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Filament Structure, 3D printing, Bone Repair Scaffolds
over time to make room for new bone tissue . Traditional salts (chloride and carbon) and some trace elements such as
[18]
scaffold fabrication techniques, such as solvent casting, silicon, zinc, and copper . Organic matter mainly refers
[27]
gas forming, membrane lamination, salt immersion, and to collagen (COL) fibers and calcium-binding protein
fiber bonding, have limitations [19,20] , including complex gels such as osteocalcin and osteophosphoprotein .
[28]
preparation processes, high costs, uncontrollable internal In view of the composition of bone tissue,
pore structure for scaffolds, incomplete matching of materials for 3D printed bone repair scaffolds mainly
shape to host bone defects, and inability to load cells for include bioceramics, polymers, cells, growth factors,
bioprinting, which are difficult to meet the actual needs and composites, with polymer materials being the most
of patients. According to ASTM standard F2792 , widely used (such as gelatin, COL, sodium hyaluronate,
[21]
ASTM classifies three-dimensional (3D) printing silk protein, polycaprolactone (PCL), polylactic acid
technologies into the binding jetting, directed energy (PLA), and polyethylene glycol) . The bioceramic
[29]
deposition, material extrusion, material jetting, powder materials used in ceramic scaffolds for bone repair
bed fusion and sheet 3D printing techniques, which mainly include calcium-phosphorus-based bioactive
are increasingly used for product design . Its layer- materials and calcium-silica-based bioactive materials.
[22]
by-layer manufacturing method can precisely regulate Calcium-phosphorus-based bioactive materials include
the complex geometric structure to make the processed HA, β-type calcium phosphate (β-TCP), and biphasic
product highly optimized, reduce the weight of the calcium phosphate (BCP), while calcium-silica-based
product at the same time, reduce material loss and reduce bioactive materials include bioactive glass, calcium
the cost of expenditure . 3D printing is also used for silicate, tricalcium silicate, magnesium yellow feldspar,
[23]
small production runs, such as model customization and and white calcium silicate. This section consolidates the
print-on-demand, and can streamline the supply process commonly used scaffold materials in the field of bone
through sub-station manufacturing . In the field of bone repair with examples of their material properties and
[24]
repair, 3D printing technology, which is simple to operate research progress (Table 1).
and has fast molding speed as well as good control, can
not only construct the complex shape matching the bone 2.1. Bioceramics
tissue defect, but also accurately regulate the internal Bioceramic materials are widely used in bone repair
pore structure, and it has become the first choice for the engineering because of their similarity to the inorganic
preparation of porous bone repair scaffolds [25,26] . composition of bone tissue. The common bioceramic
The development of bone tissue engineering materials mainly include HA, β-TCP, silicate, and
has resulted in different types of bone repair scaffold bioceramics. They have excellent osteoconductive
structures, materials, and properties to better serve properties, good bioactivity, biodegradability and strong
human needs through the unremitting efforts of a large compressive properties and have great potential for
number of researchers. The purpose of this review is to development in the treatment of bone defects .
[30]
summarize and review the current research progress of Calcium phosphate materials have significant
biodegradable extrudable bone repair scaffolds in terms osteoinductive ability due to the release of calcium and
of scaffold materials, filament structure, and scaffold phosphate ions, which contributes to a bone-like apatite
function. The filament structure of the stent, that is, the layer that can adsorb osteogenic proteins on the material
line composition inside the stent, is particularly important surface, with HA and tricalcium phosphate being the most
to the overall performance of the stent and its scope of widely used. HA is chemically similar to the minerals of
application. Therefore, this paper reviews the proposal, natural bone and is considered a substitute with high bone
design, performance, and evaluation of the scaffold repair potential . Damien et al. and Oonishi et al. [32,33]
[31]
in five major directions, including classical structure, found that HA scaffolds have better mechanical properties
bilayer structure, core-shell structure, hollow structure, as well as strong osteoinductive and osseointegration
and bionic structure of the biodegradable bone repair ability and are less prone to deformation through in vivo
scaffold, and in the end, the future development of the experiments . In contrast, HA prepared by hydrothermal
[34]
filament structure of the scaffold is prospected. liquid exchange method by Roy et al. , showed that
[35]
2. Materials HA has the defects of poor sintering properties and poor
biodegradability. Tricalcium phosphate, with its ability
Bone tissue is a kind of connective tissue composed of to bind well to hard tissues, has become another class of
a bone matrix and a variety of cells. The bone matrix calcium-phosphorus bioactive materials that have been
contains organic and inorganic substances, the inorganic widely studied and applied in the field of bone repair,
substances are mainly made of calcium and phosphorus generally in two forms: Low-temperature stable β-phase
in the form of hydroxyapatite (HA) crystals, compounds (β-TCP) and high-temperature stable α-phase (α-TCP) .
[34]
(sodium, potassium, magnesium, and fluoride) as well as Li et al. used the porous structure ceramic scaffold
[36]
44 International Journal of Bioprinting (2021)–Volume 7, Issue 4