BARBARA LEUKERS, HULYA GULKAN, STEPHAN H. IRSEN, STEFAN MILZ, CARSTEN TILLE, MATTHIAS SCHIEKER, HERMANN SEITZ
Research Center Caesar, Ludwig-Erhard-Allee 2, 53175 Bonn
Experimental Surgery and Regenerative Medicine, Department of Surgery—Downtown, UniversityofMunich, Nussbaumstrasse20, 80336 Munchen
AO Research Institute, Clavadelerstrasse, 7270 Davos, Switzerland
Nowadays, there is a significant need for synthetic bone replacement materials used in bone tissue engineering (BTE). Rapid prototyping and especially 3D printing is a suitable technique to create custom implants based on medical data sets. 3D printing allows to fabricate scaffolds based on Hydroxyapatite with complex internal structures and high resolution. To determine the in vitro behaviour of cells cultivated on the scaffolds, we designed a special test-part. MC3T3-E1 cells were seeded on the scaffolds and cultivated under static and dynamic setups. Histological evaluation was carried out to characterise the cell ingrowth. In summary, the dynamic cultivation method lead to a stronger population compared to the static cultivation method. The cells proliferated deep into the structure forming close contact to Hydroxyapatite granules.
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Synthetic bone replacement materials based on Cal- ciumphosphates are widely used in clinically routine . A synthetic scaffold for bone tissue engineering requires an inner structure with interconnecting pores. Pore sizes with diameters above 300μm are recom- mended to promote good vascularisation and attach- ment of bone cells to guide their growth into all three dimensions . The use of rapid prototyping (RP) al- lows the production of scaffolds with defined and re- producible internal structures directly from computer data . Furthermore, the outer shape of the scaffold can be designed by taking anatomical information of the patient’s target defect (e.g. CT scan, MRI images) to ob- tain a custom-tailored implant. We use the RP process 3D printing, developed at the Massachusetts Institute of Technology (MIT) . The main advantage of this tech- nique is, that an implant can be manufactured straight from a 3D data set in one step without using an addi- tional mold. We use Hydroxyapatite (HA) granulates to fabricate porous ceramic structures with designed inter- nal architecture. HA is a promising bone replacement material because of its stoichiometric similarity to the inorganic part of natural bone. The fabrication process itself  as well as studies about various HA granulates for 3D printing were objectives of earlier studies and will be published elsewhere .
The matrices generated by 3D printing can be used for bone tissue engineering using patient’s cells seeded onto the scaffolds. The scaffolds serve as three-dimensional templates for initial cell attachment
and subsequent tissue formation. For this reason it is important to ensure the cell ingrowth into the structure.
This study focuses mainly on scaffold design for histological evaluation of the seeded scaffolds. To op- timize the seeding efficiency and to observe the cell proliferation into the inner structure, we developed a special design of the scaffold. The objective of the design was maximization of the surface, facilita- tion of the seeding process to enhance cell adhesion and good supply of the interior of the scaffold with medium.
The cultivation of cells seeded onto the scaffolds was carried out under static and dynamic conditions. Histo- logical evaluation was carried out at day 1 and day 7. Cell adhesion on the designed structure was analysed. Additionally, cell ingrowth into the bulk material and cell morphology were examined.