Biodegradable Zwitterionic Polymer Coatings for Magnesium Alloy Stents.

Degradable metallic stents, most commonly composed of Mg-based alloys, are of interest as an alternative to traditional metallic stents for application in cardiac and peripheral vasculature. Two major design challenges with such stents are control of the corrosion rate and acute presentation of a nonthrombogenic surface to passing blood. In this study, several types of sulfobetaine (SB)-bearing biodegradable polyurethanes were developed and assessed as physical, chemical, and combination-type coatings for a model degradable Mg alloy, AZ31. For physical coatings, poly(ester sulfobetaine)urethane ureas, PESBUUs were synthesized using variable monomers that allowed the incorporation of a varying extent of carboxyl groups. Introduction of the carboxyl groups was associated with faster polymer degradation time. Simple physical coating of PESBUUs reduced macro- and microscopic thrombogenic deposition together with good stability of the coating attachment compared to a control coating of polylactic- co-glycolic acid. For PESBUUs incorporating carboxyl groups (PESBUUs-COOH), these groups could be converted to siloxane groups (PESBUUs-Si), thus creating polymers that could be surface reacted with the oxidized or phytic acid treated AZ31 surface. Chemical (silanization) attachment of these polymers reduced underlying alloy corrosion rates, but following the salination reaction with physical coating most reduced corrosion rates and protected the surface better from the consequences of oxidation occurring under the coating, such as blistering. The application of a multilayered coating approach using a sulfobetaine-based biodegradable elastomer thus offers options for degradable metallic stent design where thromboresistance is desired in combination with a means to control both polymeric coating degradation rates and underlying alloy corrosion rates.

Assessment of Thrombelastography and Platelet Life Span in Ovines.

Ovines are a common animal model for the study of cardiovascular devices, where consideration of blood biocompatibility is an essential design criterion. In the ovine model, tools to assess blood biocompatibility are limited and continued investigation to identify and apply additional assays is merited. Toward this end, the thrombelastograph, clinically utilized to assess hemostasis, was used to characterize normal ovine parameters. In addition, platelet labeling with biotin was evaluated for its potential applicability to quantify ovine platelet life span. Mean ovine thrombelastograph values were reaction-time: 4.9 min, K-time: 2 min, angle: 64.1°, maximum amplitude: 68.6mm, actual clot strength: 11.9 kd/s, and coagulation index: 1.5. Reaction time was significantly shorter and maximum amplitude, actual clot strength, and coagulation index were all significantly higher when compared to normal human thrombelastograph values suggesting some hypercoagulability of sheep blood. Biotinylation and reinfusion of ovine platelets allowed temporal tracking of the labeled platelet cohort with flow cytometry. These data indicated a mean ovine platelet life span of 188h with a half-life of 84h. The collection of these parameters for normal ovines demonstrates the applicability of these techniques for subsequent studies where cardiovascular devices may be evaluated and provides an indication of normal ovine values for comparison purposes.

Hollow fiber membrane modification with functional zwitterionic macromolecules for improved thromboresistance in artificial lungs.

Respiratory assist devices seek optimized performance in terms of gas transfer efficiency and thromboresistance to minimize device size and reduce complications associated with inadequate blood biocompatibility. The exchange of gas with blood occurs at the surface of the hollow fiber membranes (HFMs) used in these devices. In this study, three zwitterionic macromolecules were attached to HFM surfaces to putatively improve thromboresistance: (1) carboxyl-functionalized zwitterionic phosphorylcholine (PC) and (2) sulfobetaine (SB) macromolecules (mPC or mSB-COOH) prepared by a simple thiol-ene radical polymerization and (3) a low-molecular weight sulfobetaine (SB)-co-methacrylic acid (MA) block copolymer (SBMAb-COOH) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Each macromolecule type was covalently immobilized on an aminated commercial HFM (Celg-A) by a condensation reaction, and HFM surface composition changes were analyzed by X-ray photoelectron spectroscopy. Thrombotic deposition on the HFMs was investigated after contact with ovine blood in vitro. The removal of CO2 by the HFMs was also evaluated using a model respiratory assistance device. The HFMs conjugated with zwitterionic macromolecules (Celg-mPC, Celg-mSB, and Celg-SBMAb) showed expected increases in phosphorus or sulfur surface content. Celg-mPC and Celg-SBMAb experienced rates of platelet deposition significantly lower than those of unmodified (Celg-A, >95% reduction) and heparin-coated (>88% reduction) control HFMs. Smaller reductions were seen with Celg-mSB. The CO2 removal rate for Celg-SBMAb HFMs remained comparable to that of Celg-A. In contrast, the rate of removal of CO2 for heparin-coated HFMs was significantly reduced. The results demonstrate a promising approach to modifying HFMs using zwitterionic macromolecules for artificial lung devices with improved thromboresistance without degradation of gas transfer.

Surface modification of a biodegradable magnesium alloy with phosphorylcholine (PC) and sulfobetaine (SB) functional macromolecules for reduced thrombogenicity and acute corrosion resistance.

Siloxane functionalized phosphorylcholine (PC) or sulfobetaine (SB) macromolecules (PCSSi or SBSSi) were synthesized to act as surface modifying agents for degradable metallic surfaces to improve acute blood compatibility and slow initial corrosion rates. The macromolecules were synthesized using a thiol-ene radical photopolymerization technique and then utilized to modify magnesium (Mg) alloy (AZ31) surfaces via an anhydrous phase deposition of the silane functional groups. X-ray photoelectron spectroscopy surface analysis results indicated successful surface modification based on increased nitrogen and phosphorus or sulfur composition on the modified surfaces relative to unmodified AZ31. In vitro acute thrombogenicity assessment after ovine blood contact with the PCSSi and SBSSi modified surfaces showed a significant decrease in platelet deposition and bulk phase platelet activation compared with the control alloy surfaces. Potentiodynamic polarization and electrochemical impedance spectroscopy data obtained from electrochemical corrosion testing demonstrated increased corrosion resistance for PCSSi- and SBSSi-modified AZ31 versus unmodified surfaces. The developed coating technique using PCSSi or SBSSi showed promise in acutely reducing both the corrosion and thrombotic processes, which would be attractive for application to blood contacting devices, such as vascular stents, made from degradable Mg alloys.

Auryon Laser in Treating Symptomatic Infrainguinal Arterial Disease: 1-Year Outcome.

BACKGROUND: The Auryon 355-nm laser atherectomy system (AngioDynamics, Inc) showed a low rate of target-lesion revascularization (TLR) at 6-month follow-up in the EX-PAD-03 investigational device exemption study and the Auryon single-center experience (SCE) in treating infrainguinal arteries. In this study, we present the 1-year outcomes of the Auryon SCE study on TLR in all comers at a single center. METHODS: The Auryon SCE was a retrospective study that evaluated the outcomes of all comers treated with the Auryon laser for infrainguinal arterial disease. There was no TLR seen at 6-month follow-up. We present the TLR rate at 1 year in the same cohort of patients. TLR rates were obtained from medical record review of patients enrolled in the study who had completed office visit follow-up at 1 year. Secondary endpoints included unplanned major amputation and total mortality. Kaplan-Meier survival analysis was performed to estimate the freedom from TLR rate following index procedure. Statistical differences were analyzed for ankle-brachial index (ABI) between baseline and 1 year. RESULTS: A total of 56 patients (65 procedures, 70 lesions) were enrolled. The mean age was 70.9 ± 10 years, with 66.1% males, 48.2% diabetics, and 25% demonstrating limb ischemia. Of the 70 lesions, 31.4% had severe calcification, 38.6% were chronic total occlusions, and 48.6% were de novo disease (in-stent restenosis, 29.6%). Stenting was performed in 24/70 lesions (34.3%), with 11/70 (15.7%) bailout procedures. Embolic filters were used in 26/65 procedures (40%). The majority of treated lesions were femoropopliteal (90.0%); of all procedures, 29.2% had 2 or more prior interventions. Drug-coated balloon usage was 47.1% Lutonix (BD/Bard), 27.1% In.Pact (Boston Scientific), and 1.4% both in all lesions treated. Distal embolization occurred in 1/65 procedures (1.5%). At 1 year, mortality occurred in 3/56 patients (5.4%). Of 65 limbs treated, 2 (3.1%) had major amputation at 1 year. The probability of freedom from TLR was 83.7%. CONCLUSION: In a realworld cohort of patient with complex disease, the Auryon laser had excellent freedom from TLR at 1 year.

Auryon Laser in Peripheral Arterial Interventions: A Single-Center Experience (Auryon-SCE).

BACKGROUND: The Auryon 355-nm laser atherectomy system (AngioDynamics, Inc) showed a low rate of target-lesion revascularization (TLR) at 6-month follow-up in the investigational device exemption study. At present, real-world data are not available. In this study, we analyze major adverse events and 6-month outcomes with the Auryon laser system in treating infrainguinal arterial disease in all comers at a single center. METHODS: Consecutive patients treated with the Auryon laser between September 2017 and March 2021 were retrospectively reviewed from a single operator at a single center. Demographic, procedural, angiographic, and outcome data were extracted from patients' medical records. Descriptive and survival analyses were performed. The study's primary endpoint was the assessment of freedom from TLR at 6-month follow-up. Secondary endpoints included acute procedural results, distal embolization, bailout stenting (dissection type D or higher by National Heart, Lung, and Blood Institute [NHLBI] classification, and/or residual narrowing >30%), unplanned major amputation, death, or vascular complications. RESULTS: A total of 56 patients (65 procedures, 70 lesions) were enrolled. The mean age was 70.9 ± 10 years, 66.1% were males, 48.2% were diabetics, and 25% had limb ischemia. Of the 70 lesions, 31.4% had severe calcification, 38.6% were chronic total occlusions, and 48.6% were de novo disease (in-stent restenosis in 28.6%). The majority of treated vessels were femoropopliteal (88.6%) and 29.2% had 2 or more prior interventions. Mean stenosis was 91.3 ± 9.7% at baseline, 56.0 ± 17.3% post laser, and 11.4 ± 11.2% post final treatment. Lesion length was 117.1 ± 101.2 mm and treated length was 174.0 ± 116.0 mm. Bailout stenting occurred in 11/70 lesions (15.7%). There were no NHLBI type D dissections post laser and 1 type D dissection post laser + percutaneous transluminal angioplasty. A total of 47.1% received Lutonix drug-coated balloons (BD/Bard), 27.1% received In.Pact drug-coated balloons (Boston Scientific), and 1.4% received both. The probability of freedom from TLR per procedure was 95.6% at 6 months. CONCLUSION: In a real-world cohort of patients with complex disease, the Auryon laser had excellent freedom from TLR at 6 months, although these findings need to be replicated in a randomized trial.

Preclinical performance of a pediatric mechanical circulatory support device: The PediaFlow ventricular assist device.

OBJECTIVES: The PediaFlow (HeartWare International, Inc, Framingham, Mass) is a miniature, implantable, rotodynamic, fully magnetically levitated, continuous-flow pediatric ventricular assist device. The fourth-generation PediaFlow was evaluated in vitro and in vivo to characterize performance and biocompatibility. METHODS: Supported by 2 National Heart, Lung, and Blood Institute contract initiatives to address the limited options available for pediatric patients with congenital or acquired cardiac disease, the PediaFlow was developed with the intent to provide chronic cardiac support for infants as small as 3 kg. The University of Pittsburgh-led Consortium evaluated fourth-generation PediaFlow prototypes both in vitro and within a preclinical ovine model (n = 11). The latter experiments led to multiple redesigns of the inflow cannula and outflow graft, resulting in the implantable design represented in the most recent implants (n = 2). RESULTS: With more than a decade of extensive computational and experimental efforts spanning 4 device iterations, the AA battery-sized fourth-generation PediaFlow has an operating range of 0.5 to 1.5 L/min with minimal hemolysis in vitro and excellent hemocompatibility (eg, minimal hemolysis and platelet activation) in vivo. The pump and finalized accompanying implantable components demonstrated preclinical hemodynamics suitable for the intended pediatric application for up to 60 days. CONCLUSIONS: Designated a Humanitarian Use Device for "mechanical circulatory support in neonates, infants, and toddlers weighing up to 20 kg as a bridge to transplant, a bridge to other therapeutic intervention such as surgery, or as a bridge to recovery" by the Food and Drug Administration, these initial results document the biocompatibility and potential of the fourth-generation PediaFlow design to provide chronic pediatric cardiac support.

Biodegradable poly(ester urethane)urea elastomers with variable amino content for subsequent functionalization with phosphorylcholine.

While surface modification is well suited for imparting biomaterials with specific functionality for favorable cell interactions, the modification of degradable polymers would be expected to provide only temporary benefit. Bulk modification by incorporating pendant reactive groups for subsequent functionalization of biodegradable polymers would provide a more enduring approach. Towards this end, a series of biodegradable poly(ester urethane)urea elastomers with variable amino content (PEUU-NH2 polymers) were developed. Carboxylated phosphorycholine was synthesized and conjugated to the PEUU-NH2 polymers for subsequent bulk functionalization to generate PEUU-PC polymers. Synthesis was verified by proton nuclear magnetic resonance, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. The impact of amine incorporation and phosphorylcholine conjugation was shown on mechanical, thermal and degradation properties. Water absorption increased with increasing amine content, and further with PC conjugation. In wet conditions, tensile strength and initial modulus generally decreased with increasing hydrophilicity, but remained in the range of 5-30 MPa and 10-20 MPa, respectively. PC conjugation was associated with significantly reduced platelet adhesion in blood contact testing and the inhibition of rat vascular smooth muscle cell proliferation. These biodegradable PEUU-PC elastomers offer attractive properties for applications as non-thrombogenic, biodegradable coatings and for blood-contacting scaffold applications. Further, the PEUU-NH2 base polymers offer the potential to have multiple types of biofunctional groups conjugated onto the backbone to address a variety of design objectives.

Nonthrombogenic, biodegradable elastomeric polyurethanes with variable sulfobetaine content.

For applications where degradable polymers are likely to have extended blood contact, it is often important for these materials to exhibit high levels of thromboresistance. This can be achieved with surface modification approaches, but such modifications may be transient with degradation. Alternatively, polymer design can be altered such that the bulk polymer is thromboresistant and this is maintained with degradation. Toward this end a series of biodegradable, elastic polyurethanes (PESBUUs) containing different zwitterionic sulfobetaine (SB) content were synthesized from a polycaprolactone-diol (PCL-diol):SB-diol mixture (100:0, 75:25, 50:50, 25:75 and 0:100) reacted with diisocyanatobutane and chain extended with putrescine. The chemical structure, tensile mechanical properties, thermal properties, hydrophilicity, biodegradability, fibrinogen adsorption and thrombogenicity of the resulting polymers was characterized. With increased SB content some weakening in tensile properties occurred in wet conditions and enzymatic degradation also decreased. However, at higher zwitterionic molar ratios (50% and 75%) wet tensile strength exceeded 15 MPa and breaking strain was >500%. Markedly reduced thrombotic deposition was observed both before and after substantial degradation for both of these PESBUUs and they could be processed by electrospinning into a vascular conduit format with appropriate compliance properties. The mechanical and degradation properties as well as the acute in vitro thrombogenicity assessment suggest that these tunable polyurethanes could provide options appropriate for use in blood contacting applications where a degradable, elastomeric component with enduring thromboresistance is desired.

Biocompatibility Assessment of the CentriMag-Novalung Adult ECMO Circuit in a Model of Acute Pulmonary Hypertension.

Extracorporeal membrane oxygenation (ECMO) is rarely used in patients with severe pulmonary hypertension (PH) as a bridge to lung transplantation. In this study, we assess the blood biocompatibility of the integrated CentriMag-Novalung ECMO system (venoarterial) in an acute model of PH. Severe PH (≥2/3 systemic) was induced in eight sheep through progressive ligation of the main pulmonary artery. System performance, platelet activation, thromboelastography (TEG) parameters, fibrinogen, plasma-free hemoglobin, and total plasma protein were measured at initiation, 3, and 6 hr of support in the ECMO (N = 4) and sham (N = 4) groups. A stable ECMO flow (2.2 ± 0.1 L/min), low transmembrane pressure gradient, and steady blood O2 and CO2 levels were maintained. Platelet activation was low (<4%) in both the groups, whereas platelet responsiveness to agonist (platelet activating factor) was reduced in the sham group when compared with the ECMO group. There were no differences in the TEG parameters, fibrinogen concentration, plasma-free hemoglobin (<10 mg/dl), and plasma total protein between the two groups. The findings of low levels of platelet activation and plfHb suggest adequate blood biocompatibility of the integrated CentriMag-Novalung circuit use for short-term support in a model of PH.

Standardized methods to quantify thrombogenicity of blood-contacting materials via thromboelastography.

Blood coagulation is the most significant complication of vascular biomaterials. A straightforward, sensitive, and standard measure of the compatibility of these materials with whole blood (hemocompatibility) is necessary to avoid coagulation. Current techniques used quantify only individual clotting components and are poor predictors of coagulation. The thromboelastograph (TEG) provides a measure of overall clot formation from whole blood. Although TEG is very common in clinical settings, its application to biomaterials is limited partly due to difficulty in sample preparation. In this protocol, whole blood samples are incubated with (1) biomaterials (tube with clamped ends) and (2) endothelial cells cultured on biomaterial surfaces (12-well plate) under controlled shearing conditions (10 rpm on rocker, at 37°C), and then the blood is transferred to the TEG to measure clot formation. TEG clearly discriminates among the R-times (time until initial clot formation) of expanded poly(tetrafluoroethylene), poly(urethane), and Tygon tubing. Marked differences in R-time are also seen when endothelial cells are cultured on various extracellular matrix proteins and proteoglycans. Thus, R-time provides a robust metric of overall thrombogenicity of biomaterials, and these procedures provide a standardized method for TEG to facilitate direct comparison among candidate biomaterials undergoing in-vitro testing.

Intracellular signaling controls endothelial cell prostacyclin secretion and regulation of blood clotting time.

Blood is constantly in contact with a biological material, the blood vessel wall, without the need for anticoagulants to prevent clot formation on the vessel wall; however, man-made biomaterials require anticoagulants to prevent clot formation on the biomaterial. This study seeks to understand how some biomaterials elicit anticoagulant responses from endothelial cells (ECs), whereas others do not. Partial least squares regression analysis was used to correlate the activity of four relevant signaling molecules [extracellular signal-related kinase (ERK), c-Jun N-terminal kinase (JNK), Akt, and IκB kinase (IKK)] with human umbilical vein EC secretion of prostacyclin and clotting time of whole blood in contact with these cells. Prostacyclin secretion was increased when JNK activity (mean of all time-points) was elevated and IKK activity at 30 min was reduced. In addition, the clotting time, R-time measured by thromboelastography, was increased (reduced coagulability) when activity of both ERK and JNK (mean of all time-points) were increased and when Akt activity was increased at longer contact times (24-72 h after cell contact with material). Inhibition of each signaling molecule with subsequent testing for prostacyclin secretion and R-time confirmed the interrelationship between EC intracellular signaling and prostacyclin secretion. Generally, JNK inhibition decreased and IKK inhibition increased prostacyclin secretion. Inhibition of ERK or JNK generally increased coagulability, and Akt inhibition decreased the R-time of samples normally eliciting reduced coagulability. These findings increase our understanding of the signaling pathways involved in endothelial prostacyclin release and suggest targets for developing EC-seeded biomaterial surfaces that can minimize coagulation.

Platelet activation after implantation of the Levitronix PediVAS in the ovine model.

The Levitronix PediVAS is an extracorporeal magnetically levitated pediatric ventricular assist system with an optimal flow rate range of 0.3-1.5 L/min. The system is being tested in preclinical studies to assess hemodynamic performance and biocompatibility. The PediVAS was implanted in nine ovines for 30 days using either commercially available cannulae (n = 3) or customized Levitronix cannulae (n = 6). Blood biocompatibility in terms of circulating activated platelets was measured by flow cytometric assays to detect P-selectin. Platelet activation was further examined after exogenous agonist stimulation. Platelet activation increased after surgery and eventually returned to baseline in animal studies where minimal kidney infarcts were observed. Platelet activation remained elevated for the duration of the study in animals where a moderate number of kidney infarcts with or without thrombotic deposition in the cannulae were observed. When platelet activation did return to baseline, platelets appropriately responded to agonist stimulation, signifying conserved platelet function after PediVAS implant. Platelet activation returned to baseline in the majority of studies, representing a promising biocompatibility result for the Levitronix PediVAS.