Korean Researchers Successfully BioPrint Tissue for Corneas With Transparent Bioink

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In ‘Characterization of cornea-specific bioink: high transparency, improved in vivo safety,’ researchers Hyeonji Kim, Moon-Nyeo Park, and Jisoo Kim explore the materials and processes surrounding corneal tissue engineering.

Patients waiting for cornea transplants are often in for a long wait due to a decrease in the supply to hospitals. And while artificial corneas have been created to solve this problem, they are challenging to implant because of restricted tissue integration. With the creation of a cornea-derived decellularized extracellular matrix (Co-dECM), the researchers endeavored to make further progress in corneal regeneration.

Their new bioink demonstrates similarities to the human cornea and offer the transparency required for human vision. Because this eye tissue is vital to being able to see, damage to the cornea becomes a serious issue and can even lead to blindness. The researchers cite data from the World Health Organization stating that around 285 million individuals in the US have visual deficiencies due to corneal disease. On average, a corneal transplant involves a wait time of 2,134 days, and out of all donor list waits, it is the longest.

“Moreover, the waiting time unfortunately has become even longer because of a shortage of donor cornea due to the rapid increase in the number of procedures for laser-based treatments and surgery (e.g., laser in-situ keratomileusis (LASIK)), which makes the cornea undonatable,” state the researchers. “To replace donor corneas, clinically available synthetic corneas are widely being used including Keratoprosthesis (KPro, made of poly(methyl methacrylate) (PMMA)), and AlphaCorTM(poly(2-hydroxyethyl methacrylate), PHEMA).”

Artificial corneas have been the cause of numerous and severe reactions though, unfortunately. This is due to adverse reactions as the body begins to reject the foreign objects. Researchers turned to bioengineering to create more hospitable corneas. They began by harvesting entire corneas from bovine eyeballs, procured from a Korean slaughterhouse. The corneas were further prepared in an extensive sterilization process and then stored.

Schematic of Co-dECM gel preparation and its validation.

Gel samples were made and then evaluated for growth of tissue. The team then used their in-house bioprinting system to fabricate Co-dECM bioink encapsulating cells. Experiments were performed on mice and rabbits to assess biocompatibility of the ink, with mice functioning to demonstrate immune responses. This was true in the rabbits, but the scientists also evaluated cell activity after samples were implanted (see the research paper regarding treatment according to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research).

Optical properties of Co-dECM gel. (a) Gross images (scale bar: 2 mm). (b) Light transmittance variations of 2% Co-dECM gel, 2% Col, and human cornea at different wavelengths of visible light spectrum. (c) SEM micrographs of samples (scale bar: 10 µm). (d) Thicknesses of collagen fibers for Co-dECM gel (Co-dECM 1X), Co-dECM gel mixed with Col (Co-dECM 0.5X), and Col (Co-dECM 0X). *p < 0.05, ***p < 0.005.

The researchers analyzed the following in the Co-dECM gel:

  • Transparency and microstructure
  • Internal biomolecular growth factors
  • Gene expression pattern

The two control groups were comprised of collagen hydrogel and native human cornea.

Transparency of the Co-dECM gel was rated ‘excellent,’ with the team stating such high marks could be due to ‘thin collagen fibrils’ associated with the graft.

 “…Co-dECM gel also contains various growth factors, including fibroblast growth factor (FGF), insulin-like growth factor (IGF), and transforming growth factor (TGF), which are abundantly observed in the native cornea, stated the researchers. “In addition, we verified the biological effects of Co-dECM from the differentiation of stem cells into keratocyte lineage by culturing hTMSCs in the Co-dECM gel.”

“The representative markers for cornea stromal layer, such as Keratocan (KERA), Aldehyde dehydrogenase (ALDH), were investigated after 14-day culture, expressed, respectively, as 7.30 and 11.97 times greater than the cells cultured in the Col gel. These results indicate that the Co-dECM bioink provides microstructural and biochemical cues for cells to induce them to differentiate into keratocyte lineage.”

H&E stained images using rabbit model. Optical micrographs, OCT images with H&E stained images on day 28, and the number of immune cells on days 14 and 28. Scale bar: 50 µm.

In testing further, the researchers 3D printed lattices. They maintained their structure after crosslinking, and tissue remained alive.

“This study demonstrated the feasibility of Co-dECM bioink applications for the fabrication of patient-specific shaped artificial corneas,” concluded the researchers. “Thus, the proposed Co-dECM bioink can be applied to 3D cell printing technique to provide cornea-mimicking microenvironments. It may support progress in the field of cornea tissue engineering in future applications.”

While there are plenty of 3D printing projects created and enjoyed with sheer whimsy, the innovations brought forth in the medical field offer serious potential for changing the lives of patients. Bioprinting offers myriad benefits to the medical field and is quickly attaining superstar status as an offshoot to the 3D printing realm. The engineering of tissue alone is a huge stride for science, but of course it is the eventual potential we all see it unlocking that has everyone excited, regarding the ability to 3D print the human organ. So far, scientists and medical professionals have used bioprinting to advance the study of Alzheimer’s, fabricate a lab-grown bladder, and also create orbital implants for intricate surgeries.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: Characterization of cornea-specific bioink: high transparency, improved in vivo safety]
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