Citation: Lupu, A.; Rosca, I.; Gradinaru, V.R.; Bercea, M. Temperature Induced Gelation and Antimicrobial Properties of Pluronic F127 Based Systems. Polymers 2023, 15, 355. https://doi.org/10.3390/ polym15020355 Academic Editor: Sandra Pinto Received: 8 December 2022 Revised: 5 January 2023 Accepted: 7 January 2023 Published: 10 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Temperature Induced Gelation and Antimicrobial Properties of Pluronic F127 Based Systems Alexandra Lupu 1 , Irina Rosca 1 , Vasile Robert Gradinaru 2 and Maria Bercea 1, * 1 “Petru Poni” Institute of Macromolecular Chemistry, 41-A Grigore Ghica Voda Alley, 700487 Iasi, Romania 2 Faculty of Chemistry, Alexandru Ioan Cuza University of Iasi, 11 Carol I Bd., 700506 Iasi, Romania * Correspondence: bercea@icmpp.ro Abstract: Different formulations containing Pluronic F127 and polysaccharides (chitosan, sodium alginate, gellan gum, and κ-carrageenan) were investigated as potential injectable gels that behave as free-flowing liquid with reduced viscosity at low temperatures and displayed solid-like properties at 37 ◦ C. In addition, ZnO nanoparticles, lysozyme, or curcumin were added for testing the antimicrobial properties of the thermal-sensitive gels. Rheological investigations evidenced small changes in transition temperature and kinetics of gelation at 37 ◦ C in presence of polysaccharides. However, the gel formation is very delayed in the presence of curcumin. The antimicrobial properties of Pluronic F127 gels are very modest even by adding chitosan, lysozyme, or ZnO nanoparticles. A remarkable enhancement of antimicrobial activity was observed in the presence of curcumin. Chitosan addition to Pluronic/curcumin systems improves their viscoelasticity, antimicrobial activity, and stability in time. The balance between viscoelastic and antimicrobial characteristics needs to be considered in the formulation of Pluronic F127 gels suitable for biomedical and pharmaceutical applications. Keywords: thermosensitive gels; Pluronic F127; polysaccharide; curcumin; viscoelastic properties; antimicrobial activity 1. Introduction Last decades, stimuli-responsive polymers were extensively investigated due to their high potential for many applications. Among them, the self-assembling of amphiphilic block copolymers into micelles and the temperature-induced gelation present a high interest in biomedical and pharmaceutical applications, as carriers for drug delivery [1–3], in regen- erative medicine or dentistry [4–6], for preparing injectable hydrogels [7], in bioprinting [8], as sacrificial molding agents [9] etc. On the other hand, the proteins and renewable polysac- charides are non-toxic and endow some biological performances to biomaterials, such as biodegradability, biocompatibility, and mucoadhesive behavior. Thus, various polymers and biologically active compounds were used to develop suitable platforms for tissue engi- neering and regenerative medicine. Antimicrobial activity always represents a challenge for the design of new biomaterials because in some cases the enhancement of physicochem- ical performances implies a worsening of the biological properties or a weakening of the network structure. For example, the incorporation of different antimicrobial agents, such as curcumin and zinc oxide nanoparticles into the electrospun chitosan/polycaprolactone inhibited bacterial growth in the case of Escherichia coli and Staphylococcus aureus. How- ever, as a decrease in cell viability was observed, curcumin inhibited the proliferation and survival of L929 cells in a dose-dependent manner [10]. Pluronic ® F127 (here abbreviated as PL) is a triblock copolymer approved by the US Food and Drug Administration for pharmaceutical and biomedical use. In its structure presents a central hydrophobic poly(propylene oxide) (PPO) block and two hydrophilic poly(ethylene oxide) (PEO) blocks, i.e., (PEO) x -b-(PPO) y -b-(PEO) x , with x = 100, y = 65. Due to the gel formation ability, PL is a versatile synthetic macromolecule used to prepare Polymers 2023, 15, 355. https://doi.org/10.3390/polym15020355 https://www.mdpi.com/journal/polymers