Gentisic acid (2,5-dihydroxybenzoic acid) is primarily found naturally in plants and has demonstrated a significant range of biological activities; however, its efficacy and safety as a topical application ingredient are not yet well established. Thus, the compound’s potential antioxidant and antimicrobial properties were evaluated for efficacy, while the cytotoxicity was evaluated for safety. The antioxidant activity, measured by the DPPH kinetic method, showed an Efficiency Concentration (EC₅₀) of 0.09 with an antioxidant reducing power (ARP) of 11.1. The minimum inhibitory concentration (MIC) against Staphylococcus aureus was 4.15 mg/mL, Escherichia coli was 4.00 mg/mL, Candida albicans was 3.00 mg/mL, and Cutibacterium acnes was 3.60 mg/mL, and the MIC for C. acnes has remained unpublished until now. The substance showed low cytotoxicity by the neutral red uptake (NRU) methodology against HaCat, HDFa, and HepG2 cells at concentrations of up to 10.0, 7.3, and 4.0 mM, respectively, also representing unpublished data. This evidence demonstrates gentisic acid as a promising active substance for skin topical application in the cosmetic or pharmaceutical industry.

This study aimed to develop and characterize thermoresponsive bioinks based on Poloxamer 407 (P407) at different concentrations (20%, 25%, and 30%), modified with polyvinylpyrrolidone (PVP K30 and K90, 0.5 and 1%), alginate (3.85%), and gelatin (3.85%), and incorporated with zinc oxide nanoparticles (ZnO-NPs). The formulations were evaluated in terms of rheological properties, 3D printing performance, and post-printing drying behavior. Rheological analysis showed that P407 hydrogels at 25% and 30% exhibited pseudoplastic and thixotropic behavior, suitable for 3D printing, whereas formulations with ≤ 20% behaved as Newtonian fluids and were excluded. Drying tests revealed that the addition of PVP reduced the volume loss rate by up to 35% after 72 hours compared to pure P407, while alginate and gelatin improved the preservation of the printed cylindrical shape and reduced cracking. The incorporation of ZnO-NPs further enhanced water retention and structural stability. These findings highlight the potential of P407-based bioinks (25–30%) combined with functional additives and ZnO-NPs for biomedical applications requiring structural stability and precise printing behavior.