Directional porosity of porcine small-intestinal submucosa

A new scaffold containing small intestinal submucosa and mesenchymal stem cells improves pancreatic islet function and survival in vitro and in vivo

It is unknown whether a scaffold containing both small intestinal submucosa (SIS) and mesenchymal stem cells (MSCs) for transplantation may improve pancreatic islet function and survival. In this study, we examined the effects of a SIS-MSC scaffold on islet function and survival in vitro and in vivo. MSCs and pancreatic islets were isolated from Sprague-Dawley rats, and SIS was isolated from Bamei pigs. The islets were apportioned among 3 experimental groups as follows: SIS-islets, SIS-MSC-islets and control-islets. In vitro, islet function was measured by a glucose-stimulated insulin secretion test; cytokines in cultured supernatants were assessed by enzyme-linked immunosorbent assay; and gene expression was analyzed by reverse transcription-quantitative PCR. In vivo, islet transplantation was performed in rats, and graft function and survival were monitored by measuring the blood glucose levels. In vitro, the SIS-MSC scaffold was associated with improved islet viability and enhanced insulin secretion compared with the controls, as well as with the increased the expression of insulin 1 (Ins1), pancreatic and duodenal homeobox 1 (Pdx1), platelet endothelial cell adhesion molecule 1 [Pecam1; also known as cluster of differentiation 31 (CD31)] and vascular endothelial growth factor A (Vegfa) in the islets, increased growth factor secretion, and decreased tumor necrosis factor (TNF) secretion. In vivo, the SIS-MSC scaffold was associated with improved islet function and graft survival compared with the SIS and control groups. On the whole, our findings demonstrate that the SIS-MSC scaffold significantly improved pancreatic islet function and survival in vitro and in vivo. This improvement may be associated with the upregulation of insulin expression, the improvement of islet microcirculation and the secretion of cytokines.

Difficult-to-heal wounds of mixed arterial/venous and venous etiology: a cost-effectiveness analysis of extracellular matrix

Importance

Difficult-to-heal wounds pose clinical and economic challenges, and cost-effective treatment options are needed.

Objective

The aim of this study is to determine the cost-effectiveness of extracellular matrix (ECM) relative to standard of care (SC) on wound closure for the treatment of mixed arterial/venous (A/V) or venous leg ulcers (VLUs).

Design, setting, and participants

A two-stage Markov model was used to predict the expected costs and outcomes of wound closure for ECM and SC. Outcome data used in the analysis were taken from an 8-week randomized clinical trial that directly compared ECM and SC. Patients were followed up for an additional 6 months to assess wound closure. Forty-eight patients completed the study; 25 for ECM and 23 for SC. SC was defined as a standard moist wound dressing. Transition probabilities for the Markov states were estimated from the clinical trial.

Main outcomes and measures

The economic outcome of interest was direct cost per closed-wound week. Resource utilization was based on the treatment regimen used in the clinical trial. Costs were derived from standard cost references. The payer’s perspective was taken.

Results

ECM-treated wounds closed, on average, after 5.4 weeks of treatment, compared with 8.3 weeks for SC wounds (P=0.02). Furthermore, complete wound closure was significantly higher in patients treated with ECM (P<0.05), with 20 wounds closed in the ECM group (80%) and 15 wounds closed in the SC group (65%). After 8 months, patients treated with ECM had substantially higher closed-wound weeks compared with SC (26.0 weeks versus 22.0 weeks, respectively). Expected direct costs per patient were $2,527 for ECM and $2,540 for SC (a cost savings of $13).

Conclusion and relevance

ECM yielded better clinical outcomes at a slightly lower cost in patients with mixed A/V and VLUs. ECM is an effective treatment for wound healing and should be considered for use in the management of mixed A/V and VLUs.

In vivo assessment of two endothelialization approaches on bioprosthetic valves for the treatment of chronic deep venous insufficiency

Chronic deep venous insufficiency is a debilitating disease with limited therapeutic interventions. A bioprosthetic venous valve could not only replace a diseased valve, but has the potential to fully integrate into the patient with a minimally invasive procedure. Previous work with valves constructed from small intestinal submucosa (SIS) showed improvements in patients' symptoms in clinical studies; however, substantial thickening of the implanted valve leaflets also occurred. As endothelial cells are key regulators of vascular homeostasis, their presence on the SIS valves may reduce the observed thickening. This work tested an off-the-shelf approach to capture circulating endothelial cells in vivo using biotinylated antikinase insert domain receptor antibodies in a suspended leaflet ovine model. The antibodies on SIS were oriented to promote cell capture and showed positive binding to endothelial cells in vitro; however, no differences were observed in leaflet thickness in vivo between antibody-modified and unmodified SIS. In an alternative approach, valves were pre-seeded with autologous endothelial cells and tested in vivo. Nearly all the implanted pre-seeded valves were patent and functioning; however, no statistical difference was observed in valve thickness with cell pre-seeding. Additional cell capture schemes or surface modifications should be examined to find an optimal method for encouraging SIS valve endothelialization to improve long-term valve function in vivo. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1610-1621, 2016.

Arterial grafts exhibiting unprecedented cellular infiltration and remodeling in vivo: the role of cells in the vascular wall

OBJECTIVE

To engineer and implant vascular grafts in the arterial circulation of a pre-clinical animal model and assess the role of donor medial cells in graft remodeling and function.

APPROACH AND RESULTS

Vascular grafts were engineered using Small Intestinal Submucosa (SIS)-fibrin hybrid scaffold and implanted interpositionally into the arterial circulation of an ovine model. We sought to demonstrate implantability of SIS-Fibrin based grafts; examine the remodeling; and determine whether the presence of vascular cells in the medial wall was necessary for cellular infiltration from the host and successful remodeling of the implants. We observed no occlusions or anastomotic complications in 18 animals that received these grafts. Notably, the grafts exhibited unprecedented levels of host cell infiltration that was not limited to the anastomotic sites but occurred through the lumen as well as the extramural side, leading to uniform cell distribution. Incoming cells remodeled the extracellular matrix and matured into functional smooth muscle cells as evidenced by expression of myogenic markers and development of vascular reactivity. Interestingly, tracking the donor cells revealed that their presence was beneficial but not necessary for successful grafting. Indeed, the proliferation rate and number of donor cells decreased over time as the vascular wall was dominated by host cells leading to significant remodeling and development of contractile function.

CONCLUSIONS

These results demonstrate that SIS-Fibrin grafts can be successfully implanted into the arterial circulation of a clinically relevant animal model, improve our understanding of vascular graft remodeling and raise the possibility of engineering mural cell-free arterial grafts.

Outcome of conjunctival flap repair for corneal defects with and without an acellular submucosa implant in 73 canine eyes

OBJECTIVE

To report and compare the success rate of a conjunctival pedicle flap (CPF) alone vs. a CPF with an underlying acellular submucosa implant for the repair of deep or perforating corneal wounds in dogs.

PROCEDURES

Records of 69 dogs (73 eyes) receiving a CPF with or without an acellular submucosa implant between 2004 and 2012 were reviewed. Successful outcome was defined as a comfortable eye with vision at the last post-operative evaluation. Age, breed, underlying corneal disease, surgical time, lesion characteristics, topical therapies, and postoperative complications were investigated.

RESULTS

Groups consisted of dogs that had a CPF alone (n = 37) and dogs that had a CPF plus an acellular submucosa implant (n = 36). Age, lesion size, surgical time, and time to discontinuation of topical anti-proteolytic medications was not significant between groups. Topical antibiotic use was terminated 13 days sooner (P ≤ 0.01) in dogs with an acellular submucosa implant. The combined success rate of all corneal wounds was 93% with success rate of corneal perforations, descemetoceles, and deep stromal wounds being 89%, 95%, and 100%, respectively. There was no difference in overall success rate between groups. Increasing age was associated with a negative outcome (P ≤ 0.01). Lesion size, presence of a corneal perforation, and concurrent keratoconjunctivitis sicca was not associated with a negative outcome.

CONCLUSIONS

A comparable success rate is achieved for deep or perforating corneal wounds stabilized with a CPF alone vs. a CPF plus acellular submucosa. Glaucoma, persistent uveitis, and cataract formation were not reported as post-operative complications in this study population.

Small intestinal submucosa segments as matrix for tissue engineering: review

Tissue engineering (TE) is an emerging interdisciplinary field aiming at the restoration or improvement of impaired tissue function. A combination of cells, scaffold materials, engineering methods, and biochemical and physiological factors is employed to generate the desired tissue substitute. Scaffolds often play a pivotal role in the engineering process supporting a three-dimensional tissue formation. The ideal scaffold should mimic the native extracellular environment providing mechanical and biological properties to allow cell attachment, migration, and differentiation, as well as remodeling by the host organism. The scaffold should be nonimmunogenic and should ideally be resorbed by the host over time, leaving behind only the regenerated tissue. More than 40 years ago, a preparation of the small intestine was introduced for the replacement of vascular structures. Since then the small intestinal submucosa (SIS) has gained a lot of interest in TE and subsequent clinical applications, as this material exhibits key features of a highly supportive scaffold. This review will focus on the general properties of the SIS and its applications in therapeutical approaches as well as in generating tissue substitutes in vitro. Furthermore, the main problem of TE, which is the insufficient nourishment of cells within three-dimensional, artificial tissues exceeding certain dimensions is addressed. To solve this issue the implementation of another small intestine-derived preparation, the biological vascularized matrix (BioVaM), could be a feasible option. The BioVaM comprises in addition to SIS the arterial and venous mesenteric pedicles and exhibits thereby a perfusable vessel bed that is preserved after decellularization.

Quantification of MSCs involved in wound healing: use of SIS to transfer MSCs to wound site and quantification of MSCs involved in skin wound healing

Mesenchymal stem cells (MSCs) are known to be effective in wound healing, but not much has been reported on quantitative correlations between MSCs injected into the wound site and MSCs that actually participate in wound healing. This study traced MSCs participating in wound healing by using small intestinal submucosa (SIS) as a cell carrier, identified their moving path and calculated the number of MSCs involved in wound healing. First, MSCs were isolated from the nude mouse and 1 × 10(6) cells were seeded onto the centre of the SIS. MSC-seeded SIS complexes were injected onto full-thickness skin wounds made on the dorsum of nude mice. Tracing of MSC-seeded SIS complex transplanted to the wound site revealed that 27.6% of the MSCs were migrated to the wound site at the first attempt. Second, repeated injection of additional MSCs did not increase the number of MSCs participating in wound healing beyond a certain constant maximum amount. The number of MSCs present in the wound site remains constant in the range 2-3 × 10(5) from day 1 to day 10. The expression of skin regeneration-related growth factors was confirmed by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). MSCs participating in wound healing were found not only to suppress inflammation of the wound but also to increase the skin regeneration-related growth factors that enable the recovery of the skin. An optimal number of about 3 × 10(5) MSCs injected into the site was found to adapt themselves to the skin wound-healing process effectively.

Treatment of early avascular necrosis of femoral head by small intestinal submucosal matrix with peripheral blood stem cells

BACKGROUND

Avascular necrosis of the femoral head (ANFH) is a highly mutilating disease. There are no effective ways to treat early femoral head ischemia. Peripheral blood stem cell (PBSC) transplantation may be superior to conventional bone marrow transplantation. Small intestinal submucosae matrix (SIS) is composed of highly conserved collagens, glycoproteins, proteoglycans, and glycoaminoglycans in their natural configuration and concentrations. When implanted in a number of microenvironments in vivo, SIS has been used to induce proliferation, remodeling, and regeneration of host tissues. This study was designed to verify the curative effects of PBSC and SIS transplantation-induced vascular regeneration to improve ischemic femoral head necrosis in rabbits.

METHODS

32 New Zealand white rabbits underwent ischemic femoral head necrosis modeling in both hindlimbs by liquid-nitrogen refrigeration. All rabbits were intraperitoneally injected with grannlocytectomy-stimulating factor (250 μg/kg/d), except for normal control subjects injected with equivalent saline solution. After separation of peripheral blood stem cells (PBSCs), 64 femoral heads in 32 rabbits were randomly divided into 4 groups: group A, cancellous bone and peripheral blood stem cells cultured with small intestinal submucosa; group B, cancellous bone and PBSCs; group C, cancellous bone autografts; and group D, no treatment. The specimens were harvested at 4 and 8 weeks after surgery. All specimens were examined to observe angiogenesis and osteogenesis repairing the avascular necrosis of the femoral head by using gross observation, x-ray, histology, and immunohistochemical staining.

RESULTS

In 4 weeks after peripheral stem cell transplantation, the standing ability and activity of the transplanted hindlimbs were improved remarkably, but there were no obvious changes in the control limbs. X-rays showed a greater density of grafts than the host bone in groups A,B, and group C was unchanged at 4 weeks. Histology revealed many osteoprogenitor cells and osteoblasts and no inflammatory cell infiltration at 4 weeks with much new bone formed at 8 weeks in group A and at 4 weeks in group B. The cancellous bone autograft was absorbed completely at 8 weeks in group C. There was little osteoid tissue formed in group D at 8 weeks. The zone of new bone formation in group A was greater than that in group B (P < .05), but there was no significant difference between groups A and C (P > .05). Immunohistochemical staining with CD31 mouse antibody showed greater amounts and zones of new blood vessels in groups A and B at 4 and 8 weeks and little evidence in group D. There was no significant difference between groups A and B (P > .05) and significant differences between groups A and B versus C and D (P < .05).

CONCLUSION

Transplantation of PBSCs cultured with SIS effectively improved ischemic femoral head necrosis.

Structural characteristics of small intestinal submucosa constructs dictate in vivo incorporation and angiogenic response

The rate of angiogenesis and cellular infiltration into degradable biomaterials determines scaffold persistence in vivo. The ability to tune the degradation properties of naturally derived biomaterials has been a popular goal in tissue engineering, yet has often depended on chemical crosslinking. Small intestinal submucosa (SIS) is a naturally derived, collagen-based, bioactive scaffold that has broad clinical success in many therapeutic applications. Two methods for producing multilayer, non-crosslinked SIS constructs were compared in vitro and in vivo. Traditional and cryo SEM, mercury intrusion porosimetry, and a novel enzymatic degradation assay determined that lyophilization produced an open, porous scaffold, in contrast to the collapsed, denser structure of SIS constructs produced using a vacuum press process. The angiogenic responses to lyophilized and vacuum-pressed SIS constructs were evaluated in vivo using a subcutaneous implant assay in mice. Explanted samples were compared after 7 and 21 days using fluorescence microangiography and light microscopy. Capacity of the implant neovasculature was also determined. These experiments revealed that the lyophilized SIS was infiltrated and vascularized more rapidly than the vacuum pressed. These data demonstrate the tunable incorporation of a non-crosslinked ECM-based biomaterial, which may have implications for the persistence of this degradable scaffold in tissue engineering.

Oxygen diffusivity of biologic and synthetic scaffold materials for tissue engineering

Scaffolds for tissue engineering and regenerative medicine applications are commonly manufactured from synthetic materials, intact or isolated components of extracellular matrix (ECM), or a combination of such materials. After surgical implantation, the metabolic requirements of cells that populate the scaffold depend upon adequate gas and nutrient exchange with the surrounding microenvironment. The present study measured the oxygen transfer through three biologic scaffold materials composed of ECM including small intestinal submucosa (SIS), urinary bladder submucosa (UBS), and urinary bladder matrix (UBM), and one synthetic biomaterial, Dacron. The oxygen diffusivity was calculated from Fick's first law of diffusion. Each material permitted measurable oxygen diffusion. The diffusivity of SIS was found to be dependent on the direction of oxygen transfer; the oxygen transfer in the abluminal-to-luminal direction was significantly greater than the luminal-to-abluminal direction. The oxygen diffusivity of UBM and UBS were similar despite the presence of an intact basement membrane on the luminal surface of UBM. Dacron showed oxygen diffusivity values seven times greater than the ECM biomaterials. The current study showed that each material has unique oxygen diffusivity values, and these values may be dependent on the scaffold's ultrastructure.

Hydrated versus lyophilized forms of porcine extracellular matrix derived from the urinary bladder

Biologic scaffolds composed of naturally occurring extracellular matrix (ECM) are currently in clinical use for the repair and reconstruction of damaged or missing tissues. The material and structural properties of the ECM scaffold are important determinants of the potential clinical applications and these properties may be affected by manufacturing steps, processing steps, and storage conditions. The present study compared the structural properties of hydrated and lyophilized forms of a biologic scaffold derived from the porcine urinary bladder (urinary bladder matrix or UBM). The structural properties evaluated include: maximum load and elongation, maximum tangential stiffness, energy absorbed, suture retention strength, ball-burst strength, and the hydrostatic permeability index. Other properties that were investigated include changes in the water content, structural morphology, and thickness and the ability to support in vitro growth of NIH 3T3 cells. Lyophilization caused no changes in the structural properties evaluated with the exception of a decrease in maximum elongation. NIH 3T3 cells showed invasion of the scaffold when seeded on the abluminal side of both hydrated and lyophilized UBM, and there were more cells present on lyophilized UBM when compared to hydrated UBM devices after the 7-days culture period. Irreversible changes were observed in the microstructure and ultrastructure of lyophilized UBM devices. We conclude that lyophilization affects the overall in vitro cell growth of NIH 3T3 cells and the ultrastructural morphology of UBM devices, but does not result in significant changes in structural properties.

Rabbit Ear Cartilage Regeneration With a Small Intestinal Submucosa Graft

OBJECTIVES/HYPOTHESIS

The objective was to demonstrate that interpositional grafting with porcine small intestinal submucosa promotes cartilage regeneration following excision of rabbit auricular cartilage.

STUDY DESIGN

Blinded, controlled study.

METHODS

Eight New Zealand white rabbits underwent excision of auricular cartilage on two sites with and two sites without preservation of perichondrium. Porcine small intestinal submucosa was implanted into one site with and one site without intact perichondrium. Remaining sites served as control sites. Histological assessment was performed at 3 (n = 4) and 6 (n = 3) months and at 1 year (n = 1) after grafting.

RESULTS

Histological evaluation showed cartilage regeneration accompanied by chronic inflammation in areas in which porcine small intestinal submucosa was implanted between layers of intact perichondrium. Other sites failed to show significant cartilage regeneration.

CONCLUSION

The results of the study using porcine small intestinal submucosa as a bioscaffold for cartilage regeneration are promising and justify further animal and human studies.

Oxygen diffusion through natural extracellular matrices: implications for estimating "critical thickness" values in tendon tissue engineering

Oxygen is necessary for maintaining cell proliferation and viability and extracellular matrix (ECM) production in 3-dimensional tissue engineering. Typically, diffusion is the primary mode for oxygen transport in vitro; thus, ensuring an adequate oxygen supply is essential. In this study, we determined the oxygen diffusion coefficients of 3 natural ECMs that are being investigated as construct scaffolds for tendon tissue engineering: small-intestine submucosa (SIS), human dermis (Alloderm), and canine fascia lata. Diffusion coefficients were determined using a standard diffusion cell system. The ranges for each matrix type were: SIS: 7 x 10(-6) - 2 x 10(-5) cm2/s, Alloderm: 1.9 - 3.1 x 10(-5) cm2/s, and canine fascia lata: 1.6 - 4 x 10(-5) cm2/s. We used the experimental oxygen diffusivity data for these natural ECMs in a mathematical model of oxygen diffusion through a cell-seeded scaffold to estimate the critical size of cell-seeded scaffold that can be cultured in vitro.

Reconstructive cranioplasty using a porcine small intestinal submucosal graft

A six-year-old border collie was presented with a solid mass on the dorsal cranium. Histological examination showed the mass to be a multilobular tumour of bone. A magnetic resonance imaging scan confirmed deformation of the dorsal cranium with compression of the cerebral hemispheres. A craniotomy was performed to excise the mass and overlying skin, resulting in a substantial deficit of calvarium and skin. A cranioplasty using a small intestinal submucosal (SIS) graft was performed to reconstruct the calvarial defect. A local myocutaneous advancement flap was elevated and positioned over the cranioplasty to close the skin deficit. The outcome of this reconstruction was aesthetic and functional. The small intestinal submucosal graft provided satisfactory mechanical support and was a suitable physical barrier in place of the calvarial bone. Histological examination of the small intestinal submucosal graft 128 days after implantation showed that the graft had been replaced by a dense network of collagenous tissue, with small focal areas of partially mineralised woven bone merging with a fibrocartilaginous matrix of the deeper margin. Histological examination also confirmed regrowth of the multilobular tumour of bone in the region of the small intestinal submucosal graft indicating that it is only a suitable implant if adequate surgical margins are obtained.

Effects of sterilization on an extracellular matrix scaffold: part I. Composition and matrix architecture

The impact of peracetic acid (PAA), lyophilization, and ethylene oxide (EO) sterilization on the composition and three dimensional matrix structure of small intestinal submucosa (SIS), a biologic scaffold used to stimulate the repair of damaged tissues and organs, was examined. Fibronectin and glycosaminoglycans are retained in SIS following oxidation by peracetic acid and alkylation using ethylene oxide gas. Significant amounts of FGF-2 are also retained, but VEGF is susceptible to the effects of PAA and is dramatically reduced following processing. Further, matrix oxidation, lyophilization, and sterilization with EO can be performed without irreversibly collapsing the three dimensional structure of the native SIS. These structural features and growth promoting extracellular matrix constituents are likely to be important variables underlying cellular attachment, infiltration and eventual incorporation of SIS into healing host tissues.

Abdominal wall reconstruction using biological tissue grafts: present status and future opportunities

Surgeons often encounter the challenge of treating acquired abdominal wall defects following abdominal surgery. The current standard of practice is to repair most defects using permanent synthetic mesh material. Mesh augments the strength of the weakened abdominal wall fascia and enables the hernia repair to be performed in a tension-free manner. However, there is a risk of acute and/or chronic infection, fistula formation and chronic abdominal wall pain with the use of permanent mesh materials, which can lead to more complex operations. As a means to avoid such problems, surgeons are turning increasingly to the use of xenogenic and allogenic materials for the repair of abdominal wall defects. Their rapid evolution and introduction into the clinical operating room is leading to a new era in abdominal wall reconstruction. There are promising, albeit limited, clinical data with short-term follow-up for only a few of the many biological tissue grafts that are being promoted currently for the repair of abdominal hernias. Additional clinical studies are required to better understand the long-term efficacy and limitations of these materials.

Porcine bladder acellular matrix porosity: impact of hyaluronic acid and lyophilization

Bladder acellular matrix (ACM) is being investigated as a urinary bladder replacement scaffold. We have demonstrated that ACM is porous and theorized that this contributes to ACM fibrosis and contracture over time in vivo and may preclude uptake and retention of molecules, which may aid cellular repopulation. We sought to determine if hyaluronic acid (HA) would decrease ACM porosity. Porcine ACM was lyophilized and rehydrated in HA (SIGMA) to form the hybrid HA-ACM construct. Three groups (n = 15/group: HA-ACM, ACM, and lyophilized/rehydrated ACM) were tested for porosity to a 10 cm column of distilled water, measuring the effluent hourly for 3 h. A porosity index was determined as the total effluent divided by time and area (cc/cm2 hr). Alcian blue staining and fluorophore-assisted carbohydrate electrophoresis qualitatively and quantitatively confirmed the uptake of HA. HA-ACM and lyophilized/rehydrated ACM were significantly less porous to water than untreated ACM [mean (+/-SE): 0.09 (+/-0.02), 0.74 (+/-0.4), and 9.8 (+/-1.6) cc/cm2 hr, respectively; Mann Whitney p < 0.0001 (HA) and p < 0.0001 (lyo)]. The difference between HA-ACM and lyophilized ACM was also statistically significant (p = 0.014). ACM hybridization with HA decreases ACM porosity, in part because of ACM lyophilization during the hybridization process. In future applications, HA may function as a carrier for smaller molecules such as growth factors, and as a bioactive molecule to improve wound healing and decrease fibrosis in tissue-engineered bladder constructs.

Resorbable extracellular matrix grafts in urologic reconstruction

PURPOSE

There is an increasingly large body of literature concerning tissue-engineering products that may be used in urology. Some of these are quite complex (such as multilayer patient-specific cell-seeded implants) yet the most simple and successful products to date are also the most uncomplicated: resorbable acellular extra-cellular matrices (ECMs) harvested from animals. ECMs have been used in a variety of difficult urologic reconstruction problems, and this review is intended to summarize this complex literature for the practicing urologist.

METHODS

Medline search of related terms such as "SIS, small intestinal submucosa, ECM, extracellular matrix, acellular matrix and urologic reconstruction". Manuscripts missed in the initial search were taken from the bibliographies of the primary references.

RESULTS

Full review of potential clinical uses of resorbable extra-cellular matrices in urologic reconstruction.

CONCLUSIONS

Currently, the "state of the art" in tissue engineering solutions for urologic reconstruction means resorbable acellular xenograft matrices. They show promise when used as a pubovaginal sling or extra bolstering layers in ureteral or urethral repairs, although recent problems with inflammation following 8-ply pubovaginal sling use and failures after 1- and 4-ply SIS repair of Peyronie's disease underscore the need for research before wide adoption. Preliminary data is mixed concerning the potential for ECM urethral patch graft, and more data is needed before extended uses such as bladder augmentation and ureteral replacement are contemplated. The distant future of ECMs in urology likely will include cell-seeded grafts with the eventual hope of producing "off the shelf" replacement materials. Until that day arrives, ECMs only fulfill some of the requirements for the reconstructive urologist.

Comparison of small-intestinal submucosa and expanded polytetrafluoroethylene as a vascular conduit in the presence of gram-positive contamination

OBJECTIVE

As a vascular conduit, expanded polytetrafluoroethylene (ePTFE) is susceptible to graft infection with Gram-positive organisms. Biomaterials, such as porcine small-intestinal submucosa (SIS), have been successfully used clinically as tissue substitutes outside the vascular arena.

SUMMARY BACKGROUND DATA

In the present study, we compared a small-diameter conduit of SIS to ePTFE in the presence of Gram-positive contamination to evaluate infection resistance, incorporation and remodeling, morphometry, graft patency, and neointimal hyperplasia (NH) development.

METHODS

Adult male mongrel pigs were randomized to receive either SIS or ePTFE (3-cm length, 6-mm diameter) and further randomized to 1 of 3 groups: Control (no graft inoculation), Staphylococcus aureus, or mucin-producing S epidermidis (each graft inoculation with 10 colonies/mL). Pressure measurements were obtained proximal and distal to the graft to create the iliac/aorta pressure ratio. Morphometric analysis of the neointima and histopathologic examinations was performed. Other outcomes included weekly WBC counts, graft incorporation, and quantitative culture of explanted grafts.

RESULTS

Eighteen animals were randomized. All grafts were patent throughout the 6-week study period. Infected SIS grafts had less NH and little change in their iliac/aorta indices compared with infected ePTFE grafts. Quantitative cultures at euthanasia demonstrated no growth in either SIS group compared with 1.7 x 10(4) colonies for ePTFE S aureus and 6 x 10(2) for ePTFE S epi (each P < 0.001). All SIS grafts were incorporated. Histology demonstrated remodeling into host artery with smooth muscle and capillary ingrowth in all SIS groups. Scanning electron micrography illustrated smooth and complete endothelialization of all SIS grafts.

CONCLUSIONS

Compared with ePTFE, SIS induces host tissue remodeling, exhibits a decreased neointimal response to infection, and is resistant to bacterial colonization. SIS may provide a superior alternative to ePTFE as a vascular conduit for peripheral vascular surgery.

Physical characteristics of small intestinal submucosa scaffolds are location-dependent

Using biodegradable scaffolds as an alternative to engineer new tissues has become an attractive candidate in various transplantation protocols. In particular, small intestinal submucosa (SIS), a dense connective matrix harvested from the small intestine, has gained attention due to a number of favorable properties. However, use of SIS is constrained by obtaining reliable, reproducible products in large-scale preparations that affect the regenerative process. To better understand the heterogeneous nature of SIS, this study focused on evaluating the location-dependent alterations in the physical characteristics of the matrices harvested from distal and proximal ends and processed in-house (referred as hand-made). Additionally, results were compared with a commercially available machine-made Cook SIS. Tensile properties during monotonic loading and cyclical loading were compared in wet conditions. Furthermore, permeability of these membranes to urea was analyzed using a custom-built chamber, and the microarchitecture was analyzed via scanning electron microscopy. These results showed that distal samples were more elastic and less permeable to urea relative to other samples. However, permeability in each sample was direction-dependent, that is, mucosal to serosal direction was less permeable compared to sorasal to mucosal direction in all the samples. Cook SIS was more susceptible to cyclical loading and had a shorter range of load carrying capacity. In summary, results show that physical characteristics of SIS are location-dependent.

Porosity of porcine bladder acellular matrix: impact of ACM thickness

The objectives of this study are to examine the porosity of bladder acellular matrix (ACM) using deionized (DI) water as the model fluid and dextran as the indicator macromolecule, and to correlate the porosity to the ACM thickness. Porcine urinary bladders from pigs weighing 20-50 kg were sequentially extracted in detergent containing solutions, and to modify the ACM thickness, stretched bladders were acellularized in the same manner. Luminal and abluminal ACM specimens were subjected to fixed static DI water pressure (10 cm); and water passing through the specimens was collected at specific time interval. While for the macromolecule porosity testing, the diffusion rate and direction of 10,000 MW fluoroescein-labeled dextrans across the ACM specimens mounted in Ussing's chambers were measured. Both experiments were repeated on the thin stretched ACM. In both ACM types, the fluid porosity in both directions did not decrease with increased test duration (3 h); in addition, the abluminal surface was more porous to fluid than the luminal surface. On the other hand, when comparing thin to thick ACM, the porosity in either direction was higher in the thick ACM. Macromolecule porosity, as measured by absorbance, was higher for the abluminal thick ACM than the luminal side, but this characteristic was reversed in the thin ACM. Comparing thin to thick ACM, the luminal side in the thin ACM was more porous to dextran than in the thick ACM, but this characteristic was reversed for the abluminal side. The porcine bladder ACM possesses directional porosity and acellularizing stretched urinary bladders may increase structural density and alter fluid and macromolecule porosity.

Biaxial strength of multilaminated extracellular matrix scaffolds

Xenogeneic extracellular matrix (ECM) can be harvested and configured to function as a bioscaffold for tissue and organ reconstruction. The mechanical properties of the ECM vary depending upon the tissue from which it is harvested. Likewise, the manufacturing steps required to develop ECMs into medical grade devices will affect the surface morphology and the mechanical properties of the bioscaffold; important properties for constructive tissue remodeling. The present study compared the ball-burst strength of five different ECM scaffolds before and after treatment with peracetic acid (PAA): porcine small intestinal submucosa (SIS), porcine urinary bladder submucosa (UBS), porcine urinary bladder matrix (UBM), a composite of UBS + UBM, and canine stomach submucosa (SS). This study also compared the mechanical properties of 2- and 4-layer ECM scaffolds. Results showed 2-layer SS devices had the highest ball-burst value of all 2-layer ECM devices. Moreover, all 4-layer ECM devices had similar ball-burst strength except for 4-layer UBM devices which was the weakest. PAA-treatment decreased the ball-burst strength of SS and increased the ball-burst strength of UBS 2-layer devices. This study showed the material properties of the ECM scaffolds could be engineered to mimic those of native soft tissues (i.e. vascular, musculotendinous, etc) by varying the number of layers and modifying the disinfection/sterilization treatments used for manufacturing.

Small intestinal submucosa versus salt-extracted polyglycolic acid-poly-L-lactic acid: a comparison of neocartilage formed in two scaffold materials

This study sought to compare differences in neocartilage produced over time from two types of resorbable scaffold materials. One material was entirely synthetic and contained a polyglycolic acid-poly-L-lactic acid matrix (PGA-PLLA). The second scaffold material was bioactive and consisted of a four-layered construct of porcine small intestinal submucosa (SIS). Disk-shaped scaffolds were seeded with canine chondrocytes and implanted into athymic mice for periods of 5, 8, 12, and 24 weeks. Constructs were examined microscopically, assayed for hydroxyproline (HP) and glycosaminoglycan (GAG) content, and collagen typed (I or II) at each time period. Creep indentation tests determined aggregate and shear modulus, permeability, and thickness. Results indicated that SIS maintained its thickness through the first 12 weeks, and then doubled by week 24. The 24-week tissue appeared chondroid-like and possessed high GAG content. Tissues derived from PGA-PLLA scaffolds were lower in HP content than SIS-derived tissues, but type II collagen was demonstrated only in PGA-PLLA-derived tissues at 24 weeks. Mechanical properties were not significantly different for any tissue over time (p > 0.05), but aggregate and shear modulus mean values were consistently higher for PGA-PLLA-derived tissues at nearly every time interval. This, coupled with the presence of collagen types I and II, suggested a more congruent solid phase may be forming within the extracellular matrix of tissues derived from PGA-PLLA scaffolds. Future study is necessary to compare these materials under simulated loading conditions.

Tensile strength of cadaveric fascia lata compared to small intestinal submucosa using suture pull through analysis

PURPOSE

The modified pubovaginal sling has become popular as first line treatment for stress urinary incontinence. With the increasing use of cadaveric fascia as a sling material, widespread shortages are prevalent, hence limiting its availability. The increased morbidity with the use of synthetic sling materials and autologous fascia has stimulated investigation of other sling materials. We evaluated the tensile strength of 4 suture types, and compared tensile strength of cadaveric fascia lata to porcine small intestinal submucosa using suture pull through analysis to assess their efficacy and durability for use in anti-incontinence procedures.

MATERIALS AND METHODS

Suture breaking load was determined using 2 and 1-zero polypropylene suture, and 2 and 1-zero polyglactin suture. Freeze dried gamma irradiated human fascia lata and freeze-dried small intestinal submucosa were evaluated. Suture was fixed to sling material using the cross fold technique. Mean suture breakage and suture pull through were determined using a tensionometer by measuring the load applied to the sling/suture system. Statistical analysis was performed.

RESULTS

Mean suture breakage load was greatest with 1-zero polyglactin (8.10 pounds) and least with 2-zero polypropylene (3.68 pounds). Mean suture breakage strength was similar for 1-zero polypropylene and 2-zero polyglactin at 5.26 and 5.40 pounds, respectively. Mean suture pull through load using 1-zero polypropylene suture and the cross fold technique was 5.64 pounds for cadaveric fascia and 2.74 pounds for small intestinal submucosa (p <0.0001). Maximum load was limited by the suture strength when using cadaveric fascia, whereas, maximum load was limited in small intestinal submucosa by its inherent tensile strength. However, using a new technique for suture fixation to the small intestinal submucosa, we were able to increase significantly mean suture pull through load to 3.36 pounds (p = 0.008). Additionally, with this new technique small intestinal submucosa allowed gross stretching before suture pull through that was not seen with cadaveric fascia.

CONCLUSIONS

Despite the current standard use of 1-zero polypropylene suture for pubovaginal sling fixation, our data suggest that 1-zero polyglactin suture is the strongest, and its use with pubovaginal sling fixation warrants further investigation. Using the cross fold technique and 1-zero polypropylene suture, tensile strength was greatest with cadaveric fascia compared to small intestinal submucosa. Although small intestinal submucosa was not as strong as cadaveric fascia, our persuasive preliminary data suggest that further investigation is warranted in the use of small intestinal submucosa and other suture fixation techniques, and its observed stretch capacity. Hence, with further studies small intestinal submucosa may remain a viable option for pubovaginal sling material.

Compliance, elastic modulus, and burst pressure of small-intestine submucosa (SIS), small-diameter vascular grafts

Small-intestine submucosa (SIS) is cell-free collagen, 100 mu thick, derived from the small intestine. It has been used as a vascular graft and has the highly desirable property of remodeling itself to become host tissue. To date there has been limited reporting on its preimplantation mechanical properties as a vascular graft. In this study, compliance, elastic modulus, and burst pressure have been measured on 5- and 8-mm SIS grafts. The compliance (percent of diameter increase for a pressure rise from 80 to 120 mmHg) was 4.6% av (range 2.9 to 8.6%) for the 5-mm grafts. For the 8-mm graft, the increase in diameter for the same pressure rise was 8.7% av (range 7.2 to 9.5%). The modulus of elasticity (E) increased exponentially with increasing pressure according to E = E(o)e(alphaP), where Eo is the zero-pressure modulus and alpha is the exponent that describes the rate of increase in E with pressure; the units for E, Eo, and P are g/cm2. The mean value for Eo was 4106 (g/cm2 range 1348-5601). The mean value for alpha was 0.0059 (range 0.0028-0.0125). At 100 mmHg, the mean value for E was 8.91 x 10(3) g/cm2 (range 1.02-8.80 x 10(3)). The mean burst pressure for 5.5-mm grafts was 3517 mm Hg (range 2069-4654). In terms of preimplant compliance, the small-diameter SIS graft is about (1/2) as compliant as the dog carotid artery, about four times more compliant than a typical vein graft, and more than an order of magnitude more compliant than synthetic vascular grafts.

Repair of a full thickness corneoscleral defect in a German shepherd dog using porcine small intestinal submucosa

Porcine small intestinal submucosa (SIS) was used, in conjunction with a conjunctival graft, to repair a full thickness corneoscleral defect resulting from the excision of a limbal melanoma in a German shepherd dog. The SIS was found to provide adequate mechanical support and to act as a suitable physical barrier in place of the excised cornea and sclera. Corneal vascularisation was present distant to the graft by two weeks postoperatively but this was effectively controlled with topical cyclosporin. By six weeks postoperatively, the graft had become incorporated into the cornea and sclera, and the associated corneal neovascularisation had resolved. From this initial case, porcine SIS would appear to be a suitable material for the repair of corneoscleral defects in dogs.

Porcine small intestinal submucosa as a dural substitute

BACKGROUND

The continuing search for the ideal dural substitute is currently directed toward collagen preparations. Xenogeneic porcine small intestinal submucosa (SIS), a naturally occurring extracellular matrix rich in collagen, has been successfully used as a soft tissue graft in several body organ systems, including preliminary studies as a dural substitute in the rat.

METHODS

Eight dogs underwent temporoparietal craniotomy and dural resection with replacement by SIS. Five dogs had contralateral procedures without SIS grafting. Three dogs had contralateral SIS grafts placed 2 months after the initial procedure. Histologic assessment was obtained at 7, 30, 60, 90, and 120 days. Cerebrospinal fluid (CSF) cytological examination and routine serum chemistry preceded sacrifice.

RESULTS

Histologic evaluation showed initial graft infiltration by mononuclear round cells, spindle-shaped cells within an eosinophilic staining extracellular matrix, and neovascularity. Complete resorption of the graft was evident by 60 days. This pattern is consistent with the previously described incorporation and remodeling of the SIS graft at other sites. CSF cytology and routine serum chemistry at the time of sacrifice were normal. Response to repeat grafting was identical to that of initial exposure. There was no clinical or histologic evidence of sensitization or graft rejection. No evidence of adverse effect on the underlying cerebral cortex was observed.

CONCLUSIONS

Porcine small intestinal submucosa demonstrates a favorable biologic response as a dural substitute in the canine model. It is a promising biomaterial for dural replacement.