Biomechanics Laboratory

Mechanical testing of large (e.g., monkey, human) and small (mouse, rat) animal tissues is possible, and larger samples can be machined to smaller dimensions. Design and fabrication of loading fixtures are offered. Finite element validation and medical image analysis are also available. All methods of testing are customized to the user’s needs.

• 3- and 4-point bending: The bending tests measure the mechanical behavior of materials in simple beam loading. Specimens are supported as a simple beam, with the compressive load applied at the midpoint. Load-deflection curves are analyzed for stiffness (the slope of the initial portion of the curve), strength (maximum load), post-yield deflection, and work-to-failure. Modulus of elasticity and flexural stress can be calculated by accounting for specimen geometry. These tests primarily focus on the systematic evaluation of phenotypic changes in mouse bones, with a focus on long-bone diaphyses and cortical bone.
  
• Static compression, tension, or torsion: The structural components of the musculoskeletal system are loaded in tension, compression, bending, shear, torsion, or a combination of these modes. The failure mode and fracture mechanics of whole bones are determined by axial (both compression and tension) or torsion testing. By accounting for geometry (i.e., machining samples to consistent dimensions), we can determine tissue-specific properties.
  
• Dynamic loading (fatigue): In contrast to static loads, dynamic loads are repetitive or cyclic. Cyclic loads on a structure can lead to fatigue damage and ultimately failure or, in the case of bone, stress fracture. By applying cyclic loads, we can determine the fatigue behavior of bone, tendons, ligaments, and insertion sites.
  
• In vivo loading of musculoskeletal tissue in small animals: Small animal models that enable the application of specific loads to individual bones and tendons have been developed. These are useful in determining the biological response to changes in mechanical strains engendered by load-bearing.
  
• Mechanical testing of orthopaedic implants and devices: Many joint replacement products, most commonly for hip, spine, and knee, are marketed. As articulating joints represent the most complex mechanical systems in the body, implant designers have many challenges to overcome. The mechanical testing systems housed by the Core have the capacity for basic static testing of raw materials, impact loading of joint components, screw pull out tests, materials testing, and evaluation of fatigue and wear properties of numerous implants and devices.
  
• Finite Element Analysis via High-Performance Computing: The Yale Biomechanics Laboratory is home to a high-performance workstation that allows for the partnership of engineering and medical school faculty to create 3D models from high resolution imaging, and then create finite element models to test these constructs. The segmenting software Synopsis ScanIP is used to segment and generate 3D models, which can be utilized as 3D printed objects, or within virtual/augmented reality or mathematical model/computer simulations. Computer simulations are run using Abaqus FEA (Dassault Systemes). Finite Element (FE) models can be used to non-destructively evaluate stresses and strains generated within the bone or at interfaces between bone and orthopaedic components. The accuracy of an FE model will depend on how well the geometric shape of the model and the material properties represent the physical case. To assure the accuracy of the model, we validate it by performing a set of well-defined experiments, comparing the mechanical behavior of materials to the model.