Validation of a method for non-invasive in vivo measurement of growth factor release from a local delivery system in bone

The therapeutic benefit of local administration of growth factors using controlled release systems for bone regeneration is under study. In the present work, a PDGF release profile from chitosan granules administered into bone defect produced in the femur of Wistar rats was obtained using 125I-PDGF as tracer and a probe-type gamma counter with a suitable collimator for detection. The measurement method was validated by the radioactivity values obtained from the isolated bones using a well-type gamma counter. Both the invasive and the non-invasive measurement methods were linear in the analyzed range, with coefficients of variation around 3% and 15%, respectively. A good correlation between the two methods was found for the 125I-PDGF release profile from the chitosan granules. These results confirm that a reliable release profile can be obtained for a drug incorporated into delivery systems for local bone therapy using this non-invasive measurement method.