Biomedical Engineering Reference
In-Depth Information
Bioactive glass
(e.g. 45S5 Bioglass
®
)
Biodegradable polymer
(PDLLA, PHA, PLGA, collagen)
Biodegradable and bioactive composites
Bioactive glass as filter
or coating
Dense composites
Porous composites
Figure 9.4
Schematic diagram showing the different combinations of biodegradable
polymers and bioactive glass particles to form composite materials. (composite
materials (Adapted from [7]. Copyright (2007) Woodhead Publishing.))
are too flexible and weak to meet the mechanical demands in surgery
and in the physiological environment. This is where the bioactive glass
reinforcement comes in.
The combination of polymers and glass particles or fibres leads to
composite materials with improved mechanical properties owing to
the inherent higher stiffness and strength of the inorganic material.
Importantly, the addition of bioactive phases to bioresorbable polymers
can alter the polymer degradation behaviour, by buffering the pH of
the nearby solution and hence controlling the fast acidic degradation of
the polymer, in particular in the case of the polyesters described above.
Bioactive glass fillers have been shown to influence the degradation
mechanism of polymers by preventing the autocatalytic effect of the
acidic end groups resulting from hydrolysis of the polymer chains.
Moreover, incorporation of a bioactive phase in the polymer matrix
helps to absorb water owing to the internal interfaces formed between
the polymer and the more hydrophilic bioactive phases, hence providing
a means of controlling the degradation kinetics of the scaffolds.
The incorporation of a bioactive glass phase has an extra important
function: it allows the composite to interact with the surrounding bone
tissue by forming a tenacious bond via the growth of an HCA layer.
However, for this to happen, processing must be optimised to ensure
the glass particles or fibres are exposed at the surface of the composite,
rather than being entrapped within the polymer matrix.
Two types of reinforcements are normally used for biomedical com-
posites: fibres and particulates. The final mechanical properties of the
