IN-VITRO INFLUENCE OF APATITE-GRANULE-SPECIFIC AREA ON HUMAN GROWTH-HORMONE LOADING AND RELEASE

Although calcium phosphate biomaterials often are used as drug deliver y systems (DDS) at bone sites, the conditions affecting the loading of the therapeutic agent (TA) have not been well documented. A human gro wth hormone (hGH) adsorption method was used in this study to investig ate the influence of the formulated apatite (AP)-specific area on load ing and release. AP powders were formulated with a 200-500 mu m granul ometry and various specific areas. Two milligrams of hGH in solution w ere deposited for 24 h at 37 degrees C on 100 mg of AP with different specific areas. The amount of hGH loaded was determined by immunoradio metric assay (IRMA) and eluted stain bioassay (ESTA) using Nb2 lymphom a rat cells. Although loading was not greatly influenced by a specific area between 3 and 25 m(2)/g, dependency was noted for higher specifi c areas. Human GH release was measured by IRMA and ESTA over a 33-day period, with half-time release between 25 and 79 h. Comparison of IRMA and ESTA measurements for the hGH amounts loaded showed that hGH biol ogic activity was conserved. Results indicate that it is feasible to c ontrol the quantity of TA loading on AP by modifying specific areas fo r in vivo applications. (C) 1998 John Wiley & Sons, Inc.