Smart Adhesive Hydrogel Delivery of Apigenin Attenuates Inflammation and Oxidative Stress in Chronic Wounds

Abstract

Healing failure in chronic wounds reflects a self-reinforcing pathology of unresolved inflammation, oxidative damage, poor angiogenesis, and disordered matrix turnover, compounded by a wound bed that turns abnormally alkaline. Apigenin, a plant-derived flavonoid, counters several of these processes through antioxidant and anti-inflammatory activity, but its low aqueous solubility and weak bioavailability make topical use inefficient without a suitable carrier. To address this limitation, apigenin was incorporated into a pH-responsive poly(acrylic acid) hydrogel, in which pH-dependent swelling modulates drug release such that release increases under alkaline conditions. The principal contribution of this study is a delivery strategy that couples pH-triggered release to the alkalinity of the chronic wound bed, so that apigenin is liberated preferentially under the conditions that mark impaired healing. The gels were profiled for viscoelasticity, surface tack, and release across a pH range, and the released drug was tested on human umbilical vein endothelial cells (HUVECs) and adult human dermal fibroblasts (HDFa) for cytocompatibility and for effects on oxidative stress (ROS), inflammatory signalling (IL-6), matrix degradation (MMP-9), and endothelial network formation. Blank and drug-loaded gels were both cohesive and uniform and showed equivalent adhesion; the apigenin-loaded gel behaved as an elastic, shear-thinning solid (G′ above G″ from 0.5 to 30 Hz). Release tracked pH as intended, climbing from 8.73 ± 1.41% at pH 5.5 to 12.37 ± 1.15% at 7.4 and 30.37 ± 3.05% at 8.5 over 24 h. Viability was retained at low micromolar doses but dropped significantly at 50 µM (to 50.59 ± 8.74% in HUVECs and 59.02 ± 15.40% in HDFa; p < 0.0001), so 5 µM was carried into functional assays. In TNF-α-challenged cells, apigenin curbed ROS in both HUVECs (36,666 ± 3,257 to 28,612 ± 1,867 AU; p < 0.01) and HDFa (36,093 ± 3,063 to 25,852 ± 2,269 AU; p < 0.01), lowered IL-6 in HUVECs (32.66 ± 4.43 to 24.56 ± 3.75 pg/mL) and HDFa (31.19 ± 5.26 to 15.74 ± 3.83 pg/mL), and roughly halved MMP-9 in HDFa (477.80 ± 17.97 to 201.80 ± 10.75 pg/mL). It also recovered much of the endothelial tube formation that TNF-α had suppressed (3,308 ± 815 to 5,428 ± 819 px). By acting on oxidative, inflammatory, and matrix-degrading pathways simultaneously while timing its release to the conditions that mark impaired healing, the apigenin-loaded pH-responsive hydrogel addresses several drivers of chronic wound persistence at once and warrants further evaluation in more physiologically complex wound models.

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