The platelet reactivity of vascular graft prostheses: an in vitro model to test the effect of preclotting

An in vitro perfusion system was used to study the platelet reactivity of the following vascular graft materials when tested with human blood: expanded polytetrafluoroethylene (ePTFE), crimped Dacron Bionit (DB) and preclotted Dacron Bionit (DB/PC). These materials were simultaneously compared to silicone rubber (SR) using an identical perfusion circuit with the same donor's blood. All vascular graft materials tested in this in vitro perfusion system caused some degree of platelet activation as shown by a decrease in platelet count, an increase in platelet factor 3 activity, elevation of plasma levels of both platelet factor 4 and β-thromboglobulin and decreased platelet aggregability. The observed platelet activation was striking for Dacron and especially preclotted Dacron, with ePTFE showing low levels of platelet activation. Platelet activation fay Dacron was initially rapid and then levelled off, whereas the platelet activation with preclotted Dacron began more slowly, but reached much greater levels after three hours of in vitro perfusion.     

Application of a vascular graft material (Solcograft-P) in experimental surgery

The implantation and post-implantation behaviour of a Solcograft-P vascular prosthesis in the aortic, aorto-iliac, carotid and vena caval positions in dogs was studied up to 100 d post-surgery in order to assess the suitability of this vascular material for use in man. Solcograft-P is prepared from the carotid arteries of calves by crosslinking the collagen stroma using adipyl dichloride. During the postoperative follow-up period of 3 month, 100% of the aortal grafts, 80% of the aorto-iliac bypasses, 60% of the vena caval grafts and 35% of the carotid implants remained patent. The biochemical properties of the Solcograft-P are better than those of Solcograft, its predecessor. The intimal lining was consistently smooth and homogeneous in grafts of biological origin, and no aneurysm was observed. Infection and early thrombosis occured no more frequently than with other grafts. The new Solcograft-P, crosslinked via ester and amide groups, seems to represent a real improvement over Solcograft. Our results suggest that Solcograft-P should prove valuable in various cases of reconstructive vascular surgery of the lower limb, especially when the autologous vena saphena magna is not available, and its mechanical properties may well prove suitable for both arterial and venous replacement.     

A viscoelastic,viscoplastic model of cortical bone valid at low and high strain rates

The stress–strain behavior of cortical bone is well known to be strain-rate dependent, exhibiting both viscoelastic and viscoplastic behavior. Viscoelasticity has been demonstrated in literature data with initial modulus increasing by more than a factor of 2 as applied strain rate is increased from 0.001 to 1500 s^?1. A strong dependence of yield on strain rate has also been reported in the literature, with the yield stress at 250 s^?1 having been observed to be more than twice that at 0.001 s^?1, demonstrating the material viscoplasticity. Constitutive models which capture this rate-dependent behavior from very low to very high strain rates are required in order to model and simulate the full range of loading conditions which may be experienced in vivo; particularly those involving impact, ballistic and blast events. This paper proposes a new viscoelastic, viscoplastic constitutive model which has been developed to meet these requirements. The model is fitted to three sets of stress–strain measurements from the literature and shown to be valid at strain rates ranging over seven orders of magnitude.     

Mechanical properties of cellulose: chitosan blends for potential use as a coronary artery bypass graft

The development of intimal hyperplasia is the major cause of failure of both autologous saphenous vein and synthetic coronary artery bypass grafts. This is partially due to graft-host vessel compliance mismatch. Cellulose and chitosan (CELL:CHIT) are both biocompatible, nontoxic, and naturally occurring biopolymers that have been used extensively for biomedical applications. Elastic properties of membranes made of CELL:CHIT blends with different ratios between each polymer were determined using uniaxial tests and the ratio that yielded the less stiff membrane was chosen to prepare a small diameter hollow tube. The presence of chitosan had a favorable impact on the elasticity of the membranes, where the CELL:CHIT 5:5 ratio showed the lowest Young’s modulus. Small diameter tubular constructs were fabricated using this optimal CELL:CHIT ratio and the compliance was determined on samples with different wall thickness and internal diameter. The compliance of the hollow tube with inner diameter of 4?mm and wall thickness of 1.2?mm was found to be 5.91%/mmHg?×?10^?2, which is higher than those of Dacron, expanded polytetrafluorethylene, and saphenous vein, but very close to that of human coronary artery. Burst strength tests revealed that the tubes can withstand at least 300?mmHg. Finally, the tubes showed satisfactory cell attachment property when myofibroblast cells adhered and proliferated on the lumen of the samples.