Analytical and biological characterization of Gellan Gum-Pomegranate Peel Extract hydrogel: combining mechanical, antibacterial, anti-inflammatory and pro-regenerative properties for cartilage healing

Cartilage has extremely limited regenerative potential, posing a major challenge for tissue repair. Current treatments are pharmacological, including non-steroidal anti-inflammatory drugs or intra-articular corticosteroid injections, which can cause significant side effects upon prolonged use. In this study, an in-situ cartilage substitute was developed using a combination of low- and high-acyl Gellan Gums, incorporating pomegranate peel extract (PPE) and crosslinked with magnesium ions. The extract, whose metabolomic profile was analysed, acted both as a cross-linker and as source of anti-inflammatory and antimicrobial compounds. FTIR, NMR, and TGA characterizations revealed that the carbohydrate–polyphenol interactions involved hydrogen bonds. The PPE led to a compact structure, as shown by SEM and water-uptake tests. The hydrogel showed excellent mechanical performances (compressive Young’s modulus up to ~145 kPa, strain at break up to ~54 %). PPE in the hydrogel supported a favourable environment for human mesenchymal stromal cells (hMSCs) by providing anchorage sites and sustaining SOX9, COL2, and ACAN expression under both physiological and inflamed conditions. It appeared to promote an anti-inflammatory environment by upregulating TSG6 and IL10, downregulating CXCL8 and IL6, and reducing Peripheral blood mononuclear cells (PBMCs) migration in vitro. Finally, the scaffold significantly reduced (>95 %) Gram+ and Gram- bacteria and biofilm formation.