Articular cartilage facilitates the frictionless movement of synovial joints, however, due to its avascular and aneural nature, it has limited ability to self-repair. Current treatments for cartilage defects elicit variable results – an issue that the field of tissue engineering has aimed to address; however, the inability to mirror the complexity of native tissue with current biomaterials has hindered progress 1, 2. The advent of 3D-printing has provided a potential solution. 3D-printed (3DP) scaffolds, fabricated using biomaterials native to articular cartilage, can be designed to mimic native articular cartilage. These biomaterial-based printable inks can also be functionalised with cells, bioactive factors and/or gene therapeutics to form biomimetic ‘bioinks’, capable of repairing cartilage 3.
The aim of this study is to develop a novel 3DP scaffold composed of biomaterials native to human articular cartilage, such as collagen and hyaluronic acid, which can also be incorporated with mesenchymal stem cells (MSCs) and/or therapeutic biomolecules to promote regeneration of the native tissue.
Materials and methods:
To this end, 3.5% neutralised collagen type I was mixed in a 1:1 ratio with methacrylated hyaluronic acid (MeHA) at concentrations of 0.5-3% to formulate four distinct bioinks. The printability of each bioink was first assessed, and three formulations were carried forward to 3D print 10mm x 2mm circular mesh scaffolds. The mechanical and physiochemical properties of the scaffolds were then determined. Two suitable formulations were selected and incorporated with rat MSCs, and the cell viability of the MSCs within 3DP cell-laden scaffolds was determined over 7 days. An optimal bioink formulation was then selected and incorporated with rat MSCs at three respective cell densities. The production of articular cartilage matrix components within these cell-laden 3DP scaffolds was assessed following 21 days culture.
Results and discussion:
Three bioink formulations were found to have desirable 3DP properties and were carried forward for further analysis. Subsequent studies showed no significant difference in the mechanical properties or macro-pore size of scaffolds 3DP with each bioink. However, 3DP scaffolds with a higher concentration of MeHA did have a higher mass swelling ratio. 3DP scaffolds containing the lowest MeHA concentration were excluded from subsequent studies as they could not withstand physical manipulation.
Cell viability studies with the remaining two bioink formulations showed that 3DP scaffolds containing the highest MeHA concentration facilitated greater levels of cell proliferation. Subsequently, this optimal bioink formulation was shown to facilitate deposition of articular cartilage-specific matrix components in 3DP scaffolds in a cell density-dependent manner. Ongoing work includes improving the mechanical properties of the 3DP scaffold by co-printing with a polymer, and incorporation of therapeutic chondrogenic nanoparticles to enhance the chondrogenic potential of the bioink.
A biomimetic collagen and hyaluronic acid-based bioink with favourable 3D-printing properties was successfully developed. Scaffolds printed using this bioink facilitated proliferation of MSCs and deposition of new articular cartilage matrix.
1Moroni (et al.), Nat. Rev. Mater. 3:21-37, 2018.
2Raftery (et al), Biomaterials 216: 119277, 2019.
3Gonzalez-Fernandez (et al.), J. Control. Release 10:301, 2019.
Funding: ReCAP: ERC Advanced Grant number 788753"