_applied sciences_  
_Article_  
**Influence of the Polymer and Solvent Variables on the Nanoencapsulation of the Flavonoid Quercetin: Preliminary Study Based on Eudragit\({}^{\text{(c)}}\) Polymers**  
**[PERSON] 1,2\({}^{\text{(c)}}\)**, [PERSON] 3, [PERSON] 1,2\({}^{\text{(c)}}\)**, [PERSON] 4,5, [PERSON] 3, [PERSON] 1,2,*\({}^{\text{(c)}}\) and [PERSON] 4,*  
future since this type of carrier improves stability, bioavailability, and drug targeting due to the significant characteristics of PNPs, including size (S), which varies from 100 to 500 nm. These characteristics facilitate the entry and improve the interaction with biological substrates, giving them several advantages, such as a large contact surface, a capacity of bio-direction to specific organs or tissues, absorption of the drug in the target tissue, reduced adverse effects, decreased dosage, and internalization by cells, bacteria, or parasites [1; 2]. These pharmaceutical carriers are generally made of natural or synthetic biodegradable polymers and form structures with diverse chemical natures where the drug can be encapsulated, adhered to, or absorbed [3]. To date, there are studies of NP-based formulations made from polymers derived from methacrylic acid, where different types of drugs are encapsulated; these formulations have been shown to incorporate a wide variety of active ingredients with an encapsulation efficiency between 60% and 90%, being efficient when applied via different routes (intravenous or respiratory), both in vitro and in vivo, showing low toxicity; hence, these types of drug carriers and nanoformulations represent an excellent option for the treatment of different diseases [4; 5]. Drug encapsulation into PNPs increases the stability of active substances and protects sensitive substances from chemical changes, pH, and ultraviolet light. Encapsulation improves the drug's specificity, efficacy, and tolerability [6]. Eudragit(r) is a polymer that has demonstrated its potential as a coating material and matrix former in various drug delivery systems to control drug release. By enabling site-specific drug delivery, it can enhance the bioavailability of drugs and reduce associated side-effects or toxicity, particularly for anticancer drugs [7]. Eudragit(r) is a versatile range of polymers composed of methacrylic acid and methyl methacrylate, representing anionic copolymers commonly used to stabilize and improve the bioavailability of various substances. These polymers can protect drugs that are susceptible to breakdown in an acidic environment, such as the stomach, enabling their release only at a pH level above 6.0 in the intestine [8]; these anionic copolymers are made of methacrylic acid and methyl methacrylate and are widely used for multiple PNP formulations, constituting tiny particles that vary from 1 to 300 nm. Eudragit(r) has been successfully used to enhance the therapeutic effects and bioavailability of various substances, including berberine, curcumin, quercetin, lacases, insulin, and pantoprazole [2; 6; 8; 9; 10]. These polymers effectively encapsulate hydrophobic molecules such as the flavonoid quercetin, which is insoluble in aqueous solutions and can hinder absorption [10]. Quercetin, a natural metabolite known for its strong antioxidant activity, is commonly used as a nutritional supplement and treatment for various conditions such as diabetes, obesity, circulatory dysfunction, inflammation, and mood disorders [11]; moreover, flavonoids are present in a variety of medicinal plants [12; 13; 14]. Additionally, flavonoids such as quercetin effectively inhibit bacterial growth and possess antiparasitic properties [11; 15; 16]. However, quercetin's efficacy is limited due to its high hydrophobicity, instability in physiological media, poor gastrointestinal absorption, and extensive xenobiotic metabolism in the liver and intestine [10].