Abstract
3D bioprinting is a promising approach for the repair of cartilage tissue after damage due to injury or disease; however, the design of 3D printed scaffolds has been limited by the availability of bioinks with requisite printability, cytocompatibility, and bioactivity. To address this, we developed an approach termed in situ crosslinking that permits the printing of non-viscous, photocrosslinkable bioinks via the direct-curing of the bioink with light through a photopermeable capillary prior to deposition. Using a norbornene-modified hyaluronic acid (NorHA) macromer as a representative bioink and our understanding of thiol-ene curing kinetics with visible light, we varied the printing parameters (e.g., capillary length, flow rate, light intensity) to identify printing conditions that were optimal for the ink. The printing process was cytocompatible, with high cell viability and homogenous distribution of mesenchymal stromal cells (MSCs) observed throughout printed constructs. Over 56 days of culture in chondrogenic media, printed constructs increased in compressive moduli, biochemical content (i.e., sulfated glycosaminoglycans, collagen), and histological staining of matrix associated with cartilage tissue. This generalizable printing approach may be used towards the repair of focal defects in articular cartilage or broadly towards widespread biomedical applications across a range of photocrosslinkable bioinks that can now be printed.
Highlights
Cartilage is a load-bearing connective tissue found in articulating joints that permits movement between bones with minimal friction
After elucidating each of these respective absorption spectra, the molar extinction coefficients ( ) of ink components were determined using Beer-Lambert Law (Eq (1)), which states that the absorption of a species of interest is proportional to the pathlength of light (W), the concentration of the species (c), and the degree to which the species absorbs that specific wavelength of light ( )
To engineer precise tissues for clinical medicine, the development of scaffolds with complex, hierarchical structures are of great interest, with patient-specific defect geometries42. 3D bioprinting is a promising approach towards this, including for the repair of cartilage[3,43]; the design of 3D bioprinted scaffolds has been limited to only a small number of bioinks with the requisite properties for printability
Summary
Cartilage is a load-bearing connective tissue found in articulating joints that permits movement between bones with minimal friction. Since native cartilage does not possess any regenerative capacity, surgical interventions are often required to mitigate the progression of cartilage degeneration in afflicted patients Procedures such as microfracture aim to recruit cells (e.g., mesenchymal stromal cells, MSCs) from the underlying bone marrow, while cell-based therapies such as matrix-assisted autologous chondrocyte implantation (MACI) focus on scaffolds to elicit tissue formation from donor cells[2]. Jammed microgels have recently been used for printing, as many materials can be formed into microgels and jammed to meet printing requirements, including with encapsulated cells[30] While each of these approaches expands upon the number of candidate bioinks available, the need for additives or post-processing steps could impede or compromise the design of target cellular microenvironments
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