Regeneration of bicortical defects in the iliac crest of estrogen-deficient sheep, using new biodegradable polyurethane bone graft substitutes.

Abstract

Porous scaffolds for cancellous bone graft substitutes were prepared from new experimental biodegradable aliphatic polyurethane elastomers with varying hydrophilicity. The ratios of the hydrophilic-to-hydrophobic content in the polymers were 30-70, 50-50, and 70-30%, respectively. The hydrophilic component consisted of poly(ethylene oxide) diol and the hydrophobic component of poly(epsilon-caprolactone) diol. To promote the materials' biological performance, the calcium complexing moiety, the polysaccharide, and vitamin D(3) were incorporated into the polymer chain upon synthesis. The scaffolds had an interconnected porous structure with an average pore size in the range of 300-2,000 microm and pore-to-volume ratios of (85 +/- 5)%. The bone substitutes were implanted (press-fit) in biocortical 10 x 10 mm(2) defects created in the tuber coxae of 21 skeletally mature Warhill ewes, which were ovariectomized 12 months prior to implantation. At the time of euthanasia at 18 and 25 months, all the defects in the ilium implanted with polyurethane bone substitutes had healed with new bone. The extent of bone healing depended on the chemical composition of the polymer from which the implant was made, although for the same material there were animal-related differences in healing. The structure of the newly formed cancellous bone was radiographically and histologically similar to the native bone. The implants from polymers with the incorporated calcium-complexing additive were the most effective promoters of bone healing, followed by those with vitamin D(3) and polysaccharide-containing polymer. There was no bone healing in the control defects.