Biomedical Engineering Reference
In-Depth Information
Figure 5.2. Chemical structure of esterified hyaluronan. Solubility of the
biomaterial iscontrolled by the percentage of esterification.
demonstratedthatthesolubilityofthehyaluronanmoleculeisdras-
tically reduced such that it is solid even after extended periods in
aqueousenvironments. 16 Furthermore,byvaryingthedegreeofcar-
boxyl modification, the degradation rate can be tailored to meet the
requirements of the implantation site and application. 17 It has been
demonstrated in many studies that benzyl esterification of the car-
boxylgroups(Fig.5.2)resultsinnontoxicdegradationproducts, 18 , 19
including free hyaluronan, which is highly angiogenic. 12 Esterified
hyaluronan-based materials that have been fashioned into nonwo-
ven fleeces, membranes, and sponges have already been demon-
strated as having functional e cacy when used as scaffolds in the
reconstruction of skin, 20 cartilage, 21 and bone. 22 , 23 Moreover, it has
been demonstrated that esterified hyaluronan sponges can support
the differentiation of human adipocyte precursor cells in vitro 24
5.2.1 Experience with Esterified Hyaluronan
Numerous in vivo studies carried out by us and by our collab-
orators have failed to demonstrate mature adipocyte differentia-
tion within esterified hyaluronan sponges, 25 27 despite positive in
vitro results. 24 In a study in humans, sponges were implanted for
up to 16 weeks, both in acellular form and seeded with autol-
ogous preadipocytes. 26 In both, esterified hyaluronan was sys-
tematically replaced by a dense, fibrous collagenous extracellular
matrix network. Although no calcification was observed, a popula-
tion of inflammatory cells became well established throughout the
 
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