Phytochemical Profiling, Biological Activities, and Development of Hydrogel Sheets Containing Phanera sirindhorniae Leaf Extract

Phanera sirindhorniae (formerly known as Bauhinia sirindhorniae) is a Thai medicinal plant with reported traditional use for the treatment of inflammation; however, its comprehensive phytochemical, biological, and formulation potential remains underexplored. This study aimed to evaluate the phytochemical composition, antioxidant, anti-inflammatory, and antimicrobial activities of extracts from the flower (BSFE), stem (BSSE), and leaf (BSLE), and to develop a BSLE-loaded hydrogel sheet for topical application. Among the extracts, BSSE exhibited the highest total phenolic content (503.71 ± 7.56 mg GAE/g) and total flavonoid content (4778.67 ± 255.47 mg EGCG/g), along with strong antioxidant activity, as demonstrated by DPPH (IC50 = 17.05 µg/mL) and FRAP assays. BSLE showed superior anti-inflammatory activity by significantly suppressing nitric oxide and pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) in LPS-stimulated RAW264.7 macrophages, whereas BSSE displayed moderate effects. In antimicrobial evaluation, BSSE exhibited the strongest activity among the extracts, particularly against Escherichia coli and Staphylococcus species, although its potency remained lower than that of standard antibiotics. HPLC analysis identified 3,4-dihydroxybenzoic acid and luteolin as characteristic anti-inflammatory markers in BSLE. Based on its promising anti-inflammatory activity, BSLE was incorporated into hydrogel sheets (BSLE-F1 and BSLE-F2) using HPMC/PVA matrices with varying PEG 600 content. Both formulations demonstrated suitable physicochemical properties and skin-compatible pH. BSLE-F2 showed improved water retention and dimensional stability, whereas BSLE-F1 exhibited superior peelability, swelling capacity, and tensile strength. In conclusion, BSLE-F1 demonstrated a more favorable balance of mechanical and functional properties, suggesting its suitability as a topical anti-inflammatory hydrogel sheet. This study highlights the potential of P. sirindhorniae extracts for developing multifunctional, natural-based topical delivery systems.