Biomedical Engineering Reference
In-Depth Information
when contacting the body components, that is, biomaterials must be non-
toxic, non-carcinogenic, non-antigenic (for endogenous inflammation), and
non-oncogenic (for gene mutant) [3-6]. Potential exogenous infections may
be induced by comprehensive factors from surgical and post-surgical opera-
tions, as well as some endogenous focus like formation of thrombus that not
only provides a breeding ground for disease vectors, but also destroys ma-
terials' haemo-compatibility. For blood-contacting biomedical materials, in-
cluding cardiovascular biomaterials, haemo-compatibility, which pursues the
maintenance of blood rheological properties and biochemical compositions
by thromboresistance, is a fundamental requirement. Currently cardiovascu-
lar biomaterials are employed for various applications including (1) devices
for in vitro whole blood containing and transfer; (2) intravascular devices for
interventional therapy; and (3) devices for permanent transplantation as soft
tissue substitutes. Different applications are endowed with different criteria
for haemo-compatibility. For example, materials of heart valves for long-term
implantation should sustain their biocompatibility for longer periods than
that of instant intravascular guiding catheters [7-10].
1.1.2
Categories of Cardiovascular-Functional Polymers
Cardiovascular-functional polymers cover almost all categories of synthetic
polymers and large numbers of biopolymers. They are used to build the de-
vice bulk, act as surface-modifying additives [SMA], and also formulate tissue
adhesives [11-17].
Among the bulk materials, non-degradable synthetics are usually selected
as the primary candidates for fabricating in vitro or interventional devices,
such as catheters, sutures, tubing, blood bags, housing materials, wound
dressings, angioplasty balloons, etc; and also employed for constructing per-
manent substitutes, such as an artificial heart, heart bladders, heart valves,
etc. Permanent bulk materials include glass-state polyacetals, polyamides
(and their elastomers), polycarbonates [PC], polyesters, polyethers (epox-
ies and their elastomers), polyimides, poly(methylpentene), polyolefins (and
their elastomers, and high crystallinity films), polyurethane [PU] elastomers,
poly (vinyl chloride) [PVC], ultra high molecular weight polyethylene [PE],
acrylics (hydrogels), silicones and fluorocarbons. On the basis of the clas-
sic polymers listed above, the recent development of bioresorbable polymers
has provided hope of achieving non-secondary-surgical suture removal, con-
trolled drug-releasing substitute scaffolds, and in situ tissue-engineered im-
plants. Controllable degradation or bioresponsive degradation is the key to
fulfilling these purposes. Traditional candidates for bioresorbable materials
are poly (amino acids), polycaprolactones [PCL], and poly (lactic/glycolic
acid) [PLGA] copolymers. Biodegradable polyurethanes and polyphospho-
esters are also being examined as to their potential uses.
