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Computational Material Model of Polyurethane Bone Foam

Catalog of Regulatory Science Tools to Help Assess New Medical Devices 

This regulatory science tool (RST) is computational material model of polyurethane bone foam with a density of 20 pounds per cubic foot (PCF), which can be implemented in a finite element analysis application.

Technical Description

This material model contains specific data and formulations for simulating PCF 20 polyurethane bone foam in an explicit finite element analysis material model formulation. It provides material model parameters for transversely isotropic elasticity, crushable foam plasticity, and ductile damage initiation and evolution allowing for simulation of bone foam elastic loading, plastic deformation, and material damage followed by element deletion. 

Intended Purpose 

A calibrated material model of polyurethane bone foam has been developed for use in computational simulations. This RST can help medical device manufacturers to accelerate development of new medical devices by conducting computational finite element simulations of orthopaedic device test methods that involve polyurethane bone foam. Device types may include bone screws, intervertebral body fusion devices, or bone anchors. Examples of test methods that employ polyurethane bone foam include ASTM F543 [2], F2267 [3], and F3574 [4].

Testing

This RST was first calibrated to bench testing data of polyurethane bone foam under unconfined compression [5], laterally confined compression, tension [6], and shear [7] as described in ASTM F1839 [8] to inform the material model parameters for transversely isotropic elasticity, crushable foam plasticity, and ductile damage initiation and evolution in finite element simulations. The material model was tested in simulations of shear, compression, bone screw pullout (ASTM F543), and intervertebral body fusion device subsidence tests (ASTM F2267). This RST is qualified with demonstrating agreement with experimental data.  

Limitations

This material model was developed specifically for PCF 20 bone foam obtained from one manufacturer and may not be applicable to material obtained from other manufacturers. This material model was tested on simulations of the bone screw pullout test described in F543 and the intervertebral body fusion device subsidence test described in F2267 only and, thus, may not yield accurate results for applications that fall outside this context of use. This model was not evaluated for use in implicit finite element code and cannot be considered valid for that context of use. 

Supporting Documentation

[1] Sadeqi S & Shetye S “A Polyurethane Foam Bone Analogue Material Model for Computational Simulations: Calibration, Validation, and the Impact of Crushable Foam Yield Stress Ratio” - submitted to the Journal of Biomechanical Engineering. 

[2] ASTM F543-23, Standard Specification and Test Methods for Metallic Medical Bone Screws, ASTM International, West Conshohocken, PA, 2023.

[3] ASTM F2267-22, Standard Test Method for Measuring Load-Induced Subsidence of Intervertebral Body Fusion Device Under Static Axial Compression, ASTM International, West Conshohocken, PA, 2022.

[4] ASTM F3574-22, Standard Test Methods for Sacroiliac Joint Fusion Devices, ASTM International, West Conshohocken, PA, 2022.

[5] ASTM D1622-20, Standard Test Method for Apparent Density of Rigid Cellular Plastics, ASTM International, West Conshohocken, PA, 2022.

[6] ASTM D1623-23, Standard Test Method for Tensile and Tensile Adhesion Properties of Rigid Cellular Plastics, ASTM International, West Conshohocken, PA, 2022.

[7] ASTM C273-20, Standard Test Method for Shear Properties of Sandwich Core Materials, ASTM International, West Conshohocken, PA, 2022.

[8] ASTM F1839-21, Standard Specification for Rigid Polyurethane Foam for Use as a Standard Material for Testing Orthopaedic Devices and Instruments, ASTM International, West Conshohocken, PA, 2022.

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