Biomedical Engineering Reference
In-Depth Information
4.1 Classification of Biohybrids According to Their Function
The functional unit of a biohybrid may be described by one of the following
subgroups:
4.1.1 Three-Dimensional Spheroid Biohybrids
The use of three-dimensional spheroids has a longstanding tradition. First estab-
lished the 1950s [ 12 ], this powerful culture system was used very successfully for
developmental studies [ 13 ], in tissue engineering [ 14 ], as a basic step during
differentiation of embryonic stem cells [ 15 , 16 ] and as a monitoring system for
drugs and other bioactive agents [ 17 , 18 ]. More recently, three-dimensional
spheroids were also further developed by introducing scaffolds of biological [ 19 ]
or non-biological origin [ 20 ] as structural component. The structural component is
of minor importance and quantity in three-dimensional spheroids because they
consist mainly of cells and their extracellular matrix. However, because the three-
dimensional spheroid technique is mainly an in vitro technique, the biocompati-
bility of the structural component is only of minor importance.
4.1.2 Biohybrid Biosensors
Biohybrid biosensors have many functional similarities with three-dimensional
cultures. However in this use, the cells grow two-dimensionally and are combined
with chiplike scaffolds or matrices for sensing [ 21 , 22 ]. Since these biosensing
approaches are applied mainly in vitro, biocompatibility is currently a minor issue.
4.1.3 Drug Delivery Biohybrids
One of the most interesting clinical fields of biohybrid applications is drug delivery.
For patients who need a continuously available therapeutic, it would be a significant
benefit, if a long-term drug depot could be implanted which releases the therapeu-
tic(s) at a controlled and physiological rate. Inevitably, these constructs have to be
deposited in the organism and biocompatibility is a major concern [ 23 ]. The struc-
tural part in these drug releasing biohybrids may consist of various biomaterials, e.g.
polylactid acids [ 24 ], hydrogels [ 25 ] or specific combinations [ 26 ]. Naturally, the
structural part must be highly biocompatible and non-toxic, independent from the
fact whether the structural part consists of a permanent or a biodegradable substance.
4.1.4 Encapsulating Scaffold Biohybrids
One of the most important and promising applications for biohybrids are cells in
scaffolds for tissue repair. The bioactive component of the biohybrid may consist
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