How do you measure fracture toughness of biomaterials in vitro and in vivo?

1 In vitro methods

In vitro methods are performed in laboratory settings, using standardized specimens and testing machines. The most common method is the single-edge notched bending (SENB) test, which involves applying a bending load to a beam with a pre-existing notch. The load-displacement curve is recorded, and the fracture toughness is calculated from the critical load and the notch geometry. Other methods include the compact tension (CT) test, the double cantilever beam (DCB) test, and the chevron notched short rod (CNSR) test, which use different specimen shapes and loading modes.

3 Material factors

The fracture toughness of biomaterials depends on several material factors, such as composition, structure, porosity, and surface properties. For example, metals tend to have higher fracture toughness than ceramics or polymers, because they can deform plastically and blunt cracks. However, metals may also corrode or release ions in biological environments, which can reduce their fracture toughness. Ceramics and polymers have lower fracture toughness, but they can be reinforced with fibers, particles, or nanostructures to improve it. Porosity can also affect fracture toughness, as it can reduce the effective cross-sectional area and introduce stress concentrations. Surface properties, such as roughness, coating, or functionalization, can influence the adhesion and friction between the biomaterial and the surrounding tissue, which can affect the crack initiation and propagation.

4 Biological factors

The fracture toughness of biomaterials also depends on several biological factors, such as tissue response, remodeling, and aging. For example, tissue response can affect the fracture toughness of biomaterials by inducing inflammation, infection, or foreign body reaction, which can alter the mechanical and chemical environment around the biomaterial. Remodeling can affect the fracture toughness of biomaterials by changing the structure and composition of the tissue-biomaterial interface, which can enhance or impair the interfacial strength and toughness. Aging can affect the fracture toughness of biomaterials by causing degradation, wear, or fatigue, which can reduce the resistance to crack growth.

5 Testing challenges

Measuring fracture toughness of biomaterials in vitro and in vivo poses several challenges, such as specimen preparation, loading conditions, measurement accuracy, and data interpretation. For example, specimen preparation requires careful selection, cutting, polishing, and notching of the biomaterials, which can introduce variability and artifacts. Loading conditions require appropriate control, alignment, and monitoring of the applied force and displacement, which can affect the stress distribution and crack propagation. Measurement accuracy requires precise calibration, resolution, and synchronization of the testing instruments, which can affect the quality and reliability of the data. Data interpretation requires appropriate analysis, modeling, and comparison of the fracture toughness values, which can depend on the testing method, the material properties, and the biological factors.

6 Here’s what else to consider

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