Multi-color and Multi-Material 3D Printing of Knee Joint models

Abstract

Objective This study reports on a new method for the development of multi-color and multi-material realistic Knee Joint anatomical models with unique features. In particular, the design of a fibers matrix structure that mimics the soft tissue anatomy. Methods Various Computer-Aided Design (CAD) systems and the PolyJet 3D printing were used in the fabrication of three anatomical models wherein fibers matrix structure is mimicked: (i) Anterior cruciate ligament reconstruction (ACL-R) model used in the previous study. (ii) ACL-R model, incorporating orientations, directions, locations, and dimensions of the tunnels, as well as a custom-made surgical guide (SG) for avoiding graft tunnel length mismatch. (iii) Total knee arthroplasty (TKA) model, including custom-made implants. Before models 3D printing, uni-axial tensile tests were conducted to obtain the mechanical behaviors for individual No. 1 (A60-A50), No. 2 (A50-A50), No. 3 (A50-A40), and No. 4 (A70-A60) soft tissue-mimicking polymers. Each material combination represents different shore-hardness values between fiber and matrix respectively. Results We correlated the pattern of stress-strain curves in the elastic region, stiffness, and elastic modulus of proposed combinations with published literature. Accordingly, material combinations No. 1 and No. 4 with elastic modules of 0.76-1.82 MPa were chosen for the soft tissues 3D printing. Finally, 3D printing Knee Joint models were tested manually simulating 50 flexo-extension cycles without presenting ruptures. Conclusion The proposed anatomical models offer a diverse range of applications. These may be considered as an alternative to replacing cadaver specimens for medical training, pre-operative planning, research and education purposes, and predictive models validation. The soft tissue anatomy-mimicking materials are strong enough to withstand the stretching during the flexo-extension. The methodology reported for the design of the fiber-matrix structure might be considered as a start to develop new patterns and typologies that may mimic soft tissues.

A review on polyjet 3D printing of polymers and multi-material structures

“…Numerical and analytical approach has been employed in numerous investigations for estimating the strength of the 3D printed specimens. 16,83,105,[115][116][117][118]141 The quasi-static boundary approach has been utilized to achieve accurate solutions for the mesoscale AM, and analytical solutions for a single droplet of thermoplastic rein are presented to demonstrate the manufacturing features of the mesoscale. An explicit solver 115,118 with an actual time scale model is utilized to analyze the 3D printing process that incorporates mass scaling under dynamic loading conditions.…”

Design and Mechanical Characterization Using Digital Image Correlation of Soft Tissue-Mimicking Polymers

“…A Finite Element Analysis (FEA) was performed to evaluate the best position of the pattern inside the specimens for a mechanical tensile test. Applying the same soft tissue design approach as [40]. The cylindrical linear fiber patterns with a diameter of 0.5 mm were embedded in a matrix with the shape of the specimens.…”

“…Additional factors, such as orientation and positioning of structures, pathological conditions, age, and gender also affect their mechanical properties. Indeed, degenerative soft tissue disorders show a reduction in their mechanical properties, exhibiting a lower modulus of elasticity, strength, and strain compared to healthy controls [40,68,74,75]. In normal conditions, generally, when a progressive mechanical load is applied to a tendon or a ligament, the collagen bundles, which are randomized and crimped at rest, start to align with each other losing the initial state that represents a 2-5 strain percentage in their stress-strain curve (toe region).…”

“…This allows as well for the precise definition of complex bio-inspired shapes [38]. The entire 3D printing settings can be controlled by GrabCAD print™ software voxel-based system, which enables modifying physiological characteristics of preset materials [31,[39][40][41]. The GelMatrix™, TissueMatrix™, and BoneMatrix™ are the trade names of the three anatomical digital materials available in the printer, which are used to suit the requirements and specifications of anatomical applications.…”

Correction to Acknowledgement

“…Following publication of the articles [ 3 – 8 ], it is noticed the below sentence needs to be added to the Acknowledgement section of these articles:…”