DESIGN OF A NOVEL MICRO FEATURED POLY (GLYCEROL SEBACATE) METHACRYLATE (PGS-M) SCAFFOLD FOR CORNEAL REGENERATION

The cornea has limbal stem cells (LSC’s) located in limbal crypts (niches). LSC’s are responsible for corneal integrity, maintain a healthy equilibrium, and act as a proliferative barrier for the corneal epithelia, preventing invasion from the conjunctiva and its vascularization. Limbal stem cells deficiency (LSCD) causes this barrier to break down, leading to ingrowth from conjunctival cells and blood vessels. LSCD produce scar tissue, causing pain, blushing, and sometimes leading to blindness. Blindness is a worldwide problem which is caused by various conditions, such as blindness of the cornea. This is the 4th most common cause of loss of vision, with corneal defects impacting the lives of approximately 2 million people. Corneal transplants are the first proposed solution, though the risk of rejection and lack of donors make it an unsuitable option. Various strategies have been proposed to overcome the lack of donors and the rejection of allogeneic transplants.
Current treatments include the development cell carriers with biopolymers like collagen, fibrin, silk, fibronectin, and gelatin, among others. The cell carrier should be biocompatible and have the capacity to support both cell survival and proliferation to aid tissue regeneration. Despite the biocompatibility shown by biopolymers, some have presented acute inflammation and lacked the necessary mechanical properties for implantation and supporting tissue regeneration.
Recent research has been focused on the treatment of corneal defects with synthetic polymers, positioning them as an option for overcoming issues with biopolymers. Synthetic polymers have tuneable mechanical properties, but most are hydrophobic and lack of proper transparency.
Current reports of scaffolds have begun to include topography and microstructures that mimic the target tissue and influence cell behaviour. Numerous studies reported micro and nanostructures in the form of honeycombs, microposts, grids, and parallel lines with promising results enhancing cell proliferation, migration, differentiation, and cell alignment. The next challenge was the selection of a suitable synthetic polymer that met the necessary requirements for a corneal replacement, being able to achieve the characteristics found in the native cornea. Poly (glycerol sebacate) (PGS) was one of the polymers that stood out for its biocompatibility, transparency, elasticity, and biodegradability that resembled soft tissues, such as the cornea.
PGS has been used as scaffold and cell carrier due its characteristics as a conductive surface for cell adherence. In addition to being able to support cell growth, PGS is biocompatible, biodegradable, and has an elastomeric nature, making it highly suitable for soft tissue engineering. PGS has been used in biomedical applications as retinal graft, vascular tissue, cartilage, cardiac patch, nerve, and adhesive sutures.
However, PGS has rapid degradation rate in vivo and its crosslinking requires high temperatures and long processing times, which limit its application. Furthermore, PGS has some degree of cytotoxicity due to their non-reacted carboxylic acid groups from the sebacic acid.
To overcome these limitations methacrylate groups were added to the PGS molecule to give an additional level of control of strength, degradation, crosslinking density, and elongation. These groups allow curing under UV light, avoiding the degradation of the polymer during heat crosslinking. Additionally, the reaction is more stable and cleaner in comparison to PGS acrylation. The addition of methacrylate groups is a new promising research area in the generation of a compatible tuneable biomaterial for application in cornea regeneration.
The main challenge was the development of an efficient carrier that delivers cells to specific sites and ensures their survival, mimicking the limbal stem cell niche structure, allowing the cell survival, and offering physical protection to stem cells. The research aim of this work is to develop a cell carrier that can re-establish the healthy balance in a damaged cornea with an anatomical structure that mimics the limbus to provide physical protection to the cells ensuring their survival. This cell carrier would be biocompatible, biodegradable, and with mechanical properties that match the target tissue. Additionally, the scaffold fabrication methodology should allow for the creation of precise microfeatures and dome shape that mimic both the morphology and curvature of native cornea. This scaffold is expected to produce more optimal results in survival and delivery of the stem cells in comparison to previous work.
In the current work, poly (glycerol sebacate) methacrylate (PGS-M) was synthesized with controlled conditions to obtain samples with different degrees of methacrylation (DM). Through soft stereolithography, we achieved the development of a microfeatured dome shape scaffold that mimics the morphological characteristics of the cornea.
The results obtained in this work have not been previously reported. This data comprises the basis for future development of PGS-M scaffolds with better biocompatibility and mechanical properties close to the gold standard of a corneal scaffold.