Page 440 - IJB-10-2

International Journal of Bioprinting 3D-printed silicon nitride-PEEK implants

the most common cages, which are endowed with PEEK’s How 3D-printed Si N -PEEK composites affect the in vitro
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strength, elastic modulus comparable to that of the bone, cell response for osseointegration?
biocompatibility, and radiolucency. 10,11
2. Methods
Earlier investigations have affirmed the robust
mechanical strength of three-dimensional (3D)-printed 2.1. Si N -PEEK cages and 3D printing
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PEEK in different implant applications. Subsequent Cervical spinal cages utilized in this study were
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studies have explored ways to enhance PEEK’s bioactivity initially designed using Solidworks (2021, Dassault
by adding bioactive fillers into PEEK to allow the Systèmes, France) (see Figure S1 in Supplementary
utilization of novel materials in 3D printing technology File). Subsequently, porous sections were designed
without compromising inherent strengths of PEEK. This and incorporated using nTopology (2021, Dassault
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pragmatic approach seeks to optimize PEEK for implants, Systèmes, France) with pore size ranging between 700
aiming for a balanced performance that integrates strong and 800 microns. Cages were created using fused filament
mechanical properties with improved bioactivity. These fabrication (FFF) technology by a third-generation medical
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efforts contribute to the material’s adaptability across 3D printer (Kumovis R1, Munich, Germany) (Figure 1;
diverse medical applications. 15 Table S1 in Supplementary File). The PEEK and Si N -
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PEEK filaments (1.75 mm) used in 3D printing of cervical
However, enhancing cellular attraction on implant cages were produced by Orthoplastics (Lancashire, UK).
surfaces inherently increases the susceptibility to PEEK resin was provided by Solvay (Zeniva , Brussels,
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bacterial adhesion. Consequently, the imperative Belgium), and 15% volume submicron sintered β-Si N
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consideration of incorporating antimicrobial features powder (Flex-SN, SINTX Technologies, Salt Lake City, UT,
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into implant surfaces is crucial, especially when fostering USA) was compounded (Foster Corp., Putnam, CT, USA)
osseointegration. 1,16 Improved osteoblast adhesion with the PEEK resin to produce the composite resin used
and maturation have been achieved with additively for the Si N -PEEK filament. The cages were printed in
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manufactured solid and mesoporous PEEK materials for the upright position (Figure 1) to demonstrate the worst-
spinal cage applications 17,18 —currently, there are no cages case scenario, emphasizing the weakest layer adhesion for
that exhibit antibacterial properties. Moreover, there is a mechanical testing.
continuing unmet clinical need for biomaterials employed
in spinal cages that promote osseointegration, prevent 2.2. Mechanical testing
bacterial growth, withstand in vivo loading, and facilitate
efficient medical imaging—factors that are crucial for the 2.2.1. Compression and compression shear
Tests were conducted on an Instron 5567 system (Instron,
performance of the implant.
Norwood, MA) equipped with calibrated load and
Among spinal cages, the ceramic silicon nitride (Si N ), displacement sensors, with a load cell capacity of 30 kN
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also known as as-fired-silicon-nitride (AFSN), has shown for both compression and compression shear tests. A strain
very few infections in the clinical arena. In vitro, Si N rate of 25 mm/min was chosen as per ASTM F2077,
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shows decreased bacterial colonization compared to and load–displacement curves were plotted using the
other commonly used materials and supports osteoblast data (Figure S2 in Supplementary File). Stiffness values
maturation and mineralization. Si N is radiolucent were calculated from the curves using a custom script in
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and exhibits longevity, but like all ceramic materials, it MATLAB 2021b, using the recommendations in ASTM
exhibits high elastic modulus, raising concerns about F2077 as a guide.
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possible stress shielding and brittle fracture in cases
where the device experiences significant non-compressive 2.2.2. Torsion
loading. To overcome these concerns, we explored the Prior to and after mechanical testing, each cage underwent
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use of PEEK/Si N composites. We hypothesize that this imaging using a digital microscope (VHX-7000, Keyence).
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composite material will possess the osseointegrative and The experiments were performed utilizing an Instron 8874
antimicrobial properties of Si N while maintaining the system (Instron, Norwood, MA) fitted with calibrated load
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mechanical properties and ductility of PEEK. Accordingly, and displacement sensors, with a load cell capacity of 100
we assessed the potential suitability of composite Si N - N∙m for torque tests. Torsion tests were carried out at 60º/
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PEEK materials for fabricating 3D-printed cervical cages. min, as per the ASTM 2077 recommendations, with a
Specifically, we sought to address the following questions: (i) preloading force of 500 N applied to the cages (Figure S3
Will 3D-printed Si N -PEEK cervical cages have the in Supplementary File).
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strength of conventional cages? (ii) Will 3D-printed Si N - Torque–angle curves were plotted from the data.
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PEEK composites exhibit antimicrobial properties? (3) Stiffness, yield moment, and ultimate moment values
Volume 10 Issue 2 (2024) 432 doi: 10.36922/ijb.2124