October 08, 2019

Biopolymers to 3D print retinal cell scaffolds

Primary postnatal rat retinal cells created with Nanoscribe's additive manufacturing technology. Image: University of Iowa
Immunofluorescent image of primary postnatal rat retinal cells on 50/50 gelatin/HA microscaffold. Image: University of Iowa

Bioengineers developed biocompatible 3D cell scaffolds for future tissue modeling, regeneration, and drug testing at the cellular level. For this, the researchers used Nanoscribe’s additive manufacturing technology to create biopolymer retinal cell scaffolds that closely resemble actual characteristics of human retinal tissue.

Loss of sight from degenerative human retinal diseases is a severe problem worldwide. To cure the irreversible cell damage due to diseases such as retinitis pigmentosa and age-related macular degeneration, approaches such as gene therapy, optogenetics and cell transplants are being investigated. As part of that mission, researchers from the University of Iowa put their efforts into the development of appropriate biomaterials for tissue engineering of retinal cells. These materials need to match the biochemical and biomechanical properties of the in vivo retinal tissue to promote the cell response desired for disease treatment in the body.

The scientists investigated four different biopolymer formulations to 3D print extracellular matrices (ECM). These microscaffolds were designed to mimic the natural photoreceptor cell environment and fabricated with Nanoscribe’s Photonic Professional system using Two-Photon Polymerization. Evaluation of the biocompatibility of human induced pluripotent stem cells and rat postnatal retinal cells confirmed cell viability on the 3D printed microscaffolds over several days.

3D printing of naturally occurring polymers

The materials, described in the study published in the Journal of Ocular Pharmacology and Therapeutics, are four ECM biopolymer formulations: collagen, gelatin, hyaluronic acid (HA) and a 50/50 mixture of gelatin/HA. The authors used methacrylate-modified versions of the biomolecules and mixed them with the water-soluble photoinitiator methylene blue to prepare the materials for the printing technique of two-photon polymerization.

The flexibility of this additive manufacturing technique enabled them to tune the right printing parameters for these biopolymers, which differ from those of commonly used photoresins. To simulate the natural retinal cell environment, scaffolds were accurately printed with densely packed vertical and horizontal cross-pores. The geometry, designed as a CAD model, aims to align the photoreceptor cells in 3D and to allow cell-to-cell interaction, communication, and free diffusion of nutrients. The material stiffness of these biopolymers is similar to that of retinal tissue (10 kPa).

Cell viability on 3D microscaffolds

To evaluate the cell viability of retinal cells, both, human induced pluripotent stem cells as well as rat postnatal retinal cells, were cultured on the 3D-printed microscaffolds for up to one week. The results showed that both cell types were best viable cultured on HA/gelatin scaffolds. The manufactured microscaffolds achieved cell viability of 87%, a value similar to the control samples. Moreover, gelatin/HA scaffolds attracted a greater number of cells compared to gelatin scaffolds and cells expressed more Tuj-1 (a neuronal marker) and had characteristic neuronal morphology. The researchers also observed that postnatal retinal cells proliferated on top of the scaffolds, surrounding the scaffolds and inside the scaffolds’ pores, giving an affirmative sign of material biocompatibility.

The findings on biopolymer microscaffolds pave the way for the development of accurate tissue-engineered in vitro retinal models. With this research, future studies may be fostered to produce reliable and tissue-mimetic in vitro environments at the microscale fabricated from appropriate biopolymer compositions. These 3D printable materials could enable supporting scaffolds for retinal disease models, drug testing and not least for retinal regeneration cell transplants.

Materials development outlook

Printing materials specially developed for two-photon polymerization are decisive for 3D printing results in highest quality. Nanoscribe is continuously working on the development of new materials for specific applications and defined properties. We are currently working on novel photoresists that are biocompatible.

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