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Cardiopulmonary bypass in the clinical setting is barely 40 years old. Yet worldwide, it is used in the operating room in more than 500,000 cases a year. This broad acceptance is a tribute to the vision of gifted investigators who could see beyond the mere technical problems of perfused isolated organs. They integrated mechanical concepts, knowledge of materials, and sheer inventiveness with an appreciation of physiological issues to address the clinical needs of open-heart surgery.

This article points to the importance of penetrating micropores through the graft wall to minimize thrombosis and to enhance endothelialization in small diameter polymer skin coated vascular grafts. Four types of spongy polyurethane-polydimethylsiloxane vascular grafts (PUG) fabricated by a spray, phase-inversion technique, 1.5 mm inner diameter, 1.5-1.9 cm in length, were implanted end-to-end in the infrarenal aorta of 26 adult rats. Some had a continuous inner skin and a hydraulic permeability (HP) of 0 ml/min/cm2/ 120 mmHg (PUG-S-O). Some had an inner skin with varying amounts of isolated penetrating micropores and a mean hydraulic permeability of 11 (PUG-S-11), 37 (PUG-S-37), or 58 ml/min/cm2/120 mmHg (PUG-S-58). Twelve PUG-S-O, 6 PUG-S-11, 4 PUG-S-11, and 4 PUG-S-58 were evaluated between 2 hr and 3 months after implantation. All PUG-S-O occluded soon after implantation. The PUG that had a HP of more than 11 ml/min/cm2 showed acceptable patency. However, endothelialization was limited to anastomoses in patent PUG-S-11. In contrast, the patent PUG-S-37 and PUG-S-58 were largely endothelialized. In all patent grafts at 3 months, numerous host cells had migrated, and newly formed capillaries were seen in the voids of the graft wall, which appeared moderately to highly cellular. In conclusion, it appears that penetrating micropores through the graft wall increase patency and that a highly porous structure is needed to achieve extensive endothelialization in small diameter polymer skin coated vascular grafts.

A highly porous, distensible, gel-like tubular membrane suitable for a small diameter arterial prosthesis was fabricated by combining techniques for spraying and phase-inversion of thermodynamically unstable solutions of a biocompatible polyurethane (PU)-polydimethylsiloxane (PDMS) blend (CardiothaneTH51) over a sliding and rotating mandrel. The cylindrical membrane was characterizedin vitro for mechanical, morphological and permeability properties, and evaluatedin vivo as a 1.5 mm internal diameter prosthesis for the replacement of the rat abdominal aorta. A mature, stable luminal interface, a thin internal capsule without anastomotic hyperplasia, and the deposition of collagen within the voids of the polymer mesh were observed after 8 weeks of implantation.

The woven tubes membrane oxygenator is a suitable configuration for the intracorporeal membrane oxygenator because of a high gas exchange performance and a compact packing of tubing. In this study the oxygen transfer performance of woven tubes was evaluated by an in vitro experiment with an external perfusion mode; the blood flow is outside of the tubes in order to reveal the feasibility of designing the intravascular oxygenator (IVOX) by the woven tubes. The oxygen transfer efficiency of the external perfusion mode is superior to that with the internal perfusion mode because of the larger convective mixing effect on the external surface of the tubes. Thus the use of the external perfusion mode results in the shorter necessary tube length for the rated condition, which enables making the oxygenator unit more compact. All of these features encourage the adoption of the woven tubes for use in the intravascular oxygenator.

Microporous prostheses of 1.5 mm internal diameter were fabricated with a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE)n co-polymer by the spray phase inversion technique. Some of the grafts were made piezoelectric by poling under a high electrical field. Overall, 24 poled grafts (P) and 24 unpoled grafts (UP) (15-22 mm in length) were implanted in the infrarenal aorta of 48 adult rats. Patency rates in P were 100% (8/8) at 2 days, 100% (8/8) at 2 weeks, 75% (6/8) at 6 months, and 92% total (22 of 24). Patency rates in UP were 100% (8/8) at 2 days, 63% (5/8) at 2 weeks, 100% (8/8) at 6 months, and 88% total (21 of 24). Thus there was no significant difference in patency between the two types of grafts. Both showed similar macroscopic and microscopic findings. At 2 days, fibrin deposition was somewhat heavier on the poled grafts, but no difference in surface platelet deposition could be detected. Endothelialization was observed from both anastomoses at 2 weeks and was almost complete at 6 months. The excellent biocompatibility of PVDF-TrFE and the microporous structure of the grafts were probably the dominant factors in success with these grafts. Although piezoelectric activity in excised cleaned poled prostheses remained significantly higher than that in the control UP, the charges developed may have been too small to exert a biologic effect, either because of insufficient dipole orientation or inadequate mechanical deformation.

Bioartificial organs combine the physical aspects of implantable prostheses with the biological advantages of organ transplantation. Enclosing live cells in a permselective, synthetic envelope avoids rejection by an immunoincompatible host while the geometric limitation of the closed polymer capsule prevents overgrowth of the transplanted material. As a tenet bioartificial organs widen the range of therapeutics based on the biological activity of cell transplants and open an alternative path to gene therapy.

Mechanical systems to oxygenate blood outside of the body were first employed in clinical medicine as a component of the «heart-lung machine». The artificial lung has been an essential component of the technology underlying the progress of cardiovascular surgery since 1950. Its impact on clinical medicine can be measured by the widespread acceptance of cardiac surgery for the treatment first of congenital malformations, then valvular lesions, and more recently, coronary artery disease. Whereas the use of the artificial lung during temporary exclusion of the pulmonary circulation for surgical purposes is now well established, the chronic application of extracorporeal membrane oxygenation in end-stage respiratory failure is still controversial. Internally implantable lung prostheses are still at the conceptual or developmental stage, and are unlikely to impact on clinical medicine for another decade.

A technique allowing the deposition of an adherent thin film of turbostratic, high-density carbon on heat sensitive polymers was recently developed. The biological response to this biomaterial on yarns and fabrics of the type used in cardiovascular surgery has been studied. Polyester yarns, knitted Dacron® sheets and knitted uncrimped Dacron® vascular grafts were coated with a thin film (less than 1 μm) of turbostratic carbon using a physical vapour deposition process. Coated and control discs of knitted material, as well as coated and uncoated yarns, were implanted in pairs in the subcutaneous tissue of mice, using for each type of implant two cohorts of 12 animals, with observation periods of 4 and 8 wks respectively. Vascular grafts (8 cm long, 8 mm i.d.) coated with carbon on the luminal side only, were implanted for 12 wks in the infrarenal aortic position in six dogs, and compared to uncoated Dacron® grafts of the same dimensions inserted in the same location and for the same duration in the infrarenal aortic position in six control animals. With subcutaneous implants, there was no significant difference in the tissue reaction to either coated or uncoated patches. In contrast, the vascular grafts, all of which were patent upon retrieval, showed a much lower extent of thrombosis on the blood-exposure surface in the case of carbon-coated Dacron®, as compared to the luminal surface of control prostheses. The internal capsule (tissue formed between the polymer fabric and the blood interface) was thinner in carbon-coated grafts than in control grafts. No giant cells were observed on the Dacron® fibrils coated with turbostratic carbon, which in all cases remained firmly adherent to the polymeric substrate.