pH-responsive HA/PβAE hydrogels couple enzyme release kinetics to inflammatory acidity to modulate cytokines and promote healing

Abstract

pH-responsive hydrogels that synchronize drug delivery with the inflammatory microenvironment can accelerate wound repair. We report a UV-crosslinked poly(β-amino ester)/hyaluronic acid (PβAE/HA) hydrogel that loads the proteolytic enzyme bromelain (Br) and couples its release to acidic conditions typical of injured tissue. The bio-hybrid network showed tunable mechanics (Young's modulus reduced from ∼52 MPa in neat PβAE to ∼23–16 MPa after HA and Br incorporation), enhanced swelling at acidic pH (up to ∼222 at pH 5.6), and pH-dependent degradation (≈70–80 mass loss at pH 5.6 vs. ≈40–56 at pH 7.4 over the test period). Br release was faster and diffusion-controlled in acid (Higuchi; ≈70 by 48 h) but more regulated at neutral pH (zero-order-like; ≈50 by 48 h), indicating microenvironment-sensitive delivery. L929 fibroblasts cultured on PβAE/HA-Br exhibited high viability, improved adhesion, and elevated collagen-I expression, consistent with matrix remodeling support. In LPS-challenged RAW 264.7 macrophages, the hydrogels significantly reduced pro-inflammatory cytokines (TNF-α, IL-6) and enhanced reparative mediators (IL-10, TGF-β), while immunofluorescence imaging confirmed a phenotypic switch from M1 to M2 macrophages, collectively demonstrating robust immunomodulatory activity. Human umbilical vein endothelial cells formed substantially longer and more branched tubes on PβAE/HA-Br (≈140 of control), confirming pro-angiogenic activity. Together, these results demonstrate that PβAE/HA-Br hydrogels integrate environmental sensing with enzyme delivery to dampen inflammation, promote vascularization, and support matrix regeneration highlighting their promise as smart wound-healing dressings and adaptable platforms for regenerative medicine. © 2025 Elsevier B.V.