RESEARCH ARTICLE – Pharmaceutical Nanotechnology Poly(Acrylic Acid)–Poly(Ethylene Glycol) Nanoparticles Designed for Ophthalmic Drug Delivery ANA-MARIA VASI, 1 MARCEL IONEL POPA, 1 EDI CONSTANTIN TANASE, 2 MARIA BUTNARU, 2 LILIANA VERESTIUC 2 1 Faculty of Chemical Engineering and Environmental Protection, Gheorghe Asachi Technical University, Iasi 700050, Romania 2 Faculty of Medical Bioengineering, Grigore T. Popa University of Medicine and Pharmacy, Iasi 700454, Romania Received 30 April 2013; revised 27 October 2013; accepted 29 October 2013 Published online 19 December 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jps.23793 ABSTRACT: Poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG), four-arm, amine-terminated particles with nanometer size and spheri- cal shape were obtained by the polymers cross-linking, via activation with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride, in a w/o emulsion. The morphology and surface charge of the final particles are strongly dependent on the molar ratio of PAA–PEG and the PAA concentration. The physicochemical characteristics correlated with the drug-loading capacity, in vitro and ex vivo release kinetics of pilocarpine hydrochloride and biocompatibility results indicate that these nanoparticles exhibit the prerequisite behavior for use as carriers of ophthalmic drugs. C  2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:676–686, 2014 Keywords: nanoparticles; ophthalmic carriers; polymeric biomaterials; poly (acrylic acid); poly (ethylene glycol) four arms amine termi- nated; formulation; w/o emulsion; biocompatibility; controlled release/delivery. INTRODUCTION Ocular drug delivery is one of the most challenging fields faced by the pharmaceutical scientists. Critical and pharmacokinetic- specific environment of the eye makes it a unique structure that restricts the entry of drug molecules at a specific action site. 1 In this matter, a suitable ocular formulation should release the drug, by overcoming the protective barriers of the eye with- out causing permanent tissue damages. 2 Various formulations have been tested for ophthalmic drug delivery, such as inserts, thin films, ointments, microparticles, and nanoparticles (NPs). Compared with traditional formulations (solutions, ointments, and suspensions), 3 the particulate systems have several advan- tages: (a) an increased contact time 4 by improving the corneal uptake, the retention time and the intracellular penetration 5 ; (b) the ability to prolong drug release 6 because of the protection of the drug against chemical and enzymatic degradation 7 ; and (c) the capacity to reduce the systemic adverse effects and the risks of toxicity 8,9 with the purpose to minimize the number of administrations for a better patient compliance. 10 The progress in this field has made possible the formu- lation of NPs that are able to deliver the drugs to specific sites and to improve the pharmacokinetic profile of numer- ous bioactive compounds with biomedical applications. 11 Vari- ous biodegradable polymers including poly(acrylic acid) (PAA), poly(ethylene glycol) (PEG), poly(lactic acid), poly(lactic-co- glycolic acid), poly(alkyl cyanoacrylate), as well as natural poly- mers, such as chitosan, gelatine, alginates, and so on, were used for the preparation of ophthalmic nanocarriers because of their ability to modulate the physicochemical character- istics (hydrophilic–hydrophobic balance, zeta potential), the drug release profile (delayed, prolonged, and triggered release), and biological behavior (targeting, bioadhesion, an increased Correspondence to: Liliana Verestiuc (Telephone: +40-232-213573; Fax: +40- 232-213573; E-mail: liliana.verestiuc@bioinginerie.ro) Journal of Pharmaceutical Sciences, Vol. 103, 676–686 (2014) C  2013 Wiley Periodicals, Inc. and the American Pharmacists Association cellular uptake) of the drug delivery system. 12 However, the NPs development has not reached a satisfactory level because of the precorneal clearance mechanism; therefore, a great num- ber of studies are still needed to improve the physicochemical properties of the formulations. To achieve an enhanced ocular bioavailability, mucoadhesive polymers, which are able to prolong the precorneal residence time by interacting with ocular mucin layer, were exploited for NPs formulations. Mucoadhesive polymers were successfully utilized for their ability to interact with the drug; this approach depends on the capacity of the formulation to retain the drugs inside the carriers. 13 Acrylic-based polymers, 14 such as PAA, have been extensively used for mucoadhesive applications (eye drop formulations 15 ), as they exhibit very high adhesive bond strength in contact with tissues, enhancing the mucosal pene- tration of drugs. 16 Also, they allow the localization of the drug at the absorption site, increasing residence time, and the bioavail- ability at the required tissue. PEG is a hydrophilic, nonionic, and biocompatible polymer for pharmaceutical and biomedi- cal applications because of: (a) its excellent solubility in both aqueous and organic media; (b) nonimmunogenicity effect, anti- genicity, or toxicity; and (c) the high flexibility and hydration of the main chain. 17 Furthermore, PEG has been reported to act as an adhesion promoter between PAA and mucin by linear diffusion of the PEG chains into the acrylic networks and the mucin layer. Also, the grafted PEG chains could enhance the mucoadhesive properties of the polymers. 18 This study presents the preparation and characterization of PAA and PEG, four-arm, amine-terminated-based NPs, and evaluates the potential of this formulation to be used as an ophthalmic drug carrier. MATERIALS AND METHODS Materials Poly(acrylic acid), Mw = 300 kDa, PEG, four arms, amine termi- nated, Mw = 10 kDa, PEG–sorbitan monooleate (Tween TM 80), 676 Vasi et al., JOURNAL OF PHARMACEUTICAL SCIENCES 103:676–686, 2014