Biomedical Engineering Reference
In-Depth Information
tissue injury. Current model of hyaluronic acid appear in the early stages of wound
healing is to physically make room for white blood cells, which mediate the immune re‐
sponse and at least in part, reduce collagen deposition and therefore lead to reduced
scarring [86]. This hypothesis is in agreement with the research of West and coworkers,
who have showed that in adult and late gestation fetal wound healing process, removal
of HA results in fibrotic scarring [87].
HA can be modified through several different ways, such as chemically esterify its car‐
boxylic groups with some types of alcohol. The physico-chemical properties of the new
biopolymers allow the preparation of many biomaterials with different biocompatibilities
for various medical applications [88]. Shen and coworkers implanted hyaluronan hydro‐
gel and periodate oxidated hyaluronan hydrogel in ischemic myocardium and found
rapid degradation rates, low quantity of inflammation-mediating cells, thin fibrous cap‐
sules with dense blood vessels around the hydrogels at week 2 [89]. Praveen and cow‐
orkers used HA/polyvinyl alcohol (PVA) coating membrane to minimize the problems
related to protein deposition and fibrous tissue formation on an implanted glucose sen‐
sor [90]. HA hydrogels modified with laminin could support cell infiltration, angiogene‐
sis, and simultaneously inhibit the formation of glial scar after being implanted into the
lesion of the cortex [91]. Compared with pure gelatin hydrogen, HA/gelatin composite
has a better compatibility and contiguity with the surrounding brain tissue with no in‐
flammatory reaction and fibrous encapsulation [92]. Intravitreal implants of hyaluronic
acid esters represent useful biocompatible and biodegradable properties for a potential
drug delivery system in the treatment of posterior segment ocular diseases [93]. A cross-
linked HA hydrogel that contained a covalently bound derivative of the anti-prolifera‐
tive drug MMC was synthesized and evaluated
in vitro
and
in vivo
. This hydrogel has
strong potential as anti-fibrotic barriers for the prevention of post-surgical adhesions
[94]. Two injectable thiolated HA derivatives were coupled to four alpha, beta-unsaturat‐
ed ester and amide derivatives of poly(ethylene glycol) (PEG) 3400 and were found that
the encapsulated cells can retained their original fibroblast phenotype and secreted ECM
in vivo [95]. A fibrin/HA composite gel with autologous chondrocytes has been synthe‐
sized for tracheal reconstruction. Histologically, the grafts showed no signs of inflamma‐
tory reaction and were covered with ciliated epithelium [96].
7. Heparin
Heparin (from Ancient Greek ηπαρ (hepar), liver), a highly sulfated glycosaminoglycan,
is widely used as an injectable anticoagulant, and has the highest negative charge densi‐
ty of any known biological molecule [97]. Heparins are involved in different pathways
of the coagulation cascade with anticoagulant, antithrombotic, profibrinolytic, anti-aggre‐
gative, as well as anti-inflammatory effects [98]. As stated in the fibrin section, the pri‐
mary anticoagulant effect of heparin is through the suppression of thrombin-dependent
amplification of the coagulation cascade, and inhibition of thrombin-mediated conversion
of fibrinogen to fibrin [99].
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