title: Distribution of particles, small molecules and polymeric formulation excipients in the suprachoroidal space after microneedle injection.
abstract: The purpose of this work was to determine the effect of injection volume, formulation composition, and time on circumferential spread of particles, small molecules, and polymeric formulation excipients in the suprachoroidal space (SCS) after microneedle injection into New Zealand White rabbit eyes ex vivo and in vivo. Microneedle injections of 25-150 μL Hank's Balanced Salt Solution (HBSS) containing 0.2 μm red-fluorescent particles and a model small molecule (fluorescein) were performed in rabbit eyes ex vivo, and visualized via flat mount. Particles with diameters of 0.02-2 μm were co-injected into SCS in vivo with fluorescein or a polymeric formulation excipient: fluorescein isothiocyanate (FITC)-labeled Discovisc or FITC-labeled carboxymethyl cellulose (CMC). Fluorescent fundus images were acquired over time to determine area of particle, fluorescein, and polymeric formulation excipient spread, as well as their co-localization. We found that fluorescein covered a significantly larger area than co-injected particles when suspended in HBSS, and that this difference was present from 3 min post-injection onwards. We further showed that there was no difference in initial area covered by FITC-Discovisc and particles; the transport time (i.e., the time until the FITC-Discovisc and particle area began dissociating) was 2 d. There was also no difference in initial area covered by FITC-CMC and particles; the transport time in FITC-CMC was 4 d. We also found that particle size (20 nm-2 μm) had no effect on spreading area when delivered in HBSS or Discovisc. We conclude that (i) the area of particle spread in SCS during injection generally increased with increasing injection volume, was unaffected by particle size, and was significantly less than the area of fluorescein spread, (ii) particles suspended in low-viscosity HBSS formulation were entrapped in the SCS after injection, whereas fluorescein was not and (iii) particles co-injected with viscous polymeric formulation excipients co-localized near the site of injection in the SCS, continued to co-localize while spreading over larger areas for 2-4 days, and then no longer co-localized as the polymeric formulation excipients were cleared within 1-3 weeks and the particles remained largely in place. These data suggest that particles encounter greater barriers to flow in SCS compared to molecules and that co-localization of particles and polymeric formulation excipients allows spreading over larger areas of the SCS until the particles and excipients dissociate.
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States.
authors.forename: Bryce
authors.initials: B
authors.lastname: Chiang
authors.affiliation: H. Milton Stewart School of Industrial & Systems Engineering, Georgia Institute of Technology, Atlanta, GA, United States.
authors.forename: Nitin
authors.initials: N
authors.lastname: Venugopal
authors.affiliation: Emory Eye Center, Emory University, Atlanta, GA, United States.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Edelhauser
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States; School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, United States. Electronic address: prausnitz@gatech.edu.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Prausnitz
mesh_terms: D000818:Animals; D002829:Choroid / Q000378:metabolism; D016503:Drug Delivery Systems; D005079:Excipients / Q000008:administration & dosage* / Q000494:pharmacology; D019793:Fluorescein / Q000008:administration & dosage* / Q000493:pharmacokinetics; D005456:Fluorescent Dyes / Q000008:administration & dosage / Q000493:pharmacokinetics; D056965:Injections, Intraocular; D023421:Models, Animal; D009339:Needles; D010316:Particle Size; D011108:Polymers / Q000008:administration & dosage* / Q000493:pharmacokinetics; D057972:Posterior Eye Segment / Q000378:metabolism*; D011817:Rabbits; D012590:Sclera / Q000378:metabolism; D014018:Tissue Distribution / Q000187:drug effects
chemical_list: D005079:Excipients; D005456:Fluorescent Dyes; D011108:Polymers; D019793:Fluorescein
keywords: Microneedle injection; Suprachoroidal space; Targeted ocular drug delivery; Tissue distribution in eye