Zgryźliwość kojarzy mi się z radością, która źle skończyła.
11
S
OFT
T
ISSUE
R
EPLACEMENT
—I:
S
UTURES
,S
KIN
,
AND
M
AXILLOFACIAL
I
MPLANTS
Schematic illustration of “smart,” “intelligent,” and “reversible memory” polymer systems. The
stimulating energy can be mechanical, thermal, or chemical. Reprinted with permission from
Hoffman (2004). Copyright © 2004, Elsevier.
291
292
CH
.11:S
OFT
T
ISSUE
R
EPLACEMENT
—I
In soft tissue implants, as in other applications that involve engineering, the performance of an
implanted device depends upon both the materials used and the design of the device or im-
plant. The initial selection of material should be based on sound materials engineering practice.
The final judgment on the suitability of a material depends upon observation of the in-vivo
clinical performance of the implant. Such observations may require many years or decades.
This requirement of in-vivo observation represents one of the major problems in the selection
of appropriate materials for use in the human body. Another problem is that the performance of
an implant may also depend on the design rather than the materials themselves. Even though
one may have an ideal material and design, the actual performance also greatly depends on the
skill of the surgeons and the prior condition of patients.
The success of soft tissue implants has primarily been due to the development of synthetic
polymers. This is mainly because the polymers can be tailor made to match the properties of
soft tissues. In addition, polymers can be made into various physical forms, such as liquid for
filling spaces, fibers for suture materials, films for catheter balloons, knitted fabrics for blood
vessel prostheses, and solid forms for cosmetic and weight-bearing applications.
It should be recognized that different applications require different materials with specific
properties. The following are minimal requirements for all soft tissue implant materials.
1. They should achieve a reasonably close approximation of the physical prop-
erties, especially flexibility and texture.
2. They should not deteriorate or change properties after implantation over
time.
3. If materials are designed for degradation, rate and modes of degradation
should follow the intended pathway.
4. They should not cause adverse tissue reaction.
5. They should be non-carcinogenic, non-toxic, non-allergenic, and non-
immunogenic.
6. They should be sterilizable.
7. They should be low cost.
Other important factors include the feasibility of mass production and aesthetic qualities.
11.1. SUTURES, SURGICAL TAPES, AND ADHESIVES
One of the most common soft tissue implants is suture. Sutures are used to close wounds due
to injury or surgery. In recent years, many new surgical tapes and tissue adhesives have been
added to the surgeon's armamentarium. Although their use in actual surgery is limited to some
surgical procedures, they are indispensable.
11.1.1. Sutures
There are two types of sutures according to their physical in-vivo integrity with time: absorb-
able (biodegradable) and nonabsorbable. They may be also distinguished according to their
source of raw materials, that is, natural sutures (catgut, silk, and cotton), and synthetic sutures
(nylon, polyethylene, polypropylene, stainless steel, and tantalum). Sutures may also be classi-
fied according to their physical form — monofilament and multifilament.
The various types of sutures are summarized in Table 11-1. The absorbable suture, catgut,
is made of collagen derived from sheep intestinal submucosa. It is usually treated with a chro-
mic salt to increase its strength and is crosslinked to retard resorption. Such treatment extends
the life of catgut suture from 3–7 days up to 20–40 days. Synthetic sutures absorb more slowly
B
IOMATERIALS
:A
N
I
NTRODUCTION
293
than the catgut. Most synthetic sutures are made from PGA and its copolymer with PLLA to
control absorption and flexibility for handling, as given in Table 11-2. The weight loss is di-
rectly related to the strength change, as shown in Figure 11-1. Time for essentially complete
absorption is depicted in Figure 11-2. The catgut absorbs the fastest, while PDSII suture is the
slowest. Table 11-3 gives initial strength data for catgut sutures according to their size. The
catgut sutures are stored with needles in a physiological solution in order to prevent drying,
which would make the sutures very stiff and hard and thus not easily usable.
Table 11-1
. Various Types of Sutures Quoted by Roby and Kennedy
Generic Major clinical
Representative
Representative
Suture type structure application Type
a
product manufacturer
Natural materials
Catgut
Protein
Plain: subcutaneous, rapid-healing T
Surgical gut
Ethicon
tissues, ophthalmic
T
Surgical Gut
Ethicon
Chromic: Slower-healing tissues
T
Chromic, plain gut
Syneture
Silk
Protein
General suturing, ligation
B
Perma-Hand
Ethicon
B
Softsilk
Syneture
Synthetic nonabsorbable materials
Polyester
PET
Heart valves, vascular
B
Ethibond Excel
Ethicon
prostheses, general
B
Surgidac
Syneture
B
Ti-Cron
Syneture
B
Tevdek
Teleflex
Polybutester
Plastic, cuticular
M
Novafil
Syneture
Cardiovascular
M
Vascufil
Syneture
Polypropylene PP
General, vascular anastomosis
M
Prolene
Ethicon
M
Surgipro
Syneture
M
Surgipro II
Syneture
M
Deklene II
Teleflex
Polyamide
Nylon 6, 6,6
Skin, microsurgery, tendon
M
Ethilon
Ethicon
M
Monsof
Syneture
M
Dermalon
Syneture
B
Nurolon Ethicon
B
Surgilon
Syneture
Stainless steel
CrNiFe alloy
Abdominal and sternal
M, T
Ethisteel
Ethicon
closures, tendon
M, T
Steel
Syneture
M, T
Flexon
Syneture
Fluoropolymers
ePTFE
General, vascular anastomosis
M
Gore-Tex
W.L. Gore
PVF/PHFP
M
Pronova
Ethicon
Synthetic absorbable materials
Braids
PGA/PLLA
Peritoneal, fascial, subcutaneous
B
Vicryl
Ethicon
PGA/PLLA
B
Vicryl Rapide
Ethicon
PGA/PLLA
B
Panacryl
Ethicon
PGA/PLLA
B
Polysorb
Syneture
PGA
B
Dexon
Syneture
PGA
B
Bondek
Teleflex
Monofilaments
PDO
Application dependent on ten-
M
PDS II
Ethicon
PGAIPCL
sile strength loss profile required
M
Monocryl
Ethicon
PGA/PTMC/PDO
M
Biosyn
Syneture
PGA/PTMC
M
Maxon
Syneture
PGA/PCL/ PTMC/PLLA
M
Caprosyn
Syneture
: T, Twisted monofilament; M, monofilamene; B, multifilament braid
Reprinted with permission from Roby (1998). Copyright © 1998, Elsevier.
a
294
CH
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Table 11-2
. Polymer Composition of Synthetic Absorbable Sutures
Suture
Block structure
Polymer composition (%)
Multifilament braids
Dexon
PGA homopolymer
Vicryl
PGA/PLLA random copolymer
90/10
Polysorb
PGA/PLLA random copolymer
90/10
Panacryl
PGA/PLLA random copolymer
3/97
Monofilaments
PDS II
PDO homopolymer
–
Maxon
PGA–PTMC/PGA-PGA
100-85/15-100
Monocryl
PGA–PCL/PGA–PGA
100-45/55-100
Biosyn
PGA/PDO–PTMC/PDO–PGA/PDO
92/8-65/35-92/8
Caprosyn
PGAIPCL/PTMC/PLLA
70/16/8/5
random copolymer
Reprinted with permission from Roby and Kennedy (2004). Copyright © 2004, Elsevier.
Figure 11-1
. Weight and tensile strength loss after implantation of Vicryl
®
suture. Reprinted
with permission from Fredericks et al. (1984). Copyright © 1984, Interscience Publishers.
Figure 11-2
. Complete absorption times for various sutures. Reprinted with permission from
Roby (1998). Copyright © 1998, Sage Publications.
B
IOMATERIALS
:A
N
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NTRODUCTION
295
Table 11-3
. Minimum Breaking Loads for British-Made Catgut
Diameter (mm) Minimum breaking load (lbf)
Size
Minimum
Maximum
Straight pull
Over knot
7/0
0.025
0.064
0.25
0.125
6/0
0.064
0.113
0.5
0.25
5/0
0.113
0.179
1
0.5
4/0
0.179
0.241
2
1
3/0
0.241
0.318
3
1.5
2/0
0.318
0.406
5
2.5
0
0.406
0.495
7
3.5
1
0.495
0.584
10
5
2
0.584
0.673
13
6.5
3
0.673
0.762
16
8
4
0.762
0.864
20
10
5
0.864
0.978
25
12.5
6
0.978
1.105
30
15
7
1.105
1.219
35
17.5
Reprinted with permission from Rutter (1958). Copyright © 1958, Butterworths.
It is interesting to note that the stress concentration at a surgical knot decreases the suture
strength of catgut by half, no matter what kind of knotting technique is used. It is suggested
that the most effective knotting technique is the square knot with three ties to prevent loosen-
ing. According to one study, there is no measurable difference in the rate of wound healing
whether the suture is tied loosely or tightly. Therefore, loose suturing is recommended because
it lessens pain and reduces cutting into soft tissues.
Catgut and other absorbable sutures [e.g., copolymer of poly (glycolic acid) and (lactic
acid)] induce tissue reactions, although the effect diminishes as they are being absorbed. This
is true of other natural, nonabsorbable sutures like silk and cotton, which
showed more
reac-
tion than synthetic sutures like polyester, nylon, polyacrylonitrile, etc., as shown in Figure 11-
3. As is the case of the wound-healing process (discussed in Chapter 10), the cellular response
is most intensive one day after suturing and subsides in about a week.
As for the risk of infection, if the suture is contaminated even slightly, the incidence of in-
fection increases many fold. The most significant factor in infection is the chemical structure,
not the geometric configuration of the suture. Polypropylene, nylon, and PGA/PLA sutures
develop lesser degrees of infection than sutures made of stainless steel, plain, and chromic
catgut, and polyester. The ultimate cause of infection is a pathogenic microorganism not the
biomaterial. The role of suture in infection is to provide a conduit for ingress of bacteria, to
chemically or physically modify the body's immune response, or to provide an environment
favorable to bacterial growth.
Example 11-1
Compare the breaking strength of catgut sutures (Table 11-
3
) of sizes between 7/0 and 7. What
conclusion can you draw?
zanotowane.pl doc.pisz.pl pdf.pisz.pl hannaeva.xlx.pl
S
OFT
T
ISSUE
R
EPLACEMENT
—I:
S
UTURES
,S
KIN
,
AND
M
AXILLOFACIAL
I
MPLANTS
Schematic illustration of “smart,” “intelligent,” and “reversible memory” polymer systems. The
stimulating energy can be mechanical, thermal, or chemical. Reprinted with permission from
Hoffman (2004). Copyright © 2004, Elsevier.
291
292
CH
.11:S
OFT
T
ISSUE
R
EPLACEMENT
—I
In soft tissue implants, as in other applications that involve engineering, the performance of an
implanted device depends upon both the materials used and the design of the device or im-
plant. The initial selection of material should be based on sound materials engineering practice.
The final judgment on the suitability of a material depends upon observation of the in-vivo
clinical performance of the implant. Such observations may require many years or decades.
This requirement of in-vivo observation represents one of the major problems in the selection
of appropriate materials for use in the human body. Another problem is that the performance of
an implant may also depend on the design rather than the materials themselves. Even though
one may have an ideal material and design, the actual performance also greatly depends on the
skill of the surgeons and the prior condition of patients.
The success of soft tissue implants has primarily been due to the development of synthetic
polymers. This is mainly because the polymers can be tailor made to match the properties of
soft tissues. In addition, polymers can be made into various physical forms, such as liquid for
filling spaces, fibers for suture materials, films for catheter balloons, knitted fabrics for blood
vessel prostheses, and solid forms for cosmetic and weight-bearing applications.
It should be recognized that different applications require different materials with specific
properties. The following are minimal requirements for all soft tissue implant materials.
1. They should achieve a reasonably close approximation of the physical prop-
erties, especially flexibility and texture.
2. They should not deteriorate or change properties after implantation over
time.
3. If materials are designed for degradation, rate and modes of degradation
should follow the intended pathway.
4. They should not cause adverse tissue reaction.
5. They should be non-carcinogenic, non-toxic, non-allergenic, and non-
immunogenic.
6. They should be sterilizable.
7. They should be low cost.
Other important factors include the feasibility of mass production and aesthetic qualities.
11.1. SUTURES, SURGICAL TAPES, AND ADHESIVES
One of the most common soft tissue implants is suture. Sutures are used to close wounds due
to injury or surgery. In recent years, many new surgical tapes and tissue adhesives have been
added to the surgeon's armamentarium. Although their use in actual surgery is limited to some
surgical procedures, they are indispensable.
11.1.1. Sutures
There are two types of sutures according to their physical in-vivo integrity with time: absorb-
able (biodegradable) and nonabsorbable. They may be also distinguished according to their
source of raw materials, that is, natural sutures (catgut, silk, and cotton), and synthetic sutures
(nylon, polyethylene, polypropylene, stainless steel, and tantalum). Sutures may also be classi-
fied according to their physical form — monofilament and multifilament.
The various types of sutures are summarized in Table 11-1. The absorbable suture, catgut,
is made of collagen derived from sheep intestinal submucosa. It is usually treated with a chro-
mic salt to increase its strength and is crosslinked to retard resorption. Such treatment extends
the life of catgut suture from 3–7 days up to 20–40 days. Synthetic sutures absorb more slowly
B
IOMATERIALS
:A
N
I
NTRODUCTION
293
than the catgut. Most synthetic sutures are made from PGA and its copolymer with PLLA to
control absorption and flexibility for handling, as given in Table 11-2. The weight loss is di-
rectly related to the strength change, as shown in Figure 11-1. Time for essentially complete
absorption is depicted in Figure 11-2. The catgut absorbs the fastest, while PDSII suture is the
slowest. Table 11-3 gives initial strength data for catgut sutures according to their size. The
catgut sutures are stored with needles in a physiological solution in order to prevent drying,
which would make the sutures very stiff and hard and thus not easily usable.
Table 11-1
. Various Types of Sutures Quoted by Roby and Kennedy
Generic Major clinical
Representative
Representative
Suture type structure application Type
a
product manufacturer
Natural materials
Catgut
Protein
Plain: subcutaneous, rapid-healing T
Surgical gut
Ethicon
tissues, ophthalmic
T
Surgical Gut
Ethicon
Chromic: Slower-healing tissues
T
Chromic, plain gut
Syneture
Silk
Protein
General suturing, ligation
B
Perma-Hand
Ethicon
B
Softsilk
Syneture
Synthetic nonabsorbable materials
Polyester
PET
Heart valves, vascular
B
Ethibond Excel
Ethicon
prostheses, general
B
Surgidac
Syneture
B
Ti-Cron
Syneture
B
Tevdek
Teleflex
Polybutester
Plastic, cuticular
M
Novafil
Syneture
Cardiovascular
M
Vascufil
Syneture
Polypropylene PP
General, vascular anastomosis
M
Prolene
Ethicon
M
Surgipro
Syneture
M
Surgipro II
Syneture
M
Deklene II
Teleflex
Polyamide
Nylon 6, 6,6
Skin, microsurgery, tendon
M
Ethilon
Ethicon
M
Monsof
Syneture
M
Dermalon
Syneture
B
Nurolon Ethicon
B
Surgilon
Syneture
Stainless steel
CrNiFe alloy
Abdominal and sternal
M, T
Ethisteel
Ethicon
closures, tendon
M, T
Steel
Syneture
M, T
Flexon
Syneture
Fluoropolymers
ePTFE
General, vascular anastomosis
M
Gore-Tex
W.L. Gore
PVF/PHFP
M
Pronova
Ethicon
Synthetic absorbable materials
Braids
PGA/PLLA
Peritoneal, fascial, subcutaneous
B
Vicryl
Ethicon
PGA/PLLA
B
Vicryl Rapide
Ethicon
PGA/PLLA
B
Panacryl
Ethicon
PGA/PLLA
B
Polysorb
Syneture
PGA
B
Dexon
Syneture
PGA
B
Bondek
Teleflex
Monofilaments
PDO
Application dependent on ten-
M
PDS II
Ethicon
PGAIPCL
sile strength loss profile required
M
Monocryl
Ethicon
PGA/PTMC/PDO
M
Biosyn
Syneture
PGA/PTMC
M
Maxon
Syneture
PGA/PCL/ PTMC/PLLA
M
Caprosyn
Syneture
: T, Twisted monofilament; M, monofilamene; B, multifilament braid
Reprinted with permission from Roby (1998). Copyright © 1998, Elsevier.
a
294
CH
.11:S
OFT
T
ISSUE
R
EPLACEMENT
—I
Table 11-2
. Polymer Composition of Synthetic Absorbable Sutures
Suture
Block structure
Polymer composition (%)
Multifilament braids
Dexon
PGA homopolymer
Vicryl
PGA/PLLA random copolymer
90/10
Polysorb
PGA/PLLA random copolymer
90/10
Panacryl
PGA/PLLA random copolymer
3/97
Monofilaments
PDS II
PDO homopolymer
–
Maxon
PGA–PTMC/PGA-PGA
100-85/15-100
Monocryl
PGA–PCL/PGA–PGA
100-45/55-100
Biosyn
PGA/PDO–PTMC/PDO–PGA/PDO
92/8-65/35-92/8
Caprosyn
PGAIPCL/PTMC/PLLA
70/16/8/5
random copolymer
Reprinted with permission from Roby and Kennedy (2004). Copyright © 2004, Elsevier.
Figure 11-1
. Weight and tensile strength loss after implantation of Vicryl
®
suture. Reprinted
with permission from Fredericks et al. (1984). Copyright © 1984, Interscience Publishers.
Figure 11-2
. Complete absorption times for various sutures. Reprinted with permission from
Roby (1998). Copyright © 1998, Sage Publications.
B
IOMATERIALS
:A
N
I
NTRODUCTION
295
Table 11-3
. Minimum Breaking Loads for British-Made Catgut
Diameter (mm) Minimum breaking load (lbf)
Size
Minimum
Maximum
Straight pull
Over knot
7/0
0.025
0.064
0.25
0.125
6/0
0.064
0.113
0.5
0.25
5/0
0.113
0.179
1
0.5
4/0
0.179
0.241
2
1
3/0
0.241
0.318
3
1.5
2/0
0.318
0.406
5
2.5
0
0.406
0.495
7
3.5
1
0.495
0.584
10
5
2
0.584
0.673
13
6.5
3
0.673
0.762
16
8
4
0.762
0.864
20
10
5
0.864
0.978
25
12.5
6
0.978
1.105
30
15
7
1.105
1.219
35
17.5
Reprinted with permission from Rutter (1958). Copyright © 1958, Butterworths.
It is interesting to note that the stress concentration at a surgical knot decreases the suture
strength of catgut by half, no matter what kind of knotting technique is used. It is suggested
that the most effective knotting technique is the square knot with three ties to prevent loosen-
ing. According to one study, there is no measurable difference in the rate of wound healing
whether the suture is tied loosely or tightly. Therefore, loose suturing is recommended because
it lessens pain and reduces cutting into soft tissues.
Catgut and other absorbable sutures [e.g., copolymer of poly (glycolic acid) and (lactic
acid)] induce tissue reactions, although the effect diminishes as they are being absorbed. This
is true of other natural, nonabsorbable sutures like silk and cotton, which
showed more
reac-
tion than synthetic sutures like polyester, nylon, polyacrylonitrile, etc., as shown in Figure 11-
3. As is the case of the wound-healing process (discussed in Chapter 10), the cellular response
is most intensive one day after suturing and subsides in about a week.
As for the risk of infection, if the suture is contaminated even slightly, the incidence of in-
fection increases many fold. The most significant factor in infection is the chemical structure,
not the geometric configuration of the suture. Polypropylene, nylon, and PGA/PLA sutures
develop lesser degrees of infection than sutures made of stainless steel, plain, and chromic
catgut, and polyester. The ultimate cause of infection is a pathogenic microorganism not the
biomaterial. The role of suture in infection is to provide a conduit for ingress of bacteria, to
chemically or physically modify the body's immune response, or to provide an environment
favorable to bacterial growth.
Example 11-1
Compare the breaking strength of catgut sutures (Table 11-
3
) of sizes between 7/0 and 7. What
conclusion can you draw?