Biomedical Engineering Reference
In-Depth Information
Biopolymers utilized as bulk materials for medical devices have the ad-
vantages of specific bio-functionality and general biocompatibility, but on the
other hand, the drawbacks of difficult fabrication and the risk of stimulating
immuno-reactions have also limited their application. Two categories of bi-
ological materials are developed and employed: native organ derivatives and
bio-derived macromolecules. Widely used native organ derivatives are blood
vessels (arteries and veins, bovine), pericardium (bovine), umbilical cord
(vein, human), and heart valve (porcine) etc; bioderived macromolecules
include albumin (crosslinked), cellulose (acetates or cuprammonium), chi-
tosan, collagen, elastin, gelatin (crosslinked), phospholipids, and silk etc.
In contrast with bulk materials that take responsibility for product me-
chanics and metabolism, the superior blood-contacting functions of cardio-
vascular biomaterials are conveniently fulfilled by surface modification. The
strategy of surface modification is to introduce either passive (inert) or bioac-
tive SMA onto the blood-material interface. By surface optimization, the
material is granted with variable functions including thromboresistance, in-
fection resistance, selective protein binding, promotional cell adhesion, and
even simply lubricity. Surface-modifying approaches include chemical dec-
oration (via covalent conjugation) and physical coating (blends). Popular
passive factors rendered via SMA are albumin, alkyl oligo-chains, fluorocar-
bons, and silicones (silica-free products and oils) etc; bioactive functional
groups immobilized through SMA are usually anticoagulants (like heparin
and hirudin), antimicrobials (like chitosan), cell-adhesion peptides/proteins
(like RGD tri-peptide and fibronectin [Fn]), plasma components (polymer-
ized coatings), and thrombolytics etc. Tissue adhesives are also used for car-
diovascular applications, such as microsurgery for anastomosing vessels and
enhancement of cell adhesion. The involved categories are mainly cyanoacry-
lates, Fibrin glue and molluscan glue, etc.
1.1.3
Technical Parameters of Cardiovascular Biomaterials
From the material fabrication and performance point-of-view, nine aspects of
technical parameters are mainly involved [18-20]:
1.
Strength
. Major arteries, heart valves and angioplasty balloons require
superior strength of applied materials (using engineering plastic and syn-
thetic fiber composites); guiding catheters, surgical sutures and intravas-
cular stents require medium strength (using common plastic, elastomers,
and native organ derivatives); non-supporting and mild-shear-bearing
coatings have limited mechanical requirement (using biomacromolecules
and hydrogels).
2.
Incision anastomosis
. Long-term interventional catheters, heart or blood
vessel patches and artificial vascular grafts need to anastomose well with
