Material Overview for the Xorption TTA Cage & TTA-One
From permanent metal implants, to fully-resorbable
composites….
The proprietary bioabsorbable composite used for the Everost
Xorption TTA cage and TTA-One contains 30% biphasic calcium
phosphate dispersed in a bioabsorbable polymer matrix based
predominately on Poly(L,DL-lactide).
This composite formulation has been used in implantable
devices for over 7 years and has a proven biocompatibility track
record particularly in humans.
Material Degradation
The graph below depicts a typical trend curve for molecular weight vs. time and mass loss vs. time
for a semi-crystalline polymer. Also overlaid in the graph is the projected support curve over time.
Up until a critical point, the observed mass loss is relatively low, but increases as the material
becomes more friable.
EuroIntervention 2014;9:1271-1284
Poly(lactides) exhibit bulk degradation via hydrolysis of the ester group. The rate at which the
product degrades is governed by the level of crystallinity in the structure. Because the composite
formulation used in the Xorption TTA cage and TTA-One is amorphous and lacks an ordered
crystalline structure, a faster more uniform degradation profile would be expected. Preliminary
studies project a 12-15% reduction in molecular weight (determined through inherent viscosity)
between 0 and 6 weeks, a 31-32% reduction after 12 weeks, and an 88- 92% reduction after 48
weeks.
Products such as the Everost TTA-Tack and the Everost TTA Wing Plate, although semi-crystalline,
are processed in such a way that the level of crystallinity in the final product is low. As a result, it is
expected that they would exhibit a slightly slower degradation rate than the Xorption TTA cage and
TTA-One.
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Material Overview for the Xorption TTA Cage & TTA-One
Mechanical Performance
The load at failure for the Xorption TTA cage and TTA-One could not be determined due to limitations in
the testing equipment. However, it was observed that both products experienced compressive loads
greater than 1000 N even at 24 weeks aging under accelerated conditions without failure. This loading is
comparable to the mean load at failures determined in the study by Balligand et al.
Bioabsorption
The TTA and TTA-One cages degrade via bulk erosion. During this process hydrolysis of the ester groups
in the polymer chain causes a breakdown of the composite structure. This allows lower molecular
weight moieties to be removed from the system via metabolic pathways opening the structure to
further breakdown.
Mäder, Karsten. "RESOMER® - Biodegradable Polymers for Sutures, Medical Devices, Drug Delivery Systems and Tissue Engineering." SigmaAldrich. Sigma-Aldrich Co. LLC
Some breakdown moieties enter the Krebs cycle and are broken down into CO2 and H2O and expired
through the lungs. Other moieties may be excreted by the kidneys in urine or feces.
Biocompatibility
See biocompatibility report from Purac on PURASORB® Resorbable polymers.
Section 2.2 discusses the polymer degradation and resorption by the body.
Section 2.3 discusses biocompatibility of the materials
Section 4 outlines some of the current clinical applications of bioabsorbable materials
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Material Overview for the Xorption TTA Cage & TTA-One
Frequently Asked Questions
1) Is late stage inflammatory response a common problem with bioabsorbable polymers?
When considering a material for an implanted device, the location of the implant and the level of
vascularization at the implant site are critical. A rapid breakdown can lead to inflammation if the
material cannot be metabolized by the body at a fast enough rate. Factors such as polymer
synthesis, residual monomer content, and molecular weight all influence material quality,
performance, and degradation. If the properties of the material are tailored to the indication and
implant site correctly, then the risk of late stage inflammatory response is drastically reduced.
2) What is bulk degradation?
Bulk degradation occurs in two phases. During the first phase, water penetrates the device attacking
the chemical bonds in the amorphous regions of the structure. This causes a decrease in molecular
weight without significantly impacting the physical properties of the implant. It is not until the
water starts breaking down the crystalline regions that the integrity of the implant becomes
compromised. This leads to the second phase of degradation where the low molecular weight
moieties are metabolized by the body resulting in rapid mass loss and eventually, complete
bioabsorption of the implant.
3) What is the difference between an amorphous polymer and a crystalline polymer?
Thermoplastics are classified into two groups: amorphous polymers and semi-crystalline polymers.
Amorphous polymers lack any ordered groups in the molecular structure. Semi-crystalline
polymers, however, contain ordered regions that provide improved strength and rigidity.
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Material Overview for the Xorption TTA Cage & TTA-One
Suggested Reading
Chapter 1 provides a good overview of degradable polymers, particularly
polyesters, and their structure. It also defines some key terms that will be heard
often when working with polymeric materials.
Chapter 3, specifically the introductory section and section 3, provides an overview
on poly(lactides) and the mechanism by which they degrade.
Chapter 5 discusses the important considerations for processing bioabsorbables.
Middleton, John C., and Arthur J. Tipton. "Synthetic Biodegradable Polymers as Medical
Devices." Medical Plastics and Biomaterials 5.2 (1998)
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