Introduction: Regeneration of damaged cartilage is still challenging due to the low self-healing capacity of this tissue. Special requirements for chondral scaffolds are a three-dimensional structure with high porosity for cell colonization of chondral cells, biocompatibility, biodegradability and particularly high elasticity to withstand the mechanical forces in the joint. The use of flock technology, a common process of modern textile industry, allows to manufacture scaffolds for tissue engineering meeting these requirements[1],[2]. However, it has not yet been possible to use biodegradable biomaterials with this technique. Chitosan, a biodegradable and biocompatible biopolymer is a promising material for this approach. Due to its versatile processing options and low immunogenicity it is commonly used in tissue engineering applications. In the present study a mechanically stable flock scaffold fully consisting of chitosan was developed and the chondrogenic differentiation of human mesenchymal stroma cells (hMSC) within the scaffold was analyzed.
Materials and Methods: Wet-spun chitosan fibers with diameters between 30 and 50 µm were cut to a length of 1 to 3 mm and flocked vertically on a viscous chitosan solution, acting as flock substrate and adhesive (Fig. 1). Compressive strength and elastic behavior of the final scaffolds were analyzed. For evaluation of cytocompatibility hMSC were cultivated in the scaffolds. Cell adhesion and morphology were analyzed by scanning electron microscopy and confocal laser scanning microscopy. Cell viability was monitored by lactate dehydrogenase (LDH) activity measurement. Furthermore the flock scaffolds were seeded with hMSC embedded in different hydrogels and cultivated under chondrogenic stimulation. Gene expression of chondrogenic markers was analyzed using RT-PCR, collagen II secretion was quantified by ELISA and the amount of sulfated glycosaminoglycans was determined colorimetrically.
Results and Discussion: The chitosan fibers were shown to form a homogeneous flock structure with adjustable porosity, fiber length and compressive strength. Chitosan-based flocked scaffolds supported adhesion and proliferation of hMSC and showed no cytotoxic effects. The number of cells cultivated directly on the fibers increased continuously during the cultivation period and microscopic evaluation revealed the attachment of the cells to the fibers. Chondrogenically differentiated hMSC embedded within hydrogels into the pores of the flock scaffolds showed gene expression of chondrogenic markers as well as production of typical extracellular matrix.
Conclusion: This is the first demonstration of a scaffold made of a fully degradable material and manufactured by electrostatic flocking. Substrate and fibers are composed of chitosan, which has been widely used in tissue engineering applications. Based on the obtained results, flocked chitosan fibers are a promising biomaterial for cartilage tissue engineering.
We thank the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) for financial support (grant number GE 1133/16-1)
References:
[1] E. Steck, H. Bertram, A. Walther, K. Brohm, B. Mrozik, M. Rathmann, C. Merle, M. Gelinsky, W. Richter; Tissue Eng Part A 16, 3697-3707 (2010)
[2] A. Walther, B. Hoyer, A. Springer, B. Mrozik, T. Hanke, C. Cherif, W. Pompe, M. Gelinsky; Materials 5, 540-557 (2012)