Preclinical biocompatibility assessment of the EVAHEART ventricular assist device: Coating comparison and platelet activation

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.

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.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Surface Coatings for Rotary Ventricular Assist Devices: A Systematic Review

Rotary ventricular assist devices (VADs) are frequently used to provide mechanical circulatory support to patients suffering from end-stage heart failure. Therefore, these devices and especially their pump impeller and housing components have stringent requirements on wear resistance and hemocompatibility. Various surface coatings have been investigated to improve the wear resistance or hemocompatibility of these devices. The aim of the present systematic review was to build a comprehensive understanding of these coatings and provide potential future research directions. A Boolean search for peer-reviewed studies was conducted in online databases (Web of Science, Scopus, PubMed, and ScienceDirect), and a preferred reporting items for systematic reviews and meta-analyses (PRISMA) process was followed for selecting relevant papers for analysis. A total of 45 of 527 publications were included for analysis. Eighteen coatings were reported to improve wear resistance or hemocompatibility of rotary VADs with the most common coatings being diamond-like carbon (DLC), 2-methacryloyloxyethyl phosphorylcholine (MPC), and heparin. Ninety-three percent of studies focused on hemocompatibility, whereas only 4% of studies focused on wear properties. Thirteen percent of studies investigated durability. This review provides readers with a systematic catalogue and critical review of surface coatings for rotary VADs. The review has identified that more comprehensive studies especially investigations on wear properties and durability are needed in future work.

Rational synthesis of novel biocompatible thermoresponsive block copolymer worm gels

It is well known that reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) enables the rational design of diblock copolymer worm gels. Moreover, such hydrogels can undergo degelation on cooling below ambient temperature as a result of a worm-to-sphere transition. However, only a subset of such block copolymer worms exhibit thermoresponsive behavior. For example, PMPC26-PHPMA280 worm gels prepared using a poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC26) precursor do not undergo degelation on cooling to 6 °C (see S. Sugihara et al., J. Am. Chem. Soc., 2011, 133, 15707-15713). Informed by our recent studies (N. J. Warren et al., Macromolecules, 2018, 51, 8357-8371), we decided to reduce the mean degrees of polymerization of both the PMPC steric stabilizer block and the structure-directing PHPMA block when targeting a pure worm morphology. This rational approach reduces the hydrophobic character of the PHPMA block and hence introduces the desired thermoresponsive character, as evidenced by the worm-to-sphere transition (and concomitant degelation) that occurs on cooling a PMPC15-PHPMA150 worm gel from 40 °C to 6 °C. Moreover, worms are reconstituted on returning to 40 °C and the original gel modulus is restored. This augurs well for potential biomedical applications, which will be examined in due course. Finally, small-angle X-ray scattering studies indicated a scaling law exponent of 0.67 (≈2/3) for the relationship between the worm core cross-sectional diameter and the PHPMA DP for a series of PHPMA-based worms prepared using a range of steric stabilizer blocks, which is consistent with the strong segregation regime for such systems.

Combination of two antithrombogenic methodologies for preventing thrombus formation on a poly(ether ether ketone) substrate

To enhance the total antithrombogenicity of poly(ether ether ketone) (PEEK), we examined a combination of two methodologies for the suppression of activation in both the platelet and coagulation systems. A random copolymer (PMT) composed of a zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) unit and a cationic 2-methacryloyloxyethyl trimethylammonium chloride (TMAEMA) unit was grafted onto the PEEK surface by photoinduced self-initiated graft polymerization of the PEEK substrate (PMTx-g-PEEK). Then, negatively charged heparin was immobilized by ionic binding with TMAEMA units (Hep/PMTx-g-PEEK). The TMAEMA unit composition on grafted PMT altered the surface ζ-potentials of the PEEK substrates. Amounts of immobilized heparin depended on the ζ-potential. The concentration of heparin became constant on the sample surface where the TMAEMA unit composition was 30% or more, and was approximately 2.0 μg/cm2. The Hep/PMTx-g-PEEK with a TMAEMA unit composition of 50% showed not only decreased platelet adhesion, but also a 4-fold extension of the blood coagulation time of the poly(MPC)-g-PEEK substrate. The poly(MPC) layer could inhibit platelet adhesion and activation, resulting in surface antithrombogenic properties. Additionally, heparin released from the Hep/PMTx-g-PEEK prevented activation of the coagulation system in whole blood. Therefore, the combination of these antithrombogenic methodologies was promising for prolonging the blood coagulation period of the materials.

Poly(2-aminoethyl methacrylate)-based polyampholyte brush surface with carboxylic groups to improve blood compatibility

Zwitterionic material-based polymer brush significantly prevents protein adsorption and cell adhesion, which leads to the blood compatibility. However, zwitterionic polymer itself is difficult to be modified further, for the blood compatibility since the charged balance is impaired after the modification. In this research, chemically modifiable mixed charge polymer brush is designed, without impairing its characteristics. Condensed mixed charge polymer brush will work like zwitterionic material because neighbouring opposite charge is reported to be important in the zwitterionic material. Cationic polymer brush with primary amine group, which is based on 2-aminoethyl methacrylate (AEMA), was prepared and modified by succinic anhydride to obtain carboxylic group induced poly(AEMA). The ratio of primary amine group and carboxylic group was optimized to obtain the polyampholyte brush. The blood compatibility was evaluated by measuring coagulation/complement activation, protein adsorption and cell adhesion induced by the polymer. Our designed cationic-based polyampholyte brush prevented coagulation/complement activation comparable to poly(2-methacryloyloxyethyl phosphorylcholine) brush, based on intra-monomer interaction, because condensed mix charge works like zwitterion.

Bio-inspired immobilization of low-fouling phospholipid polymers via a simple dipping process: a comparative study of phenol, catechol and gallol as tethering groups

Low-fouling phospholipid polymer was conjugated with bio-inspired tethering groups. Immobilization efficiencies of these polymers onto various surfaces were investigated.

Feasibility study of use of rabbit blood to evaluate platelet activation by medical devices

It is important to ascertain platelet responses to blood-contacting medical devices as part of a complete hemocompatibility evaluation. Nevertheless, researchers often face the problem of insufficient quantities of human blood for evaluation of platelet activation by actual medical devices. If animal blood can replace human blood to evaluate platelet activation by medical devices, testing will be smoother and will aid for quality control of related products. Therefore, in this study, we exposed representative biomaterials to human blood, rabbit blood and mouse blood, and evaluated similarities and differences in platelet activation among the three types of blood by measuring various molecular markers. We found that rabbit blood and human blood had considerable similarity in terms of platelet activation, while mouse blood and human blood showed considerable differences. Therefore, rabbit blood may replace human blood for platelet function testing.

Osteoblast Biocompatibility and Antibacterial Effects Using 2-Methacryloyloxyethyl Phosphocholine-Grafted Stainless-Steel Composite for Implant Applications

Poor osteogenesis and bacterial infections lead to an implant failure, so the enhanced osteogenic and antimicrobial activity of the implantable device is of great importance in orthopedic applications. In this study, 2-methacryloyloxyethyl phosphocholine (MPC) was grafted onto 316L stainless steel (SS) using a facile photo-induced radical graft polymerization method via a benzophenone (BP) photo initiator. Atomic force microscopy (AFM) was employed to determine the nanoscale morphological changes on the surface. The grafted BP-MPC layer was estimated to be tens of nanometers thick. The SS-BP-MPC composite was more hydrophilic and smoother than the untreated and BP-treated SS samples. Staphylococcus aureus (S. aureus) bacteria binding onto the SS-BP-MPC composite film surface was significantly reduced compared with the pristine SS and SS-BP samples. Mouse pre-osteoblast (MC3T3-E1) cells showed good adhesion on the MPC-modified samples and better proliferation and metabolic activity (73% higher) than the pristine SS sample. Biological studies revealed that grafting MPC onto the SS substrate enhanced the antibacterial efficiency and also retained osteoblast biocompatibility. This proposed procedure is promising for use with other implant materials.

Micropatterning of a 2-methacryloyloxyethyl phosphorylcholine polymer surface by hydrogenated amorphous carbon thin films for endothelialization and antithrombogenicity

The existing first-generation drug-eluting stent (DES) has caused late and very late stent thrombosis related to incomplete stent endothelialization. Hence, biomaterials that possess sufficient anti-thrombogenicity and endothelialization with the controlled drug release system have been highly required. In this work, we have developed a newly designed drug-release platform composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, a non-thrombogenic polymer, and micropatterned hydrogenated amorphous carbon (a-C:H), a cell-compatible thin film. The platelet adhesion and the endothelial cell adhesion behavior on the micropatterned substrates were investigated in vitro. The results indicated that the micropatterned a-C:H/MPC polymer substrates effectively supported the human umbilical vein endothelial cell (HUVEC) proliferation, while suppressing the platelet adhesion. Interestingly, the HUVEC exhibited different shape and behavior by changing the island size of the micropatterned a-C:H. By introducing both a non-thrombogenic polymer and cell-compatible thin films through a simple patterning method, we demonstrated that the platform had the potential to be utilized as a base material for DES with cell controllability. STATEMENT OF SIGNIFICANCE: The current first-generation drug-eluting stents (DES) would cause late and very late stent thrombosis due to the incomplete endothelialization of the metal stent material. In this work, we have developed a new DES platform composed of a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer micropatterned by hydrogenated amorphous carbon (a-C:H). Two types of differently micropatterned a-C:H stent surface were made. Our studies revealed that the micropatterned a-C:H/MPC polymer substrates could effectively enhance the endothelial cell (EC) proliferation, simultaneously suppressing the platelet adhesion, becoming a highly biocompatible material especially for indwelling devices including a drug-release device. The new drug-release platform could be utilized as a base material for cell-controllable coating on DES.

The Biocompatibility Challenges in the Total Artificial Heart Evolution

There are limited therapeutic options for final treatment of end-stage heart failure. Among them, implantation of a total artificial heart (TAH) is an acceptable strategy when suitable donors are not available. TAH development began in the 1930s, followed by a dramatic evolution of the actuation mechanisms operating the mechanical pumps. Nevertheless, the performance of TAHs has not yet been optimized, mainly because of the low biocompatibility of the blood-contacting surfaces. Low hemocompatibility, calcification, and sensitivity to infections seriously affect the success of TAHs. These unsolved issues have led to the withdrawal of many prototypes during preclinical phases of testing. This review offers a comprehensive analysis of the pathophysiological events that may occur in the materials that compose TAHs developed to date. In addition, this review illustrates bioengineering strategies to prevent these events and describes the most significant steps toward the achievement of a fully biocompatible TAH.

Blood-Compatible Surfaces with Phosphorylcholine-Based Polymers for Cardiovascular Medical Devices

For the acquisition of blood-compatible materials, various hydrophilic polymers for surface modification have been examined. Among them, polymers with a representative phospholipid polar group, the phosphorylcholine (PC) group, are a successful example. These polymers were designed from inspiration of the cell membrane surface and provide protein adsorption resistance even following contact with plasma. This important property is based on the unique hydration state of water molecules surrounding hydrated polymer; in other words, water molecules weakly interact with the polymers and maintain their favorable cluster structure through hydrogen bonding. These polymers are not only hydrophilic, but also electrically neutral, important characteristics which make hydrogen bonding with water molecules less likely to occur and avoid hydrophobic interactions. Phosphorylcholine groups and other zwitterionic structures are significant as hydrophilic functional groups meeting these important requirements. In this review, blood compatibility of a polymer having a PC group is introduced in relation to its hydration structure, followed by a description of the applications of this polymer to cardiovascular medical devices.

Antifouling (Bio)materials for Electrochemical (Bio)sensing

(Bio)fouling processes arising from nonspecific adsorption of biological materials (mainly proteins but also cells and oligonucleotides), reaction products of neurotransmitters oxidation, and precipitation/polymerization of phenolic compounds, have detrimental effects on reliable electrochemical (bio)sensing of relevant analytes and markers either directly or after prolonged incubation in rich-proteins samples or at extreme pH values. Therefore, the design of antifouling (bio)sensing interfaces capable to minimize these undesired processes is a substantial outstanding challenge in electrochemical biosensing. For this purpose, efficient antifouling strategies involving the use of carbon materials, metallic nanoparticles, catalytic redox couples, nanoporous electrodes, electrochemical activation, and (bio)materials have been proposed so far. In this article, biomaterial-based strategies involving polymers, hydrogels, peptides, and thiolated self-assembled monolayers are reviewed and critically discussed. The reported strategies have been shown to be successful to overcome (bio)fouling in a diverse range of relevant practical applications. We highlight recent examples for the reliable sensing of particularly fouling analytes and direct/continuous operation in complex biofluids or harsh environments. Opportunities, unmet challenges, and future prospects in this field are also pointed out.

Epileptic Seizure Suppression by Focal Brain Cooling With Recirculating Coolant Cooling System: Modeling and Simulation

A focal brain cooling system for treatment of refractory epilepsy that is implantable and wearable may permit patients with this condition to lead normal daily lives. We have developed such a system for cooling of the epileptic focus by delivery of cold saline to a cooling device that is implanted cranially. The outflow is pumped for circulation and cooled by a Peltier device. Here, we describe the design of the system and evaluate its feasibility by simulation. Mathematical models were constructed based on equations of fluid dynamics and data from a cat model. Computational fluid dynamics simulations gave the following results: 1) a cooling device with a complex channel structure gives a more uniform temperature in the brain; 2) a cooling period of <10 min is required to reach an average temperature of 25.0°Cat 2 mm below the brain surface, which is the target temperature for seizure suppression. This time is short enough for cooling of the brain before seizure onset after seizure prediction by an intracranial electroencephalogram-based algorithm; and 3) battery charging would be required once every several days for most patients. These results suggest that the focal brain cooling system may be clinically applicable.

Rotary mechanical circulatory support systems

A detailed survey of the current trends and recent advances in rotary mechanical circulatory support systems is presented in this paper. Rather than clinical reports, the focus is on technological aspects of these rehabilitating devices as a reference for engineers and biomedical researchers. Existing trends in flow regimes, flow control, and bearing mechanisms are summarized. System specifications and applications of the most prominent continuous-flow ventricular assistive devices are provided. Based on the flow regime, pumps are categorized as axial flow, centrifugal flow, and mixed flow. Unique characteristics of each system are unveiled through an examination of the structure, bearing mechanism, impeller design, flow rate, and biocompatibility. A discussion on the current limitations is provided to invite more studies and further improvements.

Clinical safety and wear resistance of the phospholipid polymer-grafted highly cross-linked polyethylene liner

To reduce the production of wear particles and subsequent aseptic loosening, we created a human articular cartilage-mimicked surface for a highly cross-linked polyethylene liner, whose surface grafted layer consisted of a biocompatible phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine). Although our previous in vitro findings showed that poly(2-methacryloyloxyethyl phosphorylcholine)-grafted particles were biologically inert and caused no subsequent bone resorptive responses, and poly(2-methacryloyloxyethyl phosphorylcholine) grafting markedly decreased wear in hip joint simulator tests, the clinical safety, and in vivo wear resistance of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners remained open to question. Therefore, in the present study, we evaluated clinical and radiographic outcomes of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners 5 years subsequent to total hip replacement in 68 consecutive patients. No reoperation was required for any reason, and no adverse events were associated with the implanted liners. The average Harris Hip Score increased from 38.6 preoperatively to 96.5 5 years postoperatively, and health-related quality of life, as indicated by the Short Form 36 Health Survey, improved. Radiographic analyses showed no periprosthetic osteolysis or implant migration. Between 1 and 5 years postoperatively, the mean steady-state wear rate was 0.002 mm/year, which represented a marked reduction relative to other highly cross-linked polyethylene liners, and appeared to be unaffected by patient-related or surgical factors. Although longer follow up is required, poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners improved mid-term clinical outcomes. The clinical safety and wear-resistance results are encouraging with respect to the improvement of long-term clinical outcomes with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2007-2016, 2017.

Quantitative fabrication, performance optimization and comparison of PEG and zwitterionic polymer antifouling coatings

A versatile fabrication and performance optimization strategy of PEG and zwitterionic polymer coatings is developed on the sensor chip of surface plasma resonance (SPR) instrument. A random copolymer bearing phosphorylcholine zwitterion and active ester side chains (PMEN) and carboxylic PEG coatings with comparable thicknesses were deposited on SPR sensor chips via amidation coupling on the precoated polydopamine (PDA) intermediate layer. The PMEN coating showed much stronger resistance to bovine serum albumin (BSA) adsorption than PEG coating at very thin thickness (∼1nm). However, the BSA resistant efficacy of PEG coating could exceed that of PMEN due to stronger steric repelling effect when the thickness increased to 1.5∼3.3nm. Interestingly, both the PEG and PMEN thick coatings (≈3.6nm) showed ultralow fouling by BSA and bovine plasma fibrinogen (Fg). Moreover, changes in the PEG end group from -OH to -COOH, protein adsorption amount could increase by 10-fold. Importantly, the optimized PMEN and PEG-OH coatings were easily duplicated on other substrates due to universal adhesion of the PDA layer, showed excellent resistance to platelet, bacteria and proteins, and no significant difference in the antifouling performances was observed. These detailed results can explain the reported discrepancy in performances between PEG and zwitterionic polymer coatings by thickness. This facile and substrate-independent coating strategy may benefit the design and manufacture of advanced antifouling biomedical devices and long circulating nanocarriers.

STATEMENT OF SIGNIFICANCE

Prevention of biofouling is one of the biggest challenges for all biomedical applications. However, it is very difficult to fabricate a highly hydrophilic antifouling coating on inert materials or large devices. In this study, PEG and zwitterion polymers, the most widely investigated polymers with best antifouling performance, are conveniently immobilized on different kinds of substrates from their aqueous solutions by precoating a polydopamine intermediate layer as the universal adhesive and readily re-modifiable surface. Importantly, the coating fabrication and antifouling performance can be monitored and optimized quantitatively by a surface plasma resonance (SPR) system. More significantly, the SPR on-line optimized coatings were successfully duplicated off-line on other substrates, and supported by their excellent antifouling properties.

Shear Stress-Induced Total Blood Trauma in Multiple Species

The common complications in heart failure patients with implanted ventricular assist devices (VADs) include hemolysis, thrombosis, and bleeding. These are linked to shear stress-induced trauma to erythrocytes, platelets, and von Willebrand factor (vWF). Novel device designs are being developed to reduce the blood trauma, which will need to undergo in vitro and in vivo preclinical testing in large animal models such as cattle, sheep, and pig. To fully understand the impact of device design and enable translation of preclinical results, it is important to identify any potential species-specific differences in the VAD-associated common complications. Therefore, the purpose of this study was to evaluate the effects of shear stress on cells and proteins in bovine, ovine, and porcine blood compared to human. Blood from different species was subjected to various shear rates (0-8000/s) using a rheometer. It was then analyzed for complete blood counts, hemolysis by the Harboe assay, platelet activation by flow cytometry, vWF structure by immunoblotting, and function by collagen binding activity ELISA (vWF : CBA). Overall, increasing shear rate caused increased total blood trauma in all tested species. This analysis revealed species-specific differences in shear-induced hemolysis, platelet activation, and vWF structure and function. Compared to human blood, porcine blood was the most resilient and showed less hemolysis, similar blood counts, but less platelet activation and less vWF damage in response to shear. Compared to human blood, sheared bovine blood showed less hemolysis, similar blood cell counts, greater platelet activation, and similar degradation of vWF structure, but less impact on its activity in response to shear. The shear-induced effect on ovine blood depended on whether the blood was collected via gravity at the abattoir or by venepuncture from live sheep. Overall, ovine abattoir blood was the least resilient in response to shear and bovine blood was the most similar to human blood. These results lay the foundations for developing blood trauma evaluation standards to enable the extrapolation of in vitro and in vivo animal data to predict safety and biocompatibility of blood-handling medical devices in humans. We advise using ovine venepuncture blood instead of ovine abattoir blood due to the greater overall damage in the latter. We propose using bovine blood for total blood damage in vitro device evaluation but multiple species could be used to create a full understanding of the complication risk profile of new devices. Further, this study highlights that choice of antibody clone for evaluating platelet activation in bovine blood can influence the interpretation of results from different studies.

Inhibition of denture plaque deposition on complete dentures by 2-methacryloyloxyethyl phosphorylcholine polymer coating: A clinical study

STATEMENT OF PROBLEM

Denture plaque-associated infections are regarded as a source of serious dental and medical complications in the elderly population. Methods of managing this problem are needed.

PURPOSE

The purpose of this clinical study was to evaluate the effects of treatment with a 2-methacryloyloxyethyl phosphorylcholine polymer, PMBPAz, on plaque deposition in complete dentures.

MATERIAL AND METHODS

The study protocol was approved by the Ethics Committee of Showa University (#2013-013). Eleven individuals with maxillary complete dentures participated in this study. Their dentures were treated with PMBPAz, and the amount of denture plaque accumulation was evaluated by staining the denture surfaces with methylene blue after 2 weeks of denture usage. The same procedures were repeated to evaluate the original denture surfaces as a control. The image of the stained denture surface was captured using a digital camera, and the percentage of stained area, quantified as a pixel-based density, of the whole denture area (percentage of plaque index) was calculated for the mucosal and polished surfaces. To quantify the biofilm on the dentures, denture plaque biofilm was detached by ultrasonic vibration, resuspended in diluent, and measured with a microplate reader at an optical density of 620 nm. The effects of PMBPAz treatment on these variables were statistically analyzed with ANOVA (α=.05).

RESULTS

The mean ±SD percentage of plaque index was 40.7% ±19.9% on the mucosal surfaces and 28.0% ±16.8% on the polished surfaces of the control denture. The mean percentage of plaque index of PMBPAz-treated dentures significantly decreased to 17.4%% ±12.0% on the mucosal surfaces (P<.001) and 15.0% ±9.9% on the polished surfaces (P<.05). The quantification of plaque deposition agreed with the results of these image analyses.

CONCLUSIONS

These results demonstrated the effectiveness of the treatment with the PMBPAz to inhibit the bacterial plaque deposition on complete dentures.

In Vitro Endothelialization Test of Biomaterials Using Immortalized Endothelial Cells

Functionalizing biomaterials with peptides or polymers that enhance recruitment of endothelial cells (ECs) can reduce blood coagulation and thrombosis. To assess endothelialization of materials in vitro, primary ECs are generally used, although the characteristics of these cells vary among the donors and change with time in culture. Recently, primary cell lines immortalized by transduction of simian vacuolating virus 40 large T antigen or human telomerase reverse transcriptase have been developed. To determine whether immortalized ECs can substitute for primary ECs in material testing, we investigated endothelialization on biocompatible polymers using three lots of primary human umbilical vein endothelial cells (HUVEC) and immortalized microvascular ECs, TIME-GFP. Attachment to and growth on polymer surfaces were comparable between cell types, but results were more consistent with TIME-GFP. Our findings indicate that TIME-GFP is more suitable for in vitro endothelialization testing of biomaterials.

Complement inhibition in biomaterial- and biosurface-induced thromboinflammation

Therapeutic medicine today includes a vast number of procedures involving the use of biomaterials, transplantation of therapeutic cells or cell clusters, as well as of solid organs. These treatment modalities are obviously of great benefit to the patient, but also present a great challenge to the innate immune system, since they involve direct exposure of non-biological materials, cells of non-hematological origin as well as endothelial cells, damaged by ischemia-perfusion in solid organs to proteins and cells in the blood. The result of such an exposure may be an inappropriate activation of the complement and contact/kallikrein systems, which produce mediators capable of triggering the platelets and PMNs and monocytes, which can ultimately result in thrombotic and inflammatory (i.e., a thrombo-inflammatory) response to the treatment modality. In this concept review, we give an overview of the mechanisms of recognition within the innate immunity system, with the aim to identify suitable points for intervention. Finally, we discuss emerging and promising techniques for surface modification of biomaterials and cells with specific inhibitors in order to diminish thromboinflammation and improve clinical outcome.

Multifunctional coating based on EPC-specific peptide and phospholipid polymers for potential applications in cardiovascular implants fate

Surface biofunctional modification of cardiovascular implants via the conjugation of biomolecules to prevent thrombosis and restenosis formation and to accelerate endothelialization has attracted considerable research interest.

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.

Chitosan Grafted with Phosphorylcholine and Macrocyclic Polyamine as an Effective Gene Delivery Vector: Preparation, Characterization and In Vitro Transfection

Herein, an effective gene delivery vector phosphorylcholine and macrocyclic polyamine grafted chitosan (PC-g(6)-Cs-g(2)-Cyclen) was developed. Chemical characterization of product PC-g(6)-Cs-g(2)-Cyclen was performed by NMR, FT-IR, gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS) analysis. PC-g(6)-Cs-g(2)-Cyclen could more efficiently bind and protect plasmid DNA than macrocyclic polyamine grafted chitosan (Cs-g-Cyclen) and phosphorylcholine grafted chitosan (Cs-g-PC), as evaluated by agarose gel electrophoresis, circular dichroism spectra, and fluorescence quenching assays. PC-g(6)-Cs-g(2)-Cyclen could wrap DNA into uniform nanoparticles in the size of 112.6 ± 8.5 nm and possessed net cationic charge. UV spectroscopy and MTT assays showed excellent water-solubility and cell viability for PC-g(6)-Cs-g(2)-Cyclen. In addition, three polymer/DNA complexes showed 5.1-15.1-fold greater uptake activity and 10-14-fold higher transfection efficiency in 293 T cells as compared to chitosan/DNA complex, in which PC-g(6)-Cs-g(2)-Cyclen demonstrated the highest transfection activity. These date demonstrated that PC-g(6)-Cs-g(2)-Cyclen is a promising vector candidate for gene delivery.

The CentriMag centrifugal blood pump as a benchmark for in vitro testing of hemocompatibility in implantable ventricular assist devices

Implantable ventricular assist devices (VADs) have proven efficient in advanced heart failure patients as a bridge-to-transplant or destination therapy. However, VAD usage often leads to infection, bleeding, and thrombosis, side effects attributable to the damage to blood cells and plasma proteins. Measuring hemolysis alone does not provide sufficient information to understand total blood damage, and research exploring the impact of currently available pumps on a wider range of blood cell types and plasma proteins such as von Willebrand factor (vWF) is required to further our understanding of safer pump design. The extracorporeal CentriMag (Thoratec Corporation, Pleasanton, CA, USA) has a hemolysis profile within published standards of normalized index of hemolysis levels of less than 0.01 g/100 L at 100 mm Hg but the effect on leukocytes, vWF multimers, and platelets is unknown. Here, the CentriMag was tested using bovine blood (n = 15) under constant hemodynamic conditions in comparison with a static control for total blood cell counts, hemolysis, leukocyte death, vWF multimers, microparticles, platelet activation, and apoptosis. The CentriMag decreased the levels of healthy leukocytes (P < 0.006), induced leukocyte microparticles (P < 10(-5) ), and the level of high molecular weight of vWF multimers was significantly reduced in the CentriMag (P < 10(-5) ) all compared with the static treatment after 6 h in vitro testing. Despite the leukocyte damage, microparticle formation, and cleavage of vWF multimers, these results show that the CentriMag is a hemocompatible pump which could be used as a standard in blood damage assays to inform the design of new implantable blood pumps.

Thromboelastometric and platelet responses to silk biomaterials

Silkworm's silk is natural biopolymer with unique properties including mechanical robustness, all aqueous base processing and ease in fabrication into different multifunctional templates. Additionally, the nonmulberry silks have cell adhesion promoting tri-peptide (RGD) sequences, which make it an immensely potential platform for regenerative medicine. The compatibility of nonmulberry silk with human blood is still elusive; thereby, restricts its further application as implants. The present study, therefore, evaluate the haematocompatibility of silk biomaterials in terms of platelet interaction after exposure to nonmulberry silk of Antheraea mylitta using thromboelastometry (ROTEM). The mulberry silk of Bombyx mori and clinically used Uni-Graft W biomaterial serve as references. Shortened clotting time, clot formation times as well as enhanced clot strength indicate the platelet mediated activation of blood coagulation cascade by tested biomaterials; which is comparable to controls.

Evaluation of the durability and antiadhesive action of 2-methacryloyloxyethyl phosphorylcholine grafting on an acrylic resin denture base material

STATEMENT OF PROBLEM

The polymer 2-methacryloyloxyethyl phosphorylcholine is currently used on medical devices to prevent infection. Denture plaque-associated infection is regarded as a source of serious dental and medical complications in the elderly population, and denture hygiene, therefore, is an issue of considerable importance for denture wearers. Furthermore, because denture bases are exposed to mechanical stresses, for example, denture brushing, the durability of the coating is important for retaining the antiadhesive function of 2-methacryloyloxyethyl phosphorylcholine.

PURPOSE

The purpose of this study is to investigate the durability and antiadhesive activity of two 2-methacryloyloxyethyl phosphorylcholine polymer coating techniques: poly-2-methacryloyloxyethyl phosphorylcholine grafting and poly-2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate coating. It was revealed that 2-methacryloyloxyethyl phosphorylcholine polymer coating of the denture base resin polymethyl methacrylate decreases bacterial biofilm formation.

MATERIAL AND METHODS

Durability was examined by rhodamine staining and elemental surface analysis and by determining the wetting properties of the 2-methacryloyloxyethyl phosphorylcholine polymer-modified polymethyl methacrylate after a friction test that comprised 500 brushing cycles. Antiadhesive activity was examined by using a Streptococcus mutans biofilm formation assay.

RESULTS

Poly-2-methacryloyloxyethyl phosphorylcholine-grafted polymethyl methacrylate retained 2-methacryloyloxyethyl phosphorylcholine units and antiadhesive activity even after repetitive mechanical stress, whereas co-n-butyl methacrylate-coated polymethyl methacrylate did not.

CONCLUSION

These results demonstrated that graft polymerization of 2-methacryloyloxyethyl phosphorylcholine on denture surfaces may contribute to the durability of the coating and prevent microbial retention.

Effect of UV-irradiation intensity on graft polymerization of 2-methacryloyloxyethyl phosphorylcholine on orthopedic bearing substrate

Photoinduced grafting of 2-methacryloyloxyethyl phosphorylcholine (MPC) onto cross-linked polyethylene (CLPE) was investigated for its ability to reduce the wear of orthopedic bearings. We investigated the effect of UV-irradiation intensity on the extent of poly(MPC) (PMPC) grafting, and found that it increased with increasing intensity up to 7.5 mW/cm(2), and the remained fairly constant. It was found to be extremely important to carefully control the UV intensity, as at higher values, a PMPC gel formed via homopolymerization of the MPC, resulting in the formation of cracks at the interface of the PMPC layer and the CLPE substrate. When the CLPE was exposed to UV-irradiation during the graft polymerization process, some of its physical and mechanical properties were slightly changed due to cross-linking and scission effects in the surface region; however, the results of all of the tests exceed the lower limits of the ASTM standards. Modification of the CLPE surface with the hydrophilic PMPC layer increased lubrication to levels that match articular cartilage. The highly hydrated thin PMPC films mimicked the native cartilage extracellular matrix that covers synovial joint surface, acting as an extremely efficient lubricant, and providing high-wear resistance.

The evaluation of leukocytes in response to the in vitro testing of ventricular assist devices

Infection is a clinically relevant adverse event in patients with ventricular assist device (VAD) support. The risk of infection could be linked to a reduced immune response resulting from damage to leukocytes during VAD support. The purpose of this study was to develop an understanding of leukocyte responses during the in vitro testing of VADs by analyzing the changes to their morphology and biochemistry. The VentrAssist implantable rotary blood pump (IRBP) and RotaFlow centrifugal pump (CP) were tested in vitro under constant hemodynamic conditions. Automated hematology analysis of samples collected regularly over 25-h tests was undertaken. A new flow cytometric assay was employed to measure biochemical alteration, necrosis (7-AAD) and morphological alteration (CD45 expression) of the circulating leukocytes during the pumping process. The results of hematology analysis show the total leukocyte number and subset counts decreased over the period of in vitro tests dependent on different blood pumps. The percentage of leukocytes damaged during 6-h tests was 40.8 ± 5.7% for the VentrAssist IRBP, 17.6 ± 5.4% for the RotaFlow CP, and 2.7 ± 1.8% for the static control (all n=5). Flow cytometric monitoring of CD45 expression and forward/side scatter characteristics revealed leukocytes that were fragmented into smaller pieces (microparticles). Scanning electron microscopy and imaging flow cytometry were used to confirm this. Device developers could use these robust cellular assays to gain a better understanding of leukocyte-specific VAD performance.

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.

Grafting of poly(2-methacryloyloxyethyl phosphorylcholine) on polyethylene liner in artificial hip joints reduces production of wear particles

Despite improvements in the techniques, materials, and fixation of total hip arthroplasty, periprosthetic osteolysis, a complication that arises from this clinical procedure and causes aseptic loosening, is considered to be a major clinical problem associated with total hip arthroplasty. With the objective of reducing the production of wear particles and eliminating periprosthetic osteolysis, we prepared a novel hip polyethylene (PE) liner whose surface graft was made of a biocompatible phospholipid polymer-poly(2-methacryloyloxyethyl phosphorylcholine (MPC)). This study investigated the wear resistance of the poly(MPC)-grafted cross-linked PE (CLPE; MPC-CLPE) liner during 15×10(6) cycles of loading in a hip joint simulator. The gravimetric analysis showed that the wear of the acetabular liner was dramatically suppressed in the MPC-CLPE liner, as compared to that in the non-treated CLPE liner. Analyses of the MPC-CLPE liner surface revealed that it suffered from no or very little wear even after the simulator test, whereas the CLPE liners suffered from substantial wears. The scanning electron microscope (SEM) analysis of the wear particles isolated from the lubricants showed that poly(MPC) grafting dramatically decreased the total number, area, and volume of the wear particles. However, there was no significant difference in the particle size distributions, and, in particular, from the SEM image, it was observed that particles with diameters less than 0.50μm were present in the range of the highest frequency. In addition, there were no significant differences in the particle size descriptors and particle shape descriptors. The results obtained in this study show that poly(MPC) grafting markedly reduces the production of wear particles from CLPE liners, without affecting the size of the particles. These results suggest that poly(MPC) grafting is a promising technique for increasing the longevity of artificial hip joints.

Newer-generation ventricular assist devices

The latest generation of ventricular assist devices has evolved from the pulsatile, volume-displacement pumps of the 1990s to today's non-pulsatile, constant pressure-generating rotary pumps. These pumps include both centrifugal and axial flow devices that are currently being used or are in advanced development. Rotary pumps have the advantage of a much longer and more reliable duty life than pulsatile pumps. They are also considerably smaller than pulsatile pumps, requiring less invasive surgery for implantation and smaller transcutaneous (electrical rather than pneumatic) drivelines. Most of these devices have been approved as a bridge to transplant (BTT) while some are currently in trials for destination therapy (DT) in Europe (Conformité Européenne (CE) mark) or the United States (Food and Drug Administration (FDA)). This article discusses the current generation of pumps, examining particular design features as highlighted by the designers as well as the current approval status of each device in the United States and Europe.