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CTP Scaffolds Treated Bone Defects
1. Introduction treatment of multiple myeloma by inhibiting osteoclast
activity and pathological bone destruction through
To date, regeneration of long bone with critical-size the disruption of receptor activator for Nuclear factor
defects induced by steroid-induced osteonecrosis, tumor kappa B [NF-κB] ligand (RANKL)-induced NF-κB
resection, osteoporotic fractures, or accidental trauma signaling . It is also reported that CFZ could induce
[13]
is still challenging. Among various bone regeneration increased alkaline phosphatase activity and upregulated
therapies, autologous bone transplantation is recognized expression of the osteogenic transcription factors such as
as the gold standard [1,2] . However, its mass application is
severely restricted due to insufficient donor sources. In osterix, osteopontin, and osteocalcin (OCN) through Wnt
the past decade, scaffold-based tissue engineering has pathway by activating the β-catenin/T-cell factor (TCF)
pathway
.
[14-16]
gained increasing attention in treating bone defects [4-7] . In The Wnt pathway is a complex signaling system
addition to the required biocompatibility, biodegradability involving the mutual regulation of multiple factors, and
and appropriate mechanical properties, capability of
promoting osteogenesis and angiogenesis should also be can interact with other signaling pathways and various
imparted to the bone tissue engineering scaffolds . cytokines. It is known that β-catenin protein in the Wnt
[3]
Calcium phosphate has been widely used for the pathway enters the nucleus and binds to TCF/lymphoid
producing artificial protheses with a dense structure due to enhancer factor transcription factors to regulate the
its high compositional similarity to bone apatite and high expression of genes related to cell proliferation, migration
[17]
bioactivity . Animal studies and clinical experiments and differentiation, which are related to bone formation .
[4]
have shown that calcium phosphates have excellent The Wnt pathway not only indirectly inhibits osteoclasts
repair effects on bone regeneration [5-7] . To improve the through osteoprotection in osteoblasts but can also directly
repair capability of calcium phosphates, porous scaffolds regulate the function of osteoclasts by activating its own
made of calcium phosphate/biodegradable polyester pathway [18,19] . Activation of the Wnt/β-catenin signaling
composites which are structurally similar to native is not only related to aging or directed differentiation
[20]
cancellous bone tissue have been developed . The porous of mesenchymal stem cells into osteoblasts , but also
[8]
structure of scaffolds facilitates cell growth, migration, involved in the development, maturation, and function of
[21]
and transportation of nutrients and metabolites . To osteoblasts .
[9]
further improve the osteogenic capability of bone tissue To elucidate the combination effect of CFZ and 3D
engineering scaffolds, growth factors and drugs related to printed bony environment on the bone regeneration in
osteogenesis and/or angiogenesis can be incorporated . long bone with defect and the underlying mechanism, in
[10]
Additive manufacturing has gained increasing this study, a porous β-tricalcium phosphate/poly lactic-
attention in making bone tissue engineering scaffolds as co-glycolic acid (TCP/PLGA) scaffold incorporated
it is advantageous in producing scaffolds with customized with CFZ was fabricated through cryogenic 3D printing.
shape, pore size, porosity, and interconnectivity . The morphological and physical properties of scaffolds
[11]
Cryogenic 3D printing is a new type of additive and release behavior of CFZ were investigated. The
manufacturing technology that uses polymeric water- positive effects of drug CFZ/TCP/PLGA scaffolds on
in-oil emulsions as printing inks to deposit three- the osteogenesis and angiogenesis and the inhibitory
dimensional (3D) patterns below 0°C . The emulsion effect of CFZ on osteoclasts were studied in vivo.
[12]
inks immediately solidify when they contact the cryogenic Significantly improved new bone formation and enhanced
substrate, allowing a layer-by-layer material deposition. vascularization were observed in the regenerated tissue
After cryogenic 3D printing, as-printed 3D patterns in radial defects of rabbits. This study suggests that the
are lyophilized to remove solvents to obtain stabilized employment of 3D printed porous bone tissue engineering
scaffolds with a hierarchical structure . scaffolds incorporated with CFZ can effectively treat long
[10]
The success of scaffold-based bone tissue bone defects by activating the Wnt/β-catenin signaling.
engineering not only relies on the employment of
advanced scaffolds but also depends on the use of newly 2. Materials and methods
discovered functional drugs. However, creation of new 2.1. Scaffold fabrication
drug and its clinical approval cost a long time and a lot of
money. Therefore, producing advanced scaffolds loaded The formulation of printing inks and the fabrication
with repositioned conventional drugs with effective process of the 3D printed bone tissue engineering scaffolds
osteogenesis capability, whose biosafety has been verified (designated as “cytidine triphosphate [CTP]”) are shown
clinically, has gained increasing attention in the treatment in Figure 1. The CTP material was prepared by in situ
of critical-sized defect in long bone. Carfilzomib (CFZ) incorporation of CFZ in TCP/PLGA (TP) scaffolds using
is an approved clinical proteasome inhibitor with a cryogenic 3D printing based on TCP/PLGA (TP) material.
much fewer side effects, replacing bortezomib in the First, 3 g of PLGA (Shandong Medical Device Company,

100 International Journal of Bioprinting (2021)–Volume 7, Issue 4