Biomedical Engineering Reference
In-Depth Information
(a)
(b)
Figure 10.2
Schematics of (a) conventional polymer composite with bioactive glass
or ceramic particles within a polymer matrix and (b) cell attaching to the bioactive
glass or ceramic particles that protrude through the polymer matrix at the surface
of the composite.
require controlled degradability or bioactivity. For example, in bone
regeneration, a bioactive material is needed that can bond with the host
bone and can degrade slowly as the bone regrows. One problem with
a conventional composite is that the bioactive material may be covered
by the polymer, masking it from the blood, cells, and host bone. This
eliminates the bioactive properties. The only particles that will contact
cells will be the few that poke through the polymer (Figure 10.2b),
which can cause distortion of cells and reduced bone bonding. Another
problem relates to degradation. If the composite is designed to degrade
by using a degradable polymer matrix, it is difficult to get the polymer
and ceramic or glass to degrade at the same rate. The polymer may
degrade first, leaving the ceramic or glass particles without a matrix.
Finally, when degradable polymers are used, mechanical properties may
be lost rapidly once the polymer begins to degrade. A contributing
factor is that it is difficult to get a good interface (bonding, in other
words) between the ceramic or glass and the polymer. Hybrids have the
potential to overcome these problems. The hope is that the fine-scale
interactions between the components will mean that cells will see a
hybrid implant interface as one material and the control of the chemistry
will mean that a hybrid will also degrade as one material. Control of the
nanostructure should also give tight control over mechanical properties
and degradation rates.
Hybrids derived from atomic- or molecular-level mixtures of organic
and inorganic components seem advantageous because their properties
are controlled almost freely by adequate selection of the components
and their mixing ratios. Hybrids can be either inorganic-rich (e.g.
silica modified with some organic) or organic-rich (e.g. a polymer
