Arthroscopic Airbrush-Assisted Cell Spraying for Cartilage Repair: Design, Development, and Characterization of Custom-Made Arthroscopic Spray Nozzles

Introduction: Airbrush-assisted cell spraying would facilitate fully arthroscopic filling of cartilage defects, thereby providing a minimally invasive procedure for cartilage repair. This study provides the development and characterization of custom-made spray nozzles that could serve as a foundation for the development of a BioAirbrush, a platform technology for the arthroscopic application of (cell laden) hydrogels. Materials and Methods: Custom-made spray nozzles were designed and produced with 3D printing technology. A commercially available spraying system was used for comparison. Sprays were characterized based on spray angle, cone width, droplet size, velocity, and density. This was performed with conventional and high-speed imaging. Furthermore, cell survival of chondrocytes and mesenchymal stromal cells, as well as the chondrogenic capacity of chondrocytes after spraying were evaluated. Results: Changing nozzle design from internal to external mixing significantly increased cell survival after spraying. Custom-made spray nozzles provide larger droplets compared to the current commercially available technology, potentially improving cell survival. Sufficient mixing of two gel components was confirmed for the custom-made nozzles. Overall, custom-made nozzles improved cell survival after spraying, without significantly affecting the chondrogenic capacity of the cells. Conclusions: This study provides a platform for the development of a BioAirbrush for spray-assisted cell implantations in arthroscopic cartilage repair procedures. Evaluation of the fundamental characteristics of a spray as well as a study of cell survival after spraying have further expanded the knowledge regarding cell spraying for cartilage repair. Nozzle design and air pressure characteristics are essential parameters to consider for the clinical implementation of spray-assisted cell implantations.