Protein adsorption-resistant hollow fibers for blood purification

Blood-incompatibility in haemodialysis: alleviating inflammation and effects of coagulation

Blood-incompatibility is an inevitability of all blood-contacting device applications and therapies, including haemodialysis (HD). Blood leaving the environment of blood vessels and the protection of the endothelium is confronted with several stimuli of the extracorporeal circuit (ECC), triggering the activation of blood cells and various biochemical pathways of plasma. Prevention of blood coagulation, a major obstacle that needed to be overcome to make HD possible, remains an issue to contend with. While anticoagulation (mainly with heparin) successfully prevents clotting within the ECC to allow removal of uraemic toxins across the dialysis membrane wall, it is far from ideal, triggering heparin-induced thrombocytopenia in some instances. Soluble fibrin can form even in the presence of heparin and depending on the constitution of the patient and activation of platelets, could result in physical clots within the ECC (e.g. bubble trap chamber) and, together with other plasma and coagulation proteins, result in increased adsorption of proteins on the membrane surface. The buildup of this secondary membrane layer impairs the transport properties of the membrane to reduce the clearance of uraemic toxins. Activation of complement system-dependent immune response pathways leads to leukopenia, formation of platelet–neutrophil complexes and expression of tissue factor contributing to thrombotic processes and a procoagulant state, respectively. Complement activation also promotes recruitment and activation of leukocytes resulting in oxidative burst and release of pro-inflammatory cytokines and chemokines, thereby worsening the elevated underlying inflammation and oxidative stress condition of chronic kidney disease patients. Restricting all forms of blood-incompatibility, including potential contamination of dialysis fluid with endotoxins leading to inflammation, during HD therapies is thus still a major target towards more blood-compatible and safer dialysis to improve patient outcomes. We describe the mechanisms of various activation pathways during the interaction between blood and components of the ECC and describe approaches to mitigate the effects of these adverse interactions. The opportunities to develop improved dialysis membranes as well as implementation strategies with less potential for undesired biological reactions are discussed.

Fabrication and performance evaluation of polymeric membrane using blood compatible hydroxyapatite for artificial kidney application

In the current study, a phase inversion scheme was employed to fabricate hydroxyapatite (HA)/polysulfone (PSF)-based asymmetric membranes using a film applicator with water as a solvent and nonsolvent exchanging medium. Fourier Transform Infrared (FTIR) and X-ray diffraction (XRD) spectroscopic studies were conducted to confirm the bonding chemistry and purity of filler. The inherent thick nature of PSF generated sponge-like shape while the instantaneous demixing process produced finger-like pore networks in HA/PSF-based asymmetric membranes as exhibited by scanning electron microscope (SEM) micrographs. The FTIR spectra confirmed noncovalent weak attractions toward the polymer surface. The leaching ratio was evaluated to observe the dispersion behavior of HA filler in membrane composition. Hydrophilicity, pore profile, pure water permeation (PWP) flux, and molecular weight cutoff (MWCO) values of all formulated membranes were also calculated. Antifouling results revealed that HA modified PSF membranes exhibited 43% less adhesion of bovine serum albumin (BSA) together with >86% recovery of flux. Membrane composition showed 74% total resistance, out of which 60% was reversible resistance. Biocompatibility evaluation revealed that the modified membranes exhibited prothrombin time (PT), and thrombin time (TT) comparable with typical blood plasma, whereas proliferation of living cells over membrane surface proved its nontoxic behavior toward biomedical application. The urea and creatinine showed effective adsorption aptitude toward HA loaded PSF membranes.

Biocompatibility performance evaluation of high flux hydrophilic CO3Ap/HAP/PSF composite membranes for hemodialysis application

Carbonate apatite/hydroxyapatite (CO3Ap/HAP) additive was obtained by calcination of wasted chicken bones at 900°C. Intermolecular attraction exists between CO3Ap/HAP additive and blended polysulfone (PSF) polymer. Electron dispersive X-ray (EDX) and FTIR analysis were carried out to check the elemental composition and bonding chemistry of prepared additive. The instantaneous demixing process generated consistent finger-like networks in CO3Ap/HAP/PSF-based composite membranes while sponge-like structure was shown by PSF as revealed by SEM images. The increase in weight % of additive loading is also confirmed by EDX analysis. Furthermore, the interaction mechanism of CO3Ap/HAP additive with polysulfone medium was analyzed by FTIR exploration. The water absorption experiment defined a 93% expansion in hydrophilic performance. Change in porosity occurs with additive loading and pure water permeation flux improved up to 11 times. Approximately, antifouling results revealed that 87% of water flux was recovered after treating with a protein solution, whereas a 30% improvement in antifouling capability in case of bovine serum albumin solution occurred. In vitro cytotoxicity, and clotting times study was carried out to evaluate virulent behavior and anticoagulation activity of formulated membranes.

Biocompatible chicken bone extracted dahllite/hydroxyapatite/collagen filler based polysulfone membrane for dialysis

In the current study, dahllite/hydroxyapatite/collagen filler extracted via calcination of wasted chicken bone was blended with PSf polymer to obtain highly biocompatible, and antifoulant hemodialysis membranes. FTIR and Raman spectroscopic analysis was done to obtain information about the bonding chemistry of the obtained filler. The intermolecular interaction that existed between dahllite/hydroxyapatite/collagen filler and pristine PSf was confirmed by Raman spectroscopic study. The PSf polymer exhibited a sponge-like structure owing to its high thickness and slow exchange with non-solvent in coagulation bath whilst the instantaneous de-mixing course produced finger-like capillaries in dahllite/hydroxyapatite/collagen filler based PSf membranes as exposed by SEM photographs. The presence of different wt. % of filler composition in the PSf matrix improved the mechanical strength as revealed by fatigue analysis. The hydrophilic character improved by 78% while leaching consistency adjusted to 0%-4%. Pure water permeation (PWP) flux improved by nine times. The pore profile improved with the addition of filler as revealed by hydrophilicity experiment, PWP flux, and SEM micrographs. Fouling evaluation results disclosed that filler based membranes showed 36% less adsorption of protein (BSA) solution together with more than 84% flux recovery ratio. The biocompatibility valuation analysis unveiled that membranes composed of filler showed extended prothrombin and thrombin coagulation times, reduced activation of fibrinogen mass, and less adhesion of plasma proteins in comparison with pristine PSf membrane. The adsorption capacity of fabricated membranes for urea and creatinine improved by 31% (in the case of urea) and 34% (in the case of creatinine) in contrast with pristine PSf membrane. The overall results showed that the M-3 membrane was optimized in terms of surface properties, protein adhesion, anticoagulation activity, and adsorption amount of urea and creatinine.

Biocompatibility of a polymer-coated membrane possessing a hydrophilic blood-contacting layer: Adsorption-related assessment

OBJECTIVE

Currently, the foreign surfaces of extracorporeal circulation devices are coated with an acrylate-based copolymer that creates a hydrophilic blood-contacting layer to enhance biocompatibility. Several reports of acrylate-based copolymer with respect to biocompatibility have been published; however, the adsorption of peptide compounds on acrylate-based copolymer-coated membranes still requires clarity. In this study, we aimed to understand the adsorption of several peptide compounds of various molecular weights, including albumin, lysozyme, and vancomycin, on acrylate-based copolymer-coated membranes using in vitro studies.

METHODS

Six experimental circuits consisting of acrylate-based copolymer-coated tubes and membranes, and six comprising acrylate-based copolymer-coated tubes and non-coated membranes were prepared for comparison. An experimental solution, composed of albumin, lysozyme, vancomycin, and saline, was continuously stirred in a reservoir, recirculated in each experimental circuit, and then filtered. Concentrations of albumin, lysozyme, and vancomycin were measured after 0, 15, 30, 45, 60, 90, and 120 min of recirculation. Similar experiments were performed in all the prepared circuits.

RESULTS

The ratio of measured values at each time point to those at 0 min was not significantly different between acrylate-based copolymer-coated and non-coated membranes for albumin and lysozyme, but differed significantly for vancomycin; the ratios were higher in acrylate-based copolymer-coated than in non-coated membranes.

CONCLUSION

This study suggests that albumin is not adsorbed on either acrylate-based copolymer-coated or non-coated membranes, that lysozyme is not adsorbed on either membrane or is adsorbed at a similar rate on both membranes, and that vancomycin is less adsorbed on acrylate-based copolymer-coated membranes. Thus, acrylate-based copolymer coating could inhibit the adsorption of various peptide compounds.

Flux and Passage Enhancement in Hemodialysis by Incorporating Compound Additive into PVDF Polymer Matrix

In this study, Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS) with compound addtive. The compound additive was made with polyvinyl pyrrolidone (PVP) and Poly ethylene glycol (PEG). The results showed that the modified PVDF membrane had better separation performance than virgin PVDF membrane. The UF flux of modified PVDF membrane can reach 684 L·h⁻¹·m⁻² and lysozyme (LZM) passage is 72.6% while virgin PVDF membrane is 313 L·h⁻¹·m⁻² and 53.2%. At the same time, the biocompatibility of PVDF membranes was also improved. Compared with commercial polysulfone hemodialysis membrane (Fresenius F60S membrane), the modified PVDF membrane had better mechanical and separation performance. The stress and tensile elongation of modified PVDF membrane was 0.94 MPa and 352% while Fresenius F60S membrane was 0.79 MPa and 59%. The LZM passage reached 72.6% while Fresenius F60S membrane was 54.4%. It was proven that the modified PVDF membrane showed better hydrophilicity, antithrombogenicity, less BSA adsorption, and lower hemolytic ratio and adhesion of platelets. Water contact angle and BSA adsorption of the modified PVDF membrane are 38° and 45 mg/m² while Fresenius F60S membrane are 64° and 235 mg/m². Prothrombin time (PT) and activated partial thromboplastin time (APTT) of the modified PVDF membrane are 56.5 s and 25.8 s while Fresenius F60S membrane is 35.7 s and 16.6 s. However, further biocompatibility evaluation is needed to obtain a more comprehensive conclusion.

Crosslinked duplex DNA nanogels that target specified proteins

Specific detection of protein biomarkers plays an important role in diagnostics and therapeutics. We have fabricated polymeric nanogels, which can specifically interact with the cancer biomarker thrombin to serve as a model. Two types of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymers bearing a thrombin-binding oligonucleotide aptamer and its complementary chain were independently synthesized by redox-initiated radical polymerization. These MPC polymers associate in a complimentary fashion due to double strand formation of the oligonucleotides in aqueous media, leading to the spontaneous formation of spherical nanogels. Nanogel formation was confirmed by dynamic light scattering (DLS) and transmittance microscopy. The average size of nanogel particles was 124 ± 2 nm and the nanogels were mono-dispersed (polydispersity index 0.21). Functional intercalators could be stably incorporated into nanogels through the physical interaction between the intercalators and the oligonucleotides. The ethidium bromide (EtBr)-incorporating nanogels were used as detectors for thrombin. The fluorescence intensity of solutions containing the EtBr-incorporating nanogels was decreased with an increase in the concentration of thrombin. The transformation of quadruplex-thrombin structure from complementary double-stranded structures resulted in the decrease in fluorescence intensity. In contrast, the intensity did not change when the nanogels were incubated with albumin. Thrombin is only one such model used to demonstrate this technique; oligonucleotide aptamers can be freely designed to interact with versatile bio-substances. Therefore, aptamer-crosslinked nanogels can be appropriate nanomaterials for disease diagnosis and therapy.

Research on polyvinylidene fluoride (PVDF) hollow-fiber hemodialyzer

In this study, polyvinylidene fluoride (PVDF) hollow-fiber hemodialysis membranes were prepared by non-solvent-induced phase separation. The PVDF hollow-fiber hemodialyzers were prepared by centrifugal casting. The results showed that the PVDF membrane had better mechanical and separation properties when the membrane wall thickness was 40 μm and the N,N-dimethylacetamide in the core was 70 Vol%. Compared with commercial polysulfone hemodialysis membrane (Fresenius F60S membrane), the PVDF membrane had better mechanical property and ultrafiltration (UF) flux of pure water. The PVDF dialyzer's removal efficiency for middle molecules was proven to be much higher than that of the F60S dialyzer. The UF coefficient of a high-flux PVDF dialyzer is 62.6 ml/h/mm Hg, whereas F60S is 42.5 ml/h/mm Hg, which can promote clearance for middle molecules.

Fabrication and evaluation of polymeric membranes for blood dialysis treatments using functionalized MWCNT based nanocomposite and sulphonated-PES

The use of polyethersulfone based membranes for dialysis therapy is increasing, but the poor bio-compatibility of the PES membrane can raise severe blood reactions affecting the rate of morbidity and mortality of hemodialysis (HD) patients.

Preparation and preliminary dialysis performance research of polyvinylidene fluoride hollow fiber membranes

In this study, the separation properties of Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were improved by optimizing membrane morphology and structure. The results showed that the PVDF membrane had better mechanical and separation properties than Fresenius Polysulfone High-Flux (F60S) membrane. The PVDF membrane tensile stress at break, tensile elongation and bursting pressure were 11.3 MPa, 395% and 0.625 MPa, respectively. Ultrafiltration (UF) flux of pure water reached 108.2 L∙h⁻¹∙m⁻² and rejection of Albumin from bovine serum was 82.3%. The PVDF dialyzers were prepared by centrifugal casting. The influences of membrane area and simulate fluid flow rate on dialysis performance were investigated. The results showed that the clearance rate of urea and Lysozyme (LZM) were improved with increasing membrane area and fluid flow rate while the rejection of albumin from bovine serum (BSA) had little influence. The high-flux PVDF dialyzer UF coefficient reached 62.6 mL/h/mmHg. The PVDF dialyzer with membrane area 0.69 m² has the highest clearance rate to LZM and urea. The clearance rate of LZM was 66.8% and urea was 87.7%.

Preparation of Polyvinylidene Fluoride (PVDF) Hollow Fiber Hemodialysis Membranes

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDF membrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was found that membrane thickness and PEG content affected both the structure and performance of hollow fiber membranes. The tensile strength and rejection of bovine serum albumin (BSA) increased with increasing membrane thickness, while the Ultrafiltration flux (UF) flux of pure water was the opposite. The tensile strength, porosity and rejection of BSA increased with increasing PEG content within a certain range. Compared with commercial F60S membrane, the PVDF hollow fiber membrane showed higher mechanical and permeable performance. It was proven that PVDF material had better hydrophilicity and lower BSA adsorption, which was more suitable for hemodialysis. All the results indicate that PVDF hollow fiber membrane is promising as a hemodialysis membrane.

The isolation of cell derived extracellular matrix constructs using sacrificial open-cell foams

Extracellular matrix derived from human and animal tissues is being used to repair and reconstruct a variety of tissues clinically. The utility of such constructs is limited by the geometry, composition and constitutive properties of the tissue or organ from which the ECM is harvested. To address this limitation, we have developed an approach to isolate extracellular matrix in bulk from populations of living cells grown in culture on three-dimensional substrates. Human biopsy derived fibroblasts were seeded within open-cell foams and cultured in-vitro for periods up to three weeks, after which the synthetic component was removed by incubation in a water miscible solvent. After several wash steps and lyophilization, a white, lacy, multi-molecular construct was isolated. Tandem mass spectroscopy showed that it contained 22 extracellular matrix constituents, including such proteins and proteoglycans as collagen type I and type III, fibronectin, transforming growth factor beta, decorin and biglycan among others. On average 47 mg of construct was isolated for each gram of synthetic substrate initially seeded with cells. The biomaterial harvested from human tracheal fibroblasts had an elastic modulus (250 kPa) and a composition similar to that of human vocal fold tissue, and supported reseeding with human tracheal derived fibroblasts. An important finding was that the approach was useful in isolating ECM from a variety of cell lineages and developmental stages including skin fibroblasts, brain derived astrocytes and mesenchymal stem cells. The results, together with the archival literature, suggest that the approach can be used to produce a range of cell derived constructs with unique physical and chemical attributes for a variety of research and medical applications.

Promotion of U937 cell adhesion on polypropylene surfaces bearing phosphorylcholine functionalities

Phosphorylcholine (PC) groups were grafted onto ammonia plasma-treated biaxially-oriented polypropylene (BOPP) surfaces, via (a) reductive amination of phosphorylcholine glyceraldehyde and (b) a two-step procedure involving the chemical amplification of surface amine groups with tris(2-aminoethyl amine) and subsequent reductive amination of phosphorylcholine glyceraldehyde. The occurrence of grafting was ascertained by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier-transform infrared (ATR-FT-IR) spectroscopy. The wettability of PC-modified surfaces was assessed by dynamic contact-angle measurements using the Wilhelmy plate method. Human U937 macrophages adhered and proliferated to a significantly larger extent on PC-modified surfaces, compared to unmodified or ammonia plasma-modified BOPP.

In vitro sampling and storage of proteins with an ultrafiltration collection device (UCD) and analysis with absorbance spectrometry and SELDI-TOF-MS

Frequent in vivo sampling of blood proteins is often stressful, making it difficult to obtain more than a few samples. As a result, only limited time-profiles can be made. We have developed an ultrafiltration collection device (UCD) for continuous sampling. The UCD consists of a hollow fiber, a coil and a flow creator. Hollow fiber membranes are often hydrophobic and this can result in adsorption of protein and/or peptides, leading to clogged membranes. Adsorption was tested with a hydrophobic and hydrophilic peptide and two biocompatible hollow fibers made from different materials. The hollow fiber made from poly(ethylene) coated with ethylenevinyl alcohol gave near 100% recovery for both peptides. This was in contrast to the poly(sulfone) hollow fiber when sampling the hydrophobic peptide. Filling the coil with various peptide concentrations gave good recovery and insignificant diffusion even after storage for 6 d at 37 degrees C. Continuous pulse-free sampling was tested by vacuum. An average flow rate of 423 +/- 50 nl min(-1) over a period of 4 d was created using S-Monovette. The flow rate gradually declined during this period by <5% every consecutive day. In addition, we also examined a complex sample-serum in the poly(ethylene) hollow fiber. Serum and ultrafiltrate were spotted onto a protein chip and analyzed by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Six proteins out of 64 were found to be significantly different between serum and the ultrafiltrate (p < 0.05). The UCD has the potential to be used for in vivo real-time monitoring.

Protein resistant polyurethane surfaces by chemical grafting of PEO: amino-terminated PEO as grafting reagent

The objective of this work was to gain a better understanding of the mechanism of resistance to protein adsorption of surfaces grafted with poly(ethylene oxide) (PEO). A polyurethane-urea was used as a substrate to which PEO was grafted. Grafting was carried out by introducing isocyanate groups into the surface followed by reaction with amino-terminated PEO. Surfaces grafted with PEO of various chain lengths (PUU-NPEO) were prepared and characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). XPS data indicated higher graft densities on the PUU-NPEO surfaces than on analogous surfaces prepared using hydroxy-PEO (PUU-OPEO) as reported previously [J.G. Archambault, J.L. Brash, Colloids Surf. B: Biointerf. 33 (2004) 111-120]. Protein adsorption experiments using radiolabeled myoglobin, concanavalin A, albumin, fibrinogen and ferritin as single proteins in buffer showed that adsorption was reduced on the PEO-grafted surfaces by up to 95% compared to the control. Adsorption decreased with increasing PEO chain length and reached a minimum at a PEO MW of 2000. Adsorption levels on surfaces with 5000 and 2000 MW grafts were similar. There was no clear effect of protein size on resistance to protein adsorption. Adsorption on the PUU-NPEO surfaces was significantly lower than on the corresponding PUU-OPEO surfaces, again suggesting higher graft densities on the former. Adsorption of fibrinogen from plasma was also greatly reduced on the grafted surfaces. From analysis (SDS-PAGE, immunoblotting) of the proteins eluted after plasma exposure, it was found that the grafted surfaces and the unmodified substrate adsorbed the same proteins in roughly the same proportions, suggesting that adsorption to the PEO surfaces occurs on patches of bare substrate. The PEO grafts did not apparently cause differential access to the substrate based on protein size.

Novel Biodegradable Polyphosphate Cross-Linker for Making Biocompatible Hydrogel

To obtain a novel biodegradable cross-linker, polymerizable polyphosphate (PIOP) was synthesized by ring-opening polymerization of 2-i-propyl-2-oxo-1,3,2-dioxaphospholane with 2-(2-oxo-1,3,2-dioxaphosphoroyloxyethyl methacrylate) (OPEMA). The number averaged molecular weight of the PIOP was 1.2 x 10(4), and the number of OPEMA units in one PIOP molecule was 2.2. Nonenzymatic degradation of the PIOP was evaluated in various pH aqueous media. The degree of hydrolysis was dependent on the pH; that is, it increased with an increase in the pH of the medium. At pH 11.0, the PIOP completely degraded in only 6 days. The poly[2-methacryloyloxyethyl phosphorylcholine (MPC)] cross-linked with the PIOP was prepared by radical polymerization. This polymer could form hydrogel, and the free water fraction in the hydrogel was high. The enzymatic activity of trypsin in contact with the hydrogel was similar to that in buffer solution. There is no adverse effect caused by the hydrogel to reduce the function of the trypsin. The cytotoxicity of poly(MPC) and degraded PIOP was evaluated using v79 cells, and it was not observed in either case. In conclusion, PIOP is a hydrolyzable polymer, which can be used as a cross-linker, and novel hydrogels having biodegradability and biocompatibility were prepared from poly(MPC) cross-linked with the PIOP.