Evaluation of in vivo adsorption of blood elements onto hydrogel-coated silicone rubber by scanning electron microscopy and fourier transform infrared spectroscopy

Thermoresponsive P(HEMA-co-OEGMA) copolymers: synthesis, characteristics and solution behavior

Random, thermoresponsive copolymers of 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methyl ether methacrylate M _n = 300 (OEGMA) were synthesized via atom transfer radical polymerization (ATRP) in a DMSO/H₂O solvent mixture. Reactivity ratios were determined by the extended Kelen-Tudos method and found to be close to 1. Studies confirmed the randomness of the obtained copolymers. The thermoresponsiveness in water and in phosphate buffer (PBS) solutions and the influence of copolymer composition and solution concentration on the cloud point temperature (T _cp) were investigated. Phase transitions in water solutions were reversible and narrow. The response of P(HEMA-co-OEGMA) to temperature could be adjusted in the range from 66.5 °C to 21.5 °C by changing the HEMA content. In PBS solutions, significant differences in the heating/cooling cycle were observed for all investigated concentrations. The presence of kosmotropic salts in PBS decreased the T _cp value and caused thermal aggregation of chains to form a macroscopic aggregate at temperatures above the T _cp.

Protein Resistant Polymeric Biomaterials

Toward improving implantable medical devices as well as diagnostic performance, the development of polymeric biomaterials having resistance to proteins remains a priority. Herein, we highlight key strategies reported in the recent literature that have relied upon improvement of surface hydrophilicity via direct surface modification methods or with bulk modification using surface modifying additives (SMAs). These approaches have utilized a variety of techniques to incorporate the surface hydrophilization agent, including physisorption, hydrogel network formation, surface grafting, layer-by-layer (LbL) assembly and blending base polymers with SMAs. While poly(ethylene glycol) (PEG) remains the gold standard, new alternatives have emerged such as polyglycidols, poly(2-oxazoline)s (POx), polyzwitterions, and amphiphilic block copolymers. While these new strategies provide encouraging results, the need for improved correlation between in vitro and in vivo protein resistance is critical. This may be achieved by employing complex protein solutions as well as strides to enhance the sensitivity of protein adsorption measurements.

Poly(HEMA-co-HEMA-PFPA): Synthesis and preparation of stable micelles encapsulating imaging nanoparticles

We report the preparation of stable micelles from random copolymers of 2-hydroxyethyl methacrylate (HEMA) and perfluorophenyl azide (PFPA)-derivatized HEMA (HEMA-PFPA). The copolymers were synthesized by RAFT polymerization at room temperature under mild conditions without affecting the azide functionality. Upon addition of water to the copolymer solution in DMSO, the random copolymers self-assembled into micelles even at the percentage of HEMA-PFPA as low as 4.5%. The size of the micelles can be controlled by the molecular weight and the concentration of the copolymer, and the percentage of HEMA-PFPA in the copolymer. In addition, iron oxide nanoparticles and quantum dots were successfully encapsulated into the micelles with high encapsulation efficiency (∼80%). These nanoparticles, which were hydrophobic and formed agglomerates in water, became fully dispersed after encapsulating into the micelles. The micelles were stable and the size remained unchanged for at least 6months.

In vitro hemocompatibility on thin ceramic and hydrogel films deposited on polymer substrate performed in arterial flow conditions

Hydrogel coatings were stabilized by titanium carbonitride a-C:H:Ti:N buffer layers deposited directly onto the polyurethane (PU) substrate beneath a final hydrogel coating. Coatings of a-C:H:Ti:N were deposited using a hybrid method of pulsed laser deposition (PLD) and magnetron sputtering (MS) under high vacuum conditions. The influence of the buffer a-C:H:Ti:N layer on the hydrogel coating was analysed by means of a multi-scale microstructure study. Mechanical tests were performed at an indentation load of 5 mN using Berkovich indenter geometry. Haemocompatible analyses were performed in vitro using a blood flow simulator. The blood-material interaction was analysed under dynamic conditions. The coating fabrication procedure improved the coating stability due to the deposition of the amorphous titanium carbonitride buffer layer.

Synthesis and Postpolymerization Modification of Thermoresponsive Coatings Based on Pentaerythritol Monomethacrylate: Surface Analysis, Wettability, and Protein Adsorption

Properties of novel temperature-responsive hydroxyl-containing poly(pentaerythritol monomethacrylate) (PPM) coatings, polymerized from oligoperoxide grafted to glass surface premodified with (3-aminopropyl)triethoxysilane, are presented. Molecular composition, chemical state, thickness, and wettability are examined with time of flight-secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), ellipsometry, and contact angle measurements, respectively. Temperature-induced changes in hydrophobicity of grafted PPM brushes are revealed by water contact angle and ellipsometric measurements. Partial postpolymerization modification of hydroxyl groups (maximum a few percent), performed with acetyl chloride or pyromellitic acid chloride, is demonstrated to preserve thermal response of coatings. Adsorption of bovine serum albumin to PPM brushes, observed with fluorescence microscopy, is higher than on glass in contrast to similar hydroxyl-containing layers reported as nonfouling. Enhanced and temperature-controlled protein adsorption is obtained after postpolymerization modification with pyromellitic acid chloride.

Use of catheters with the AgION antimicrobial system in kidney transplant recipients to reduce infection risk

Microbial blood infection represents a high risk for immuno-suppressed patients. Of all catheter-related infections in the bloodstream, 90% result from the use of central venous catheters, the main cause being microbial colonization at the catheter's insertion point or the catheter hub. Between January 2003 and December 2004, 102 patients received a renal transplant including 57 who received a triple-lumen central venous catheter (CVC) during the procedure. Two catheters were used: a standard polyurethane catheter placed in the jugular veina or the subclavian veina for group I, and polyurethane catheters with the AgION antimicrobial system always placed in the subclavian veina for group II. Care and maintenance of the CVCs was standardized in both groups. After catheter removal, the tips were analyzed microbiologically. Of 57 (43.9%) CVCs, 25 were found to be contaminated. In the first group 24 out of 41 CVCs (58.5%) showed bacterial growth, whereas in group II only one catheter (6.6%) had a biofilm. The most common contaminant (18 out of 25, 72%) was Staphylococcus epidermidis. In group II, two patients had positive blood cultures yet a microbiologically sterile CVC. None of the catheters with the AgION antimicrobial system had to be removed owing to local infection or intolerance. The continuous release of silver ions increases the protection against bacteria and fungi during the entire time of catheterization. Use of catheters with the AgION antimicrobial system lead to a marked reduction in catheter-associated infections of the bloodstream.

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane): synthesis, characterization, in vitro protein adsorption and platelet adhesion

In vitro protein adsorption, platelet adhesion and activation on new hydrogel surfaces, composed of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) or poly(dimethyl siloxane) (PDMS), were investigated. By varying PEO length (MW = 2000 or 3400), hydrophobic components (PTMO or PDMS) or polymer topology (block or graft copolymers), various physical hydrogels were produced. Their structures were verified by 1H NMR and ATR-IR and the molecular weights were determined by gel permeation chromatography. The hydrogels were soluble in a variety of organic solvents, while absorbed a significant amount of water with preserved three-dimensional structure by physical crosslinking. The dynamic contact angle measurement revealed that the surface hydrophilicity increased by incorporating longer PEO, PEO grafting, and adopting PDMS as a hydrophobic segment instead of PTMO. It was observed from in vitro protein adsorption study that the hydrogels exhibited significantly lower adsorption of human serum albumin (HSA), human fibrinogen (HFg), and IgG, when compared with Pellethane, a commercial polyurethane taken as a control. The hydrogels were attractive for HSA but not sensitive to HFg and IgG. And more than 65% of the proteins detected on the surfaces of the hydrogels were reversibly detached by being treated with an SDS solution. It was evident that the hydrogels synthesized in this study were much more resistant to platelet adhesion than the control, which might depend on the composition of proteins adsorbed on the surfaces and their degree of denaturation. Among the hydrogels tested, PEO3,4kPDMS exhibited albumin-rich and platelet-resistant surfaces, implying a potential candidate for biomaterial.

Biological reactions to cerebrospinal fluid shunt devices: a review of the cellular pathology

OBJECTIVE

To understand the interaction between cerebrospinal fluid shunt components and the brain and other tissues.

METHODS

A systematic review of the medical literature directly pertaining to shunt complications, and that dealing with tissues' reactions to implants in general, was conducted.

RESULTS

Vascularized pedicles of glial tissue or choroid plexus grow into ventricular catheters, primarily as a mechanical phenomenon. Cellular debris or blood can cause dysfunction of valve components. Chronic inflammation, which is nonspecific, might contribute to degradation of the components.

CONCLUSION

Care must be taken to prevent early entry of debris or blood into the shunt system. Ventricular collapse onto the shunt must be avoided. Refinement of manufacturing methods or modification of shunt materials could reduce the susceptibility of shunts to infection and improve longevity of the apparatus.

In vivo evaluation of protein adsorption to sterically stabilised colloidal carriers

A diffusion chamber implanted intraperitoneally in the rabbit was employed as an in vivo model to evaluate the interaction of peritoneal proteins with block copolymer (poloxamer and poloxamine)-coated polystyrene microspheres (PS). Using a desorption technique followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, six proteins of 94, 86, 66, 53, 40, and 20 kDa were desorbed from the carrier systems after incubation with peritoneal fluid in vitro. The 40- and 20-kDa proteins dominated the protein profile. A similar pattern was observed when proteins were desorbed from PS microspheres removed after 24-h implantation in chambers in the peritoneal cavity, although the protein profile was dominated by the 94- and 53-kDa proteins. In general, coating of PS with block copolymers reduced the amount of protein bound to the microspheres in vitro and in vivo but did not change the types of proteins bound.

In vitro assessment of bacterial adhesion to Hydromer-coated cerebrospinal fluid shunts

The adherence of five strains of Staphylococcus epidermidis and one strain of S. aureus to both untreated and Hydromer-coated silicone rubber cerebrospinal fluid shunts was studied in vitro using epifluorescent image analysis. All five strains of S. epidermidis showed similar levels of adherence to untreated shunts, whilst S. aureus adhered slightly better. The Hydromer coating, a hydrogel material which creates a hydrophilic layer on the shunt surface, was found to reduce bacterial adhesion levels by approximately 90% in the six strains of bacteria tested. Unfortunately, uniform coverage of the shunt surfaces (particularly internally) with Hydromer coating was not achieved during sample preparation. Bacterial adhesion levels in such areas were identical to untreated controls. This may pose problems in the in vivo use of Hydromer-coated shunts.

Synthesis and non-thrombogenicity of polyurethanes with poly(oxyethylene) side chains in soft segment regions

Epoxidized polybutadiene-urethanes were synthesized and grafted with poly(oxyethylene)s. The non-thrombogenicity of the graft polyurethanes was investigated in relation to the content of poly(oxyethylene). The grafting of poly(oxyethylene) to polyurethane suppressed adsorption and denaturation of plasma proteins and platelet adhesion. It was also found that there exists an optimum content of poly(oxyethylene) for the graft polyurethane to attain the highest non-thrombogenicity.

Surface characterization of heparin-complexing poly(amido amine) chains grafted on polyurethane and glass surfaces

Poly(amido-amine) chains grafted onto polyurethanes and glass form stable complexes with heparin yielding potential nonthrombogenic surfaces. The characterization of the surfaces, and the product of each chemical reaction including final heparinized surfaces, has been studied by contact angle data and scanning electron microscopy (SEM). Air in water, octane in water, and drop-on-plate contact angle data were used to estimate surface (gamma sv) and interfacial (gamma sw) free energies. Solid-water work of adhesion (Wa) and its dispersive (Wda) and polar (Ipsw) components were calculated for all studied surfaces. It has been found that the viscosity of polyurethane solution used for film casting influences wetting properties of these films. It has also been found that a direct correlation exists between the Ipsw/Wda values and the degree of coverage of the surfaces by cellular deposits after their exposure to platelet-rich plasma. Final heparinized polyurethane and glass materials are hydrophilic, their Ipsw/Wda ratio is high, and little or no cellular deposit is observed on their surfaces.