Physical property analysis and bacterial adhesion on a series of phosphonated polyurethanes

Functional Zwitterionic Polyurethanes: State-of-the-Art Review

Recent advancements in bioengineering and medical devices have been greatly influenced and dominated by synthetic polymers, particularly polyurethanes (PUs). PUs offer customizable mechanical properties and long-term stability, but their inherent hydrophobic nature poses challenges in practically biological application processes, such as interface high friction, strong protein adsorption, and thrombosis. To address these issues, surface modifications of PUs for generating functionally hydrophilic layers have received widespread attention, but the durability of generated surface functionality is poor due to irreversible mechanical wear or biodegradation. As a result, numerous researchers have investigated bulk modification techniques to incorporate zwitterionic polymers or groups onto the main or side chains of PUs, thereby improving their hydrophilicity and biocompatibility. This comprehensive review presents an extensive overview of notable zwitterionic PUs (ZPUs), including those based on phosphorylcholine, sulfobetaine, and carboxybetaine. The review explores their wide range of biomedical applications, from blood-contacting devices to antibacterial coatings, fouling-resistant marine coatings, separation membranes, lubricated surfaces, and shape memory and self-healing materials. Lastly, the review summarizes the challenges and future prospects of ZPUs in biological applications.

A practical review on the measurement tools for cellular adhesion force

Cell-cell and cell-matrix adhesions are fundamental in all multicellular organisms. They play a key role in cellular growth, differentiation, pattern formation and migration. Cell-cell adhesion is substantial in the immune response, pathogen-host interactions, and tumor development. The success of tissue engineering and stem cell implantations strongly depends on the fine control of live cell adhesion on the surface of natural or biomimetic scaffolds. Therefore, the quantitative and precise measurement of the adhesion strength of living cells is critical, not only in basic research but in modern technologies, too. Several techniques have been developed or are under development to quantify cell adhesion. All of them have their pros and cons, which has to be carefully considered before the experiments and interpretation of the recorded data. Current review provides a guide to choose the appropriate technique to answer a specific biological question or to complete a biomedical test by measuring cell adhesion.

Developing a synthetic composite membrane for cleft palate repair

An oronasal fistula is a passage between the oral and nasal cavity. Currently, surgical procedures use mucosal flaps or collagen grafts to make a barrier between oral and nasal cavities. Our aim was to develop a cell-free synthetic repair material for closure of nasal fistulas. We surface functionalized electrospun polyurethane (PU) and poly-L-lactic acid (PLLA) and composite polymer (PU-PLLA) membranes with acrylic acid through plasma polymerization. Membranes were treated in a layer-by-layer approach to develop highly charged electrostatic layer that could bind heparin as a pro-angiogenic glycosaminoglycan. The properties were evaluated through physical, chemical, and mechanical characterization techniques. Cytotoxicity was tested with MC3T3 pre-osteoblast cell lines for 3, 7, and 14 days, and vasculogenesis was assessed by implantation into the chorio-allantoic membrane in chick embryos for 7 days. In vivo biocompatibility was assessed by subcutaneous implantation in rats for 1, 3, and 6 weeks. The membranes consisted of random fibers of PLLA-PU with fiber diameters of 0.47 and 0.12 μm, respectively. Significantly higher cell proliferation and migration of MC3T3 cells at 3, 7, and 14 days were shown on plasma-coated membranes compared with uncoated membranes. Further, it was found that plasma-coated membranes were more angiogenic than controls. In vivo implantation of membranes in rats did not reveal any gross toxicity to the materials, and wound healing was comparable with the native tissue repair (sham group). We therefore present a plasma-functionalized electrospun composite polymer membrane for use in the treatment of fistulas. These membranes are flexible, non-cytotoxic, and angiogenic, and we hope it should lead to permanent closure of oronasal fistula.

Modern Strategies in the Prevention of Implant-Associated Infections

The application of medical devices either for temporary or permanent use has become an indispensible part of almost all fields of medicine. However, foreign bodies are associated with a substantial risk of bacterial and fungal infections. Implant-associated infections significantly contribute to the still increasing problem of nosocomial infections.

To reduce the incidence of such infections, specific guidelines providing evidence-based recommendations and comprising both technological and nontechnological strategies for prevention have been established. Strict adherence to hygienic rules during insertion or implantation of the device are aspects of particular importance. Besides such basic and indispensable aspects, the development of new materials which could withstand microbial adherence and colonization has become a major topic in recent years. Modification of surface by primarily physico-chemical methods may lead to a change in specific and unspecific interactions with microorganisms and, thus, to a reduction in microbial adherence. Medical devices made out of a material that would be ideally antiadhesive or at least colonization-resistant would be the most suitable candidates to avoid colonization and subsequent infection. However, it appears impossible to create a surface with an absolute “zero”-adherence due to thermodynamical reasons and due to the fact that a modified material surface is in vivo rapidly covered by plasma and connective tissue proteins. Therefore, another concept for the prevention of implant-associated infections involves the impregnation of devices with various antimicrobial substances such as antibiotics, antiseptics, and/or metals.

In fact, already commercially available materials for clinical use such as antimicrobial catheters have been introduced, in part with considerable impact on subsequent infections. However, future studies are warranted to translate the knowledge on the pathogenesis of device-associated infections into applicable prevention strategies.

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.

Review: Antimicrobial efficacy validation using in vitro and in vivo testing methods

Pre-clinical antimicrobial validation testing for single and combination products, and parameters that should be considered when testing the antimicrobial performance of a medical device, are discussed. Guidance is provided on key elements required for in vitro and in vivo antimicrobial validation, including validation of microbial growth, microbial recovery, neutralization, and antimicrobial activity. An important consideration, both in terms of practicality and economics, is designing in vitro studies that bridge to in vivo testing: A representative in vitro model is used to generate data on many clinically relevant microorganisms, and then one microorganism is selected for use in in vivo testing. If the in vivo results correlate to the in vitro results, it can reasonably be extrapolated that the same would be true for the remaining microorganisms tested in vitro. Thus, the selection of relevant in vitro models for testing is critical for successful antimicrobial validation testing.

Addressing skin abrasions on artificial turfs with zwitterionic polymer brushes

Zwitterionic polymer brushes were investigated for their skin-friendliness outside of the common aqueous environment, exhibiting superior lubrication and antifouling properties.

Graphene as a chain extender of polyurethanes for biomedical applications

Chemically tagged graphene nanohybrid for a controlled drug delivery vehicle.

Introducing a semi-coated model to investigate antibacterial effects of biocompatible polymers on titanium surfaces

Peri-implant infections from bacterial biofilms on artificial surfaces are a common threat to all medical implants. They are a handicap for the patient and can lead to implant failure or even life-threatening complications. New implant surfaces have to be developed to reduce biofilm formation and to improve the long-term prognosis of medical implants. The aim of this study was (1) to develop a new method to test the antibacterial efficacy of implant surfaces by direct surface contact and (2) to elucidate whether an innovative antimicrobial copolymer coating of 4-vinyl-N-hexylpyridinium bromide and dimethyl(2-methacryloyloxyethyl) phosphonate (VP:DMMEP 30:70) on titanium is able to reduce the attachment of bacteria prevalent in peri-implant infections. With a new in vitro model with semi-coated titanium discs, we were able to show a dramatic reduction in the adhesion of various pathogenic bacteria (Streptococcus sanguinis, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis), completely independently of effects caused by soluble materials. In contrast, soft tissue cells (human gingival or dermis fibroblasts) were less affected by the same coating, despite a moderate reduction in initial adhesion of gingival fibroblasts. These data confirm the hypothesis that VP:DMMEP 30:70 is a promising antibacterial copolymer that may be of use in several clinical applications.

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

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

Polyurethanes containing zwitterionic sulfobetaines and their molecular chain rearrangement in water

Novel polyurethanes with zwitterionic sulfobetaines, termed PUR-APS, were designed and synthesized by chain-extension of biodegradable poly(ε-caprolactone) containing N,N'-bis (2-hydroxyethyl) methylamine ammonium propane sulfonate (PCL-APS) with hexamethylene diisocyanate (HDI). The bulk properties of polymers were characterized by nuclear magnetic resonance spectrum (NMR), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatograph (GPC), and differential scanning calorimetry (DSC). Results showed that the polymers were successfully synthesized. Water contact angles (WCAs) and X-ray photoelectron spectroscopy (XPS) revealed that molecular chains of the polymers rearranged after soaking in water. The amount of protein adsorption, determined by bicinchoninic acid (BCA) assay, was less than 300 ng/cm(2) and decreased after hydration. The blood compatibility of the polymers was evaluated by the degree of hemolytic and activated partial thromboplastic time (APTT) and prothrombin time (PT). Results indicated that PUR-APS polymers had good blood compatibility. Therefore, polyurethanes containing sulfobetaines have a great potential for biomedical application.

Rechargeable biofilm-controlling tubing materials for use in dental unit water lines

A simple and practical surface grafting approach was developed to introduce rechargeable N-halamine-based antimicrobial functionality onto the inner surfaces of continuous small-bore polyurethane (PU) dental unit waterline (DUWL) tubing. In this approach, tetrahydrofuran (THF) solution of a free-radical initiator, dicumyl peroxide (DCP), flowed through the PU tubing (inner diameter of 1/16 in., or 1.6 mm) to diffuse DCP into the tubing's inner walls, which was used as initiator in the subsequent grafting polymerization of methacrylamide (MAA) onto the tubing. Upon chlorine bleach treatment, the amide groups of the grafted MAA side chains were transformed into acyclic N-halamines. The reactions were confirmed with attenuated total reflectance infrared (ATR) spectra and iodometric titration. The mechanical properties of the tubing were not significantly affected by the grafting reactions. The biofilm-controlling function of the new N-halamine-based PU tubing was evaluated with Pseudomonas aeruginosa (P. aeruginosa), one of the most isolated water bacteria from DUWLs, in a continuous bacterial flow model. Bacteria culturing and SEM studies showed that the inner surfaces of the new N-halamine-based PU tubing completely prevented bacterial biofilm formation for at least three to four weeks. After that, bacteria began to colonize the tubing surface. However, the lost function was fully regenerated by exposing the tubing inner surfaces to diluted chlorine bleach. The recharging process could be repeated periodically to further extend the biofilm-controlling duration for long-term applications.

Synthesis of a novel biodegradable polyurethane with phosphatidylcholines

A novel polyurethane was successfully synthesized by chain-extension of biodegradable poly (l-lactide) functionalized phosphatidylcholine (PC) with hexamethylene diisocyanate (HDI) as chain extender (PUR-PC). The molecular weights, glass transition temperature (Tg) increased significantly after the chain-extension. The hydrophilicity of PUR-PC was better than the one without PC, according to a water absorption test. Moreover, the number of adhesive platelets and anamorphic platelets on PUR-PC film were both less than those on PUR film. These preliminary results suggest that this novel polyurethane might be a better scaffold than traditional biodegradable polyurethanes for tissue engineering due to its better blood compatibility. Besides, this study also provides a new method to prepare PC-modified biodegradable polyurethanes.

Colorimetric Assay and Antibacterial Activity of Cotton, Silk, and Wool Fabrics Dyed with Peony, Pomegranate, Clove, Coptis chinenis and Gallnut Extracts

To investigate the antibacterial functionality of natural colorant extracts, five kinds of natural dying aqueous solutions were obtained by extraction from peony, pomegranate, clove, Coptis chinensis and gallnut using water at 90 °C for 90 min with a liquor ratio (solid natural colorant material/water, weight ratio) of 1:10. The colorimetric assay and antibacterial activity of cotton, silk, and wool fabrics dyed with these natural colorant extracts were examined. It was found that these properties were significantly dependent on the structure of colorant and the kind of fabrics. The hues (H) of all fabrics dyed with these natural colorants were in the range of 6.05YR -1.95Y. The order of value (V) was wool, silk and cotton. The chroma (C) of all samples was found to be at very low levels indicating the natural tone. All the fabrics dyed with the five natural colorants (peony, pomegranate, clove, Coptis chinensis and gallnut) extracts displayed excellent antibacterial activity (reduction rate: 96.8 - 99.9%) against Staphylococcus aureus. However, in the case of Klebsiella pneumoniae, the antibacterial activity was found to depend on the kind of natural colorant extract used.

AcyclicN-halamine-based biocidal tubing: Preparation, characterization, and rechargeable biofilm-controlling functions

In this study, the surfaces of polypropylene tubing were hydroxylated with potassium persulfate. The resultant tubing surfaces were grafted with methacrylamide (MAA) using ceric(IV) ammonium nitrate as an initiator. Upon chlorination treatment with diluted chlorine bleach, some of the amide groups in the grafted MAA side chains were transformed into stable acyclic N-halamines. The reactions were confirmed with attenuated total reflectance infrared, X-ray photoelectron spectra, and iodimetric titration. The resultant tubing was challenged with Pseudomonas aeruginosa (P. aeruginosa) in a continuous flowing model. Bacteria culturing and scanning electron microscope studies showed that the chlorinated MAA-grafted tubing could provide potent and rechargeable biofilm-controlling functions against the test microorganisms.

Use of telechelic cis-1,4-polyisoprene cationomers in the synthesis of antibacterial ionic polyurethanes and copolyurethanes bearing ammonium groups

New crosslinked ionic polyurethanes and copolyurethanes were yielded by reaction of telechelic cis-1,4-oligoisoprenes, bearing a variable number of ammonium and hydroxy groups, with isocyanurate of isophorone diisocyanate (I-IPDI). Aiming for a comparative study, polyurethane elastomers based on non-ionic telechelic oligomers were also synthesized. Thermo-mechanical behavior and crosslinking density of these three families of materials were investigated by DMTA and swelling test, respectively. Surface properties were examined by static contact angle measurements and AFM imaging. The bactericidal activity of the polymers was investigated by enumerating living Pseudomonas aeruginosa on material surfaces and on water suspensions. The number of attached living bacteria was found to depend on the chemical structure of the material and on the contact time between the microorganisms and the surface. An exclusive bactericidal activity was obtained with the ionic copolyurethane family. Materials with weak crosslinking density were found to release bactericidal moieties. The abilities of the polymers to prevent bacterial growth were examined through zone of inhibition experiments against P. aeruginosa, which shown a bacteriostatical effect for each synthesized material. These experiments were not sufficiently sensitive to detect the leaching of bactericidal moieties from the materials with weak crosslinking density. When the zone of inhibition experiments was performed on more sensitive bacteria, namely Staphylococcus epidermidis, the leaching of bactericidal moieties as well as bacteriostatic effect was detected. This work demonstrates the potentiality for making functional biomaterials from natural rubber, a renewable resource.

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.

Infections associated with medical devices: pathogenesis, management and prophylaxis

The insertion or implantation of foreign bodies has become an indispensable part in almost all fields of medicine. However, medical devices are associated with a definitive risk of bacterial and fungal infections. Foreign body-related infections (FBRIs), particularly catheter-related infections, significantly contribute to the increasing problem of nosocomial infections. While a variety of micro-organisms may be involved as pathogens, staphylococci account for the majority of FBRIs. Their ability to adhere to materials and to promote formation of a biofilm is the most important feature of their pathogenicity. This biofilm on the surface of colonised foreign bodies is regarded as the biological correlative for the clinical experience with FBRI, that is, that the host defence mechanisms often seem to be unable to handle the infection and, in particular, to eliminate the micro-organisms from the infected device. Since antibacterial chemotherapy is also frequently not able to cure these infections despite the use of antibacterials with proven in vitro activity, removal of implanted devices is often inevitable and has been standard clinical practice. However, in specific circumstances, such as infections of implanted medical devices with coagulase-negative staphylococci, a trial of salvage of the device may be justified. All FBRIs should be treated with antibacterials to which the pathogens have been shown to be susceptible. In addition to systemic antibacterial therapy, an intraluminal application of antibacterial agents, referred to as the 'antibiotic-lock' technique, should be considered to circumvent the need for removal, especially in patients with implanted long-term catheters. To reduce the incidence of intravascular catheter-related bloodstream infections, specific guidelines comprising both technological and nontechnological strategies for prevention have been established. Quality assurance, continuing education, choice of the catheter insertion site, hand hygiene and aseptic techniques are aspects of particular interest. Furthermore, all steps in the pathogenesis of biofilm formation may represent targets against which prevention strategies may be directed. Alteration of the foreign body material surface may lead to a change in specific and nonspecific interactions with micro-organisms and, thus, to a reduced microbial adherence. Medical devices made out of a material that would be antiadhesive or at least colonisation resistant would be the most suitable candidates to avoid colonisation and subsequent infection. Another concept for the prevention of FBRIs involves the impregnation of devices with various substances such as antibacterials, antiseptics and/or metals. Finally, further studies are needed to translate the knowledge on the mechanisms of biofilm formation into applicable therapeutic and preventive strategies.

Properties of phospholipid monolayer deposited on a fluorinated polyurethane

A simple procedure for surface modification of polyurethane by the Langmuir-Blodgett (LB) method using the amphiphile 1,2-distearoyl-sn-glycero-3-phosphocholine dihydrate (DSPC) was developed. The polyurethane containing the fluorinated moiety was prepared via the perfluoro-containing chain extender 2,2,3,3-tetrafluoro-1,4-butanediol. The fluorinated polyurethane (FPU) films were prepared by spin coating and dipping methods. The spin-coated FPU films exhibited hydrophobic characteristic and, thus, enhanced the transferability of DSPC. Held at constant pressure of 45 mN/m, the DSPC monolayer was transferred successfully to FPU films with a near-unity transfer ratio. The in vitro platelet adhesion assay revealed that the FPU modified with DSPC monolayer was more platelet compatible than the unmodified FPU substrates with no pseudopods and flattening of adherent platelets as well as lower platelet adhesion density. Moreover, the DSPC monolayer remained intact after platelet adhesion testing. In addition, the platelet compatibility of the unmodified FPU was affected by the film preparation methods. This might be attributed to the distinctive surface micromorphology formed. This simple DSPC deposition scheme by a LB technique would be very useful to further enhance the platelet compatibility of hydrophobic substrate and can be utilized for biomedical application in which the flow shear rate is not too high.

Novel dendrimer based polyurethanes for PEO incorporation

A series of segmented polyurethanes based on methylene diisocyanate/poly (tetramethylene oxide) and chain extended with either ethylene diamine or butane diol in combination with a generation 2 polypropylenimine octaamine dendrimer were synthesized. For polymer synthesis, the dendrimers were protected with either t-boc or Fmoc groups and were incorporated into the polyurethane microstructure to permit further functionalization with biologically active groups. Following deprotection, the dendrimers were reacted with succinimidyl propionate polyethylene oxide (SPA-PEO) to improve the protein resistance of the polymers and to examine the potential of this technique for polymer functionalization. Different synthesis techniques were examined to optimize the incorporation of the PEO into the polymer microstructure. Incorporation of the dendrimers and the PEO were confirmed by NMR and FTIR. Gel permeation chromatography was used to examine the molecular weights of the various polyurethanes. The dendrimer incorporated polymers had significantly lower molecular weights than the ED or BDO chain extended controls, likely due to lower reactivity of the dendrimers as a result of steric factors. Following PEO reaction, the molecular weights of the resultant polymers were consistent with the levels of PEO incorporation noted by comparison of peak intensities in the NMR spectra. Due to the highly hydrophilic nature of the PEO, some migration to the polymer surface was expected. Water contact angles and XPS, used to characterize the surfaces, suggest that there was some PEO enrichment at the surface of the polymers. Adsorption of radiolabeled fibrinogen to the polymer surfaces was decreased by a factor of approximately 40% in some of the PEO incorporated polymers. There were also differences in the patterns of plasma protein adsorption on the various surfaces as evaluated by SDS PAGE and immunoblotting. Therefore, the use of dendrimers in biomaterials for incorporation of a large number of functional groups seems to be promising.

Cell adhesion on supported lipid bilayers

The cell and protein repellent properties of supported phospholipid bilayer (SPB) membranes were investigated. The SPBs were prepared by vesicle adsorption on SiO(2) surfaces. The vesicles of phosphatidylcholine fuse and rupture, and form a supported bilayer covering the surface. We carried out cell culture experiments on several surfaces, including SPBs, using two types of epithelial cells to address the cell adhesional properties. The Quartz Crystal Microbalance Dissipation (QCM-D) technique was used to monitor the SPB formation and subsequent protein adsorption. Neither cell type adhered or proliferated on SiO(2) surfaces coated with SPBs, whereas both cell types adhered and proliferated on the three control surfaces of SiO(2), tissue culture glass, and TiO(2). The QCM-D measurements showed that about two orders of magnitude less mass adsorbed on a SPB surface compared to a TiO(2) surface, from serum-containing media (10% fetal bovine serum). The reduced adsorption on the SPB is a likely explanation for the nondetectable epithelial cell adhesion on the SPB surface. Biomembranes are therefore attractive candidate systems to achieve alternating cell-resistant and cell-interacting regions on surfaces, by including specific cell-binding proteins in the latter regions.

In vitro interactions of biomedical polyurethanes with macrophages and bacterial cells

Three commercial medical-grade polyurethanes (PUs), a poly-ether-urethane (Pellethane), and two poly-carbonate-urethanes, the one aromatic (Bionate) and the other aliphatic (Chronoflex), were tested for macrophages and bacterial cells adhesion, in the presence or absence of adhesive plasma proteins. All the experiments were carried out on PUs films obtained by solvent casting. The wettability of these films was analysed by measuring static contact angles against water. The ability of the selected PUs to adsorb human fibronectin (Fn) and fibrinogen (Fbg) was checked by ELISA with biotin-labelled proteins. All PUs were able to adsorb Fn and Fbg (Fn > Fbg). Fn adsorption was in the order: Pellethane > Chronoflex > Bionate, the highest Fbg adsorption being detected onto Bionate (Bionate > Chronoflex > Pellethane). The human macrophagic line J111, and the two main bacterial strains responsible for infection in humans (Staphylococcus aureus Newman and Staphylococcus epidermidis 14852) were incubated in turn with the three PUs, uncoated or coated with plasma proteins. No macrophage or bacterial adhesion was observed onto uncoated PUs. PUs coated with plasma, Fn or Fbg promoted bacterial adhesion (S. aureus > S. epidermidis), whereas macrophage adhered more onto PUs coated with Fn or plasma. The coating with Fbg did not promote cell adhesion. Pellethane showed the highest macrophage activation (i.e. spreading), followed, in the order, by Bionate and Chronoflex.

Antithrombogenic polymer alloy composed of 2-methacryloyloxyethyl phosphorylcholine polymer and segmented polyurethane

To evaluate the antithrombogenicity of a new polymeric biomaterial in vivo, a polymer alloy tube composed of poly[2-methacryloyloxyethyl phosphorylcholine(MPC)-co-2-ethylhexyl methacrylate](PMEH) polymer and a segmented polyurethane (SPU) was prepared by a solvent evaporation method on a Teflon rod from a homogeneous solution containing both the PMHE and SPU. The composition of the PMEH vs the SPU was 10 wt%. The inner and outer surfaces of the polymer alloy tubing were characterized by X-ray electron spectroscopic (XPS) measurements. The MPC units were located on the inner surface of the polymer alloy tubing rather than the outer surface. After immersion in aqueous media, a higher concentration of the MPC units was observed on both surfaces. Selective staining of the MPC units with osmium tetraoxide was carried out to observe the morphology of the PMEH domain on the surface of the polymer alloy. There were large-sized PMEH domains on the inner surface of the tubing but small-sized domains were found on the outer surface. This result was in good agreement with the XPS results. Blood compatibility of the polymer alloy was evaluated by observation of fibrinogen adsorption and platelet adhesion from human plasma. A lot of fibrinogen was adsorbed and many platelets adhered to the inner surface of the original SPU tubing. On the other hand, the PHEH/SPU polymer alloy tubing suppressed these adsorptions and adhesions. When the PMEH/SPU polymer alloy tubing was implanted into a rabbit's artery, thrombus could not be observed even after a 7-day implantation but the original SPU tubing was almost totally occluded only after a 90-min implantation due to serious thrombus deposition on the surface. These results clearly indicated that the PMEH in the SPU matrix acted as an antithrombus reagent by suppression of protein adsorption and platelet adhesion and activation. Particularly, the MPC units played a significant role in this function.

The influence of thrombus components in mediating bacterial adhesion to biomaterials

Thrombosis and infection represent the two largest limiting factors determining the long term success of implanted biomaterials. Infections associated with biomaterials are difficult to treat, and appear to evade the host defense systems. Mechanisms relating infection to thrombosis are described. Investigations into the role of receptors in mediating adhesion to thrombi are also discussed, in addition to strategies to reduce bacterial adhesion to biomaterial surfaces.

Synthesis and characterization of non-leaching biocidal polyurethanes

The biocidal activities of a series of quaternized polyurethanes were examined against Staphylococcus aureus and Escherichia coli. The percentage of dead cells on a surface was found to depend on the alkyl halide used for quaternization, the concentration of quaternized moieties in the polyurethane, the gram-type of the microorganism, and the contact time of the organism with the surface. N,N-bis(2-hydroxyethyl)isonicotinamide (BIN) was incorporated as the chain extender in a series of poly(tetramethylene oxide)-based polyurethane block copolymers. Three families of materials were synthesized that contained increasing hard segment fractions and therefore increasing concentrations of BIN. The pyridine ring in BIN was quaternized with a variety of alkyl halides to form cationic polyurethanes that possessed biocidal activity. The effect of quaternization on material properties was examined with tensile testing, water absorption analysis, and contact angle measurements. The antibacterial action of the polymers was investigated with zone of inhibition experiments and fluorescence microscopy, which was established as a reliable technique to determine the viability of organisms attached to a polymer surface.

Photoinduced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine on polyethylene membrane surface for obtaining blood cell adhesion resistance

Phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)], was grafted with polyethylene (PE) membrane using photoinduced polymerization technique to make the membrane resistant to cell adhesion. The water contact angle on the PE membrane grafted with poly(MPC) decreased with an increase in the photopolymerization time. This decrease corresponded to the increase in the amount of poly(MPC) grafted on the PE surface. The same graft polymerization procedure was applied using other hydrophilic monomers, such as acrylamide (AAm), N-vinylpyrrolidone (VPy) and methacryloyl poly(ethylene glycol) (MPEG). These monomers were also polymerized to form grafted chains on the PE membrane, and the grafting was confirmed with X-ray photoelectron spectroscopy. Analysis of amount and distribution of plasma proteins at the plasma-contacting surface of the original and the modified PE membranes were analyzed using immunogold assay. The grafting of poly(MPC) and poly(VPy) on PE membrane reduced the plasma protein adsorption significantly compared with that on the original PE membrane. However, the PE membranes grafted with poly(AAm) or poly(MPEG) did not show any effects on protein adsorption. Platelet adhesion on the original and modified PE membranes from platelet-rich plasma was also examined. A large number of platelets adhered and activated on the original PE membrane. Grafting with poly(AAm) did not suppress platelet adhesion, but grafting with poly(MPC) or poly(VPy) on the PE membrane was effective in preventing platelet adhesion. It is concluded that the introduction of the phosphorylcholine group on the surface could decrease the cell adhesion to substrate polymer.

Phosphorylcholine-based polymers and their use in the prevention of biofouling

This article provides an overview of work carried out on the synthesis and non-fouling properties of phosphorylcholine (PC)-containing polymers. The concept of biomimicry is outlined and the major classes of synthetic PC-based materials described. Studies on the interaction of these materials with various proteins are collated and the mechanism for their protein-resistant nature is discussed. Similarly, cellular interactions are also reviewed, with ex-vivo and in-vivo clinical data provided to demonstrate the usefulness of these materials for improving the properties of medical devices.

Leukocyte adhesion on model surfaces under flow: effects of surface chemistry, protein adsorption, and shear rate

The effect of specific chemical functionalities on the adhesion of polymorphonuclear leukocytes (PMNs) under flow was investigated using a set of well-characterized, chemically functionalized surfaces prepared by self-assembly of alkanethiolate monolayers on gold surfaces. Terminal functionalities included CH(3), CH(2)OH, COOH, and (OCH(2)CH(2))(3)OH groups. A new surface modification was used to incorporate a phosphorylcholine moiety on the hydroxyl-terminated monolayer. Surface modification was verified using contact-angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. Adhesion on the surfaces was studied in the presence and absence of pre-adsorbed fibrinogen. Fibrinogen adsorption on self-assembled monolayers (SAMs) was quantified using radioisotope detection. PMN adhesion was found to be dependent on the monolayer's terminal functionality. Adhesion was higher on the hydrophobic CH(3) surface and the polar COOH monolayer. Leukocyte adhesion was least on the phosphorylcholine-rich surface, followed by the ethylene-oxide-containing monolayer. Cell adhesion also was low on the hydrophilic OH monolayer. Attachment was decreased with increasing shear rate, exhibiting a three-fold decrease between 20 and 100 s(-1). Fibrinogen adsorption was higher on the CH(3) monolayer but comparable for the other four SAMs. Preincubation of the surfaces with fibrinogen decreased adhesion on all SAMs examined.

Bacterial colonization of functionalized polyurethanes

A protocol was developed for studying the growth of bacteria upon polyurethanes subsequent to the establishment of an adherent bacterial population. An inocula of approximately 10(5) cfu S. aureus were spread on functionalized polyurethanes which included Pellethane, sulfonated Pellethane, phosphonated Pellethane, quaternized amine polyurethanes, and a zwitterionic phosphonated polyurethane. After 24 h incubation, Pellethane, sulfonated Pellethane, and phosphonated Pellethane showed bacterial growth by at least a factor of 10. In contrast, the zwitterionic phosphonated polyurethane showed a factor of 10 decrease in bacteria after 24 h and the quaternized amine polyurethanes reduced the bacteria to only a few hundred after only 1 h. When treated with bovine serum albumin, Pellethane, sulfonated Pellethane, and phosphonated Pellethane again showed bacterial growth by as much as a factor of 10 over 24 h. The quaternized amine polyurethanes and the zwitterionic phosphonated polyurethane still exhibited bactericidal abilities even when coated with bovine serum albumin, with the zwitterionic material reducing bacteria by more than a factor of 10 over 24 h and the quaternized amine polyurethane reducing the bacteria to only a few hundred after only 1 h. A zone of inhibition study suggested that the bactericidal activity of the zwitterionic phosphonated polyurethane was due to the leaching of cadmium ions. A quaternized amine polyurethane which contained chloride instead of iodide as the counterion to the amine moiety was less bactericidal than the iodide-containing polymer when treated with albumin. Thus, bacteria were able to colonize Pellethane, phosphonated sulfonated Pellethane, and phosphonated Pellethane, but the iodide-containing quaternized amine polyurethane and the zwitterionic polyurethane prevented colonization.

Phosphorylcholine-containing polyurethanes for the control of protein adsorption and cell attachment via photoimmobilized laminin oligopeptides

In this study, we synthesized a biomaterial whose surface inhibits non-specific protein and cell attachment. The polymer was designed to mimic the external cell plasma membrane properties through the introduction of particular chemical constituents of the cell membrane: phospholipid polar headgroups. This was done by copolymerizing phosphorylcholine (PC) groups into a polyurethane polymer backbone (PCPUR). Peptides known to induce specific cell attachment were subsequently bound to the surface of this copolymer in a photoadressible manner to obtain surfaces that allowed the attachment of cells in a specific pattern. Two polymers with different phosphorylcholine concentrations were synthesized and their bulk and surface properties were characterized through differential scanning calorimetry, wettability measurements, angle-resolved X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Protein and lipid adsorption investigation using optical waveguide light mode spectroscopy showed that the irreversible adsorption of both proteins and lipids is drastically reduced as a result of simultaneous contributions of the PC groups, molecular mobility and strong hydrophilicity of the polymers. Consequently, this leads to a marked reduction in the cellular attachment response, which further decreases with increasing PC concentration. Finally, when the polymer surface was photo-derivatized, attachment of the neural NG108-15 cell line occurred only on the areas of the PCPUR where the laminin CDPGYIGSR peptide sequence was photoimmobilized. Cell attachment was nevertheless found to be non-specific with respect to the peptide sequence used and reasons for such results are therefore discussed.

The effect of the chemical structure of the phospholipid polymer on fibronectin adsorption and fibroblast adhesion on the gradient phospholipid surface

The interaction between biocomponents and the polyethylene (PE) surface modified with poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)] was considered taking into account the surface characteristics, i.e., density, mobility, and orientation of the poly(MAPC). The PE surface, grafted gradually with the poly(MAPC) was prepared by corona irradiation method. The amount of peroxide produced on the PE surface which was determined with 1,1-diphenyl-2-picryl-hydrazyl, increased with an increase in the energy of the corona. The surface density of the poly(MAPC) was increased with an increase in the amount of the peroxides produced by the corona irradiation. The orientation and mobility of the poly(MAPC) grafted on the PE surface was evaluated with 1,6-diphenyl-1,3,5-hexatriene. The orientation of the poly[6-methacryloyloxyhexyl phosphorylcholine (MHPC)] which has six methylene chains between the phospholipid polar group and the backbone was higher than that of other poly(MAPC)s. The mobility of the poly(MAPC) decreased with an increase in the methylene chain length in the MAPC unit. The fibronectin adsorption on the gradient PE sheet grafted with poly(MAPC) was determined with enzyme-labeled immunoassay. The amount of adsorbed fibronectin on the PE grafted with poly[2-methacryloyloxyethyl phospohorylcholine(MPC)] and poly(MHPC) decreased with an increase in their surface density. Especially, the PE sheet grafted with the poly(MHPC) was effectively reduced compared with other poly(MAPC)s. On the poly[10-methacryloyloxydecyl phosphorylcholine (MDPC)], there is a minimum amount of adsorbed fibronectin. The fibronectin adsorption pattern on the PE sheet grafted with poly(MAPC) was quite different from the chemical structure of the MAPC unit. The human normal diploid fibroblasts (WI-38 cells) were cultured on the gradient PE sheet grafted with poly(MAPC) changing the concentration of seeded WI-38 cells. The adhesion behavior of the WI-38 cells was different depending on the concentration of the seeded WI-38 cells. When the concentration was low, the number of the adherent WI-38 cells had the same tendency as fibronectin adsorption. The gradient PE sheet grafted with the poly(MHPC) effectively reduced WI-38 cells adhesion even when the concentration of the WI-38 cells was high. The biocompatibility of polymer surfaces can be improved by highly oriented phosphorylcholine group.

Neutrophil Adhesion on Polyurethanes Preadsorbed With High Molecular Weight Kininogen

Interaction of biomaterials with blood components including neutrophils is responsible for some of the clinical complications that have occurred in cardiopulmonary bypass, hemodialysis, and ventricular assist procedures. The possibility of inhibiting the initial adhesion of neutrophils to biomaterials has been studied extensively, but the problem remains unsolved. In this study, we investigated the effect of HK adsorption on polyurethane, a widely used component of extracorporeal and intracorporeal devices. HK and HKa were allowed to adsorb on 4 different charged polyurethanes: noncharged (PU), cationic (NR4), anionic (SO3), and zwitterionic (GPC) polyurethanes. The effect of kininogen adsorption on neutrophil adhesion, the surface density of the adsorbed kininogen, and the exposure of HK domains 3 and 5 (D3 and D5H), which are responsible for the binding of HK to the neutrophil integrin mβ2 or Mac-1, were examined. On PU, NR4, and SO3, kininogen adsorption reached 80% of monolayer coverage when 100 pmol/mL or higher concentration of protein solutions were used. The NR4 surface adsorbed the most kininogen along with a high exposure of D3 and D5H. The availability of D3 and D5Hallowed neutrophils to bind to the surface via the Mac-1 receptor; thus, on the NR4 surface, adsorbed kininogens lost their antiadhesive property, which resulted in a high degree of neutrophil adhesion. Increasing Mac-1 expression by exposure to fMLP increased the neutrophil adhesion on this surface. In contrast, exposure of D3 and D5H on SO3 was significantly less, because HK binds to anionic surfaces with similar protein sequences used for cell binding. This low binding site exposure preserved the antiadhesive property of HK. GPC was resistant to neutrophil adhesion even in the absence of adsorbed kininogens because of its phosphorylcholine moiety. Thus, both SO3 coupled with kininogen (or kininogen peptides) and GPC have the potential to markedly reduce neutrophil adhesion to biomaterial devices.

Behavior of blood cells in contact with water-soluble phospholipid polymer

Omega-Methacryloyloxyalkyl phosphorylcholine (MAPC) polymer, which has various methylene chain lengths between the phosphorylcholine group and the backbone, was synthesized with attention to formation of the biomembrane. The effect of water-soluble poly(MAPC) on the function and activation of blood cells was evaluated to determine the interaction between blood cells and the MAPC polymer. The poly(MAPC) and the MAPC copolymer with a small amount of fluorescent units were synthesized by a conventional radical polymerization technique. Using a fluorescence spectrometer, it was determined that the MAPC polymer was adsorbed on the plasma membrane of platelets when the platelets were suspended in an aqueous solution of the MAPC copolymer. The hemolytic activity of poly(MAPC) was less than that of other water-soluble polymers, such as poly(ethylene glycol) and poly(1-vinyl-2-pyrrolidone) (PVPy). The change in the plasma membrane fluidity of platelets on contact with poly(MAPC) was determined with 1,6-diphenyl-1,3,5,-hexatriene. The plasma membrane fluidity of platelets decreased with an increase in the methylene chain length of the MAPC unit. The aggregation activity of platelets after contact with poly(MAPC) was also evaluated, but no significant difference between that of polymer-contacted platelets and native platelets was observed. Finally, the activity of platelets on contact with poly(MAPC) was determined by measuring the cytoplasmic calcium ion concentration ([Ca2+]i) in platelets. The increase in [Ca2+]i in the platelets after contact with poly(MAPC) was similar to that of native platelets. We conclude that the poly(MAPC) reduced platelet activation even though the poly(MAPC) adsorbed on the membrane surface of the platelets. In particular, poly(10-methacryloyloxydecyl phosphorylcholine) significantly reduced platelet activation compared with PVPy.