Additive manufacturing approaches have the potential to address a number of major challenges in the field of meniscus tissue engineering (TE), in particular the development of anatomically defined grafts with a spatial architecture and composition mimetic of the native tissue. Here, we report a novel method to engineer organized soft tissues, with a collagen architecture and mechanical behaviour similar to native meniscus. We compared the capacity of two direct material writing techniques, specifically fused deposition modelling (FDM) and melt electrowriting (MEW), to generate guiding structures for cells that are deposited using inkjet bioprinting. We hypothesised that by fabricating polymeric scaffolds with specific architectures it is possible to control collagen fibre organization and the mechanical behaviour of the engineered fibrocartilaginous tissue, thereby better recapitulating the native meniscal tissue
Materials and methods
FDM and MEW were employed to fabricate polycaprolactone (PCL) scaffolds with various defined geometric architectures. Furthermore, large volume MEW scaffolds with micro-fibrous features were fabricated to replicate the complex wedge-shaped macro-architecture of the human meniscus. A custom alginate based bioink was developed and inkjet bioprinting was used for the dispensing of cell-laden bioinks into scaffolds. After inkjetting, the cells were cultured in presence of TGF-β3 to induce chondrogenesis. Mechanical testing was conducted to determine the compressive and tensile properties of the engineered tissues.
First, we assessed the suitability of the developed bioink for cartilaginous TE applications, finding that its rapid degradation allows cells to condense and begin the process of generating new tissue while exhibiting high levels of cell viability. The multicellular aggregates which formed within the defined boundaries provided by the PCL fibres generate a neo-tissue where the organization is determined by the architecture of the scaffold. Both FDM and MEW fibrous architectures facilitated the formation of anisotropic collagen networks resembling those of the native meniscus. However, PCL scaffolds fabricated using FDM displayed mechanical properties that are unsuitable for meniscus replacement, as they are too stiff in compression. By using MEW as a fabrication technique, the mechanical strength of the engineered tissues after 5 weeks of in vitro culture was similar to the native tissue. After demonstrating the benefit of using MEW to create scaffolds for meniscus regeneration, we fabricated larger (5 mm height) scaffolds replicating the shape of the meniscus. The pore architecture of these large scaffolds remained open even at the highest sections, enabling the bioprinting of cells and facilitating tissue growth throughout the entire scaled-up construct.
In the present work, we have successfully developed a biofabrication approach that allows precise control over the orientation of the deposited collagen tissue. By using MEW as a fabrication technology we could better mimic not only the collagen network architecture but also engineer tissues with similar anisotropic mechanical behaviour. We have also succeeded in the fabrication of large volume MEW scaffolds of up to 5 mm height with well-defined micro-fibrous and macro-architectural features. This work demonstrates the potential of integrating MEW and bioprinting to engineer structurally organised soft tissues.