In clinical orthopedics suitable materials that induce and restore biological functions together with the right mechanical properties are particularly needed for the regeneration of musculoskeletal tissue. An innovative solution to answer this need is represented by tissue engineering. This technique could overcome the limits of traditional approaches involving the use of homologous, autologous or allogenetic tissue (e.g. tissue availability, immune rejection and pathogen transfer). In this field, rapid prototyping techniques are emerging as the most promising tool to realize three-dimensional tissue constructs with highly complex geometries.

Based on CAD/CAM technology, rapid prototyping allows development of patient-specific 3D scaffolds from digital data obtained with latest generation imaging tools. These structures can be realized in different materials, tailoring their mechanical properties and architectural features. Most rapid prototyping techniques allow the creation of acellular 3D scaffolds, which must be subsequently seeded with cells. Conversely, 3D bioprinting can deposit bio-ink containing molecules/cells, providing desired spatial distribution of growth factors/cells within the scaffold. The need of printable materials suitable for processing with inkjet, dispensing, or laser-print technologies, forces the use of matrices within a specific range of viscosity. However, these materials have low mechanical features. To overcome this problem and to obtain a final construct with good mechanical properties, bioprinting tissue fabrication can rely on the alternate deposition of thermoplastic materials and cell-laden hydrogels. Since mechanical performance is determined not only by the material properties but also by the geometry (microarchitecture) of the structure, printing parameters can be modified to obtain the desired features.

The new 3D platform available at Rizzoli Orthopaedic Institute, consisting of a Computer Tomography (GE Medical Systems, Milano, Italia) and a 3D Bio-Printer (RegenHU, Villaz-St-Pierre, Switzerland) is used to address the above-mentioned issues. Preliminary results showed that it is possible to modify the microarchitecture of the printed structures adjusting their apparent density and stiffness in the range of the trabecular bone tissue. Additionally, it has been proven that the calcium phosphate based paste, used as bioink, allows cell attachment and proliferation. Therefore, the platform allows to print scaffolds with open and interconnected porosities and suitable mechanical properties. They can be filled with different components such as cells or soluble growth factors at specific locations.