E. Jorge-herrero et al., Influence of different chemical cross-linking treatments on the propertiesof bovine pericardium and collagen, BIOMATERIAL, 20(6), 1999, pp. 539-545
The use of biological materials in the construction of bioprostheses requir
es the application of different chemical or physical procedures to improve
the mechanical performance of the material without producing any undesirabl
e effects. A number of cross-linking methods have been tested in biological
tissues composed mainly of collagen. The basis for most of them is the use
of glutaraldehyde (GA), which acts on the Lys or Hyl residues. We have stu
died the effects of alternative chemical treatments: diphenylphosphorylazid
e (DPPA) and ethyldimethylaminopropyl carbodiimide (EDAC). Their mechanism
of action is based on the activation of the carboxyl groups, which then per
mits their cross-linking to amino groups. As a control, we employed convent
ional treatment with GA, applying it to bovine pericardium and collagen mem
branes removed from bovine pericardium. The analysis of the Lys and Hyl res
idues showed that DPPA and EDAC produced 50% of the chemical change provoke
d by GA. This value was even lower in the trials with collagen. In terms of
the resistance to collagenase degradation, chemical cross-linking with GA
provided much greater protection in both materials (3.81 +/- 3.47 nmol of a
mino acid/mg dry tissue for pericardium and 4.41 +/- 1.13 nmol of amino aci
d/mg dry tissue for collagen).
Treatment with DPPA also protected pericardium (13.11 +/- 6.57 nmol amino a
cid/mg dry tissue) although the values for collagen was lower (50.0 +/- 32.
4 nmol amino acid/mg dry tissue).Treatment with EDAC was much less protecti
ve than the other two chemical reagents (43.28 +/- 17.4 and 55.85 +/- 14.57
nmol amino acid/mg dry tissue for pericardium and collagen, respectively).
The degree of tissue calcification after implantation of the chemically tre
ated materials into young rats was considerably greater for GA and DPPA (32
.9 +/- 18.8 and 36.3 +/- 13.3 mg g(-1) dry tissue, respectively) than with
EDAC (18.0 +/- 7.2 mg g(-1) dry tissue; P < 0.001). After 60 days of implan
tation, the values for GA and EDAC were higher (124.1 +/- 31.3 and 124.6 +/
- 21.0 mg g(-1) dry tissue, respectively) versus 34.6 +/- 19.2 mg g(-1) dry
tissue for DPPA. There were no significant differences in collagen levels
in samples treated with GA or EDAC after 30 days of implantation, although
both groups showed significant differences when compared with DPPA-treated
samples (P < 0.001). After 60 days of implantation, there were no significa
nt differences among these three treatments in terms of the calcium accumul
ated on samples. (C) 1999 Elsevier Science Ltd. All rights reserved.