Electrospun Scaffolds for Corneal Tissue Engineering: A Review

Abstract

Corneal diseases constitute the second leading cause of vision loss and affect more than 10 million people globally. As there is a severe shortage of fresh donated corneas and an unknown risk of immune rejection with traditional heterografts, it is very important and urgent to construct a corneal equivalent to replace pathologic corneal tissue. Corneal tissue engineering has emerged as a practical strategy to develop corneal tissue substitutes, and the design of a scaffold with mechanical properties and transparency similar to that of natural cornea is paramount for the regeneration of corneal tissues. Nanofibrous scaffolds produced by electrospinning have high surface area-to-volume ratios and porosity that simulate the structure of protein fibers in native extra cellular matrix (ECM). The versatilities of electrospinning of polymer components, fiber structures, and functionalization have made the fabrication of nanofibrous scaffolds with suitable mechanical strength, transparency and biological properties for corneal tissue engineering feasible. In this paper, we review the recent developments of electrospun scaffolds for engineering corneal tissues, mainly including electrospun materials (single and blended polymers), fiber structures (isotropic or anisotropic), functionalization (improved mechanical properties and transparency), applications (corneal cell survival, maintenance of phenotype and formation of corneal tissue) and future development perspectives.

Keywords: corneal tissue; electrospinning; nanofibrous scaffold; polymer.

Figure 1

Scanning electron micrographs of the scaffolds. (A) Cross-section (foam layer on the left and fibers on the right). Reproduced from [48], with permission from © 2014 Tylor and Francis; (B) Oriented nanofibers of silk scaffold. Reproduced from [51], with permission from © 2015 Tylor and Francis; (C) Randomly oriented PCL scaffold. Reproduced from [44], with permission from © 2014 The Association for Research in Vision and Ophthalmology; (D) A section of the electrospun scaffold showing a horseshoe electrospun micro-pocket. Reproduced from [27], with permission from © 2012 Elsevier; (E) Electrospun nanofibrous membranes with binary COL-PEO (a and b) and ternary COL-HA-PEO compositions (c and d). Reproduced from [43], with permission from © 2014 The Royal Society of Chemistry.

Figure 2

The electrospinning collector for the aligned nanofibers. (A) A rotating copper wire drum. Reproduced from [55], with permission from © 2015 The Royal Society of Chemistry; (B) Auxiliary electrode/electrical field. Reproduced from [72], with permission from © 2007 American Chemical Society; (C) Two spinnerets with opposite voltages and directions. Reproduced from [73], with permission from © 2006 Elsevier; (D) Frame collector. Reproduced from [74], with permission from © 2003 Elsevier; (E) Parallel double-thin plates collector. Reproduced from [75], with permission from © 2015 Elsevier.

Figure 3

SEM images of randomly aligned PLGA scaffolds: (A) Cross-sectional view of cell-free scaffolds; (B) Cross-sectional view of scaffolds cultured with limbal epithelial cells for 14 days. Panels (A,B) Reproduced from [47], With permission from © 2010 Future Medicine; (C) SEM image of aligned fibrous PEUU scaffold. Reproduced from [8], with permission from © 2012 Elsevier; (D) Stained human corneal epithelial cells with DAPI (blue, nuclei) and phalloidin (yellow, F-actin) after three days of culturing on the aligned PGS/PCL nanofibrous scaffolds. Reproduced from [53], with permission from © 2014, The Royal Society of Chemistry.

Figure 4

Transmission of light in nanofibrous membranes. (A) General transmission of light with different blend ratios; (B) Accurate transmission percentage compared with the control group of A. Panels (A,B), Reproduced from [56], with permission from © 2015 Chen et al; (C) Restorative process of the corneal transparency of NZWRs during a 32-week post-operative slit-lamp examination. Reproduced from [55], with permission from © 2015 The Royal Society of Chemistry.

Figure 5

A comparison of stress-strain curves of (A) randomly oriented and (B) aligned electrospun gelatin mats under two different loading orientations. Reproduced from [52], with permission from © 2013 Elsevier.

Figure 6

(A) Biocompatibility assessment of electrospun PCL nanofibers. (a) Phase contrast picture shows migration of human corneal epithelial cells over nanofibers (black stars line); (b) Epithelial cell sheet demonstrates high viability ratio of human corneal epithelial cells on nanofibers by their positive green staining. Cells were observed at 200× magnification. Reproduced from [14], with permission from © 2011 Molecular Vision; (B) Changes in gene expression of hCSSCs seeded on aligned fibrous substrates (black), random fibrous substrates (red) and cast films (green). mRNA abundance was compared with hCSSCs cultured in SCGM. Ratios of abundance of each transcript between hCSSCs seeded on different substrates cultured in keratocyte differentiation medium and in SCGM are expressed on a linear scale. Since KERA has no expression in hCSSCs cultured in SCGM, it is expressed in an absolute manner. Error bars show the SD of three independent samples. For each gene, expression levels were significantly different between the studied substrates (p < 0.05), except for CHST6 and PTGDS on aligned fibrous substrate and cast film. Reproduced from [8], with permission from © 2012 Elsevier.

Figure 7

(A) Average aspect ratio for human-derived corneal stromal cells seeded in the hydrogel constructs with and without the inclusion of nanofibrous meshes cultured under F, K and K * media for seven and 14 days. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001. (B–G) are representative actin-stained cells of collagen hydrogel constructs with (E–G) and without (B–D) the incorporation of nanofibrous meshes following 14 days in culture in F, K and K * media, respectively. When cultured in fiber-free constructs, cells grown in serum-containing F media had a shorter, fusiform morphology (B) compared to the more elongated morphology of cells cultured in serum-free K and K * media (C,D). The addition of nanofibers increased organization within the constructs and encouraged all cells to align and adopt a more elongated morphology (E–G). Yellow arrows indicate the direction of fibers, scale bar = 50 μm. Reproduced from [1], with permission from © 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Figure 8

(A) Two-photon images of hCSSCs-secreted ECM varying with: (a) aligned fibrous, (b) random fibrous PEUU mat and (B) SEMs of hCSSCs and the elaborated ECM on the (a,b) aligned fibrous. Reproduced from [8], with permission from © 2012 Elsevier.