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International Journal of Bioprinting 3D bone: Current & future

Figure 3. The structure of a long bone and the cells of the bone. This figure was created using BioRender.

refers to the ability of bones to absorb energy before dissipating forces as their porous structure allows for the
breaking, i.e., when bones are subjected to sudden impacts redistribution of forces, reducing the strain on the bone and
or high forces, such as during physical activities or preventing fractures. This is particularly important for bones
accidents. The toughness of bone is primarily influenced in joints that are subjected to various forces during movement.
by the amount and orientation of collagen fibers and the At the microscopic level, lamellar bones are known for
quality and distribution of calcium phosphate crystals. A their strength and stiffness, while woven bones are used in
higher amount of collagen and a more organized structure bone remodeling and have poorer mechanical properties.
would result in increased toughness, making bone tissue Accordingly, fibrolamellar bones combine the properties of
more resistant to fracture. both lamellar and woven bones, and the secondary osteons

While all bone types serve imperative functions in provide high resistance to bending and torsional forces. 10
providing support and protection, they have distinct The mechanical properties of bones can be determined
differences in their mechanical properties that can be from bone specimens, i.e., samples cut from the bones.
observed from both the macroscopic and microscopic levels. However, the measured mechanical properties of bones
In compact bones, the arrangement of osteons induces may differ due to non-standardized procedures, different
compressive force resistance, making it strong and rigid. sample sites, and other conditions. While these properties
These bones are commonly found in areas of the body that may vary along the bone structure due to the non-
require strength and support, such as the shafts of long homogeneity and varied geometry, they are relevant for 3D
bones. In contrast, spongy bones are naturally porous and bioprinting (Table 1). 11,12
strong and can resist forces from multiple directions. One
of the critical differences between compact and spongy 2.1.1. Bone cells
bones is their response to mechanical stress. Compact bones There are four types of bone cells: osteoprogenitors,
can withstand compressive forces due to their dense and osteoblasts, osteocytes, and osteoclasts (Figure 3).
organized structure, as well as bending and twisting forces, Osteoprogenitor cells, commonly found in the periosteum
making them ideal for supporting the body’s weight and and endosteum, are derived from MSCs and can
movement. Likewise, spongy bones are better suited for subsequently differentiate into osteoblasts. These cells are
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Volume 10 Issue 3 (2024) 144 doi: 10.36922/ijb.2056