Dialysis membrane: from convection to adsorption

Abstract

Although patients undergoing dialysis have a complex illness, there are compelling reasons to believe that the inadequate removal of organic waste is an important contributing factor to the illness itself. This paper focuses on the transport phenomena that occur within a dialyser. An attempt is made to clarify how transport phenomena are related to the performance of a dialysis session and how they depend on the membrane characteristics. Our study offers some discussion points on the complex issue of defining what the best parameters could be in comparing the efficiency of different membranes. The new high-flux dialysers have improved larger-molecule clearance and biocompatibility. Membrane performance is a very hard process to evaluate, and different membranes can only be compared by establishing adequate points of comparison. At the same time, the points of comparison themselves may change depending on the type of co-morbidities of the specific patient who is considered for membrane selection. This editorial (together with all the papers presented in this issue) seeks to focus on the membrane's own merits in improving the dialysis therapy.

Nondialyzable Uremic Toxins

“…These include dialyzer membranes with a larger pore size and a higher porosity/surface unit ratio [3], and adsorption methods that may be operated through the same dialyzer membrane in the case of PMMA biomaterial [79] or by (synthetic or natural) sorbents used to trap uremic solutes in the dialysate (reviewed by Meyer et al and Vanholder et al [80,81]). Pioneering preclinical studies have suggested the use of oral sorbents to neutralize circulating uremic toxins or to prevent the absorption of food- or colonic microflora-derived toxicants in the GI tract [recently reviewed in [15,21,82,83,84]].…”

“…As far as synthetic PMMA hemodialyzer membranes are concerned, they may combine the concept of adsorption with that of diffusive removal of some classes of uremic retention solutes [79]. Pioneering studies by our group have shown that this type of approach, applied to protein-leaking dialysis carried out with conventional diffuse methods, produces one of the highest performances of depuration for protein-bound solutes and PTMs, such as Hcy [60] and HSA-bound PT, protein carbonyls and AOPP [86], and polyaminated proteins that show in vitro activity as erythropoiesis inhibitors [87].…”

“…On the other hand, β2-M, soluble CD40 and free IgG chains as well as inflammatory cytokines are some examples of species removed by absorption with these dialyzer membranes so far reported in the literature [79]. These are described in detail in other articles published in this issue.…”

Advances in Hemodialysis Techniques

“…The technology of dialysis membranes have yielded thicker type of membranes (more than conventional 1 micron thickness) that have a great affinity to stick larger size molecules to their surfaces, hence known as adsorptive membranes [96]. Adsorption can occur at the outer surface of the membrane when molecules cannot pass through the pores of the membrane and/or within the inner membrane matrix when the molecules can permeate the membrane [97].…”

The <under>D</under>oubl<under>e</under> Po<under>l</under>ym<under>e</under>thylmethacryla<under>te</under> Filter (DELETE System) in the Removal of Light Chains in Chronic Dialysis Patients with Multiple Myeloma

“…Among these, the synthetic membranes made of PMMA are characterised by their symmetrical structure (fig. 1), which associates with the transmembrane diffusive and convective transport capacities and also the possibility of solute removal by means of adsorption on the membrane itself [17]. Under experimental conditions using in vitro tests, Hutchison et al [6] described a reduction of around 80% for both the κ and λ chains in serum submitted to dialysis treatment in vitro for 4 h, with a PMMA membrane of 2.1 m 2 surface.…”