Stem Cell and Encapsulated Drug Delivery to the Inner Retina using a Fibrin Polymer Spray System

Abstract

Purpose: A significant obstacle to the development of stem cell based therapies for the inner retina is the achievement of an adequate distribution of cells across the neural retina. Fibrin scaffolds have been shown to provide a permissive environment for the proliferation and differentiation of embryonic stem cells in culture and commercially available fibrin polymer spray systems have also been used to deliver mesenchymal stem cells to human subjects in wound healing studies. This study aimed to investigate the feasibility of adapting a fibrin polymer spray to distribute retinal stem cells and enzymes encapsulated in microcarriers to the inner retina of the larger mammalian eye through a conventional vitreoretinal approach.

Methods: Human Müller glia with stem cell characteristics (hMSCs) were initially cultured in fibrin scaffolds. The fibrinogen:thrombin ratio was optimised in order to maximise the viability and survival of hMSCs in culture (as determined by Ki67/Apoptosis staining), to minimise scaffold density and to promote scaffold degradation in culture. PLGA microcarriers containing Chondroitinase ABC (ChABC) were then prepared by thermally induced phase separation (TIPS) prior to surgery. Pars plana vitreolensectomy was performed on cadaveric pig eyes stabilised with a vacuum fixated pad. Following fluid/air exchange, GFP labelled hMSCs and ChABC TIPS microcarriers were delivered with a fibrin polymer spray system into the posterior segment via an enlarged vitrectomy port. Cell distribution was assessed by fluorescence and confocal microscopy after a brief period in culture.

Results: The survival and viability of hMSCs was not adversely affected by culture within fibrin scaffolds. 1mg/ml fibrinogen resulted in a thin scaffold with almost complete degradation after one week in culture. Study of the ex-vivo surgical model showed that aerosol delivery of cells through a conventional vitrectomy port offered coverage of a large surface area as shown by the distribution of labelled cells.

Conclusions: The fibrin polymer spray system shows potential as a delivery tool for cell-based therapies both to the inner retina and other body cavities, due to its ability to provide coverage of a large surface area and ability to incorporate synchronous drug delivery. The availability of fibrin products licensed for human application may help streamline the translation of this model towards clinical use.

Keywords: 721 stem cells • 607 nanotechnology • 762 vitreoretinal surgery