Abstract:
Chronic inflammation, infection, and fixation stability disrupts bone tissue regeneration by implants. The
elevated levels of inflammatory markers and reactive oxygen species (ROS) damage tissues, inhibit osteoblastic
differentiation, and promote bone resorption. Activation of local and chronic inflammatory responses due to the
implantable biomaterial poses a high risk of implant failure and compromised bone repair in several pathological
conditions. Not much progress has been made in the development of biomaterials that can counter inflammation
and ROS along with inducing osteogenic activities for managing bone defects/injuries. We have developed, for
the first time, injectable polymeric hydrogels by crosslinking oxidized pullulan (OP, 1% w/v) and 8-arm PEG
hydrazine (PEG-HY, 10% w/v) using pH-sensitive and dynamic hydrazone linkages at 37 ◦C in buffer. The
hydrogels were loaded with dexamethasone (Dex), an anti-inflammatory corticosteroid and osteogenic inducer,
by covalently linking it to PEG-HY by hydrazone linkages, and their morphological, injectability, viscoelastic,
self-healing, swelling, and drug-release properties were investigated. The hydrogels provided a pH-sensitive
sustained release of PEG-Dex conjugate (3.62 wt%, 9.22 × 10− 5 mol of Dex/gram) for 28 days, with 74.54
and 55.15% PEG-Dex conjugate being released at pH 6.5 and 7.4. ABTS assay showed that hydrogels inhibited
68% radicals within 1 h, and treatment with hydrogel releasates inhibited the pro-inflammatory markers, IL-6
and IL-1β, and elevated the anti-inflammatory marker, TGF-β, in murine osteoblast precursor cells (MC3T3-
E1). The hydrogels were found suitable for cell encapsulation and they exhibited 110% viability on treatment
with releasates. Finally, the osteogenic activities of hydrogels were ascertained by alkaline phosphatase (ALP)
activities, alizarin red S staining, and osteogenic gene expressions- RUNX2, Col-I, OPN, and IBSP. Overall, PEGDex conjugate released from hydrogels improved the cell viability and proliferation, and induced the osteoblastic
differentiation. The hydrogels with their promising antioxidant and anti-inflammatory properties along with the
osteogenic activities show a strong potential as an injectable, extracellular matrix (ECM)-mimicking implantable
drug-depot for bone repair applications in chronic inflammatory conditions.
