Small Intestinal Submucosa as an Intra-Articular Ligamentous Graft Material: A Pilot Study in Dogs

This pilot study was performed to determine the potential for using small intestinal submucosa (SIS) xenografts for intra-articular ligament reconstruction. Porcine SIS was used to replace the excised cranial cruciate ligament (CCL) in five normal dogs. Grafts were evaluated histologically at 10, 12, 16, and 26 weeks after implantation. Two grafts were evaluated biomechanically at 26 weeks. All of the SIS neoligaments appeared macroscopically as white fibrous bands. The histological appearance progressed, with time, from disorganized immature connective tissue to large bundles of organized connective tissue, covered by a synovial membrane, that resembled the native CCL. There was no histological evidence of immune-mediated nor any foreign body reaction to the xenogeneic SIS graft material. The neoligaments 26 weeks after implantation had a maximum force to failure that was 16.2 and 21.4 times greater than the original SIS graft material and were 7.6 and 11.1 percent as strong as the contralateral control CCLs. We conclude that porcine SIS, used as an intra-articular graft material to replace the normal CCL in dogs, supported host tissue ingrowth, remodelled to form a ligamentous structure, and is worthy of further investigation.

Small intestinal submucosa was used to replace the excised cranial cruciate ligament (CCL) in five normal dogs. The histo-logical appearance of the grafts progressively changed, with time, from disorganized immature connective tissue to large bundles of organized connective tissue that resembled the native CCL. Graft strength increased between implantation and 26 weeks after the operation, however remained weaker than controls.

Repair of experimental Achilles tenotomy with porcine renal capsule material in a rat model

Porcine small intestinal submucosa (SIS) is a collagenous acellular matrix which has found substantial utility as a tissue growth scaffold. In the present study, the utility of porcine renal capsule matrix (RCM) was compared to SIS in a rat Achilles tenotomy repair model. Groups of rats underwent surgical tenotomy followed by either no repair, repair with a SIS graft, or repair with a RCM graft. The weight-bearing ability of the manipulated limb was evaluated for 10 days following surgery using a subjective scale. Tenotomy sites sampled 28 days after surgery were numerically graded for degree of histologic change. There were no statistically significant differences between groups with respect to return to weight-bearing ability (p >or= 0.05) or degree of histologic change (p >or= 0.001); however, a non-significant trend suggested that rats treated with SIS or RCM experienced a faster return to limb function than untreated rats, and RCM-treated rats had slightly higher scores for degree of histologic change, suggesting a more rapid repair of the tenotomy site than in SIS-treated or untreated rats. The harvested tenotomy sites in all treatment groups were characterized by marked fibroplasia and presence of macrophages. Remnants of SIS surrounded by macrophages and multi-nucleated giant cells were still present in some rats, however remnants of RCM were not observed, suggesting more rapid incorporation of RCM. The results show that RCM is equivalent to SIS as a material for repair of Achilles tendon injury and merits further study in other tendon injury models.

An investigation of the long-term bioactivity of endogenous growth factor in OASIS Wound Matrix

OBJECTIVE

To examine the retention and bioactivity of endogenous FGF-2 after prolonged storage within a complex matrix. FGF-2 is a growth factor found in OASIS Wound Matrix, a purified collagen wound-care product containing other endogenous components of the extracellular matrix.

METHOD

FGF-2 content was measured by ELISA. FGF-2 activity was measured using an in vitro bioassay in rat pheochromocytoma (PC12) cells.

RESULTS

FGF-2 content ranged from 15.3 ng/g to 84.3 ng/g. The bioassay showed that the FGF-2 retained in the matrix was present in a bioactive form able to cause differentiation of cells in culture.

CONCLUSION

The results demonstrate that wound-care products can be developed to retain their bioactivity over time and that inherently unstable purified growth factors are preserved if stored as bound factors within their natural extracellular matrix. The results also suggest that use of acellular matrices containing active growth factors would have advantages in terms of simplicity and cost over purified recombinant growth factor therapies.

Use of porcine renal capsule matrix as a full-thickness dermal wound-healing material in rats

OBJECTIVE

To compare the utility of porcine renal capsule matrix (RCM) with porcine small intestinal mucosa (SIS) in a rat full-thickness skin wound model.

METHOD

Groups of rats had surgically-created wounds filled with either SIS or RCM. On each rat a contralateral wound was left unfilled (RCM-U or SIS-U). Wound diameter was measured 3, 7, 12, 17, 26 and 30 days after creation. Wound sites sampled 3, 7, 14, 28, 42 and 56 days after wound creation were numerically graded for degree of histologic change and for collagen content, based on intensity of trichrome staining.

RESULTS

Wounds in all groups rapidly contracted to less than 50% of the original diameter within 12 days. There were no differences in wound diameter between RCM- and SIS-treated wounds at any time point, but these wounds had significantly greater (p < 0.001) diameters than their unfilled counterparts on days 7, 12 and 17. There were no differences in histologic scores or trichrome-staining scores between RCM- and SIS-treated wounds and their unfilled counterparts at any time point, except for a greater (p < 0.05) histologic score in SIS-treated wounds compared with unfilled controls on day 14. In both treatment groups an acute inflammatory response at the wound site was soon replaced by an influx of macrophages and fibroblasts.

CONCLUSION

The results show that RCM is equivalent to SIS for the treatment of full-thickness wounds and that these materials may enhance wound healing in terms of wound-tissue collagenisation and maturation. These materials therefore merit further study in other wound-care models.

Improved biocompatibility of small intestinal submucosa (SIS) following conditioning by human endothelial cells

Small intestinal submucosa (SIS) is a naturally occurring tissue matrix composed of extracellular matrix proteins and various growth factors. SIS is derived from the porcine jejunum and functions as a remodeling scaffold for tissue repair. While SIS has proven to be a useful biomaterial for implants in vivo, problems associated with endothelialization and thrombogenicity of SIS implants may limit its vascular utility. The goal of this study was to determine if the biological properties of SIS could be improved by growing human umbilical vein endothelial cells (HUVEC) on SIS and allowing these cells to deposit human basement membrane proteins on the porcine substrate to create what we have called "conditioned" SIS (c-SIS). Using an approach in which HUVEC were grown for 2 weeks on SIS and then removed via a technique that leaves behind an intact basement membrane, we hypothesized that the surface properties of SIS might be improved. We found that when re-seeded on c-SIS, HUVEC exhibited enhanced organization of cell junctions and had increased metabolic activity compared to cells on native SIS (n-SIS). Furthermore, HUVEC grown on c-SIS released lower amounts of the pro-inflammatory prostaglandin PGI2 into the media compared to cells grown on n-SIS. Additionally, we found that adhesion of resting or activated human platelets to c-SIS was significantly decreased compared to n-SIS suggesting that, in addition to improved cell growth characteristics, conditioning SIS with human basement membrane proteins might decrease its thrombogenic potential. In summary, conditioning of porcine SIS by human endothelial cells improves key biological properties of the material that may improve its usefulness as remodeling scaffold for tissue repair. Identification of critical modifications of SIS by human endothelial cells should help guide future efforts to develop more biocompatible vascular grafts.

Calcification potential of small intestinal submucosa in a rat subcutaneous model

Glutaraldehyde treatment of collagen biomaterials promotes calcification, poor host-tissue incorporation, and ultimately mechanical failure of bioprotheses. Porcine small-intestinal submucosa (SIS) is a biomaterial which has been investigated for several applications including arterial and venous grafts and repair of tendon, ligament, body wall, and urinary bladder defects. The calcification potential of peracetic acid (PAA)-sterilized SIS was studied. Four test samples, (1) native (cleaned, untreated) SIS, (2) SIS sterilized with 0.1% PAA, (3) SIS treated with 0.25% glutaraldehyde for 20 min, and (4) commercially available glutaraldehyde-preserved porcine bioprosthetic heart valve cusp segments (GPV), were each implanted subcutaneously in each of 24 weanling rats. Six rats were euthanatized at 1, 2, 4, and 8 weeks. Evaluation of calcium concentration by atomic absorption spectroscopy and extent of mineralization and fibrosis by light microscopy were performed. Atomic absorption revealed no calcification in native or peracetic acid-treated SIS at any time point compared with preimplant calcium concentration. Statistically significant (P < 0.0001) calcification occurred in glutaraldehyde-treated materials (SIS and GPV) at each evaluation as compared to native and peracetic acid-treated samples. Histopathology indicated native and peracetic acid-treated SIS showed no implant mineralization (P < 0.0001) and little peri-implant fibrosis (P < 0.0001). Results suggested that native and peracetic acid-treated SIS have a low calcification potential and further study of this biomaterial is warranted.

Intestine submucosa and polypropylene mesh for abdominal wall repair in dogs

Continuing investigations of abdominal body wall reconstruction materials suggest that unacceptable implant complications continue and that the ideal material has not yet been found. This pilot study compared xenogeneic (porcine) small intestine submucosa (SIS) with polypropylene mesh (PPM) for repair of created partial-thickness (six dogs) and full-thickness (six dogs) abdominal wall defects. Postoperative clinical evaluation of all dogs showed no evidence of implant failure. Dogs were euthanized at 1, 2, and 4 months after surgery. The SIS implants were completely replaced by host tissue at 4 months as determined by immunohistochemistry. The resultant repair was well-organized, smooth, dense collagenous connective tissue that was well incorporated into the adjacent fascia and skeletal muscle fiber bundles. In the full-thickness defect dogs, omentum covered a significantly larger portion of PPM (P = 0.001) and was more firmly attached to PPM (P = 0.0001) compared to SIS/connective tissue repair. We conclude that xenogeneic SIS can be used as an abdominal body wall repair material in the dog and warrants further investigations.

Mechanical properties of xenogeneic small-intestinal submucosa when used as an aortic graft in the dog

Small-intestinal submucosa (SIS) has been shown to induce tissue remodelling in vivo when used as a vascular graft. The present study investigated in physical and mechanical properties of remodeled aortic grafts derived from xenogeneic SIS material. Eight infrarenal aortic grafts were implanted in mongrel dogs. The grafts were explanted at 1 or 2 months and tested for compliance and hoop mechanical properties. The morphologic changes within the grafts were also characterized. The remodeling process produced graft structures which were significantly stronger than both the normal artery (P = .012) and the original SIS graft (P = .0001), and the compliance of these structures was one third that of normal artery and similar to the original SIS grafts. The remodeled grafts were > 10 times the thickness of the implanted SIS. Immunohistochemical analysis of remodeled tissues suggest that the SIS material was degraded and resorbed over time. The remodeling process transformed a material which was physically and mechanically quite different from normal aorta into a blood conduit which had the physical and mechanical properties needed to function in this mammalian arterial system.

Experimental evaluation of small intestinal submucosa as a microvascular graft material

The evaluation of porcine small intestine submucosa (SIS) in a microsurgical model was conducted using an interpositional graft in the rat femoral artery. The SIS grafts were fabricated from processed porcine material that was wrapped around a glass tube and oversewn longitudinally to produce a tubular structure. Of the 42 animals studied, 7 received grafts of untreated SIS (group I), 7 of the grafts were presoaked (PSH) in heparin (Group II), 7 animals were treated with systemic heparin prior to implantation of PSH-SIS (group III), 7 animals received SIS grafts crosslinked to heparin (group IV), 7 animals received SIS grafts crosslinked to urokinase (group V), and 7 animals received untreated autologous epigastric vein grafts (group VI). Patency was assessed postoperatively and selected grafts were evaluated by histology. All SIS grafts failed to maintain patency beyond the first postoperative hour. Histologic examination of the thrombosed graft surfaces revealed a smooth luminal surface with a thick layer of attached fibrin and platelets with a central occluding thrombus. The thickness of the induced fibrin layer appears to narrow intraluminal space significantly at the microvascular level. While having excellent success at vessel diameters greater than 3 mm, and in a variety of nonporcine animal models without xenographic rejection, SIS in this model was thrombogenic despite a favorable surface morphology as demonstrated by SEM. Even with use of heparin and urokinase SIS graft thrombosis occurred.

Detection of ventricular tachycardia and fibrillation using coronary sinus blood temperature: a feasibility study

This study investigated the potential of coronary sinus blood temperature to detect ventricular arrhythmias. A rapid-response, thermistor-tipped catheter placed in the coronary venous system of anesthetized dogs was used to record the blood temperature during periods of induced bradycardia, tachycardia, and ventricular fibrillation. A second catheter was used to measure blood temperature in the aortic arch during these same episodes. A pulsatile component of venous blood temperature, typically 40 m degrees C in amplitude, was well correlated with the cardiac cycle, while another, slightly larger, pulsatile component was well correlated with respiration. The cardiac component peaked during ventricular systole, and the respiratory component peaked during expiration. As compared with sinus rhythm, the cardiac signal diminished during bradycardia and tachycardia and nearly disappeared during asystole and ventricular fibrillation. The baseline component of venous blood temperature rose during periods of tachycardia and fibrillation, while respiration proved to be an important factor in the baseline temperatures. The presence of small, cyclic, thermal variations in the coronary venous system was verified, and the concept of measuring metabolic activity to assess ventricular function was substantiated. These studies show promise that this concept could be incorporated into medical devices that use these temperature signals for diagnosis of ventricular arrhythmias.

Directional porosity of porcine small-intestinal submucosa

Small-intestinal submucosa (SIS) has been shown to be a promising biomaterial for vascular graft applications. This study examines the directionality property of SIS porosity using 35 SIS specimens from 13 pigs. In addition, the effects of the weight of the donor pig, pre-conditioning of 13 additional SIS specimens, and the duration of the test of five additional SIS specimens on such porosity are reported. The porosity from serosal to mucosal direction was found to be four times greater than the porosity in the opposite direction. The weight of the donor pig was not found to be an important factor in SIS porosity. Preconditioning served to increase the average serosal porosity index at 120 mm Hg static water pressure from 2.99 to 8.33 mL/(min cm2). The porosity in the mucosal direction was not affected by preconditioning. Porosity in both directions decreased with increasing test duration. The directionality property of SIS porosity may be an important factor in its success as a vascular graft. The term 'porosity' is used throughout this article, but current standards also refer to the term 'permeability' to describe the passage of liquid through a vascular graft.

Small intestinal submucosa as a vascular graft: a review

Continuing investigations of vascular graft materials suggest that unacceptable graft complications continue and that the ideal graft material has not yet been found. We have developed and tested a biologic vascular graft material, small intestine submucosa (SIS), in normal dogs. This material, when used as an autograft, allograft, or xenograft has demonstrated biocompatibility and high patency rates in aorta, carotid and femoral arteries, and superior vena cava locations. The grafts are completely endothelialized at 28 days post-implantation. At 90 days, the grafts are histologically similar to normal arteries and veins and contain a smooth muscle media and a dense fibrous connective tissue adventitia. Follow-up periods of up to 5 years found no evidence of infection, intimal hyperplasia, or aneurysmal dilation. One infection-challenge study suggested that SIS may be infection resistant, possibly because of early capillary penetration of the SIS (2 to 4 days after implantation) and delivery of body defenses to the local site. We conclude that SIS is a suitable blood interface material and is worthy of continued investigation. It may serve as a structural framework for the application of tissue engineering technologies in the development of the elusive ideal vascular graft material.

Porosity of porcine small-intestinal submucosa for use as a vascular graft

The porosity of a vascular graft material has been suggested as a major factor affecting the rate and degree of neovascularization of newly implanted grafts, with higher porosities generally associated with better performance. The objective of this study was to determine the water porosity of a new vascular graft material, small-intestinal submucosa (SIS), and to compare the values to those reported for other common vascular graft materials. In addition, the porosity of SIS was investigated with respect to applied pressure and applied uniaxial tension. Both rectangular, flat specimens and tubular specimens of SIS were subjected to static water pressure, and water was collected as it passed through the SIS material. SIS has a typical porosity of 0.52 mL/min.cm-2 at an applied pressure of 120 mm Hg. Although porosity appeared to be unaffected by uniaxial tension, it increased in proportion to applied pressure at a rate of 4.8 x 10(-3) mL/min.cm-2/mm Hg. These low porosity values and the past success of SIS as a vascular graft material suggest that high-porosity materials are not required for implant success.

Treatment of reperfusion injury in dogs with experimentally induced gastric dilatation-volvulus

In dogs, gastric dilatation-volvulus (GDV) is characterized by cardiogenic shock, with resulting hypoperfusion. Treatment goals include reperfusion of transiently ischemic tissues, which indicates that reperfusion injury may be a factor in the physiopathogenesis of GDV. Recently, we obtained data that indicate that reperfusion injury may be involved in experimentally induced GDV. Using this GDV model, we evaluated mortality in 24 dogs of 4 equal groups, treated with deferoxamine (an iron chelator), dimethylsulfoxide (a free radical scavenger), a combination of the 2 drugs, or isotonic saline solution. All 6 dogs that were given deferoxamine survived; however, 3 dogs of the dimethylsulfoxide-treated group, 2 dogs of the combination-treated group, and 4 dogs of the saline-treated group died. Results of the study indicate that mortality associated with experimentally induced GDV is reduced by appropriate and timely pharmacologic intervention to prevent or attenuate reperfusion injury, and that deferoxamine may be more effective than dimethylsulfoxide.