Synthesis and characterisation of a cancerous liver for presurgical planning and training applications

Abstract

Objectives: Oncology surgeons use animals and cadavers in training because of a lack of alternatives. The aim of this work was to develop a design methodology to create synthetic liver models familiar to surgeons, and to help plan, teach and rehearse patient-specific cancerous liver resection surgery.

Design: Synthetic gels were selected and processed to recreate accurate anthropomorphic qualities. Organic and synthetic materials were mechanically tested with the same equipment and standards to determine physical properties like hardness, elastic modulus and viscoelasticity. Collected data were compared with published data on the human liver. Patient-specific CT data were segmented and reconstructed and additive manufactured models were made of the liver vasculature, parenchyma and lesion. Using toolmaking and dissolvable scaffolds, models were transformed into tactile duplicates that could mimic liver tissue behaviour.

Results: Porcine liver tissue hardness was found to be 23 H00 (±0.1) and synthetic liver was 10 H00 (±2.3), while human parenchyma was reported as 15.06 H00 (±2.64). Average elastic Young's modulus of human liver was reported as 0.012 MPa, and synthetic liver was 0.012 MPa, but warmed porcine parenchyma was 0.28 MPa. The final liver model demonstrated a time-dependant viscoelastic response to cyclic loading.

Conclusion: Synthetic liver was better than porcine liver at recreating the mechanical properties of living human liver. Warmed porcine liver was more brittle, less extensible and stiffer than both human and synthetic tissues. Qualitative surgical assessment of the model by a consultant liver surgeon showed vasculature was explorable and that bimanual palpation, organ delivery, transposition and organ slumping were analogous to human liver behaviour.

Keywords: COLORECTAL METASTASES; HEPATIC SURGERY; HEPATOCELLULAR CARCINOMA; SURGICAL TRAINING.

Figure 1

Frontal view of the final smoothed model prior to additive manufacture, showing the tumour (red), inferior vena cava (IVC) and hepatic veins (grey), hepatic artery (beige), portal vein (pink) and gall bladder (cyan), parenchyma (transparent blue). The discs at both distal ends of the model are used to fix the blood vessels in space to prevent model distortion and used as an orientation/ location marker during embedding of the surrogate vascular model. The use of hollow and dissolvable additive manufactured scaffolds for the creation of an accurate, multilayered vascular system that could be embedded in the surrogate parenchyma was previously unknown in the literature and may be useful in a variety of other applications and organs.

Figure 2

Bar chart showing the comparative hardness among 150 test specimens during indentation tests with a stand-mounted shore 00 calibrated durometer measured as per the standards. Each bar represents the arithmetic mean of 25 specimens tested. Error bars indicate an SD of 2.39. Live human liver parenchyma was previously reported as 15.06 H00 (±2.64) and ex vivo porcine liver was 30.52 H00±1.520. in the current study. Ex vivo porcine liver parenchyma was found to be 23 H00 (±2.39), and the synthetic liver parenchyma was 10 H00 (±2.09). The hardness of the surrogate vascular tissue was 44 H00 (±1.03). Hardness of porcine hepatic vascular tissue thickness did not meet requirements for test standards, but the literature assigns an aortic vascular tissue (bovine) hardness average of 41 H00. No specific published data could be found on the shore 00 hardness of tumours for comparison. The standard ASTM D2240-15 2021- (table x1.1), used to gather this data, specifies that the 00 shore hardness scale is the only agreed method for characterisation of both extremely soft rubber, human and animal tissues alike.

Figure 3

The final prototype organ model features all the internal anatomy shown in figure 1, modified additive manufactured using the materials and methods discussed previously. The prototype surrogate organ demonstrated characteristic softness and slumping characteristics of the real organ when handled. Slumping and relaxation of the soft tissue were reflective of the real organ especially during delivery and transposition of the organ and during palpation.

Figure 4

View of the model’s vascular aperture taken from the upper distal end of the inferior vena cava. Insert: internal view of the hepatic artery showing the smoothness of internal vessel walls.

Figure 5

Surgical rehearsal of lesion removal on prototype organ by a consultant liver surgeon, conducted without gloves to demonstrate its authenticity as a surrogate. On palpation, the liver tumour was identifiable as a discrete hard lesion on a background soft tissue with a rubbery texture. The incision reveals the tumour attached to the left hepatic vein, which ‘bled’ when the surgeon attempted removal. The procedure emulated the relationship between the tumour and major vascular structures that would be encountered during the actual procedure on the real patient, beneficial to teach surgery understudies about surgical protocol in such instances.