Covalently grafted phospholipid monolayer on silicone catheter surface for reduction in platelet adhesion

Microfluidics-assisted optimization of highly adhesive haemostatic hydrogel coating for arterial puncture

Although common in clinical practice, bleeding after tissue puncture may cause serious outcomes, especially in arterial puncture. Herein, gelatin-tannic acid composite hydrogels with varying compositions are prepared, and their adhesive properties are further optimized in microfluidic channel-based simulated vessels for haemostasis in arterial puncture. It is revealed that the composite hydrogels on the syringe needles used for arterial puncture should possess underwater adhesion higher than 4.9 kPa and mechanical strength higher than 86.0 kPa. The needles coated with the gelatin-tannic acid composite hydrogel completely prevent blood loss after both vein and arterial puncture in different animal models. This study holds great significance for the preparation of haemostatic needles for vessel puncture, and gelatin-tannic acid hydrogel coated needles may help to prevent complications associated with arterial puncture.

•

Haemostatic needles were prepared with coating of gelatin-tannic acid hydrogel.

•

Microfluidic system was employed to optimize the underwater adhesion of gelatin-tannic acid hydrogel coating.

•

Needles coated with the gelatin-tannic acid hydrogel exhibited complete haemostasis after arterial puncture.

How the dynamics of subsurface hydration regulates protein-surface interactions

The role of water structure near surfaces has been scrutinized extensively because it is accepted to control protein-surface interactions, however, often avoiding effects of hydration dynamics. Relating to this, we have recently discussed how the amount and state of water, accumulated within various hydrophobic-to-hydrophilic subsurface gradients of plasma polymer films, influence the magnitude of adsorbed bovine serum albumin, spurring the hypothesis of the presence of a subsurface dipolar field. This study now analyzes the kinetics of hydration by systematically introducing modified gradient architectures and relating different hydration times to the adsorption of a dipolar probing protein. We find that dry-stored subsurface gradients, owing nominally identical surface characteristics, exhibits comparable surface potential and protein adsorption values, while they behave in a different manner at transient hydration times of few hours, before reaching near-equilibrium state of the hydration. A characteristic hydration time is found where protein adsorption on gradient films is minimal, unveiling the transient nature of the effect. In general, protein adsorption is sensitive to the time allowed for hydration of the adsorbent surface, supporting our initial hypothesis inasmuch as the quantity as well as quality of water inside the subsurface matrix is crucial for controlling protein-surface interactions.

Phosphatidylethanolamine biomimetic coating increases mesenchymal stem cell osteoblastogenesis

Previous observations (e.g., decreased bacterial adhesion) have shed the light on the auspicious possibility to use phosphatidylethanolamine as biomimetic coating for metal implants. Additionally, it was experimentally shown that phosphatidylethanolamine induces bone formation, however, up to now no study was performed to understand this observation or to find an explanation. In an attempt to unveil how and why phosphatidylethanolamine can improve cell metabolism and osteogenic differentiation, primary cells (human umbilical cord perivascular cells) were cultured on native or phosphatidylethanolamine coated surfaces. Several parameters were followed on gene (real time polymerase chain reaction) and protein (e.g., dot-blot and ELISA tests) levels. It was determined that phosphatidylethanolamine potentiates cell metabolism, osteogenic differentiation, and mineralisation early processes. By preventing biofilm formation while promoting new bone formation, phosphatidylethanolamine could be easily implemented as implant bio-mimicking coating.

Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions

Staphylococcus comprises up to two-thirds of all pathogens in orthopedic implant infections and they are the principal causative agents of two major types of infection affecting bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone. Bacterial adhesion is the first and most important step in implant infection. It is a complex process influenced by environmental factors, bacterial properties, material surface properties and by the presence of serum or tissue proteins. Properties of the substrate, such as chemical composition of the material, surface charge, hydrophobicity, surface roughness and the presence of specific proteins at the surface, are all thought to be important in the initial cell attachment process. The biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. This work will provide an overview of the mechanisms and factors involved in bacterial adhesion, the techniques that are currently being used studying bacterial-material interactions as well as provide insight into future directions in the field.

Surface Engineering of Polycaprolactone by Biomacromolecules and their Blood Compatibility

Improving blood compatibility of biodegradable polymers is an area of intensive research in blood contacting devices. In this study, curdlan sulphate and heparin-modified poly (caprolactone) (PCL) hybrids were developed by physically entrapping these molecules on the PCL surface. This modification technique was performed by reversible gelation of the PCL surface region following exposure to a solvent and nonsolvent mixture. The presence of these biomacromolecules on the PCL surface was verified by atomic force microscopy (AFM) and scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDAX) analysis, while wettability of the films was investigated by dynamic contact angle measurements. The blood compatibilities of the surface-modified films were examined using in vitro platelet and leukocyte adhesion and thrombus formation. Mouse RAW 264.7 macrophage cells were used to assess the cell adhesion and inflammatory response to the modified surface by quantifying mRNA expression levels of proinflammatory cytokines namely TNF-α and IL-1β using real-time polymerase chain reaction (RT-PCR). A lower platelet and leukocyte adhesion and activation was observed on the modified films incubated with whole human blood for 2 h. The thrombus formation on the PCL was significantly decreased upon immobilization of both curdlan sulphate (39%, *p<0.05) and heparin (28%, *p<0.01) when compared to bare PCL (80%). All of these results revealed that improved blood compatibility was obtained by surface entrapment of both curdlan sulphate (CURS) and heparin (HEP) onto PCL films. Both PCL-CURS and PCL-HEP films reduced RAW 264.7 macrophage cell adhesion (*p<0.05) with respect to the base unmodified PCL. The cellular inflammatory response was suppressed on the modified substrates. The mRNA expression levels of proinflammmatory cytokines (TNF-α and IL-1β) were upregulated on bare PCL, while it was significantly lower on PCL-CURS and PCL-HEP substrates (**p<0.001). Thus, this biomacromolecule entrapment process can be applied on PCL in order to achieve improved blood compatibility and reduced inflammatory host response for its future blood contacting applications.

The biocompatibility of sulfobetaine engineered polymethylmethacrylate by surface entrapment technique

Sulfobetaine-modified polymethylmethacrylate (PMMA) systems were created by physically entrapping the zwitterionic species on the PMMA surface. The presence of the sulfobetaine molecules on these surfaces were verified by ATR-FTIR and SEM-EDAX analysis, while wettability of the films was investigated by dynamic contact angle measurements. The short-term (4 h) adhesion of two bacterial species (gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa) on these surfaces were studied. Mouse RAW 264.7 macrophage cells were used to assess the cell adhesion and inflammatory response by quantifying the expression levels of proinflammatory cytokines namely TNFalpha and IL1beta by measuring their mRNA profiles in the cells using real-time polymerase chain reaction (RT-PCR) normalized to the house keeping gene GAPDH. Whilst mouse L-929 fibroblast cells were used to assess the propensity for the materials to support fibroblast cell adhesion. A decrease in the adhesion of S. aureus by 63% and P. aeruginosa by 49% was observed on sulfobetaine modified PMMA films after 4 h. In all the cases, sulfobetaine modified PMMA films reduced cellular adhesion events (*P < 0.05) with respect to the base materials, which could be linked to the reduced protein adsorption observed on these surfaces. The cellular inflammatory response was suppressed on sulfobetaine modified substrates as expression levels of pro-inflammatory cytokines (TNFalpha and IL1beta) was found to be up regulated on bare PMMA, while it was significantly lower on sulfobetaine modified PMMA (**P < 0.001). Thus the sulfobetaine entrapment process can be applied on polymethylmethacrylate in order to achieve low biointeractions and reduced inflammatory host responses for various biomedical and biotechnological applications.

A novel nanostructured poly(lactic-co-glycolic-acid)-multi-walled carbon nanotube composite for blood-contacting applications: thrombogenicity studies

Composite films of poly(lactic-co-glycolic-acid) with multi-walled carbon nanotubes (PLGA-MWCNT) having two different nanotube orientations, namely random and vertically aligned, have been fabricated and characterized. The effect of these nanostructured surfaces on platelet adhesion is evaluated. In particular, the thrombogenicity of the nanostructured composite films is compared with that of pristine graphite (a low thrombogenic material) and PLGA film, in order to determine the influence of surface chemistry and topography on platelet adhesion. The results in this study show that the PLGA-MWCNT composite with vertically aligned nanotubes exhibits very low levels of fibrinogen adsorption and platelet adhesion, which can be attributed to both chemical and topographical effects. Platelet adhesion shows a good correlation with the presence of COOH groups and appears to be sensitive to the topographic features of the composite films. The results in this study suggest that in addition to chemistry, nanotopographical surface modifications could be an effective strategy in the development of low thrombogenic and hemocompatible materials.

The biocompatibility of sulfobetaine engineered poly (ethylene terephthalate) by surface entrapment technique

Sulfobetaine-modified poly(ethylene terephthalate) (PET) systems were created by physically entrapping the zwitterionic species on the PET surface. The presence of the sulfobetiane molecules on these surfaces were verified by ATR-FTIR and SEM-EDAX analysis, while wettability of the films was investigated by water contact angle measurements. The blood compatibility of the modified films was evaluated by platelet adhesion in human platelet-rich plasma (PRP). The adhesion and inflammatory response of Mouse RAW 264.7 macrophage cells were studied. The surface induced cellular inflammatory response was determined by quantifying the expression levels of proinflammatory cytokines namely TNF-alpha and IL-1beta by measuring their mRNA profiles in the cells using real time polymerase chain reaction normalized to the housekeeping gene GAPDH. L-929 fibroblast cells were used to assess the propensity of the materials to support the fibroblast cell adhesion. A lower platelet adhesion and activation were observed on the sulfobetaine-modified PET film incubated in PRP after 2h when compared to control. The modified film reduced cellular adhesion events ( p<0.05) with respect to the base material, which could be linked to the reduced protein adsorption observed on this surface. The cellular inflammatory response was suppressed on sulfobetaine-modified substrate. Expression levels of pro-inflammmatory cytokines (TNF-alpha and IL-1beta) was found to be upregulated on bare PET, while it was significantly lower on modified PET ( p<0.001). Thus the sulfobetaine entrapment process can be applied on PET in order to achieve low biointeractions and reduced inflammatory host response for various biomedical and biotechnological applications.

Isopropyl Myristate-Modified Polyether-Urethane Coatings as Protective Barriers for Implantable Medical Devices

Polyurethane films have potential applications in medicine, especially for packaging implantable medical devices. Although polyether-urethanes have superior mechanical properties and are biocompatible, achieving water resistance is still a challenge. Polyether based polyurethanes with two different molecular weights (PTMO1000, PTMO2000) were prepared from 4,4’-diphenylmethane diisocyanate and poly(tetra-methylene oxide). Polymer films were introduced using different concentrations (0.5-10 wt %) of isopropyl myristate lipid (IPM) as a non-toxic modifying agent. The physical and mechanical properties of these polymers were characterised using physical and spectroscopy techniques (FTIR, Raman, DSC, DMA, tensile testing). Water contact angle and water uptake of the membranes as a function of IPM concentration was also determined accordingly. The FTIR and Raman data indicate that IPM is dispersed in polyurethane at ≤ 2wt% and thermal analysis confirmed this miscibility to be dependent on soft segment length. Modified polymers showed increased tensile strength and failure strain as well as reduced water uptake by up to 24% at 1-2 wt% IPM.

Preparation and characterization of asymmetric planar supported bilayers composed of poly(bis-sorbylphosphatidylcholine) on n-octadecyltrichlorosilane SAMs

Planar supported lipid bilayers (PSLBs) have been widely studied as biomembrane models and biosensor scaffolds. For technological applications, a major limitation of PSLBs composed of fluid lipids is that the bilayer structure is readily disrupted when exposed to chemical, mechanical, and thermal stresses. A number of asymmetric supported bilayer structures, such as the hybrid bilayer membrane (HBM) and the tethered bilayer lipid membrane (tBLM), have been created as an alternative to symmetric PSLBs. In both HBMs and tBLMs, the inner monolayer is covalently attached to the substrate while the outer monolayer is typically composed of a fluid lipid. Here we address if cross-linking polymerization of the lipids in the outer monolayer of an asymmetric supported bilayer can achieve the high degree of stability observed previously for symmetric PSLBs in which both monolayers are cross-linked [E.E. Ross, L.J. Rozanski, T. Spratt, S.C. Liu, D.F. O'Brien, S.S. Saavedra, Langmuir 19 (2003) 1752]. To explore this issue, HBMs composed of an outer monolayer of a cross-linkable lipid, bis-sorbylphosphatidylcholine (bis-SorbPC), and an inner SAM were prepared and characterized. Several experimental conditions were varied: vesicle fusion time, polymerization method, and polymerization time and temperature. Under most conditions, bis-SorbPC cross-linking stabilized the HBM such that its bilayer structure was largely preserved after drying; however these films invariably contained sub-micron scale defects that exposed the hydrophobic core of the HBM. The defects appear to be caused by desorption of low molecular weight oligomers when the film is removed from water, rinsed, and dried. In contrast, poly(bis-SorbPC) PSLBs prepared under similar conditions by Ross et al. were nearly defect free. This comparison shows that formation of a cross-linked network in the outer leaflet of an asymmetric supported bilayer is insufficient to prevent lipid desorption; inter-leaflet covalent linking appears to be necessary to create supported poly(lipid) assemblies that are impervious to repeated drying and rehydration. The difference in stability is attributed to inter-leaflet cross-linking between monolayers which can form in symmetric bis-SorbPC PSLBs.

Atomic force microscopy probing platelet activation behavior on titanium nitride nanocoatings for biomedical applications

There is increasing interest in developing novel coatings to enhance the biocompatibility of medical implants. A key issue in biocompatibility research is platelet activation and aggregation on the biomaterials' surface. Stoichiometric and nonstoichiometric titanium nitride (TiN(x)) films were developed by sputtering as case study materials, for probing platelet activation behavior onto them. Atomic force microscopy (AFM) facilitates the real-time studies of cells and guarantees cellular viability. In this work a methodology for platelets study by AFM was developed. The morphological, structural, optical, and wettability properties of the TiN(x) films were obtained by AFM, x-ray diffraction, spectroscopic ellipsometry, and contact angle measurements.The properties of TiN(x) films were correlated with their thrombogenicity involving platelets' adhesion, activation and protein clustering mechanisms. It was found that the TiN(x) films stoichiometry and surface roughness affect the platelet response. The stoichiometric and smoother TiN films promote platelets adhesion and activation.

Surface modification of poly(oligoethylene oxide methacrylate) for resisting protein adsorption

We prepare poly(2-methoxyethyl-, 2-(2-methoxyethoxy)ethyl-, 2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) (p(nEOMA), n=1, 2, and 3) brushed surfaces with varying the polymer density by surface initiated polymerization. The amount of bovine serum albumin (BSA) adsorbed on the surfaces is investigated. The mobility of the polymer chain in the polymer/water interfaces and the structure of adsorbed water on the surfaces are characterized by Electron Spin Resonance (ESR) and transmission-Fourier transform infrared (FT-IR) spectroscopy, respectively. This work reports the relationship between these surface properties and albumin adsorption. As a result, the surface having both a high molecular mobility and bulk-like water found to be very effective in preventing albumin adsorption.

Bacterial biofilms within the clinical setting: what healthcare professionals should know

Bacterial biofilm formation is the prevailing microbial lifestyle in natural and manmade environments and occurs on all surface types. Biofilm formation develops in several phases and is influenced by various parameters, both environmental and inherent to the attaching cell. Biofilms also serve as protective niches for particular pathogens when outside a host. Although it is accepted that biofilms are ubiquitous in nature, the significance of biofilms in clinical settings, especially with regard to their role in medical-related infections, is often underestimated. It has been found that several aspects of human pathogenesis within a clinical context are directly related to biofilm development. Various types of surfaces in clinical settings are prone to biofilm development and an increased risk of disease may be a direct consequence of their formation. This review describes the process of biofilm formation, highlights the importance of bacterial associations with surfaces in clinical settings and describes various methods for biofilm visualization and control.

Cell mimetic monolayer supported chitosan-haemocompatibility studies

Chitosan is a natural polymer, widely explored for biomedical and tissue engineering applications. However the thrombogenic nature limits their application in blood contacting devices and implants. Here, we have attempted to understand the haemocompatibility of chitosan by immobilizing a monolayer of cell mimetic lipid compositions. The phosphatidylcholine/cholesterol/galactocerebroside lipid composition (PC/Chol/GalC, 1:0.35:0.125) was deposited onto the chitosan films. Characterization of the modified surface was done by sessile drop contact angle measurement. The contact angle of the chitosan film reduced from 80.65 +/- 1.4 to 23.5 +/- 1.9 after the surface modification. Swelling nature of chitosan seemed to influence the orientation and packing of the lipid monolayer. In vitro calcification studies with metastable salt solution indicated increased calcification on the modified surface. This may be due to formation of nuclei for calcification on the expanding monolayer. The preliminary haemocompatibility studies with washed platelets, leukocytes and erythrocytes showed overall reduction in blood cell adhesion to the modified surfaces. Scanning electron microscopy was used for morphological characterization of platelet adhesion and activation on the surfaces. On the bare chitosan surface, fully spread platelets with extending pseudopodia indicated platelet activation. The smooth surface of the modified film did not activate platelets. These studies showed that, though the lipid monolayer on chitosan film is able to reduce the over all blood cell adhesion and platelet activation it is prone to calcification.