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International Journal of Bioprinting Biomimetic osteochondral scaffold

4. Discussion porous structures, the desired mechanical strength, and the
sustained biological activity of GFs and even living cells.
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The regeneration of osteochondral tissue is an In this study, we used water-in-DCM emulsions, containing
intricately complex process, where the physiological BMP-2 (or FGF-18), P(DLLA-TMC) (or PLGA), or β-TCP
microenvironments vary significantly at different regions powders, as printing inks with subsequent lyophilization
and repair phases. 20,41 Hyaline cartilage, a hydrogel-like via cryogenic 3D printing to develop osteochondral
elastic osteochondral tissue, consists of rounded hyaline scaffolds with heterogeneous mechanical features and
chondrocytes and cartilage ECM rich in hyaluronic
acid, COL II, and chondroitin sulfate. Meanwhile, the desirable microporous structures for in situ spatial delivery
subchondral tissue is loose but mechanically strong, of BMP-2/FGF-18. DCM served as a solvent for polyester
consisting of trabecula made of COL I and bone apatite, blood dissolution and a temporary bonding adhesive between
vessels, fusiform osteoblasts, osteoclasts, and osteocytes. layers. Upon freeze-drying, DCM removal enabled the
20
This study aims to develop an engineered osteochondral convenient fabrication of integrated scaffolds with closely
scaffold with biomimetic structures, a spatiotemporally bonded subchondral, interface, and cartilage layers.
controlled delivery of osteogenic/chondrogenic GFs, and Notably, our osteochondral scaffolds could maintain
an efficient loading of rBMSCs with varied organizational high levels of GF biological activity, efficiently inducing
morphologies. This approach ensures a match of the osteogenic and chondrogenic differentiation of rBMSCs.
release timing and location of osteogenic/chondrogenic There are currently numerous studies focusing on
GFs during the natural osteochondral tissue regeneration either bone repair or cartilage regeneration. 50,51 However,
process and stimulates the formation of osteochondral the construction of multi-layer scaffolds for subchondral
tissues with a heterogeneous structure containing and cartilage integration to promote osteochondral repair
differentiated cells with appropriate phenotypes. 42,43 remains challenging. 6,42 In our previous study, to achieve
Biomanufacturing techniques are increasingly osteochondral regeneration, we utilized a double-layer
employed to fabricate biomimetic scaffolds, as they can scaffold, which exhibited osteogenic and chondrogenic
endow scaffolds with controlled structural, biological, properties in the subchondral and cartilage layers,
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and even cellular features that affect cell behavior and respectively. However, the absence of an interface layer
achieve desirable outcomes. 44,45 In this study, given the resulted in the spreading of GFs from the subchondral
spatiotemporal presence of GFs and regional loading of layer to the cartilage layer and vice versa, thereby
rBMSCs with varied organizational morphologies in the disrupting their respective differentiation processes.
osteochondral scaffolds, an engineered osteochondral Therefore, in this study, we fabricated a tri-phasic
tissue having regionally distributed osteoblasts and hyaline osteochondral scaffold, comprising the subchondral,
chondrocytes was developed. Compared to traditional interface, and cartilage layers, to facilitate osteochondral
fabrication techniques (e.g., molding, electrospinning, and repair. Given that subchondral tissue is a mechanically
salt leaching), 3D printing is advantageous in fabricating strong calcified tissue with a porous structure, BMP-
porous scaffolds with controlled and tailored pore sizes, 2/β-TCP/PLGA composites were selected as the matrix
thereby facilitating the efficient exchange of oxygen, to print the subchondral layer due to their excellent
nutrients, and cellular metabolic wastes to support cell/ biocompatibility, mechanical property, osteoconductivity,
tissue growth. 46,47 However, traditional 3D printing and osteoinductivity. 53,54 To segregate the subchondral
technologies face challenges in generating scaffolds with layer from the cartilage layer, densely arranged β-TCP/
desirable microenvironments, which are critical for PLGA struts were utilized as the calcified non-porous
inducing favorable cellular responses. For instance, in interface layer. Meanwhile, P(DLLA-TMC), a thermo-
fused deposition modeling (FDM)-based 3D printing, the responsive shape-memory polyester that could become
high temperatures during the printing process can lead soft and elastic at 37°C, was used as the matrix to print
to the deactivation of biologically active biomolecules, the grid-like frame in the cartilage layer, providing the
such as GFs loaded in bioinks. In contrast, digital light cartilage layer with suitable elastic modulus, which was
46
processing (DLP)-based 3D printing with either toxic comparable to the native cartilage tissue. Besides, the
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photocrosslinkable resins or biocompatible hydrogels P(DLLA-TMC) frame was filled with GelMA hydrogel to
being used as the printing inks, the inherent cytotoxicity or provide the 3D-printed cartilage layer with a non-porous
insufficient mechanical strength further restricts its use in hydrogel-like feature and further serve as a barrier to slow
making biocompatible scaffolds with desirable mechanical down the release rate of FGF-18. BMP-2 and FGF-18 are
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properties. Recently, cryogenic 3D printing has been osteogenic and chondrogenic growth factors, respectively,
48
widely employed to fabricate bone tissue engineering commonly employed in osteochondral tissue engineering.
scaffolds as it can fabricate scaffolds with hierarchically Compared to the control medium (DMEM with 10% FBS

Volume 10 Issue 5 (2024) 211 doi: 10.36922/ijb.3229