In the repair of bone- and cartilage tissue both the biological activity and the mechanical properties of the implant are relevant. Optimal and sufficiently complex biological properties can be best provided by using cultured cells while the mechanical properties of constructs are still largely dependent on scaffold properties. As a consequence, tissue engineering is a subtle interplay between biological- and material sciences. In this presentation we will demonstrate some of the strategies that were developed in our group in order to develop appropriate hybrid technology for tissue engineering.
Although bone and cartilage are quite different tissues, as clearly exemplified by the absence of vasularization in mature cartilage whereas the presence of vascularization is pivotal for bone metabolism, they require rather similar approaches in tissue engineering.
First: scaffolds need to be manufactured that can be truly designed in order to provide a fully functional three-dimensional system with appropriate porosity and sufficient mechanical properties. In our hands conventional production methods do not have adequate capabilities and much better results are obtained by employing 3-D printing technology. By these methods we have made promising scaffolds for cartilage replacement with a family of degradable PEO/PBT copolymers. For bone substitution rapid prototyping technology resulted in highly reproducible calcium phosphate scaffolds.
Second: another critical factor in tissue engineering is supplying sufficient nutrients to the cells in the scaffolds, even in the center. This involves the use of bioreactor technology. We have successfully cultured up to 10 cc of human osteoprogenitor cells in bioreactor systems. Cells were multiplied to useful numbers and retained osteogenic properties after implantation.
Finally: one of the major challenges in multiplying cells further lies in retaining differentiation capacity. Recent findings by our group indicate that the use of tissue-inductive materials may play an important role in achieving this goal, thereby possibly reducing or substituting the use of growth factors.
The main challenge in tissue engineering will be in combining all developments as described in the above into one practical technology.