Page 181 - IJB-10-4

International Journal of Bioprinting Effects of structure on the interbody cage

1. Introduction mechanical and biological properties differ greatly from
the actual bones, which are prone to stress-shielding
The prevalence of spinal degenerative illnesses, such as disc phenomenon. The pores can be modified to adjust the
herniation, spinal stenosis, and vertebral body slippage, elastic modulus for improving the mechanical match
has rapidly increased in recent years, and the disease onset between the cage and the surrounding bone tissues and
is becoming common among the younger populations. to provide a larger surface area for cell adhesion. The
1,2
The gold-standard surgical procedure for the treatment designed interconnecting channels can transfer nutrients
of lumbar and cervical spine disorders is spinal interbody and excrete metabolic wastes, provide a suitable growth
fusion, through which a fusion of the upper and lower environment for cell growth and proliferation and bone
cones is performed on the vertebra where the lesion occurs reconstruction, and further enhance the bonding strength
by restoring the height of the intervertebral space and the of the cage and the human bones to effectively promote
physiological curvature by means of an autogenous bone spinal fusion. 30-33
graft, an allogeneic bone graft, or an interbody fusion cage
between the upper and the lower diseased vertebral bodies Three-dimensional (3D) printing technology is a multi-
to amalgamate them into a single unit. 3-6 purpose additive manufacturing technology. 3D printing
in spinal surgery is mainly utilized for surgical assistance,
Interbody fusion cages are available in metallic or tissue engineering, creating personalized implants, etc. 34-36
non-metallic classes, with titanium alloy and poly-ether- In terms of advantages, 3D-printed spinal interbody fusion
ether-ketone (PEEK) materials being the most common cages are superior to traditional cages. Capitalizing upon
ingredients. 7-11 However, non-biodegradable cages are digitalization, precision, and controllability, macro-meso-
not resorbable after implantation and become permanent integrated production of numerous materials and multi-
foreign entities in the body, increasing the likelihood of level structures for replicating natural bone qualities can
long-term complications. Polycaprolactone (PCL) is a be accomplished. It is possible to adjust the pore size, pore
12
promising polymer material for bone tissue engineering shape, porosity, and interpore penetration features of the
with strong biocompatibility and degradation qualities, porous cage. In addition, by combining individual 3D
37
and is thus extensively utilized for bone tissue repair. To computed tomography (CT) data, the interbody fusion
overcome the limitations of a single material and improve cage can be customized for the patient, and precisely
the bioactivity and biocompatibility of implants, as well matched with the upper and lower endplates to accurately
as their mechanical properties, a growing number of restore the vertebral space and meet individualized needs.
studies have fortified polymer materials with bioactive Han et al. designed a cage with an outer frame and triple-
particles such as β-tricalcium phosphate (β-TCP) 13-17 and beam structure, and prepared samples with different PCL/
hydroxyapatite (HA). 18-26 The biological properties of β-TCP ratios by using 3D printing technology. In vitro
15
PCL and HA, such as cell attachment, proliferation, and degradation and cellular experiments demonstrated that
osteogenic activity, have been shown to be favorable in all the cages conformed to the mechanical properties of
these studies. It should be emphasized that most of the human cancellous bone while maintaining their structural
present research on PCL/HA composites has been done integrity. Egan et al. designed a variety of beam-based cubic
on basic cylindrical or square tissue-engineered scaffolds cell topologies and found that the modulus of elasticity all
for various studies, and has not taken into consideration decreased with an increase in porosity. Suitable for spinal
38
alterations in the shape and structure of the interbody fusion, a spinal interbody fusion cage with 50% porosity
fusion cage employed in spinal fusion. and a pore size of 600 μm was fabricated using PolyJet
The structural characteristics of the spinal interbody printing, with a stiffness of up to 5.6 kN/mm.
fusion cage have a substantial impact on spinal fusion In summary, there has been extensive research on
efficiency and surgical time. Because the vertebral body orthopedic implants, especially regarding composite
morphology and upper and lower endplates are irregular, materials. Probably due to preparation constraints and
the impact of bone fusion will be hampered if the design other limitations, studies related to meso-structural
of the interbody fusion cage does not fit with the form features remain scarce, and most of them had only
and size of the intervertebral space and the upper and attempted tissue-engineering simple scaffolds, which
lower endplates. Aside from the macroscopic shape and are seldom applied to spinal fusion. Given the previous
27
structure, the meso-structure of the cage has a considerable research results, the present study focuses on using PCL,
influence on its mechanical qualities, degradation rate, with the addition of HA as a functional filler, to fabricate
and fusion efficiency, among other things. 28,29 The most porous and degradable spinal interbody fusion cages by
commonly used spinal interbody fusion cages in the means of polymer melt differential 3D printing technology.
clinic are mostly solid or box-type instruments, whose The influence of the 3D structural features of the cage on

Volume 10 Issue 4 (2024) 173 doi: 10.36922/ijb.1996