A hybrid additive manufacturing platform for bone scaffolds applications

bulk and surface composition gradients on scaffolds for tissue regeneration

The main result of the European project FAST (Functionally graded Additive Manufacturing scaffolds by hybrid manufacturing) was the coupling of the Plasma Jet to a 3D printer, thus creating a hybrid platform for additive manufacturing. Currently there is no technology capable of selectively generating surface functional gradients within a bone scaffold (porous structure made in 3D printing in bioresorbable polymers): this hybrid platform is able to promote cell adhesion, decreasing rejection and speeding up recovery times after implant surgery.

The 3D printing technology with dual material printhead combined with Nadir Plasma Jet to selectively functionalize the scaffold filaments during 3D printing, has allowed to combine two technologies in a single platform. Given its small size, the Plasma Jet can easily be housed next to the extrusion head of FFF printers.

  The use of argon to ignite the Plasma Jet was not only necessary for the ignition of the plasma in Dielectric Barrier Discharge configuration, but also provides an additional protective atmosphere for the precursor used during chemical functionalization, thus avoiding unwanted processes of oxidation, processes that can occur in air-fed atmospheric plasma devices. Argon is also used in the Nadir Plasma Jet as a carrier gas for the transport of precursor vapors. The interaction of the chemical precursor with the high-energy electrons of the plasma leads to the formation of radicals and the initiation of chemical reactions, in particular condensation and polymerization reactions. This generates a nanometric thin coating on all selected areas of the extruded polymer during 3D printing.

To obtain the desired chemical functionalization it is necessary to set the most conservative plasma parameters: the radio frequency of the Plasma Jet regulated in pulsed mode generates a safe plasma for the functional groups of the precursor. Thanks to the intuitive interface of the control unit, it is possible to vary the ON and OFF times of the plasma, in order to obtain a pulsed plasma with a high density of ions and electrons and at a low temperature, with a high deposition efficiency even on dielectric substrates, and at the same time allowing to maintain the chemical functionalities of the precursors.

The results of the study demonstrated that, thanks to a hybrid FFF/Plasma Jet 3D printing technology, it is possible to obtain compositional gradients, on 3D printed bone scaffolds to better mimic the tissues. Furthermore, the ability to increase the mechanical properties and to selectively improve cell adhesion within the bone scaffold has been demonstrated.

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