Material model measurements and predictions for a random pore poly(epsilon-caprolactone) scaffold.
We investigated material models for a polymeric scaffold used for bone. The material was made by co-extruding poly(epsilon-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 will be useful for designers for quasi-static analysis as it provides a simple form that can easily be used in finite element models. The ASTM D-1621 standard recommends using a secant modulus based on 10% strain. The resulting modulus has a smaller scatter in its value compared with the coefficients of the hyperbolic model, and it is therefore easier to compare differences in material processing and ensure quality of the scaffold. A prediction of the small-strain elastic modulus was constructed from images of the microstructure. Each pixel of the micrographs was represented with a brick finite element and assigned the Young's modulus of bulk PCL or a value of 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 with Hooke's law for a linear-elastic isotropic material. The model was able to predict the small-strain elastic 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.
Quinn
T P
TP
National Institute of Standards and Technology, Boulder, Colorado 80305, USA. quinn@boulder.nist.gov
Oreskovic
T L
TL
Landis
F A
FA
Washburn
N R
NR
D018786:Bone Substitutes / Q000737:chemistry*; D008954:Models, Biological; D011091:Polyesters / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D016062:Porosity; D012995:Solubility; D013314:Stress, Mechanical; D014867:Water / Q000737:chemistry
D018786:Bone Substitutes; D011091:Polyesters; D014867:Water; C016240:polycaprolactone; D011092:Polyethylene Glycols