Designing the Biocompatibility of Biohybrids - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 291

of proteins [ 27 ] or cells, while the scaffold serves as necessary placeholder or
mechanical framework for the cells in all aspects of tissue engineering. Tissue
engineering is one of the most quickly expanding areas in biomedicine [ 28 ]. There
is an overwhelming amount of very different approaches focusing on many dif-
ferent cell types, tissues and functions which cannot be reviewed in detail here.
However, independent from its composition, these are the most challenging
biohybrid constructs, since the host has not only to face a structural non-biological
component, but moreover foreign proteins, cells or even a functionalized tissue
with hardly predictable reactions of the host immune system.
4.2 Classification of Biohybrids According
to Their Therapeutical Application
The most common use of the term biohybrid can be found in various fields of
regenerative medicine. It is obvious that biohybrids can be classified according to
their therapeutical use in different organ systems. Examples of therapeutical
biohybrids and their use are given below:
4.2.1 Neuronal Biohybrids
The central nervous system is the most complex human organ system and its
unique capacity is the foundation which distinguishes humans from their evolu-
tionary relatives. Therefore, non- or malfunction of parts of the nervous system
deeply impacts not only individual sensory or physiological functions, but also
affects a human's self-image. Whereas the human peripheral nervous system has
some capacity to regenerate, axon regeneration in the central nervous system is
extremely limited [ 29 ] and the presence of adult stem cells has been discovered
only recently [ 30 , 31 ]. Nevertheless, neural prostheses for the electric stimulation
of specific neural regions (e.g. cochlea implants, retina implants, deep brain
stimulation) have a partly long tradition and were successfully applied in clinical
settings [ 32 ]. Only recently, attempts were made to introduce real biohybrid
constructs for the therapy of degenerative diseases [ 33 ]. The biocompatibility of
neuronal prostheses is determined by the reaction of the central nervous system
specific microglia cells, which are the keyplayers in the immune system beyond
the blood-brain barrier [ 34 ].
4.2.2 Kidney and Liver Biohybrids
There are several approaches to develop artificial organs as an alternative in case
of failure or malfunction of the kidney or the liver system. With respect to kidney,