**Background:** Corneal blindness affects millions worldwide, with an estimated 4.3 million cases of corneal opacity by 2020, and a severe shortage of donor corneas exists globally (only 1 in 70 patients receive a transplant). 3D bioprinting offers a promising alternative by enabling precise spatial arrangement of biomaterials and cells to create artificial corneas. The cornea is particularly suitable for bioprinting due to its avascular nature. This review discusses bioprinting technologies, biomaterials, and the current state of printed corneal models, focusing on key characteristics like cell viability, light transmission, biomechanics, protein expression, and in vivo studies.
**Methods:** The authors conducted a narrative review of the literature on 3D bioprinting of corneal models. They evaluated 16 research articles, covering various bioprinting technologies (extrusion, drop-on-demand, laser-assisted, electrospinning/melt-electrowriting, and light-based methods) and biomaterials (collagen, gelatin/GelMA, alginate, decellularized extracellular matrix, chitosan, hyaluronic acid, and agarose). The review assessed studies on cell viability, light transmission, biomechanical properties, protein/gene expression, swelling, degradation, and in vivo transplantation in animal models (rabbits, rats, mice).
**Key Results:** Extrusion bioprinting is the most commonly used technology, with cell densities up to 5 million per ml and printing times under 10 minutes for one cornea. Cell viability was generally high: Wu et al. reported 94.6% for human corneal epithelial cells, Isaacson et al. 92% on day 1 (decreasing to 83% on day 7), and Kutlehria et al. 96% on day 1 (86% on day 14). Light transmission varied widely: Zhang et al. achieved 85-94% at 300-700 nm, Mahdavi et al. 80-94% at 450-600 nm, while Ulag et al. reported less than 61% at 400-800 nm. Biomechanical properties showed Young's moduli ranging from 0.0103 MPa (Mörö et al.) to 0.506 MPa (Gibney et al.), compared to native cornea values of 0.1-57 MPa in literature. Kong et al. achieved a tensile strength of 3.47 MPa (close to native 3.8 MPa) and Young's modulus of 0.12 MPa. Protein expression studies showed positive markers for keratocan, lumican, and type I collagen in several constructs, with low or absent α-SMA expression indicating minimal myofibroblast differentiation. In vivo studies in rabbits and rats demonstrated transparency, biocompatibility, and integration, with He et al. showing faster corneal healing with cell-laden bilayer constructs over 28 days.
**Clinical Implications:** 3D bioprinting holds significant potential to address the global donor cornea shortage and provide patient-specific implants. However, current constructs still face challenges in simultaneously achieving optimal biomechanical strength, transparency, and cell viability. Most studies have focused on single-layer printing (primarily stroma), with only two groups printing both epithelium and stroma. No bioprinted corneas have been transplanted into humans yet. Future directions include developing multi-layer constructs with all three major cell types, improving bioink formulations for better mechanical properties, and conducting more extensive in vivo studies and clinical trials. The technology also offers promise for in vitro drug screening, though regulatory frameworks for bioprinted products are still evolving.