(181e) Surface Functionalization of Polymer Particles for Cell Targeting By Modifying Emulsifier Chemistry

Introduction: The oil in water (O/W) emulsion solvent extraction method stands out as the most commonly used fabrication method for FDA approved poly(lactide-co-glycolide) (PLG) controlled release formulations. However, these formulations do not currently benefit from cell targeting that can be afforded through tuning particle surface chemistry. Poly(vinyl alcohol) (PVA) is the emulsifier used in most of these FDA-approved formulations, and has been shown to coat the surface of particles. We hypothesized that the hydroxyl side groups in PVA could be substituted with other functional groups using isothiocyanate chemistry and these modifications would not impact emulsifier properties while endowing the particle surface with new functionality. We modified PVA with three molecules, fluorescein isothiocyanate (FITC), rhodamine isothiocyanate (RITC), and mannopyranosyl isothiocyanate (MITC). While FITC and RITC were selected to establish proof of concept, MITC was selected to enhance particle interactions with macrophages through the mannose receptor.

Methods and Results: We demonstrate that isothiocyanate containing molecules can be covalently attached to the OH groups on PVA by mixing the reagents together in an appropriate solvent and stirring in a one-step reaction. Addition of isothiocyanate containing molecules onto PVA was confirmed with FTIR and extent of OH group conversion was quantified using NMR. Mixing PVA with a mass of FITC that contained an equivalent number of molecules to 10% of the OH groups present in the PVA led to conversion of 8% of the OH groups (80% of FITC reacted). Additional evidence for a successful reaction was a color change of the polymer (Figure 1A). Similar results were found with RITC. The modification of PVA with MITC occurred less readily. When PVA was reacted with a mass of MITC equivalent to 20% of the OH groups, 8% conversion was achieved (40% of MITC reacted). Using the modified PVA polymers, PLG particles were fabricated using the O/W emulsion solvent extraction process as previously described¹. Particles with sizes between 2-5 microns could be fabricated with modified PVA and had similar mass yields and size distributions to particles made with unmodified PVA, indicating that emulsifier properties were not significantly impacted. PLG particles fabricated with the FITC-PVA exhibited fluorescent coronas when viewed using confocal microscopy (Figure 1B), indicating FITC was present on the surface of the particle. Similar results were demonstrated for RITC-PVA. Meanwhile, particles made with MITC-PVA were found to bind macrophages to a higher extent than particles made with unmodified PVA, suggesting mannose was bioactive on the particle surface.

Discussion and Conclusion: We present here a method for attaching ligands to PVA using isothiocyanate chemistry and show that extent of reaction depends on the molecule being added. Additionally, we demonstrate that the modified PVA can be used for surface functionalization of PLG microparticles, enabling the presentation of fluorophores or a glycan. Surface modification of the particles was functional, endowing fluorescence or enhanced macrophage binding (FITC versus MITC). This process is desirable because it can be easily implemented in microparticle fabrication systems that are already FDA approved. In addition, the results suggest many isothiocyanate containing molecules can be linked to polymer particles in this way. Thus, this process could have broad implications for polymer particle targeting strategies.

1. Isely, C., Stevens, A. C., Tate, G. L., Monnier, J. R. & Gower, R. M. Fabrication of biodegradable particles with tunable morphologies by the addition of resveratrol to oil in water emulsions. Int. J. Pharm. 590, 119917 (2020).