Zwitterionic poly-carboxybetaine coating reduces artificial lung thrombosis in sheep and rabbits

Flexible coatings based on hydrogel to enhance the biointerface of biomedical implants

The use of biomedical implants in surgical techniques promotes the restoration of lost tissue or organ physiological functions in the body. The interface between different materials determines their interactions and ultimately affects the physicochemical properties of biomedical implants. After implantation, the biointerface plays a crucial role in determining the biocompatibility and functionality of biomedical implants. Surface modification of biomaterials by developing novel biomaterials like various flexible coatings to meet the requirements of biointerfaces, such as mechanical performance, compatibility safety, and biological activities, can improve material-biological interactions by maintaining its original volumetric characteristics. Hydrogels possess excellent plasticity, biodegradability, biocompatibility, and extracellular-matrix-like properties, making them widely used in the biomedical field. Moreover, due to their unique three-dimensional crosslinked hydrophilic network, hydrogels can encapsulate a variety of materials, such as small molecules, polymers, and particle. In recent years, it has been proved that coating biomedical implant materials with flexible hydrogels can optimize the biointerface and holds vast potential for implant surface modification. In this review, we first discussed the potential requirements of the biointerface on the surface of implantable materials in both in vitro and in vivo biological microenvironments. Based on these comprehensive reviews, we also introduced the potential applications of hydrogels in both in vitro and in vivo settings. Finally, this review focused on the challenges faced by the biointerface of implantable materials constructed based on hydrogels and proposed future approaches to inspire researchers with new ideas.

Progress towards permanent respiratory support

PURPOSE OF REVIEW

Although lung transplantation stands as the gold standard curative therapy option for end-stage lung disease, the scarcity of available organs poses a significant challenge in meeting the escalating demand. This review provides an overview of recent advancements in ambulatory respiratory assist systems, selective anticoagulation therapies that target the intrinsic pathway, and innovative surface coatings to enable permanent respiratory support as a viable alternative to lung transplantation.

RECENT FINDINGS

Several emerging ambulatory respiratory assist systems have shown promise in both preclinical and clinical trials. These systems aim to create more biocompatible, compact, and portable forms of extracorporeal membrane oxygenation that can provide long-term respiratory support. Additionally, innovative selective anticoagulation strategies, currently in various stages of preclinical or clinical development, present a promising alternative to currently utilized nonselective anticoagulants. Moreover, novel surface coatings hold the potential to locally prevent artificial surface-induced thrombosis and minimize bleeding risks.

SUMMARY

This review of recent advancements toward permanent respiratory support summarizes the development of ambulatory respiratory assist systems, selective anticoagulation therapies, and novel surface coatings. The integration of these evolving device technologies with targeted anticoagulation strategies may allow a safe and effective mode of permanent respiratory support for patients with chronic lung disease.

An endothelium membrane mimetic antithrombotic coating enables safer and longer extracorporeal membrane oxygenation application

Thrombosis and plasma leakage are two of the most frequent dysfunctions of polypropylene (PP) hollow fiber membrane (PPM) used in extracorporeal membrane oxygenation (ECMO) therapy. In this study, a superhydrophilic endothelial membrane mimetic coating (SEMMC) was constructed on polydopamine-polyethyleneimine pre-coated surfaces of the PPM oxygenator and its ECMO circuit to explore safer and more sustainable ECMO strategy. The SEMMC is fabricated by multi-point anchoring of a phosphorylcholine and carboxyl side chained copolymer (PMPCC) and grafting of heparin (Hep) to form PMPCC-Hep interface, which endows the membrane superior hemocompatibility and anticoagulation performances. Furthermore, the modified PPM reduces protein adsorption amount to less than 30 ng/cm2. More significantly, the PMPCC-Hep coated ECMO system extends the anti-leakage and non-clotting oxygenation period to more than 15 h in anticoagulant-free animal extracorporeal circulation, much better than the bare and conventional Hep coated ECMO systems with severe clots and plasma leakage in 4 h and 8 h, respectively. This SEMMC strategy of grafting bioactive heparin onto bioinert zwitterionic copolymer interface has great potential in developing safer and longer anticoagulant-free ECMO systems. STATEMENT OF SIGNIFICANCE: A superhydrophilic endothelial membrane mimetic coating was constructed on surfaces of polypropylene hollow fiber membrane (PPM) oxygenator and its ECMO circuit by multi-point anchoring of a phosphorylcholine and carboxyl side chain copolymer (PMPCC) and grafting of heparin (Hep). The strong antifouling nature of the PMPCC-Hep coating resists the adsorption of plasma bio-molecules, resulting in enhanced hemocompatibility and anti-leakage ability. The grafted heparin on the zwitterionic PMPCC interface exhibits superior anticoagulation property. More significantly, the PMPCC-Hep coating achieves an extracorporeal circulation in a pig model for at least 15 h without any systemic anticoagulant. This endothelial membrane mimetic anticoagulation strategy shows great potential for the development of safer and longer anticoagulant-free ECMO systems.

Stability Enhancement by Hydrophobic Anchoring and a Cross-Linked Structure of a Phospholipid Copolymer Film for Medical Devices

Surface modification using zwitterionic 2-methacryloyloxyethylphosphorylcholine (MPC) polymers is one of the most reasonable ways to prepare medical devices that can suppress undesired biological reactions such as blood coagulation. Usable MPC polymers are hydrophilic and water soluble, and their surface modification strategy involves exploiting the copolymer structures by adding physical or chemical bonding moieties. In this study, we developed copolymers composed of MPC, hydrophobic anchoring moiety, and chemical cross-linking unit to clarify the role of hydrophobic interactions in achieving biocompatible and long-term stable coatings. The four kinds of MPC copolymers with cross-linking units, such as 3-methacryloxypropyl trimethoxysilane (MPTMSi), and four different hydrophobic anchoring moieties, such as 3-(methacryloyloxy)propyltris(trimethylsiloxy)silane (MPTSSi) named as PMMMSi, n-butyl methacrylate (BMA) as PMBSi, 2-ethylhexyl methacrylate (EHMA) as PMESi, and lauryl methacrylate as PMLSi, were synthesized and coated on polydimethylsiloxane, polypropylene (PP), and polymethyl pentene. These copolymers were uniformly coated on the substrate materials PP and poly(methyl pentene) (PMP), to achieve hydrophilic and electrically neutral coatings. The results of the antibiofouling test showed that PMBSi repelled the adsorption of fluorescence-labeled bovine serum albumin the most, whereas PMLSi repelled it the least. Notably, all four copolymers suppressed platelet adhesion similarly. The variations in protein adsorption quantities among the four copolymer coatings were attributed to their distinct swelling behaviors in aqueous environments. Further investigations, including 3D scanning force microscopy and neutron reflectivity measurements, revealed that the PMLSi coating exhibited a higher water intake under aqueous conditions in comparison to the other coatings. Consequently, all copolymer coatings effectively prevented the invasion of platelets but the proteins penetrated the PMLSi network. Subsequently, the dynamic stability required to induce shear stress was evaluated using a circulation system. The results demonstrated that the PMMMSi and PMLSi coatings on PMP and PP exhibited exceptional platelet repellency and maintained high stability during circulation. This study highlights the potential of hydrophobic moieties to improve hemocompatibility and stability, offering potential applications in medical devices.

Recent advances of multifunctional zwitterionic polymers for biomedical application

Zwitterionic polymers possess equal total positive and negative charges in the repeating units, making them electrically neutral overall. This unique property results in superhydrophilicity, which makes the zwitterionic polymers highly effective in resisting protein adsorption, thus endowing the drug carriers with long blood circulation time, inhibiting thrombus formation on biomedical devices in contact with blood, and ensuring the good sensitivity of sensors in biomedical application. Moreover, zwitterionic polymers have tumor-targeting ability and pH-responsiveness, rendering them ideal candidates for antitumor drug delivery. Additionally, the high ionic conductivity of zwitterionic polymers makes them an important raw material for ionic skin. Zwitterionic polymers exhibit remarkable resistance to bacterial adsorption and growth, proving their suitability in a wide range of biomedical applications such as ophthalmic applications, and wound dressings. In this paper, we provide an in-depth analysis of the different structures and characteristics of zwitterionic polymers and highlight their unique qualities and suitability for biomedical applications. Furthermore, we discuss the limitations and challenges that must be overcome to realize the full potential of zwitterionic polymers and present an optimistic perspective for zwitterionic polymers in the biomedical fields. STATEMENT OF SIGNIFICANCE: Zwitterionic polymers have a series of excellent properties such as super hydrophilicity, anti-protein adsorption, antibacterial ability and good ionic conductivity. However, biomedical applications of multifunctional zwitterionic polymers are still a major field to be explored. This review focuses on the design and application of zwitterionic polymers-based nanosystems for targeted and responsive delivery of antitumor drugs and cancer diagnostic agents. Moreover, the use of zwitterionic polymers in various biomedical applications such as biomedical devices in contact with blood, biosensors, ionic skin, ophthalmic applications and wound dressings is comprehensively described. We discuss current results and future challenges for a better understanding of multifunctional zwitterionic polymers for biomedical applications.

Protein adsorption on blood-contacting surfaces: A thermodynamic perspective to guide the design of antithrombogenic polymer coatings

Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. Thrombosis is fundamentally initiated by the nonspecific adsorption of proteins to the material surface, which is strongly governed by thermodynamic factors established by the nature of the interaction between the material surface, surrounding water molecules, and the protein itself. Along these lines, different surface materials (such as polymeric, metallic, ceramic, or composite) induce different entropic and enthalpic changes at the surface-protein interface, with material wettability significantly impacting this behavior. Consequently, protein adsorption on medical devices can be modulated by altering their wettability and surface energy. A plethora of polymeric coating modifications have been utilized for this purpose; hydrophobic modifications may promote or inhibit protein adsorption determined by van der Waals forces, while hydrophilic materials achieve this by mainly relying on hydrogen bonding, or unbalanced/balanced electrostatic interactions. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications. STATEMENT OF SIGNIFICANCE: Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. A plethora of polymeric coating modifications have been utilized for addressing this issue. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications.

An antifouling electrochemical aptasensor based on a polydopamine-polyzwitterion copolymer for tetracycline analysis

Matrix interference resulting from the nonspecific adsorption of non-target components, particularly proteins (fouling), onto sensor surfaces poses a persistent challenge in electrochemical detection of food hazards. The development of antifouling sensor surfaces presents a viable approach to mitigate nonspecific adsorption. In this study, a novel antifouling electrochemical aptasensor, utilizing a zwitterionic polymer, was developed for the sensitive, accurate, and selective detection of tetracycline (TC) in milk. This sensor employs a poly (dopamine)-poly (sulfobetaine methacrylate) (PDA-PSBMA) antifouling copolymer, which is synthesized through an in-situ initiated copolymerization of dopamine on the sensor's surface. Subsequently, the thiol-containing aptamers were immobilized onto the PDA-PSBMA coating through a Michael addition reaction with the poly(dopamine). The resulting antifouling electrochemical aptasensor exhibited robust antifouling performance in various single protein solutions and diluted milk samples, coupled with sensitive and selective recognition of TC. The sensor demonstrated a broad linear response range of 0.1-1000.0 ng mL-1 and a low limit of detection (LOD) of 68.0 pg mL-1. The antifouling electrochemical aptasensor proved effective in assaying TC in diluted milk, with recoveries ranging from 100.0 % to 104.4 %, eliminating the need for additional pretreatments due to its exceptional resistance to nonspecific adhesion.

Zwitterion mediated anti-protein adsorption on polypropylene mesh to reduce inflammation for efficient hernia repair

The effectiveness of polypropylene (PP) mesh is often compromised by severe inflammation. Engineering anti-inflammatory coatings has significant implications for PP mesh to repair unwanted hernias. Here, we presented a facile strategy to develop an anti-fouling coating consisting of zwitterionic poly(carboxybetaine methacrylate) (PCBMA), which could prohibit protein adsorption to endow PP mesh with anti-inflammatory efficacy. The incorporation of PCBMA coating had little impact on the raw features of PP mesh. While the modified mesh PCBMA-PP possessed noticeable hydrophilicity increase and surface charge reduction. The excellent lubricity and surface stability enabled PCBMA-PP to exhibit superior anti-fouling capacity, thus efficiently inhibiting the adsorption of proteins. In vivo experiments showed that incorporating the PCBMA layer could provide PP meshes with outstanding anti-inflammatory effects and tissue compatibility for repairing hernias.

Superior antibacterial surfaces using hydrophilic, poly(MPC) and poly(mOEGMA) free chains of amphiphilic block copolymer for sustainable use

Surface modification of electrically neutral hydrophilic polymers is one of the most promising methods for preventing biofouling and biological contamination by proteins and bacteria. Surface modification of inorganic materials such as silica-based glass can render them more durable and thus help in achieving the sustainable development goals. This study reports a novel method for the simple and effective surface modification of glass surfaces with amphiphilic block copolymers possessing the silane coupling segment composed of 3-(methacryloyloxy)propyltris (trimethylsilyloxy) silane and 3-methacryloxypropyltrimethoxysilane. The ability of hydrophilic segments composed of either 2-methacryloyloxyethyl phosphorylcholine (MPC) or poly(ethylene glycol) methyl ether methacrylate (mOEGMA) to prevent bacterial adhesion was investigated. The target block copolymers were prepared by reversible addition-fragmentation chain transfer polymerization and the monomer units of the hydrophilic segments were controlled to be either 120 or 160. The polymers were modified on the substrate by dip-coating. Contact angle measurements indicated that the block copolymer with the PMPC hydrophilic segment formed a hydrophilic surface without pre-hydration, while those with the PmOEGMA hydrophilic segment-coated surface became hydrophilic upon immersion in water. The block copolymer-coated surfaces decreased S. aureus adhesion, and a significant reduction was observed with the MPC-type block copolymer. The following surface design guidelines were thus concluded: (1) the block copolymer is superior to the random copolymer and (2) increasing the hydrophilic segment length further decreases bacterial adhesion.

Effect of zwitterionic sulfobetaine incorporation on blood behaviours, phagocytosis, and in vivo biodistribution of pH-responsive micelles with positive charges

pH-responsive micelles with positive charges are challenged by their significant effect on the cells/proteins and compromise their final fate due to electrostatic interactions. As one of the promising strategies, zwitterion incorporation in micelles has attracted considerable attention and displayed improved protein adsorption and blood circulation performances. However, previous reports in this field have been mostly limited in hemolysis for studying blood behaviour and lack a comprehensive understanding of their interactions with blood components. Herein, we present a prelimilary study on the effect of zwitterionic sulfobetaine incorporation on blood behaviour, phagocytosis, and in vivo biodistribution of pH-responsive micelles with positive charges. Amphiphilic triblock copolymers, namely poly(ε-caprolactone)-b-poly(N,N-diethylaminoethyl methacrylate)-(N-(3-sulfopropyl-N-methacryloxyethy-N,N-diethylammonium betaine)) (PCL-PDEAPSx, x = 2, 6, 10), containing different numbers of sulfobetaine groups were synthesized through four steps to prepare the pH-responsive micelles with positive charges. The effect of the sulfobetaine incorporation displayed different profiles, e.g., the micelles had no effect on RBC aggregation, thrombin time (TT), and platelet aggregation, while the cytotoxicity, hemolysis, RBC deformability, activated partial thromboplastin time (APTT), prothrombin time (PT), platelet activation, protein (albumin, fibrinogen, plasma) adsorption, phagocytosis, and in vivo biodistribution decreased with the increase in the sulfobetaine number, in which the transition mainly occurred at a sulfobetaine/tertiary amine group ratio of 3/7-1/1 compared to that of the mPEG control. In addition, the micelles displayed a strong inhibitory effect on the intrinsic coagulation pathway, which was associated with a significant decrease in the coagulation factor activity. Based on these findings, the related mechanism is discussed and proposed, which can aid the rational design of pH-responsive micelles for improved therapeutics.

Achieving superior anticoagulation of endothelial membrane mimetic coating by heparin grafting at zwitterionic biocompatible interfaces

Thrombosis and bleeding are common complications of blood-contacting medical device therapies. In this work, an endothelium membrane mimetic coating (PMPCC/Hep) has been created to address these challenges. The coating is fabricated by multi-point anchoring of a phosphorylcholine copolymer (poly-MPC-co-MSA, PMPCC) with carboxylic side chains and end-group grafting of unfractionated heparin (Hep) onto polydopamine precoated blood-contacting material surfaces. The PMPCC coating forms an ultrathin cell outer membrane mimetic layer to resist protein adsorption and platelet adhesion. The tiny defects/pores of the PMPCC layer provide entrances for heparin end-group to be inserted and grafted onto the sub-layer amino groups. The combination of the PMPCC cell membrane mimetic anti-fouling nature with the grafted heparin bioactivity further enhances the anticoagulation performance of the formed endothelium membrane mimetic PMPCC/Hep coating. Compared to conventional Hep coating, the PMPCC/Hep coating further decreases protein adsorption and platelet adhesion by 50 % and 90 %, respectively. More significantly, the PMPCC/Hep coating shows a superior anticoagulation activity, even significantly higher than that of an end-point-attached heparin coating. Furthermore, the blood coagulation function is well preserved in the PMPCC/Hep coating anticoagulation strategy. All the results support that the PMPCC/Hep coating strategy has great potential in developing more efficient and safer blood-contacting medical devices.

Pilot Testing of a Lightweight, Pulmonary Assist System in an Ambulatory Sheep Model of Destination Therapy Respiratory Support

A new, lightweight (2.3 kg), ambulatory pulmonary assist system (PAS) underwent preliminary evaluation in ambulatory sheep. The PAS was purposefully designed for long-term extracorporeal respiratory support for chronic lung disease and utilizes a novel, small (0.9 m 2 surface area) gas exchanger, the pulmonary assist device, with a modified Heart Assist 5 pump fitting in a small wearable pack. Prototype PAS were attached to two sheep in venovenous configuration for 7 and 14 days, evaluating ability to remain thrombus free; maintain gas exchange and blood flow resistance; avoid biocompatibility-related complications while allowing safe ambulation. The PAS achieved 1.56 L/min of flow at 10.8 kRPM with a 24 Fr cannula in sheep one and 2.0 L/min at 10.5 kRPM with a 28 Fr cannula in sheep 2 without significant change. Both sheep walked freely, demonstrating the first application of truly ambulatory ECMO in sheep. While in vitro testing evaluated PAS oxygen transfer rates of 104.6 ml/min at 2 L/min blood flow, oxygen transfer rates averaged 60.6 ml/min and 70.6 ml/min in studies 1 and 2, due to average hemoglobin concentrations lower than humans (8.9 and 10.5 g/dl, respectively). The presented cases support uncomplicated ambulation using the PAS.

Extracorporeal life support without systemic anticoagulation: a nitric oxide-based non-thrombogenic circuit for the artificial placenta in an ovine model

BACKGROUND

Clinical translation of the extracorporeal artificial placenta (AP) is impeded by the high risk for intracranial hemorrhage in extremely premature newborns. The Nitric Oxide Surface Anticoagulation (NOSA) system is a novel non-thrombogenic extracorporeal circuit. This study aims to test the NOSA system in the AP without systemic anticoagulation.

METHODS

Ten extremely premature lambs were delivered and connected to the AP. For the NOSA group, the circuit was coated with DBHD-N2O2/argatroban, 100 ppm nitric oxide was blended into the sweep gas, and no systemic anticoagulation was given. For the Heparin control group, a non-coated circuit was used and systemic anticoagulation was administered.

RESULTS

Animals survived 6.8 ± 0.6 days with normal hemodynamics and gas exchange. Neither group had any hemorrhagic or thrombotic complications. ACT (194 ± 53 vs. 261 ± 86 s; p < 0.001) and aPTT (39 ± 7 vs. 69 ± 23 s; p < 0.001) were significantly lower in the NOSA group than the Heparin group. Platelet and leukocyte activation did not differ significantly from baseline in the NOSA group. Methemoglobin was 3.2 ± 1.1% in the NOSA group compared to 1.6 ± 0.6% in the Heparin group (p < 0.001).

CONCLUSIONS

The AP with the NOSA system successfully supported extremely premature lambs for 7 days without significant bleeding or thrombosis.

IMPACT

The Nitric Oxide Surface Anticoagulation (NOSA) system provides effective circuit-based anticoagulation in a fetal sheep model of the extracorporeal artificial placenta (AP) for 7 days. The NOSA system is the first non-thrombogenic circuit to consistently obviate the need for systemic anticoagulation in an extracorporeal circuit for up to 7 days. The NOSA system may allow the AP to be implemented clinically without systemic anticoagulation, thus greatly reducing the intracranial hemorrhage risk for extremely low gestational age newborns. The NOSA system could potentially be applied to any form of extracorporeal life support to reduce or avoid systemic anticoagulation.

Epoxy silane sulfobetaine block copolymers for simple, aqueous thromboresistant coating on ambulatory assist lung devices

Developing an ambulatory assist lung (AAL) for patients who need continuous extracorporeal membrane oxygenation has been associated with several design objectives, including the design of compact components, optimization of gas transfer efficiency, and reduced thrombogenicity. In an effort to address thrombogenicity concerns with currently utilized component biomaterials, a low molecular weight water soluble siloxane-functionalized zwitterionic sulfobetaine (SB-Si) block copolymer was coated on a full-scale AAL device set via a one pot aqueous circulation coating. All device parts including hollow fiber bundle, housing, tubing and cannular were successfully coated with increasing atomic compositions of the SB block copolymer and the coated surfaces showed a significant reduction of platelet deposition while gas exchange performance was sustained. However, water solubility of the SB-Si was unstable, and the coating method, including oxygen plasma pretreatment on the surfaces were considered inconsistent with the objective of developing a simple aqueous coating. Addressing these weaknesses, SB block copolymers were synthesized bearing epoxy or epoxy-silane groups with improved water solubility (SB-EP & SB-EP-Si) and no requirement for surface pretreatment (SB-EP-Si). An SB-EP-Si triblock copolymer showed the most robust coating capacity and stability without prior pretreatment to represent a simple aqueous circulation coating on an assembled full-scale AAL device.

Reusable Zwitterionic Porous Organic Polymers for Bilirubin Removal in Serum

Herein, we report a straightforward strategy to construct reusable, hemocompatible, and highly efficient bilirubin adsorbents by installing zwitterionic modules into a porous organic polymer (POP) for hemoperfusion application. Three types of zwitterions with different amounts are used to evaluate their impacts on the characteristics of POPs, including carboxybetaine methacrylate (CB), sulfobetaine methacrylate (SB), and 2-methacryloyloxyethyl phosphorylcholine (MPC). Results show that zwitterions can improve hemocompatibility, hydrophilicity, and bilirubin uptake of the POP. Among all zwitterionic POPs, POP-CB-40% exhibits the best bilirubin uptake, ∼46.5 times enhancement compared with the non-zwitterionic POP in 100% serum. This enhancement can be attributed to the improved hydrophilicity and protein resistance ability in biological solutions. More importantly, the reusability test shows that POP-CB-40% maintains ∼99% of bilirubin uptake capacity at fifth recycling in 100% serum. Findings in this work provide a guideline for the design of biocompatible and efficient POP-based bilirubin adsorbents for hemoperfusion therapy.

Controlled swelling of biomaterial devices for improved antifouling polymer coatings

Nonspecific interactions between cells and implantable elastomers often leads to failure modes for devices such as catheters, cosmetic and reconstructive implants, and sensors. To reduce these interactions, device surfaces can be coated with hydrophilic polymers, where greater polymer density enhances antifouling properties. Although graft-from coating techniques result in higher density polymer films and lower fouling in controlled settings, simpler graft-to methods show similar results on complex implanted devices, despite limited density. To address the need for improved graft-to methods, we developed Graft then shrink (GtS) where elastomeric materials are temporarily swollen during polymer grafting. Herein, we demonstrate a graft-to based method for poly(oligo(ethylene glycol) methyl ether methacrylate) (pOEGMA) on swollen silicone, GtS, that enhances grafted polymer content and fouling resistance. Total grafted polymer content of pOEGMA on toluene swollen silicone increased over ~ 13 × compared to non-swollen controls, dependent on the degree of silicone swelling. Increases in total grafted polymer within the top 200 µm of the material led to bacterial and mammalian cell adhesion reductions of 75% and 91% respectively, compared to Shrink then Graft (StG) antifouling polymer coated controls. GtS allows for the simple 3D coating of swellable elastomers (e.g., silicone medical devices) with improved antifouling pOEGMA coatings.

Current knowledge gaps in extracorporeal respiratory support

Extracorporeal life support (ECLS) for acute respiratory failure encompasses veno-venous extracorporeal membrane oxygenation (V-V ECMO) and extracorporeal carbon dioxide removal (ECCO2R). V-V ECMO is primarily used to treat severe acute respiratory distress syndrome (ARDS), characterized by life-threatening hypoxemia or ventilatory insufficiency with conventional protective settings. It employs an artificial lung with high blood flows, and allows improvement in gas exchange, correction of hypoxemia, and reduction of the workload on the native lung. On the other hand, ECCO2R focuses on carbon dioxide removal and ventilatory load reduction ("ultra-protective ventilation") in moderate ARDS, or in avoiding pump failure in acute exacerbated chronic obstructive pulmonary disease. Clinical indications for V-V ECLS are tailored to individual patients, as there are no absolute contraindications. However, determining the ideal timing for initiating extracorporeal respiratory support remains uncertain. Current ECLS equipment faces issues like size and durability. Innovations include intravascular lung assist devices (ILADs) and pumpless devices, though they come with their own challenges. Efficient gas exchange relies on modern oxygenators using hollow fiber designs, but research is exploring microfluidic technology to improve oxygenator size, thrombogenicity, and blood flow capacity. Coagulation management during V-V ECLS is crucial due to common bleeding and thrombosis complications; indeed, anticoagulation strategies and monitoring systems require improvement, while surface coatings and new materials show promise. Moreover, pharmacokinetics during ECLS significantly impact antibiotic therapy, necessitating therapeutic drug monitoring for precise dosing. Managing native lung ventilation during V-V ECMO remains complex, requiring a careful balance between benefits and potential risks for spontaneously breathing patients. Moreover, weaning from V-V ECMO is recognized as an area of relevant uncertainty, requiring further research. In the last decade, the concept of Extracorporeal Organ Support (ECOS) for patients with multiple organ dysfunction has emerged, combining ECLS with other organ support therapies to provide a more holistic approach for critically ill patients. In this review, we aim at providing an in-depth overview of V-V ECMO and ECCO2R, addressing various aspects of their use, challenges, and potential future directions in research and development.

Preparation and Properties of PDMS Surface Coating for Ultra-Low Friction Characteristics

Polydimethylsiloxane (PDMS) has excellent physical-chemical properties and good biocompatibility. Thus, PDMS has been widely applied in biomedical applications. However, the low surface free energy and surface hydrophobicity of PDMS can easily lead to adverse symptoms, such as tissue damage and ulceration, during medical treatment. Therefore, the construction of a hydrophilic low-friction surface on the PDMS surface could be helpful for alleviating patient discomfort and would be of great significance for broadening the application of PDMS in the field of interventional medical catheters. Existing surface modification methods such as hydrogel coatings and chemical grafting suffer from several deficiencies including uncontrollable thickness, surface fragility, and low surface strength. In this study, a hydrophilic surface with ultra-low friction properties was prepared on the surface of PDMS by an ultraviolet light (UV) curing method. The monomer acrylamide (AM) was induced by a photoinitiator to form a coating on the surface of the silicone rubber by in situ polymerization. The surface roughness of the as-prepared coatings was regulated by adding different concentrations of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to the monomer solution, and the coating properties were systematically characterized. The results indicated that the roughness and thickness of the as-prepared coatings decreased with increasing AMPS concentration and the as-prepared coatings had good hydrophilicity and low-friction properties. The Coefficient of Friction (CoF) was as low as 0.0075 in the deionized water solution, which was 99.7% lower than that of the unmodified PDMS surface. Moreover, the coating with a lower surface roughness exhibited better low-friction properties. The results reported herein provide new insight into the preparation of hydrophilic, low-friction coatings on polymer surfaces.

Pediatric pulmonary valve replacements: Clinical challenges and emerging technologies

Congenital heart diseases (CHDs) frequently impact the right ventricular outflow tract, resulting in a significant incidence of pulmonary valve replacement in the pediatric population. While contemporary pediatric pulmonary valve replacements (PPVRs) allow satisfactory patient survival, their biocompatibility and durability remain suboptimal and repeat operations are commonplace, especially for very young patients. This places enormous physical, financial, and psychological burdens on patients and their parents, highlighting an urgent clinical need for better PPVRs. An important reason for the clinical failure of PPVRs is biofouling, which instigates various adverse biological responses such as thrombosis and infection, promoting research into various antifouling chemistries that may find utility in PPVR materials. Another significant contributor is the inevitability of somatic growth in pediatric patients, causing structural discrepancies between the patient and PPVR, stimulating the development of various growth-accommodating heart valve prototypes. This review offers an interdisciplinary perspective on these challenges by exploring clinical experiences, physiological understandings, and bioengineering technologies that may contribute to device development. It thus aims to provide an insight into the design requirements of next-generation PPVRs to advance clinical outcomes and promote patient quality of life.

Nanofibers with homogeneous heparin distribution and protracted release profile for vascular tissue engineering

In clinic, controlling acute coagulation after small-diameter vessel grafts transplantation is considered a primary problem. The combination of heparin with high anticoagulant efficiency and polyurethane fiber with good compliance is a good choice for vascular materials. However, blending water-soluble heparin with fat-soluble poly (ester-ether-urethane) urea elastomer (PEEUU) uniformly and preparing nanofibers tubular grafts with uniform morphology is a huge challenge. In this research, we have compounded PEEUU with optimized constant concentration of heparin by homogeneous emulsion blending, then spun into the hybrid PEEUU/heparin nanofibers tubular graft (H-PHNF) for replacing rats' abdominal aorta in situ for comprehensive performance evaluation. The in vitro results demonstrated that H-PHNF was of uniform microstructure, moderate wettability, matched mechanical properties, reliable cytocompatibility, and strongest ability to promote endothelial growth. Replacement of resected abdominal artery with the H-PHNF in rat showed that the graft was capable of homogeneous hybrid heparin and significantly promoted the stabilization of vascular smooth muscle cells (VSMCs) as well as stabilizing the blood microenvironment. This research demonstrates the H-PHNF with substantial patency, indicating their potential for vascular tissue engineering.

Commercial and novel anticoagulant ECMO coatings: a review

Extracorporeal membrane oxygenation (ECMO) is an invasive and last-resort treatment for circulatory and respiratory failure. Prolonged ECMO support can disrupt the coagulation and anticoagulation systems in a patient, leading to adverse consequences, such as bleeding and thrombosis. To address this problem, anticoagulation coatings have been developed for use in ECMO circuits. This article reviews commonly used commercial and novel anticoagulant coatings developed in recent years and proposes a new classification of coatings based on the current state. While commercial coatings have been used clinically for decades, this review focuses on comparing the effectiveness and stability of coatings to support clinical selections. Furthermore, novel anticoagulation coatings often involve complex mechanisms and elaborate design strategies, and this review summarises representative studies on mainstream anticoagulation coatings to provide a point of reference for future studies.

Zwitterionic Polysulfobetaine Coating and Antiplatelet Liposomes Reduce Fouling in Artificial Lung Circuits

The artificial lung has provided life-saving support for pulmonary disease patients and recently afforded patients with severe cases of COVID-19 better prognostic outcomes. While it addresses a critical medical need, reducing the risk of clotting inside the device remains challenging. Herein, a two-step surface coating process of the lung circuit using Zwitterionic polysulfobetaine methacrylate is evaluated for its nonspecific protein antifouling activity. It is hypothesized that similarly applied coatings on materials integrated (IT) or nonintegrated (NIT) into the circuit will yield similar antifouling activity. The effects of human plasma preconditioned with nitric oxide-loaded liposome on platelet (plt) fouling are also evaluated. Fibrinogen antifouling activities in coated fibers are similar in the IT and NIT groups. It however decreases in coated polycarbonate (PC) in the IT group. Also, plt antifouling activity in coated fibers is similar in the IT and NIT groups and is lower in coated PC and Tygon in the IT group compared to the NIT group. Coating process optimization in the IT lung circuit may help address difference in the coating appearance of outer and inner fiber bundle fibers, and the NO-liposome significantly reduces (86%) plt fouling on fibers indicating its potential use for blood anticoagulation.

Current and Future Engineering Strategies for ECMO Therapy

Extracorporeal membrane oxygenation (ECMO) is a last resort therapy for patients with respiratory failure where the gas exchange capacity of the lung is compromised. Venous blood is pumped through an oxygenation unit outside of the body where oxygen diffusion into the blood takes place in parallel to carbon dioxide removal. ECMO is an expensive therapy which requires special expertise to perform. Since its inception, ECMO technologies have been evolving to improve its success and minimize the complications associated with it. These approaches aim for a more compatible circuit design capable of maximum gas exchange with minimal need for anticoagulants. This chapter summarizes the basic principles of ECMO therapy with the latest advancements and experimental strategies aiming for more efficient future designs.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Polyzwitterionic Coating of Porous Adsorbents for Therapeutic Apheresis

Adsorbents for whole blood apheresis need to be highly blood compatible to minimize the activation of blood cells on the biomaterial surface. Here, we developed blood-compatible matrices by surface modification with polyzwitterionic polysulfobetainic and polycarboxybetainic coatings. Photoreactive zwitterionic terpolymers were synthesized by free-radical polymerization of zwitterionic, photoreactive, and fluorescent monomers. Upon UV irradiation, the terpolymers were photodeposited and mutually crosslinked on the surface of hydrophobic polystyrene-co-divinylbenzene and hydrophilic polyacrylamide-co-polyacrylate (DALI) beads. Fluorescent microscopy revealed coatings with an average thickness of 5 µm, which were limited to the bead surface. Blood compatibility was assessed based on polymer-induced hemolysis, coagulation parameters, and in vitro tests. The maintenance of the adsorption capacity after coating was studied in human whole blood with cytokines for polystyrene beads (remained capacity 25-67%) and with low-density lipoprotein (remained capacity 80%) for polyacrylate beads. Coating enhanced the blood compatibility of hydrophobic, but not of hydrophilic adsorbents. The most prominent effect was observed on coagulation parameters (e.g., PT, aPTT, TT, and protein C) and neutrophil count. Polycarboxybetaine with a charge spacer of five carbons was the most promising polyzwitterion for the coating of adsorbents for whole blood apheresis.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Bioinspired zwitterionic microgel-based coating: Controllable microstructure, high stability, and anticoagulant properties

Zwitterionic polymers have shown promising results in non-fouling and preventing thrombosis. However, the lack of controlled surface coverage hinders their application for biomedical devices. Inspired by the natural biological surfaces, a facile zwitterionic microgel-based coating strategy is developed by the co-deposition of poly (sulfobetaine methacrylate-co-2-aminoethyl methacrylate) microgel (SAM), polydopamine (PDA), and sulfobetaine-modified polyethyleneimine (PES). The SAMs were used to construct controllable morphology by using the PDA combined with PES (PDAS) as the intermediate layer, which can be easily modulated via adjusting the crosslinking degree and contents of SAMs. The obtained SAM/PDAS coatings exhibit high anti-protein adhesive properties and can effectively inhibit the adhesion of cells, bacteria, and platelet through the synergy of high deposition density and controllable morphology. In addition, the stability of SAM/PDAS coating is improved owing to the anchoring effects of PDAS to substrate and SAMs. Importantly, the ex vivo blood circulation test in rabbits suggests that the SAM/PDAS coating can effectively decrease thrombosis without anticoagulants. This study provides a versatile coating method to address the integration of zwitterionic microgel-based coatings with high deposition density and controllable morphology onto various substrates for wide biomedical device applications. STATEMENT OF SIGNIFICANCE: Thrombosis is a major cause of medical device implantation failure, which results in significant morbidity and mortality. In this study, inspired by natural biological surfaces (fish skin and vascular endothelial layer) and the anchoring ability of mussels, we report a convenient and efficient method to firmly anchor zwitterionic microgels using an oxidative co-deposition strategy. The prepared coating has excellent antifouling and antithrombotic properties through the synergistic effect of physical morphology and chemical composition. This biomimetic surface engineering strategy is expected to provide new insights into the clinical problems of blood-contacting devices related to thrombosis.

Polycarboxybetaine-Based Hydrogels for the Capture and Release of Circulating Tumor Cells

Circulating tumor cells (CTCs) are indicators for the detection, diagnosis, and monitoring of cancers and offer biological information for the development of personalized medicine. Techniques for the specific capture and non-destructive release of CTCs from millions of blood cells remain highly desirable. Here, we present a CTC capture-and-release system using a disulfide-containing poly(carboxybetaine methacrylate) (pCB) hydrogel. The non-fouling characteristic of pCB prevents unwanted, nonspecific cell binding, while the carboxyl functionality of pCB is used for the conjugation of anti-epithelial cell adhesion molecule (anti-EpCAM) antibodies for the capture of CTCs. The results demonstrated that the anti-EpCAM-conjugated pCB hydrogel captured HCT116 cells from blood, and the capture ratio reached 45%. Furthermore, the captured HCT116 cells were released within 30 min from the dissolution of the pCB hydrogel by adding cysteine, which breaks the disulfide bonds of the crosslinkers. The cells released were viable and able to grow. Our system has potential in the development of a device for CTC diagnosis.

A pumpless artificial lung without systemic anticoagulation: The Nitric Oxide Surface Anticoagulation system

BACKGROUND

Artificial lungs have the potential to serve as a bridge to transplantation or recovery for children with end-stage lung disease dependent on extracorporeal life support, but such devices currently require systemic anticoagulation. We describe our experience using the novel Nitric Oxide (NO) Surface Anticoagulation (NOSA) system-an NO-releasing circuit with NO in the sweep gas-with the Pediatric MLung-a low-resistance, pumpless artificial lung.

METHODS

NO flux testing: MLungs (n = 4) were tested using veno-venous extracorporeal life support in a sheep under anesthesia with blood flow set to 0.5 and 1 L/min and sweep gas blended with 100 ppm NO at 1, 2, and 4 L/min. NO and NO₂ were measured in the sweep and exhaust gas to calculate NO flux across the MLung membrane. Pumpless implants: Sheep (20-100 kg, n = 3) underwent thoracotomy and cannulation via the pulmonary artery (device inflow) and left atrium (device outflow) using cannulae and circuit components coated with an NO donor (diazeniumdiolated dibutylhexanediamine; DBHD-N₂O₂) and argatroban. Animals were connected to the MLung with 100 ppm NO in the sweep gas under anesthesia for 24 h with no systemic anticoagulation after cannulation.

RESULTS

NO flux testing: NO flux averaged 3.4 ± 1.0 flux units (x10^-10 mol/cm²/min) (human vascular endothelium: 0.5-4 flux units). Pumpless implants: 3 sheep survived 24 h with patent circuits. MLung blood flow was 716 ± 227 mL/min. Outlet oxygen saturation was 98.3 ± 2.6%. Activated clotting time was 151±24 s. Platelet count declined from 334,333 ± 112,225 to 123,667 ± 7,637 over 24 h. Plasma free hemoglobin and leukocyte and platelet activation did not significantly change.

CONCLUSIONS

The NOSA system provides NO flux across a gas-exchange membrane of a pumpless artificial lung at a similar rate as native vascular endothelium and achieves effective local anticoagulation of an artificial lung circuit for 24 h.

Graft-Then-Shrink: Simultaneous Generation of Antifouling Polymeric Interfaces and Localized Surface Plasmon Resonance Biosensors

Antifouling polymer coatings that are simple to manufacture are crucial for the performance of medical devices such as biosensors. "Grafting-to", a simple technique where presynthesized polymers are immobilized onto surfaces, is commonly employed but suffers from nonideal polymer packing leading to increased biofouling. Herein, we present a material prepared via the grafting-to method with improved antifouling surface properties and intrinsic localized surface plasmon resonance (LSPR) sensor capabilities. A new substrate shrinking fabrication method, Graft-then-Shrink, improved the antifouling properties of polymer-coated Au surfaces by altering graft-to polymer packing while simultaneously generating wrinkled Au structures for LSPR biosensing. Thiol-terminated, antifouling, hydrophilic polymers were grafted to Au-coated prestressed polystyrene (PS) followed by shrinking upon heating above the PS glass transition temperature. Interestingly, the polymer molecular weight and hydration influenced Au wrinkling patterns. Compared to Shrink-then-Graft controls, where polymers are immobilized post shrinking, Graft-then-Shrink increased the polymer content by 76% in defined footprints and improved the antifouling properties as demonstrated by 84 and 72% reduction in macrophage adhesion and protein adsorption, respectively. Wrinkled Au LSPR sensors had sensitivities of ∼200-1000 Δλ/ΔRIU, comparing favorably to commercial LSPR sensors, and detected biotin-avidin and desthiobiotin-avidin complexation in a concentration-dependent manner using a standard plate reader and a 96-well format.

Anti-thrombogenic Surface Coatings for Extracorporeal Membrane Oxygenation: A Narrative Review

Extracorporeal membrane oxygenation (ECMO) is used in critical care to manage patients with severe respiratory and cardiac failure. ECMO brings blood from a critically ill patient into contact with a non-endothelialized circuit which can cause clotting and bleeding simultaneously in this population. Continuous systemic anticoagulation is needed during ECMO. The membrane oxygenator, which is a critical component of the extracorporeal circuit, is prone to significant thrombus formation due to its large surface area and areas of low, turbulent, and stagnant flow. Various surface coatings, including but not limited to heparin, albumin, poly(ethylene glycol), phosphorylcholine, and poly(2-methoxyethyl acrylate), have been developed to reduce thrombus formation during ECMO. The present work provides an up-to-date overview of anti-thrombogenic surface coatings for ECMO, including both commercial coatings and those under development. The focus is placed on the coatings being developed for oxygenators. Overall, zwitterionic polymer coatings, nitric oxide (NO)-releasing coatings, and lubricant-infused coatings have attracted more attention than other coatings and showed some improvement in in vitro and in vivo anti-thrombogenic effects. However, most studies lacked standard hemocompatibility assessment and comparison studies with current clinically used coatings, either heparin coatings or nonheparin coatings. Moreover, this review identifies that further investigation on the thrombo-resistance, stability and durability of coatings under rated flow conditions and the effects of coatings on the function of oxygenators (pressure drop and gas transfer) are needed. Therefore, extensive further development is required before these new coatings can be used in the clinic.

Bioengineering Progress in Lung Assist Devices

Artificial lung technology is advancing at a startling rate raising hopes that it would better serve the needs of those requiring respiratory support. Whether to assist the healing of an injured lung, support patients to lung transplantation, or to entirely replace native lung function, safe and effective artificial lungs are sought. After 200 years of bioengineering progress, artificial lungs are closer than ever before to meet this demand which has risen exponentially due to the COVID-19 crisis. In this review, the critical advances in the historical development of artificial lungs are detailed. The current state of affairs regarding extracorporeal membrane oxygenation, intravascular lung assists, pump-less extracorporeal lung assists, total artificial lungs, and microfluidic oxygenators are outlined.

Tissue Engineering for Mimics and Modulations of Immune Functions

In the field of regenerative medicine, advances in tissue engineering have surpassed the reconstruction of individual tissues or organs and begun to work towards engineering systemic factors such as immune objects and functions. The immune system plays a crucial role in protecting and regulating systemic functions in the human body. Engineered immune tissues and organs have shown potential in recovering dysfunctions and aplasia of the immune system and the evasion from immune-mediated inflammatory responses and rejection elicited by engineered implants from allogeneic or xenogeneic sources are also being pursued to facilitate clinical transplantation of tissue engineered grafts. Here, current progress in tissue engineering to mimic or modulate immune functions is reviewed and elaborated from two perspectives: 1) engineering of immune tissues and organs per se and 2) immune evasion of host immunoinflammatory rejection by tissue-engineered implants.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Universal Intraductal Surface Antifouling Coating Based on an Amphiphilic Copolymer

Surface modification on the inner wall of medical or industrial polymeric catheters with a high length/diameter ratio is highly desired. Herein, a universal and facile method based on an amphiphilic copolymer was developed to immobilize an intraductal surface antifouling coating for a variety of polymeric catheters. A fouling-repelled thin layer was formed by swelling-driven adsorption via directly perfusing an amphiphilic copolymer [polyvinylpyrrolidone-polydimethylsiloxane-polyvinylpyrrolidone (PVP-PDMS-PVP)] solution into catheters. In this copolymer, hydrophobic PDMS was embedded into a shrinking cross-linked network of catheters; also, PVP segments migrated to the surface under driving water to form a hydrophilic antifouling coating. Moreover, because of the coordination between I₂ and pyrrolidone of PVP, the copolymer-modified intraductal surface was then infused with aqueous I₂ to form the PVP-I₂ complex, endowing this coating with bactericidal activity. Notably, diverse catheters with arbitrary shapes (circular, rectangular, triangular, and hexagonal) and different components (silicone, polyurethane, and polyethylene) were also verified to work using this interfacial interpenetration strategy. The findings in this work provide a new avenue toward facile and universal fabrication of intraductal surface antifouling catheters, creating a superior option for decreasing the consumable costs in industrial production and alleviating the pain of replacing catheters for patients.

Establishment and evaluation of a rat model of extracorporeal membrane oxygenation (ECMO) thrombosis using a 3D-printed mock-oxygenator

Background

Extracorporeal membrane oxygenation (ECMO) research using large animals requires a significant amount of resources, slowing down the development of new means of ECMO anticoagulation. Therefore, this study developed and evaluated a new rat ECMO model using a 3D-printed mock-oxygenator.

Methods

The circuit consisted of tubing, a 3D-printed mock-oxygenator, and a roller pump. The mock-oxygenator was designed to simulate the geometry and blood flow patterns of the fiber bundle in full-scale oxygenators but with a low (2.5 mL) priming volume. Rats were placed on arteriovenous ECMO at a 1.9 mL/min flow rate at two different heparin doses (n = 3 each): low (15 IU/kg/h for eight hours) versus high (50 IU/kg/h for one hour followed by 25 IU/kg/h for seven hours). The experiment continued for eight hours or until the mock-oxygenator failed. The mock-oxygenator was considered to have failed when its blood flow resistance reached three times its baseline resistance.

Results

During ECMO, rats maintained near-normal mean arterial pressure and arterial blood gases with minimal hemodilution. The mock-oxygenator thrombus weight was significantly different (p < 0.05) between the low (0.02 ± 0.006 g) and high (0.003 ± 0.001 g) heparin delivery groups, and blood flow resistance was also larger in the low anticoagulation group.

Conclusions

This model is a simple, inexpensive system for investigating new anticoagulation agents for ECMO and provides low and high levels of anticoagulation that can serve as control groups for future studies.

Combination of polycarboxybetaine coating and factor XII inhibitor reduces clot formation while preserving normal tissue coagulation during extracorporeal life support

Blood contact with high surface area medical devices, such as dialysis and extracorporeal life support (ECLS), induces rapid surface coagulation. Systemic anticoagulation, such as heparin, is thus necessary to slow clot formation, but some patients suffer from bleeding complications. Both problems might be reduced by 1) replacing heparin anticoagulation with artificial surface inhibition of the protein adsorption that initiates coagulation and 2) selective inhibition of the intrinsic branch of the coagulation cascade. This approach was evaluated by comparing clot formation and bleeding times during short-term ECLS using zwitterionic polycarboxybetaine (PCB) surface coatings combined with either a potent, selective, bicyclic peptide inhibitor of activated Factor XII (FXII900) or standard heparin anticoagulation. Rabbits underwent venovenous ECLS with small sham oxygenators for 60 min using three means of anticoagulation (n = 4 ea): (1) PCB coating + FXII900 infusion, (2) PCB coating + heparin infusion with an activated clotting time of 220-300s, and (3) heparin infusion alone. Sham oxygenator blood clot weights in the PCB + FXII900 and PCB + heparin groups were 4% and 25% of that in the heparin group (p < 10^-6 and p < 10^-5), respectively. At the same time, the bleeding time remained normal in the PCB + FXII900 group (2.4 ± 0.2 min) but increased to 4.8 ± 0.5 and 5.1 ± 0.7 min in the PCB + heparin and heparin alone groups (p < 10^-4 and 0.01). Sham oxygenator blood flow resistance was significantly lower in the PCB + FXII900 and PCB + heparin groups than in the heparin only group (p < 10^-6 and 10^-5). These results were confirmed by gross and scanning electron microscopy (SEM) images and fibrinopeptide A (FPA) concentrations. Thus, the combined use of PCB coating and FXII900 markedly reduced sham oxygenator coagulation and tissue bleeding times versus the clinical standard of heparin anticoagulation and is a promising anticoagulation method for clinical ECLS.

Advances in extracorporeal membrane oxygenator design for artificial placenta technology

Extreme prematurity, defined as a gestational age of fewer than 28 weeks, is a significant health problem worldwide. It carries a high burden of mortality and morbidity, in large part due to the immaturity of the lungs at this stage of development. The standard of care for these patients includes support with mechanical ventilation, which exacerbates lung pathology. Extracorporeal life support (ECLS), also called artificial placenta technology when applied to extremely preterm (EPT) infants, offers an intriguing solution. ECLS involves providing gas exchange via an extracorporeal device, thereby doing the work of the lungs and allowing them to develop without being subjected to injurious mechanical ventilation. While ECLS has been successfully used in respiratory failure in full-term neonates, children, and adults, it has not been applied effectively to the EPT patient population. In this review, we discuss the unique aspects of EPT infants and the challenges of applying ECLS to these patients. In addition, we review recent progress in artificial placenta technology development. We then offer analysis on design considerations for successful engineering of a membrane oxygenator for an artificial placenta circuit. Finally, we examine next-generation oxygenators that might advance the development of artificial placenta devices.