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

Current understanding of intimal hyperplasia and effect of compliance in synthetic small diameter vascular grafts

Despite much effort, synthetic small diameter vascular grafts still face limited success due to vascular wall thickening known as intimal hyperplasia (IH). Compliance mismatch between graft and native vessels has been proposed to be one of a key mechanical factors of synthetic vascular grafts that could contribute to the formation of IH. While many methods have been developed to determine compliance both in vivo and in vitro, the effects of compliance mismatch still remain uncertain. This review aims to explain the biomechanical factors that are responsible for the formation and development of IH and their relationship with compliance mismatch. Furthermore, this review will address the current methods used to measure compliance both in vitro and in vivo. Lastly, current limitations in understanding the connection between the compliance of vascular grafts and the role it plays in the development and progression of IH will be discussed.

Controlled delivery of therapeutics from microporous membranes. I. Fabrication and characterization of microporous polyurethane membranes containing polymeric microspheres

This paper describes a process for the inclusion of polymer microspheres in microporous polyurethane tubes and membranes. These composites were fabricated via a spray, phase-inversion technique using Cardiothane 51, a medical grade polyurethane, and either spray-dried poly(D,L-lactide-co-glycolide 50:50) microspheres or commercially available fluorescent polystyrene-latex microspheres. Characterization of the polyurethane membranes was performed using Fouriertransform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, hydraulic permeability testing, scanning electron microscopy, and visible and fluorescence light microscopy. The results indicated the feasibility of layering microspheres throughout the microporous membrane or wall of the microporous tube, and the potential of such composite structures for local delivery of bioactive substances.

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.

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.