Medical manufacturing company Cook Biotech developed a new category in the evolution of tissue repair. President Mark Bleyer describes the design process for SIS technology.
What is SIS technology?
Tissue engineering, the process of using certain materials to replicate tissue, is made up of three core components: cells, cell signaling, which is cell communication with pockets of chemicals and the least understood component, substrate, which is the base that cells grow on. This substrate makes a tremendous difference in cell behavior. Cook Biotech found the layered intestine of a pig is a matrix loaded with cell signals. Based on this discovery, we developed several product families out of this biomaterial made from porcine small intestinal submucosa (SIS). This material supports tissue repair by acting as a scaffold with an all-natural structure and composition. Over time, the material rapidly recruits cells from the body to repair the afflicted area and replace the original tissue, leaving behind a very functional repair of good, healthy tissue.
How are SIS products designed?
We use a lot of computer-aided drawing and simulation, because we have to simulate the forces that would be in the abdomen when someone coughs or sneezes or laughs — all stress conditions each product is required to survive. From a software point of view, we use standard CAD programs, namely Solid Edge and Pro/ENGINEER, along with mathematical modeling software to look at the physiologic systems. We then use bench testing to test the devices we design. It's very important to mimic the system — for example, for a fistula plug, an unwanted opening in the bowel, we create a model requiring the plug, place the plug in the model and then input expected pressure requirements to make sure the plug doesn't extrude through the tissue with internal abdominal pressure.
What are the challenges in designing a product like this?
When you get into mathematical modeling and simulation, how do you approximate tissue characteristics? That's why we rely on bench testing and taking a look at tissue models — because of the complexity of tissue. Another challenge is coming up with a manufacturing process that's reproducible. Process validation is important to ensure a consistent product. The key to designing the proper manufacturing process itself is getting clinical feedback and understanding clinical and physiologic issues of an application. We need to design with an understanding of both the tissue and the environment it's going into. We also do human studies to test products for accuracy. We get the products out to physicians to get their input.
What successes has your product seen?
With our application of tissue engineering, design size, shape and thickness strength can be customized to be appropriate for any type of repair. This biomaterial is being used for hernia repair with various sizes and thicknesses and it's also being used in more delicate applications, such as replacing a baby's diaphragm. In the past, when babies were born with a hole in their diaphragm and underdeveloped lungs, an operation was necessary to put plastic material in to repair the diaphragm. This patched the hole, but didn't grow with the baby and often required repeat surgeries. Because our material is a living tissue, it grows with the baby and no repeat surgeries are necessary. And the material and our design process make it possible to manufacture this dainty product specifically for pediatric use out of the same material we use for hernia repairs.