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International Journal of Bioprinting 3D bioprinting techniques & hydrogels materials

smooth tissue surface devoid of blood vessels, nerves, and Owing to these limitations, more novel and effective
lymphatics. In contrast, the subchondral bone layer is rich therapeutic approaches need to be developed. Tissue
in blood vessels and nerves, with a calcified hard texture engineering can generate functional substitutes resembling
that plays a crucial role in buffering mechanical stress. 8-10 natural tissues for restoring or replacing damaged tissues.
Thus, owing to the inherent differences between bone Additionally, it possesses the advantages of accessible
and cartilage, simultaneous regeneration of both tissues is materials, straightforward operation, and excellent
often challenging and requires spatially targeted delivery of biocompatibility, thereby becoming a promising therapeutic
different stimulus factors within the scaffold for sustained approach for clinical tissue defects. 28-30 Currently, there are
and responsive repair. 11,12 Currently, common surgical two principal approaches for repairing OCDs through
treatments for OCD include autologous chondrocyte tissue engineering. The first involves creating artificial
implantation (ACI), matrix-induced autologous cartilage structures that mimic the structural traits,
chondrocyte implantation (MACI), osteochondral mechanical strength, and biological functions of natural
autografts and allografts, microfracture and total articular cartilage tissues. And the second approach emphasizes
replacement. 13-18 Although these treatment methods are regenerative medicine by employing appropriate biological
widely used in clinical practice, there are still many defects materials as artificial extracellular matrices or loading
and deficiencies. The principle of ACI lies in restoring the with biological factors (cells or growth factors) to facilitate
integrity of cartilage lesions by inducing the formation of cell growth, proliferation, and differentiation at the defect
hyaline-like cartilage, and it has been clinically applied site. 31-34 Generally, to ensure the uniform distribution of
for more than 20 years. Nevertheless, there are still biological factors within the matrix, conventional tissue
19
drawbacks, such as the scarcity of chondrocyte sources, engineering is typically characterized by a homogeneous
the prolonged time for obtaining chondrocytes, the composition. 35,36 Nevertheless, given the significant
difficulty in immobilizing the chondrocyte solution, anisotropy of articular cartilage, it is widely acknowledged
20
and the poor efficacy for older individuals and patients that the field requires more effective strategies to capture the
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with a long duration of symptoms. Notably, ACI is spatial complexity of natural tissues and their subchondral
22
unable to repair the osteochondral interface and achieve bone interfaces. Another challenge in cartilage tissue
37
integrated osteochondral regeneration. MACI is an engineering lies in the fact that the mechanical properties
enhanced method of ACI, where a cell-loaded membrane of tissue-engineered cartilage tend to be relatively weak
is employed to evenly distribute chondrocytes and mitigate and are unable to withstand the high levels of compression
the risk of graft hypertrophy, demonstrating a superior and shear loads that occur in the joint after implantation.
35
therapeutic outcome and minor trauma as it can be Therefore, the fabrication of osteochondral engineering
applied via arthroscopic technology. 23,24 However, it still scaffolds requires flexible and high-precision machining.
does not fully meet the requirements for osteochondral
integrative repair. Osteochondral autografts and allografts 3D bioprinting, also known as additive manufacturing
are therapeutic strategies for direct cartilage repair, which (AM), is based on the digital model created through
immediately fills the defect with mature articular cartilage. computer-aided design. By employing various 3D printers
However, autografts are not only difficult to perform and computer-aided manufacturing, materials are
but may also cause complications at the donor site. accurately and rapidly accumulated layer by layer to obtain
Furthermore, challenges persist in restoring the surfaces of a genuine, physical 3D entity. The application of 3D printing
both the cartilage and bone to form a smooth, convex joint technology in bone and cartilage tissue engineering presents
surface. For allografts, challenges include limited tissue several advantages. Firstly, by leveraging patient-specific
25
supply, immune rejection, inadequate integration, low cell medical imaging data, such as computed tomography
viability due to graft storage, and the possibility of disease (CT) or magnetic resonance imaging (MRI) scans,
transmission. Microfractures are treated by drilling holes personalized scaffolds can be developed in accordance
26
in cartilage and subchondral bone areas to increase blood with individual requirements. Secondly, 3D printing
flow and bone marrow supply to the defect site. Recently, facilitates the fabrication of complex geometric structures,
there has been extensive research on the potential of particularly complex layered porous structures, which are
injecting stem cells or biomolecules into defect sites to challenging to achieve through traditional manufacturing
increase the efficacy of microfractures. However, it may approaches. 35,38,39 The precision of 3D printing makes
lead to the formation of less functional fibrocartilage. the fabricated scaffold closer to the structure of natural
27
Total articular replacement is considered the gold standard cartilage, which is more conducive to cartilage integration.
for various joint diseases but often requires more than one Thirdly, 3D printing exhibits flexibility and compatibility
revision for young people. For mildly damaged joints, joint with a variety of biocompatible materials, guaranteeing an
replacement is often too aggressive (Table 1). efficient manufacturing process for structures composed
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Volume 10 Issue 6 (2024) 68 doi: 10.36922/ijb.4472