As an introduction to injection molding in Integrated Computer-Aided Design, a graduate level course, we did urethane casting over-molding. I decided to create "quills" by over-molding a feather onto a pen.
I surface modeled the feather in SolidWorks. I then 3D printed the model and used that to create a silicone mold. Using that mold I urethane casted the "quills". This was stepping stone to created an injection molded version. Click here to see this.