Challenges in creating dissectible anatomical 3D prints for surgical teaching

Abstract

Three-dimensional (3D) printing, or additive manufacturing, is now a widely used tool in pre-operative planning, surgical teaching and simulator training. However, 3D printing technology that produces models with accurate haptic feedback, biomechanics and visuals for the training surgeon is not currently available. Challenges and opportunities in creating such surgical models will be discussed in this review paper. Surgery requires proper tissue handling as well as knowledge of relevant anatomy. To prepare doctors properly, training models need to take into account the biomechanical properties of the anatomical structures that will be manipulated in any given operation. This review summarises and evaluates the current biomechanical literature as it relates to human tissues and correlates the impact of this knowledge on developing high fidelity 3D printed surgical training models. We conclude that, currently, a printer technology has not yet been developed which can replicate many of the critical qualities of human tissue. Advances in 3D printing technology will be required to allow the printing of multi-material products to achieve the mechanical properties required.

Keywords: additive manufacturing; biomechanical; multi-material; surgery; three-dimensional printing; training.

Figure 1

Object subjected to uniaxial normal stress and shear stress. The direction of the normal is indicated in grey (perpendicular to surface ‘A’). (A) Normal force F_N acting on surface ‘A’ of object results in a normal stress. (B) Shear force F_S acting across surface ‘A’ of object, results in a shear stress.

Figure 2

Example of stress–strain curve for soft tissue adapted from Korhonen & Saarakkala (2011). (A) Initial toe region, with straightening of collagen fibrils and non‐linear stress–strain relationship. (B) Elastic region of stress–strain curve where stress is linearly proportional to strain. The slope of this region is equal to Young's modulus of the tissue. All changes are reversible in this region. (C) Plastic region: the yield point is at the start of this region and permanent deformation occurs beyond this point. (D) At the end of the plastic region, sudden failure of the tissue occurs (the failure point) and the stress dissipates.

Figure 3

Hysteresis loop.

Figure 4

Typical 3‐point bending test with force applied to beam.

Figure 5

Multi‐material prints (Centre for Human Anatomy Education) created using the Stratasys ‘J750’ Multi‐material 3D printer (Stratasys Ltd). (A) Base of skull showing path of internal carotid artery and sigmoid sinus/internal jugular vein (superior bulb). (B) Multi‐material print of fetus.

Figure 6

Comparison of the tensile strength of various body tissues.

Figure 7

Tensile test adapted from Lardner (1994). (A) The test specimen (blue) is subjected to a uniaxial force ‘P’. This results in displacement δ. (B) For each value of ‘P’, the value for δ can be measured and plotted to form a load‐displacement curve. This curve is linear for linear‐elastic materials (Lardner, 1994). (C) The force ‘P’ gives rise to uniform axial stress σ which equals ‘P’ divided by ‘A’, where ‘A’ is the cross‐sectional area of the specimen. The normal strain ε is given by δ divided by the original length of the specimen. The slope of this stress–strain curve equals the Young's modulus for the material, denoted by ‘E’.