Biomedical Engineering Reference
In-Depth Information
6.2
Biocompatibility
Cell Culture Studies
Cell culture experiments using a mixed population of ovine vascular cells
(consisting of smooth muscle cells, endothelial cells, and fibroblasts) showed
a significantly lower number of cells adherent to P3HO-3HH porous films
as compared to PGA mesh, which was explained by the different porosities
(50-60% for P3HO-3HH vs. 95% for PGA). P3HO-3HH and P4HB porous ma-
trices showed comparable cell numbers in these experiments. Additionally,
the deposition of ECM (collagen) on P3HO-3HH was low in comparison to
that on PGA and P4HB [44]. There was no detectable elastin deposition in
similar experiments [281].
In Vivo Studies
The biocompatibility of P3HO-3HH microspheres, tubes, and pellets have
been tested by s.c. implantation in mice for up to 40 weeks. A very mild host
reaction to the implants with formation of a thin fibrotic layer encapsulat-
ing the materials was described [3]. A good biocompatibility of P3HO-3HH
have also been demonstrated in rats after s.c. implantation of P3HO-3HH-
impregnated Dacron prostheses. The secretion of alkaline phosphatase by
polymorphonuclear cells (acute inflammatory phase) was significantly en-
hanced after 2 days. Acid phosphatase secretion indicating macrophage activ-
ity (chronic inflammatory phase) was highest between 5 and 10 days after im-
plantation. The secretion of both enzymes was low for the remaining periods
of implantation of up to 6 months. Histologic examination revealed a discrete
acute inflammatory phase, which progressed from acute to chronic between
10 and 15 days after implantation. The intensity of this chronic inflammatory
reaction decreased with time from a mild reaction at 30 days to a more dis-
crete response after 6 months. A thick collagenous capsule surrounding the
implants had been formed by this time [53].
Blood Compatibility
When tested as substitutes of the infrarenal aorta in dogs, two out of four
P3HO-3HH impregnated Dacron grafts were covered by a thick thrombotic
matrix laying over the entire graft, with occasional islets of endothelial-like
cells. The remaining two grafts were characterized by isolated small thrombi
and the development of a thin collagenous capsule together with endothelial
cell coverage [53]. Severe thrombus formation was also observed on all three
leaflets made from porous P3HO-3HH films after 4 weeks of implantation in
sheep [268]. In contrast, incomplete endothelialization, but no thrombus for-
mation, was reported from another study testing porous P3HO-3HH heart
valve scaffolds in sheep [280].
