A drug delivery system for biologically active agents targeted to spec
ific cells could be used to improve tissue repair in orthopaedics. The
system should be controllable and capable of drug release over an ext
ended period of time. Biodegradable, membrane-moderated, monolithic mi
crospheres for the controlled release of growth hormone (GH) were deve
loped and the release of GH was monitored in vitro. Cross-linked gelat
in microspheres were used as the vehicle, with the drug dispersed with
in the gelatin. The amount of GH released from the microspheres was in
creased following ultrasonication. The release of growth hormone was m
onitored in phosphate buffered saline and horse serum. Interestingly,
a higher level of GH was detected in the phosphate buffered saline tha
n in serum. In addition, both pH and enzyme-induced degradation had an
effect on the swelling kinetics of the gelatin microspheres. The rele
ase of GH from the microspheres was diffusion controlled, during the t
ime period studied.