Bioprinting: Beyond the Natural Order of Creation

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Science Translational Medicine  10 Jul 2013:
Vol. 5, Issue 193, pp. 193ec112
DOI: 10.1126/scitranslmed.3006919

The design of new biomaterials that are durable, lightweight, and tunable requires the ability to arrange materials in complex hierarchical patterns, mimicking naturally occurring composites such as those found in bone. Bone is strong and tough owing to the highly ordered microstructure of its two constituent materials, soft collagen protein and stiff hydroxyapatite mineral. Currently used bone substitutes exhibit far inferior mechanical properties, even when natural bone components are used, because they do not recapitulate the intricate composite structure required to improve fracture-resistance beyond that of the constituent materials. In a recent paper, Dimas et al. used soft and stiff polymers placed in computer-optimized geometric configurations that replicate nature’s own patterns and a three-dimensional (3D) printer that prints two materials at once in order to successfully build bonelike materials featuring fracture resistance similar to that of natural bone.

The authors used stereolithography (“3D printing”) to print two materials with dramatically different stiffnesses into three composite structures so as to mimic the structure of bone, biocalcite, or a rotated bone-like geometry. The authors performed mechanical characterization of the individual materials and developed a computer simulation of deformation and fracture of these composites under tensile strain. The resulting model showed a great deal of agreement with the experimental data. Notably, much of the strain was carried by the more compliant component and served as the site of fracture propagation, akin to the way it functions in natural bone. The bonelike topology exhibited the highest resistance to fracture, with toughness values more than 20 times those of its individual components. This increased toughness was due to the tortuous path of crack propagation around the stiffer “plates” of mineral-like material, which were capable of absorbing much of the energy. Interestingly, other topologies did not show as much improvement in toughness, despite containing virtually the same materials.

The combination of detailed computer modeling and rapid prototyping paves the way for the creation of multicomponent materials, arranged in any variation of patterns. Such materials could be custom-designed to perform specific functions and have predictable properties for medical applications, enabling rapid preclinical to clinical translation. The performance of these materials in preclinical models and in vivo biocompatibility have yet to be demonstrated. However, bioprinting of biologically relevant materials, such as collagen and calcium phosphate in the case of bone substitutes, can open up new avenues for developing superior devices to address unmet clinical needs.

L. S. Dimas et al., Tough composites inspired by mineralized natural materials: Computation, 3D printing, and testing. Adv. Func. Mater., published online 17 June 2013 (10.1002/adfm.201300215). [Abstract]

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