Biomedical Engineering Reference
In-Depth Information
7.3.1 Smart Composites Based on Biomimetic Matrices
During development, the shape of tissues is highly influenced by the mutual
interaction between cells and the surrounding extracellular matrix (ECM).
Biomimetic materials, that may be a protein of ECM, e.g., collagen, are
widely proposed for biomedical use.
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Protein-based biomaterials are de-
rived from many biological sources that vary in size from microorganisms to
mammals and this would affect the cost of manufacture and processing.
Those derived from plants, e.g., wheat, are relatively cheap and abundant but
often require chemical modification to improve their properties.
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Some
protein-based biomaterials with similar structural composition to those
obtained from mammals can also be derived from prokaryotic bacteria of-
fering an alternative route for biomaterials production.
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Silk-based proteins
are produced by a wide variety of larvae of insects including silkworms,
mites and flies.
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Commercially available collagen is typically derived from
bovine or porcine sources.
Protein-based biomaterials have been exploited for a number of bio-
medical applications. Their fragile mechanical properties, associated risk of
infection, antigenicity and possible deterioration after long-term implant-
ation, however, restrict their widespread use as a pure biomaterial. Some of
these problems may be overcome by combining different proteins to make
composites, e.g., fibrinogen/factor XIII/fibronectin and thrombin.
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Due to
their biocompatibility and availability, they have considerable potentials as
matrices for drug delivery and tissue engineering applications. Fibrin as a
form of fibrous protein has been used as a hemostatic agent, sealant or
glue,
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in cosmetic surgery
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and ophthalmology.
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With recent advances
in biotechnology, protein-based biomaterials derived from living organisms
could be designed with specific chemical, mechanical or structural prop-
erties
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and used in a form of hydrogels, cross-linked hydrogels or decel-
lularized native tissues.
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7.3.2 On-demand Responsive Composites
On-demand responsive composites have been prepared by the combination
of hydrogel matrices with other polymers or fillers. The hydrogels convey the
on-demand responsive property to the composite. Hydrogel benefits include
tunable hydration and softness which make them extracellular matrix-like.
Virtually all water-soluble polymers can be assembled into hydrogels that
can be tailored to respond controllably to different external or internal
stimuli (e.g., temperature,
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light, pH, ionic concentration, chemical re-
action
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and electric current
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). A key feature of the smartness of these
hydrogels involves their ability to return to their original state after stimulus
removal. To be stimulus-responsive, a hydrogel (produced from natural
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or
synthetic polymers
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) may be coupled with a specific functional group that is
dependent upon the intended functionality. The hydrogel becomes func-
tionally active when treated with the correct stimulus. Due to their excellent
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