Page 302 - IJB-10-5

International Journal of Bioprinting Proteins-loaded 3D-printed PEEK cage

vertebrae, typically in the disc space, to restore disc height activity and long-term release of BMP2 is a key issue when
and facilitate fusion. Currently, most interbody fusion used in spinal fusion.
devices used in clinical practice are made of titanium alloy Substance P (SP) is a neuropeptide belonging to the
(Ti) or polyetheretherketone (PEEK). 8,9 tachykinin family, originally isolated from extracts of
Polyetheretherketone (PEEK) is a high-performance intestinal tissues. It has a sequence composed of a chain
23
polymer that has found various applications in the medical of 11 amino acid residues: Arg-Pro-Lys-Pro-Gln-Gln-
field, including bone repair. Unlike other bone repair Phe-Phe-Gly-Leu-Met-NH . SP was first discovered in
24
2
materials, PEEK has mechanical properties similar to the 1931 and is widely distributed throughout the peripheral
human bone, which helps minimize stress shielding and and central nervous systems, where it functions mainly
bone resorption caused by a high modulus of elasticity. as a pain signaling transmitter. Meanwhile, SP acts
25
10
Moreover, PEEK features good biocompatibility, as a chemoattractant and activator for macrophages,
radiolucency, and corrosion resistance, making it highly lymphocytes, neutrophils, and eosinophils. The role
26
suitable for widespread use in orthopedic and spinal of SP in inflammation and skeletal system diseases has
implants. 11,12 PEEK has several advantageous properties been extensively debated. Some research has indicated
for bone repair applications, but it also has some that SP produces a variety of proinflammatory effects by
inadequacies and challenges that need to be considered. binding and activating the NK-1 receptor (NK-1R) on
These challenges include processing difficulties, its bioinert target cells. Conversely, some researchers suggest that
27
nature, and weak osteointegration capabilities. 13,14 Due to supplementing MSCs with SP increases the secretion of
its thermoplastic nature, it is difficult to process PEEK into paracrine/angiogenic factors, such as VEGF, SDF-1a, and
complex shapes. Therefore, 3D printing technology is an PDGF-BB, in vitro. It is believed that SP can restore the
28
appropriate method for achieving precise and consistent cellular potential of senescent stem cells by modulating
manufacturing, especially for the production of intricate the generation of paracrine factors from MSCs, potentially
implants. Although the bioinert property of PEEK is enhancing MSC-mediated tissue repair. Additionally,
advantageous for reducing inflammatory responses, it studies have demonstrated that SP can recruit endogenous
may restrict its capacity to actively regulate immune MSCs to facilitate bone healing. 29,30
response and promote bone regeneration. It has been To prepare a novel intervertebral fusion device, we
15
observed that using pure PEEK for interbody fusion initially scanned and performed a 3D reconstruction of
without autograft increases the occurrence of lumbar rabbit intervertebral discs. Thereafter, we fabricated the
isthmic spondylolisthesis. 16
device via FDM. As displayed in Figure 1, sulfonation
Fused deposition modeling (FDM) is a material treatment was applied to create a network of porous
extrusion-based 3D printing process that is widely adopted structures on the surface, enhancing its fusion effect.
for fabricating high-performance polymer components This increases surface roughness and creates a reservoir
with complex geometries, particularly for clinical for BMP2. The resulting structure has the potential for
applications. PEEK filament is heated to its melting point improved bone repair. To achieve long-term release of
17
within the nozzle of the 3D printer and subsequently BMP2, gelatin (Gel) and chitosan (Chi) multilayer films
extruded layer-by-layer (LBL) to fabricate the desired were coated via LBL self-assembly. SP was grafted onto
structure. The mechanical properties of 3D-printed the outermost Chi layer through a Schiff base reaction.
PEEK can be influenced by various parameters, including Upon implantation of the modified PEEK, SP is released
heating temperature (extrusion temperature and ambient first, attracting more MSCs to the implant. Subsequently,
temperature), filling rate, and construction direction. 18,19 BMP2 is slowly released to promote osteogenic

Bone morphogenetic protein 2 (BMP2) is a protein differentiation of MSCs and enhance bone repair. In vitro
that belongs to the transforming growth factor-β (TGF-β) and in vivo experiments were conducted to evaluate the
superfamily. It plays a crucial role in bone development, fusion effect.
regeneration, and repair by inducing bone formation. 2. Materials and methods
BMP2 promotes the differentiation of mesenchymal stem
cells (MSCs) into osteoblasts, which are responsible for 2.1. Materials
producing bone matrix and initiating the mineralization Medical grade PEEK powder was provided by Beijing YUNS
process. 20,21 This process is crucial for the development Technology Co., Ltd. (China). BMP2 was purchased from
of new bone tissue. BMP2 has been highly effective in Zhong Ke Wu Yuan Biotechnology Co., Ltd. (China). SP was
promoting spinal fusion by enhancing bone growth purchased from Aladdin Industrial Co. (China). Chi (with
between vertebrae, thereby stabilizing the spine and aldehyde groups) and Gel were purchased from ZiKER
accelerating the fusion process. Maintaining the biological Biotechnology Co., Ltd. (China). Alkaline phosphatase
22
Volume 10 Issue 5 (2024) 294 doi: 10.36922/ijb.3574