Selective laser melting (SLM), a method used in the nuclear, space, and racing industries, allows the creation of customized titanium alloy scaffolds with highly defined external shape and internal structure using rapid prototyping as supporting external structures within which bone tissue can grow. Human osteoblasts were cultured on SLM-produced Ti6Al4V mesh scaffolds to demonstrate biocompatibility using scanning electron microscopy (SEM), fluorescence microscopy after cell vitality staining, and common biocompatibility tests (lactate dihydrogenase (LDH), 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), 5-bromo-2-deoxyuridine (BrdU), and water soluble tetrazolium (WST)). Cell occlusion of pores of different widths (0.45-1.2 mm) was evaluated. Scaffolds were tested for resistance to compressive force. SEM investigations showed osteoblasts with well-spread morphology and multiple contact points. Cell vitality staining and biocompatibility tests confirmed osteoblast vitality and proliferation on the scaffolds. Pore overgrowth increased during 6 weeks' culture at pore widths of 0.45 and 0.5 mm, and in the course of 3 weeks for pore widths of 0.55, 0.6, and 0.7 mm. No pore occlusion was observed on pores of width 0.9-1.2 mm. Porosity and maximum compressive load at failure increased and decreased with increasing pore width, respectively. In summary, the scaffolds are biocompatible, and pore width influences pore overgrowth, resistance to compressive force, and porosity.

Hydroxyapatite (HAP) and tricalcium phosphate (TCP) are two very common ceramic materials for bone replacement. However, in general HAP and TCP scaffolds are not tailored to the exact dimensions of the defect site and are mainly used as granules or beads. Some scaffolds are available as ordinary blocks, but cannot be customized for individual perfect fit. Using computer-assisted 3D printing, an emerging rapid prototyping technique, individual three-dimensional ceramic scaffolds can be built up from TCP or HAP powder layer by layer with subsequent sintering. These scaffolds have precise dimensions and highly defined and regular internal characteristics such as pore size. External shape and internal characteristics such as pore size can be fabricated using Computer Assisted Design (CAD) based on individual patient data. Thus, these scaffolds could be designed as perfect fit replacements to reconstruct the patient's skeleton. Before their use as bone replacement materials in vivo, in vitro testing of these scaffolds is necessary. In this study, the behavior of human osteoblasts on HAP and TCP scaffolds was investigated. The commonly used bone replacement material BioOss(R) served as control. Biocompatibility was assessed by scanning electron microscopy (SEM), fluorescence microscopy after staining for cell vitality with fluorescin diacetate (FDA) and propidium iodide (PI) and the MTT, LDH, and WST biocompatibility tests. Both versions were colonised by human osteoblasts, however more cells were seen on HAP scaffolds than TCP scaffolds. Cell vitality staining and MTT, LDH, and WST tests showed superior biocompatibility of HAP scaffolds to BioOss, while BioOss was more compatible than TCP. Further experiments are necessary to determine biocompatibility in vivo. Future modifications of 3D printed scaffolds offer advantageous features for Tissue Engineering. The integration of channels could allow for vascular and nerve ingrowth into the scaffold. Also the complex shapes of convex and concave articulating joint surfaces maybe realized with these rapid prototyping techniques.

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