Advancing In Vitro Microfluidic Models for Pressure-Induced Retinal Ganglion Cell Degeneration: Current Insights and Future Directions from a Biomechanical Perspective

Abstract

Glaucoma is the leading cause of irreversible blindness, primarily characterized by retinal ganglion cell (RGC) loss and optic nerve damage due to abnormal alterations in intraocular pressure (IOP). While in vivo models provide valuable insights into its pathophysiology, they face limitations in controlling biomechanical parameters and long-term IOP monitoring. In vitro models offer greater experimental control but often lack the complexity of the ocular microenvironment, limiting their physiological relevance. To better understand RGC degeneration from a biomechanical perspective, advancements are needed to improve these models, including precise pressure manipulation and more realistic cell culture conditions. This review summarizes current in vitro approaches for studying pressure-induced RGC degeneration and explores the potential of microfluidic technologies to enhance model fidelity. Incorporating microfluidic technologies holds promise for creating more physiologically relevant models, potentially advancing our understanding of IOP-related RGC degeneration from biomechanical perspectives.

Keywords: biomechanics; glaucoma; intraocular pressure; microfluidics; retinal ganglion cell degeneration.

Figure 4

Microelectrode platforms to be translated to study single RGC. (A) Positions of electrodes with overlaid recorded signals. Left: spontaneous extracellular action potentials (EAPs). Middle: EAPs after current stimulation. Right: EAPs after voltage stimulation [146]. (B) Signals from the readout electrodes in (A) that are indicated by the numbered box 1, 2, 3. Left: extracellular signals captured during spontaneous neuronal activity. Middle and Right: extracellular signals captured during current and voltage stimulation [146]. (C) Upper panel: cross-section and top view of one rGO microelectrode. Lower panel: array design of various electrode sizes and pitches [148]. Compared to traditional metal-based MEAs, rGO MEAs boast the advantages of low impedance and high charge injection limits, enhancing stimulation and recording efficiency [148,164]. (D) Gray shades: HD-MEA recording areas. Yellow squares: optical stimulation sites. Blue and red dots: directly and indirectly responding individual neurons. Directly responding neurons are those targeted by optical stimulation, which transmit electrical signals via synaptic connections and activate indirectly responding neurons [161]. (E) Signals recorded by two widely separated electrodes, 1 and 2. 1: direct responses. 2: indirect responses. The blue bars indicate stimulation period. Gray: signal at each stimulus. Blue: stimulus-time-triggered averaged signals [161]. (F) MEA on a substrate, (a) readout electrodes and (b) counter electrode. A glass ring for confining culture medium. (G) A PDMS layer attached onto the substrate to create microwell and microchannel geometries. Cells are seeded through the four circular openings. (H) A PDMS cap sealing the culture. (I,J) Cross-section and top view of internal architectures. Five electrodes monitor axons along each channel [163]. All the sub-figures in Figure 4 are under the terms of the Creative Commons CC-BY license http://creativecommons.org/licenses/by/4.0/ (accessed on 23 September 2025).

Figure 1

Schematics of current in vitro static pressure platforms. (A) Pressurized chamber model [27,28,30,31,32,33,34,39,40,42], (B) liquid-column pressure model [29,43,44], (C) centrifugal force loading model [37], and (D) pressurized flask model [38].

Figure 2

Representative images showing the varied spatial distributions and interconnections of neurons growing in microfluidic devices that separate soma and dendrites from axons of neural cells. Soma chambers are indicated by the red dotted rectangles. (A) Numerous cortical neurons from C57BL/6 mice are seeded in the soma chambers (left). Axons then grow along the microfluidic channels to the right [117]. (B) Cortical neurons from mice, with gene transfection, are cultured within the microfluidic device, allowing isolated neurites to elongate in microgrooves [118]. (C) Motor neurons differentiated from embryonic stem cell line (Hb9-GFP) are growing in the microfluidic chambers (right) and extending into the axonal compartment (left), with various immunostaining including GFP, Isl1/2, Map2, and Tau [116]. Scale bar: 500 μm. All the sub-figures in Figure 2 are under the terms of the Creative Commons CC-BY license.

Figure 3

Schematics showing the types of biomechanical stimuli acting on RGCs at different regions within the eye. (A) Schematic showing the RGCs at various regions within the eye under normal IOP. (B) Elevated IOP directly induces compression, tension and shear forces on RGCs at various regions within the eye, which can be modeled using in vitro flexible microfluidic platforms.