Introduction
Tissue engineering in the field of ophthalmology has been present over the last decade and is quite promising. This tool has opened new pathways for treating various eye disorders, from corneal damage to retinal deterioration. However, more important ocular tissue substitutes are required for further studies.
What Is Tissue Engineering?
Tissue engineering is an essential tool for understanding certain conditions' progress and treatment. It came to light in the early 1990s. It is a part of bioengineering - a wide field combining biology and engineering. Tissue engineering tries to determine treatment strategies for badly injured tissues or organs. The damaged tissues are restored and replaced with a version that would help the individuals overcome graft rejections, donor shortages, and inflammatory responses post-transplantation. Tissue engineering harbors two strategies:
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Cell-Based Strategy - The cells are manipulated in such a way as to create their habitat before they are transplanted to the host.
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Scaffold-Based Strategy - In this strategy, an extra-cellular matrix is developed to resemble the structures in the body.
What Are Scaffolds?
Scaffolds are important in tissue engineering, regenerative medicine, and drug release. Most of them are made artificially. Composite scaffolds contain both natural and synthetic compounds. In tunable scaffolds, the mechanics, three-dimensional architecture, and degradation rate can be controlled during the formation of the scaffold. Any alteration to these factors can change the body's response toward them. A type of scaffold that ophthalmologists can research is recombinant human elastin polypeptides. These polymers can assemble on their own, leading to the formation of structures resembling the trabecular meshwork. The three-dimensional architecture can be altered, allowing for the generation of a bioengineered trabecular meshwork.
What Is the Role of Tissue Engineering in Various Ocular Tissues?
Corneal Tissue Engineering:
The cornea is the curved, transparent structure of the eyes that helps to focus the light into the eyes. The role of tissue engineering in corneal damage is important in maintaining the barrier between the eyes and the environment. The most difficult corneal layer to replace is the stroma. The stroma is the cornea's transparent middle layer, made up of collagen fibers and keratocytes. Around 200 collagen fibril layers constitute around 90 percent of the total thickness of the cornea. The replacement of damaged corneas is primarily done by corneal transplantation. In corneal transplantation, the damaged corneal tissue is substituted by donated cornea either entirely (penetrating keratoplasty) or some part of it (lamellar keratoplasty). There are a few problems involving the surgical procedure, such as a shortage of donor corneas, infection risks, and rejection of the graft tissues. As an alternative, successful corneal stroma cultivation and corneal endothelium and endothelium have been carried out, but data on their successful long-term usage still needs to be provided. Much tissue-engineered corneal epithelium has been developed with the help of both cell and scaffold-based approaches. Amniotic membranes have also been used as tissue grafts. Mucosal epithelial cells and limbal stem cells have also been successfully used for transplantation. However, long-term evaluation is still required to evaluate their benefit, though they are quite promising in dealing with corneal blindness and decreasing the reliability of the donors.
Lens Tissue Engineering:
The lens is a curved structure of the eyes that helps focus the light on the retina, thus allowing one to see clearly. The number of studies concerning tissue engineering for the treatment of damaged lenses is very few. At present, cataracts are surgically treated by removing the lens and substituting it with artificial lenses. Most individuals undergo a second surgery because of posterior capsule opacification (PCO). Therefore, alternatives should be a priority. Whether tissue engineering for lens-related problems is applicable remains a question.
Retinal Tissue Engineering:
Tissue engineering in the retinal cells has mostly been carried out in animal models. Homologous retinal pigment epithelium has been used as a transplant but in vain. However, autologous retinal pigment epithelium transplantation led to improved vision. The use of polymers for retinal tissue engineering has existed only for the last decade.
The required polymer for retinal transplantation should be thin, porous, and biodegradable. The polymers used are poly lactic-co-glycolic acid, poly lactic acid, poly glycerol-sebacate, and polycaprolactone. The combination of the poly lactic acid-poly lactic-co-glycolic acid polymer has been found to show good adhesion and proliferation. Embryonic stem cells and induced pluripotent stem cells closely resemble the retinal pigment epithelium, thus, they are a better choice.
Optic Nerve Tissue Engineering:
The optic nerve is the nerve that transmits the signal from the retina to the brain. Optic nerve injuries can lead to permanent visual loss. Optic nerve tissue engineering helps regenerate damaged nerve fibers. More research is being carried out in this field on using biomaterials, stem cells, and growth factors to help optic nerve regeneration. However, there are challenges to restoring vision through optic nerve tissue engineering, and it requires further research.
Tissue Engineering of the Other Ocular Surfaces:
Infections or trauma can injure the ocular surfaces like the conjunctiva and cornea. Tissue engineering can help construct damaged ocular surfaces. Biocompatible scaffolds are being developed to support the growth of epithelial cells and promote the healing of damaged tissues of the eyes. The transplantation of the amniotic membrane, a type of tissue engineering, has been found to reduce inflammation and promote the epithelialization of the cornea.
What Is the Future of Tissue Engineering in Ophthalmology?
There are several challenges in the field of tissue engineering in ophthalmology. The cost-effectiveness of tissue-engineered products should be improved to promote their acceptance. For a smooth translation of these tools from the laboratory to clinical practice, long-term safety and efficacy assessments and standardization of regulatory considerations are needed. Collaborating between ophthalmologists, researchers, and regulatory authorities is critical to overcoming such challenges.
Conclusion:
The role of tissue engineering in the field of ophthalmology is quite promising. The conventional treatments for eye diseases affecting the cornea include the placement of grafts. But these procedures have certain limitations, like graft rejection and donor problems. Thus, a growing interest has been shown in developing tissue-engineered products to treat several eye conditions. The only challenge is the collaboration of the researchers, ophthalmologists, and scientists to work as a team to curb the challenges and provide the best possible treatment to needy individuals.
