Page 449 - IJB-10-2

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

in this study. Another limitation was that our antibacterial transferring some stress from polymer to ceramic and
testing concentrated on S. epidermidis and E. coli, which leveraging on the ceramic’s higher strength. Conversely,
33
might not encompass the full spectrum of potentially discussions on strength reduction highlight concerns about
relevant pathogens. Furthermore, although we assessed the limited interfacial interaction between the polymer and
cell proliferation and osteogenic activity using mouse ceramic. It is crucial to acknowledge that factors such as
34
preosteoblasts, these cells show only weak osteoblastic cell volume content, microstructure, chemical composition,
activity, and the interactions will best be determined in ceramic properties, and the bonding between PEEK and
studies that place the implants into bone defects. ceramic play pivotal roles in simultaneously enhancing
29
Previously, Peck et al. investigated the mechanical mechanical strength. In our study, Si N -PEEK cages showed
28
3
4
performance of cervical cages that were submitted to the higher torsional strength than PEEK cages. Regarding the
Food and Drug Administration (FDA), and they included designs, solid cages achieved the highest torsional strength,
and porous cages were stronger than porous cages with
unique materials other than metal and PEEK. Using these windows. In a similar manner, Fogel et al. investigated the
35
data as benchmarks, our results showed that all the designs design influence on mechanical performance of spinal cages
with both materials (Si N -PEEK and PEEK) achieved and indicated higher stiffness for solid design.
3
4
more than 5th percentile stiffness under all three forces. In
addition, cages were tested above 50th percentile of ultimate Previous studies investigated Si N 4 19,20,36 and Si N -
4
3
3
compression and compression shear strength defined by PEEK 37-39 for their ability to enhance the biological activities
28
Peck et al. Furthermore, the cervical cages examined in of PEEK-based implants—including maturation of
this study surpassed 104% of the ultimate load capacity in osteoblasts and antimicrobial activity. 20,39 Gorth et al. found
compression and exhibited over 3 times the shear strength decreased biofilm formation as well as fewer live bacteria on
compared to machined cages previously reported in the both the as-fired (AFSN) and polished Si N compared with
3
4
literature. While the primary goal of incorporating Si N 4 PEEK and titanium surfaces. In a companion in vivo study,
20
17
3
into PEEK was to enhance its antibacterial properties, it Webster et al. observed improved osseointegration for
19
was notable that this process resulted in an increased Si N samples relative to PEEK and Ti6Al4V implanted into
3
4
torsional strength of the cages. rat calvaria wound sites contaminated with S. epidermidis.
Bock et al. showed similar results in vitro using a human
36
Contrastingly, the stiffness of solid cages was found to
be lower than that of porous designs under compression plasma-based inoculum with S. epidermidis and E. coli
exposed to a range of surface-modified Si N materials.
and shear. This unexpected result may be attributed to Pezzotti et al. found that incorporating 15 vol.% coarse
4
3
37
varying loading mechanisms, which necessitate testing in (approx. 50–250 µm) Si N into PEEK led to improved
compression, shear, and torsion, as mandated by ASTM proliferation and mineralization of SaOS2 cells in addition
3
4
standards for cages. The current study focused on the to a 1-log reduction in adherent S. epidermidis relative
22
worst-case scenario, emphasizing the critical role of layer to monolithic PEEK following a 24-h exposure in vitro.
10
bonding in interpreting results. The lower stiffness observed Marin et al. observed increased alkaline phosphatase
38
in solid cages under compression and shear forces was activity and mineralization of KUSA-A1 mesenchymal
unforeseen. The 3D printer used in the study employed an stem cells exposed to the same coarse, 15 vol.% Si N -
additional cooling setting, partially activated to facilitate PEEK composite relative to monolithic PEEK, but cell
4
3
inter-layer cooling for subsequent layers. Excessive proliferation was not improved. It was hypothesized that
cooling, however, could compromise layer adhesion. The the large regions of PEEK between the coarse silicon nitride
porous sections, having less material and shorter cooling particles were responsible for this lack of improvement
times, may have exhibited better adherence under similar since Si N is thought to act at short distances, very near
cooling conditions than their solid counterparts. This its surface, through the products of hydrolysis reactions.
3
4
phenomenon is less pronounced in torsion testing, where This observation, along with 3D printing requirements,
the unique loading conditions involve layer compression up led to the modification of the powder feedstock used for
to 500 N, followed by layer twisting, favoring solid layers. the composite in this study to obtain a submicron size
This underscores the significance of carefully controlling distribution. Hu et al. demonstrated the potential of Si N -
39
printing conditions when working with PEEK implants. 3 4
PEEK in biomedical applications as it exhibited osteogenic
There exist differing opinions regarding the incorporation and antibacterial activities. Our findings clearly showed that
of ceramics into PEEK. Some studies suggest an increase 29,30 a 3D-printed Si N -PEEK composite was able to achieve a
4
3
while others have demonstrated a decrease in strength. 31,32 significant reduction in numbers of adherent bacteria, with
Research indicating increased strength implies the ability of slightly greater activity against gram-negative bacteria. This
polymer–ceramic matrix to endure higher loads, effectively latter finding is of importance as these microorganisms are
Volume 10 Issue 2 (2024) 441 doi: 10.36922/ijb.2124