Patency rates of minute vascular replacements: the glutaraldehyde modified mandril-grown conduit

Bovine type I collagen as an endovascular stent-graft material: biocompatibility study in rabbits

PURPOSE

To study the biocompatibility of a bovine type I collagen preparation as a material for small-vessel stent-grafts in rabbits.

MATERIALS AND METHODS

A composite nitinol-collagen endovascular stent-graft with a 4-mm inner diameter was deployed in the abdominal aorta in nine rabbits. Angiography was performed, and the rabbits were sacrificed at 1, 2, and 7 days and at 1 and 3 months. The portion of the aorta containing the stent-graft was excised and was histologically evaluated.

RESULTS

All stent-grafts were patent at all time points. On days 1, 2, and 7 after implantation, scattered red and white blood cells adhered to the stent-graft. At 1 month, the stent-graft was endothelialized and was infiltrated with fibroblasts that deposited collagen within the interstices of the implanted collagen material. At 3 months, there was additional collagen deposition within the interstices of the stent-graft that did not narrow the lumen of the stent-grafts.

CONCLUSION

Type I collagen as a intravascular stent-graft material is biocompatible for at least 3 months in rabbits. It is rapidly endothelialized and does not cause reactive stenosis. As a versatile and biocompatible polymer, collagen is potentially useful in the construction of endovascular stent-grafts for use in human arteries.

Effects of mesh modification on the structure of a mandrel-grown biosynthetic vascular prosthesis

Mandrel-grown, mesh-reinforced vascular prostheses require adequate tissue coverage of the mesh for effective clinical function, particularly in low blood flow situations. Development of the ovine collagen-based Omniflowtrade mark vascular prosthesis has shown that the extent of this tissue cover is dependent on the interactions of the mandrel and the mesh with the sheep host. In the present study, the effects of chemical changes to the mesh have been examined. These data indicate that certain treatments of the mesh, particularly collagen or heparin, lead to increased tissue coverage while the number of sheep cells present and the ultrastructure of the resulting vessel remain unchanged.

Structural analysis of a collagen--polyester composite vascular prosthesis

The Omniflow Vascular Prosthesis is a collagen--polyester composite which has been used successfully for peripheral vascular replacement. In this study, we have examined the distribution of the various connective tissue components and the ultrastructural organisation of these in order to understand and allow improvement of its functional properties. Using immunohistology with specific monoclonal antibodies, types I and III collagens were found to be the major components throughout the prosthesis. Type VI collagen was also present but was mainly associated with cells, particularly around the polyester mesh and silicone interfaces. While elastin was absent, two elastic tissue microfibrillar proteins were present uniformly throughout the structure. Ultrastructurally, clear differences existed between the local environments of the inner surface, which had formed around the silicone mandrel, the polyester mesh within the prosthesis, and the outer collagenous tissue which formed the central wall. At the inner surface, the amount of collagen was less and the orientation of these fibres was not well defined. The collagen fibrils in the polyester region were smaller than those of the main wall, which were well ordered and orientated along the axis of the device.

Development of an ovine collagen-based composite biosynthetic vascular prosthesis

The search for an ideal vascular prosthesis to bypass peripheral vascular obstructive lesions is necessary where autologous tissues are either unavailable or unsuitable. This paper will outline the development and use of vascular conduits, principally of biological origin. The clinical benefits and limitations of these materials are discussed. The development of a composite biosynthetic prosthesis (Omniflow¿) is described, together with the testing methods used to determine and predict its suitability for use as an arterial substitute. The ovine biosynthetic prosthesis has significantly improved surface and mural properties over previous attempts at producing prostheses for vascular reconstruction. Immunohistological studies on samples recovered from dogs after 4 years show that the original ovine collagen is still present after 4 years, and it is further augmented by the deposition of new, host-derived connective tissue.

Development of monoclonal antibodies to collagens for assessing host-implant interactions

The biologic response to surgical implants is of importance in understanding the host interactions relating to long-term patency of implants. The methodology currently available for the assessment of host-biomaterial interactions is subjective and is limited to identification of inflammatory responses and general histopathological staining procedures associated with these processes. A clearer appraisal of the nature and type of extracellular matrix components related to the host response to the implanted biomaterials would assist in the development of biomaterials and would allow an earlier means of predicting biocompatibility. The extracellular matrix consists of a range of similar collagen types which are difficult to distinguish using polyclonal antibodies. However, with the advent of hybridoma technology, monoclonal antibodies with the desired specificities can be produced to provide very powerful probes for assessing host-implant interactions. There were several problems associated with the production of these antibodies, mainly arising from collagens being extremely poor immunogens. The present study has examined these problems and has demonstrated that monoclonal antibodies against a range of collagen types can be produced. These antibodies were all highly specific for collagen type, but for a given collagen type, antibodies with different species specificities could be obtained. These antibodies were shown to be suitable for immunohistology of various connective tissue samples and were used to examine collagen-based vascular prostheses (Omniflow Vascular Graft) after retrieval from canine models. These data demonstrated that the monoclonal antibodies to collagens were excellent for the analysis of surgical implants and biomaterials after retrieval.

Collagen organization in mandrel-grown vascular grafts

The organization of collagen in custom-built biosynthetic vascular prostheses (Omniflow Vascular Graft), which are suitable for peripheral revascularization, has been examined. The grafts were a glutaraldehyde-tanned ovine-collagen composite with a polymer mesh reinforcement. Comparisons were made between grafts using different mesh fiber polymers and knit patterns. There was a basic similarity in the arrangement of the tissue structure in all graft types. Scanning electron microscopy and light microscopy showed that the collagen formed a layered structure which fully encased the polymer mesh and held it firmly in position. Rather than polymer mesh, the inner surface of the graft was found to be collagen, and lined with a layer of flattened cells. Collagen formed a continuous layer surrounding the mesh, with no distinct boundary, membrane or structurally weak point being apparent. Immunohistology, using a monoclonal antibody specific for type III collagen, and chemical analysis, indicated that there was high proportion of type III collagen in the grafts, particularly in the region surrounding the mesh fibers.

The role of physical and chemical characteristics in assessing the performance of a new biological vascular graft

Information obtained from physical and chemical characterization of vascular grafts can prove valuable in obtaining a preliminary assessment of potential in vivo performance. The data presented illustrate the concept and show that the new biological graft made from bovine ureters has adequate performance characteristics for use as a potentially successful vascular graft.

Glutaraldehyde tanned ovine collagen compared with polytetrafluoroethylene (Gore-Tex) as a conduit for small calibre artery substitution; an experimental study in dogs

Collagen tubes with a polyester mesh endoskeleton were grown in sheep around silastic mandrils and were then tanned in alkaline glutaraldehyde. Tanned ovine collagen conduits and polytetrafluoroethylene conduits (Gore-Tex), each 10 cm long and 6 mm wide, were deployed in parallel as aorto-iliac bypass grafts in 10 dogs. The grafts remained patent for periods up to and exceeding 23 months. No grafts showed aneurysmal dilatation. All grafts formed a neointima lined with cells. In the Gore-Tex grafts there was fibrous tissue ingrowth through the wall which resulted in progressive and irregular luminal narrowing. This was not seen in the tanned ovine collagen grafts.