Making Better 3D Printed Bone Scaffolds at Low Temperatures with Robocasting Technique

Scaffolds are an important part of bioprinting, as they provide necessary structure to printed cells while they grow and develop. 3D printed bone scaffolds can help with tissue regrowth, as well as improve bone regeneration. Scaffold structures also have an effect on how cells express signaling proteins that help cancer grow, and can be used to study how bone cancer cells respond to stimuli like shear stress.

A group of researchers from several hospitals in China are working to fabricate better 3D printed bone scaffolds at low temperatures, without the use of toxic chemicals, using a unique technology known as robocasting – a freeform 3D printing technique that allows dense ceramics and composites to be used as ‘highly colloidal slurries.’

Human bone cross-section.

Low-temperature robocasting is a fairly new 3D printing technology, and it can be used to manufacture ceramic scaffolds with complex geometries.

The researchers, working in orthopedic departments at the Fourth Military Medical University, the Fuzhou General Hospital of Nanjing Military Area Command of Chinese PLA, the Xi’an Hong Hui Hospital, and the 251st Hospital of Chinese PLA, recently published a paper in the International Journal of Nanomedicine, available to read here, detailing their work to make low-temperature, 3D printed ceramic bone scaffolds, using nano-biphasic calcium phosphate (BCP), polyvinyl alcohol (PVA), and platelet-rich fibrin (PRF). Co-authors include Yue Song, Kaifeng Lin, Shu He, Chunmei Wang, Shuaishuai Zhang, Donglin Li, Jimeng Wang, Tianqing Cao, Long Bi, and Guoxian Pei.

The introduction reads, “Large bone defects are frequently encountered by orthopedic surgeons in clinical practice and are great surgical challenges. Bone traumas exceeding a critical size become scarred and lose the ability to regenerate. Autologous bone grafting is considered the gold standard repair method; however, the transplantation process may lead to hemorrhage, nerve injury, and dysfunction. The failure of autograft is mostly due to the necrosis of grafts, which is usually caused by poor blood supply and secondary infection. To avoid these postoperative complications, the currently favored solution is to repair bone defects with inert bone graft materials (scaffolds) that simply function as a supporting structure but provide limited skeletal regeneration ability.”

Schematic representation illustrating production and testing of 3D printed scaffolds.

It’s important to consider the specific biomaterials that go into bone repair scaffolds, because cellular behavior and function can actually be affected by their biochemical and biophysical characteristics; equally as important are the scaffold design and the technology chosen to fabricate them. Low-temperature 3D printing of scaffolds, which allows scientists to use bioactive molecules, is possible thanks to the robocasting 3D printing method.

Not much research has been conducted on combining these three materials for bone repair, or for 3D printing, but the team made a 3D printed porous nano-BCP/PVA/PRF scaffold, believing that the combination would work. The scaffolds were fabricated on a 3D bioprinter, and corresponding scaffolds were prepared with a freeze-drying method; the biological effects of both types were later assessed in vitro on bone marrow-derived mesenchymal stem cells taken from rabbits.

Micro-CT scans and 3D reconstructions to visualize healing of critical size bone defects in the rabbit radius after implantation of scaffolds seeded with BMSCs. The scaffolds are blue, and newly formed radius bone is orange.

When the researchers compared the results later, they noted that the 3D printed scaffolds had well-connected internal structures and specific shapes, unlike the conventionally fabricated ones. Using the PRF in the scaffolds allowed for the sustained release of bioactive factors from the scaffolds, and it also improved biocompatibility and biological activity toward the stem cells in vitro. As a whole, the 3D printed scaffolds made with BCP, PVA, and PRF promoted much better adhesion, osteogenic differentiation, and proliferation than the scaffolds without PRF.

Macroscopic and microscopic structures, hydrophobicity, and porosity of the scaffolds.

These results have led the research team to posit that low-temperature 3D printed BCP/PVA/PRF scaffolds may, according to the research paper, “represent a promising new approach to overcome the significant hurdles that currently prevent successful segmental bone defect and bone nonunion repair in clinical practice.”

The conclusion states, “These experiments indicate that low-temperature robocasting could potentially be used to fabricate 3D printed BCP/PVA/PRF scaffolds with desired shapes and internal structures and incorporated bioactive factors to enhance the repair of segmental bone defects.”

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