Cardiac applications of 3D printed patient-specific models (PSMs) include surgical training, complex procedural planning, and the creation or refinement of cardiac devices. As structural heart interventions become increasingly complex, the ability to effectively model patient-specific geometry, as well as the interaction of devices within and around that geometry, becomes even more valuable to advance surgical interventions. Until now, the focus of PolyJet™ 3D printing technology and other traditional anatomical modeling methods has been on achieving precise external anatomical geometry and appearance. The next frontier in 3D printed PSMs is the simulation of the biomechanical properties of human tissue.
Compliance
The Digital Anatomy material properties were either within the same range of compliance as the porcine myocardium or stiffer. At anatomically relevant thicknesses, stiffness values of printed Digital Anatomy samples corresponded to most of the chambers of the porcine heart (Figure 1).
Compliance Variability
Porcine myocardium showed considerable variability in compliance from chamber to chamber and within
each chamber (Figure 2). In contrast, the Digital Anatomy samples were highly consistent (Figure 3).
Elasticity
Elasticity was measured for each of the printed samples to determine each material’s flexural and tensile behavior. The moduli of the printed materials ranged from 0.262 to 0.536 MPa with Agilus being the least flexible, compared with the digital myocardial material blends. Furthermore, the standard deviation for each material type tested was small, providing a high degree of confidence the printed samples would behave in the same way every time (Table 2).
Puncture Testing
Both Digital Anatomy and porcine myocardium had similar failure mechanisms. Both saw an initial peak force as the first tough layer was punctured; endocardium for the tissue and the first Agilus layer for the Digital Anatomy samples.
Suture Testing
The sutures cut through the printed material more easily than porcine tissue. However, this is also given the specific suture setup used to prevent preliminary tearing of printed samples. If standard suture techniques were used it would’ve resulted in the printed material failing prior to testing. Regardless, the tissue and printed myocardium both showed delamination prior to failure.
Conclusion
Digital Anatomy 3D printed materials have great potential in fabricating patient-specific myocardium with accurate mechanical properties associated with gender, age, ethnicity, and other physiological and pathological characteristics. The results of this study suggest that the fabrication of patientspecific tissue-mimicking heart models with both geometrical and mechanical accuracy is possible with the Stratasys J750 Digital Anatomy printer, software and material. Specifically, the Digital Anatomy material shows promise in its ability to replicate porcine tissue compliance consistently with minimal variation. This is a major advantage given the wide variability of porcine compliance in samples tested from the same area of the heart.
When developing new devices and understanding their functionality, repeatability between samples and times of testing is very important to minimize confounding variables. The Digital Anatomy printed myocardium shows high repeatability in stiffness value within the same sample tested multiple times, as well as between samples. This presents a significant advantage to medical device manufacturers seeking bench testing models to produce reliable and consistent results with minimal variability. It therefore lends itself to applications in product development where repeatability and reliability are of paramount importance.
Future work will be directed at improving the suturing and cutting properties of the Digital Anatomy material blends to more closely match the compliance of native tissue. Stratasys will continue to collaborate with leading medical device companies, hospitals, and research institutions to compare the digital anatomy materials to native tissue and bone. The data received from these organizations will be used to perfect new anatomical applications that more closely match the biomechanical properties of human anatomy in healthy and diseased states. The goal is to ultimately eliminate or at least minimize the need for cadaver and animal models.
