Rheological and Biological Impact of Printable PCL‐Fibers as Reinforcing Fillers in Cell‐Laden Spider‐Silk Bio‐Inks

Abstract

The development of bio‐inks capable of being 3D‐printed into cell‐containing bio‐fabricates with sufficient shape fidelity is highly demanding. Structural integrity and favorable mechanical properties can be achieved by applying high polymer concentrations in hydrogels. Unfortunately, this often comes at the expense of cell performance since cells may become entrapped in the dense matrix. This drawback can be addressed by incorporating fibers as reinforcing fillers that strengthen the overall bio‐ink structure and provide a second hierarchical micro‐structure to which cells can adhere and align, resulting in enhanced cell activity. In this work, the potential impact of collagen‐coated short polycaprolactone‐fibers on cells after being printed in a hydrogel is systematically studied. The matrix is composed of eADF4(C16), a recombinant spider silk protein that is cytocompatible but non‐adhesive for cells. Consequently, the impact of fibers could be exclusively examined, excluding secondary effects induced by the matrix. Applying this model system, a significant impact of such fillers on rheology and cell behavior is observed. Strikingly, it could be shown that fibers reduce cell viability upon printing but subsequently promote cell performance in the printed construct, emphasizing the need to distinguish between in‐print and post‐print impact of fillers in bio‐inks.

Creation of Porous, Perfusable Microtubular Networks for Improved Cell Viability in Volumetric Hydrogels

“…As demonstrated, cells in a cast construct with perfusable channels indeed show improved cell viability and metabolic activity within the proximity of the channels. , Despite their demonstrated potential for vitalizing encapsulated cells, both strategies suffer from significant limitations. For example, many hydrogels used in the bioprinting of vascular channels lack the adequate mechanical strength and stability to support loads or tissue growth before channels inevitably collapse from material degradation. − Inclusion of other materials, such as polymeric fiber fragments, carbon nanotubes, or hydroxyapatite particles into hydrogels, can partially improve the mechanical stability and can be physically blended without involving cytotoxic solvents. − However, these additives may affect printability, and the degradation byproducts need to be considered for their cytocompatibility. In addition, only a few select materials (e.g., sugar) can be adopted for template-based channel formation without harming cells. − Solvents used for template dissolution can often damage cells or lead to high localized concentrations of template material byproducts.…”