Heparin-Immobilized Polyethersulfone for Hemocompatibility Enhancement of Dialysis Membrane: In Situ Synchrotron Imaging, Experimental, and Ex Vivo Studies

The goal of the current study is to enhance the hemocompatibility of polyethersulfone (PES) membranes using heparin immobilization. Heparin was immobilized covalently and via electrostatic interaction with the positively charged PES surface (pseudo-zwitterionic (pZW) complex) to investigate the influence of each method on the membrane hemocompatibility. In situ synchrotron radiation micro-computed tomography (SR-µCT) imaging, available at the Canadian Light Source (CLS), was used to critically assess the fibrinogen adsorption to the newly synthesized membranes qualitatively and quantitatively using an innovative synchrotron-based X-ray tomography technique. The surface roughness of the synthesized membranes was tested using atomic force microscopy (AFM) analysis. The membrane hemocompatibility was examined through the ex vivo clinical interaction of the membranes with patients' blood to investigate the released inflammatory biomarkers (C5a, IL-1α, IL-1β, IL-6, vWF, and C5b-9). The presence and quantitative analysis of a stable hydration layer were assessed with DSC analysis. Surface modification resulted in reduced surface roughness of the heparin-PES membrane. Both types of heparin immobilization on the PES membrane surface resulted in a decrease in the absolute membrane surface charge from -60 mV (unmodified PES) to -13 mV for the pZW complex and -9.16 mV for the covalently attached heparin, respectively. The loss of human serum fibrinogen (FB) was investigated using UV analysis. The PES membrane modified with the heparin pseudo-ZW complex showed increased FB retention (90.5%), while the unmodified PES membrane and the heparin covalently attached PES membrane exhibited approximately the same level of FB retention (81.3% and 79.8%, respectively). A DSC analysis revealed an improvement in the content of the hydration layer (32% of non-freezable water) for the heparin-coated membranes compared to the unmodified PES membrane (2.84%). An SR-µCT analysis showed that the method of heparin immobilization significantly affects FB adsorption distribution across the membrane thickness. A quantitative analysis using SR-µCT showed that when heparin is attached covalently, FB tends to be deposited inside the membrane pores at the top (layer index 0-40) membrane regions, although its content peak distribution shifted to the membrane surface, whereas the unmodified PES membrane holds 90% of FB in the middle (layer index 40-60) of the membrane. The ex vivo hemocompatibility study indicates an improvement in reducing the von Willebrand factor (vWF) for the heparin pseudo-ZW PES membrane compared to the covalently attached heparin and the untreated PES.

Silymarin modified polysulfone hollow fiber membranes with antioxidant, anti-M1 macrophage polarization and hemocompatibility for blood purification

Oxidative stress is highly prevalent in maintenance hemodialysis patients and increases the risk of cardiovascular morbidity and mortality. Silymarin (SM) is a natural compound extracted from plants, and has been shown to have pharmacological effects such as antioxidant, anti-inflammatory, cytoprotective, and anti-nephrotoxicity. SM-modified polysulfone (PSF) hemodialysis membranes were prepared by an immersion-precipitation phase transition method. The experimental results showed that the modified membranes effectively scavenged free radicals, significantly inhibited lipid peroxidation, and had good antioxidant stability (60 days). The PSF/SM antioxidant membranes (H-3) had no pro-inflammatory effect, which was confirmed by the result of anti-M1 macrophage polarization. Furthermore, the hemolysis rate (2%), blood cell deformation (3.7%), and inhibition of erythrocyte and platelet adhesion were improved by the SM-modified PSF membranes. All the results suggest that PSF/SM blended hollow fiber membranes are promising for application in hemodialysis membranes to improve oxidative stress status and reduce inflammation and complications in patients.

Investigation on Human Serum Protein Depositions Inside Polyvinylidene Fluoride-Based Dialysis Membrane Layers Using Synchrotron Radiation Micro-Computed Tomography (SR-μCT)

Hemodialysis (HD) membrane fouling with human serum proteins is a highly undesirable process that results in blood activations with further severe consequences for HD patients. Polyvinylidene fluoride (PVDF) membranes possess a great extent of protein adsorption due to hydrophobic interaction between the membrane surface and non-polar regions of proteins. In this study, a PVDF membrane was modified with a zwitterionic (ZW) polymeric structure based on a poly (maleic anhydride-alt-1-decene), 3-(dimethylamino)-1-propylamine derivative and 1,3-propanesultone. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and zeta potential analyses were used to determine the membrane's characteristics. Membrane fouling with human serum proteins (human serum albumin (HSA), fibrinogen (FB), and transferrin (TRF)) was investigated with synchrotron radiation micro-computed tomography (SR-μCT), which allowed us to trace the protein location layer by layer inside the membrane. Both membranes (PVDF and modified PVDF) were detected to possess the preferred FB adsorption due to the Vroman effect, resulting in an increase in FB content in the adsorbed protein compared to FB content in the protein mixture solution. Moreover, FB was shown to only replace HSA, and no significant role of TRF in the Vroman effect was detected; i.e., TRF content was nearly the same both in the adsorbed protein layer and in the protein mixture solution. Surface modification of the PVDF membrane resulted in increased FB adsorption from both the protein mixture and the FB single solution, which is supposed to be due to the presence of an uncompensated negative charge that is located at the COOH group in the ZW polymer.

Impact of Membrane Modification and Surface Immobilization Techniques on the Hemocompatibility of Hemodialysis Membranes: A Critical Review

Despite significant research efforts, hemodialysis patients have poor survival rates and low quality of life. Ultrafiltration (UF) membranes are the core of hemodialysis treatment, acting as a barrier for metabolic waste removal and supplying vital nutrients. So, developing a durable and suitable membrane that may be employed for therapeutic purposes is crucial. Surface modificationis a useful solution to boostmembrane characteristics like roughness, charge neutrality, wettability, hemocompatibility, and functionality, which are important in dialysis efficiency. The modification techniques can be classified as follows: (i) physical modification techniques (thermal treatment, polishing and grinding, blending, and coating), (ii) chemical modification (chemical methods, ozone treatment, ultraviolet-induced grafting, plasma treatment, high energy radiation, and enzymatic treatment); and (iii) combination methods (physicochemical). Despite the fact that each strategy has its own set of benefits and drawbacks, all of these methods yielded noteworthy outcomes, even if quantifying the enhanced performance is difficult. A hemodialysis membrane with outstanding hydrophilicity and hemocompatibility can be achieved by employing the right surface modification and immobilization technique. Modified membranes pave the way for more advancement in hemodialysis membrane hemocompatibility. Therefore, this critical review focused on the impact of the modification method used on the hemocompatibility of dialysis membranes while covering some possible modifications and basic research beyond clinical applications.

Hierarchical Surface Architecture of Hemodialysis Membranes for Eliminating Homocysteine Based on the Multifunctional Role of Pyridoxal 5'-phosphate

Patients with end-stage renal disease are prone to developing a complication of hyperhomocysteinemia, manifesting as an elevation of the homocysteine (Hcy) concentration in human plasma. However, Hcy as a protein-bound toxin is barely removed by conventional hemodialysis membranes. Here, we report a novel hemodialysis membrane by preparing a bioactive coating of pyridoxal 5'-phosphate (PLP) and adding biocompatible hyperbranched polyglycerol (HPG) brushes to achieve Hcy removal. The dip-applied PLP coating, a coenzyme with a role in Hcy metabolism, dramatically promoted a decrease in the Hcy concentration in human plasma. Moreover, the aldehyde group of PLP had an intrinsic chemical reactivity toward the terminal amino group to immobilize the HPG brushes on the hemodialysis membrane surface. The hierarchical PLP-HPG layer-functionalized membranes had a high efficacy for eliminating Hcy, with a concentration from the initial stage of 150 μmol/L reduced to a nearly normal level of 20 μmol/L in simulated dialysis. By analyzing the impact of HPG brushes with various chain lengths, we found that HPG brushes with a medium length enabled the PLP coating with the bioactive function of Hcy conversion to additionally protect Hcy-attacked target cells by providing excellent hydrophilicity and a dense enough chain volume overlap of the hyperbranched architecture. Simultaneously, the densely packed HPG brushes generated a maximal steric and hydration barrier that significantly improved biofouling resistance against blood proteins. The optimally functionalized membranes showed a clearance of 83.1% urea and 49.6% lysozyme and a rejection of 96.0% bovine serum albumin. The diversely functionalized PLP-HPG layers demonstrate a potential route for a more integrated hemodialysis membrane that can cope with the urgent issue of hyperhomocysteinemia in clinical hemodialysis therapy.

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.