Abstract:

Objective Corneal repair materials refer to artificial or biological substitutes designed to restore damaged corneal tissue. An ideal corneal repair material must exhibit excellent biocompatibility, mechanical stability, and optimal optical characteristics. Current research indicates that while pure collagen-based scaffolds demonstrate promising biological properties, they often suffer from inadequate mechanical strength. Although this limitation can be partially addressed by incorporating polymeric components, such modifications may compromise other critical parameters, including optical clarity and controlled degradation behavior. To address these challenges, the present study proposes the use of natural silk fibroin(SF) fibers as functional reinforcing elements. This approach is expected to provide innovative solutions for the development of advanced collagen-based corneal repair materials with balanced performance characteristics.

Method This study first carboxylated natural silk fibroin(CSF) fibers and then introduced it into collagen(Col) system. Col-CSF composite scaffold with "reinforced concrete" structure was successfully prepared by chemical crosslinking of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and n-hydroxysuccinimide (NHS). Through precisely designed chemical modification strategies, we aim to achieve molecular-level integration and synergistic interaction between silk fibroin and collagen molecules.

Results The infrared spectra showed that the C—H telescopic vibrational absorption peak appeared at 2 930 cm^-1 after carboxylation treatment was weakened compared with that of the filipin protein, and the telescopic vibrational absorption peak of C══O appeared at 1 730 cm^-1, and the characteristic absorption peak of C—O—C appeared at 1 160 cm^-1, indicating that modified silk fibroin had been prepared. In the blended film, the N—H stretching vibration absorption peak gradually approached from 3 310 cm^-1 to 3 280 cm^-1. It showed that hydrogen bond was formed between two macromolecules in the blended film, leading to redshift of absorption band. After the addition of CSF, the tensile strength as well as the elongation at break of the films reached (12.66±0.11) MPa and (49.80±0.52)%, respectively, which were significantly higher than that of the pure collagen material. Compared with SF, CSF has more —COOH and provides more cross-linking sites for the material, thus increasing the steric hindrance effect of the fiber molecular conformational change. The plots of water absorption, specific surface area change, and thickness change of the three films demonstrated that the Col-CSF film had higher water absorption (93.6 ± 0.9)% and CSF was with more —COOH, and the interaction between —COOH and collagen —NH₂ led to an increase in the degree of cross-linking, which promotes water absorption. Transmittance was taken as one of the key parameters for evaluating the performance of corneal repair materials and it played an important role in assessing the compatibility between the molecules of the blends. It showed that the light transmittance of all materials increased with the increase of wavelength, which was similar to that of human natural corneal tissue. It is worth noting that the maximum transmittance of Col-SF was more than 80%, while the maximum transmittance of Col-CSF reached 95%. Col-CSF fibers with better ordered arrangement effectively improved the light transmittance, and the samples exhibited good optical properties on a macroscopic scale as a result. In addition, Col-CSF also showed good biocompatibility, which is favorable for cell growth, adhesion and proliferation on it.

Conclusion In this study, filipin protein was carboxylated and dispersed in a collagen hydrogel system. The two were chemically crosslinked using EDC/NHS to form a composite scaffold with a reinforced concrete structure. The experimental results showed that the saturated water content of the target material was (93.6±0.9)% and the light transmittance was up to 95%, which were similar to or higher than that of the natural cornea. It was also found that the addition of CSF significantly enhanced the mechanical properties of the material, with the tensile strength and elongation at break reaching (12.66±0.11)MPa and (49.80±0.52)%, respectively, which endowed the material with stronger operability and stability. In addition to this, in vitro cellular experiments showed that the composites had good cytocompatibility, with corneal epithelial cells(HCECs) being able to adhere, proliferate and rapidly cover the entire material surface. Therefore, the artificial corneal repair materials with good biocompatibility and light transmission properties prepared in this study provide a new strategy to improve corneal injury and reduce corneal blindness, and have potential future applications in the field of corneal repair engineering.

Key words: silk fibroin fiber modification, silk fibroin, collagen, mechanical property, corneal repair material, medical material