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Synthetic Membranes Could Restore Impaired Vision
Researchers from the University of Sheffield have developed a method for the production of synthetic, biodegradable membranes that would made possible to incorporate stem cells into the eyes. This technique allows scientists, whose research is published in the journal Acta Biomaterialia to produce membranes that mimic the structure of the eye. They hope to be able to use this novelty in treating a great number of damaged corneal injuries which are responsible for a large number of cases of blindness in the world.

Synthetic Membranes

This project, funded by the Wellcome Trust and Engineering and Physical Sciences Research Council (EPSRC), is managed in cooperation with Dr. Virender Sangwan, assistant director and head of clinical research at the Institute for Ophtalmology LV Prasad in Hyderabad in India. The researchers are confident that their synthetic membranes significantly increase the availability of reparative operation using corneal stem cells.
Sheila MacNeil, professor in the Department of Tissue Engineering, Faculty of Engineering at the University of Sheffield, talked about the improvements that this method could allow. For starters it is a question of the production of these synthetic membranes.

Electrospin and Microstereolithography

"First, we use a technique called electrospin," she said. "It's kind of like making the spider web of thin fibers. These fibers are made from a material called PLGA, which is used for the production of degradable sutures. PLGA is placed in the syringe and the polymers which are gathered on the rotating drum are squeezed. At the end we get a soft fabric fiber thickness of approximately 100 microns. This fabric is not much structurally different from a paper tissue. Then we use a technique called microstereolithography by which we install protective pockets where stem cells can "hide". We actually imitate the natural environment of the limbal stem cells in the eye. This is a great, but very hard work. It takes a long time to produce adequate membranes using microstereolithography.

Fortunately, we were able to overcome this obstacle as we accidentally discovered how to achieve it more easily. We covered the drum by material that bakers use to prevent their cakes to stick to the casserole. In this material, there is a certain pattern of which in the beginning we did not even think. However, as we have put PLGA on drum covered by this method, we noticed that it shapes by that pattern. So we came up with the idea to use as a mold the membranes which are already processed by microstereolithography. On the surface of the drum we put the membrane as a template and inflicted on her soft fibers using the electrospin. That way, we achieved the shape of “micro pockets” the same as on the template. Now we work with a company that uses the electrospin method and with this method we are able to produce between 20 and 24 pieces every couple of hours. "

Approach to the use of membranes in stem cell therapy is not new. However, the production of large quantities of synthetic membranes could increase the availability of this type of therapy.

"Stem cells can be taken from the patient's healthy eye and, when they are grown enough, they can be incorporated into the damaged eye," explained Professor MacNeil. "However, the damaged area is so avascular that the cells would not survive without additional substrate. Scientists currently use small pieces of amniotic membrane – the tissue in which a child is wrapped in childbirth – on which they put the stem cells. This method is successful. Amniotic membrane is a good biological substrate, cells can easily connect to it, it breaks down relatively quickly and, once decomposed, corneal cells remain in the right position. Unfortunately, there is a shortage. "

The Disadvantages

"These membranes are part of human tissue. Material must therefore be taken by patients who have agreed to it - from women who have given birth and who willingly agree to have their amniotic membrane used for these purposes. Furthermore, since it is human tissue, results vary from case to case. However, the biggest problem is that the fabric must be kept under conditions approved by the tissue bank. This means that the tissue can be obtained in a safe way if you have access to an accredited tissue bank has the tissue in stock. In reality, most of the ophthalmic surgeons do not have such access. If we manage to produce an efficient synthetic material, it will be necessary to have access to bank tissue. Membranes will simply be stored under sterile conditions until they are needed. This method would be safer and more accessible. It is the goal of our research. "

This project is not yet at the stage of clinical testing, but the team has achieved very promising results in the laboratory. According to Professor MacNeil, an improvement in vision can come in less than a month after the surgery.

Preclinical Investigations

"To make sure that this method is effective, we are currently testing the eyes of rabbits," she said. "I stress that we use only the eyes of rabbits killed for commercial purposes and that we do not kill new rabbits. We make an incision on the cornea of the eye to create the injured area, remove part of the cornea using ethanol, grown the cells on our artificial membranes, and then using glue we paste fibers of the membrane on damaged cornea. Membrane begins to dissolve and the cells form a new corneal epithelium. In the laboratory, a new epithelium of several layers is produced in about three weeks. "

"We believe that the vision would improve in people in that short time if we used cells grown on human corneas," continues Professor MacNeil. "How much will the vision improve, varies depending on the patient. In some cases, patients are practically blind because of an injury, and others can see the movement and some basic shapes. In Hyderabad, our collaborators using amniotic membranes, have almost completely restored vision in some patients. Vision will not always be perfect, but it will be significantly improved. Dr. Sangwan performed approximately eight hundred these processes and the results were stunning. Within a year this method was successful in 80% of cases. "

At the end, we asked Professor MacNeil on the next steps in this exciting research project.

"We are currently in the process of negotiations with regulatory agencies in India," he answered. "We reported it to our colleagues from Hyderabad for a license for the first human trials. While much remains to be done before this, we would like to conduct a study with our synthetic membranes by the end of next year. "
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