The effect of an admixture of sodium hydrogen phosphate or heparin-coating to poly(D,L)lactide--results of an animal study.

The study was aimed at investigating the effect of an admixture of sodium hydrogen phosphate (NaP) on the pH value around degrading poly(D,L)lactide (PDLLA) and the possible improvement of PDLLA biocompatibility by coating its surface with heparin. PDLLA +/- NaP was injection-molded to form rods (20 x 3 x 2 (mm)) and cubes (3 x 2 x 2 (mm)). Half of the pure PDLLA samples were surface-coated using heparin. One rod and cube each of PDLLA, PDLLA + NaP and PDLLA/Hep were implanted into the dorsal muscles of 42 rats. From the 2nd to 52nd week after operation, pH measurements were performed in the environment around the implants. The samples were then harvested for histological and mechanical analyses. No significant decrease in pH-values was observed in the tissue around the implants. Pure PDLLA and PDLLA/Hep samples were macroscopically resorbed after 52 weeks, while the degradation of PDLLA + NaP was still in progress. Approximately 80% of the initial bending strength of PDLLA or PDLLA/Hep rods was present after six weeks, while the bending strength of PDLLA + Nap was reduced to 50% after 4 weeks. Heparin-coating of PDLLA did not improve its biocompatibility but did increase its resorption. While no significant effect of NaP on pH value was found, its admixture did reduce the mechanical characteristics of the implants.