Review A New Biomaterial Derived from Small Intestine

Review
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A New Biomaterial Derived from Small Intestine
Submucosa and Developed into a
Wound Matrix Device
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Marie Brown-Etris, RN, CWOCN;1 William D. Cutshall, MD;2 Michael C. Hiles, PhD3
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From 1Etris Associates, Inc., Philadelphia, Pennsylvania; 2Bloomington, Indiana;
and 3Cook Biotech Inc., West Lafayette, Indiana
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Abstract: A biomaterial derived from porcine intestinal submucosa has been used in the development of a new
biologic wound matrix. This review describes the origin of the wound matrix device, including the discovery of the
biomaterial and its properties, to the development of the commercial product currently in clinical use. The composition and structure of this biomaterial are described and considered as mechanisms that contribute to its effectiveness
in wound management. The wound matrix developed from this unique biomaterial was evaluated in a pilot study of
human partial-thickness dermal wounds and was found to be beneficial, especially in its dehydrated form. Other
applications of this biomaterial, as well as its limitations, are also discussed.
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Disclosure: This study was supported by a study grant from Cook Biotech, Inc., West Lafayette, Indiana. Dr. Hiles has
partial ownership in patents related to the subject matter of this manuscript and is employed by the company that manufactures the biomaterial.
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iomaterials have become critical components in the development of effective new
medical therapies for wound care. As limitations of previous generations of biologically derived materials are overcome, many new
and impressive applications for biomaterials are
being examined. A new biomaterial was first discovered in 1987 at Purdue University (West
Lafayette, Indiana) when researchers were evaluat-
ing various biological materials as blood conduits.
This biomaterial was derived from small intestine
submucosa (SIS). The SIS biomaterial has since been
developed into several medical products currently
used by healthcare providers in the clinical setting.1,2
Initial investigations leading to the evaluation of
SIS as an implantable biomaterial began with the
use of sections of whole small intestine. However,
the sections of small intestine tissue proved to be
Address correspondence to:
Marie Brown-Etris, RN, CWOCN, Etris Associates Inc., 14450 Bustleton Ave., Philadelphia, PA 19116
Phone: (215) 673-3600; Fax (215)673-9892; E-mail: [email protected]
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“smart remodeling” by researchers.5 A biomaterial
with such properties was anticipated to provide a
suitable covering for dermal wounds, and a preclinical animal study has specifically demonstrated
the potential effectiveness of SIS as a biologicalderived dressing in the clinical setting.9
In this review, we report the results of a pilot
study showing the initial clinical experiences with
the wound matrix device (WMD)* developed from
the SIS biomaterial. A discussion of the need for and
advantages associated with biological-derived
dressings as compared to synthetic dressings is followed by a brief review of the discovery and development of the SIS biomaterial. The significant properties revealed in pre-clinical studies and the mechanisms behind the effective tissue restorative properties of the biomaterial are detailed. Finally, the initial clinical experiences with the WMD designed for
dermal application and the development of other
healthcare products from the SIS biomaterial are
discussed.
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too active enzymatically to retain sutures. Subsequent implantation studies used intestine with various layers removed. In the end, the most successful
graft was composed solely of the thin, translucent,
but resilient, submucosal layer that remained after
removing the mucosal and muscular layers. The
submucosal layer of the small intestine is approximately 0.15 to 0.25mm thick and consists primarily
of a collagen-based extracellular matrix (ECM) containing relatively few resident connective tissue
cells.3 This layer provides structural support, stability, and biochemical signals to the rapidly regenerating mucosal cell layer. The naturally cross-linked
collagen network of the submucosal layer also gives
strength to the whole intestine. For these reasons,
SIS biomaterial was derived from this intestinal
layer and used initially for vascular graft studies.4,5
Currently, SIS biomaterial is harvested from a
porcine source and minimally processed to lyse all
resident cells and remove cellular debris as
described elsewhere.6,7 SIS biomaterial is sterilized
using a proprietary method that includes treatment
with ethylene oxide. This sequential processing
method allows long-term storage of the acellular
sheet of ECM without destroying its ability to support wound healing and tissue repair.8
Following the initial discovery and evaluation,
this naturally occurring ECM-based biomaterial
was tested in a number of pre-clinical studies to
evaluate its biocompatibility and persistence upon
implantation. The SIS biomaterial is biocompatible
in all host species tested. In addition, the biomaterial was remodeled gradually into new tissue by the
host. This phenomenon was particularly remarkable because the new tissue generated by the host
was specific to the site of implantation rather than a
generalized fibrotic tissue. For example, when SIS
was implanted in place of a blood vessel, within
four months the biomaterial had been incorporated
and replaced by new tissue, which appeared nearly
identical to the original vessel.4 Even though the
conduit had been formed from a single layer of the
thin SIS biomaterial, a multilayered vessel was
formed, which was several times thicker than the
original SIS. The implanted graft supported the
development of new artery tissue with an intimal
lining of endothelial cells and a supporting outer
layer of muscle tissue. This regeneration of tissue
structures following implantation has been termed
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Synthetic and Biological-Derived
Wound Dressings
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Accepted goals of state-of-the-art wound care
include wound hydration, thermal insulation, protection from infection and desiccation, and facilitation of healing. Additionally, wound care dressings
must be devoid of toxins and infectious agents, be
easily placed and replaced, and be an aid to wound
drainage. The wound healing process, in dermal or
other tissue sites, is a complex process of tissue
restoration.10,11 The wound healing process can lead
either to fibrotic tissue replacement (scarring) with
limited functional restoration or to natural tissue
restoration, particularly in healing by second intention. Very few, if any, current wound care products
have the capacity to direct the healing process
towards tissue restoration.
The hundreds of wound care dressings presently
available can be divided into two broad categories:
synthetic (including biosynthetic) and biologic (tissue origin). Synthetic wound dressings are typically
inexpensive, have long shelf life, induce minimal
inflammatory reaction, and lack the risk of disease
agent transmission. Such synthetics/biosynthetics
include textiles, polyurethane films, foams, hydrogels, hydrocolloids, and collagen/alginate combina151
ETRIS, ET AL.
Table 1. Summary of pre-clinical studies with SIS biomaterial\
References
Key Property
Study
Result
Smart remodeling: SIS
scaffolds regenerate into
host tissue structures, with
SIS biomaterial responding
to site-specific stressors
Evaluated implanted SIS
scaffold as a bladder wall
patch with pressurized static flow
SIS scaffold remodeled into
bladder wall having measurable contractile activity
and active nerve receptors
comparable to normal
bladder
Evaluated implanted SIS
scaffolds in tendonous and
ligamentous sites
Newly deposited connective tissue replacing SIS
was highly organized
along lines of stress
31–33
Evaluated implanted single
layer of SIS as a blood
vessel
SIS scaffolds remodeled, at
four months, into multilayer
vessel having intimal lining
of endothelial cells and
supporting outer layer of
muscle tissue
3, 4, 19, 23
Rapid cellular infiltration
and angiogenesis was
observed with capillary
ingrowth occurring after
four days, and the scaffolds remodeled into host
tissues
3, 5, 19, 20–22, 24,
28–30, 34
Evaluated and compared
resistance to bacterial
infection, SIS vs. synthetic
graft materials
SIS implants were less likely to harbor infection than
synthetic graft implants.
Thought to be due to 1)
rapid and high levels of
vascularization induced by
SIS and 2) degradation of
material unable to provide
a nidus for infection
4, 5, 40, 41
Evaluated implanted SIS
scaffolds in a full-thickness
rat skin replacement study;
in a dural replacement
study; in a bone regeneration study
SIS produced less contracture than control wounds
with good epithelialization; no evidence of infection or acute or delayed
hypersensitivity reactions
at any sites
9, 35–37, 44
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Greater resistance to infection
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Lack of adverse immunological reaction
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Evaluted implanted SIS
scaffolds in the vascular,
urological, and muscular
systems
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Rapid capillary ingrowth:
thought critical to successful tissue replacement
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F i g u r e 1 . SIS biomaterial provides a natural,
extracellular matrix scaffold with three-dimensional
structure and a biochemical composition that is
attractive to host cell infiltration and conducive to tissue
regeneration. A) After SIS is implanted, nutrients and
cells infiltrate from adjacent tissues. B) Host cells rapidly
invade the SIS biomaterial scaffold and begin to signal
for capillary ingrowth. C) SIS is remarkably strong at
time of implant, but gradually is remodeled by host cells
into the appropriate replacement tissue for the damaged
site. D) The integrity of the tissue is restored and the new
tissue becomes completely “self.”
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tions. Synthetics, such as these, have been designed
primarily around the moist wound theory of
wound healing put forth by Winter12 and function
well as short-term moisture barriers. However, others have challenged the theory as being insufficient
to the promotion of regenerative wound healing.13
Biological-derived wound dressings have been
advocated for their ability to more effectively promote granulation and epithelialization of dermal
wounds than synthetic dressings. In addition, biological-derived wound dressings effectively regulate evaporation and exudation and effectively protect the wound site from bacterial infection. Biologic-derived wound dressings are not new, but their
effectiveness has increased greatly with recent innovative developments. Early biological-derived
dressings include a collagen-based dressing made
from porcine skin in the 1960s14 with the first reported clinical use of a porcine skin dressing in 1973.15
Sheets of collagen, laboriously harvested from
sheep intestine, have also been used as wound
dressings.16 More specialized biological-derived
dressings have been developed since these early
studies were reported. These products include a
product derived from human cadaver skin, which is
treated to be acellular and deepidermalized to provide a near natural neodermis for skin re-growth**;
a product prepared by seeding dermal fibroblasts
on a biodegradable matrix***; and a tissue-engineered human skin equivalent made by layering a
sheet of stratified human epithelium onto a bovine
collagen matrix impregnated with human foreskin
fibroblasts (HSE)†. Such technologically advanced
products are approaching the equivalent of human
skin replacement; however, they are still limited by
the extensive preparation time (17–20 days for
HSE), the high cost of manufacture, and the short
shelf life.17,18 Autologous skin grafts probably present the optimal wound dressing when considered
in terms of healing alone. However, additional site
morbidity and limited supply dramatically compromise the benefits of these wound dressings. Cellular
xenograft dressings remain immunologically
incompatible for human use.
An ideal wound dressing would be one made
from a readily available biomaterial that requires
minimal processing and, after sterilization and storage, retains the biological characteristics that promote wound healing. Such an acellular biologic
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Vol. 14, No. 4
May 2002
dressing would incorporate both the advantages
typical of synthetic dressings (low cost, long shelf
life, and low risk of immunological reaction) and
those typical of biological-derived dressings (regulated fluid flow, increased resistance to bacterial
contamination, and enhanced wound healing). SIS
biomaterial, derived as a by-product from porcine
small intestine, has demonstrated these characteristics.
Development of SIS Biomaterial into a
Wound Matrix: Pre-Clinical Studies with
SIS Biomaterial
The development of the new SIS biomaterial
began at Purdue University with a search for suitable vascular graft materials. SIS biomaterial was
observed to have excellent implant healing characteristics when implanted as a vascular replacement,
so the idea of its potential application to other sites
of tissue destruction, including healing of dermal
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SIS biomaterial induces rapid capillary
ingrowth. Pre-clinical studies also demonstrated
rapid capillary ingrowth after implantation of SIS
scaffolds. This rapid cellular infiltration and angiogenesis, thought critical to successful tissue replacement, was observed following implantation of SIS
scaffolds in the vascular,21,39 urological,25,26,28 and
muscular systems.32,34 In vascular implants, capillary
ingrowth was present after just four days.3
SIS biomaterial shows resistance to bacterial
infection. In pre-clinical implantation studies,
wounds treated with SIS have demonstrated
greater resistance to bacterial infection compared to
those treated with synthetic graft materials.4,40 A
subsequent study involving direct inoculation of
abdominal wall graft sites with Staphyloccocus
aureus (S. aureus) resulted in persistent infection in
the control group grafted with synthetic mesh,
while effective graft remodeling and absence of
infection were observed in the SIS biomaterial
group one month after implantation.41 One mechanism thought responsible for this infection resistance is the rapid and high levels of vascularization
induced by implantation of SIS biomaterial. A second possible mechanism is the fact that the SIS scaffold degrades as host tissue replaces it and therefore the tissue is unable to provide a long-term
nidus for infection.
SIS biomaterial does not induce an adverse
immunologic reaction. In none of the SIS pre-clinical implantation studies was there evidence of the
pronounced, chronic, foreign body reaction characterized by a high density of mononuclear
macrophages and often seen with synthetic
implants. The lack of adverse immunological reaction is thought to be related to the acellular condition and significant collagen composition of the SIS
biomaterial. Collagen proteins are highly conserved
across species and appear to be readily degraded
and/or incorporated into the new tissue with minimal antigenicity even when the implant source
material is xenogeneic.42,43 A high density of fibroblasts present in the neotissue 26 weeks after SIS
implantation into a ligamentous tissue site also suggested that collagen production and tissue remodeling can continue without adverse immune
response for an extended time until full regeneration is achieved.33 Furthermore, mice that showed
chronic inflammation and graft rejection when
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wounds, was nurtured in the context of numerous
pre-clinical studies. These studies repeatedly
demonstrated the ability of SIS biomaterial to
regenerate as host tissue, induce rapid capillary
ingrowth, be resistant to infection, and induce little
or no immunologic reaction (Table 1). The mechanisms behind these physiological phenomena are
beginning to be understood as inherent properties
of the architecture and composition of the SIS biomaterial.
SIS biomaterial regenerates as host tissue. The
results of numerous pre-clinical studies have
demonstrated that SIS biomaterial is capable of
inducing host tissue proliferation and replacement
when implanted in various tissue sites (Table 1). SIS
accomplishes this through smart remodeling. That
is, the SIS biomaterial provides a scaffold for regeneration of the host tissue with the SIS biomaterial
responding to natural, site-specific stressors (Figure
1). SIS biomaterial induction of host tissue proliferation and replacement has been demonstrated in
many tissues, including blood vessels,3,19–23 lower
urinary tract, 24–28 body wall,29,30 tendon,31,32 ligament,33,34 dura,35,36 and bone.37 Tissue regeneration
upon implantation of SIS biomaterial as diaphragmatic prosthesis also has been observed.38 Upon
implantation of the SIS biomaterial into these sites,
the biomaterial was remodeled by the host into
replacement tissue with site-specific structural and
functional properties. For example, following placement of SIS as an arterial vessel with pressurized,
pulsatile flow, the biomaterial was remodeled into
tissue with identifiable smooth muscle layers organized along lines of stress. 5 Similarly, when
implanted in a bladder site with pressurized static
flow, SIS was remodeled into a tissue with measurable contractile activity. In addition, SIS-regenerated bladder wall contained active nerve receptors
comparable to normal bladder.25 In contrast, SIS
biomaterial implanted into a venous location did
not evidence any actin-containing spindle cells.5
Similar results were reported for implantation of
SIS into tendonous and ligamentous sites. Newly
deposited connective tissue replacing the SIS was
highly organized along lines of stress.31,33 The poorly
organized fibrous granulomas surrounding
implanted synthetic materials observed in comparisons in abdominal wall sites contrasted greatly
with the remodeling of SIS biomaterial.30
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environment for the resident cells of a tissue. In the
absence of resident cells, such a collagen matrix provides an immediately stable environment for infiltrating host cells.
Other critical components of the ECM are naturally embedded within or attached onto the collagen scaffold of the biomaterial (Table 2). Some of
the more important components are complexes of
protein and carbohydrate: glycoproteins, proteoglycans, and glycosaminoglycans (GAG). Many glycoproteins and proteoglycans contain specific sites on
their protein portion that help cells to attach and
settle within the matrix.46,47 By providing such cell
attachment sites in the matrix, these molecules contribute to the re-population of the matrix and to the
regulation of cell migration, proliferation, and differentiation. Each of these cellular processes is necessary for remodeling tissue to mature into fully
functional tissue.
Glycosaminoglycans are integral to the matrix
architecture and consist of a core protein molecule
extensively decorated with long complex carbohydrate chains. Many of the carbohydrates are electrostatically charged, and when linked together they
form highly charged, space-filling complexes. These
complexes are responsible for the high water retention properties and the compressibility of the
matrix. Five types of GAG molecules have been
identified in SIS biomaterial: heparan sulfate,
hyaluronic acid, chondroitan sulfate A, dermatan
sulfate, and heparin.48 Preliminary evidence also
exists for several essential proteoglycans and glycoproteins in the SIS biomaterial, including the important cell-regulating molecule fibronectin.49
Another component of the SIS biomaterial critical to its mechanism of action is its growth factor
content. Growth factors are typically small protein
molecules found in limited quantities in cells and
cell environments. These highly potent molecules
regulate many aspects of cellular activity, including
stimulating growth and cell division, migration,
and differentiation. These activities are essential to
the regenerative aspect of wound healing.11 Two
important molecules, identified as the major growth
factor components of SIS, are fibroblast growth factor-2 (FGF-2) and a transforming growth factor(TGF- ) related protein.50 Both of these proteins are
known to participate in wound repair, particularly
in vascular development. In addition, vascular
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implanted with xenogeneic tissue had only an acute
inflammatory response and active tissue remodeling when implanted with SIS biomaterial grafts.
The type of immune response induced by the SIS
biomaterial was consistent with graft accommodation based upon antibody and cytokine analysis.44
In a full-thickness, rat skin replacement study, no
acute or delayed hypersensitivity reactions were
observed.9 Additionally, many aspects of the tissue
regenerative healing response to implantation of SIS
were reproduced in this animal study directed
toward dermal application. The SIS biomaterial significantly reduced the contraction observed in control wounds. SIS-treated wounds developed a
healthy epithelial layer covering and had no signs
of infection.
These pre-clinical implantation studies provided
the basis for developing a clinical wound care product from the SIS biomaterial. Additional research on
the basic properties of SIS biomaterial have provided a clearer understanding of the fundamental
mechanisms by which such a wound care product
could function.
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Studies on the Mechanisms Behind the
Tissue Repair Properties of SIS
Biomaterial
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The working hypothesis has been that both the
composition and the architecture of the SIS biomaterial contribute to its induction and enhancement
of tissue remodeling.4,5,7 The actual mechanisms
behind this tissue restoring property of SIS biomaterial have been investigated at biochemical, structural, and cell biological levels (Table 2).
Biochemical composition of SIS biomaterial.
Studies on the composition of SIS have revealed
that the biomaterial has a water content of approximately 90 percent in its fully hydrated form. This
high water content is consistent with having originated from a natural tissue source. The nonwater
portion of the biomaterial is approximately 90-percent protein with the remainder comprised of mainly carbohydrate and some lipid. The high protein
content consists primarily of collagens, with types I,
III, and V predominating.45 In tissue, these collagen
proteins form the scaffolding of the robust threedimensional network of the ECM. This threedimensional matrix provides a suitable structural
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Table 2. Mechanisms of tissue repair properties of SIS biomaterial
Functional Effect
Component
Property
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Biochemical Composition
• Water content 90%, remainder proteins primarily collagens
• Predominately types I, III, V
• Three-dimensional collagen matrix provides immediately stable environment
for infiltrating host cells
• Collagens are highly conserved across
species
Protein-carbohydrate complexes
• Glycoproteins (including fibronectin)
• Proteoglycans
• Glycosaminoglycans (including
heparin sulfate, hyaluronic acid, chondroitan sulfate A, dermatan sulfate and
heparin)
• Provide cell attachment sites in the
matrix
• Regulation of cell migration, proliferation, and differentiation necessary for
maturation of developing tissue
• Structual organizers for tissues as well
as signaling molecules for cells
• High water retention properties and
compressibility of the matrix
Growth factors
• Fibroblast growth factor-2 and transforming growth factor- related protein
• Vascular endothelial growth factor
• Other growth factors still being identified
Structural Properties
• Microscopic pores and tunnels
• Limited porosity; hydrated form has
porosity between nonporous ureter and
relatively porous caron mesh
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Porosity
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Proteins
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Strength and flexibility
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Cell Growth Properties
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• Participate in vascular repair and
development; stimulate migration and
proliferation of fibroblasts and other
cells
• Promotes the formation of new capillaries (angiogenesis)
• May aid cellular infiltration and rapid
new vessel in-growth
• Limited water flow suggests that the
material may serve as an effective barrier to wound bed dehydration while
preventing sub-dressing seroma formation
• Interwoven pattern of collagen fibers of
varying sizes
• Naturally cross-linked collagen and
matrix components
• Retains strength and flexibility similar
to the intestinal tissue from which it is
derived
• More compliant than venous or synthetic graft materials
• Substrate for multiple cell types in culture
• Stimulation of cell proliferation and differentiation was observed
• Various cell types exhibited their natural phenotype and morphology when
grown on the SIS biomaterial
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endothelial growth factor (VEGF) has been identified as a component of SIS.51 VEGF is also an important regulatory molecule that induces the migration
of endothelial cells. Several other known growth
factors have been tentatively identified in the SIS
biomaterial and are thought to contribute to the
development of a healthy epithelial cell layer.52
Several of the bioactive components of ECM tissues are highly labile when isolated in solution. This
is particularly true of growth factors. However,
these components show remarkable stability when
bound to the matrix,53,54 even when exposed to fairly
harsh chemical treatments. This appears to be true
for the SIS biomaterial as well, where growth factor
activity remained detectable after terminal sterilization.8 SIS biomaterial used in pre-clinical studies
was routinely disinfected before implantation.
Treatments such as 0.05-percent gentamycin, 10percent neomycin, or 0.1-percent peracetic acid
were without effect on the remodeling properties of
the biomaterial.7,26,31,33 In addition, various sterilization methods for the biomaterial were evaluated
and their effect on biological activity was found to
be treatment dependent.45
These many biologically important components
together with the matrix of collagen as a scaffold, in
a natural architectural configuration, appear to offer
a remarkable environment for induction and regulation of tissue regeneration, particularly for a dermal wound.
Structural properties of SIS biomaterial. The
microstructure of the SIS biomaterial has been studied using high-resolution microscopy.7 Such studies
have determined that the natural three-dimensional
architecture of the tissue ECM is retained in the SIS
biomaterial (Figure 2). The orientation changes
across the thickness ranging from a definite crosshatch pattern to a random weave pattern. In lower
power optical images, remnant structures of blood
vessels are observed as regularly interspersed
throughout the patterns of collagen fibers (Figure
3). Such microscopic pores and tunnels give the biomaterial a limited porosity55 and may aid in the cellular infiltration and the rapid new vessel in-growth
observed upon implantation of the SIS biomaterial.
Several additional structural properties of this
biomaterial also have been investigated. The measured porosity values of hydrated SIS were lower
from the luminal (mucosal) than the abluminal
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Figure 2. High resolution imaging of SIS biomaterial
reveals the pattern of collagen fibers of the tissue. A)
SEM of the abluminal (serosal) surface of the
biomaterial reveals a “loose-weave” pattern of collagen
fibrils. B) Scanning electron microscopy of the lumenal
(mucosal) surface of the biomaterial shows the dense
packing of collagen fibrils.
(serosal) side due to the oriented architecture of the
biomaterial. These values were intermediate
between those of nonporous bovine ureter and relatively porous, synthetic Dacron mesh used for vascular grafts.4,55,56 These results indicated that the biomaterial has a limited capacity for water flow
through. This suggests that the material might serve
as an effective barrier to wound bed dehydration
while preventing sub-dressing seroma formation;
both of which are critical to the effective clinical
management of acute and chronic skin wounds.
Fully hydrated SIS biomaterial exhibits strength
and flexibility values similar to the intestinal tissue
from which it is derived, even after being
lyophilized for long-term storage. The nominal
burst force of SIS biomaterial was determined to be
between the lower values of bladder wall, aorta,
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Table 4. Time to wound healing
Patients Available
for Follow Up
Time to Wound healing
4 weeks
or less
5 to 8
weeks
8 weeks
or more
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2
4
1
Hydrated
7
1
2
0
7/7 (100%)
3/7 (40%*)
A
Lyophilized
Complete Healing
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Form of Wound
Matrix
for each wound and divided into three categories:
1) less than four weeks, 2) five to eight weeks, and
3) greater than eight weeks (Table 4). Three wounds
(two treated with WMD stored lyophilized and one
treated with the stored hydrated form) were completely epithelialized within four weeks. Six more
wounds (four with lyophilized and two with
hydrated) were observed to be completely epithelialized within the five-to-eight-week duration. One
wound (treated with the dressing stored
lyophilized) persisted for more than eight weeks,
but did completely epithelialize in ten weeks. Of the
remaining four wounds, all of which had been
treated with WMD stored hydrated, three were
switched to calcium alginate and one was switched
to the lyophilized form. The wound switched to the
lyophilized form of WMD at week two was completely epithelialized at week three.
The patient (32-year-old man) that was switched
to the lyophilized form of WMD presented with a
venous ulcer of the lower leg (Figure 5A). The patient
had recurring ulcerations due to congenital venous
abnormalities, and the present ulcer had persisted for
one month. At the initial visit, the wound was managed with WMD stored hydrated, and a compression bandage was applied and used throughout. At
the one-week visit, the wound was evaluated (Figure
5B). After cleansing, the wound area was determined
to have decreased in size by more than 50 percent
(Figure 5C), and a second application of WMD
stored hydrated was made (Figure 5D). At the second visit (14 days) the wound was again evaluated
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3). Most patients were nonsmokers and were nondiabetic. Several partial-thickness wound types were
present in the evaluation, including pressure ulcers,
venous ulcers, trauma wounds, and drug-induced
ulcers (hydroxyurea, a chemotherapeutic agent).
Wounds were measured, photographed, and traced
for accurate surface area determination.63 The average wound area measured 3.96cm 2 (range
0.42–15.48) at time of initial treatment. One patient
(87-year-old man) expired due to congestive heart
failure (CHF) eight days after the initial treatment.
This left 14 patients to follow up for wound healing
evaluation.
The lyophilized (i.e., dry) WMD was easily
placed and hydrated without difficulty in all cases
and was preferred due to the greater ease of handling. The hydrated form was found to be less useful on highly exudative wounds as it resisted adherence to the wound bed. At various times in the
course of healing, the dressing became translucent
in appearance on the wound bed or became incorporated into the granulating bed (Figure 4). In most
wounds the absorption of the dressing was
observed to be primarily in the central region of the
wound. Where the dressing had become translucent
or absorbed, new dressing was applied directly on
top of the region without attempting to remove that
portion of the previous dressing which typically
presented with attachment to the wound margin.
Wounds were epithelialized with minimal to no
scar formation (Figure 4).
Time to complete epithelialization was evaluated
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* Patient 10—switched to calcium alginate after eight weeks of treatment.
Patient 11—switched to calcium alginate after three weeks of treatment.
Patient 12—switched to lyophilized WMD after two weeks of treatment; wound healed within one week of treatment with lyophilized WMD.
Patient 14—switched to calcium alginate after eight weeks of treatment.
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were evaluated in these studies: 1) Could the apparent stimulation of cell proliferation and differentiation, observed in SIS implantation studies, be
observed in cell culture? and 2) Would different cell
types respond differently to the SIS biomaterial? SIS
biomaterial supported cell morphologies that
resembled the morphologies observed in the tissue
of origin for the four different cell types tested:
squamous epithelial (pulmonary artery), fibroblastic (embryo), smooth muscle-like (urinary bladder),
and glandular epithelial (adenocarcinoma).7 This
propensity for maintaining or restoring phenotypic
morphology was in contrast to two other materials
used for growing cells in culture: a pure collagen
based gel substance (Vitrogen, Cohesion Technologies) and a basement membrane extract formed into
a gelled matrix (Matrigel™, Becton, Dickinson and
Co.). The pure collagen gel allowed cell proliferation without significant differentiation. In contrast,
the gelled basement membrane extract greatly limited cell proliferation and induced an altered morphology not common to the cells in their tissue of
origin. These results supported the hypothesis that
SIS biomaterial retains a unique structure and composition that enables cells to develop and maintain
a natural tissue morphology. These results also are
in agreement with the theory put forth by Bissell,61
that the architecture and structural properties of the
extracellular matrix are equally as important to cell
response as the composition of the matrix. These
observations were confirmed using a different selection of cells that included primary human keratinocytes, human microvascular endothelial cells
(HMECs), and an established rat osteosarcoma
(ROS) cell line.59 Each of these cell types also maintained the ability to attach and proliferate on the SIS
biomaterial. The keratinocytes migrated more freely
into the three-dimensional scaffold of the SIS
matrix, whereas the ROS cells and the HMECs
remained on the surface. In addition, a study of cell
attachment properties of SIS biomaterial using
HMECs demonstrated that the adherence of
HMECs to hydrated SIS was greater than to several
other ECM components tested individually.62
These studies of cell attachment, proliferation,
and migration in and through the SIS biomaterial
further demonstrated its ability to orchestrate physiological cell behavior even in culture. Since the SIS
biomaterial retains the matrix architecture and com-
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and colon and the higher value of abdominal body
wall.57 The compliance (expandability) of SIS biomaterial configured as a small-diameter graft is about
50 percent of that of the dog carotid artery. However, SIS biomaterial is much more compliant (four
times) than a typical vein graft, and more than an
order of magnitude compliant than synthetic vascular grafts.58 In studies of tensile strength, force measurements were made of the maximum force
required to tear a multilayer SIS device used for ligament replacement.33 The strength of the multilayer
SIS biomaterial greatly increased from before
implantation to after 26 weeks of remodeling as a
ligament. The suture retention strength for singlelayer SIS biomaterial also was significantly higher
than the calculated physiologic forces exerted by tissues in several common implantation sites including bladder wall, aorta, colon, and abdominal body
wall.
Cell biological properties of SIS biomaterial.
The unusual tissue remodeling ability of the SIS biomaterial prompted in-vitro cell culture studies into
the responses of various cell types to this extracellular matrix material. In-vitro cell culture, using SIS
biomaterial as a substrate, provides an environment
very similar to wounded tissue in which to study
cellular responses. Cells in this environment can
migrate, proliferate, attach to the substrate, and differentiate in a liquid medium with serum and cell
stimulating factors present. Such studies have
involved isolated cell lines, both primary cultures
and established cultured lines, grown in the presence of the SIS biomaterial.7,59,60 Two basic questions
IC
Figure 3. Lower power optical image of SIS showing
the collagen fiber matrix regularly interspersed with the
remnant structures of blood vessels.
158
WOUNDS: A Compendium of Clinical Research and Practice
ETRIS, ET AL.
Gender
Men
Women
Race
Caucasian
Age (years)
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Wound
Characteristics
Mean ± SD
Range
Etiology
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Vol. 14, No. 4
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Wound area
(cm2)
8, 53.3%
7, 46.7%
15, 100%
72 ± 19
37–92
Pressure
Venous
Trauma or DrugInduced
3, 20%
9, 60%
3, 20%
Foot
Lower Leg
4, 26.7%
11, 73.3%
Mean ± SD
Range
3.96 ± 4.15
0.42–15.48
PL
WMD, developed from SIS biomaterial, was subjected to biocompatibility testing prior to its use in a
clinical setting. Following completion of standard
in-vitro and in-vivo biocompatibility testing, WMD
was cleared by the Food and Drug Administration
(FDA) for the intended use of management of partial-thickness wounds.
WMD was evaluated in a pilot study for effectiveness in treating partial-thickness skin wounds.
The dressings used in this study were supplied as
7cm x 10cm sheets having a thickness of approximately 0.15mm. The sterile dressings, intended for
one time use, were stored either at room temperature in a lyophilized (i.e., dry) state or refrigerated
in a fully hydrated state. At the time of application,
the WMD was cut to size, slightly larger than the
wound, and the lyophilized form was hydrated
with sterile saline after placement. The lyophilized
form had preferred handling characteristics to the
fully hydrated form. However, both forms were
evaluated to determine if their effects on wound
management differed in any way from each other.
Wounds presenting with clinical signs of infection
were treated with antibiotic therapy prior to or coincident with the initial application of WMD. A secondary absorbent film dressing was applied after
placement of the WMD to further protect the healing environment and to maintain good contact with
the wound bed, although the WMD, particularly
the dry form, was immediately adherent to the
wound. Necessity of repeat applications of the
WMD was determined for each wound based on
the amount of dressing observed on the surface of
the wound and the extent of epithelialization at
each change of secondary dressing.
The simplicity of application of the WMD
N, %
Patient
Demographics
TE
Initial Clinical Experience with the
Wound Matrix
Table 3. Patient demographics and wound
characteristics
A
position of healthy tissue, it encourages cell growth
and development towards a normal tissue state.
This orchestration of cellular response is believed to
be a significant mechanism behind the healing
properties observed in preclinical studies. Taken
together, all of the in-vitro studies of the SIS biomaterial fully supported the development of a clinical
wound care product particularly oriented toward
dermal repair.
allowed for patients enrolled in this pilot study to
be treated at a variety of clinical sites, including
long-term care facilities, a wound care facility treating outpatients, or in home care. Occasionally
patients were instructed to reapply the dressing by
themselves between visits.
Patients were selected based on the following
broad inclusion criteria: greater than 18 years of age
and presence of at least one partial-thickness
wound. Exclusion criteria included life expectancy
less than five months, concurrent adjunct treatment
modalities, such as whirlpool treatment or electrical
stimulation to target wound, uncontrolled diabetes,
and known allergy or cultural/religious objections
to porcine products. Wound assessments were
made at baseline and weekly or more frequent
intervals depending upon wound severity, frequency of dressing changes, and stage of healing until
wounds were considered healed. Additionally, the
patient’s response to treatment and the condition of
the WMD were evaluated.
A total of 15 patients were evaluated (8 men, 7
women) with an average age of 72 ± 19 years (Table
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ETRIS, ET AL.
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body’s wound repair mechanisms. The mechanism
of action of this ECM biomaterial appears to be
linked to its basic tissue-like composition and architecture.7 SIS biomaterial retains the three-dimensional architecture created by the fibroblasts in vivo.
ECM architecture has been demonstrated to be a
critical component of tissue development and necessary for regenerative wound healing. 64,65 The
three-dimensional architecture of the SIS biomaterial is built upon the complex composition of various
collagens, proteoglycans, and glycosaminoglycans,
which provide the structural integrity, flexibility,
and elasticity appropriate for dermal wound covering and subsequent epithelialization. In wound
healing studies, the SIS biomaterial served as a scaffold for rapid vascularization and cellular invasion.
Both of these processes are necessary to provide
nutrients and signals in support of dermal regeneration and epithelial cell proliferation. In addition, the
presence of multiple growth factors, each having a
significant role on the stimulation and regulation of
tissue regeneration, is likely an important component contributing to the wound healing properties
of the biomaterial.50
With ECM biomaterials, the structural integrity
of the matrix provides a barrier to dehydration and
infection, the regulatory factors provide the signals
necessary for the propagation of new and healthy
tissue, and the native tissue architecture provides a
stable structure for cell attachment, proliferation,
and differentiation. Together these elements were
expected to combine to provide an exceptional environment to apply to dermal wounds. In light of this,
the initial clinical results demonstrating the utility
of the ECM based dressing are completely consistent with this expectation.
Several additional characteristics of the SIS biomaterial provide an advantage to any wound care
product developed from it. First, the biomaterial is
prepared from a porcine tissue, which is abundantly
available being a by-product of the meat packing
industry. Second, the SIS is minimally processed to
provide a cell-free, sterile biomaterial, which retains
many biological properties. The absence of severe,
complicated, or highly technological processing
means that production costs will be lower. Development of lower cost wound care alternatives is
becoming increasingly important due to projections,
which indicate that the patient population over 65
Discussion
U
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(Figure 5E) and switched to the stored dry form of
WMD because of the obvious exudate accumulation
beneath the dressing and because of the greater ease
of application for the patient. During the evaluation
in the third week, the wound was observed to be
completely epithelialized (Figure 5F).
With respect to clinical events observed during
the course of the study, two patients treated with
WMD stored hydrated developed infections; one of
these required hospitalization. Both of these
patients had venous ulcers with a history of recurrent cellulitis. There was no sign of infection in
patients treated with WMD stored dry, but a second
patient had CHF (in addition to the death due to
CHF mentioned above), and one patient had a
chemotherapy related drug toxicity which, on further exploration by the oncologist, was determined
to be the cause of the initial leg ulceration. However, there was no evidence of dressing-induced toxicity, clinical signs of rejection of the biomaterialbased dressing, or sub-dressing seroma as the
wounds progressed to full healing.
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This pilot study of the use of a new dermal
wound dressing made from SIS biomaterial demonstrated that the WMD was easy to apply (particularly the dry storage form), was nontoxic, and did not
induce an adverse immunological reaction even in
patients given repeated applications. The results
also demonstrated that placement of WMD on various nonhealing skin wounds and ulcers resulted in
initiation and complete epithelialization of the
wound. The complete epithelialization of wounds
treated with dry stored WMD versus the partial
epithelialization with the hydrated stored form
indicated that, for dermal applications, the dry form
was more effective. These observations and initial
clinical findings are consistent with the known
properties of the biomaterial, derived from the submucosa of porcine small intestine, and from which
the dressing was prepared. Results indicate that
WMD can be used to successfully manage acute
and chronic partial-thickness wounds due to its
excellent protective properties and ability to act as a
natural template for tissue regrowth.
Dressings derived from acellular ECM tissues are
likely to provide environments well suited for the
Vol. 14, No. 4
May 2002
161
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ETRIS, ET AL.
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Figure 4. Healing of partial-thickness skin wound using WMD. A) Wound measurement at initial visit. B) Placement of
lyophilized WMD onto the ulcer. The matrix adheres easily to the wound. C) Partial incorporation of the WMD into the
center of the wound. There was no need to remove the matrix after incorporation had begun. D) The wound is
prepared for a second application of lyophilized WMD. E) Reapplication of the matrix. F) The wound was completely
epithelialized by week four.
D
years of age will increase much faster than the general population. These patients require longer treatments for poorly healing wounds. Third, the facilitated epithelialization with the biomaterial results in
a tissue that has minimal scarring. This is especially
relevant to dermal wounds where cosmetically
162
acceptable appearance is often as important as functional restoration. In fact, in two recent studies in
which SIS biomaterial was placed into in-vivo models of growing animals, the SIS biomaterial was able
to provide functional tissue replacement even as the
tissue was growing with the host animal.38,66 Such
WOUNDS: A Compendium of Clinical Research and Practice
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Figure 5. Case study of patient treated initially with WMD stored hydrated and switched after two weeks to the
lyophilized form. A) Initial observation of nonhealing venous ulcer (1.5cm x 0.5cm) on the lower leg. B) Evaluation
after one week of treatment. C) After cleansing the wound area was measured. D) Second application of hydrated
WMD to the upper wound. The lyophilized WMD that was placed onto the lower wound ulcer is also visible. E)
Second week evaluation before wound cleansing and switching upper wound to WMD stored lyophilized. F) Final
visit, one week later, the wound was completely epithelialized.
preliminary reports suggest that SIS biomaterial
based wound care products can have even broader
applications to restoring functional tissue. Finally,
because the biomaterial is almost completely composed of proteins and carbohydrates, all of which
Vol. 14, No. 4
May 2002
are basic components of the extracellular matrix of
all species, there are no anticipated problems with
biocompatibility. Therefore, the wound care and
other medical products derived from this biomaterial are likely to rapidly become accepted among
163
ETRIS, ET AL.
A
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complications and has been used successfully in
pre-clinical studies of wound healing. This SIS biomaterial now has been developed into WMD. In
this pilot clinical study, this new wound matrix was
found to have similar outcomes as the biomaterial
when applied to partial-thickness wounds in
humans. These promising results justify further
evaluation of this biological-derived matrix for its
effectiveness toward the treatment of full-thickness
wounds.
IC
*OASIS ® Wound Matrix (Cook Biotech, Inc., West
Lafayette, Indiana)
** Alloderm® (LifeCell Corp., Branchburg, New
Jersey)
***Dermagraft ® (Smith & Nephew Inc., Largo,
Florida)
†Apligraf® (Novartis Pharmaceuticals Corp., East
Hanover, New Jersey)
‡ SURGISIS ® and SURGISIS ® ES (enhanced
strength) (Cook Biotech, Inc., West Lafayette,
Indiana)
N
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healthcare professionals.
SIS biomaterial has been recently developed into
several other medical products, which are sterile
biomaterial devices‡ intended for use as soft tissue
reinforcements. These products are implanted into
low-stress and high-stress body systems, respectively, and provide the additional strength and support
necessary to proper functioning of body tissue.
Other nondermal applications for the SIS biomaterial, which are already in clinical evaluation, include
urological, gynecological, and orthopedic uses.
This initial clinical study had several limitations
related to it being a pilot study. Progress in wound
management was monitored only out to 12 weeks,
and none of the wounds were large in surface area.
Patients were not defined by any specific pathophysiology (e.g., diabetes), and only partial-thickness wounds were addressed in this study. WMD
has recently been cleared by the FDA for full-thickness wounds, and fully controlled clinical studies
for partial- and full-thickness wounds are now in
progress.67,68
There are few limitations to the WMD produced
from SIS biomaterial, one of which is that a patient
with known sensitivity or with cultural and religious objections to porcine materials will not be able
to be treated with the product. A second limitation
is that even though the biomaterial has limited
porosity and provides a well-hydrated environment
for wound healing, it is not a moisture barrier.
Therefore, the wound covered by WMD must be
protected by an appropriate secondary dressing to
avoid wound dehydration.
The authors wish to acknowledge the professional contributions of Marian Punchello, LPN, and
Deborah Shields, RN, BSN, CWOCN, in the pilot
clinical study.
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D
O
Criteria that define dressings optimal for the
treatment of wounds with the goal of facilitating
rapid, pain-free, regenerative healing are directing
researchers and clinicians towards biologicalderived dressings. The development of effective
biological-derived dressings previously has been
limited by complications of immunologic rejection
and risk of disease/infection transfer. Problems of
insufficient structural integrity or, in contrast, insufficient elasticity and flexibility have also hampered
the use of biomaterials as wound dressings. A new
biomaterial derived from the submucosal portion of
porcine small intestine is not limited with these
164
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