Introduction: Innovative, organ-like tissue models are expected to make an important contribution as in-vitro test systems for drug development in the future. Thanks to the latest technological advances in bioprinting, ever more complex constructs can be generated. However, the spatial orientation of functional cells in such hydrogel-based tissue models remains one hurdle to be overcome.
Objectives: Production, modification, and characterisation of electrospun polycaprolactone (PCL) fibre fragments for cell adhesion in hydrogel-based bioinks.
Materials & methods: In this study, PCL fibremats were produced via electrospinning and their morphology and fibre diameter were examined using scanning electron microscopy. The resulting fibremats were then coated with chitosan using 1) a one-step coating or 2) a layer-by-layer (LbL) technique with hyaluronic acid and chitosan. Sucessful chitosan deposition was analysed by fluorescence microscopy and quartz crystal microbalance (QCM). Subsequently, cells were seeded on the biofunctionalized scaffolds and cell adhesion, proliferation and morphology were analysed using a metabolic assay and fluorescence microscopy.
PCL fragments were generated using a motor driven razorblade, filtered and dried by lyophilization. Morphology and length of the fragments were analysed by light microscopy. Finally, cells and fibre fragments were integrated into an agarose-based bioink with the help of a positive displacement pipette.
Results: Bead-free PCL fibre mats were successfully produced with virtually no molten junctions and fibre diameters of approx. 2.5 µm. A reproducible one-step coating and LbL coating consisting of 5 bilayers of hyaluronic acid and chitosan could be observed. Cells seeded on PCL mats showed good adhesion and proliferation and the usual morphology on all fibre surfaces. With the help of the motor-driven razor blade, PCL fibre fragments with an average length of less than 100 µm could be generated and evenly mixed into the bioink, allowing cell adhesion.            
Conclusion: Electrospun PCL fibre mats are a well-suited carrier substrate for the adhesion and proliferation of liver cells. The fibre fragments can be mixed homogeneously into bioinks and can thus enable cells to orientate themselves in bioprinted constructs.

We thank the BMBF for financial support (13XP5177, 16LW0360) and all project partners, especially Hot Screen GmbH for providing cells and Heppe Medical Chitosan GmbH for providing chitosan.