Page 143 - IJB-9-4

International Journal of Bioprinting 3D-printed scaffolds for osteochondral defects

DLP conventional printing is up to 50 μm, which is Despite their advantages of better mechanical
between MEW/ES and ME . The basic materials used properties, higher plasticity, controlled degradation rate,
[62]
in these techniques are compatible with many of the and availability of a wide range of sources, synthetic
above-mentioned materials, but usually require extensive scaffold materials are poorly biocompatible and less
modification . SLA and DLP printing technologies are hydrophilic and their degradation products may be toxic .
[67]
[63]
not as widely used in scaffold preparation as ME, probably Bioceramics such as bioglass, hydroxyapatite (HA), and
due to the high upfront investment and maintenance TCP have been common scaffold materials in bone tissue
costs of these systems. To date, SLA- and DLP-printed engineering because of their high mechanical strength, but
scaffolds have no porosity advantage (50%–65%) over they also have the disadvantage of brittleness.
other technologies . These techniques can be used to A combination of two or more materials is used to design
[50]
construct multilayered articular osteochondral scaffolds. the ideal osteochondral scaffold in order to overcome the
For example, Zhu et al. prepared a multilayered disadvantages of a single material. Composite scaffolds
[64]
osteochondral scaffold by combining poly(ethylene glycol) incorporate the advantages of each constituent material:
(PEG) material with natural bovine cartilage ECM using controlled degradation rate, good cytocompatibility and
the DLP technique. hydrophilicity, and suitable biomechanical strength.

Of various 3D printing solutions, ME is the most Natural biomaterials, including ECM, are enriched
commonly used due to its wide availability, material with favorable molecules for cells (e.g., GAGs, collagen,
versatility and low cost. Second, MEW and ES are mainly and GAGs-like polysaccharides), and therefore, these
used in the cartilage phase and their achievable scaffold materials can be incorporated into composite scaffolds to
thickness is limited. This so-called “limitation” makes it enhance their affinity for the host tissue . Inspired by the
[68]
suitable for the fabrication of thin and dense boundary collagen fiber structure and ECM composition gradients
structures, but its technical potential needs to be further in osteochondral tissue, Qiao et al. prepared a layered
[69]
developed. The delicate connection of CCZ to the adjacent scaffold composed of MSCs-laden GelMA hydrogel with
structures provides excellent mechanical properties of the zone-specific growth factor delivery and melt electro-
entire articular osteochondral unit. In order to achieve its written triblock polymer of poly (e-caprolactone) and poly
maximum bionic potential, the imitation of this connection (ethylene glycol) (PCEC) networks with depth-dependent
should also be a key direction to be considered. Therefore, fiber organization. It was found that the introduction of
3D printing technology with higher precision should be a PCEC fibers into GelMA hydrogels significantly improved
major priority in the future. the mechanical strength. Considering the osteochondral
anatomy and physiology and the properties and functions
3.2. Composition of various scaffold materials, the cartilage layer prefers
The materials used in osteochondral tissue engineering hydrogels derived from natural or synthetic polymers
scaffolds are mainly categorized into the following groups, (because their hydration properties and viscoelasticity
such as natural biomaterials, synthetic materials and are similar to natural ECM), reinforcing materials favor
bioceramics. Due to their composition and structure, the subchondral bone layer, such as bioceramics and hard
various types of osteochondral scaffolds have different polymers, and the combination of cartilage and bone
biological and mechanical properties. layer materials with a specific ratio is suitable for the
Natural biological scaffold materials have the advantages intermediate layer (osteochondral interface).
of excellent biocompatibility, high degradability, and
favorable cell attachment and proliferation for subsequent 3.3. Seed cells for the osteochondral tissue
recruitment and infiltration. However, they also have engineering
disadvantages, including excessive degradation rates, poor The seed cells are an important basis for osteochondral
mechanical properties, and limited sources . Collagen tissue engineering to achieve clinical translation.
[65]
is the major constituent of osteochondral ECM and its Currently, the most researched seed cells are various types
role is to maintain the structural integrity of ECM . of stem cells, including MSCs, cartilage stem/progenitor
[66]
Studies have shown that chondrocytes in 3D collagen gels cells, embryonic stem cells, skeletal stem cells, and induced
maintain their normal phenotype and that collagen also pluripotent stem cells.
plays a crucial part in tissue repair and wound healing. The Bone marrow-derived MSCs (BMSCs), which have
chemical structure of chitosan is similar to that of GAGs in a strong proliferative capacity, can easily differentiate
the cartilage ECM and its biomimetic structure is highly into chondrocytes and maintain their phenotype in vitro.
conducive to the morphogenesis, differentiation, and In addition, large numbers of cells can be obtained
proliferation of chondrocytes. from many different bone marrow sites, making them

Volume 9 Issue 4 (2023) 135 https://doi.org/10.18063/ijb.724