The skull bone in the human body serves very important functions, such as protecting the brain and enabling the passage of cranial nerves that are essential for physiological function. Defects in the skull of critical size can affect both the physical and mental well-being of patients. Restoring critical-sized skull defects through cranioplasty presents a challenge for reconstructive surgeons who prefer using autologous bone grafts. Acquiring autologous bone requires additional surgical procedures and carries risks such as free flap loss, infections, deep vein thrombosis, and nerve injuries. These limitations necessitate the development of alternatives to autologous bone grafts for skull defect restoration.
Biomaterials that mimic the composition and microstructure of natural bone are widely considered ideal for bone defect regeneration. The skull bones are mainly composed of calcium phosphate and are typical flat bones that are generally thin and broad with a flattened or curved surface. The flat bone has two outer compact tables of cortical bone. The region between the two tables is called diploë and consists of cancellous bone. Cortical bone has low porosity (5 to 10%) with interconnected tubular pores known as Haversian and Volkmann canals. Cancellous bone consists of irregular sponge-like trabeculae with a high specific surface area, and the mean curvature of the trabecular surface is close to zero. The architectural properties of cancellous bone resemble the pore topology with triply periodic minimal surface (TPMS) of the gyroid type.
Inspired by the composition and structural features of the skull bones, scientists at the South China University and Technology developed two flat, bone-like bioceramic scaffolds made from β-tricalcium phosphate (Gyr-Comp and Gyr-Tub) using high-precision 3D printing based on voxel-photopolymerization. Both scaffolds had two outer layers and an inner layer with gyroid pores that mimicked the diploë structure. The outer layers of the Gyr-Comp scaffolds simulated the low porosity of the outer tables, while those of the Gyr-Tub scaffolds mimicked the tubular pore structure of flat bone tables. The Gyr-Comp and Gyr-Tub scaffolds possessed higher compressive strength and significantly promoted cell proliferation, osteogenic differentiation, and angiogenic activities in vitro compared to conventional scaffolds with lattice structures. After 12-week implantation in rabbit skull defects, Gyr-Tub achieved the best repair effects by accelerating the formation of bone tissue and blood vessels. The Gyr-Tub scaffolds have good prospects for the treatment of skull bone defects in clinical applications. This work provides an advanced strategy for the production of biomimetic biomaterials that meet the structural and functional requirements of effective bone regeneration.
Zhang, Y., He, F., Zhang, Q., Lu, H., Yan, S. & Shi, X. (2023). 3D-printed, flat, bone-like bioceramic scaffolds for skull restoration. Research. doi.org/10.34133/research.0255.