Designing the Biocompatibility of Biohybrids - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 286

1 Introduction
During the last decades, great progress was achieved in many fields of biomedical
research. Although classical clinical or pharmacological research remain the major
scientific fields, technical aspects of many biomedical issues have become more
and more important. Many different fields in biomedical research and also in
clinical applications took advantage of ideas and concepts of neighbouring
scientific areas, especially from engineering sciences. Although the clinical use of
ortheses, prostheses or even implants as compensation or replacement of lost body
parts is known since prehistoric times, the development of more complex technical
solutions was the outcome of the past twenty years of research. The sustained
emergence and the increasing importance of all aspects of regenerative medicine
and stem cell based therapies opened many fascinating approaches for the treat-
ment of various serious health problems. Amongst other merely technical oriented
approaches, the development of biohybrid systems hereby faced a remarkable
upturn.
In the literature, there is no specific definition for a biohybrid system, but
generally, biohybrids are regarded as the functional combination of both a bio-
active and a structural component, thus adding the benefits and advantages of both
components. The structural component is normally referred to as a biomaterial and
consists of metals, polymers, ceramics, decellularised extracellular matrices or
composites. The bioactive component could either consist of active molecules or
cells.
Based on this idea, cells are combined, for example, with carbon nanofibers to
be used in nerve and spinal cord regeneration or cells are linked to hip prothesis or
surfaces of cardiovascular devices to create so called biofunctionalized surfaces or
implants. However, the combination of cells and materials have been always in
the focus of tissue engineering approaches and in regenerative medicine, since
surgeons and patients are demanding faster healing after surgery and sustained
functionality of the implant. The combination of bioactive cells and a mechanical
framework is necessary, since the treatment with sole cell constructs or suspen-
sions is usually lacking sufficient mechanical support or guidance.
However, biohybrids are also used for innovative analytical tools in vitro.
In this application the biocompatibility and immunogenicity of the bioactive and
structural component is not important. However, in any case the cytocompatiblity
of the structural component seems to be important in these applications, especially
in bioreactors for the production of bioactive molecules.
In this review, we want to elaborate which applications are currently summa-
rized under the term biohybrid and which challenges and design strategies exist for
biohybrids in various clinical applications, especially in musculoskeletal approa-
ches. However, since there is no classification for the term biohybrid, it can
create some confusion if used in brief abstracts without any further explanation.
Therefore, we would like to suggest a classification system of biohybrids in
this chapter.