Porcine small intestinal submucosa as a dural substitute

Evaluation of porcine-derived small intestine submucosa as a biodegradable graft for gastrointestinal healing

High-risk anastomoses in the gut may benefit from the application of a synthetic reinforcement to prevent an enteric leak. Recently a porcine-derived small intestine submucosa (SIS) was tested as a bioscaffold in a number of organ systems. The aim of this study was to evaluate the effectiveness of SIS in stimulating healing in the stomach. Twelve rats underwent surgical removal of a full-thickness gastric defect (1 cm) and subsequent repair with a double-layer patch of porcine-derived SIS. The graft was secured with interrupted sutures placed within 1 mm of the edge of the graft. After 21 days, the animals were killed and their stomachs harvested for histologic examination. Cross sections were processed for paraffin embedding and 4-micron sections were stained with hematoxylin and eosin. All animals survived, gained weight, and demonstrated no signs of peritonitis over the 3-week postoperative period. On postmortem examination, the defect was completely closed in all animals by granulation tissue and early fibrosis. Although most of the luminal surface of the grafted areas remained ulcerated, early regeneration of normal gastric mucosa was seen at the periphery of the defect. SIS may act as an effective scaffolding agent for intestinal mucosa and may offer protection in high-risk anastomoses.

The effect of a porcine-derived small intestinal submucosa product on wounds with exposed bone in dogs

OBJECTIVE

To determine the effect of a porcine-derived small intestinal submucosa product (PSIS) on healing time, epithelialization, angiogenesis, contraction, and inflammation of wounds with exposed bone on the distal aspect of the limbs of dogs.

STUDY DESIGN

Prospective, controlled, experimental study.

ANIMAL POPULATION

10 young adult, purpose-bred, male Beagles.

METHODS

Small wounds with exposed bone were created on the lateral aspect of metatarsal V and the medial aspect of metatarsal II on both hindlimbs. Three sheets of PSIS were sutured into the wounds of the treated limb, and the other limb served as a control. On day 10, punch biopsies of the medial metatarsal wounds were collected and were evaluated microscopically after routine hematoxylin and eosin and phosphotungstic acid hematoxylin (PTAH) staining. The lateral metatarsal wounds were evaluated by planimetry and laser Doppler perfusion imaging on days 7, 14, and 21. Time until complete wound healing was also recorded. The level of significance was set at P < or =.05 for all statistical analyses.

RESULTS

Laser Doppler perfusion measurements were significantly higher in control wounds on day 7, but no differences were noted on days 14 and 21. No significant differences in planimetric values, histopathologic appearance, or time until complete wound healing were noted among treated and control groups.

CONCLUSIONS

No objective differences in healing were noted between control wounds and wounds treated with PSIS.

CLINICAL RELEVANCE

There appears to be no contraindication to the use of PSIS on clean wounds with exposed bone on the distal limbs of dogs. However, our objective data provides no evidence that this product affects epithelialization, contraction, or time to complete healing in wounds with exposed bone.

The extracellular matrix as a scaffold for tissue reconstruction

The extracellular matrix (ECM) consists of a complex mixture of structural and functional proteins and serves an important role in tissue and organ morphogenesis, maintenance of cell and tissue structure and function, and in the host response to injury. Xenogeneic and allogeneic ECM has been used as a bioscaffold for the reconstruction of many different tissue types in both pre-clinical and human clinical studies. Common features of ECM-associated tissue remodeling include extensive angiogenesis, recruitment of circulating progenitor cells, rapid scaffold degradation and constructive remodeling of damaged or missing tissues. The ECM-induced remodeling response is a distinctly different phenomenon from that of scar tissue formation.

Small intestinal submucosa as a tunica albuginea graft material

PURPOSE

We evaluated the morphological, immunological and functional response to small intestinal submucosa grafting of the tunica albuginea to determine its potential as a grafting material for penile surgery.

MATERIALS AND METHODS

Male New Zealand White rabbits underwent a sham procedure (6) or tunical excision and grafting with small intestinal submucosa (6). The erectile response to the intracavernous vasoactive agents sodium nitroprusside plus a papaverine, phentolamine and prostaglandin E1 combination (Sigma Chemical Co., St. Louis, Missouri) was evaluated 45-day postoperatively. The area under the graft was evaluated for stromal collagen and smooth muscle content by Masson's trichrome stain. Protein expression of smooth muscle specific alpha-actin and the inflammatory markers inducible nitric oxide synthase (NOS) and transforming growth factor-beta1 (TGF-beta1) was evaluated by immunohistochemical methods. Total RNA was extracted from the corpora cavernosum underlying the small intestinal submucosa graft and reverse transcriptase-polymerase chain reaction (RT-PCR) was done using an Access system (Promega, Madison, Wisconsin) with gene specific primers for inducible NOS, TGF-beta1 and vascular endothelial growth factor (VEGF).

RESULTS

Grafting of the tunica albuginea with small intestinal submucosa had no significant effect on the magnitude or duration of the erectile response to intracavernous vasoactive agents. Histological examination demonstrated no inflammatory changes in the tunica albuginea or corporeal tissue underlying the area of the small intestinal submucosa graft and there was no appreciable alteration in smooth muscle or collagen content. The 2 groups showed intense positive immunostaining to alpha-actin. Weak expression of TGF-beta1 predominantly associated with smooth muscle fibers was identified in the 2 groups of rabbits by immunostaining and RT-PCR. No significant inducible NOS was detected by immunostaining or RT-PCR in either group. Strong VEGF expression was observed in grafted rabbits. The most noticeable (3-fold) increase in expression was detected in splice variant 165.

CONCLUSIONS

Small intestinal submucosa grafting of the tunica albuginea preserves the duration and magnitude of the erectile response to vasoactive agents. This type of tunical grafting does not stimulate a significant inflammatory response, or cause corporeal fibrosis or loss of cavernous smooth muscle content. Stimulating VEGF may facilitate wound healing and the maintenance of normal erectile function.

Small intestinal submucosa as a bioscaffold for biliary tract regeneration

BACKGROUND

Porcine small intestinal submucosa (SIS) biograft is used as a bioscaffold for regeneration of a variety of tissues. To date, SIS has not been used as a biliary tract graft. The purpose of this study was to evaluate the feasibility of using SIS as a scaffold for bile duct tissue regeneration in a canine model.

METHODS

Fifteen, 25- to 35-kg mongrel dogs underwent midline laparotomy and exposure of the common bile duct. Nine dogs had a longitudinal choledochotomy and a 2- x 1-cm elliptical patch of 4-ply SIS placed using 6-0 polypropylene suture. Six dogs had the anterior two thirds of the bile duct resected and a 2- to 3-cm tubularized 4-ply SIS interposition graft placed. Dogs were killed at intervals ranging from 2 weeks to 5 months. Before killing, liver function tests (alkaline phosphatase [U/L] and total bilirubin [mg/dL]) were evaluated, cholangiograms were performed, and the bile duct was examined histologically.

RESULTS

Fourteen out of 15 dogs survived and were healthy at the time of killing. The one failure was a result of a bile leak in a patched animal. The SIS showed signs of incorporation with infiltration of native fibroblasts, blood vessels, and biliary mucosa within 2 weeks. Within 3 months the SIS graft was replaced with native collagen covered with a biliary epithelium. No changes occurred at 5-month follow-up. One animal with an interposition graft developed a stricture at the proximal anastomosis within 2 months. In the remaining dogs, liver enzymes were normal, and the caliber of the common bile duct remained normal.

CONCLUSIONS

SIS can be used for regeneration of bile duct tissue in a canine model. In 13 of 15 dogs SIS resulted in regeneration of canine common bile duct when used as a patch or as an interposition graft. The potential for the use of SIS as a patch for biliary stricturoplasty, or as an interposition graft for repair of complex biliary injuries is encouraging.

Naturally occurring scaffolds for soft tissue repair and regeneration

Cell growth supports (i.e., scaffolds) that provide a conducive environment for normal cellular growth, differentiation, and angiogenesis are important components of tissue engineered grafts because rapid integration with the host is essential for long-term graft viability. While many of these scaffold materials are synthetic biodegradable polymers, others are naturally derived from mammalian tissue sources. Naturally occurring scaffold materials include small intestinal submucosa, acellular dermis, amniotic membrane tissue, cadaveric fascia, and the bladder acellular matrix graft. Upon implantation, these materials elicit a host-tissue response that initiates angiogenesis, encourages tissue deposition and culminates in restoration of structure and function specific to the grafted site. The sources, the methods of procurement and processing, and the effects of these naturally occurring materials on angiogenesis and tissue deposition are reviewed.

Fibronectin peptides mediate HMEC adhesion to porcine-derived extracellular matrix

Extracellular matrices (ECM) derived from porcine tissues have been shown to support the successful repair and remodeling of injured tissues when evaluated in animal models. Cell-matrix interactions, including ligand-integrin associations that facilitate endothelial cell adhesion, are clearly important in the tissue remodeling process. The goal of the present study was to identify the peptide sequences within the ubiquitous protein fibronectin (FN) that may be important in the initial interactions between the host endothelial cells and the ECM scaffold. Human microvascular endothelial cells (HMEC) were seeded upon porcine ECM after having been subjected to pretreatment with peptide ligands derived from tissue FN and were allowed to attach for 20 min. Non-adherent cells were removed and the remaining, tritium-labeled cells attached to the ECM were counted. Results showed that cyclo-RGD and REDV, but not LDV or PHSRN, play a role in mediating the attachment of HMEC to porcine ECM.

Retention of endothelial cell adherence to porcine-derived extracellular matrix after disinfection and sterilization

Extracellular matrices (ECM) derived from porcine tissue are associated with rapid and extensive repopulation with host cells when used as scaffolds for in vivo tissue repair. Cell adhesion to substrates used for tissue engineering has been studied extensively but the factors that mediate this phenomenon in ECM scaffolds following treatment with oxidants and sterilants have not been examined. Cell adhesion assays were used to examine human microvascular endothelial cell (HMEC) attachment to ECM graft materials harvested from small intestinal submucosa (SIS) and urinary bladder matrix (UBM) following decellularization and sterilization procedures designed to render the ECM safe for clinical use. HMECs were able to attach directly to these ECM scaffolds via several attachment proteins present within the ECM, including type I collagen, type IV collagen, and fibronectin. The ability of the SIS ECM and UBM ECM to support the growth and proliferation of HMEC was also examined. HMEC were able to grow to single-layer confluence on both surfaces of SIS and UBM sheets. The endothelial cells were also able to penetrate the SIS and UBM at later time points if they were seeded on the abluminal side of the ECM sheets. The ability of the processed ECM to support HMEC attachment and proliferation is similar to that reported for unprocessed ECM and may therefore play a role in the rapid remodeling response observed when these matrices are implanted in vivo as scaffolds for wound repair.

Morphologic study of small intestinal submucosa as a body wall repair device

BACKGROUND

The extracellular matrix (ECM) derived from porcine small intestinal submucosa (SIS) has been used as a constructive scaffold for tissue repair in both preclinical animal studies and human clinical trials. Quantitative characterization of the host tissue response to this xenogeneic scaffold material has been lacking.

MATERIALS AND METHODS

The morphologic response to a multilaminate form of the SIS-ECM was evaluated in a chronic, 2-year study of body wall repair in two separate species: the dog and the rat. Morphologic response to the SIS-ECM was compared to that for three other commonly used bioscaffold materials including Marlex mesh, Dexon, and Perigard. Quantitative measurements were made of tissue consistency, polymorphonuclear cell response, mononuclear cell response, tissue organization, and vascularity at five time points after surgical implantation: 1 week, 1, 3, and 6 months, and 2 years.

RESULTS

All bioscaffold materials functioned well as a repair device for large ventral abdominal wall defects created in these two animal models. The SIS-ECM bioscaffold showed a greater number of polymorphonuclear leukocytes at the 1-week time point and a greater degree of graft site tissue organization after 3 months compared to the other three scaffold materials. There was no evidence for local infection or other detrimental local pathology to any of the graft materials at any time point.

CONCLUSIONS

Like Marlex, Dexon, and Perigard, the SIS-ECM is an effective bioscaffold for long-term repair of body wall defects. Unlike the other scaffold materials, the resorbable SIS-ECM scaffold was replaced by well-organized host tissues including differentiated skeletal muscle.

Evaluation of small-intestinal submucosa implants for repair of meniscal defects in dogs

OBJECTIVE

To assess the effects of porcine small intestinal submucosa (SIS) implants on the healing of meniscal lesions in dogs.

ANIMALS

16 adult Greyhounds of both sexes.

PROCEDURE

Unilateral osteotomy was performed at time 0 to disrupt the medial collateral ligament attachment, and two (1 cranial and 1 caudal) 4-mm circular defects were created in the avascular portion of the medial meniscus. One defect was filled with an SIS graft, and the other defect remained empty (control). Three months later, the identical procedure was performed on the contralateral limb. Three months after the second surgery, dogs were euthanatized, and meniscal tissue specimens from both stifle joints were collected for gross, histologic, biomechanical, and biochemical evaluations.

RESULTS

Regenerative tissue was evident in 4 (2 SIS-implanted and 2 control) of 16 defects examined histologically. In 3 defects, this thin bridge of tissue was composed of immature haphazardly arranged fibrous connective tissue with a relatively uniform distribution of fibroblasts. Aggregate modulus, Poisson ratio, permeability, and shear modulus were not significantly different between control and SIS-implanted defects either 3 or 6 months after surgery. Hydroxyproline content also did not differ between SIS-implanted and control defects at 3 or 6 months.

CONCLUSIONS AND CLINICAL RELEVANCE

Implantation of porcine SIS into experimentally induced meniscal lesions in dogs did not promote tissue regeneration.

Antimicrobial activity associated with extracellular matrices

Materials derived from extracellular matrices (ECMs) are being evaluated as scaffolds for surgical reconstruction of damaged or missing tissues. It is important to understand the susceptibility of these biological materials to bacterial infections. ECMs derived from porcine small intestinal submucosa (SIS) and urinary bladder submucosa (UBS) were found to possess antimicrobial activity. ECM extracts, obtained by digesting these acellular matrices in acetic acid, demonstrated antibacterial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Antimicrobial activity was determined using a minimal inhibitory concentration assay. Bacteriostatic activity was detected at protein concentrations of ECM extracts equivalent to 0.77-1.60 mg/mL. ECM extracts were found to inhibit bacterial growth for up to at least 13 h. The resulting extracts consisted of water-soluble peptides and proteins with molecular weights ranging from <4 to >100 kDa and lower molecular weight compounds, as determined by size exclusion liquid chromatography.

Tissue-engineered skin substitutes

The last two years have seen new tissue-engineered skin substitutes come onto the market and begin to resolve the various roles to which each is best suited. It is becoming evident that some of the very expensive cell-based products have cost-benefit advantage despite their high price and are valuable within the restricted applications for which they are intended. The use of skin substitutes for testing purposes has extended from epidermal keratinocytes to other integumentary epithelia and into preparations containing multiple cell types in which reactions resulting from paracrine interactions can be examined. Challenges remain in the application of gene therapy techniques to skin substitutes, both the control of transgene expression and in the selection of suitable genes to transfect. A coming challenge is the production of tissue-engineered products without the use of animal products other than human cells. A challenge that may be diminishing is the importance of acute rejection of allogeneic tissue-engineered skin substitutes.

Marrow-derived cells populate scaffolds composed of xenogeneic extracellular matrix

INTRODUCTION

The source of cells that participate in wound repair directly affects outcome. The extracellular matrix (ECM) and other acellular biomaterials have been used as therapeutic scaffolds for cell attachment and proliferation and as templates for tissue repair. The ECM consists of structural and functional proteins that influence cell attachment, gene expression patterns, and the differentiation of cells.

OBJECTIVE

The objective of this study was to determine if the composition of acellular matrix scaffolds affects the recruitment of bone marrow-derived cellular elements that populate the scaffolds in vivo.

METHODS

Scaffolds composed of porcine tissue ECM, purified Type I collagen, poly(L)lactic coglycolic acid (PLGA), or a mixture of porcine ECM and PLGA were implanted into subcutaneous pouches on the dorsum of mice. The origin of cells that populated the matrices was determined by first performing bone marrow transplantation to convert the marrow of glucose phosphate isomerase 1b (Gpi-1(b)) mice to cells expressing glucose phosphate isomerase 1a (Gpi-1(a)).

RESULTS

A significant increase in Gpi-1(a) expressing cells was present in sites implanted with the porcine ECM compared to sites implanted with either Type I collagen or PLGA. Use of recipient mice transplanted with marrow cells that expressed beta-galactosidase confirmed that the majority of cells that populated and remodeled the naturally occurring porcine ECM were marrow derived. Addition of porcine ECM to the PLGA scaffold caused a significant increase in the number of marrow-derived cells that became part of the remodeled implant site.

CONCLUSION

The composition of bioscaffolds affects the cellular recruitment pattern during tissue repair. ECM scaffolds facilitate the recruitment of marrow-derived cells into sites of remodeling.

Strength over time of a resorbable bioscaffold for body wall repair in a dog model

The change in strength over time of a biomaterial derived from the small intestinal submucosa (SIS) was determined in a dog model of body wall repair. Full-thickness body wall defects measuring 8 x 12 cm were surgically created and then repaired with a multilaminate eight-layer form of SIS in 40 dogs. Five dogs were sacrificed at each of the following time points: 1 day, 4 days, 7 days, 10 days, and 1, 3, 6, and 24 months. Ball burst tests that measured biaxial ultimate load-bearing capability were performed on the device prior to implantation and on the device/implant site at the time of sacrifice. The strength of the device at the time of implant was approximately 73 +/- 12 pounds. The strength of the implant site diminished to 40 +/- 18 pounds at 10 days, and then progressively increased to a value of 156 +/- 26 pounds at 24 months (P < 0.05). The clinical utility of a degradable biomaterial such as SIS depends on a balance between the rate of degradation and the rate of host remodeling. Naturally occurring extracellular matrix scaffolds such as SIS show rapid degradation with associated and subsequent remodeling to a tissue with strength that exceeds that of the native tissue when used as a body wall repair device.

Porcine small intestinal submucosa (SIS): a bioscaffold supporting in vitro primary human epidermal cell differentiation and synthesis of basement membrane proteins

The growth pattern of human epidermal cells, fibroblasts or Swiss mouse 3T3/J2 fibroblasts cultured upon the extracellular matrix (ECM) derived from small intestinal submucosa (SIS) was evaluated. The cell/SIS composites were grown submerged, then maintained in air/liquid interface for 2, 7, 10 or 14 days. The presence of differentiation-related keratins 10, 14 and 16, FN, laminin, collagen type VII and collagen type IV was determined by immunohistochemical methods in SIS alone and in the SIS/cell composite. Only FN could be detected in SIS alone. SIS supported the formation of an epithelial structure with suprabasal expression of K16 and regional suprabasal expression of K10. The epidermal cells were K14 positive and tended to 'invade' the SIS to various degrees. Following the growth of epidermal cells and fibroblasts on the SIS substratum, immunolabeling of FN, laminin, collagen type VII and collagen type IV was observed in a cell-associated pattern. The fibroblasts commonly invaded the SIS, when co-cultivated with epidermal cells on the opposite side of the SIS. The ability of SIS to support epidermal cell/fibroblast attachment, migration and/or proliferation and differentiation with deposition of basement membrane (BM) components indicates that the composite model may be useful for studying cell-matrix interactions and for investigation as a dermal substitute.

Endothelial cell adherence to small intestinal submucosa: an acellular bioscaffold

Degradable biomaterials to be used as scaffolds for tissue repair will ideally be able to support new blood vessel growth. The present study evaluated the adherence of human dermal microvascular endothelial cells (HMECs) to an acellular resorbable scaffold material derived from the small intestinal submucosa (SIS). HMECs were exposed to hydrated and dehydrated forms of SIS and to plastic surfaces coated with one of four different known components of the SIS extracellular matrix: collagen Type I, collagen Type IV, fibronectin, and laminin. Results showed that adherence of HMECs to hydrated SIS was greater than to any of the other tested surfaces (P < 0.05). Exposure of HMECs to either soluble collagen Type IV or soluble fibronectin prior to exposure of these cells to hydrated SIS showed only partial inhibition of HMEC attachment. We conclude that HMECs find hydrated SIS to be a suitable substrate for adherence and that dehydration of SIS adversely affects the ability of HMECs to adhere in vitro. The cause of HMEC adherence to SIS appears to be a combination of both its composition and architecture.

Naturally occurring extracellular matrix as a scaffold for musculoskeletal repair

The use of naturally occurring extracellular matrix materials as scaffolds for the repair and regeneration of tissues is receiving increased attention. The present study evaluates the use of the extracellular matrix derived from porcine small intestinal submucosa as a scaffold for anterior cruciate ligament replacement in a goat model. Sixty healthy adult female goats were divided into two equal groups of 30 each. The right anterior cruciate ligament of each goat was removed surgically and replaced with either a patellar tendon autograft or a small intestinal submucosa anterior cruciate ligament scaffold. Three animals from each group were sacrificed at 6 weeks, 3 months, 6 months, and 1 year after surgery and grafts were harvested for histopathologic examination. Six animals from each group were sacrificed immediately after surgery, 3 months, and 1 year after surgery and the grafts were harvested for biomechanical testing. There was no evidence for an adverse clinical response to the xenogeneic small intestinal submucosa scaffold. Anterior drawer values were not different between the two groups at any point. The failure force of the patellar tendon autograft increased from 253 N at Time 0 to 879 N at 12 months. The failure force for the small intestinal submucosa repair device was 721 N at Time 0, decreased to 293 N at 3 months, followed by an increase to 706 N at 12 months. Histopathologic analysis showed a mixed inflammatory cell presence within the small intestinal submucosa scaffold including macrophages and lymphocytes in the early months after surgery. The inflammatory cells disappeared in the later stages of remodeling and the histologic appearance of the small intestinal submucosa remodeled grafts and the patellar tendon autografts were indistinguishable at 12 months. Xenogeneic small intestinal submucosa holds promise as a resorbable bioscaffold for anterior cruciate ligament repair in the goat model.