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BiomechanicalTests Confirm
the Potential for
3D Printing
SyntheticMyocardium
With the Stratasys
J750 Digital
Anatomy Printer2Biomechanical Tests Confirm the Potentialfor 3D Printing Synthetic Myocardium
With the Stratasys J750 Digital Anatomy PrinterIntroduction
Cardiac applications of 3D printed patient-specificmodels (PSMs) include surgical training, complex
procedural planning, and the creation or refinementof cardiac devices. As structural heart interventions
become increasingly complex, the ability toeffectively model patient-specific geometry, as wellas the interaction of devices within and aroundthat geometry, becomes even more valuable toadvance 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 thesimulation of the biomechanical properties ofhuman tissue.
Objective
To replicate the physiological response of native
cardiac tissue including vessel walls, chamber
walls, and valve leaflets, Stratasys studied
the mechanical behavior of each structure incollaboration with medical device manufacturers,
world-class research institutions, hospitals andmedical personnel. Findings from these studies
were used to develop software and materials
to simulate those properties. Scientists andengineers from Medtronic, a global leader inmedical device manufacturing, conducted anindependent third-party comparison of the Digital
Anatomy myocardium materials to porcine cardiac
tissue. The following summarizes the findings andpresents implications for future work in material
development.
Methods
The mechanical properties of porcine myocardium
were compared to those from a wide spectrum of
3D printed myocardium material blends (Table 1).
Porcine myocardium was chosen as the baseline
for comparison because of its similarity to humantissue, availability, and the precedent for its use in
cardiac device preclinical testing. All samples wereprinted on the Stratasys J750™ Digital Anatomy™
3D printer.

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Table 1 - Digital Anatomy Myocardium Material Properties
Material

Biomechanical Property

Description

Myocardium 1

Highly Contractile

Softest infill wrapped in 0.4 mm Agilus™*

Myocardium 2

Moderately Stiff

Second softest infill wrapped in 0.4 mm Agilus

Myocardium 3

Stiffened

Second stiffest infill wrapped in 0.4 mm Agilus

Myocardium 4

Very stiff

Stiffest infill wrapped in 0.4 mm Agilus

Myocardium 5

Extremely Stiff

Softest infill wrapped in 0.6 mm Agilus*Agilus is a soft, flexible PolyJet 3D printing material.

3Key Findings

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
Figure 15: Comparison between porcine myocardium and printed myocardium using a small pin and five millimeters ofsamples corresponded to most of the chambers of the porcine heart (Figure 1).
displacement. The sample size used for porcine myocardium is included on the key. All the printed materials used asample size of six.

Figurebetweenthicknesses,
porcine myocardium
andofprinted
myocardium
a smallpin and ten
Figure 116:
- AtComparison
anatomically relevant
stiffness values
printed Digital
Anatomyusing
samplescorresponded
to most of thechambers of theporcine heart. The sample size used for porcine myocardium is included on the key. All the printed
millimetersof displacement.
materials used a sample size of six.

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4bioRxiv preprint first posted online Oct. 31, 2019; doi: http://dx.doi.org/10.1101/825794. The copyright holder for this preprint(whichwas not peer-reviewed)
is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.
Compliance
Variability
It is made available under a CC-BY 4.0 International license.

Porcine myocardium showed considerable variability in compliance from chamber to chamber and withineach chamber (Figure 2). In contrast, the Digital Anatomy samples were highly consistent (Figure 3).

bioRxiv preprint first posted online Oct. 31, 2019; doi: http://dx.doi.org/10.1101/825794. The copyright holder for this preprint(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.
It is made available under a CC-BY 4.0 International license.

Figure 2 - The porcine tissue had significant variability between samples.

Figure 11: Average slope values and their confidence intervals for two levels of displacement for porcine myocardium from theright atrium, left atrium, right ventricle, left ventricle, and ventricular septum using a small pin.

Large Pin: Slope of Load vs. Extension in Printed Discs
95% CI for the Mean

Slope (N/mm)

3.0SIZE
12mm
2mm
7mm

2.5
2.0
1.5
1.0SIZEWhite Paper

TYPEm m mm m mm m mm 2m 7mm 2m 7mm m 7m
121212 2YOM

1
M0toO
Y4MOY

512m m mm 2m 7 m
YOM

12m m mm 2m 7 m

1Mm5m

Figure 3 - Digital Anatomy printed materials showed very little variability.

5toOY10m

412m m mm 2m 7 m
OYM

5m

Figure14: Stiffness
valuesat two displacement
usingthea large
pin. Three printed digital anatomy materials were tested at
Individual
standarddeviations
to levels
calculateintervals.
Figure12: Averagevaluesareandusedtheirconfidence
intervals
for two levels of displacement for porcine myocardium from thethreeclinically
relevantslope
thicknesses.

right atrium, left atrium, right ventricle, left ventricle, and ventricular septum using a large pin.

Comparisons Between Printed Materials and Porcine Tissue5Elasticity

Puncture Testing

Elasticity was measured for each of the printed
samples to determine each material’s flexuraland tensile behavior. The moduli of the printed
materials ranged from 0.262 to 0.536 MPa with
Agilus being the least flexible, compared with thedigital myocardial material blends. Furthermore, thestandard 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).

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.

Material

Modulus (N/m2)

The sutures cut through the printed material moreeasily 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.

Agilus

0.536 ± 0.009Conclusion

Myocardium A

0.262 ± 0.004

Myocardium 1

0.294 ± 0.003

Myocardium 20.310 ± 0.003

Myocardium 30.327 ± 0.005

Myocardium 40.342 ± 0.007

Myocardium B

0.334 ± 0.010

Table 2 - Analogue of Young’s Modulus Values
for Printed Materials

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Suture Testing

Digital Anatomy 3D printed materials have great
potential in fabricating patient-specific myocardiumwith accurate mechanical properties associatedwith gender, age, ethnicity, and other physiologicaland pathological characteristics. The results ofthis study suggest that the fabrication of patientspecific tissue-mimicking heart models with bothgeometrical 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 toreplicate porcine tissue compliance consistently
with minimal variation. This is a major advantage
given the wide variability of porcine compliance insamples 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 Anatomyprinted myocardium shows high repeatability instiffness 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 toproduce reliable and consistent results with minimalvariability. It therefore lends itself to applicationsin product development where repeatability andreliability are of paramount importance.

6Table 3 - Summary of Printed Myocardium
Comparison to Porcine Tissue
Biomechanical Testing Demonstrated Various
Degrees of Success
Similar compliance to real tissue
Similar failure modes to real tissue
High repeatability of results
Ability to target stiffness values
Much closer to real tissue than other currently available 3D
printing materials

Opportunities for Improvement
Increase toughness to accommodate realistic suturing
Reduce stickiness to facilitate accurate cutting and suturing

Future work will be directed at improving thesuturing and cutting properties of the Digital
Anatomy material blends to more closely matchthe compliance of native tissue. Stratasys willcontinue to collaborate with leading medical devicecompanies, hospitals, and research institutions
to compare the digital anatomy materials tonative tissue and bone. The data received fromthese organizations will be used to perfect new
anatomical applications that more closely matchthe biomechanical properties of human anatomy
in healthy and diseased states. The goal is toultimately eliminate or at least minimize the needfor cadaver and animal models.

View the complete study findings at the following
link: “PolyJet 3D printing of tissue-mimicking
materials: how well can 3D printed synthetic
myocardium replicate mechanical properties oforganic myocardium?”

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