To verify the practical efficacy of our prodrug-loaded fibers for
inhibition of inflammation, we then performed in vivo experiments.
Subcutaneous implantation of different PLA fibers (i.e.,
unloaded PLA, small molecular drug-loaded PLA-IBU and prodrugloaded
PLA-PIBU60) in SpragueeDawley rats was used to investigate
their abilities to inhibit biodegradation-induced inflammatory
response in vivo. We first examined the degradation
characteristics of PLA fibers in vivo. All the subcutaneous PLA fi-
bers in rats were totally absorbed in 14 weeks (almost the same as
the above mentioned in vitro biodegradation), indicating that the
in vivo biodegradation was similar to the enzymatic process
in vitro. Previous studies revealed that in vivo inflammatory
response during biodegradation could lead to the proliferation of
leukocytes, neovascularization and the formation of fibrous capsules
in the surrounding tissue [42e44]. Therefore, we then
checked the inflammation by means of immunohistological
staining of the leukocytes and neovascularization at different
time-intervals after implantation (Fig. 8a and b). Due to the nearly
identical biodegradation period between in vivo and in vitro in this
system, the time points were chosen as 4, 8 and 12 weeks, which
corresponded to the early-, middle- and later-stage of the
biodegradation. CD45 antibody (anti-CD45) and smooth muscle
actin antibody (anti-a-SMA) were used for staining leukocytes
and vessels [42,43], respectively (histologic sections showed in
Fig. 8d and e). Statistical results in Fig. 8a and b showed that,
besides significant inhibitory effect in the early stage, the CD45
positive leukocytes and the a-SMA positive vessels around PLAPIBU60
fibers were obviously less than that of PLA-IBU fibers in the
middle and later stage (weeks 8 and 12). More importantly, the
PLA-PIBU60 fibers did not appear an increased amount of leukocytes
and neovascularization in the later stage, while such increase
is remarkable in the PLA-IBU fibers. This result clearly
demonstrated that sustained release of IBU from the prodrugloaded
fiber scaffold could efficiently inhibit the later-stage
inflammation which was caused by the accelerated biodegradation
of implanted fibers. Histologic sections stained with hematoxylin
and eosin (H&E) were further used to measure the
thickness of fibrous capsules in the surrounding tissue of
implanted fibers (Fig. 8c and f). As expected, the formation of
fibrous capsules on PLA-PIBU60 was steadily inhibited during the
biodegradation, and still there is not a later-stage increase of the
capsules which was obvious in the PLA-IBU fibers. This result
further demonstrated a full-course inhibition of biodegradationinduced
inflammation in the prodrug-loaded system