The corneal epithelium is the first cellular barrier to protect the cornea. Thus, functional tissue engineering of the corneal epithelium is a strategy for clinical transplantation. In this study, the optimization of silk films (SFs) as substrates for functional human corneal epithelium growth was investigated with primary human corneal epithelial cells on SFs, poly-D-lysine (PDL) coated SFs, arginine-glycine-aspartic acid (RGD) modified SFs and PDL blended SFs. PDL coated SFs significantly promoted cell adhesion at early phases in comparison to the other study groups, while PDL blended SF significantly promoted cell migration in a "wound healing" model. All film modifications promoted cell proliferation and viability, and a multi-layered epithelium was achieved in 4 weeks of culture. The epithelia formed were tightly apposed and maintained an intact barrier function against rose bengal dye penetration. The results suggested that a differentiated human corneal epithelium can be established with primary corneal epithelial cells on SFs in vitro, by optimizing SF composition with PDL.

Although synthetic polymers may have suitable physicochemical properties for biomedical applications, biological properties are generally lacking. Poly(ethylene glycol) (PEG) is a frequently used polymer for the preparation of hydrogels. Due to its hydrophilic character, however, cellular interactions with PEG hydrogels are minimal or absent. To improve the cell adhesive properties of PEG hydrogels, we developed hybrid hydrogels based on PEG and the natural polymer gelatin. PEG dimethacrylate (PEG-dMA) and gelatin methacrylate (GelMA) macromers were prepared, which were photo-crosslinked in water in different ratios (75:25, 50:50 and 25:75 % (v/v)). The obtained hybrid networks showed macrophase separation, which could be prevented by photo-crosslinking in 0.5 % (v/v) acetic acid in water. The toughness of 50:50 % PEG-dMA:GelMA hydrogels prepared in 0.5 % acetic acid was 2.5 times higher than that of single polymer hydrogels made of PEG-dMA or GelMA. Hybrid hydrogels crosslinked in 0.5 % acetic acid supported the proliferation of human mesenchymal stem cells to the same extent as compared to 100 % gelatin hydrogel, whereas the cells did not proliferate on 100 % PEG hydrogel. In conclusion, our results show that both the cell adhesive and mechanical properties of a photocrosslinked PEG network can be improved by incorporation of gelatin in the network.

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. Purpose:  This study aims to investigate the effects of systemic application of sphingosine 1‐phosphate receptor 1(S1P1) on allogeneic corneal transplantation in mice. Methods:  A total of 112 BALB/c mice received corneal grafts from C57BL/6 donors. Recipients were randomly divided into seven groups and treated with intraperitoneal injections of S1P1 (5 mg/kg/days), cyclosporine A (5 mg/kg/days), dexamethasone (1 mg/kg/days) and rapamycin (2 mg/kg/days). S1P1was combined with rapamycin or cyclosporine A, and saline served as negative control. Serum levels of IL‐2, IL‐10, TGF‐β1 and IFN‐γ were measured by Elisa. The numbers of CD4+ T and regulatory (Treg) cell phenotype were measured by flow cytometry. Cytokine mRNA expression was analysed by real‐time quantitative PCR. CD4+ T cells and cytokines were histologically identified by immunofluorescence staining. Results:  Corneal graft survival was prolonged by intraperitoneal injections in S1P1 alone (mean survival time MST, 35.3 ± 5.6 days), S1P1 combined with rapamycin (MST, 38.7 ± 6.5 days) or S1P1 and cyclosporine A (MST, 32.7 ± 4.8 days) compared with the controls (MST, 14.6 ± 0.2 days; n = 5, p < 0.01). S1P1 alone increased CD4+ T (p < 0.01) and Treg cells (p < 0.01; n = 5) in the cervical and mesenteric lymph nodes compared with the controls and S1P1 + rapamycin (p < 0.05; n = 5). TGF‐β1 and IL‐10 mRNA transcriptions in corneal grafts following S1P1+ rapamycin increased (both p < 0.01; n = 3), and TGF‐β1 and IL‐10 in the serum level following S1P1 alone increased (both p < 0.01; n = 3). These results paralleled the findings obtained from immunofluorescence. Conclusion:  S1P1 has significant effect in corneal allograft rejection inhibition. The combined treatment of S1P1 and rapamycin results in synergistic effect.

This review on hybrid hydrogels prepared from methacrylated gelatin (GelMA) and synthetic polymers presents their advantageous properties and potential applications in biomedical engineering. It describes the preparation of the different types of frequently used hybrid hydrogel networks: co-networks, interpenetrating networks (IPNs), and semi-interpenetrating networks (semi-IPNs) and gives an overview of the different methods of preparing biomedical devices from these materials.