Solid freeform fabrication of porous calcium polyphosphate structures for bone substitute applications: in vivo studies.

Porous calcium polyphosphate (CPP) structures with 30 volume percent porosity and made by solid freeform fabrication (SFF) were implanted in rabbit femoral condyle sites for 6-wk periods. Two forms of SFF implants with different stacked layer orientation were made in view of prior studies reporting on anisotropic/orthotropic mechanical properties of structures so formed. In addition, porous CPP implants of equal volume percent porosity made by conventional sintering and machining methods were prepared. Bone ingrowth and in vivo degradation of the three different implant types were compared using back-scattered scanning electron microscopy (BS-SEM) of implant samples and quantitative analysis of the images. The results indicated bone ingrowth with all samples resulting in 30-40% fill of available porosity by bone within the 6-wk period. In the 6-wk in vivo period, approximately 7-9% loss of CPP by degradation had occurred.