Gelatin microspheres (GMSs) are widely used as drug carriers owing to their excellent biocompatibilities
and toxicologically safe degradation products. The drug release profile is easily tailored by controlling the
cross-linking density and surface-to-volume ratio, i.e. size, of the GMS. In this study, we employed GMSs
which are 25 lm in diameter and cross-linked with 0.03125% glutaraldehyde, to enable rapid initial and a
subsequent sustained release. Therapeutic potency of human recombinant osteopontin (rhOPN) with or
without encapsulation into GMSs was investigated after administrating them to rat stroke model
(Sprague–Dawley; middle cerebral artery occlusion, MCAO). The administration of rhOPN/GMS
(100 ng/100 lg) at 1 h post-MCAO reduced the mean infarct volume by 81.8% of that of the untreated
MCAO control and extended the therapeutic window at least to 12 h post-MCAO, demonstrating a markedly
enhanced therapeutic potency for the use of OPN in the post-ischemic brain. Scanning electron
microscopy micrographs revealed that GMSs maintained the three-dimensional shape for more than
5 days in normal brain but were degraded rapidly in the post-ischemic brain, presumably due to high levels
of gelatinase induction. After encapsulation with GMS, the duration of OPN release was markedly
extended; from the period of 2 days to 5 days in normal brain, and from 2 days to 4 days in the postischemic
brain; these encompass the critical period for recovery processes, such as vascularization,
and controlling inflammation. Together, these results indicate that GMS-mediated drug delivery has huge
potential when it was used in the hyperacute period in the post-ischemic brain.