomedical materials and implants and identify and evaluate critical factors for their reliability.

R&D services for the evaluation of biomedical materials and implants

Statistical testing of the strength of materials, interfaces, implants, screws and ostheosynthesis components

• Design of auxiliary bodies and joints for defined force or instant loading
  • Static and dynamic loads
  • Viscoelasticity or creep
  • Determination of the bulk strength of composites and interfaces, compressive strength, diametral tensile strength, flexural strength, biaxial strength (ball-on-3-balls), double torsion
• Determination of adhesive and interfacial strength by pull-off tests, compressive shear strength and others
• Simulation of the load distribution
• Storage and testing in a physiological environment and temperature
• Analysis of the damage, e.g. fracture patterns
• Description of failure scenarios and comparison with load assumptions

Fatigue testing and degradation progress of materials and components: small implants, dental implants

• Determination of fatigue strength by creating Wöhler curves or using the staircase method
• Displacement or load-guided tests
• Design of auxiliary bodies and joints for defined force or instantaneous loading
• Oscillating loads and simulation of the load function
• Storage and testing in a physiological environment and temperature
• Analysis and documentation of fracture patterns

Characterization of the creep behavior and physical aging of materials

• Test in 3-point bending arrangement based on standard ASTM D2990-17
• Consideration of the phenomenon of "physical aging"
• Hydrothermal pre-deposits
• Testing at different load levels
• Testing in physiological media and temperature
• Evaluation of various creep laws (for physical aging according to Struik)

Measurement of fracture toughness

• Linear-elastic fracture toughness according to ASTM E399-20.
• Single Edge V-Notched Beam (SEVNB)" - Determination of the initial KIc
• EXAKT 6000EA Testing machine in air at room temperature designed for R-curve
• Other K methods: chevron notch beam, crack lengths in hardness indentations

Characterization of dimensional behavior, shrinkage and swelling

• Measurement of the continuous volume change using the buoyancy method
• Swelling tendency, water absorption by sequential weighing after aging at selected temperature
• Model adaptation of kinetics: autocatalytic, Arrhenius, light and dark polymerization and as required

Failure analysis of materials and components: small implants, dental implants

• Damage description, inventory, damage hypothesis, instrumental analyses, evaluation of investigation results and analyses, determination of the cause of damage
• Fracture pattern analysis both microscopically and with SEM
• Model simulation for hypothesis testing of the critical load
• Recommendations for remedial measures

Simulation of component loads and design support

• Illustration of creep and viscoelasticity
• Mapping the multiaxial bulk strength of homogeneous materials and composites
• Illustration of adhesive and interface strength
• Application of the kinetic and mechanical models in finite element or continuum mechanical simulation to calculate the load during the change as well as for stable states
• Mesh and simulation of 3D structures to determine the local and homogenized mechanical behavior.
• Design of friction-locked joints
• Design adjustments using visual methods such as tension triangles, push squares, force cones for rapid design improvement

Statistical calculation of the probability of failure

• Statistical strength models for analytical or finite element calculation of volume-based or surface-based failure probabilities
• Local evaluation of component reliability (probability of failure) and service life based on FE load analyses and experimentally determined statistical strength and crack growth models

Development of digital test databases for the customer

• Use of OPENBIS for process and data acquisition
• Application of script-based data analysis in R or Python
• Continuous data storage and data retrieval in databases

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Selected research projects 

Biomechanical simulation of finger joint implants and reliability assessment

In the FingerKIt project, five Fraunhofer institutes have developed a concept with which individualized finger joint implants made of metallic or ceramic materials can be manufactured quickly, safely and certified in an automated process chain.

The focus of the work at Fraunhofer IWM was on evaluation. For this purpose, central criteria of load, continuous load and stiffness had to be defined, on the basis of which biomechanical simulations could be carried out. The results of this simulation are mechanical stresses on the implant in its immediate vicinity.

Further information:

Publication:

Koplin, C.; Schwarzer-Fischer, E.; Zschippang, E.; Löw, Y. M.; Czekalla, M.; Seibel, A.; Rörich, A.; Georgii, J.; Güttler, F.; Yarar-Schlickewei, S.; Kailer, A., Design of reliable remobilisation finger implants with geometry elements of a triple periodic minimal surface structure via additive manufacturing of silicon nitride, J — Multidisciplinary Scientific Journal,  6/1 (2023) 180-197; 42/2023 Link

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C. Koplin, R. Jaeger, and P. Hahn, “Kinetic model for the coupled volumetric and thermal behavior of dental composites.,” Dent. Mater., vol. 24, no. 8, pp. 1017–24, Aug. 2008

C. Koplin, R. Jaeger, and P. Hahn, “A material model for internal stress of dental composites caused by the curing process.,” Dent. Mater., vol. 25, no. 3, pp. 331–8, Mar. 2009.

R. R. Braga, C. Koplin, T. Yamamoto, K. Tyler, J. L. Ferracane, and M. V. Swain, “Composite polymerization stress as a function of specimen configuration assessed by crack analysis and finite element analysis,” Dent. Mater., vol. 29, no. 10, pp. 1026–1033, 2013

C. Koplin, G.VdS Rodriguez and R.d Jaeger (2014), "Multiaxial Strength and Stress Forming Behavior of Four Light-Curable Dental Composites," Journal of Research and Practice in Dentistry, Vol. 2014 (2014), Article ID 396766, DOI: 10.5171/2014.396766

V. F. Steier, C. Koplin, A. Kailer, and V. Franco Steier, “Influence of pressure-assisted polymerization on the microstructure and strength of polymer-infiltrated ceramics,” J. Mater. Sci., vol. 48, no. 8, pp. 3239–3247, Jan. 2013.

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