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Wang, et al.
with corneal characteristics using biomaterials, thereby printed IOLs with PMMA-like materials had a good level
successfully printing a layered corneal tissue that mimics of transparency and showed the properties of biconvex
the natural cornea . In addition, the mesenchymal stem lens, but were still limited by the surface roughness and
[28]
cells derived from the turbinate can also use to produce optical performance (e.g., wavefront aberrations) in
cells of keratocyte lineage that can be used for corneal comparison to the qualified implants . Similar results
[59]
regeneration . were also observed in the study by John et al., which
[31]
demonstrated higher levels of surface roughness, figure
3. Function and applications errors, and wavefront deformations than the control
[60]
In a general sense, bioprinting refers to 3D printing product . A better performance on the curvature radii
for medical applications, which can be divided into was obtained on smaller lenses when printed. Although
four stages of development . Stage I is to print non- printing technology has great advantage over the
[55]
biocompatible structures that can be used as the models manufacture of irregular and asymmetric products, it
for surgery planning. Stage II is to print biocompatible but still has room for improvement in the future replication
non-biodegradable products, such as implanted prothesis. of IOLs. Further improvement on the surface figure is
Stage III is to print biocompatible and biodegradable needed to make the printed lens fulfill the requirements
products, which can be used as scaffolds to improve of clinical implant.
tissue damage repair or regeneration. Stage IV is to print (3) Choroidal models
biomimic 3D structures with cells. In the narrow sense,
bioprinting can also be defined as cellular printing . The choroid is a soft membrane layer formed mainly by
[27]
In the present review, our definition of bioprinting blood vessels between retina and sclera. It is the main
encompasses all four stages of development. blood supply for the retina and the surrounding ocular
tissues. The reduction of choroidal vessels due to tumor
3.1. Treatment device and prosthesis or other ocular diseases will result in the loss or death
of tissues in the supply areas. To evaluate the structural
(1) Contact lens and scleral cover shell prothesis
changes of choroidal vessels, Maloca et al. printed
Contact lens are used for vision correction or other 3D models of choroidal vessels based on the optical
therapeutic or cosmetic purposes. In addition, they can coherence tomography images from normal eyes and
be incorporated with sensors for disease diagnosis and pigmented choroidal tumors . The group segmented the
[6]
management (e.g., measure glucose composite in tears or choroidal vessels in the interested areas by a threshold
monitor intraocular pressure for glaucoma) . Through filter, and printed the 3D models with transparent resin
[56]
3D printing technology, different sensor components by SLA printing or gypsum power by additive fused
have been designed and printed to make cost-efficient deposition modeling. The resolution of the models was
and smart contact lens [7,8,57] . The nanostructures patterned limited to 1 mm in wall thickness, which was able to
by direct laser writing help to detect the disease at early characterize the choroidal vessels in details. This helps
stages, while techniques still need to be further developed to better understand the architecture of choroidal vessels
for commercial utilization. and their interactions with the adjacent tissues and
The scleral cover shell prosthesis is used to tumors.
correct the eye diagram in pathological conditions. It
covers the corneal and adjacent scleral areas during the (4) Artificial eyes
treatment. In the pilot study, Sanchez-Tena et al. printed In the study by Xie et al., an eye model with different
a prosthesis with polylactic acid (PLA) using fused ametropia state was produced using 3D printing
filament fabrication printing . Further attempts using technology for the fundus viewing system . The optical
[58]
[10]
biocompatible materials to simulate the corneoscleral parameters of printed models are adjustable and the
profile fitting are necessary. models can simulate the optical performance of human
eye. The technique developed by Xie et al. could be a
(2) Intraocular lenses (IOLs)
useful tool for fundus range viewing research and training
IOLs are common personalized devices to treat cataract in for fundus examination in future. Besides, conformer
clinic. The products mimic the shape and dimensions of shells are clear plastic lens fitted to support the shape
crystalline lens and provide the substitute optical functions. of the eye socket and maintain the natural appearance
Studies have been performed to reproduce the IOLs with without glasses after an enucleation/eye removal surgery.
a patented 3D printing technology called Print Optical. 3D printing of conformer shells makes the production of
In the method, the photopolymer material (e.g., Luxexcel individualized shells possible.
polymer) was deposited onto a poly(methylmethacrylate) A lot of attempts have also been pursued to generate
(PMMA) substrate and cured with ultraviolet [59,60] . The “bionic eyes” using 3D printing technology. By printing

International Journal of Bioprinting (2022)–Volume 8, Issue 2 151