We investigate material models for a porous, polymeric scaffold used for bone. The material was made by co-extruding poly (e-caprolactone) (PCL), a biodegradable polyester, and poly(ethylene oxide)(PEO). The water soluble PEO was removed resulting in a porous scaffold. The stress-strain curve in compression was fit with a phenomenological model in hyperbolic form. This material model willbe useful for designesrs for quasi-static analysis as it provides a simple form that can easily be used in fifnite element models. The ASTM D-1621 standard recommends using a secant modulus based on 10 % strain. The resulting modulus had a smaller scatter in its value compared to the coefficients of the hyperbolic model, and it is therefore easier to compare material processing differences and ensure quality of the scaffold. A third maerial modelw was constructed from images of the mircrostructure. Each pixel of the micrographs was represented with a brick finite element and assigned the Young's modulus of bulk PCL or a value if 0 for a pore. A compressive strain was imposed on the model and the resulting stresses were calculated. The elastic constants of the scaffold were then computed using Hooke's law for a linear-elastic, isotropic material. The model was able to predict the small strain Young's modulus measured in the experiments to within one standard deviation. Thus, by knowing the microstructure of the scaffold, its bulk properties can be predicted from the material properties of the constituents.
Proceedings Title: Annual Rocky Mountain Bioengineering Symposium|41st|Biomedical Sciences Instrumentation|Instrument Society of America
Conference Dates: April 1, 2004
Conference Title: Proceedings of the Rocky Mountain Bioengineering Symposium
Pub Type: Conferences
finite element analysis, hyperbolic model, material model, PCL, poly (e-caprolactone), secant modulus, tissue engineering