In an effort to understand the biological
capability of polyphosphazene-based
polymers, three-dimensional biomimetic bone scaffolds were fabricated
using the blends of poly[(glycine ethylglycinato)75(phenylphenoxy)25]phosphazene (PNGEGPhPh) and poly(lactic-co-glycolic acid) (PLGA), and an in vivo evaluation was performed in
a rabbit critical-sized bone defect model. The matrices constructed
from PNGEGPhPh–PLGA blends were surgically implanted into 15
mm critical-sized radial defects of the rabbits as structural templates
for bone tissue regeneration. PLGA, which is the most commonly used
synthetic bone graft substitute, was used as a control in this study.
Radiological and histological analyses demonstrated that PNGEGPhPh–PLGA
blends exhibited favorable in vivo biocompatibility and osteoconductivity,
as the newly designed matrices allowed new bone formation to occur
without adverse immunoreactions. The X-ray images of the blends showed
higher levels of radiodensity than that of the pristine PLGA, indicating
higher rates of new bone formation and regeneration. Micro-computed
tomography quantification revealed that new bone volume fractions
were significantly higher for the PNGEGPhPh–PLGA blends than
for the PLGA controls after 4 weeks. The new bone volume increased
linearly with increasing time points, with the new tissues observed
throughout the defect area for the blend and only at the implant site’s
extremes for the PLGA control. Histologically, the polyphosphazene
system appeared to show tissue responses and bone ingrowths superior
to PLGA. By the end of the study, the defects with PNGEGPhPh–PLGA
scaffolds exhibited evidence of effective bone tissue ingrowth and
minimal inflammatory responses. Thus, polyphosphazene-containing biomaterials
have excellent translational potential for use in bone regenerative
engineering applications.