Zgryźliwość kojarzy mi się z radością, która źle skończyła.
12
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I
NTERFACING
I
MPLANTS
The injection syringe. One of the important inventions in medicine. Reprinted with permission
from Platt (1994). Copyright © 1994, Marcel Dekker.
331
332
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Blood-interfacing materials can be divided into two categories: (1) short-term extracorporeal
devices such as membranes for artificial organs (kidney and heart/lung machine), tubes, and
catheters for the transport of blood, and (2) long-term in-situ implants such as vascular im-
plants and implantable artificial organs. Although pacemakers for the heart are not interfaced
with blood directly, they are considered here since they are devices that help the heart to circu-
late blood throughout the body.
The single most important requirement for blood-interfacing implants is blood compatibil-
ity (review §10.3). Blood coagulation is the most important aspect of blood compatibility: the
implant should not cause the blood to clot. In addition, implants should not damage proteins,
enzymes, and the formed elements of blood (red blood cells, white blood cells, and platelets).
The implants should not cause hemolysis (red blood cell rupture) or initiation of the platelet
release reaction.
Blood is circulated throughout the body according to the sequence shown in Figure 12-1.
Implants are usually used to replace or patch large arteries and veins as well as the heart and its
valves. Surgical treatment without using implants is usually preferred. However, there are
many clinical situations in which the surgeon in consultation with the patient chooses to anas-
tomose or replace a large segment with implants.
Figure 12-1
. Schematic diagram of blood circulation in the body.
Table 12-1
. Comparison of Cell Properties
Normal
Cell
Average
Sedimentation
concentration
diameter
density
coefficient
Components
in blood (/liter)
(μm)
(g/ml)
(
S
q 10
7
)
Red blood cell
4.2–6.2 q 10
12
8
1.098
12.0
White blood cell
4.0–11.0 q 10
9
–
–
–
Lymphocyte
1.5–3.5 q 10
9
7–18
1.072
1.2
Granulocyte
2.5–8.0 q 10
9
10–15
1.082
–
Monocyte
0.2–0.8 q 10
9
12–20
1.062
–
Platelet
150–400 q 10
9
2–4
1.058
0.032
Plasma
–
–
1.027
–
Modified with permission from Malchesky (2004). Copyright © 2004, Elsevier.
B
IOMATERIALS
:A
N
I
NTRODUCTION
333
12.1. BLOOD SUBSTITUTES AND ACCESS CATHETERS
Table 12-1 gives some properties of blood for reference. If much blood is lost in an injury or in
surgery, there may be insufficient transport of oxygen to tissues. Blood transfusions can make
up for lost blood, but such blood may not always be available in sufficient amounts for emer-
gencies. Also, some people object to blood transfusions on religious grounds. Therefore, blood
substitutes have been explored. Artificial blood substitutes are in clinical trials. Red blood cell
substitutes based on perfuloroctyl bromide (C
8
F
17
Br) or perfluorodichloroctane (C
8
F
16
Cl
2
) make
use of the solubility of oxygen in some materials. The other formed elements of blood —white
blood cells and platelets — cannot be substituted at this time. The hemoglobin of the red cells
can be crosslinked by glutaraldehyde in the presence of red cell enzyme, catalase to improve
the flexibility of the crosslinked cells, and, more importantly, solubility of oxygen.
Blood is circulated throughout the body according to the sequence shown in Figure 12-1.
Blood access catheters have been developed for transient and more permanent indwelling de-
vices, as shown in Figures 12-2 and 12-3. Implantable venous access ports of various sizes and
septum diameters made of silicone rubber are shown in Figure 12-4. These are used to admin-
ister drugs and draw blood for diagnosis.
Figure 12-2
. A transient blood access device of triple lumen; central venous catheter made of
polyurethane. Reprinted with permission from Raaf and Vinton (1993). Copyright © 1993,
Churchill Livingstone.
12.2. CARDIOVASCULAR GRAFTS AND STENTS
The blood vessels walls in disease states may become thinner in aneurysms or thicker in the
intima in the case of atherosclerosis (see §9.3.4). Replacement of the artery or reinforcing the
wall can be made by autograft of vein, artificial prosthesis, reinforcement by stent, and open-
ing of completely blocked arteries using balloons with or without an embedded stent. These
remedies can be transient (short term) or long term. Ideal stents should have:
334
CH
.12:S
OFT
T
ISSUE
R
EPLACEMENT
—II
Figure 12-3
. Semipermanent indwelling dual-lumen atrial catheter having a large bore and
staggered tip (
a
) and placement (
b
). Reprinted with permission from Raaf (1991). Copyright ©
1991, Williams and Wilkins.
Figure 12-4
. Implantable venous access ports of various sizes and septum diameters, made of
silicone rubber. Reprinted with permission from Raaf and Vinton (1993). Copyright © 1993,
Churchill Livingstone.
B
IOMATERIALS
:A
N
I
NTRODUCTION
335
1. Ease of visualization with x-rays,
2. High hoop strength to resist arterial recoil,
3. Longitudinal flexibility to pass tortuous vessels and bifurcation with a con-
tralateral approach,
4. Radial elasticity under external compression,
5. Minimal or no change after implantation,
6. High expansion ratio and low profile for passage through small introducers
or guiding catheters or through tight stenosis,
7. Retrievability,
8. Side-branch accessibility,
9. Minimal induction of hyperplasia of intima,
10. Thromboresistance,
11. Fatigue resistance,
12. Biocompatibility.
Figure 12-5
. Stent grafts. (
a
) Configuration of device showing composite metal and fabric por-
tions. (
b
) Low-power photomicrograph of well-healed experimental device explanted from a
dog aorta. The lumen is widely patent and the fabric and metal components are visible. (
c
)
High-power photomicrograph of stent graft interaction with the vascular wall, demonstrating
mild intimal thickening. Reprinted with permission from Padera and Schoen (2004). Copyright
© 2004, Elsevier.
Angioplasty employs balloons made of a polymer (polyethylene terephthalate) sheet
wrapped around a tube for insertion and expands after placement. The expanded artery may
not remain patent for long times. In some instances stents are deployed to prevent reoccurrence
of stenosis. A typical stent is shown in Figure 12-5 before after implantation in canine aorta.
The stent is a composite of balloon and metal wire, as can be seen in the histology. The self-
zanotowane.pl doc.pisz.pl pdf.pisz.pl hannaeva.xlx.pl
S
OFT
T
ISSUE
R
EPLACEMENT
— II:
B
LOOD
I
NTERFACING
I
MPLANTS
The injection syringe. One of the important inventions in medicine. Reprinted with permission
from Platt (1994). Copyright © 1994, Marcel Dekker.
331
332
CH
.12:S
OFT
T
ISSUE
R
EPLACEMENT
—II
Blood-interfacing materials can be divided into two categories: (1) short-term extracorporeal
devices such as membranes for artificial organs (kidney and heart/lung machine), tubes, and
catheters for the transport of blood, and (2) long-term in-situ implants such as vascular im-
plants and implantable artificial organs. Although pacemakers for the heart are not interfaced
with blood directly, they are considered here since they are devices that help the heart to circu-
late blood throughout the body.
The single most important requirement for blood-interfacing implants is blood compatibil-
ity (review §10.3). Blood coagulation is the most important aspect of blood compatibility: the
implant should not cause the blood to clot. In addition, implants should not damage proteins,
enzymes, and the formed elements of blood (red blood cells, white blood cells, and platelets).
The implants should not cause hemolysis (red blood cell rupture) or initiation of the platelet
release reaction.
Blood is circulated throughout the body according to the sequence shown in Figure 12-1.
Implants are usually used to replace or patch large arteries and veins as well as the heart and its
valves. Surgical treatment without using implants is usually preferred. However, there are
many clinical situations in which the surgeon in consultation with the patient chooses to anas-
tomose or replace a large segment with implants.
Figure 12-1
. Schematic diagram of blood circulation in the body.
Table 12-1
. Comparison of Cell Properties
Normal
Cell
Average
Sedimentation
concentration
diameter
density
coefficient
Components
in blood (/liter)
(μm)
(g/ml)
(
S
q 10
7
)
Red blood cell
4.2–6.2 q 10
12
8
1.098
12.0
White blood cell
4.0–11.0 q 10
9
–
–
–
Lymphocyte
1.5–3.5 q 10
9
7–18
1.072
1.2
Granulocyte
2.5–8.0 q 10
9
10–15
1.082
–
Monocyte
0.2–0.8 q 10
9
12–20
1.062
–
Platelet
150–400 q 10
9
2–4
1.058
0.032
Plasma
–
–
1.027
–
Modified with permission from Malchesky (2004). Copyright © 2004, Elsevier.
B
IOMATERIALS
:A
N
I
NTRODUCTION
333
12.1. BLOOD SUBSTITUTES AND ACCESS CATHETERS
Table 12-1 gives some properties of blood for reference. If much blood is lost in an injury or in
surgery, there may be insufficient transport of oxygen to tissues. Blood transfusions can make
up for lost blood, but such blood may not always be available in sufficient amounts for emer-
gencies. Also, some people object to blood transfusions on religious grounds. Therefore, blood
substitutes have been explored. Artificial blood substitutes are in clinical trials. Red blood cell
substitutes based on perfuloroctyl bromide (C
8
F
17
Br) or perfluorodichloroctane (C
8
F
16
Cl
2
) make
use of the solubility of oxygen in some materials. The other formed elements of blood —white
blood cells and platelets — cannot be substituted at this time. The hemoglobin of the red cells
can be crosslinked by glutaraldehyde in the presence of red cell enzyme, catalase to improve
the flexibility of the crosslinked cells, and, more importantly, solubility of oxygen.
Blood is circulated throughout the body according to the sequence shown in Figure 12-1.
Blood access catheters have been developed for transient and more permanent indwelling de-
vices, as shown in Figures 12-2 and 12-3. Implantable venous access ports of various sizes and
septum diameters made of silicone rubber are shown in Figure 12-4. These are used to admin-
ister drugs and draw blood for diagnosis.
Figure 12-2
. A transient blood access device of triple lumen; central venous catheter made of
polyurethane. Reprinted with permission from Raaf and Vinton (1993). Copyright © 1993,
Churchill Livingstone.
12.2. CARDIOVASCULAR GRAFTS AND STENTS
The blood vessels walls in disease states may become thinner in aneurysms or thicker in the
intima in the case of atherosclerosis (see §9.3.4). Replacement of the artery or reinforcing the
wall can be made by autograft of vein, artificial prosthesis, reinforcement by stent, and open-
ing of completely blocked arteries using balloons with or without an embedded stent. These
remedies can be transient (short term) or long term. Ideal stents should have:
334
CH
.12:S
OFT
T
ISSUE
R
EPLACEMENT
—II
Figure 12-3
. Semipermanent indwelling dual-lumen atrial catheter having a large bore and
staggered tip (
a
) and placement (
b
). Reprinted with permission from Raaf (1991). Copyright ©
1991, Williams and Wilkins.
Figure 12-4
. Implantable venous access ports of various sizes and septum diameters, made of
silicone rubber. Reprinted with permission from Raaf and Vinton (1993). Copyright © 1993,
Churchill Livingstone.
B
IOMATERIALS
:A
N
I
NTRODUCTION
335
1. Ease of visualization with x-rays,
2. High hoop strength to resist arterial recoil,
3. Longitudinal flexibility to pass tortuous vessels and bifurcation with a con-
tralateral approach,
4. Radial elasticity under external compression,
5. Minimal or no change after implantation,
6. High expansion ratio and low profile for passage through small introducers
or guiding catheters or through tight stenosis,
7. Retrievability,
8. Side-branch accessibility,
9. Minimal induction of hyperplasia of intima,
10. Thromboresistance,
11. Fatigue resistance,
12. Biocompatibility.
Figure 12-5
. Stent grafts. (
a
) Configuration of device showing composite metal and fabric por-
tions. (
b
) Low-power photomicrograph of well-healed experimental device explanted from a
dog aorta. The lumen is widely patent and the fabric and metal components are visible. (
c
)
High-power photomicrograph of stent graft interaction with the vascular wall, demonstrating
mild intimal thickening. Reprinted with permission from Padera and Schoen (2004). Copyright
© 2004, Elsevier.
Angioplasty employs balloons made of a polymer (polyethylene terephthalate) sheet
wrapped around a tube for insertion and expands after placement. The expanded artery may
not remain patent for long times. In some instances stents are deployed to prevent reoccurrence
of stenosis. A typical stent is shown in Figure 12-5 before after implantation in canine aorta.
The stent is a composite of balloon and metal wire, as can be seen in the histology. The self-