In vivo evaluations of a new thromboresistant polyurethane for artificial heart blood pumps

Improvement of cytocompatibility of 3D-printing resins for endothelial cell adhesion

We developed a new method for improving the biocompatibility of 3D-printing photosensitive resins using waterborne polyurethane (WPU) as the coating material.

Occlusion of canine aneurysms using microporous self-expanding stent grafts: long-term follow-up

PURPOSE

The treatment of large or giant cerebral aneurysms by surgical and/or endovascular techniques is difficult and poses relatively high risks. Therefore, a microporous self-expanding (hybrid) stent graft composed of a thin, expandable, segmented polyurethane (SPU) membrane with micropores and a drug-delivery system was developed.

MATERIALS AND METHODS

A commercially available, self-expanding carotid stent was covered with a thin microporous SPU membrane fabricated by the dip-coating method and the excimer laser ablation technique, with an intraluminal coating of argatroban. Experimentally fabricated lateral-wall aneurysms in canine carotid arteries using venous pouches were occluded with the hybrid stent graft (bale-shaped pore density of 23.6%) on one side and a bare-metal stent on the other side without systemic antiplatelet therapy.

RESULTS

Angiography at 1, 6, and 12 months of stenting revealed that all arteries were patent without marked stenosis without systemic antiplatelet therapy. All aneurysms treated with hybrid stent grafts remained occluded throughout the 12-month period, while among those treated by bare-metal stents, 2 of 3 aneurysms were occluded at 6 months (67%) and only 1 of 3 aneurysms were occluded at 12 months (33%). Histology revealed that the novel hybrid stent graft had less intimal hyperplasia than the bare-metal stent. The hybrid stent graft was useful for the successful occlusion of these canine carotid aneurysms, even at 12 months.

CONCLUSIONS

The novel hybrid stent grafts are expected to overcome the disadvantages of fully covered stent grafts and simple bare-metal stents, while combining both their merits, and appear to be useful in the treatment of large or giant cerebral aneurysms.

Treatment of rabbit carotid aneurysms by hybrid stents (microporous thin polyurethane-covered stents): preservation of side-branches

Objective

We sought to determine the patency of normal arterial branches from the covered segments of an artery after stenting.

Background

Most intracranial aneurysms occur at arterial branching points (bifurcations, side-branches, or perforators). The post-stenting patency of normal arterial branches from the covered segments of the artery is important. We have previously developed a hybrid stent with micropores to prevent early parent artery occlusion by more early endothelialization, and mid- to long-term parent artery stenosis by control of intimal hyperplasia after aneurysm occlusion.

Methods

We created aneurysms in 10 rabbits by distal ligation and intraluminal incubation of elastase within an endovascularly trapped proximal segment of the common carotid artery. All animals were treated with hybrid stents having micropores. Four animals were observed for one month and three each for three and 12 months. The patency of the side-branches of the subclavian artery was evaluated angiographically and in some cases, histologically.

Results

Aneurysms were completely occluded at all time points other than 12 months. The subclavian artery and brachiocephalic artery were patent, without significant stenosis. All the side-branches of the subclavian artery detected on the preoperative angiogram remained patent at the final assessment.

Conclusion

The use of hybrid stents for aneurysm repair and side-branch patency seems to be effective, as per the long-term results obtained in an animal model.

Early Experience with a Newly Developed Electrospun Polycarbonate-urethane Vascular Graft for Hemodialysis Access

Purpose

In this pilot study, we tested a newly developed electrospun multilayered, self-sealing graft, AVflo™, specifically designed for early hemodialysis access.

Methods

Ten eligible consenting patients had a polycarbonate-urethane graft (AVflo™) implanted and were followed up prospectively for at least six months. Performance measures included graft patency, complications and time to first cannulation. Mean age of the patients was 66.7 ± 10 years. Chronic glomerulonephritis was the most common cause of renal failure. A total of 70% of the patients had a history of previous vascular access and 40% history of minimally invasive radiologic procedures for patency maintenance. In 40% of the cases the need for AV graft implantation was because of recurrent infections from permanent catheter for dialysis. Seven grafts were placed in the upper arm and three in the thigh. Mean follow up was 230 ± 75 days.

Results

There were no systemic or local reactions to the graft and we did not report any graft infections. Two grafts thrombosed because of severe bleeding post-cannulation due to an incorrect needle puncture. Both grafts were successfully thrombectomized. Primary and secondary patency rates at six months were 60% and 78%, respectively. These patency rates were comparable to those reported for other polyether-urethane and ePTFE grafts. Median time to first cannulation was seven days (3-21) and all puncture sites sealed in less than five minutes.

Conclusions

This newly developed electrospun polycarbonate-urethane graft is safe in humans, permits early access obviating the need for venous catheters, and has equivalent patency as other prosthetic grafts.

Synthesis and hemocompatibity evaluation of segmented polyurethane end-capped with both a fluorine tail and phosphatidylcholine polar headgroups

To improve the hemocompatibility of polyurethanes, an amine monomer containing a long fluorine tail and phosphatidylcholine polar headgroups, 2-amino-3-oxo-3-(2-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctan amido) ethyl amino) propyl phosphorylcholine (FASPC) was firstly synthesized and characterized. Then four kinds of fluorinated phosphatidylcholine end-capped polyurethanes with different chemical structures were prepared. The surface properties of these prepared polyurethanes were characterized using X-ray photoelectron spectroscopic analysis (XPS) and water contact angle measurements. The results indicated that the phosphatidylcholine (PC) polar headgroups along with the fluorine tail could be easily enriched on the top surfaces, and the PC groups could be highly oriented on the outmost surface when the polymer film was in contact with water for only 30 s at room temperature. The evaluation of hemocompatibity was carried out via fibrinogen adsorption and platelet adhesion. Fibrinogen adsorption (37°C for 90 min) decreased by 98% to 87% compared to that on ordinary polyurethane surfaces, and almost no platelet adhesion and activation was observed at 37°C for 2 h.

Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia

Treatment of large (diameter 12-25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 μm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 μm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 μm) than the bare stents (341 ± 146 μm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 μm). A pore ratio of 23.6% was found to control intimal growth.

Sirolimus-Loaded Polyurethane Graft for Hemodialysis Access in Sheep

Intimal hyperplasia is the most common final pathway for hemoaccess occlusion in dialysis patients. Drug eluting stents have been shown to decrease intimal hyperplasia in coronary arteries and possibly in peripheral arteries. We evaluated the use of a sirolimus loaded polyurethane graft as prophylaxis in hemodialysis access. Grafts were loaded with sirolimus and elution curves were determined for the polyurethane material. The arteriovenous grafts were then placed in the neck of 20 sheep. A non-loaded graft was placed in the contralateral neck. Patency rates, ultrasound evaluation, angiography and histomorphometry were determined for each graft. At 30, 60 and 90 days the drug loaded graft had improved patency rates compared to the control, with a 25% improvement noted at 3 months. Life table analysis showed the drug loaded graft consistently better patency than the control (p = .136). The control graft had greater neointimal stenosis (14.5% vs 9.17%) over the course of the study (p = .157). Although none of these findings was statistically significant in this pilot study, the sirolimus coated graft out-performed the control in every measured parameter at each time point evaluated. Further work to asses the validity of drug coated materials to prevent intimal hyperplasia in hemodialysis access is warranted.

Development of self-expandable covered stents

We newly developed self-expandable covered stents by combining two of our original technologies. Of these, the first is the dip-coating covering method that was developed previously for balloon-expandable stents; the other is the newly developed self-expandable Nitinol stents, namely, Sendai stents. The three types of covered stents with the expansion diameter of 4.5, 5.0, or 6.0 mm thus obtained had a laser-processed microporous elastomeric cover film (pore diameter: 100 microm, interpore distance: 250 microm). Although the film was extremely thin (approximately 15 microm), the film could be expanded without causing any damage, the strut was completely embedded within the film, and the luminal surface of the film was smooth and flat. Mechanical properties such as ideal flexibility to follow the shapes of arteries were almost retained even after covering. As appropriate drugs, the blood-contacting inner and tissue-contacting outer surfaces of the film were differentially coated with argatroban for antithrombogenicity or FK506 for anti-inflammation, respectively. The preliminary in vivo study indicated that the covered stents mounted in the delivery catheter were navigated and placed to appropriate position in the arteries, and permissible neointimal thickening after 1-month implantation was observed similarly in noncovered stents.

Incorporation of a lauric acid-conjugated GRGDS peptide directly into the matrix of a poly(carbonate-urea)urethane polymer for use in cardiovascular bypass graft applications

Gly-Arg-Gly-Asp-Ser (GRGDS) was modified by conjugation to lauric acid (LA) to facilitate incorporation into the matrix of a poly(carbonate-urea)urethane (PCU) used in vascular bypass grafts. GRGDS and LA-GRGDS were synthesized using solid phase Fmoc chemistry and characterized by high performance liquid chromatography and Fourier transform infrared spectroscopy. LA-GRGDS was passively coated and incorporated as nanoparticle dispersion on the PCU films. Biocompatibility of the modified surfaces was investigated. Endothelial cells seeded on LA-GRGDS coated and incorporated PCU showed after 48 h and 72 h a significant (p < 0.05) increase in metabolism compared with unmodified PCU. The platelet adhesion and hemolysis studies showed that the modification of PCU had no adverse effect. In conclusion, LA-conjugated RGD derivatives, such as LA-GRGDS, that permit solubility into solvents used in solvent casting methodologies should have wide applicability in polymer development for use in coronary, vascular, and dialysis bypass grafts, and furthermore scaffolds utilized for tissue regeneration and tissue engineering.

Biostability of Thoralon Left Ventricular Assist Device Blood Pumping Sacs After Long-Term Clinical Use

The purpose of this paper is to investigate the biostability of Thoralon polyurethane blood pumping sacs that have been used for up to 14 months in the Thoratec ventricular assist device (VAD) in human subjects. Thoralon is a proprietary polyetherurethaneurea (PEUU) blended with siloxane based surface modifying additive (SMA). Samples of Thoralon blood sacs that were used in Thoratec LVAD pumps for 53, 171, 336, and 434 days were taken from three distinct regions identified as high flex, medium flex, and low flex for physicochemical analysis. Explanted samples exhibited a slight but not significant increase in physical properties. The molecular weight of the blood sacs had also increased significantly in all blood sacs regardless of duration of use. SEM images did not indicate any cracking, pitting, or surface erosion; however, in a small area of the high flex region of the 336 day sac some biofilm was seen. The Attenuated Total Reflectance Fourier Transform Infra Red Spectroscopy (ATR-FTIR) analysis showed no significant reduction of surface ether content. The surface chemistry analyzed using Electron Spectroscopy for Chemical Analysis (ESCA) also indicated no significant change compared with control. These results confirm the biostability of Thoralon for long-term clinical applications in the Thoratec VAD.

Long-term Follow-up of Polyurethane Vascular Grafts for Hemoaccess Bridge Fistulas

The new polyurethane vascular graft (PVG) has been reported to be better than the expanded polytetrafluoroethylene (PTFE) graft in terms of early access and prompt hemostasis, but long-term patency and safety of PVGs have not been investigated objectively. To evaluate late clinical outcome of the PVG, we compared the complication and patency rates of stretch PTFE grafts with those of PVGs implanted for hemodialysis vascular access. Subjects were 53 patients who received 58 arteriovenous grafts between October 1997 and July 2000. They were divided in a prospective fashion into two groups according to the type of implanted graft: PVG ( n = 30) or PTFE ( n = 28). The study group comprised 27 men and 31 women with a mean age of 61.7 +/- 10.9 years (range: 23-84 years). The average number of previous accesses was 5.1 +/- 3.1 (range: 0-12). There were no differences between the groups in term of age, sex, body surface area, etiology of renal disease, presence of diabetes, previous access procedures, anatomical positions of grafts, or mean follow-up period. Primary patency rates for the PVG and PTFE grafts were equivalent at 1 year (60.7% vs. 56.5%) and at 2 years (54.7% vs. 51.8%). Similarly, secondary patency rates for the two groups did not differ at 1 year (78.7% vs. 79.9%) or at 2 years (78.7% vs. 69.3%). These findings indicate that the PVG is an acceptable alternative to the PTFE graft for blood access.

Adhesion, apoptosis and cytokine release of human mononuclear cells cultured on degradable poly(urethane urea), polystyrene and titanium in vitro

Early interactions between materials and mononuclear cells may influence the viability and secretory response of the cells. Such effects may in turn influence the subsequent inflammatory and repair phases around the materials. In the present study, it was examined if mononuclear cells cultured in vitro either unstimulated or stimulated with lipopolysaccharide (LPS) (10ng/ml) revealed differences regarding cell viability and apoptosis. A major interest was to study the influence of different material properties on the parameters of the inflammatory response upon cell adhesion to materials with widely different surface chemical properties but similar surface topography: degradable poly(urethane urea) (PUUR), cell culture treated polystyrene (PS) surfaces, and commercially pure (c.p.) titanium (Ti). Finally, the secretion of the proinflammatory tumor necrosis factor-a (TNF-alpha) and the downregulating interleukin-10 (IL-10) cytokines was examined in the supernatants from 24h mononuclear cell cultures. No differences in cell viability as measured by lactate dehydrogenas (LDH) were observed between the three materials. The number of material-surface adherent cells was higher on PUUR than the more hydrophilic PS and Ti as judged by quantification of material surface-associated DNA, light microscopic morphological examination of DAPI-stained cells and SEM. LPS increased the number of adherent cells, irrespective of the type of material. The lowest number of apoptotic (annexin-V) and necrotic (propidium iodide) mononuclear cells was detected on PUUR. LPS decreased the number of both apoptotic and necrotic cells, irrespective of material. Low TNF-alpha levels were detected in unstimulated conditions, irrespective of material types. A significantly lower amount of TNF-alpha was found with unstimulated cells on PUUR than on Ti. A significantly higher IL-10 level was detected in unstimulated Ti cultures compared with PUUR and PS. Secretion of IL-10 was predominantly stimulated by LPS on PUUR and Ti. The data indicate that material-related differences are expressed in differences in cell adherence, apoptosis and cytokine secretion. Further, degradable PUUR has equal or less cell-activating properties than Ti and PS under in vitro conditions.

Synthesis and properties of degradable poly(urethane urea)s to be used for ligament reconstructions

In the present study we describe the synthesis, wet spinning, mechanical testing, and degradation of poly(urethane urea)s (PUURs) intended for clinical use in anterior cruciate ligament (ACL) reconstruction. The effects of soft segment chemical composition and molar mass and the kind of diamine chain extender on the material properties were investigated. It was found that the fibers made of PUUR with polycaprolactone diol (PCL530) as soft segment and MDI/1,3-DAP as hard segment (PCL530-3) have high tensile strength and high modulus and when degraded keep their tensile strength for the time demanded for the application. In conclusion, from a chemical and mechanical point of view PUUR fibers of PCL530-3, ARTELON, are suitable for designing a degradable ACL device.

A versatile intracorporeal ventricular assist device based on the thoratec VAD system

BACKGROUND

As patients are supported for longer durations with paracorporeal Thoratec left ventricular and biventricular assist devices (longest durations: 515 and 457 days, respectively), there is a need for implantable options.

METHODS

We are developing a small, simple, and versatile intracorporeal ventricular assist device (IVAD) for left, right, or biventricular support as an alternative to the large, implantable, pulsatile left ventricular assist device (LVAD) systems available today. The new device is based on the Thoratec paracorporeal VAD that has been used in more than 1,400 patients weighing from 17 to 144 kg and for durations exceeding 1 year including patient discharge (using the portable driver).

RESULTS

The IVAD has the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD, but the housing is a smooth contoured, polished titanium alloy. The IVAD has a new sensor to detect when the pump is full and empty, and is controlled with the Thoratec TLC-II portable VAD driver, which is a small, briefcase-sized, battery-powered, pneumatic control unit. A small flexible (9 mm OD) percutaneous pneumatic driveline for each VAD is tunneled out of the body from the LVAD or right VAD in a pre- or intraperitoneal position. Small size and simplicity are the major advantages of the new device. The IVAD weight (339 g) and implanted volume (252 mL) are approximately one-half that of the current implantable pulsatile electromechanical LVAD systems.

CONCLUSIONS

The small size of the IVAD should not only allow support of a large range of patient sizes and body habitus, but also provide options for implantable left, right, or biventricular support. By implanting only the mechanically simple blood pump, the more complex control unit is external, where it can be serviced and replaced without surgery. The IVAD with the portable driver will be a viable alternative to large implanted electromechanical systems and should address a larger segment of the physically diverse patient population.

SMA circuits reduce platelet consumption and platelet factor release during cardiac surgery

BACKGROUND

Platelet count and function are particularly damaged by cardiopulmonary bypass (CPB). This study evaluated the effects of a novel CPB circuit in terms of platelet count and activation, and postoperative need for blood products.

METHODS

One hundred patients undergoing coronary grafting were randomized in two groups: control group (n = 50) and test group (n = 50, surface modifying additives circuit, SMA group). Blood samples were taken before, during, and after CPB. Postoperative blood loss, number of transfused blood products, and postoperative variables were recorded.

RESULTS

The platelet count decreased less in the SMA group compared to the control group (end of CPB: respectively, 165 +/- 9 x 10(3)/mm3 vs 137 +/- 8 x 10(3)/mm3; p < 0.01). This was paralleled by a reduction in beta-thromboglobulin plasma levels in the SMA group. There was a trend to decreased blood loss in the SMA group, but the difference was significant only in patients taking aspirin preoperatively (p < 0.05). In the SMA group nearly 50% less fresh frozen plasma and platelet units were administered (p < 0.01). No operative deaths were observed.

CONCLUSIONS

The use of circuits with surface additives is clinically safe, preserves platelet levels, and attenuates platelet activation. This may lead to a reduced need for blood products.

Mechanical Circulatory Support Sources of Emboli and Neurological Outcome

Long-term mechanical circulatory support devices are currently used as bridges to transplantation or myocar dial recovery and represent a major step forward in the treatment of end-stage heart failure. Examples of left ventricular assist devices/systems are Thoratec Labora tories (Berkley, CA), Baxter Novacor (Oakland, CA), and Thermo Cardiosystems Inc Heartmate (Woburn, MA). The CardioWest (Tucson, AZ) is the current total artifi cial heart device under clinical evaluation. These de vices are associated with neurological complications usually resulting from thromboembolic events to the cerebrum, cerebellum, or brainstem. The device itself is the commonest source of these emboli. Thrombus formation within the device occurs as a result of the interaction between the blood contacting surfaces of the device, the flow of blood through the device, and thrombotic tendency of the blood. There is a wide range of clinical presentation, from asymptomatic emboli detected by transcranial Doppler to devastating strokes. Strategies aimed to reduce the tendency to form throm bus are based on aggressive prevention with anticoagu lation and antiplatelet therapy and/or by design modifi cation. In particular, the use of a textured inner surface that encourages the formation of a pseudoneointima seems successful in reducing anticoagulation require ments and neurological complications.

Development of an intracorporeal Thoratec ventricular assist device for univentricular or biventricular support

There is a need for a small, simple, and versatile intracorporeal ventricular assist device (IVAD) as an alternative to the large implantable electromechanical LVAD systems in current use. Because the basic design of the Thoratec paracorporeal VAD has been demonstrated in over 1,000 patients, weighing from 17 to 144 kg, and for durations up to 515 days including patient discharge (by using the portable driver), we are developing a new intracorporeal version of our VAD. This IVAD has a smooth contoured, polished titanium housing, and maintains the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD. The IVAD is controlled with the Thoratec TLC-II Portable VAD Driver, which is a small briefcase sized, battery powered, pneumatic control unit. Intracorporeal LVADs and/or RVADs are implanted in a preperitoneal position, with a single small (9 mm OD) percutaneous pneumatic driveline for each VAD. The major advantages of the new IVAD design are size and simplicity. The IVAD weight (339 g) and implanted volume (252 ml) are substantially smaller than current implantable electromechanical LVAD systems. Only the small blood pump is implanted, leaving the more complex control unit external, where it can be serviced and replaced. The versatile design is intended for left and/or right heart support in large or small patients. The IVAD in combination with the TLC-II portable driver will be a viable and attractive alternative to large, implanted electromechanical systems.

The continuing evolution of mechanical ventricular assistance

A great number of patients suffer and die of the sequelae of acute and chronic heart failure each year. Although advances in medical and surgical therapy have benefited many of these patients, most have disease that is refractory to any definitive therapy. For these patients cardiac transplantation is the only remaining hope. Unfortunately, because of the increasing demand for donor organs in the face of a fixed and limited supply, this option is available to only a small percentage of these patients. Even in patients accepted for transplantation, a significant waiting list mortality has been observed. A variety of VADs have been developed since the first successful case of mechanical cardiac assistance more than 30 years ago. These devices differ in basic mechanical function, method of insertion, and degree of implantability and thus have different indications and potential applications. Whereas the intraaortic balloon pump and centrifugal pumps are effective short-term support modalities, extracorporeal and implantable pulsatile devices have been used successfully for long-term support of patients with reversible and nonreversible cardiac failure. Although these pumps have most commonly been used as bridges to transplantation, increasing clinical experience has supported the notion of long-term mechanical assistance as a definitive therapy for patients with end-stage heart disease. Although complications, particularly infection and thromboembolism, pose significant challenges and long-term device reliability remains to be fully determined, available implantable devices appear to be capable of providing effective long-term support. As data are obtained from currently ongoing trials comparing VAD support with medical therapy for end-stage heart failure, ethical and economic issues will assume increasing importance.

The pulsatile impeller pump for left ventricular assist

Because of severe hemolysis, especially on producing pulsatile flow by changing the rotating speed of the impellers, the traditional centrifugal pump was rarely used for long-term support of the failing heart. We therefore developed a motor driven pulsatile implantable impeller pump. The pulsatility was achieved by changing the rotating speed via introducing a square waveform voltage into the motor coil. The impeller vane was designed to have both radial and axial curves according to the stream surface and stream lines to reduce the thrombosis and hemolysis. Nine calves weighing 80 to 100 kg were used. With the calves under endotracheal general anesthesia, left posterolateral thoracotomy was performed to connect the inflow tube with the left atrial appendage and to anastomose the outflow tube with the descending aorta. The calves usually awoke and stood up within hours after discontinuation of anesthetics. Within 7 days, continuous monitoring of electrocardiogram, systemic and pulmonary arterial pressures, and central venous pressure were performed to adjust the pump flow to 40% to 50% of the cardiac output. During the survival of 4 to 54 days (mean 16.3 +/- 19.3 days with two calves surviving longer than 1 month), no significant deterioration of liver or renal function was noted. Because of bleeding, hemoglobin reduced from 11.4 +/- 1.8 to 9.0 +/- 1.3 g/dl, and the hematocrit decreased from 34.5 +/- 4.7 to 26.7 +/- 4.6%. No significant changes of free hemoglobin were noted. In our results, the device revealed competent pulsatile function without severe blood damage or organ dysfunction.

Effect of forms of collagen linked to polyurethane on endothelial cell growth

Collagen has been widely coated or grafted onto polymer surfaces to improve the biocompatibility of materials. To better support the growth of endothelial cells on polyurethane (PU), collagen was grafted to the carboxyl group enriched PU through 1,2-bis(2,3-epoxypropoxy)ethane linking. Our results demonstrated that collagen in various conditions may result in different forms being grafted to the PU substrate, which subsequently affected the growth of endothelial cells. Collagen predialyzed against physiological phosphate buffered saline (PBS) could be reconstituted into native type fibrils with a bigger diameter at 37 degrees C than could collagen neutralized by titration with NaOH. At low temperature, titrated collagen formed floss-like fibrils packed in a ball with cobblestone-like morphology. The amount of collagen grafted was related to the condition of the collagen used, which in consequence affected the diameter of the collagen fibril formed and the growth of endothelial cells. In conclusion, reconstituted collagen fibrils formed from collagen in PBS at 37 degrees C grafted in the highest amounts to an epoxy-PU substrate and that optimally supported the growth of endothelial cells. Such prepared materials may be potentially good vascular bioprosthetic materials and may provide a wide range of biological applications.

Australian multicentre evaluation of a new polyurethane vascular access graft

BACKGROUND

A new three-layered cast polyurethane vascular access graft (Thoratec VAG) is the most recent addition to the list of materials used in the search for the perfect prosthetic graft material for haemodialysis vascular access. Despite its use in 23 countries, a clinical assessment has not been published.

METHODS

An independent retrospective evaluation by questionnaire was obtained for 145 implantation procedures performed by 30 surgeons.

RESULTS

Ninety-two per cent of procedures were performed for an acute need for vascular access and 73% had prior failed vascular access surgery. Patients were hospitalized for a median of 4 days and the graft was initially used at a median of 3 days. Median follow-up was 306 days. Thoratec VAG had a problem-free (primary) patency of 44.9% and a functional (secondary) patency 64.5% at 1 year. Major causes of graft loss were thrombosis (17%) and infection (11%). Intra-operative thrombosis was the only significant risk factor for subsequent thrombosis (P = 0.013). Infection was less in patients with antibiotic prophylaxis that included vancomycin (P = 0.02).

CONCLUSION

The ability to use the graft soon after surgery is a major advance for patients who urgently need reliable medium to long-term haemodialysis access.

Cannula selection and cannulation techniques for nonpulsatile mechanical ventricular assistance

The successful use of mechanical ventricular assistance is, in large part, dependent upon easy insertion of well designed inflow and outflow cannulas. This manuscript describes a family of cannulas specifically designed for use in a nonpulsatile ventricular assist device (VAD) circuit. Although a variety of commercially available cannulas can be employed in a nonpulsatile VAD circuit, the cannulas described in this manuscript possess a number of unique design features. The reinforced thin-walled design and end hole construction optimize fluid flow characteristics in both the inflow and outflow cannula. The extended length allows the cannulas to transverse the skin at a point far distant from the mediastinum, reducing the potential for ascending cannula site infection. The purpose of this manuscript is not to review all cannulas available for nonpulsatile VAD circuits, but rather to describe in detail a family of cannulas that are ideal VAD cannulas based on their design characteristics. In addition individual cardiac surgeons implant very few of these devices annually. Thus the advantages and disadvantages of common cannulation sites and a proven technique for cannula insertion will also be presented.

Alprostadil: an effective antiplatelet agent for calves

Aspirin and other nonsteroidal, antiinflammatory drugs inhibit human platelets, but their effect as an antiplatelet agent on bovine platelets is not certain. Since calves are used for cardiovascular implant research, need exists for an effective antiplatelet agent for this animal model. After screening a number of potential antiplatelet drugs for calves, Alprostadil (prostaglandin E1) appeared to be the most promising. Alprostadil was administered (intravenous continuous drip) to 8 calves. The concentration of the drug administered was gradually increased until 50% inhibition of platelet aggregation was obtained. Platelet function, blood pressure, body temperature, and hematologic parameters were closely monitored. For in vitro evaluation, Alprostadil was added to human or bovine blood, and the platelet aggregation and cyclic adenosine monophosphate levels were measured. Alprostadil inhibited both bovine and human platelets, although bovine platelets were relatively more responsive to this drug. At an infusion rate of approximately 0.20 micrograms/kg/min in vivo, Alprostadil showed 50% inhibition of platelet aggregation with slightly decreased blood pressure (7 +/- 6 mm Hg) but no adverse effects. Complete reversal of in vivo platelet inhibition was noted within 24 h after cessation of drug administration. This short half-life and the lack of significant adverse effects make Alprostadil an attractive antiplatelet agent for calves with cardiovascular implants.

Univentricular and biventricular Thoratec VAD support as a bridge to transplantation

As of October 1991, the Thoratec ventricular assist device (VAD) system has been used in 154 transplant candidates who were in imminent risk of dying before donor heart procurement at 39 medical centers in 10 countries. The VAD system consists of a prosthetic ventricle with a 65-mL pumping chamber made from Thoratec's BPS-215M polyurethane, cannulas for atrial or ventricular inflow and arterial outflow connections, and a pneumatic drive console. The devices can be used for partial or complete support of the pulmonary, systemic, or both circulations. In all patients (average age, 42 years; range, 11 to 64 years), the pumps were placed in a paracorporeal position on the anterior abdominal wall and connected to the heart and great vessels by cannulas crossing the chest wall. Biventricular support was used in 120 patients (78%) and isolated left VADs were used in 34. Average flow rate was 5.0 +/- 0.9 L/min for the left VAD and 4.3 +/- 0.8 L/min for the right VAD. The most frequent complications were bleeding (42% incidence, 7% mortality) and infection (36% incidence, 8% mortality). Ninety-eight patients (65%) recovered sufficiently to undergo heart transplantation after 8 hours to 226 days of support (average, 17.5 days), and 3 are waiting on VADs for transplantation. Eighty-two patients who received transplants have been discharged. This is an 84% early post-transplantation survival and a 54% overall survival. The actuarial survival 1 year after transplantation is 82%, comparable with that of conventional heart transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)