Holding power and reinforcement of cancellous screws in human bone.

The authors report an in vitro biomechanical evaluation of a biodegradable material that might be used for the reinforcement of surgical screws in fractures involving severely osteoporotic bone. The material is a particulate composite with a matrix phase consisting of a hydrolyzable prepolymer, polypropylene fumarate (PPF), crosslinked with methacrylate monomer, and a particulate phase consisting of tricalcium phosphate and calcium carbonate. Pullout force and stripping load of cancellous screws were determined along with screw pullout force before and after reinforcement with either polymethylmethacrylate (PMMA) or PPF composite. Pullout force was moderately correlated (R2 = 0.59) with apparent density by a power law relationship of the form 0.065p1.37-1.77. Stripping load was strongly correlated (R2 = 0.91) with apparent density by a power law of the form 0.13p1.35-93.8. Mean pullout force before and after reinforcement with PMMA was 382 +/- 100 N (mean +/- standard deviation) and 879 +/- 315 N, respectively. Mean pullout force before and after reinforcement with PPF composite was 571 +/- 294 N and 829 +/- 354 N, respectively. Although the increase in pullout force with cement reinforcement was highly significant in both cases, the magnitude of the increase did not depend on the type of cement. Thus PPF seems to provide reinforcement that is equivalent to that provided by PMMA.

Phosphorylated variant of bovine prolactin.

Bovine pituitary explants and cell cultures were incubated with [32P]orthophosphate. Extracts were prepared from the explants and analyzed by sodium dodecyl sulfate-containing acrylamide gel electrophoresis and autoradiography revealing a phosphoprotein that co-migrated with authentic bovine prolactin. Clonal antibodies to bovine prolactin were produced, purified and used to prepare affinity columns. Extracts of [32P]orthophosphate-labeled explants and cells or media were applied to prolactin affinity columns and a radiolabeled protein was eluted with a pH 2.8 wash. The eluted protein was identified as prolactin by co-migration with standard on gel electrophoresis and by amino acid analysis. Treatment of immunoaffinity-purified pituitary prolactin with alkaline phosphatase reduced the phosphate associated with prolactin in a time-dependent manner, indicating a covalent phosphate linkage. Autoradiography of gels revealed prolactin from explants, cells and their associated media to be a phosphoprotein. A phosphorylated variant of bovine prolactin is synthesized and secreted in both explant and cell cultures.