Development of a novel low-background noise blood loop model for testing blood-contacting biomaterials and medical devices in fresh human blood.

A novel low volume blood loop model (Ension Triad System [ETS]) incorporating pulsatile flow and a proprietary low-activation blood-contacting surface (Ension bioactive surface [EBS]) enabling high signal-to-noise performance is described. The ETS system incorporates a test chamber that allows direct comparison of material samples or finished medical devices such as catheters with varying compositions and/or surface treatments. ETS performance is presented from two independent organizations (Medtronic and MLM Labs) and includes results for hemolysis (pfHgb), platelet count, platelet activation (ßTG), coagulation (TAT), inflammation (PMN Elastase, PMN CD112b, and monocyte CD112b) and immune response (SC5b-9) were made on: (1) the EBS-treated system itself without a test material (No Material, NM); (2) the EBS-treated system with an idealized untreated catheter (UC); and (3) the EBS-treated system with the prototype catheter treated with the EBS surface treatment (CC). The untreated catheter (UC) was associated with significant elevation of all activation marker levels (pfHgb excluded). The EBS-treated catheter, in direct comparison to the UC and NM catheters, appeared invisible with respect to the activation markers (all markers statistically different than the UC and equivalent to the NM control). Based on these data, we conclude that using a relatively small surface area test sample and a small volume of fresh human blood, the high signal-to-noise performance of the ETS system demonstrates comprehensive and statistically significant material differences in the major ISO 10993-4 categories of blood interaction. These data underscore the important benefit of minimal confounding of test/device responses with non-test-material/model-related responses. ETS offers a practical alternative to the common one-test-category-at-a-time approach when assessing blood/medical device interactions.

Profiling of time-dependent human plasma protein adsorption on non-coated and heparin-coated oxygenator membranes.

Patients with severe lung diseases are highly dependent on lung support systems. Despite many improvements, long-term use is not possible, mainly because of the strong body defence reactions (e.g. coagulation, complement system, inflammation and cell activation). The systematic characterization of adsorbed proteins on the gas exchange membrane of the lung system over time can provide insights into the course of various defence reactions and identify possible targets for surface modifications. Using comprehensive mass spectrometry analyses of desorbed proteins, we were able to identify for the first time binding profiles of over 500 proteins over a period of six hours on non-coated and heparin-coated PMP hollow fiber membranes. We observed a higher degree of remodeling of the protein layer on the non-coated membrane than on the coated membrane. In general, there was a higher protein binding on the coated membrane with exception of proteins with a heparin-binding site. Focusing on the most important pathways showed that almost all coagulation factors bound in higher amounts to the non-coated membranes. Furthermore, we could show that the initiator proteins of the complement system bound stronger to the heparinized membranes, but the subsequently activated proteins bound stronger to the non-coated membranes, thus complement activation on heparinized surfaces is mainly due to the alternative complement pathway. Our results provide a comprehensive insight into plasma protein adsorption on oxygenator membranes over time and point to new ways to better understand the processes on the membranes and to develop new specific surface modifications.

Development and in vitro evaluation of infection resistant materials: A novel surface modification process for silicone and Dacron.

Silicone and Dacron are used in a wide spectrum of implantable and indwelling medical products. They elicit a foreign body response, which results in a chronic inflammatory environment and collagenous encapsulation of the medical device that compromises the immune system's ability to effectively fight infections at the biomaterial surface. The objective of this work is to evaluate a novel process to modify silicone and Dacron with a bioactive collagen surface coupled to a gentamicin impregnated hydrogel graft and assess the surface's cytocompatibility and infection resistance properties. Samples of silicone and polyethylene terephthalate (Dacron velour) were modified by plasma deposition and activation followed by a co-polymer acrylic acid (AA)/acrylamide (AAm) hydrogel graft and covalent immobilization of a bioactive collagen surface. The modified surfaces were characterized using FTIR, contact angle, staining, SEM, and XPS. The poly (AA-AAm) hydrogel was impregnated with gentamicin and tested for controlled release characteristics. Each modified surface was evaluated for its ability to resist infection and to promote normal healing as measured by bacterial growth inhibition (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa) in both broth and agar conditions as well as using fluorescence microscopy to observe adherence of 3T3-NIH fibroblasts. The addition of the poly (AA-AAm) hydrogel with gentamicin inhibited bacterial growth and the subsequent addition of the collagen surface promoted robust fibroblast adhesion on both silicone and Dacron materials. Thorough surface characterization and in vitro bacterial and fibroblast evaluation results suggest that this novel surface bioengineering process generated a highly effective surface on silicone and Dacron with the potential to reduce infection and promote healing.

In vitro assessment of blood compatibility: residual and dynamic markers of cellular activation.

The blood compatibility of materials and surfaces used for medical device fabrication is a crucial factor in their function and effectiveness. Expansion of device use into more sensitive and longer term applications warrants increasingly detailed evaluations of blood compatibility that reach beyond the customary measures mandated by regulatory requirements. A panel of tests that assess both deposition on the surface and activation of circulating blood in contact with the surface has been developed. Specifically, the ability of a surface to modulate the biological response of blood is assessed by measuring: (1) dynamic thrombin generation; (2) surface-bound thrombin activity after exposure to blood; (3) activation of monocytes, polymorphonuclear leukocytes, lymphocytes, and platelets; (4) activation of complement; and (5) adherent monocytes, polymorphonuclear leukocytes, lymphocytes, and platelets on blood-contacting surfaces. The tests were used to evaluate surfaces modified with immobilized heparin (Ension's proprietary bioactive surface) and demonstrated that the modified surfaces reduced platelet activation, leukocyte activation, and complement activation in flowing human blood. Perfusion of the surfaces with human platelet-rich plasma showed that the immobilized heparin surfaces also reduce both dynamic thrombin levels in the circulating plasma and residual thrombin generated at the material surface.

Direct left ventricle-to-coronary artery stent restores perfusion to chronic ischemic swine myocardium.

BACKGROUND: Direct left ventricle (LV)-to-coronary artery shunts (VSTENT) have been proposed as an alternative means of myocardial revascularization. The goal of this study was to examine quantitative changes in myocardial perfusion and possible mechanisms of revascularization with an LV-to-coronary shunt. METHODS: Ameroid occluders were implanted on the proximal left anterior descending coronary artery (LAD) of 6 pigs to create chronic ischemia. Four weeks later, a VSTENT was placed to directly connect the distal LAD with the LV chamber. Animals survived for an additional 3 weeks and received periodic bromodeoxyuridine (BrdU) injections to identify dividing cells to identify and quantify angiogenesis. Regional myocardial perfusion (RMP) was measured with color microspheres under adenosine vasodilatory stress before and 3 weeks after VSTENT implantation. Vascularity was assessed histologically by an overall vascularity index and a growth index reflecting the density of BrdU-positive vascular cells. RESULTS: Three weeks after VSTENT placement, RMP improved from 38.4% +/- 19.6% of non-ischemic flow to 86.8% +/- 13.7% in treated animals (P < .05). This benefit was accompanied by histological evidence of increased vascularity and vascular proliferation. Four of 5 animals had patent and functional devices at the end of the study. CONCLUSION: Chronic VSTENT placement improves RMP and may promote arterial remodeling in chronically ischemic porcine myocardium.

Direct left ventricle to great cardiac vein retroperfusion: a novel alternative to myocardial revascularization.

BACKGROUND: As the number of patients with diffuse coronary artery disease continues to grow, there is renewed interest in alternative methods of perfusing the ischemic myocardium. We tested the feasibility of myocardial retroperfusion via a direct left ventricle-to-great cardiac vein (LV-GCV) conduit to support regional contractility in this setting. METHODS: LV-GCV flow was established using an extracorporeal circuit in 5 dogs. Left ventricle (LV) pressure, aortic pressure, regional myocardial segment length, and circuit blood flow were measured prior to left anterior descending coronary artery (LAD) ligation, following LAD ligation, and after LV-GCV circuit placement. To eliminate backward flow during diastole, an in-line flow regulator was placed. Regional myocardial function was quantified by pressure-segment length loop area divided by end-diastolic segment length (PSLA/EDSL). RESULTS: LAD ligation reduced PSLA/EDSL from 10.0 +/- 1.2 mm Hg mm to 1.6 +/- 0.3 mm Hg mm (P < .05). With LV-GCV retroperfusion, mean peak systolic flow was +152 +/- 14 mL/min, mean peak diastolic flow was -39 +/- 11 mL/min, and net mean flow was +36 +/- 13 mL/min. Regional function recovered to approximately 39% of baseline (3.9 +/- 0.4 mm Hg mm, P < .05). Upon elimination of backflow, mean flow increased to +41 +/- 12 mL/min and regional function recovered even further to approximately 47% of baseline (4.6 +/- 0.7 mm Hg mm, P < .05). CONCLUSIONS: A LV-GCV circuit can significantly restore regional function to the acutely ischemic myocardium. An inline valve that eliminates backward diastolic flow improves regional function even further. This approach may provide an effective therapy for diffuse coronary disease not amenable to traditional revascularization strategies.

Intramyocardial left ventricle-to-coronary artery stent: a novel approach for the treatment of coronary artery disease.

BACKGROUND: The direct intramyocardial left ventricle-to-coronary artery stent may provide an optional minimally invasive technique for coronary artery bypass graft surgery. We seek to test whether blood flow and regional myocardial function improve with this stent in totally ischemic myocardium. METHODS: The stent device was implanted in 8 anesthetized dogs using an open chest approach, arteriotomy of the proximal left anterior descending coronary artery, and connection of the vessel to the left ventricular chamber. Regional coronary blood flow and myocardial function were monitored under three conditions: normal coronary flow (baseline), coronary ligation, and stent flow. RESULTS: Left anterior descending coronary ligation markedly reduced coronary artery blood flow and regional myocardial function. With flow solely from the stent, the blood flow pattern changed to one with high peak forward flow during systole compared with baseline (94.8 +/- 48.9 versus 56.8 +/- 21.1 mL/min; p < 0.05) and one with significant negative backflow during diastole compared with baseline (-37.4 +/- 23.1 versus 11.3 +/- 17.2 mL/min; p < 0.05). However, the resultant mean forward flow increased to approximately 50% of baseline compared with less than 5% of baseline after coronary ligation. Regional myocardial function diminished entirely after coronary ligation, but recovered to approximately 60% of baseline with the stent. Normal systemic hemodynamics and global ventricular contractile function were maintained with the stent. CONCLUSIONS: The left ventricle-to-coronary artery stent is a simple and readily deployable device that allows the perfusion of epicardial vessels directly from the left ventricle and can provide significant blood flow to improve the performance of ischemic myocardium. It may provide an effective, alternative means of treating coronary artery disease when standard coronary artery bypass graft surgery is not suitable.

Thrombogenicity of polysaccharide-coated surfaces.

Heparinization of artificial surfaces has been proven to reduce the intrinsic thrombogenicity of such surfaces. The mechanism by which immobilized heparin reduces thrombogenicity is not completely understood. In the present study heparin-, alginic acid- and chondroitin-6-sulphate-coated surfaces were examined for protein adsorption, platelet adhesion and thrombin generation. The protein-binding capacity from solutions of purified proteins was significantly higher for heparin-coated surfaces when compared with alginic acid- and chondroitin sulphate-coated surfaces. Yet, when the surfaces were exposed to flowing plasma, only the heparinized surface adsorbed significant amounts of antithrombin. None of the surfaces adsorbed fibrinogen under these conditions, and as a result no platelets adhered from flowing whole blood. Our results indicate that protein adsorption and platelet adhesion from anticoagulated blood cannot be used to assess the thrombogenicity of (coated) artificial surfaces. Indeed, the thrombin generation potentials of the different surfaces varied remarkable: while non-coated surface readily produced thrombin, alginic acid- and chondroitin sulphate-coated surfaces showed a marked reduction and virtually no thrombin was generated in flowing whole blood passing by heparinized surfaces.