Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions

Research and Application of Medical Polyetheretherketone as Bone Repair Material

Polyetheretherketone (PEEK) can potentially be used for bone repair because its elastic modulus is similar to that of human natural bone and good biocompatibility and chemical stability. However, its hydrophobicity and biological inertness limit its application in the biomedical field. Inspired by the composition, structure, and function of bone tissue, many strategies are proposed to change the structure and functionality of the PEEK surface. In this review, the applications of PEEK in bone repair and the optimization strategy for PEEK's biological activity are reviewed, which provides a direction for the development of multifunctional bone repair materials in the future.

Pneumolysin/Plasma Protein Adsorption, Bacterial Adherence, and Cell Adhesion Characteristics of a Cell-Membrane-Mimicking Polymer System

This study delivers the first report on a cell-membrane-mimicking polymer system, poly[oxy(4-(13-cholenoatenonyl)-1,2,3-triazoyl-1-methyl)ethylene-random-oxy(4-(13-phosphorylcholinenonyl)-1,2,3-triazoyl-1-methyl)ethylene] (PGA-Chol_mPC_n) films in various compositions in terms of physicochemical properties, protein adsorptions, bacterial adherences, and human cell adhesions. Higher Chol-containing PGA-Chol_mPC_n in a self-assembled multi-bilayer membrane structure is confirmed to show excellently high affinity to pneumolysin (a cytolysin) and its C-terminal fragment (domain 4) but substantially suppressed affinity to the N-terminal fragment (domains 1-3) and further to plasma proteins. Furthermore, the adherences of pathogenic bacteria are increased favorably; however, the adhesion and proliferation of a human HEp-2 cell line are hindered severely. In contrast, higher-PC-containing PGA-Chol_mPC_n membranes promote HEp-2 cell adhesion and proliferation but significantly suppress the adsorptions of pneumolysin and its fragments and plasma proteins as well as bacterial adherence. The results collectively confirm that PGA-Chol_mPC_n can yield a membrane platform enriched with hydrophobic Chol and hydrophilic and zwitterionic PC moieties in any desired compositions, providing highly selective and sensitive physicochemical characters and biocompatibilities which are demanded for applications in various fields including biomedicine, cosmetics, and environmentally friendly consumer products.

Antifouling Silicone Hydrogel Contact Lenses with a Bioinspired 2-Methacryloyloxyethyl Phosphorylcholine Polymer Surface

Inspired by the cell membrane surface as well as the ocular tissue, a novel and clinically applicable antifouling silicone hydrogel contact lens material was developed. The unique chemical and biological features on the surface on a silicone hydrogel base substrate were achieved by a cross-linked polymer layer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), which was considered important for optimal on-eye performance. The effects of the polymer layer on adsorption of biomolecules, such as lipid and proteins, and adhesion of cells and bacteria were evaluated and compared with several conventional silicone hydrogel contact lens materials. The MPC polymer layer provided significant resistance to lipid deposition as visually demonstrated by the three-dimensional confocal images of whole contact lenses. Also, fibroblast cell adhesion was decreased to a 1% level compared with that on the conventional silicone hydrogel contact lenses. The movement of the cells on the surface of the MPC polymer-modified lens material was greater compared with other silicone hydrogel contact lenses indicating that lubrication of the contact lenses on ocular tissue might be improved. The superior hydrophilic nature of the MPC polymer layer provides improved surface properties compared to the underlying silicone hydrogel base substrate.

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.

Zwitterionic Molecularly Imprinted Cross-Linked Micelles for Alkaloid Recognition in Water

Molecular imprinting within surface/core doubly cross-linked micelles afforded water-soluble nanoparticle receptors for their template molecules. Extremely strong imprinting effects were consistently observed, with the imprinting factor >100:1 in comparison to nonimprinted nanoparticles prepared without the templates. The ionic nature of the cross-linkable surfactant strongly impacted the imprinting and binding process. Imprinted receptors prepared with a zwitterionic cross-linkable surfactant (4) outperformed a similar cationic one (1) when the template was zwitterionic or cationic and preferred their templates over structural analogues regardless of their ionic characteristics. Electrostatic interactions, however, dominated the receptors made with the cationic surfactant. The same micellar imprinting applied to simple as well as complex alkaloids. Imprinted receptors from 4 were also shown to categorize their alkaloid guests according to their structural similarity.

New Aliphatic Glycerophosphoryl-Containing Polyurethanes: Synthesis, Platelet Adhesion and Elution Cytotoxicity Studies

In this study new poly(ether)urethanes (PEUs) based on aliphatic diisocyanates were synthesized with phospholipid-like residues as chain extenders. The primary objective was to prepare new polyurethanes from diisocyanates that are less toxic than the aromatic ones widely used in medical-grade polyurethanes, in order to investigate the effect of the different aromatic or aliphatic hard segment content on the final properties of the materials. Some glycerophospho residues were simultaneously introduced to enhance the hemocompatibility of these materials. Polymers were prepared by a conventional two-step solution polymerization procedure using hexamethylene diisocyanate (HDI) and dodecametilendiisocyanate (DDI) and poly(1,4-butanediol) with molecular weight 1000 to form prepolymers, which were subsequently polymerized with 1-glycerophosphorylcholine (1-GPC) or glycerophosphorylserine (GPS) to act as chain extenders. The reference polymers bearing 1,4-butandiol (BD) were also synthesized. The polymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H NMR), and differential scanning calorimetry (DSC). The hemocompatibility of synthesized segmented polyurethanes was preliminarily investigated by platelet-rich plasma contact studies and related scanning electron microscopy (SEM) photographs as well as by cell viability assay after cell exposure to material elutions to assess the effect of any toxic leachables coming out from the samples. Two of the polymers gave interesting results, suggesting the desirability of further investigation into their possible use in biomedical devices.

Balancing microbial and mammalian cell functions on calcium ion-modified implant surfaces

Implant integration is a complex process mediated by the interaction of the implant surface with the surrounding ions, proteins, bacteria, and tissue cells. Although most implants achieve long-term bone-tissue integration, preventing pervasive implant-centered infections demands further advances, particularly in surfaces design. In this work, we analyzed classical microrough implant surfaces (only acid etched, AE; sandblasted then acid etching, SB + AE) and a new calcium-ion-modified implant surface (AE + Ca) in terms of soft- and hard-tissue integration, bacterial adhesion, and biofilm formation. We cultured on the surfaces primary oral cells from gingiva and alveolar bone, and three representative bacterial strains of the oral cavity, emulating oral conditions of natural saliva and blood plasma. With respect to gingiva and bone cells and in the presence of platelets and plasma proteins, AE + Ca surfaces yielded in average 86% higher adhesion, 44% more proliferation, and triggered 246% more synthesis of extracellular matrix biomolecules than AE-unmodified controls. Concomitantly, AE + Ca surfaces regardless of conditioning with saliva and/or blood plasma showed significantly less bacterial adhesion (67% reduction in average) and biofilm formation (40% reduction in average) than unmodified surfaces. These results highlight the importance of a calcium-rich hydrated interface to favor mammalian cell functions over microbial colonization at implant surfaces. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 421-432, 2018.

Comprehensive genetic analysis of early host body reactions to the bioactive and bio-inert porous scaffolds

To design scaffolds for tissue regeneration, details of the host body reaction to the scaffolds must be studied. Host body reactions have been investigated mainly by immunohistological observations for a long time. Despite of recent dramatic development in genetic analysis technologies, genetically comprehensive changes in host body reactions are hardly studied. There is no information about host body reactions that can predict successful tissue regeneration in the future. In the present study, porous polyethylene scaffolds were coated with bioactive collagen or bio-inert poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB) and were implanted subcutaneously and compared the host body reaction to those substrates by normalizing the result using control non-coat polyethylene scaffold. The comprehensive analyses of early host body reactions to the scaffolds were carried out using a DNA microarray assay. Within numerous genes which were expressed differently among these scaffolds, particular genes related to inflammation, wound healing, and angiogenesis were focused upon. Interleukin (IL)-1β and IL-10 are important cytokines in tissue responses to biomaterials because IL-1β promotes both inflammation and wound healing and IL-10 suppresses both of them. IL-1β was up-regulated in the collagen-coated scaffold. Collagen-specifically up-regulated genes contained both M1- and M2-macrophage-related genes. Marked vessel formation in the collagen-coated scaffold was occurred in accordance with the up-regulation of many angiogenesis-inducible factors. The DNA microarray assay provided global information regarding the host body reaction. Interestingly, several up-regulated genes were detected even on the very bio-inert PMB-coated surfaces and those genes include inflammation-suppressive and wound healing-suppressive IL-10, suggesting that not only active tissue response but also the inert response may relates to these genetic regulations.

Currently available ventricular-assist devices: capabilities, limitations and future perspectives

The continuous progress in ventricular-assist device (VAD) technology and the management of patients with VADs has broadened the treatment options for end-stage heart failure patients. The available line-up of clinical devices provides the current optimal therapies to meet the specific needs of each patient. The extended durability, safety, efficacy and improved quality of life of the patients provides sufficient proof for the VAD to be a likely alternative therapy to heart transplantation. The sequential progress from the first-, to the second- and to the third-generation VAD technology is expected to bring increasing benefits to clinical outcomes. This article reviews the current status, capabilities, limitations and future perspectives of currently available VADs by generally classifying them via support duration, alignment of pump devices and via pulsatile or nonpulsatile mode of perfusion. Furthermore, the future direction of research and development for next-generation VADs is presented based on the lessons learned from currently available VADs.

Reduced platelets and bacteria adhesion on poly(ether ether ketone) by photoinduced and self-initiated graft polymerization of 2-methacryloyloxyethyl phosphorylcholine

Aromatic poly(ether ether ketone) (PEEK) is a super engineering plastic, which has good mechanical properties and is resistant to physical and chemical stimuli. We have, therefore, attempted to use PEEK in cardiovascular devices. Synthetic cardiovascular devices require both high hemocompatibility and anti-inflammatory activity in addition to the mechanical properties. We modified the PEEK surface by photoinduced and self-initiated graft polymerization with 2-methacryloyloxyethyl phosphorylcholine (MPC; PMPC-grafted PEEK) for obtaining good antithrombogenicity. Polymerization was carried out on the surface of PEEK under radiation of ultraviolet (UV) light during which we controlled monomer concentrations, temperatures, and UV intensities. The biological performance of the PMPC-grafted PEEK was examined and compared with that of unmodified PEEK. With increase in the thickness of the PMPC layer, the amount of fibrinogen adsorption decreased significantly in comparison to that in the case of unmodified PEEK. When placed in contact with human platelet-rich plasma, surface of the PMPC-grafted PEEK clearly showed inhibition of platelet adhesion and activation. Also, bacterial adhesion was reduced dramatically on the PMPC-grafted PEEK. Thus, the PMPC grafting on PEEK improved the antithrombogenicity.

Does pelvic mesh treated with phosphorylcholine improve outcomes? An early experience

OBJECTIVES

Implantable devices treated with phosphorylcholine (PC) have been successfully used in cardiac, ophthalmic, and other applications. This surface modification has resulted in a reduction in the host inflammatory responses. This pilot study tested the safety and efficacy of PC treated polypropylene mesh grafts implanted for the treatment of pelvic organ prolapse.

STUDY DESIGN

Surgeons from five U.S. sites collected data on subjects implanted with Perigee IntePro Lite+PC. Pre-procedure data collected included demographics and prolapse severity. At follow-up, subjects were assessed for anatomical outcomes (success≤stage I POPQ or Baden Walker), symptomatic improvement, and complications, particularly mesh exposure.

RESULTS

A total of 40 subjects were enrolled with 80% (32/40) of them completing at least 5-7 months of follow-up. Mean patient age was 60 years (range 36-78 years) and the mean BMI was 28 (range 20-40). There were no cases of mesh exposure/extrusion or granuloma formation. The anatomical success rate was 100% at 5-7 months (32/32).

CONCLUSIONS

This is the first publication on pelvic mesh treated with PC. There were no adverse events attributed to this surface modification. However, as the numbers are small, the results are not statistically significant. PC surface modification of pelvic mesh shows promise in its application for the reduction of mesh related complications.

An implantable biochip to influence patient outcomes following trauma-induced hemorrhage

Following hemorrhage-causing injury, lactate levels rise and correlate with the severity of injury and are a surrogate of oxygen debt. Posttraumatic injury also includes hyperglycemia, with continuously elevated glucose levels leading to extensive tissue damage, septicemia, and multiple organ dysfunction syndrome. A temporary, implantable, integrated glucose and lactate biosensor and communications biochip for physiological status monitoring during hemorrhage and for intensive care unit stays has been developed. The dual responsive, amperometric biotransducer uses the microdisc electrode array format upon which were separately immobilized glucose oxidase and lactate oxidase within biorecognition layers, 1.0-5.0 μm thick, of 3 mol% tetraethyleneglycol diacrylate cross-linked p(HEMA-co-PEGMA-co-HMMA-co-SPA)-p(Py-co-PyBA) electroconductive hydrogels. The device was then coated with a bioactive hydrogel layer containing phosphoryl choline and polyethylene glycol pendant moieties [p(HEMA-co-PEGMA-co-HMMA-co-MPC)] for indwelling biocompatibility. In vitro cell proliferation and viability studies confirmed both polymers to be non-cytotoxic; however, PPy-based electroconductive hydrogels showed greater RMS 13 and PC12 proliferation compared to controls. The glucose and lactate biotransducers exhibited linear dynamic ranges of 0.10-13.0 mM glucose and 1.0-7.0 mM and response times (t(95)) of 50 and 35-40 s, respectively. Operational stability gave 80% of the initial biosensor response after 5 days of continuous operation at 37 °C. Preliminary in vivo studies in a Sprague-Dawley hemorrhage model showed tissue lactate levels to rise more rapidly than systematic lactate. The potential for an implantable biochip that supports telemetric reporting of intramuscular lactate and glucose levels allows the refinement of resuscitation approaches for civilian and combat trauma victims.

Engineering the polymer backbone to strengthen nonfouling sulfobetaine hydrogels

We have demonstrated that molecularly engineering the chemical structure of a monomer can lead to hydrogels with improved mechanical strength. In this case, hydrogels from zwitterionic sulfobetaine methacrylate monomers were compared to sulfobetaine vinylimidazole (pSBVI) hydrogels. We show that the introduction of the vinylimidazole backbone improves the tensile and compressive mechanical properties of the sulfobetaine hydrogel by an order of magnitude over the same properties of a methacrylate hydrogel. Zwitterionic groups have been shown to create surface coating materials with ultralow fouling properties, and we demonstrate here that the presence of the imidazole group does not compromise the nonfouling properties attributed to the zwitterionic sulfobetaine: surfaces coated with pSBVI exhibited exceptionally low nonspecific protein adsorption, and cell adhesion was reduced by 97% relative to low-fouling poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels.

Zwitterionic carboxybetaine polymer surfaces and their resistance to long-term biofilm formation

In this work, we report a systematic study of zwitterionic poly(carboxybetaine methacrylate) (pCBMA) grafted from glass surfaces via atom transfer radical polymerization (ATRP) for their resistance to long-term bacterial biofilm formation. Results show that pCBMA-grafted surfaces are highly resistant to non-specific protein adsorption (fibrinogen and undiluted blood plasma) at 25, 30 and 37 degrees C. Long-term (over 24 h) colonization of two bacterial strains (Pseudomonas aeruginosa PAO1 and Pseudomonas putida strain 239) on pCBMA surface was studied using a parallel flow cell at 25, 30 and 37 degrees C. Uncoated glass cover slips were chosen as the positive reference. Results show that pCBMA coatings reduced long-term biofilm formation of P. aeruginosa up to 240 h by 95% at 25 degrees C and for 64 h by 93% at 37 degrees C, and suppressed P. putida biofilm accumulation up to 192 h by 95% at 30 degrees C, with respect to the glass reference. The ability of pCBMA coatings to resist non-specific protein adsorption and significantly retard bacterial biofilm formation makes it a very promising material for biomedical and industrial applications.

Surface modification of silicone intraocular lens by 2-methacryloyloxyethyl phosphoryl-choline binding to reduce Staphylococcus epidermidis adherence

PURPOSE

To analyse the in vitro adherence of Staphylococcus epidermidis to the 2-methacryloyl oxyethyl phosphorylcholine (MPC)-modified silicone intraocular lens (IOL).

METHODS

The test IOLs were modified by using an air plasma treatment to bind MPC to the surface. The control IOLs were not modified. Chemical changes on the IOL surface were analysed by X-ray photoelectron spectroscopy (XPS) to confirm the covalent binding of MPC. IOL hydrophilicity was determined by measuring the water contact angle. Two different techniques, direct counting of viable adherent bacteria released by sonication, and scanning electron microscopy (SEM), were used to observe and compare the adherence of S. epidermidis to the IOLs after 1- and 18-h incubation.

RESULTS

XPS analysis confirmed that the test IOLs were surface-modified with MPC. The hydrophilicity of the IOLs was improved by surface modification, and the MPC-modified IOLs exhibited significantly reduced adhesion of S. epidermidis (P = 0.002) after an incubation period of 1 h. The SEM results showed that the MPC modification also suppressed the accumulation of bacteria and biofilm production after 18 h incubation.

CONCLUSIONS

MPC-modified hydrophilic silicone IOLs reduce bacterial adherence and colonization, and thus may help reduce the incidence of postoperative endophthalmitis.

Synthesis, platelet adhesion and cytotoxicity studies of new glycerophosphoryl-containing polyurethanes

In this work we synthesized new MDI -based poly(ether)urethanes (PEUs) with phospholipid-like residue as chain extender. Polymers were prepared by a conventional two-step solution polymerization procedure using 4,4' diphenylmethanediisocyanate (MDI) and poly(1,4- butanediol) with 1000 as molecular weight to form prepolymers which were successively polymerized with 1 glycerophosphorylcholine (1-GPC), 2-glycerophosphorylcholine (2-GPC) or glycerophosphorylserine (GPS) as chain extenders. Two reference polymers bearing 1,4-butandiol (BD) have been also synthesized. The polymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and modulated scanning calorimetry (MDSC). The biocompatibility of synthesized segmented polyurethanes was then investigated by platelet-rich plasma contact studies and related scanning electron microscopy (SEM) photographs for blood compatibility and cytotoxicity assay (MTT test) on material elution to assess the effect of any toxic leachables on cellular viability. Three polymers among all have given very satisfactory results suggesting to investigate more deeply their possible use in biomedical devices.

Highly efficient non-biofouling coating of zwitterionic polymers: poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)

This work describes the formation of highly efficient non-biofouling polymeric thin films of poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide), (poly(MPDSAH)). The poly(MPDSAH) films were generated from the self-assembled monolayers terminating in an initiator of atom transfer radical polymerization (ATRP) by the surface-initiated ATRP of MPDSAH. The poly(MPDSAH) films on a gold surface were characterized by ellipsometry, FT-IR spectroscopy, contact angle goniometery, and X-ray photoelectron spectroscopy. The copper complexes and unpolymerized monomers trapped inside the polymer brushes were completely washed out by soaking the poly(MPDSAH)-coated substrate in water at 40 degrees C for 4 days. The amount of proteins nonspecifically adsorbed onto the poly(MPDSAH) films was evaluated by surface plasmon resonance spectroscopy: the adsorption of proteins was <0.6 ng/cm(2) on the surfaces for all the model proteins. The ability of the poly(MPDSAH) films to resist the nonspecific adsorption of proteins was comparable to that of the best known systems.

S. epidermidis biofilm formation: effects of biomaterial surface chemistry and serum proteins

Most infections due to implanted cardiovascular biomaterials are initiated by bacterial adhesion of Staphylococcus epidermidis, followed by colonization and biofilm formation on the surface of the implant. This study examined the role of serum proteins and material surface chemistry in the formation of S. epidermidis biofilm on polyurethanes (Elasthane 80A, hydrophobic) modified with polyethylene oxide (Elasthane 80A-6PEO, hydrophilic) and fluorocarbon (Elasthane 80A-6F, hydrophobic). Initial adhesion, aggregation, biofilm thickness, viability, and slime formation of S. epidermidis strain, RP62A in phosphate buffered saline (PBS), tryptic soy broth (TBS), and 20% pooled human serum was quantified. In the presence of adsorbed serum proteins, initial bacterial adhesion was suppressed significantly to <2% relative to adhesion in TSB or PBS. However, adhesion, aggregation, and proliferation increased dramatically in the 12-24 h period on Elasthane 80A and Elasthane 80A-6F, which resulted in an extensive network of biofilm. A contrasting trend was observed on the hydrophilic Elasthane 80A-6PEO surface, with minimal bacterial adhesion, which decreased steadily over 24 h. In the presence of serum proteins, an increasingly thick ( approximately 20 mum) biofilm formed on the hydrophobic surfaces over 48 h whereas the formation of a mature biofilm on the hydrophilic surface was impeded with few viable bacteria present over 48 h. Furthermore, slime was detected during the initial phase of bacterial adhesion at 2 h and increased over time with the formation of biofilm. These results have shown that while initial S. epidermidis adhesion is suppressed in the presence of adsorbed proteins, inter-bacterial adhesion possibly aided by slime production leads to the formation of a robust mature biofilm. Also, biomaterial surface chemistry affected biofilm formation and, most notably, polyethylene oxide significantly inhibited S. epidermidis biofilm formation over 48 h in vitro.

Antibody immobilization to phospholipid polymer layer on gold substrate of quartz crystal microbalance immunosensor

To modify gold electrode for immunosensor to construct an artificial cell membrane structure, water-soluble amphiphilic phospholipid polymer, poly[2-methacryloyloxyehtyl phosphorylcholine-co-n-butyl methacrylate-co-p-nitrophenyloxycarbonyl poly(ethylene glycol) methacrylate (PMBN)] was applied. The polymer had active ester groups for immobilization of biomolecules and it was converted partially to thiol groups for binding to gold substrates. The partially thiolated PMBN was adsorbed on a gold electrode of quartz crystal microbalance (QCM). Surface characterization of adsorbed PMBN layers was thoroughly investigated with reflectance anisotropy spectroscopy, ellipsometry spectroscopy, dynamic contact angle and X-ray photoelectron spectroscopy measurements. Among several PMBN, having different degree of thiolation, it was concluded that 21.5% thiolated PMBN layer had the most well-ordered phosphorylcholine groups in its outer surface. The proteins adsorption test revealed that the phosphorylcholine group on the outer side of PMBN layers, which was substituted their active ester groups by glycine, showed suppress the non-specific adsorption of proteins, such as bovine serum albumin and gamma-globulin. Also, through antigen-antibody binding evaluation, the anti-C-reactive protein antibody immobilized on the PMBN surface worked well and it was confirmed that denaturation of the antibody on the PMBN layers was hardly occurred in spite of 60 days storage at 4 degrees C. The antibody conjugated phospholipid polymer layer with well-ordered phosphorylcholine group could be outstanding functional membrane for biomedical diagnostic devices without non-specific binding and reduction of immunologic activity of immobilized antibody.

Phospholipids as implant coatings

Bio-interfaces such as bio-membranes are of outmost importance for a variety of live processes. Among them are cell-interactions which take place in, on or through cell membranes. Therefore we propose to cover metallic surfaces with phospholipids to facilitate cell-material interaction. Four lipids, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2- oleoyl-sn-glycero-3-[phospho-L-serine] (POPS) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (POPG), were applied to four metallic growth substrates with different surface structure, roughness and porosity. The interaction of the osteosarcoma cell line MG-63 was investigated in terms of cell adhesion and viability (MTT (methylthiazolyldiphenyl-tetrazolium bromide) assay). While POPS in general had a negative influence, the most suitable combination in terms of viability per adherent MG-63 is the coating of porous Ti6Al4V material with the phospholipids POPE or POPC. The analysis of viability of mouse macrophages RAW 264.7 and their tumor necrosis factor alpha (TNF-alpha) release showed that the adhesion and viability is worst on POPS while the TNF-alpha release was highest. To elucidate the potential of phospholipids to prevent or support bacterial growth, the bacterial number of Gram positive and Gram negative bacteria was investigated. For lipid concentrations higher than 1 mM in solution a growth stimulating effect independent of the lipid type was detected. On a lipid coated surface the number of bacteria was reduced by 81%, 74% and 51% for POPC, POPG and POPE.

Photoinduced phospholipid polymer grafting on Parylene film: Advanced lubrication and antibiofouling properties

Poly(p-xylylene) (Parylene C) coatings have been applied in implantable electronic devices because of their electrical insulation and moisture barrier properties. To provide lubrication and an antibiofouling surface, a biomimetic phospholipid polymer--poly(2-methacryloyloxyethyl phosphorylcholine (MPC))--was grafted from the surface using UV irradiation with benzophenone as an initiator. The poly(MPC) grafting on the Parylene C films was confirmed by attenuated total reflection-Fourier transfer inflated irradiation, X-ray photoelectron spectroscopy and ellipsometry. These analyses indicated that the Parylene C films were completely covered by the poly(MPC)-graft layer with an average thickness of 140 nm under dry condition. The atomic force microscope (AFM) images revealed that the poly(MPC)-graft chains extended under wet condition. However, they formed globular structures under dry condition. Water contact angle measurements revealed a decreased receding angle of 29.5 degrees on the poly(MPC)-grafted surface with a high hysteresis of 41.4 degrees. These results indicate that the poly(MPC)-graft chains gain mobility in a wet environment. The average kinetic friction coefficient of the poly(MPC)-grafted surface in water was 0.018, which was 90% lower than that of the original surface. The in vitro single protein adsorption reduced by over 70% due to the poly(MPC) grafting. The hydrated poly(MPC)-graft chains are considered to provide lubrication and antibiofouling properties. The surface zeta potential measurement clarified the electroneutrality of the poly(MPC)-grafted surface. We concluded that the poly(MPC) grafting from the Parylene C layer significantly improved its surface properties and, subsequently, its biological properties.

Biocompatibility and drug release behavior of spontaneously formed phospholipid polymer hydrogels

Hydrogels containing 2-methacryloyloxyethyl phosphorylcholine (MPC) moieties were formed from aqueous solutions with water-soluble MPC polymers with carboxylic acid and alkyl groups because of hydrogen bonding formation. To investigate the biocompatibility and drug release behavior of the hydrogels, we used random- and block-type carboxylic acid MPC polymers, such as poly [MPC-co-methacrylic acid (MA)] (rPMA), poly[MPC-co-4-(2-methacryloyloxyethyl) trimellitic acid (MET)] (rPMT), poly (MA-block-MPC-block-MA) (bPMA) and poly(MET-block-MPC-block-MET) (bPMT), and alkyl MPC polymers, such as poly[MPC-co-n-butyl methacrylate] (PMB) and poly(MPC-co-benzyl methacrylate) (PMBz). We investigated the biocompatibility of the spontaneously formed MPC polymer hydrogels by a hemolysis test and an in vivo injection test. The random MPC polymers having carboxylic acid groups expressed more hemolytic activity compared to the block polymers. The results of the in vivo injection test also indicated low biocompatibility of the carboxylic acid polymers especially at high concentration. The alkyl MPC polymers, the PMB and PMBz showed excellent biocompatibility in both hemolysis and in vivo injection test. However, the hydrogels, the rPMA/PMB hydrogel (rABgel) and the rPMT/PMBz hydrogel (rTZgel) lowered the hemolytic activity of elemental polymers, the rPMA and rPMT. Thus, suppression of the ionization of the carboxylic acid groups is necessary for biocompatibility. We also investigated the drug release behavior with attention to the interaction between the polymer and the drugs. The release behavior of a relatively low-molecular-weight hydrophilic drug, 5-fluorouracil, did not depend on the structure of the polymers. The higher-molecular-weight drugs, ketoprofen and indomethacin, were released faster from the block polymer hydrogel than the random polymer hydrogel, the rABgel, while the highest-molecular-weight drug, doxorubicin, was released faster from the random polymer hydrogel. A probable reason for this is the difference in the molecular structure; that is, the separated hydrophilic and hydrophobic sections in the block polymers constructed pathways where a drug can diffuse. In addition, the rTZgel suppressed the release of a drug with a large number of aromatic rings probably because of the stacking effect. The results of the compression test also suggested the existence of the stacking effect between the rTZgel and the drugs. Based on these results, control of drug release is possible by selecting a reservoir with an appropriate chemical structure to interact with the drug. For example, release of a relatively linear-structured drug with less aromatic rings can be suppressed in the rABgel rather than in the rTZgel. Thus, it can be concluded that if the ionization is suppressed, these MPC polymer hydrogels can be used as a material for a drug reservoir that can be selected according to the drug.

Dual mode bioreactions on polymer nanoparticles covered with phosphorylcholine group

We investigated the preparation of polymer nanoparticles covered with phosphorylcholine (PC) groups and the immobilization of proteins in order to observe dual mode bioreactions on the nanoparticles. For the surface modification on the nanoparticles, a water-soluble amphiphilic phospholipid polymer with PC groups as a hydrophilic moiety was synthesized. In this polymer, an active ester group, which can immobilize proteins, was introduced. Using the phospholipid polymer as a solubilizer, poly(L-lactic acid) nanoparticles were prepared from its methylene chloride solution in an aqueous medium by the solvent evaporation method. The diameter of the nanoparticles was ca. 200 nm and the surface was covered with the PC groups and active ester groups. Proteins could immobilize on the nanoparticles under mild conditions by the reaction between the active ester group and amino group in the proteins. Both an antibody and enzyme were immobilized on the nanoparticles and bioreactions such as the antigen/antibody reaction and enzymatic reaction were observed. When an antigen was added to the suspension of the nanoparticles, aggregation of the nanoparticles occurred and then they precipitated. Also, the enzymatic reaction proceeded well when the enzyme substrate was added to the suspension. Based on these results, we provided polymer nanoparticles functionalized with both the antibody and enzyme, and the dual mode bioreactions could occur. We concluded that the novel polymer nanoparticles could be used for nano-/micro-scaled diagnostic and medical treatment systems.