Collagen composite inks for Aerosol Jet® printing in bone tissue engineering applications

Abstract

Aerosol Jet® printing (AJP) is an additive manufacturing technique based on the atomization of a liquid ink, followed by aerodynamic collimation of the aerosol, allowing for high-resolution printing (~20-50µm). This makes AJP an ideal candidate for the fabrication of scaffolds at a biologically relevant scale, such as collagen micro-structures for bone tissue engineering applications. In this work, collagen type I solutions were prepared, and hydroxyapatite was added at a biomimetic concentration of 6 v/v% to resemble the composition of bone tissue. Moreover, the potential of cellulose nanocrystals (CNCs) to improve the printing process was assessed. The inks were characterized for their rheology, and degradation of collagen due the aerosolization was characterized by SDS-PAGE. Furthermore, the in vitro biocompatibility of the inks was assessed using Live-Dead staining on MC3T3 cells, seeded on films prepared by neutralization, and drying of the inks. The collagen-based inks were successfully printed into 3D structures, such as hollow pillars using an Optomec AJ300. Cross-linking procedures still require further optimization though. In addition, from the SDS-PAGE results, some degradation was observed after 30 minutes of atomization, but intense α1(I) and α2(I) bands remained. The in vitro biocompatibility assessment suggests that the presence of CNCs could potentially induce cytotoxicity. The use of HAp and CNCs with collagen has shown promise for the production of 3D structures. However, additional work is needed towards the formulation of suitable ink compositions, which allow for 3D printing.