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International Journal of Bioprinting 3D bioprinting for musculoskeletal system

3.5. IVD to electrospinning, 3D printing allows customization of
Located between adjacent vertebrae, IVD consists of three the scaffold without additional assembly steps. Bhunia
elements: nucleus pulposus (NP), annulus fibrosus (AF), et al. fabricated an engineered AF scaffold based on silk
and cartilaginous endplate. It is a complex fibrocartilaginous fibroin (SF) and carrageenan by 3D printing technology.
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structure that absorbs and transfers mechanical load from The scaffold simulated the multilamellar structure of the
various directions and allows flexible movement of the native AF and showed good mechanical properties. In
spine. IVD is prone to degradation and has poor self- addition, the scaffold supported cell growth and promoted
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healing ability due to its avascularity. IVD degeneration the production of AF-specific ECM. The accuracy of
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(IVDD) is a pathological process characterized by disorder printing is an important factor affecting the structure
of ECM structure, loss of proteoglycan, herniation of NP, and function of 3D-printed scaffolds. Liu et al. used the
and loss of disc height. The etiology of IVDD is complex electrohydrodynamic 3D printing technique to prepare
and involves many pathogenic factors, such as trauma, an AF scaffold with high resolution for IVD regeneration
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aging, spinal deformities, and genetic factors. As the (Figure 5). After finite element analysis, the design of the
most common cause of low back pain, IVDD results in a structure was optimized before printing. The implanted
large number of patients with disability. Every year, more scaffold maintained the height of the disc and promoted
than 500 million people worldwide suffer from low back the partial recovery of the biomechanical function of IVD.
pain, imposing tremendous socioeconomic burden on Hu et al. developed a bioink composed of gellan gum
humans . The current treatment for IVDD includes and PEGDA for the bioprinting of IVD in combination
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conservative treatments and surgical treatments. The former with poly(lactic acid) (PLA). The bioprinted construct
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includes steroid injections, nonsteroidal anti-inflammatory exhibited excellent mechanical properties and supported
drugs, and physiotherapy, and the latter includes spinal high cell viability. Although bioprinted tissue constructs
fusion, total IVD replacement, and discectomy. These have shown promising results in musculoskeletal tissue
interventions can relieve symptoms; however, none of engineering, 3D bioprinting of IVD is still rudimentary.
them has been successful in reversing IVDD progression
and restoring disc function. Moreover, some treatments, 4. 3D bioprinting for disease modeling
such as spinal fusion, can alter the biomechanics of the For a long time, preclinical drug screening mainly
spine, leading to an increased risk of degeneration of relies on the use of animal models. As an alternative to
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adjacent discs. Hence, novel intervention measures that human disease research, animal models offer a controlled
can effectively slow down the degeneration process and experimental system, which maintains the overall
regenerate degenerated IVD are urgently needed. complexity of cells, tissues, and other factors within
Several studies have attempted to use tissue organ systems. However, biomedical results of animal
engineering for IVD regeneration but have encountered models often do not fully represent the actual status of
many challenges. 172-174 Among them, the preparation of human diseases due to the vast genetic, phenotypic, and
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engineered scaffolds is a tricky problem because of the physiological differences between animals and humans.
complex microstructure of IVD, especially the AF. Accurate Even by means of genetically engineered animal models, it
simulation of biomimetic AF anatomical structure is is difficult to simulate the critical biological characteristics
the key to the function restoration of IVD. This relies on of diseased cells and their microenvironment, diseased
advanced scaffold preparation methods. Electrospinning tissues or organs, or their physiology in patients. Moreover,
is a widely used technique for the preparation of fibers, ethical concerns must be taken into account when carrying
which can be several microns or even nanometers in out animal experiments. These limitations impede the
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diameter. Electrospun nanofibers are considered excellent translation of results from animal experiments into human
engineered materials due to their good biocompatibility, treatments. Another approach for drug validation is 2D
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controllable mechanical properties, and similar culture of human cells that provides valuable insights into
characteristics to natural ECM. To mimic the hydrophilic pathological mechanisms in a more controlled manner. This
environment and hierarchical structure of native AF, Yang approach has the advantages of ease of use, low cost, and
et al. used electrospinning technology to prepare a scaffold potentially high throughput, thus enabling the testing of
consisting of PCL, poly(lactic-co-glycolic acid) (PLGA) multiple conditions and treatments in a short time. Despite
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and type I collagen. In vivo experiments showed that the these advantages, 2D cultured cells are obviously deficient
scaffold achieved good integration with the surrounding in complex 3D structures and interactions found in vivo,
host tissues and promoted the recovery of disc function. In which are essential for maintaining proper functional
recent years, 3D printing technology has risen in popularity phenotypes in the musculoskeletal system. Shortcomings
and has been used in IVD tissue engineering. In contrast in existing drug screening strategies have led to a growing

Volume 10 Issue 1 (2024) 91 https://doi.org/10.36922/ijb.1037