Imitating human soft tissue on basis of a dual-material 3D print using a support-filled metamaterial to provide bimanual haptic for a hand surgery training system

Abstract

Background: Currently, it is common practice to use three-dimensional (3D) printers not only for rapid prototyping in the industry, but also in the medical area to create medical applications for training inexperienced surgeons. In a clinical training simulator for minimally invasive bone drilling to fix hand fractures with Kirschner-wires (K-wires), a 3D-printed hand phantom must not only be geometrically but also haptically correct. Due to a limited view during an operation, surgeons need to perfectly localize underlying risk structures only by feeling of specific bony protrusions of the human hand. Methods: The goal of this experiment is to imitate human soft tissue with its haptic and elasticity for a realistic hand phantom fabrication, using only a dual-material 3D printer and support-material-filled metamaterial between skin and bone. We present our workflow to generate lattice structures between hard bone and soft skin with iterative cube edge (CE) or cube face (CF) unit cells. Cuboid and finger shaped sample prints with and without inner hard bone in different lattice thickness are constructed and 3D printed. Results: The most elastic available rubber-like material is too firm to imitate soft tissue. By reducing the amount of rubber in the inner volume through support material (SUP), objects become significantly softer. Without metamaterial, after disintegration, the SUP can be shifted through the volume and thus the body loses its original shape. Although the CE design increases the elasticity, it cannot restore the fabric form. In contrast to CE, the CF design increases not only the elasticity but also guarantees a local limitation of the SUP. Therefore, the body retains its shape and internal bones remain in its intended place. Various unit cell sizes, lattice thickening and skin thickness regulate the rubber material and SUP ratio. Test prints with higher SUP and lower rubber material percentage appear softer and vice versa. This was confirmed by an expert surgeon evaluation. Subjects adjudged pure rubber-like material as too firm and samples only filled with SUP or lattice structure in CE design as not suitable for imitating tissue. 3D-printed finger samples in CF design were rated as realistic compared to the haptic of human tissue with a good palpable bone structure. Conclusions: We developed a new dual-material 3D print technique to imitate soft tissue of the human hand with its haptic properties. Blowy SUP is trapped within a lattice structure to soften rubber-like 3D print material, which makes it possible to reproduce a realistic replica of human hand soft tissue.

Optically tracked and 3D printed haptic phantom hand for surgical training system

“…By reducing the amount of TP in the inner volume through SUP, an object becomes significantly softer. This makes it possible to soften the raw TP material to reproduce a realistic replica of human hand soft tissue (17). The CF design convinced with its elasticity and softened the TP material.…”

“…This corresponds to a value less than five on the shore A scale (16). Thus, in previous work a support-material-filled (supportmaterial, SUP) metamaterial to soften raw TP and imitate human soft tissue with its haptic and elastic properties was introduced (17). Metamaterials in 3D printing allow to change the haptic features assembling small-scaled structural components (18)(19)(20).…”

Insights into 3D printing in medical applications

“…In the remaining two original studies researchers reported their experiences of developing a realistic 3D printed hand phantom for surgery training purpose, and a multi-purpose breast phantom suitable for multi-modality imaging examinations (27,28). Maier and colleagues provided a very detailed approach of creating 3D printed hand model with haptic properties (27). Their design was based on using the metamaterial filled with blowy support material.…”

3D printed coronary models offer new opportunities for developing optimal coronary CT angiography protocols in imaging coronary stents

“…An increasing trend in research and publications have been observed recently in the journal of Quantitative Imaging in Medicine and Surgery (QIMS), especially in the 2019 January special issue with a focus on 3D printing in medicine. In that special issue, a number of publications (original studies, technical notes and review articles) were contributed by researchers from different countries with expertise in different fields highlighting the importance of 3D printing in medical applications (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). In addition to these applications, a recent paper in this issue of QIMS presents another new research direction of using personalized 3D printed coronary artery models for simulation of coronary stenting procedure (14).…”