Biomedical Engineering Reference
In-Depth Information
Regenerative medicine is highly interdisciplinary and deals with the restitution,
substitution, regeneration of nonfunctional or more or less functionally impaired
cells, tissues, organs through biological replacement, for example, through tissues
produced
in vitro
or through the stimulation of the body's own regeneration and/
or repair processes [3, 4].
Important success in stem cell research [5, 6] and the extracorporeal tissue
growth in bioreactors show the potential of regenerative medicine [7-9]. The
euphoric visions to grow complete and functional organs
in vitro
right now,
however, were recognized to be very premature. This is also due to a lack in basic
research and the development of multifunctional implant materials [10].
13.1.3
Functionalized Implant Materials
The experience with polymer implants used in medicine led to a profi le of require-
ments for future polymeric implant materials. The functionality of implant materi-
als has to be broadened. They should be stimuli sensitive and, for example, change
their physicochemical behavior due to external stimuli or to biological processes
induced at the site of implantation. Bioactive substances like peptides, proteins,
or carbohydrates might be immobilized by polymers or released from implants in
a well - defi ned process. The most up-to-date trend in polymer sciences is the devel-
opment of degradable biomaterials showing multifunctionality. This implies
that specifi c functionalities like hydrolytic degradation, physiological and biome-
chanical tissue compatibilities, and shape-memory can be adjusted to regiospecifi c
requirements at the site of implantation [11, 12].
AB-copolymer networks are an example for an implant material that can be
functionalized.
These networks are produced by photocrosslinking of
n
- butyl acrylate with
oligo(
- caprolacton)dimethacrylate as macrocrosslinker [13, 14]. The incorporation
of fl exible polybutylacrylate segments allows, for example, the tailoring of material
elasticity, which is an important determinant of the biomechanical functionality
of this polymer system in the temperature range between room and body tem-
perature. AB-copolymer networks are slowly biodegradable due to their hydrolyti-
cally cleavable polyester chain segments. Another group of multifunctional,
degradable polymers are multiblock copolymer systems [15-17] containing poly(
p
-
dioxanone) hard segments and crystallizable poly(
ε
- caprolactone) soft segments.
Due to their degradability, stimuli sensitivity, biocompatibility, and functionality,
these copolymer networks are termed multifunctional. Biomechanical character-
istics as well as types and periods of degradation can be adjusted as well.
ε
13.1.4
Sterilization of Polymer-Based Degradable Implant Materials
The sterilization of implant materials is a precondition for their biomedical use.
Polymer-based and especially hydrolytically degradable biomaterials in general
