Hybrid Hydrogel Composed of Polymeric Nanocapsules Co-Loading Lidocaine and Prilocaine for Topical Intraoral Anesthesia

www.nature.com/scientificreports OPEN Received: 31 May 2018 Accepted: 15 November 2018 Published: xx xx xxxx Hybrid Hydrogel Composed of Polymeric Nanocapsules CoLoading Lidocaine and Prilocaine for Topical Intraoral Anesthesia Bruno Vilela Muniz1, Diego Baratelli2, Stephany Di Carla1, Luciano Serpe1, Camila Batista da Silva1, Viviane Aparecida Guilherme3, Lígia Nunes de Morais Ribeiro 3, Cintia Maria Saia Cereda3, Eneida de Paula3, Maria Cristina Volpato1, Francisco Carlos Groppo1, Leonardo Fernandes Fraceto2 & Michelle Franz-Montan 1 This study reports the development of nanostructured hydrogels for the sustained release of the eutectic mixture of lidocaine and prilocaine (both at 2.5%) for intraoral topical use. The local anesthetics, free or encapsulated in poly(ε-caprolactone) nanocapsules, were incorporated into CARBOPOL hydrogel. The nanoparticle suspensions were characterized in vitro in terms of particle size, polydispersity, and surface charge, using dynamic light scattering measurements. The nanoparticle concentrations were determined by nanoparticle tracking analysis. Evaluation was made of physicochemical stability, structural features, encapsulation efficiency, and in vitro release kinetics. The CARBOPOL hydrogels were submitted to rheological, accelerated stability, and in vitro release tests, as well as determination of mechanical and mucoadhesive properties, in vitro cytotoxicity towards FGH and HaCaT cells, and in vitro permeation across buccal and palatal mucosa. Anesthetic efficacy was evaluated using Wistar rats. Nanocapsules were successfully developed that presented desirable physicochemical properties and a sustained release profile. The hydrogel formulations were stable for up to 6 months under critical conditions and exhibited non-Newtonian pseudoplastic flows, satisfactory mucoadhesive strength, non-cytotoxicity, and slow permeation across oral mucosa. In vivo assays revealed higher anesthetic efficacy in tail-flick tests, compared to a commercially available product. In conclusion, the proposed hydrogel has potential for provision of effective and longer-lasting superficial anesthesia at oral mucosa during medical and dental procedures. These results open perspectives for future clinical trials. Topical anesthetics are applied superficially to reduce or control pain in medical and dental procedures such as local anesthetic injection, placement of orthodontic bands, simple extraction of primary teeth, rubber-dam clamp placement, biopsies, abscess incision, endotracheal intubation, and endoscopy1. Nevertheless, variables such as the class and concentration of the anesthetic agent, pH, additives, contact time at the mucosa, duration of action, and site of application influence the success of superficial anesthesia2. Lidocaine (LDC) and prilocaine (PLC) are amine-amide local anesthetics (LAs) widely used in biomedical procedures worldwide1. When these LAs are combined, they form an eutectic mixture that is commercially available as EMLA, a topical formulation originally designed for dermal use, with proven effectiveness inside the oral cavity3. However, the formulation also presents organoleptic characteristics such as a bitter taste (pH = 9.0) and a burning sensation during application, which can hinder its acceptance by patients2. The advantages and disadvantages of EMLA led to the development of new formulations containing the eutectic mixture of LDC and 1 Department of Physiological Sciences, Piracicaba Dental School, University of Campinas – UNICAMP, Piracicaba, São Paulo, Brazil. 2São Paulo State University – UNESP, Institute of Science and Technology of Sorocaba, Department of Environmental Engineering, Sorocaba, São Paulo, Brazil. 3Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas – UNICAMP, Campinas, São Paulo, Brazil. Correspondence and requests for materials should be addressed to M.F.-M. (email: ) SCIENTIFIC REPOrTS | (2018) 8:17972 | DOI:10.1038/s41598-018-36382-4 1 www.nature.com/scientificreports/ PLC in drug delivery systems such as mucoadhesive films and nanostructured lipid carriers, aiming at topical oral application4,5. Several approaches have been adopted for optimization of the effective loading of LAs into polymeric nanoparticles. The encapsulation of benzocaine, lidocaine, and articaine in polymeric nanoparticles composed of poly(lactide-co-glycolide), poly-L-lactide, and poly-ε-caprolactone resulted in long-term stability, sustained release, and increased anesthetic efficacy in vivo6–11. Polymeric nanocapsules consist of an oily core and an ultrathin polymeric wall, providing particles smaller than 1 μm12. Poly-ε-caprolactone (PCL) is among the biodegradable polymers most widely employed for the preparation of nanocapsules, due to its desirable properties for incorporation in semisolid drug delivery systems, such as hydrophobicity and biocompatibility13. Hydrogels are three-dimensional polymer networks cross-linked by physical or chemical agents, which can absorb large amounts of biological fluids. Their useful properties include biocompatibility, flexibility, and suitable rheological behavior, enabling their use in a wide range of applications including wound healing and topical delivery of active molecules at the skin and mucosa14,15. CARBOPOL is an acrylic acid copolymer employed as a matrix in several semisolid formulations, with interesting properties such as mucoadhesion, which promotes adherence to the mucus layer, leading to prolonged residence times of incorporated drugs15,16. CARBOPOL formulations containing benzocaine17, lidocaine18, or ropivacaine19–21 encapsulated in liposomes were shown to be effective in promoting topical anesthesia in the human oral mucosa. The objective of the present study was to determine whether a hybrid system based on poly(ε-caprolactone) nanocapsules in CARBOPOL hydrogel could increase the biocompatibility, permeation capacity, and anesthetic efficacy of 5% lidocaine-prilocaine, aiming at topical intraoral anesthesia. Results and Discussion Characterization of poly(ε-caprolactone) nanocapsules. The encapsulation of different LAs using other polymeric nanocapsules has been described previously7,22–24, with the aim of prolonging analgesia and minimizing side effects25. Particle size and polydispersity index (PDI) are critical parameters of nanostructured systems that influence drug encapsulation efficiency, formulation stability, and release behavior26. The surface charge of nanoparticles (zeta potential, ZP) can be used as a predictive index of particle stability, as well as to elucidate the location of the active molecules in the nanocapsule27. The nanoparticle concentration is another parameter that affects the stability and biological activity of drug delivery systems28. The results obtained for particle size, PDI, ZP, nanoparticle concentration, and pH, according to time, for nanocapsules with and without LAs, are provided (...truncated)