Hydrogels for diabetic eyes: Naltrexone loading, release profiles and cornea penetration

Naltrexone (NTX) is a potent opioid growth factor receptor (OGFR) antagonist proved to be useful for treatment of ocular surface complications. The aim of this work was to explore the feasibility of designing NTX-imprinted 2-hydroxyethyl methacrylate-based hydrogels for sustained drug release on the ocular surface. Acrylic acid (AAc) and benzyl methacrylate (BzMA) were chosen as functional monomers able to form binding cavities mimicking OGFR binding sites for NTX. Imprinted hydrogels containing functional monomers loaded higher amounts of NTX compared to non-imprinted ones by simple soaking in drug aqueous solution. In addition, possibility of carrying out the loading and sterilization processes in one step was investigated. NTX release was evaluated both under agitated sink conditions and in a microfluidic flow chamber mimicking the hydrodynamic conditions of the eye, namely the small volume of lachrymal fluid and its renovation rate. Sustained release profiles together with adequate swelling degree (46 to 57% w/w), light transparency (over 85%) and oxygen permeability may make these hydrogels suitable candidates to NTX-eluting contact lenses. NTX-loaded and non-loaded discs successfully passed the chorioallantoic membrane test for potential ocular irritation and were cytocompatible with human mesenchymal stem cells. Finally, NTX-imprinted hydrogels tested in the bovine corneal permeability assay provided therapeutically relevant amounts of NTX inside the cornea, reaching drug levels similar to those attained with a concentrated aqueous solution in spite the discs showed sustained release.