Spatial and temporal changes in compliance following implantation of bioresorbable vascular grafts

Abstract

Compliance matching between the host vessel and vascular grafts used for small-diameter arterial replacements is thought to be important for long-term patency. However, currently available grafts elicit fibroplastic reactions, resulting in decreasing compliance with time after implantation. Bioresorbable prostheses elicit ingrowth of myofibroblasts containing abundant contractile elements. This led us to investigate whether compliance of implanted bioresorbable prostheses decreased as a function of time and if the kinetics of change correlated with the progression of tissue ingrowth. Woven polyglactin 910 prostheses (10 mm x 4 mm i.d.) were implanted into adult NZW rabbit infrarenal aortas and replicates were harvested serially through 8 months. Control grafts were implanted, and immediately resected. Dynamic compliance was measured at 1-mm axial increments along each explant using a pulse duplicator apparatus which exposed the harvested samples to realistic pulsatile hemodynamics. Compliance was calculated for proximal, mid, and distal segments of each graft and averaged at each time point by grouping into control (zero time, n = 3), early (1-4 weeks, n = 13), and late (6-36 weeks, n = 9) explant periods. At late explant periods both proximal and distal compliance were significantly greater than mid graft compliance (p < .02 and p < .03, respectively). There was a significant increase in proximal compliance between early and late explant times (p < .01). Measured increases in mid and distal segment compliance over time did not reach statistical significance. Myofibroblast laden tissue ingrowth into the inner capsule followed macrophage phagocytosis and was nearly complete prior to the time that an increase in compliance was demonstrated. Thus since the major histologic episodes precede the change in compliance, these are not likely initiated by this biomechanical change. We hypothesize the graft resorption coupled with the ingrowth of more compliant tissue likely leads to the increased compliance of the graft material.

Bacterial cellulose as a potential vascular graft: Mechanical characterization and constitutive model development

“…The interaction of bacterial cellulose with vascular cells, such as that demonstrated here for SMCs, may even suggest adaptive remodeling of bacterial cellulose grafts in vivo and hence better compliance matching with host arteries in the long term. This is supported by the work of Greisler et al 28 where cellular ingrowth was found to increase the compliance of woven polyglactin 910 grafts implanted into rabbits. In addition, in the work by Roy et al, 29 decellularization of porcine carotid arteries was found to significantly reduce arterial compliance.…”

Engineering of vascular ingrowth matrices: Are protein domains an alternative to peptides?

“…Not surprisingly, pro-angiogenic growth factors were added to natural ingrowth matrices like fibrin (Greisler et al, 1992a) soon after their potential was discovered in vitro (Montesano et al, 1986). Alternatively, bioresorbable scaffolds were used for vascular grafts as soon as the potential of host tissue to regenerate structures became fully comprehended (Greisler et al, 1992b). The central role that macrophages play in this concept certainly contributed to a less "engineerable" outcome.…”

Biodegradable poly(ethylene oxide)/poly(ϵ‐caprolactone) multiblock copolymers

“…In addition to their use in classic applications, such as bioabsorbable sutures 1,2 and drug delivery systems, 3,4 their applicability recently expanded into new areas, such as selectively biodegradable vascular grafts, [5][6][7] noninvasive surgical procedures, 8,9 the prevention of postsurgical adhesions, [10][11][12] and tissue engineering. [13][14][15] Poly(-caprolactone) (PCL) is being used in clinics as a surgical material, and some of the most commonly reported PCL biomedical applications are controlled drug delivery systems 16 and implants for orthopedic surgery.…”