Hydrogel optimisation for biofabrication considering shape stability/mechanical properties and cell response is challenging. One approach to tackle this issue is to combine different additive manufacturing techniques, e.g., hot-melt extruded thermoplastics together with bioplotted cell loaded hydrogels in a sequential plotting process. This method enables the fabrication of 3D constructs mechanically supported by the thermoplastic structure and biologically functionalised by the hydrogel phase. In this study, polycaprolactone (PCL) and polyethylene glycol (PEG) blend (PCL-PEG) together with alginate dialdehyde gelatine hydrogel (ADA-GEL) loaded with stromal cell line (ST2) were investigated. PCL-PEG blends were evaluated concerning plotting properties to fabricate 3D scaffolds, namely miscibility, wetting behaviour and in terms of cell response. Scaffolds were characterised considering pore size, porosity, strut width, degradation behaviour and mechanical stability. Blends showed improved hydrophilicity and cell response with PEG blending increasing the degradation and decreasing the mechanical properties of the scaffolds. Hybrid constructs with PCL-PEG blend and ADA-GEL were fabricated. Cell viability, distribution, morphology and interaction of cells with the support structure were analysed. Increased degradation of the thermoplastic support structure and proliferation of the cells not only in the hydrogel, but also on the thermoplastic phase, indicates the potential of this novel material combination for biofabricating 3D tissue engineering scaffolds.

Hydrogels are gaining interest as scaffolds for bone tissue regeneration due to ease of incorporation of cells and biological molecules such as enzymes. Mineralization of hydrogels, desirable for bone tissue regeneration applications, may be achieved enzymatically by incorporation of alkaline phosphatase (ALP). Additive manufacturing techniques such as bioplotting enable the layer-by-layer creation of three-dimensional hydrogel scaffolds with highly defined geometry and internal architecture. In this study, we present a novel method to produce macroporous hydrogel scaffolds in combination with cell-loaded capsule-containing struts by 3D bioplotting. This approach enables loading of the capsules and strut phases with different cells and/or bioactive substances and hence makes compartmentalization within a scaffold possible. 3D porous alginate scaffolds enriched with ALP and MG-63 osteoblast-like cells were produced by bioplotting struts of alginate which were loaded with pre-fabricated alginate capsules. Two combinations were compared, namely ALP in the struts and cells in the capsules and vice-versa. Both combinations were cytocompatible for cells and mineralization of scaffolds could be detected in both cases, according to an OsteoImage staining. ALP had no adverse effect on cytocompatibility and enhanced mitochondrial activity.