Modification, crosslinking and reactive electrospinning of a thermoplastic medical polyurethane for vascular graft applications.

Thermoplastic polyurethanes are used in a variety of medical devices and experimental tissue engineering scaffolds. Despite advances in polymer composition to improve their stability, the correct balance between chemical and mechanical properties is not always achieved. A model compound (MC) simulating the structure of a widely used medical polyurethane (Pellethane) was synthesized and reacted with aliphatic and olefinic acyl chlorides to study the reaction site and conditions. After adopting the conditions to the olefinic modification of Pellethane, processing into flat sheets, and crosslinking by thermal initiation or ultraviolet radiation, mechanical properties were determined. The modified polyurethane was additionally electrospun under ultraviolet light to produce a crosslinked tubular vascular graft prototype. Model compound studies showed reaction at the carbamide nitrogen, and the modification of Pellethane with pentenoyl chloride could be accurately controlled to up to 20% (correlation: rho=0.99). Successful crosslinking was confirmed by insolubility of the materials. Initiator concentrations were optimized and the crosslink densities shown to increase with increasing modification. Crosslinking of Pellethane containing an increasing number of pentenoyl groups resulted in decreases (up to 42%, p<0.01) in the hysteresis and 44% in creep (p<0.05), and in a significant improvement in degradation resistance in vitro. Modified Pellethane was successfully electrospun into tubular grafts and crosslinked using UV irradiation during and after spinning to render them insoluble. Prototype grafts had sufficient burst pressure (>550 mm Hg), and compliances of 12.1+/-0.8 and 6.2+/-0.3%/100 mm Hg for uncrosslinked and crosslinked samples, respectively. It is concluded that the viscoelastic properties of a standard thermoplastic polyurethane can be improved by modification and subsequent crosslinking, and that the modified material may be electrospun and initiated to yield crosslinked scaffolds. Such materials hold promise for the production of vascular and other porous scaffolds, where decreased hysteresis and creep may be required to prevent aneurismal dilation.

Late presentation of aorto-right ventricular fistula and associated aortic regurgitation following penetrating chest trauma.

We present a case in which a 39-year-old man was assaulted in 2002 and sustained penetrating chest trauma. He was treated conservatively, and presented six years later with exertional dyspnoea and a continuous murmur. Echocardiography detected an aorta-right ventricular fistula and an important aortic regurgitation. The aorta-right ventricular fistula was repaired and the aortic valve was replaced with a mechanical prosthesis. Traumatic aorto-right ventricular fistulas and aortic regurgitation are often masked by the primary injury and may take months or years to become clinically evident.

[Embolic retinitis in Haemophilus parainfluenzae endocarditis]. / Rétinite embolique au cours d'une endocartite à Haemophilus parainfluenzae.

Infectious embolic retinopathy occurring secondary to a bacterial endocarditis is described in a 38-year-old woman with known aortic disease. The infectious organism was a haemophilus parainfluenzae confirmed by serial blood cultures and characterized by an embolic power equal to fungal infection. After four-weeks period of appropriate and intensive antibiotic therapy, blood cultures became negative but new emboli were observed in the fundus. This report describes ocular lesions rarely observed in endogenous bacterial retinitis. The delay between the bacterial endocarditis and the occurrence of the retinitis emphasizes the need for a long-term follow-up. Ophthalmologic examination can be acline for changing the heart valve.