Michael C. Hiles

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.

Bioactivity of Small Intestinal Submucosa and Oxidized Regenerated Cellulose/Collagen

OBJECTIVE: This study examined the bioactivity of porcine small intestinal submucosa (SIS Wound Matrix [SISWM], USP) and oxidized regenerated cellulose/collagen (ORC). DESIGN: Bioactivity was assessed in vitro as the ability to stimulate neurite outgrowth in rat pheochromocytoma (PC12) cells, proliferation of human fibroblasts, secretion of vascular endothelial growth factor (VEGF) from human fibroblasts, and in an in vivo angiogenesis model. In the angiogenesis model, SISWM and ORC were implanted subcutaneously into the mice, and vessel ingrowth was assessed at day 21 after implantation using fluorescence microangiography and histology. MAIN OUTCOME MEASURES: The change in cellular differentiation, proliferation, growth factor secretion, and angiogenesis over the negative control was measured after exposure to SISWM or ORC. MAIN RESULTS: SISWM increased neurite outgrowth in PC12 cells by approximately 22% over negative controls and induced proliferation in 50.8% of human fibroblasts. These increases were comparable to positive controls. ORC was not active in either of these assays. SISWM also stimulated fibroblast VEGF secretion to a greater extent (422.4 pg/mL) than ORC (4.2 pg/mL) (P < .001). At 21 days, fluorescence microangiography showed dense infiltration of blood vessels in the SISWM that extended approximately 3 mm from the edge of the disc. In contrast, the ORC implant showed blood vessel incursion less than 1 mm from the edge of the disc, and it dissolved in the site. CONCLUSIONS: SISWM shows much greater bioactivity than ORC. This is likely related to its close structural and biochemical approximation to natural dermal extracellular matrix and may help explain the strong clinical successes of SISWM.

Tissue engineering a clinically useful extracellular matrix biomaterial

Implantable biomaterials are one of the most useful tools in the surgeon’s armamentarium, yet there is much room for improvement. Chronic pain, tissue erosion, and late infections are just a few of the serious complications that can occur with conventional, inert materials. In contrast, tissue-inductive materials exist today. Combinations of biologically important molecules for directing cell growth and providing structural stability can be found in naturally occuring extracellular matrices. These “soft-tissue skeletons” of Mother Nature can be harvested, processed, and provided in a medically safe and biologically active form for repairing many different tissues in the human body. The future of surgical practice may well be determined by how well these new implant materials recreate the tissues they replace.

Suppression and Activation of the Malignant Phenotype by Extracellular Matrix in Xenograft Models of Bladder Cancer: A Model for Tumor Cell “Dormancy”

A major problem in cancer research is the lack of a tractable model for delayed metastasis. Herein we show that cancer cells suppressed by SISgel, a gel-forming normal ECM material derived from Small Intestine Submucosa (SIS), in flank xenografts show properties of suppression and re-activation that are very similar to normal delayed metastasis and suggest these suppressed cells can serve as a novel model for developing therapeutics to target micrometastases or suppressed cancer cells. Co-injection with SISgel suppressed the malignant phenotype of highly invasive J82 bladder cancer cells and highly metastatic JB-V bladder cancer cells in nude mouse flank xenografts. Cells could remain viable up to 120 days without forming tumors and appeared much more highly differentiated and less atypical than tumors from cells co-injected with Matrigel. In 40% of SISgel xenografts, growth resumed in the malignant phenotype after a period of suppression or dormancy for at least 30 days and was more likely with implantation of 3 million or more cells. Ordinary Type I collagen did not suppress malignant growth, and tumors developed about as well with collagen as with Matrigel. A clear signal in gene expression over different cell lines was not seen by transcriptome microarray analysis, but in contrast, Reverse Phase Protein Analysis of 250 proteins across 4 cell lines identified Integrin Linked Kinase (ILK) signaling that was functionally confirmed by an ILK inhibitor. We suggest that cancer cells suppressed on SISgel could serve as a model for dormancy and re-awakening to allow for the identification of therapeutic targets for treating micrometastases.

Absorption of bioactive molecules into OASIS wound matrix.

OBJECTIVE: To examine the ability of OASIS Wound Matrix to absorb, retain, and protect bioactive molecules from solution. DESIGN: Samples of OASIS Wound Matrix were incubated in solutions of bioactive molecules, specifically heparin, albumin, fibronectin, basic fibroblast growth factor 2, and platelet-derived growth factor (PDGF). Half of the samples were then rinsed, and all of the samples were evaluated using enzyme-linked immunosorbent assays (ELISAs) and dye-mediated spectrophotometric methods for absorption and retention of the bioactive molecules. Protection of PDGF was measured by placing PDGF-incubated and control samples into a degradation solution containing plasmin. Intact PDGF levels were then evaluated using a PDGF-specific ELISA. MAIN OUTCOME MEASURES: The main outcome measures were the amount of each bioactive molecule that was absorbed after incubation in solutions and retained after rinses as well as the amount of PDGF remaining after plasmin degradation. MAIN RESULTS: OASIS Wound Matrix absorbed bioactive molecules from solution, selectively absorbed PDGF from serum, and protected PDGF from protease degradation. CONCLUSIONS: Although OASIS Wound Matrix potentially has multiple functions in wound healing, it likely promotes wound healing, in part, by absorbing, retaining, and protecting bioactive molecules from the wound environment.

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°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 hradycardia 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.

Addition of nimesulide to small intestinal submucosa biomaterial inhibits postsurgical adhesiogenesis in rats

Adhesion formation is a common complication in abdominal surgery with incidence as high as 93% and small bowel obstruction a common complication. Because the extracellular matrix material, small intestinal submucosa (SIS), is commonly used in various surgical procedures, methods to inhibit adhesiogenesis are of great interest. This study was undertaken to determine if incorporation of nimesulide (NM), a selective cyclooxygenase (COX)-2 inhibitor, could reduce the extent and tenacity of intraabdominal adhesion formation associated with SIS implantation. Female Sprague-Dawley rats underwent a cecal abrasion surgical procedure to induce adhesiogenesis. Rats were either left untreated or treated by direct application over the injured cecum with polypropylene mesh (PPM); SIS; SIS containing a low dose of NM; or SIS containing a high dose of NM. Rats were euthanized 21 days later, and adhesion extent and tenacity were evaluated using standard scales (0 = minimal adhesiogenesis; 4 = severe adhesiogenesis). Addition of NM to SIS resulted in a significant (p < 0.05) reduction in adhesion extent and in a similar reduction in adhesion tenacity for SIS containing a low dose of NM. Adhesions typically extended from the abraded cecal surface to the body wall and were characterized histologically by fibrous tissue adherent to the cecal wall. In conclusion, addition of the nonsteroidal anti-inflammatory, COX-2 selective drug, NM, to SIS attenuates adhesion extent and tenacity when compared with surgical placement of SIS or PPM alone.

Transforming surgery through biomaterial template technology

Templates inserted into surgical wounds strongly influence the healing responses in humans. The science of these templates, in the form of extracellular matrix biomaterials, is rapidly evolving and improving as the natural interactions with the body become better understood.