New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 204

The tissue reaction in vivo to implanted PHB ¿ lms and medical devices was stud-
ied. In most cases a good biocompatibility of PHB was demonstrated. In general, no
acute inÀ ammation, abscess formation, or tissue necrosis was observed in tissue sur-
rounding of the implanted PHB materials. In addition, no tissue reactivity or cellular
mobilization occurred in areas remote from the implantation site [10, 13, 24, 58]. On
the one hand, it was shown that PHB elicited similar mild tissue response as PLA did
[13], but on the other hand the use of implants consisting of polylactic acid, polygli-
colic acid and their copolymers is not response without a number of sequelae related
with the chronic inÀ ammatory reactions in tissue [65-69].
Subcutaneous implantation of PHB ¿ lms for 1 month has shown that the samples
were surrounded by a well-developed, homogeneous ¿ brous capsule of 80-100 —m
in thickness. The vascularized capsule consists primarily of connective tissue cells
(mainly, round, immature ¿ broblasts) aligned parallel to the implant surface. A mild
inÀ ammatory reaction was manifested by the presence of mononuclear macrophages,
foreign body cells, and lymphocytes. Three months after implantation, the ¿ brous cap-
sule has thickened to 180-200 —m due to the increase in the amount of connective
tissue cells and a few collagen ¿ ber deposits. A substantial decrease in inÀ ammatory
cells was observed after 3 months, tissues at the interface of the polymer were densely
organized to form bundles. After 6 months of implantation, the number of inÀ amma-
tory cells had decreased and the ¿ brous capsule, now thinned to about 80-100 —m,
consisted mainly of collagen ¿ bers, and a signi¿ cantly reduced amount of connective
tissue cells. A little inÀ ammatory cells effusion was observed in the tissue adherent to
the implants after 3 and 6 months of implantation [10, 13]. The biocompatibility of
PHB has been demonstrated in vivo under subcutaneous implantation of PHB ¿ lms.
Tissue reaction to ¿ lms from PHB of different molecular weight (300, 450, 1000 kDa)
implanted subcutaneously was relatively mild and did not change from tissue reaction
to control glass plate [24].
At implantation of PHB with contact to bone the overall tissue response was
favorable with a high rate of early healing and new bone formation with some in-
dication of an osteogenic characteristic for PHB compared with other thermoplas-
tics, such as polyethylene. Initially there was a mixture of soft tissue, containing
active ¿ broblasts, and rather loosely woven osteonal bone seen within 100 —m of
the interface. There was no evidence of a giant cell response within the soft tissue
in the early stages of implantation. With time this tissue became more orientated in
the direction parallel to the implant interface. The dependence of the bone growth
on the polymer interface is demonstrated by the new bone growing away from
the interface rather than towards it after implantation of 3 months. By 6 months
postimplantation the implant is closely encased in new bone of normal appearance
with no interposed ¿ brous tissue. Thus, PHB-based materials produce superior
bone healing [37].
Regeneration of a neointima and a neomedia, comparable to native arterial tis-
sue, was observed at 3-24 months after implantation of PHB nonwoven patches as
transannular patches into the right ventricular outÀ ow tract and pulmonary artery. In
the control group, a neointimal layer was present but no neomedia comparable to na-
tive arterial tissue. Three layers were identi¿ ed in the regenerated tissue: neointima