David Gamm, MD, PhD – Slide of the Week

David Gamm, MD, PhD - Slide of the Week

Title: Biodegradable 3D scaffolds for high-density photoreceptor layer reconstruction

Legend: A) Human pluripotent stem cell-derived photoreceptors (cell bodies labeled in red [CRX-TdTomato], nuclei in blue [DAPI], and synaptic vesicles labeled in green [VGLUT1]) grown on a novel biodegradable micropatterned ice cube tray (ICT) scaffold. B) Scaffolds were designed to deliver a dense layer of photoreceptors to the human macula, a region responsible for high-acuity vision. The two main layers—a top “reservoir” layer for capturing cells and a “through-hole” layer to facilitate nutrient exchange—total just 30 microns in thickness (less than half the thickness of a sheet of office paper). C) Scaffolds were constructed from polyglycerol sebacate (PGS), a biodegradable and highly elastic polymer. PGS ICT scaffolds were highly stable in vitro; scaffold thickness remained at 100±5.4% of baseline by 6 weeks in culture, providing a wide time window to seed and maintain scaffolds while patients are prepared for surgery . Relatively rapid degradation was observed in vivo; 12.6±3.5% of starting scaffold thickness remained by 2 months post-implantation in the subretinal space of nude rats. D) Immunohistochemistry and 3D confocal reconstructions of seeded scaffolds revealed robust, organized expression of PR-specific protein, including synaptic protein vesicular glutamate transporter-1 (VGLUT1), which localized to the top half of the scaffold (cell bodies labeled in red [CRX-TdTomato], nuclei in blue [DAPI]).

Citation: Lee I# Ludwig AL#, Phillips MJ#, Lee J#, Xie R, Sajdak BS, Jager LD, Gong S†, Gamm DM†, Ma Z†. Ultrathin Micromolded 3D Scaffolds for High-Density Photoreceptor Layer Reconstruction. Science Advances 2021 (in press). [#co-first authors; †co-corresponding authors].

Abstract: Polymeric scaffolds are revolutionizing therapeutics for blinding disorders affecting the outer retina, a region anatomically and functionally defined by light-sensitive photoreceptors. Recent engineering advances have produced planar scaffolds optimized for retinal pigment epithelium monolayer delivery, which are being tested in early stage clinical trials. We previously described a 3D scaffold supporting a polarized photoreceptor monolayer, but photoreceptor somata typically occupy multiple densely packed strata to maximize light detection. Thus, patients with severe photoreceptor degeneration are expected to extract greater benefits from higher-density photoreceptor delivery. Herein we describe the microfabrication of a biodegradable scaffold patterned for high-density photoreceptor replacement. The “ice cube tray” structure optimizes mechanical properties and cell-to-biomaterial load, enabling production of a multi-cellular photoreceptor layer designed for outer retinal reconstruction. Our approach may also be useful in the production of a multitude of micro- and nanoscale structures for multi-layered cell delivery in other tissues.

About the Lab: David Gamm’s laboratory at the Waisman Center uses stem cell technology to investigate the cellular and molecular events that occur during human retinal differentiation and to generate cells for use in human retinal disease modeling and cell-based rescue or replacement strategies. To meet these goals, Gamm utilizes a variety of human cell types, including ES and iPS cells, which have the capacity to mimic retinal development and disease, as well as to delineate the genetic “checkpoints” necessary to produce particular retinal cell types. By understanding the behavior of these cell types in vitro and in vivo, Gamm hopes to optimize strategies to delay or reverse the effects of blinding disorders such as retinitis pigmentosa and age–related macular degeneration.

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